j. build. mater. struct. (2014) issn 2353-0057 ii editorial for inaugural issue of “journal of building materials and structures” bouziani tayeb structures rehabilitation and materials laboratory (sreml), university amar teliji-laghouat, 03000, algeria. email: t.bouziani@lagh-univ.dz, t.bouziani@oasis-pubs.com welcome to the inauguration issue of our new publication: journal of building materials and structures (jbms). jbms has been installed thanks to the open source solutions developed by public knowledge project. my great thanks also goes out to my co-editors and editorial office team for accepting to guide with me this journal from initial planning to the first steps it is taking now. the main objective of jbms is to provide a repository of knowledge for building materials and structural engineering sciences. the choice of open access format to jbms is to ensure free access to knowledge which is linked to the economic development and seems in agreement to the spirit of scientific thought. it is important to note that all contributions, upon approval by our peer review process, are for beginning, indexed in google scholar and archived in the open archive initiative (oai). the peer review procedure will match knowledgeable reviewers with submitted manuscripts to produce high quality articles of interest and scientific merit. the procedure is confidential so that recommendations and revisions are made in the fairest way possible. the final decision on publication will be made by the editor in charge. as new teaching systems, such as license-master-doctorate (lmd) system or the national project works carried out by researchers, take root in universities and laboratories, especially across algeria, the roles that conducting research projects and writing scientific articles play within these institutions are increasing. in light of this development, our new journal looks at the potential of new researches and high quality contribution works within laboratories and universities, as well as the ways in which research development can impact beyond higher journal articles quality. finally, i thank our contributors and readers for their interest and efforts in completing this inauguration issue and i also look forward to a most interesting future for jbms. mailto:t.bouziani@lagh-univ.dz, https://pkp.sfu.ca/ http://scholar.google.com/scholar?q=%22journal+of+building+materials+and+structures%22&btng=&hl=fr&as_sdt=0%2c5 http://www.openarchives.org/ http://www.openarchives.org/ j. build. mater. struct. (2018) 5: 95-101 original article doi : 10.34118/jbms.v5i1.48 issn 2353-0057, eissn : 2600-6936 numerical prediction and experimental validation of sound transmission loss for different acoustic materials kirti s *, mahavir s, yudhister k y 1 a & v metrology, pmm division, csir-national physical laboratory, new delhi -110012, india * corresponding author: soniks@mail.nplindia.org received: 07-02-2018 revised: 01-05-2018 accepted: 07-05-2018 abstract. this paper examines the sound transmission loss (stl) through multilayer panel materials commonly used in the building industry. the acoustic characteristics of different materials and multilayer panels are studied. experimental data for the noise reduction coefficient in the frequency range 100 to 4000 hz have been obtained using the two room’s method. mass theory is also used to predict the acoustic performance of these systems and to improve their acoustic performance with noise treatment. key words: acoustic sample, airborne sound insulation, sound transmission loss, mass theory. 1. introduction increase in population, transportation, modern urbanization has applied pressure on all available resources. one of the severe problems of our urbanized society is related with unwanted and potentially unsafe noise. for the healthy and pleasant living and working environment, the development of effective ways and materials are required to minimize the noise pollution. it is essential to know the sound transmission loss of walls and floors so as to be able to compare different constructions, to determine acoustic privacy between flats or noise levels from outside sources. transmission loss (tl) is a performance of sound insulation measured in reverberation chambers and sound transmission class (stc) is an integer rating of how well a building partition attenuates airborne sound. several studies have been focused on the development and analysis of sound absorbing devices made of a variety of porous materials, for example, fibrous, foams and granular materials etc. moore and lyon (1991); lin et al., (2007); wang et al., (2010) and jung et al., (2015) reported the sound transmission loss characteristics of various acoustics materials. building acoustics is the complex science of controlling noise in buildings. this contains the minimization of noise transmission from one space to another and the control of the characteristics of sound within spaces themselves. this study presents a comparison of experimental measurements of the sound transmission of walls, floor, ceilings etc. with the theoretical models. 2. methodology of testing and sample details 2.1. measurement facilities and procedures the acoustical measurements were made in the suite of reverberation chambers in the acoustical block of the acoustics and vibration metrology section of csir-national physical laboratory, new delhi. wall panel samples are mounted in a removable test frame between two chambers, without rigid contact to either reverberation chambers. the panel test opening measures 0.93 m x 0.63 m. both rooms are irregular in shape with no parallel surfaces and are equipped with stationary diffusers. the volume of the source room is 257 m3. the volume of the mailto:soniks@mail.nplindia.org 96 kirti et al., j. build. mater. struct. (2018) 5: 95-101 adjacent receiving room is 271 m3. both reverberation chambers are supported on pillar with suitable vibration isolators. test signals are supplied to each room by duo-decahedral loudspeakers system with independent pseudorandom noise sources. to measure transmission loss, white noise is fed to loudspeaker system in the source room. pink noise is used to measure decays in the receiving room. the testing of acoustical materials (i.e., samples) was conducted in accordance with the requirement of iso 10140-1:2016 sound pressure level and reverberation time measurements are made for 1/3-octave band with center frequencies from 100 hz to 4000 hz. the data are then used to calculate sound transmission loss for each frequency band as per specified standards. a stc rating was obtained for each panel in accordance with iso 101401:2016 and astm standard classification e413 (astm e413-87). the sound transmission loss has been calculated as: ( ) (1) and the time constant governing the growth of the acoustic energy in the room is given by the reverberation time t, defined as the time required for the level of the sound to drop by 60 db, is: t = 13.8 = with speed of sound in air c = 343 m/s (200c) this becomes (lawrence et al., 1982) where, l1: average sound pressure level in source room (db) l2: average sound pressure level in receiving room (db) s : area of the test partition (in square meter) a : total absorption area of receiving room (in square meter) v : volume of receiving room ( in cubic meter) t : reverberation time (sec) the evaluated uncertainty in measurement is ±1.0 db which is at a coverage factor k = 2 and which corresponds to a coverage probability of approximately 95% for normal distribution. fig. 1. measurement of sound transmission loss, stl, in the laboratory kirti et al., j. build. mater. struct. (2018) 5: 95-101 97 2.2. theory for prediction in the present study, mass theory has been used to predict the measured sound transmission loss. mass law provides a good working rule to predict the airborne sound insulation of a partition up to the region of the critical frequency and the coincidence effect according to mass law, a doubling in mass or frequency results in a 6 db increase in the sound insulation of a single leaf partition over a defined frequency range. ( ) (2) where, f = frequency of the sound m = mass of the partition to predict the performance of a material using the mass law the parameters density of the material, thickness of the material, young’s modulus, damping coefficient etc. are required. table 1. samples details. sample name of manufacturer description of items sound transmission class sample 1. m/s. shivathene linopack, parwanoo hp 2 mm thick layer with pu based 2 component sound insulating paint (shivabond 603) coated on 2mm thick ms panel sample 2. m/s. alstrong enterprises india private limited, new delhi 4 mm thick aluminium composite panel sample 3. m/s. fusion building materials private limited, hyderabad 150 mm thick aac block of density 550-650 kg/m3 sample 4. m/s. pimpri chinchwad municipal corporation, pimpri) 12 mm thick polycarbonated noise barrier hexagonal/01 inner cells hexagonal in section sample 5. m/s. pimpri chinchwad municipal corporation, pimpri 12 mm thick polycarbonated noise barrier rectangle/02 inner cells rectangular in section 3. results and discussion the scope of this paper is the prediction of sound transmission loss (stl) of different panel systems as typically used by the building industry. experimental and theoretical methods are used to estimate the acoustic performance of typical panels. the construction details of these panels are described in table 1. the sample 1 is 2 mm mild steel panel coated with 2mm sound insulating polyurethane (pu) shivabond 603 paint (total thickness 4mm), its measured stc value is 39 and predicted value is 38. sample 2 is same in thickness as sample 1. however the 4 mm thick aluminum composite panel with simple design paint have measured stc value is 26 and predicted value is 29. both sample 1 and 2 have same thickness but sample one stc value is high as compared to the sample 2 stc value due to the acoustical polyurethane paint. pu paints are broadly known for their inherent toughness and flexibility. shivabond 603 is a specially formulated two-component polyurethane paint; it is used for sound insulation purposes. 98 kirti et al., j. build. mater. struct. (2018) 5: 95-101 sample 3 is a high density (550-650 kg/m3) 150 mm concrete block and its stc value is highest than sample one and two. wes (2007) reported that solid concrete walls are great for sound insulation particularly when used in floors and walls due to the material’s rigidity, i.e., it will not flex and create sound waves on the inaudible side of the wall. nothing stops sound waves to a certain extent like massive materials. concretes are mainly capable of stopping the critical low frequencies that are so tough to stop with less massive materials. brick and stone are very alike to concrete in mass. steel is a quite dense material but not as concrete, and its density actually becomes an obligation in structural uses where its dense nature causes it to carry sound vibrations for long distances. mass theory also has been used for the prediction of stc of sample 1 to 3. the results from sound transmission loss measurements for the different materials are presented in figure 2 to 4. it is observed from the figures that for the sample 1 and 3 the predicted transmission loss shows good agreement with the measured results while for sample 2 measured and predicted results match closely except for 3250 hz. fig. 2. sound transmission loss as a function of frequency for sample 1. apart from the steel, aluminium and concrete materials two layer polycarbonated panel of 12mm thickness (i.e., sample 4 and 5) with hexagonal and rectangle structure inner cell y = 0.5316x + 15.472 r² = 0.8057 30 32 34 36 38 40 42 44 30 35 40 45 50 55 p re d ic te d s t l measured stl sample -1 kirti et al., j. build. mater. struct. (2018) 5: 95-101 99 structure have also been studied and shown in figure 5. the polycarbonated panel with different inner cell structures is used as a noise barrier. noise barriers are the best effective technique of mitigating roadway, industrial, and railway noise sources other than termination of the source activity. from figure 5 it is observed that the inner layer structure also influence the stc results. higher sound transmission loss value has been observed for rectangle inner cell (i.e., stc 21) than the hexagonal inner cell (i.e., stc 19). numbers of sound bridges are higher in hexagonal structure than the rectangle structure. hence, the stc value is high for rectangle structure than the hexagonal structure. fig. 3. sound transmission loss as a function of frequency for sample 2. y = 1.1279x 2.1368 r² = 0.5959 15 20 25 30 35 15 20 25 30 35 p re d ic te d s t l measured stl sample -2 100 kirti et al., j. build. mater. struct. (2018) 5: 95-101 fig. 4. sound transmission loss as a function of frequency for sample 3. fig. 5. sound transmission loss as a function of frequency for sample 4 & 5. y = 1.3777x 16.046 r² = 0.9318 30 35 40 45 50 55 60 65 70 30 40 50 60 p re d ic te d s t l measured stl sample -3 kirti et al., j. build. mater. struct. (2018) 5: 95-101 101 4. conclusions this paper examines the sound transmission loss (stl) through different panel materials commonly used in the building industry. experimental and predictive methods are used to evaluate the acoustic performance of these materials and to improve their acoustic performance with noise treatment.  predicted results show better agreement with experimental results for different configuration of acoustics materials.  materials with high density and with acoustic paint represent high stc.  acoustic coat is an inexpensive, easy to apply, sound deadening paint providing both sound deadening and insulation properties to painted ceilings and walls etc.  from the rectangle and hexagonal inner cell structure study, it is observed that inner cell structure play an important role, for high stc value sound bridges in the inner cell structure should be minimum.. 5. references astm e413-87, classification for rating sound insulation (american society for testing and materials, washington dc,usa) 1999. iso 16283-1:2014 acoustics -field measurement of sound insulation in buildings and of building elements -part 1: airborne sound insulation jung, j.-d., hong, s.-y., song, j.-h. and kwon, h.-w. (2015) a study on transmission loss characteristics of honeycomb panel for offshore structures. journal of applied mathematics and physics, 3, 172176. http://dx.doi.org/10.4236/jamp.2015.32027 lawrence e. kinsler, austin r. frey, alan b. coppens and james v. sanders (1982). fundamentals of acoustics, third edition, john wiley & sons. lin, h.-j., wang, c.-n. and kuo, y.-m. (2007) sound transmission loss across specially orthotropic laminates. applied acoustics, 68, 1177-1191. http://dx.doi.org/10.1016/j.apacoust.2006.06.007 moore, j.a. and lyon, r.h. (1991) sound transmission loss characteristics of sandwich panel constructions. j acoust soc am, 89, 777-791. wang, s.c., deng, z.x. and shen, w.d. (2010) sound transmission loss characteristics of unbounded orthotropic sandwich panels in bending vibration considering transverse shear deformation. composite structures, 92, 28852889. http://dx.doi.org/10.1016/j.compstruct.2010.04.014 wes l., (2007). materials and their uses in architectural acoustics. taliesin in spring green, wisconsin, on july 19, 2007,http://www.weslachot.com/new/articles_materials_content.html. http://dx.doi.org/10.1016/j.compstruct.2010.04.014 http://www.weslachot.com/new/articles_materials_content.html j. build. mater. struct. (2020) 7: 60-66 original article doi : 10.34118/jbms.v7i1.328 issn 2353-0057, eissn : 2600-6936 pathology, evaluation and repair of bridges in masonry rehab bekkouche s 1,*, boukhatem g 2, mendjel d 1, messast s 1 1 university august 20, 1955 skikda, department of civil engineering, lmghu laboratory, algeria 2 university badji mokhtar annaba, department of civil engineering, algeria. * corresponding author: solrehab@yahoo.fr received: 05-02-2020 accepted: 13-04-2020 abstract. the field of repair and rehabilitation of civil engineering works is evolving. indeed, most of these structures, especially masonry structures, are over 50 years old and many of them require maintenance and repair work due to their deteriorated condition. to achieve this objective, a study was carried out concerning the different pathologies affecting the masonry bridges, but also the ways and means necessary for the evaluation and repair of the affected works. the results of this work have not only helped to carry out the diagnosis and verification of the structural state of the bridge over river kentra stora skikda (north-east of algeria), on the section of the 3aa national road skikda, but also for the proposal of repair solutions best adapted to the disorders observed. key words: bridge, masonry, diagnosis, expertise, repair. 1. introduction masonry is a composite material, a mixture of stones or bricks and mortar joints. the behaviour of masonry structures depends on their physicochemical characteristics (porosity, capillarity, permeability, gelling), thermal and mechanical behaviour. the simple compressive strengths vary greatly depending on the rocks (from 20 to 200 mpa). bricks are blocks of hardened clay (raw bricks) or artificially (cooked bricks). whose resistance to simple compression is lower than stone, of the order of 5 to 15 mpa. the overall mechanical operation of a masonry bridge is related not only to the individual functioning of each part (vault, walls, abutments) but also to the connections and transmissions of forces between the zones. the filling distributes the charges on the vault and pushes on the eardrums. he participates in the lift of the structure by these splitter effects. the vault, the active part of the structure, has for main role to take the efforts due to the loading and to transmit them to the foundations. the ground transmission of the loads is carried out by the stacks, the abutments and the walls in return. the siding is the resistant part of the pile: the loads pass mainly in the facings and leave the filling if it offers less rigidity (stablon, 2011; mohammadzadeh et al., 2018; edwards, 2005; valluzzi et al., 2005). bridges are aging, but given their social importance, they must be given special care so that they can perform their functions for the life they have been assigned (modena, 2004). they are indeed works, which, even if they do not all have an architectural aspect, constitute economic, transport and security vectors, built with the aim of ensuring a service combining high level of quality, safety and reliability. bridges are not always in good condition, and it is not easy to diagnose pathology, and then prescribe the right remedy. for several years now, heritage management has suggested that the entire park is regularly monitored, evaluated and evaluated (hua, 1993). the first goal is to ensure the safety of users. secondly, asset management must make it possible to respect or even extend the life of works (tatiana, 2011). mailto:solrehab@yahoo.fr rehab et al., j. build. mater. struct. (2020) 7: 60-66 61 the selection of repair strategies is conditioned by the type of defect, its causes and the features that are intended to be improved (stability, structural and fire safety, thermal and acoustic comfort, energy efficiency, water-tightness, or others) (sousa, 2014). in this article we present the various pathologies affecting the masonry bridge on river kentra stora skikda (north-east of algeria), the ways and means necessary for evaluation and repair and finally the repair solutions best suited to disorders observed. 2. status of the algerian bridges the age of the park is at the same time an essential factor in the assessment of its condition, and is of paramount importance to enable managers to enforce protection measures before deterioration is too advanced. the part of very old works (built before 1962) is very small but it nevertheless represents 23% of the bridges. these are 920 bridges distributed in algeria as follows: 227 whose age is more than 100 years such as bridge el-kantara built in constantine by salah bey in 1792 and the sidi rached bridge built between 1908 and 1912; and these works are of great historical value. 693 of them are between 50 and 100 years old; and it can be pointed out that more than 70% of these structures are in masonry or reinforced concrete. therefore, in general, aged structures are works that have experienced advanced aging, and must therefore be maintained regularly to avoid reducing their life and worsening their condition, which generates maintenance costs or often significantly increased (hamlaoui, 2012). 3. the case study: the bridge on river kentra stora skida (north-east of algeria) aged over sixty-five years (65) (fig. 1), the bridge over river kentra stora located on the national road 3aa was built in the 1950, it has the following characteristics (table 1): table 1. characteristics of the bridge geometric data infrastructure superstructure trace: right material: unreinforced concrete pile: masonry number of spans: 03 apron: low vaul range: 26.40 + 2 x 9.60m structure: hyperstatic opening: (6,00 + 22,80 + 6,00) material: masonry length of the work: 46m foundations: well (probably) width of deck: 9.50m [carriageway: 7.00m + 2 sidewalks of 1.25m] to ensure their functions, the bridges must be maintained in a permanent acceptable level of service through the various maintenance operations. because they show signs of fatigue and disorders that amplifies over time. it is possible to classify two types of pathologies in masonry. these are problems related to materials and structure (gharib, 2015; o'neil, 1995; coignet and coignet, 2007). when priority of intervention is given to a certain historical building, a preliminary survey is essential. the main objective of the preliminary survey is to get acquinted with the structure and to see if temporary emergency interventions are needed (ersoy, 1989). in this section we used the information required to establish a summary of the nature and causes of the most frequent disorders either at the superstructure or accessories after the collection of expert reports of the bridge on river kentra stora, the treatment and analysis of the information collected as well as the estimation of the probable causes of these impairments (hamlaoui, 2012). 62 rehab et al., j. build. mater. struct. (2020) 7: 60-66 fig 1. elevation view of the structure the modern environment conditions can also have considerable effect on buildings and be the cause of damage. it is well known what a dangerous effect pollution of the atmosphere can have on building materials; or the effect of vibration from vehicular traffic on buildings, or even only adjacent construction sites and the thus necessary changes in the groundwater table. such influences can be the cause of damage; one should therefore investigate and document them (mann, 1989). the presence of significant cracks on the entire structure: the slab of the deck also has significant delamination areas in addition to having a thickness insufficient by standards. the vault and the abutment show traces of water infiltration. the bursting of concrete with stripping and corrosion of the reinforcement at the cornices. cracks are also visible on the masonry in fig. 2. they usually run along the joints. locally, splinters between the rubble are also visible. the cracking developed is due to the presence of microcracking in the mass of the mortar and to the weaknesses of the stone mortar interface (stablon, 2011). fig 2. bridge over the river river kentra stora, in skikda. rehab et al., j. build. mater. struct. (2020) 7: 60-66 63 as the bridge is located in an area close to the sea, special attention has been paid to this factor in order to limit the problems and damages related to this environment (fig.3 and fig.4). fig 3. defects affecting the reinforcing concrete. fig 4. cracks and stains on the surface. 4. choice of the repair technique the term repair means that the damaged structural or non-structural elements achieve a minimum of strength, rigidity and ductility. so the repair is limited only to the damaged elements. the choice among solutions traditional or innovative is controversial, but if with traditional techniques it is possible to obtain satisfactory solutions of the structural point of view, economic and constructive, its use should be preferred, not only for aesthetic and cultural reasons, but also for compatibility reasons between the new elements and the original ones. frequently it is not easy to repair the structural damages with the exclusive resource to a traditional solution, because no longer they are available original materials, as mortars or wood, because qualified labour doesn't exist ("artisans") for this type of constructive techniques, or 64 rehab et al., j. build. mater. struct. (2020) 7: 60-66 still for economical reasons. the most frequent reason to go through modern techniques or innovations is related with the need of significant increases of resistance, that are only gotten with much more efficient materials than the original ones. however, whenever possible the "interventions in masonry should be made with masonry". apart from the deteriorations observed, our structure is in an "acceptable" state from the point of view of mechanical functioning. thus, we offer maintenance and repair of degraded parts of the work (fig. 5 and fig. 6), this work which lasts approximately two months and essentially comprises the following stages: • paved body debris on a thickness of 30 cm. • realization of a screed of 5cm concrete cleanliness. • realization of a slab (high seal) to the right of the 15cm structure with reinforced national road 27 concrete mesh welded after cleaning, surface preparation and all subjections of good execution. • implementation of a sealing complex. • implementation of an asphalt concrete wearing course (8cm thick). • washing masonry and reinforced concrete facings with pressurized water (6 bars). • stitching and blowing in the compressed area of degraded concrete surface (corniche + railing) with energetic brushing of exposed steel. • repair of degraded concrete (cornice + guardrail) with hydraulic mortar based on resin emulsion, including primer primer on any thickness <5cm. • injection of fissures with the resin (sikadur 52 or equivalent). • sanding of railings. • applying layers of paint on railings fig 5. bridge repair works. rehab et al., j. build. mater. struct. (2020) 7: 60-66 65 fig 6. bridge after rehabilitation works. 5. conclusion in order to rehabilitate a masonry structure, it is important to make a diagnosis. this step makes it possible to identify the various pathologies present, their magnitude as well as their cause. thanks to this, it is possible to propose an adequate method of repair as well as protection against future attacks. a follow-up of the book can be done to determine the evolution of the different pathologies. the detailed visual inspection carried out on the bridge on river kentra stora skikda, allows us to conclude that this one was not the object of a permanent surveillance, which makes it possible to detect in time the malfunctions and to take corrective measures. the rehabilitation works of the studied bridge allowed to give a second life to the work and to preserve its architecture. 6. acknowledgements the authors gratefully acknowledge the management of public works at skikda, and more particularly miss omeiri zahra, head of the design office, for the excellent collaboration they demonstrated during the production of this work. 7. references coignet, j., & coignet, l. (2007). maçonnerie de pierre: matériaux et techniques, désordres et interventions. eyrolles. edwards, j. (2005). cracking in historic masonry and surface finishes: conservation approaches and solutions. journal of building appraisal, 1(1), 20-33. ersoy, u. (1989), diagnosis, assessment and emergency interventions for historic masonry structures, international technical conference athens, 31.x. — 3.xi., structural conservation of stone masonry, athenes, pp. 13-19. gharib, t. (2015). renforcement des structures historiques en maçonnerie par matériaux composites: application aux murs en pierres calcaires. doctoral dissertation. université claude bernard lyon i. hamlaoui, s. (2012). maintenance, entretien et réparation des ponts, mémoire de magistère, biskra. hua, w. g. (1993). procedures for diagnosis and assessment of concrete buildings, doctoral dissertation, university of adelaid australia. mann. w, (1989), diagnosis and assessment of existing structures, international technical conference athens, 31.x. — 3.xi, structural conservation of stone masonry, athenes. pp. 1-12. modena, c. (2004). design approaches of interventions for the safety and conservation of historic buildings. invited keynote lecture, structural analysis of historical constructions, 1, 75-83. 66 rehab et al., j. build. mater. struct. (2020) 7: 60-66 mohammadzadeh, s., miri, a., & nouri, m. (2018). assessing ballast cleaning as a rehabilitation method fo r railway masonry arch bridges by dynamic load tests. proceedings of the institution of mechanical engineers, part f: journal of rail and rapid transit, 232(4), 1135-1148. o'neil, e. f. (1995). repair and maintenance of masonry structures: case histories, technical report remr-cs-46. sousa h., (2015), defects in masonry walls. guidance on cracking: identification, prevention and repair coordination, portugal, cib publication 403. stablon, t. (2011). méthodologie pour la requalification des ponts en maçonnerie. doctoral dissertation, université toulouse iii-paul sabatier. tatiana. s. t. n., (2011), pathologie, evaluation et réparation de ponts en béton armé étude de cas : ouvrages sur le tronçon atakpame – kara de la route nationale n°1 au togo, mémoire de master. valluzzi, m. r., binda, l., & modena, c. (2005). mechanical behaviour of historic masonry structures strengthened by bed joints structural repointing. construction and building materials, 19(1), 6373. j. build. mater. struct. (2018) 5: 239-245 original article doi : 10.34118/jbms.v5i2.62 issn 2353-0057, eissn : 2600-6936 an empirical enquiry into windows used in tropical office spaces gyimah k. a. *, amos-abanyie s. department of architecture, college of art and built environment, kwame nkrumah university of science and technology, ghana. * corresponding author: kobbygyimah@gmail.com received: 28-06-2018 revised: 20-12-2018 accepted: 18-12-2018 abstract. environmental health is very instrumental to the survival of the human race and there is the need for behavioural change for its quality. grounded in literature is the fact that amongst all the elements of the building fabric, window is the only element which contributes holistically to indoor environmental quality (ieq). however, there is no certainty that building professionals or clients consider ieq in the selection of windows for buildings and spaces holistically. this study seeks to evaluate the various types of windows mostly used in office spaces and establish the rational for their choice. questionnaires in the form of google forms were developed and sent to a convenient sampled population of architects and clients in ghana. results shows that none of the architects or clients choice of window had a holistic rational towards achieving all the variables of ieq thermal comfort, lighting quality, air quality and sound quality. most of the choices by respondents were based on at least one of the variables of ieq as a rational. in some cases, the rational of clients had no link to ieq. both clients and professionals suggested modifications to current office windows for better ieq. it is also recommended that further research is carried out to validate the findings. the relevance of this study cannot be down played as knowledge is acquired for re-engineering of appropriate and holistic window towards ieq. key words: environmental health, indoor environmental quality, offices, tropics, windows constructions. 1. introduction the 21st century is fluxed with various organisations and institutions with the aim of solving problems of man to make life better. life improvement is always evident in the development of the society, country or world at large. however, this cannot be realised if high levels of productivity are not achieved in our institutions responsible for specific task. higher productivity has a direct link to occupants being comfortable in the spaces they work in. to chua et al. (2016), “the physical environment comfort in a workplace is claimed to be vital as it will encourage healthier, more productive and lower absenteeism rate among employees”. employee turnover rate is also reduced as a result of high comfort levels. therefore companies should invest into developing high user comforts to yield better results (feige et al, 2013). the link of ieq to comfort, health and productivity cannot be disputed as researchers like mahbob et al., (2011); huizenga et al., (2006); abbaszadeh et al., (2006) and moschandreas (1998) have established it in their studies. for total comfort to be achieved in indoor spaces, indoor environmental quality (ieq) must be achieved in spaces. ieq is achieved when thermal comfort, acoustic comfort, lighting comfort and air comfort are achieved (rehva, 2010; bluyssen, 2009; dascalaki et al., 2009). rehva (2010) further explains the inter relationship between ieq and other factors as in figure 1. mailto:kobbygyimah@gmail.com 240 gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 fig 1. inter relationship between ieq and other factors (rehva, 2010) leaman (1995) reports that space users who are not happy with lighting levels, air quality, temperature and noise conditions have effects on their productive levels. this then establishes the need for a holistic ieq in all indoor spaces. one key element of the building fabric that contributes naturally for a holistic ieq to be achieved is windows (gyimah et al., 2017). there are various windows across the globe used for different purposes. according to the singapore building and construction authority (sbca), the tropics is characterised by different kinds of windows and some notable ones are top or bottom hung, casement and louvers (sbca, 2016). figure 2 exhibits some windows used in the tropics for specific ieq level. fig 2. different windows styles (source: aluminiumwindows.com; sideshare.net) gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 241 the different windows styles in figure 2 have specific contribution to ieq levels within a space. some are for air quality whiles others are for thermal quality and thus care must be taken when choosing any. air quality is achieved through ventilation by windows introducing fresh air into spaces (persram et al., 2007); lighting quality is realised through windows allowing natural day light into spaces (barrett et al., 2012); heat influx for discomfort can be reduced through windows with phase change materials (alawadhi, 2012); noise pollution is minimised through closed windows (koranteng et al., 2016). these studies above have shown that tropical windows play a key to ieq, but no known research into tropical windows presents a holistic solution to ieq. as one part of ieq is achieved, the other suffers and therefore space users are struggling to have a total ieq. there is therefore the need for further research to re-engineer tropical office windows for a holistic ieq (gyimah et al., 2017). according to hammer and champy (2006) re-engineering cannot be achieved without asking the questions: “why do we do what we do? and why do we do it the way we do?” this means that there is the need to know what is done, why that is done and why is it done that way. questions thus formulated to deal with windows re-engineering in the tropics are: which window type is used for tropical offices? and what is the rationale behind the choice of these windows? this study seeks to establish window types used for topical office spaces and the rationale behind its choice. the objectives set to achieve aim and thus answer questions asked are: to establish window(s) used for tropical office spaces, to know the rationale behind the choice of tropical office windows and make recommendations to guide the re-engineering tropical office windows. knowledge of the type(s) of windows specifically used for office spaces will help to narrow the scope of window re-engineering. the theory of reductionism comes into play here and as explained by mandik (2013), it gives a clearer answer to the question of correlation. these clearer answers will help guide the process of re-engineering. the relevance of this study cannot be down played as knowledge will be acquired for re-engineering of appropriate and holistic window towards ieq. 2. materials and methods the research design for this study was mixed and used both qualitative and quantitative approaches. quantitative aspects dealt with the use of descriptive frequencies and percentages for data analysis. qualitatively, phenomenology is the key philosophy that drives this study. phenomenology as a philosophy deals with knowledge from a person’s point of view on a particular object based on first hand experiences (gyimah et al., 2017). these experiences are intentionally sought within a specific scope to understand situations. therefore the use of phenomenology for this study is to know the rationale behind the choice of various windows based on their experiences. the bottom-up approach was used to sample out a unit thus normal office users, then professionals (architects). sample method convenient sampling due to time constraints. 120 users and 80 architects totalling 200 respondents were sampled as the size for this study. the research tool used for data collection was questionnaire (google forms). most questionnaires were used open ended questions and thus more qualitative data was collected and analysed. 3. results and discussion data realised from questionnaires totalled 129 of the sample size of 200, representing 64.5% response rate. with response rate over 50%, analysis were done for results and discussions. 242 gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 fig 3. office location of respondents fig 4. office type used or design by respondents from figure 3 and 4, most offices are low rise and found in the central business district (cbd) and thus noise pollution can have effect on office spaces. sound influx into a building is however determined by the building enclosure especially windows used. data collected on windows used for office spaces depicts a higher number of respondents using sliding windows as in figure 5. fig 5. office window type used or designed by respondents gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 243 interestingly, table 1 shows sliding windows performance to ieq as weak but has other attributes such as elegance, corporate and modern. awning which performs better towards ieq however has low usage. therefore further research is needed to understand this development. table 1. rationale for office window choice lighting quality air quality thermal comfort sound quality others awning good natural lighting good natural ventilation thermally comfortable sound proofing when closed aesthetics louver good natural lighting good natural ventilation thermally comfortable not sound proof n/a sliding good natural lighting not good for natural ventilation not thermally comfortable sound proofing when closed aesthetics, elegance, modern corporate fixed good natural lighting not good for natural ventilation not thermally comfortable sound proofing aesthetics sliding windows is challenged with thermal comfort and natural ventilation whiles louvers has a challenge with sound proofing. however, awning which seem not to have major issues with ieq is the least patronised by users and architects. therefore an argument can be made that clients and architects do not holistically take into consideration ieq when choosing windows. since majority of windows currently used in office spaces does not achieve ieq, 53% of respondents are of the view that modifications are needed on existing office windows for better ieq (figure 6). table 2 presents various recommendations outlined by respondents on windows for better ieq. fig 6. modification of current office windows 244 gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 table 2. recommended modifications from respondents window recommendation from respondents awning n / a louver sound proofing qualities should be inculcated sliding bigger windows for better natural ventilation hybrid of louver and sliding increase glass thickness for better sound proofing fixed should be operable 4. conclusions study has shown that no window has been able to holistically achieve ieq. sliding windows which is the predominantly used needs some modifications for total ieq. louvers which is ranked second to sliding need to have sound proofing properties. awning with its low usage seems to perform better when it comes to ieq. an argument can thus be made that clients and architects don’t holistically take into consideration ieq when choosing windows. the following recommendations are therefore given to guide window choice for holistic ieq:  window show be operable and big enough to allow for natural lighting and ventilation  when a window is closed, it should be air tight to prevent infiltration  window thickness should be increase for better sound proofing further research is however recommended to physically measure the performance of these windows either to confirm or debunk these findings before re-engineering. acknowledgements this paper is part of a phd thesis at the department of architecture, kwame nkrumah university of science and technology. appreciation goes to the college of engineering of the kwame nkrumah university of science and technology for the opportunity to present this research at the conference on engineering, science, technology, and entrepreneurship (este 2015) 5. references abbaszadeh, s., zagreus, l., lehrer, d., & huizenga, c. (2006). occupant satisfaction with indoor environmental quality in green buildings. proceedings, healthy buildings, 3, 365-370 alawadhi, e. m. (2012). using phase change materials in window shutter to reduce the solar heat gain. energy and buildings, 47, 421-429. barrett, p., zhang, y., moffat, j., & kobbacy, k. (2013). a holistic, multi-level analysis identifying the impact of classroom design on pupils’ learning. building and environment, 59, 678-689. bluyssen, p. (2009). the indoor environment handbook: how to make buildings healthy and comfortable. routledge. london, earthscan. chua, s. j. l., ali, a. s., & lim, m. e. l. (2016). physical environment comfort impacts on office employee’s performance. in matec web of conferences (vol. 66, p. 00124). edp sciences. dascalaki, e. g., gaglia, a. g., balaras, c. a., & lagoudi, a. (2009). indoor environmental quality in hellenic hospital operating rooms. energy and buildings, 41(5), 551-560. feige, a., wallbaum, h., janser, m., & windlinger, l. (2013). impact of sustainable office buildings on occupant's comfort and productivity. journal of corporate real estate, 15(1), 7-34. gyimah, k. a., amos – abanyie, s. and kootin – sanwu, v. (2017) the importance of windows in attaining indoor environmental quality in the tropics: a review. in ayarkwa j., ahadzie d. k., adinyira e., gyimah and amos-abanyie, j. build. mater. struct. (2018) 5: 239-245 245 kwofe t. and owusu-manu d., paper presented at the 6th international conference on infrastructure development in africa (icida) (pp 358 – 367). kumasi, ghana, college of art and built environment, knust. hammer, m. and champy, j. (2006). reengineering the corporation: a manifesto for business revolution, harper collins publishers, new york huizenga, c., abbaszadeh, s., zagreus, l., & arens, e. a. (2006). air quality and thermal comfort in office buildings: results of a large indoor environmental quality survey. proceedings, healthy buildings, 3, 393-397 koranteng, c., amos-abanyie, s., & kwofie, t. e. (2016). environmental noise exposure on occupants in naturally ventilated open-plan offices: case of selected offices in kumasi, ghana, international journal of scientific & technology research 5(10) 138-146 leaman, a. (1995). dissatisfaction and office productivity. facilities, 13(2), 13-19. mahbob, n. s., kamaruzzaman, s. n., salleh, n., & sulaiman, r. (2011). a correlation studies of indoor environmental quality (ieq) towards productive workplace, 2nd international conference on environmental science and technology, 2, 434438. mandik, p. (2013). this is philosophy of mind: an introduction, john wiley & sons, vol. 22. moschandreas, d. j. (ed.). (1998). design, construction, and operation of healthy buildings: solutions to global and regional concerns. ashrae, usa. persram, s., lucuik, m., & larsson, n. (2007). marketing green buildings to tenants of leased properties. canada green building council. sbca (2016). singapore building and construction authority, accessed 02/09/16 at https://www.bca.gov.sg/professionals/iquas/..%5ciquas%5cgpgs%5cawindow%5cawdesign.pdf https://www.bca.gov.sg/professionals/iquas/..%5ciquas%5cgpgs%5cawindow%5cawdesign.pdf j. build. mater. struct. (2014) 1: 23-29 https://doi.org/10.34118/jbms.v1i1.5 issn 2353-0057 excess paste method to formulate a self-compacting concrete mebrouki a *, bendani k, bouhamou n and belas n lctpe laboratory, umab-mostaganem university, bp 227, 27000 mostaganem, algeria. * corresponding author: mebroukiaek@yahoo.fr , tel & fax: +213 45 20 39 33. abstract. on the basis of the principle that a concrete is composed of a liquid phase (paste) and a solid phase (aggregates with fixed gravel/sand ratio), the concrete self-compacting properties come necessarily from those of the paste. the present work is the continuity of a first phase of the testing already conducted, which resulted in obtaining an optimal selfcompacting cement paste composition. this paste will be used to prepare a self-compacting concrete (scc), while passing from the scale of the cement paste to that of the concrete, by injecting wet aggregate to the self-compacting paste. the excess paste theory was used to determine the thickness of the paste coating each aggregate with a given diameter of constituting granular skeleton, then generalized for the determination of the quantity of total paste allowing the flow of the concrete by decreasing frictions between the grains of its granular skeleton. this approach was also experimentally validated. the influence of the granular distribution was minimized by the use of the approach based on the determination of the average diameter of the aggregates. this required the determination of a homothetic factor “k” similar for all concretes with different aggregate grading. formulation of a selfcompacting concrete passes initially by the determination of a sufficient quantity of paste allowing its flow without frictions between its aggregates and to balance the mixture by the quantity of water retained by the aggregates. the self-compacting concrete characteristics would come from those of the cement paste which composes it. key words: self-compacting concrete, excess paste method, homothetic, compactness, formulation. 1. introduction concrete is a biphasic material, consisting of a fluid phase (paste) and a solid phase (aggregates with fixed gravel/sand ratio (nanthagopalan, 2010). the self-compacting concrete properties result inevitably from those of the paste (pedersen, 2003). in this context, the studies of formulations were based on paste and its constituents. a first phase already conducted, concerned the determination of the optimal composition of the self-compacting cement paste (mebrouki, 2010). this paste will serve to elaborate a self-compacting concrete by injecting into it wet aggregates. table 1 presents constituents proportions necessary to elaborate a volume of paste (vp = 0.225 m3) of the optimal self-compacting paste. table 1. composition of the optimal paste. component volume (m3) density (kg/m3) mass (kg) rate (%) cement (c) 0.111 3150 349.65 86.6% filler (f) 0.021 2800 58.80 14.4% superplasticizer (sp) 0.005 1085 05.43 1.3% water (w) 0.088 1000 88.00 w/(c+f) = 0.22 using this paste with a granular skeleton defined only by a weight ratio gravel/sand (g/s), it would be possible to make concretes satisfying the self-compacting criteria admitted in the fresh state. for a chosen granular skeleton having defined g/s weight ratio, a sufficient optimal selfcompacting paste is prepared, to which will be added the granular mixture; a part of this paste is going to cover the aggregates and the rest fits between these grains and fills the space, thus causing separation of the skeleton, which would induce a difficulty of flow of the concrete thus formed. mailto:mebroukiaek@yahoo.fr 24 mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 in addition, sand and gravels have a capacity for absorption of considerable water; this water if absorbed will cause a deficiency in the paste composition, it is necessary thus to correct it by water addition to compensate this deficit. it is difficult to compensate the adsorbed water but even more difficult to be able to calculate theoretically this quantity, since this one would have already caused an increase in the capillary pores. 2. principle of the formulation method the method used gave conclusive results with materials employed in materials and constructions durability laboratory (l.m.d.c applied sciences national institute ups, toulouse, france), it will be then applied to algerian local materials to formulate a selfcompacting concrete. figure 1 schematizes the formulation principle to elaborate a self-compacting concrete. fig 1. scc formulation principle. in the following, it is presented the conventional hypothesis to formulate 1m3 of scc. for that purpose, it is necessary to determine the corresponding volume of cement paste, the volume of aggregates to be injected (with fixed g/s ratio) and that of water to be added. the unit volume of the concrete finally obtained contains a volume of the pores estimated at 2.5 % of total volume. the following first equation can be written: (1) v : unit volume of concrete (1 m3). vp: optimal self-compacting paste absolute volume. va: added volume accumulates of aggregates and water absolute volumes. vv: volume of occluded voids in concrete (2.5 %). to be able to work out a scc on the basis of a self-compacting paste of volume (vp), one gradually adds alternate volumes of aggregates and water during the kneading, while observing the aspect of the concrete which must resemble that of a scc. the procedure will be stopped when the sum of added volumes would have reached the volume (va). 3. pastegranular skeleton association aggregates with g/s ratio varying from 0.8 and 1.2 were chosen to elaborate the concretes. in addition to the tests of determination of experimental compact nesses on the basis of stacking compressible model, the determination of the water quantity retained by the aggregates is also necessary since, if the aggregates are not humidified beforehand, they would draw water of the paste with which they will be mixed. 3.1. granular skeleton characterization results table 2 gives the various granular grading going from 0.08 to 16 mm. the representative (dri) and arithmetic average diameters (dami) were calculated theoretically by suitable formulas (bui, 2002; el-barrak, 2009). these values will be used as data for the continuation of work. mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 25 these values represent various sections of different granular classes chosen to calculate experimental compactness. table 2. representative and arithmetic diameters of the granular classes. n° class granular class dri (mm) dami(mm) 1 12,5 – 16 14,106 14,25 2 6,3 12,5 8,75 9,4 3 3,15 6,3 4,368 4,725 4 1,25 3,15 1,917 2,2 5 0,315 1,25 0,583 0,7825 6 0,08 0,315 0,148 0,1975 found values are in the interval [150 300 µm] which comply with that recommended by (bui, 2002). tests of compactness were made to estimate the experimental and the maximal compactness, according to the dri and the dami given in table 3, according to the granular pile model (nanthagopalan, 2010). table 3. experimental and maximal calculated compactness values. g/s experimental compactness (γ) maximal compactness with dri with dami 0.8 0.729 0.782 0.801 1 0.731 0.801 0.807 water filtration passes by three stages, an initial and fast phase corresponding to the filtration of the water in excess in the heap of aggregates, the second stage in which the water results from capillary meniscus destruction by pumping strengths, then the third and slower phase of water recovery contained in aggregates pores, it is the water retained by the aggregates which quantification is researched. for g/s = 0.8 and g/s=1, this quantity corresponds to points (p1) and (p2) respectively (figure 2). fig 2. filtration curves for g/s= 0.8 and g/s = 1. obtained results are gathered in table 4. the total water represents the sum of paste water and added water. table 4. retained water and added water to concretes. g/s retained water (l/m3 of concrete) total water complement 0.8 147 196 49 1 165 188 23 26 mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 3.2. homothety factor determination homothety factor determination is based on paste excess theory. the representative plan (figure 3) shows a concrete (biphasic mixture) with aggregates immersed in cement paste. the compaction highlights a part of volume (vpe) representing excess paste coating of aggregates, a second part constituted by squeezed aggregates (volume vg) and a compact paste (volume vpc) serving to fill voids. fig 3. explanatory plan of the excess paste theory. homothety factor for every ratio (g/s) can be determined by the following relation: √ ∑ √ (2) (ni) is aggregates number with diameter (di) of the class (i), vg > 80 is aggregates volume with diameters greater than 80 µm (without fillers). found values are given in table 5. table 5. homothety factor values. g/s homothety facteur k 0.8 1.141 1 1.131 3.3. validation on concretes in self-compacting paste already formulated, aggregates were injected in alternate way with a certain quantity of water to obtain concretes of which workability depends initially on the visual aspect. indeed, if the mixture seems firm, a moderate quantity of water is added, if contrary, it presents a fluid aspect, a known aggregates quantity is injected. table 6 illustrates a concrete preparation example with g/s= 1. table 6. procedure of alternated additions. stage volumes of added aggregates (accumulated) volume of added water (accumulated) visuel aspect total volume added 1 0.65 va 0 pulverulent and heterogeneous 0.65 va 2 0.65 va 0.08 va very firm and sticky 0.73 va 3 0.65 va 0.10 va fluid 0.75 va 4 0.70 va 0.10 va plastic 0.80 va 5 0.70 va 0.12 va fluid 0.82 va 6 0.76 va 0.12 va firm 0.88 va 7 0.76 va 0.15 va fluid 0.91 va 8 0.79 va 0.15 va firm 0.94 va 9 0.79 va 0.17 va pasty 0.96 va 8 0.81 va 0.17 va acceptable 0.98 va 9 0.81 va 0.18 va satisfactory 0.99 va 10 0.82 va 0.18 va satisfactory va mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 27 this alternation ends by workability tests recommended by the french civil engineering association (afgc, 2008) to verify self-compacting properties, and by measures of compressive strength at age of 28 days. results are illustrated in table 7. table 7. results of scc characterization (g/s = 0.8 and g/s = 1). g/s 0.8 1 afgc recommandations abrams cone t50 (s) 2.1 1.8 not specified dmoy (mm) 693 712 600 – 750 mm l box t40 (s) 1.8 1.2 not specified h2/h1 0.89 0.92 ≥ 0.8 sieve stability π% 9.65 11.02 ≤ 15% occluded air % 2.6 2.9 not specified density(kg/m3) 2290 2310 not specified compressive strength rc28 (mpa) 33.2 38.7 not specified results obtained show that the properties of the concrete at fresh state are in accordance with afgc requirements. concrete obtained is then a self-compacting concrete, this is due to the narrow relation between the excess paste and the flow (wong, 2008). to verify suitability of the found formulation, components parameters were estimated and used to make concretes in a traditional way. the characterization results obtained are shown in table 8. table 8. characterization results of concretes made in a classical way g/s 0.8 1 abrams cone t50 (s) 1.8 1.8 dmoy (mm) 728 712 l box t40 (s) 2.1 1.2 h2/h1 0.91 0.92 sieve stability π% 11.96 9.54 occluded air % 2.3 1.9 density(kg/m3) 2290 2310 compressive strength rc28 (mpa) 36.4 40.2 3.4. application example for validation for various granular mixtures with variable ratios g/s, and with values of the coefficient "k" previously calculated, figure 4 can be plotted. this illustration allows determining values of this coefficient corresponding to different ratios g/s. fig 4. variation of parameter "k" with respects to g/s. 28 mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 to validate this approach on a concrete made with a g/s = 1.3, with the corresponding value of parameter k=1.078 (figure 4); the continuation consists to determine the volume of aggregates to associate with a volume (vp) of self-compacting cement paste. for that purpose, we determine values of coefficients a and b. coefficient a represents aggregates proportion having diameters greater than 80 microns in total granular volume (eq.3). for g/s = 1.3, grading analysis gave (a = 0.918). (3) coefficient b represents the transformed value of aggregates mass absorption, its value is (b = 8.102) %. considering uncertainty (± 5 liters) with which aggregates measures were made, total granular volume (sand and gravels) calculated is then: vg = 687 ± 5 liters/m3 of concrete. the proportion of water retained by aggregates can be determined through (figure 5), representing a linear regression of the ratio (ver/vg) with respects to values of g/s. fig 5. water retained by aggregates with respects to g/s. once the necessary elements were determined, concrete is made with the same procedure and in the same conditions as the previous concretes, and then workability characterization will be made. table 9 shows concrete composition with g/s = 1.3. table 9. concrete composition with g/s = 1.3. component volume (l/m 3 of concrete) mass (kg/m3 of concrete) g gravel (3/8) : 181.4 488 gravel (8/15) : 184.8 499 s 296.2 785 c 103.2 325 f 17.2 48.25 sp 4.2 4.6 w 187.9 187.9 total 975 2337.8 workability characterization tests results are shown in table 10, according to afgc recommendations, it shows that the concrete obtained presents self-compacting characteristics. mebrouki et al. j. build. mater. struct. (2014) 1: 23-29 29 table 10. concrete properties with g/s=1.3. g/s 1.3 abrams cone t50 (s) 2.8 dmoy (mm) 696 l box t40 (s) 1.9 h2/h1 0.95 sieve stability π % 12.8 occluded air % 3 density 2380 compressive strength rc28 (mpa) 42.3 the results prove that obtained concrete is self-compacting, also, visually the made concrete does not present segregation or blocking during its characterization in spreading and l-box tests respectively. 4. conclusions excess paste theory was used in this study to determine cement paste thickness coating every aggregate of diameter given constituting the granular skeleton, and then generalized for total paste quantity determination, allowing the flow of concrete by decreasing frictions between grains of its granular skeleton. the approach was also validated experimentally. influence of granular distribution was minimized by using an approach based on aggregates average diameter determination. this required bringing in calculations a homothety factor "k", which can be similar for concretes of different size grading but of the same aggregates type (crushed in our study). concrete formulations having self-compacting characteristics pass at first by determination of a sufficiency paste allowing its flow without frictions between its aggregates and to balance the mixture by a quantity of water retained by aggregates. this method based on the cement paste optimization is interesting in the sense where it is based on a mixed study: theoretical and experimental. self-compacting cement pastes into which it is injected wet aggregates form self-compacting concrete; which at fresh state satisfies the afgc recommendations. in other words, it can be concluded that self-compacting characteristics of a concrete would come from the cement paste which compose it. 5. references afgc, association française de génie civil (2008). recommendations for use of self-compacting concrete. scientific and technical documents, p n b@p. bui vk, akkaya y, shah s p (2002). rheological model for self-consolidating concrete. aci mater j, 99: 54959. el-barrak m, mouret m, bascoul a (2009). self-compacting concrete paste: hierarchical classification of their influence on flow properties of the paste. cement concrete compos 31: 12-21. mebrouki a, belas n, bouhamou n (2010). experimental plans method to formulate a selfcompacting cement paste. mater tehnol, 44:13-20. nanthagopalan p, santhanam m (2010). a simple and systematic mix design procedure for selfcompacting concrete. 6th international rilem symposium on scc, montreal, canada, pp: 54-63. pedersen b, smeplass s (2003). the relationship between the rheological properties of scc and the corresponding matrix phase. proceedings of 3rd rilem international symposium on self compacting concrete, reykjavik, iceland, pp:106-16. wong hhc, kwan akh (2008), packing density of cementitious materials: part 1-measurement using a wet packing method. mater struct, 41: 689–701. j. build. mater. struct. (2018) 5: 218-226 original article doi : 10.34118/jbms.v5i2.60 issn 2353-0057, eissn : 2600-6936 a study on strengthening of building foundation for storey extension zumrawi m. m. e.1,*, aldaw h. k. e.2 1,* department of civil engineering, faculty of eng., university of khartoum, khartoum, sudan. 2 department of civil engineering, faculty of eng., university of khartoum, khartoum, sudan. * corresponding author: magdi.zumrawi@yahoo.com received: 23-06-2018 revised: 24-10-2018 accepted: 28-10-2018 abstract. storey extensions are an increasingly popular way to crowded cities. lack experience and knowledge concerning strengthening of structures are major challenges for engineers. this paper presents strengthening practice adopted for foundations of existing building when storey extension is needed. literature concerning strengthening techniques commonly adopted and some historical cases were reviewed. a complex hall building in university of khartoum which was rehabilitated in 2009 by strengthening the structural members of the existing building to accommodate additional floors was undertaken as a case study. the records and reports of the original design and last rehabilitation of the building were reviewed. field inspection of the building condition before rehabilitation was carried out. the study results showed that the appropriate design, the strengthening materials used and the procedure followed are the key factors for economical and successful strengthening. key words: storey extension, foundation, strengthening technique, rehabilitation. 1. introduction capacity enhancement of foundations may be required to accommodate additional loads during expansion of existing structures. to achieve this, effective approaches to strengthen existing foundations are of paramount concern in engineering practice (bian et al., 2006). in fact, strengthening practice is necessary when replacing existing buildings with higher or denser ones, changing building functions or internal apartment arrangements to enable more people to live in already built structures, or vertically extend already existing buildings. the latter approach is the one that has been considered in this study (johansson and thyman, 2013). when new floors are added, the building will be subjected to higher loads both vertically and horizontally. these must in some way safely be transferred downwards through the superstructure to the foundation. in some cases there is an excess capacity of the existing building and its foundation, but if the capacity is too low, it might sometimes be necessary to strengthen the existing structure and its foundation (islam and qaiyum, 2013). the main focus of this study is strengthening of pad foundations of existing buildings for story extension. the paper reviews the most common and efficient strengthening techniques that can be used for reinforced concrete structures. 2. literature review 2.1. general strengthening and repair of any structure are commonly used in rehabilitation process. strengthening is a method used to improve the structural stability of a building to accommodate additional load, this enables the use of the building for intended purpose. in case of a damaged or deteriorated reinforce concrete element, strengthening must be associated with structural repair (islam and qaiyum, 2013). the need to strengthen a structure may be required at any mailto:email@email.com zumrawi & aldaw, j. build. mater. struct. (2018) 5: 218-226 219 time from the beginning of the construction phase until the end of the building service. during the construction phase may occur deficient in concrete production, errors in the design or bad execution processes, while during the service life, it may arise on account of earthquake, changing in the structure functionality, developing of more demanding code requirements and damaging of structure by an accident, such as collisions, fire, explosions (branco and silva, 2003). the selection of strengthening system depend on many technical factors including serviceability, strength, durability and non-technical factors such as constructability, aesthetics and cost/ benefit analysis. the latter one is paramount principle to determine the most effective and economical strengthening methods among the alternative options (rodriguez and park, 1991). in most cases with any of the selected strengthening system, there is also an associated increase in the stiffness of the structure. caution must be taken to avoid an irregular stiffness distribution in the strengthened structure (rodriguez and park, 1991). 2.2. strengthening concrete structures most strengthening techniques used for concrete structures are based on the assessment of engineers only and, often empirical knowledge and current practice have an important role in the decisions to be made, materials and approaches used to strengthen reinforce concrete structures mostly are independent of which structural member to be treated. there are mainly three different techniques when strengthening a structural element; sectional enlargement with additional reinforced or plain concrete, strengthening with externally mounted steel and strengthening with fiber reinforced polymers (johansson and m. thyman, 2013). sectional enlargement with additional reinforced or plain concrete is one of the simplest way for strengthen concrete members. it aims to increase the thickness of the member. however, there are some important aspects considered, when fresh concrete is applied to old. to achieve good bond the old surface must be roughened and cleaned. sometimes epoxy glue might be useful to further strengthen the bond. if the shear forces at the joint interface are significant, additional anchors in the shape of bolts or stirrups might be needed as well (statens råd, 1978). regular reinforcement bars can be used in the added concrete, when performing a section enlargement on a member. also, steel can be mounted externally by means of sheets and profiles or apply a prestressing force (nordin, 2005). it is important to attach them and achieve interaction with the concrete. however, the durability problem exhibited by steel in form of corrosion can affect the bond between the plate and the concrete (norris et al., 1997). fiber reinforced polymers (frp) is a composite material consisting of fibers surrounded by a polymer matrix. the matrix is what keeps the fibers together and transfers the forces between the individual fibers. the matrix also acts as protection for the fibers. different materials can be used as matrix, but epoxy based is the most commonly used. the main types of fibers are carbon, glass, and aramid (carolin, 2003). all fibers behave elastically until a brittle failure and normally have a higher tensile strength than steel. carbon fibers have several benefits in a structural context such as its high strength to weight ratio and high modulus of elasticity (cozmanciuc et al., 2009). carbon fibers are therefore the most common type used when strengthening buildings. 2.3. previous experiences on strengthening several researches have been conducted on strengthening of structural members. islam and qaiyum (2013) performed some analytical analysis for structural elements. models were first submitted to structural elements before extension, then for the future anticipated load, the results show that the column and foundation were not capable to carry extra load from additional storey as the design vertical load for four storeys exceeded the load carrying capacity 220 zumrawi & aldaw j. build. mater. struct. (2018) 5: 218-226 of the element and hence, strengthening is required for column and foundation. also, they stated that both the reinforced concrete (rc) jacketing and frp could increase the capacity of column, but the cost analysis shows that the total cost of rc jacketing to be about 15% the frp strengthen cost. besides this, the installation cost is also high for frp strengthening and for the foundation strengthening the enlargement of the section was used, and the required size was measured to carry the additional loads safely (islam and qaiyum, 2013). johansson and thyman (2013) studied strengthening of a foundation with different techniques when six storeys were added. the building in goteborg region in turkey is founded in a deep layer of clay and the original foundation was performed with 18 m long timber trunks as cohesion end-bearing piles that rest on the bedrock piles. from the new design it was found that the piles and soil could take the increased load, but the pile caps were too weak. to shift the new load from the pile cap, it was decided to strengthen the foundation with winged steel piles as illustrated in fig 1. the vkr-profiles were prestressed to ensure that the winged steel piles were loaded immediately. many of the columns also needed to increase their capacity by section enlargement with self-compacting concrete to ensure proper filling. the increased area of the column reduces the local shear force per unit width on the pile cap. fig 1. illustration of how the foundation was strengthened johansson and thyman (2013). shihada and al-jerjawy (2011) assessed a sixteen-storey building in gaza which damaged by air attack in 2009. they considered the option of repair and strengthening of the building than demolition and rebuilding. design checks for slab, column, shear wall and mat foundation were carried out. moreover, soil pressures under the mat before and after the incurred damage were evaluated. the results showed that the design of all structural elements of the building is satisfactory. the soil pressure under the mat is within the allowable bearing capacity of the soil. based on the assessment results by computer software modeling for the damaged structural members, the columns showed minor damage were repaired by straightened or tied the existing bars with new bars of the same diameter if they were cut then patching new concrete cast on them. the columns showing major cracking, they were strengthening by rc jacketing. 3. case study the current investigation was carried out on a selected project in khartoum. this project was redesigned to accommodate additional floor for the existing building. the investigation consisted of field survey of the site condition and data collection about the design and any other information assist in investigation. the site visual inspection and photographs taken for the foundation of the building were used to assist in diagnosis the current condition. the case selected for this study is located at university of khartoum in khartoum. 3.1. project description complex hall lecture, located in the main campus of university of khartoum, was built in 2007 and initially reached 8 m height above the ground. the building consists mainly of a big hall in the ground floor with some rooms and a number of offices are located in the first floor. the zumrawi & aldaw, j. build. mater. struct. (2018) 5: 218-226 221 building is a two-story reinforced concrete frame founded on footings in a sandy clay soil. the structural system consists of in-situ cast reinforced concrete columns, beams, slabs and isolated footings. one new storey was added in 2009, giving the building a new height of 12 m as shown in fig. 2. the building original structural elements have been strengthened to be able to support the additional load of storey extension. the study was conducted to evaluate the new foundation design. the main feature of this design was enlarging the footing sections to increase their load carrying capacity to accommodate the additional load. fig 2. the building after storey extension. 3.2. foundation design the original design of the building was done by dal company and based on bs 8110 (1997). the plan area of the building, size and reinforcement of columns and foundations are shown in figure 3 and table 1. fig 3. layout plan of foundation. item old (o) new (n) footings columns 222 zumrawi & aldaw j. build. mater. struct. (2018) 5: 218-226 table1. result of original design for foundations. footing quantity size reinforcement f1 10 2.250*2.250*(400-500) t16@150 c/c b.w. f2 14 2.000*2.000*400 t16@150 c/c b.w. f3 12 1.500*1.500*300 t16@150 c/c b.w. f4 4 2.000*2.000*500 t16@150 c/c b.w. in the new design a floor was added to the building to become three-storey reinforced concrete frame. the strengthening technique adopted is sectional enlargement for the existing footings. in this research, the new design for the footings of the building was carried out based on bs (1997). the results obtained of the new foundation design are given below in table 2. table 2. the result of the new foundation design footing quantity size f1, f1′&f1″ 10 3.000*3.000*800 f2, f2′&f2″ 12 2.85*2.85*750 f3 8 2.30*2.30*600 f4 2 2.00*2.00*750 f5 2 (part of r.c wall footing) f6 4 2.00*2.00*750 f7 4 2.00*2.00*600 (new) f8 1 6.600*3.200*800 (combined) f9 2 2.285*1.00*600 (new) 4. footing strengthening guidelines these guidelines describe the procedure for footing strengthening by sectional enlargement. after adding a storey, the imposed load by the superstructure may exceed the capacity of the structure elements. as the design load exceeds the capacity, thus strengthening is required. enlargement of the footing section is needed for increasing the capacity. the strengthening of the existing footings was done by enlarging their sections. the construction started by excavating the area around the footing to the required dimensions as shown in fig 4. fig 4. excavation around the footing. zumrawi & aldaw, j. build. mater. struct. (2018) 5: 218-226 223 small holes were drilled with epoxy grout at the surface and sides of the footing. then dowel bars were inserted in the drilled holes as shown in fig 5. fig 5. drilled holes and inserted dowels bars. additional plain concrete of 10cm thick was casted in the extended area of the footing before arranging the reinforcement bars surrounding the footing as shown in fig. 6. the reinforcement of the enlarged footing is plotted in fig. 7. fig 6. plain concrete in the extended area and the reinforcement bars arranged surrounding the footing. 224 zumrawi & aldaw j. build. mater. struct. (2018) 5: 218-226 (a) reinforcement plan (b) reinforcement cross-section fig 7. reinforcement plan and cross-section of the footing enlarged area fresh concrete was casted with proper compaction to cover the enlarged area of the footing as shown in fig. 8. expanding agents must be added to the concrete mixture to ensure gab fillings. to insure bonding of fresh concrete with old one, a polymer bonding agent was applied over the exposed surface of the footing. after a curing period, backfilling of fooding with selected material took place to the ground level. zumrawi & aldaw, j. build. mater. struct. (2018) 5: 218-226 225 fig 8. fresh concrete casted in the enlarged area of the footing 5. conclusion this paper focused on strengthening of pad footing for storey extension by sectional enlargement. based on the study findings, the following conclusions can be drawn:  results show that the foundation after strengthening is capable to carry extra load from additional storey.  strengthening of foundation by sectional enlargement using concrete and steel reinforcement is found to be the most effective and economical strengthening technique to increase the load carrying capacity of existing foundations.  to enhance bonding of existing concrete with fresh one, footing surface must be painted by epoxy agent. also, shear connectors must be covered by bonding agents to guarantee fixation in old concrete.  experimental and analytical investigations are required to provide further information on the material, strength, and behavior of reinforced concrete structure. 6. references bian, y., hutchinson, t. c., wilson, d., & laefer, d. f. (2006). grouted helical piers for use in foundation rehabilitation: centrifuge testing. in paper presented at the international conference on re-use of foundations for urban sites (rufus). 19-20 october, 2006, watford, uk. bre press.. branco, f. & silva, v. d. (2003). structural rehabilitation of columns with reinforced concrete jacketing. no. february 2003, pp. 29–37. british standard (bs) (1997). structural use of concrete, vol. 3. bs 8110-1. carolin, a. (2003). carbon fibre reinforced polymer for strengthening of structural elements, doctoral thesis, division of structural engineering, lulea university of technology, lulea. cozmanciuc, c., oltean, r., & munteanu, v. (2009). strengthening techniques of rc columns using fibre reinforced polymeric materials. buletinul institutului politehnic din lasi. sectia constructii, arhitectura, 55(3), 85-92. 226 zumrawi & aldaw j. build. mater. struct. (2018) 5: 218-226 islam, s., islam, m. r., talukder, m. a. q., & hossain, s. r. (2013). strengthening technique of reinforce concrete structure: bangladesh perspective. american academic & scholarly research journal, 5(6), 17-23. johansson, b. & thyman, m. (2013). strengthening of buildings for storey extension. master’s thesis, department of civil and environmental engineering, division of structural engineering, chalmers university of technology, göteborg, sweden, p 113. nordin, h. (2005). strengthening structures with externally prestressed tendons: literature review, technical report, division of structural engineering, luleå university of technology, luleå. norris, t., saadatmanesh, h., & ehsani, m. r. (1997). shear and flexural strengthening of r/c beams with carbon fiber sheets. journal of structural engineering, 123(7), 903-911. rodriguez, m., & park, r. (1991). repair and strengthening of reinforced concrete buildings for seismic resistance. earthquake spectra, 7(3), 439-459. shihada, s. m., & al-jerjawy, m. (2011). assessment and strengthening of a sixteen storey rc building damaged by air attack. the islamic university journal, 19(2), 37-56. statens, råd förbyggnadsforskning, förstärkning av betongkonstruktioner (1978). strengthening of concrete structures. in swedish, svensk byggtjänst, stockholm. j. build. mater. struct. (2017) 4: 84-92 original article doi : 10.34118/jbms.v4i2.35 issn 2353-0057, eissn : 2600-6936 repair of reinforced concrete beams in shear using composite materials prfg subjected to cyclic loading boumaaza m 1, *, bezazi a 2, bouchelaghem h 2,3, benzannache n 1, amziane s 4, scarpa f 5 1* laboratory of civil engineering & hydraulics (lgch)/guelma university, algeria 2 laboratory of applied mechanics of new materials ((lmanm)/university of guelma, algeria 3 department of mechanical engineering/university of constantine1, algeria 4 department of civil engineering, polytech clermont ferrand/blaise pascal university, france 5 advanced composites center for innovation and science (ccctb)/university of bristol, uk * corresponding author: messaoudabeb@yahoo.fr abstract. nowadays, finding new approaches to attenuate the effects of the catastrophic shear failure mode for reinforced concrete beams is a major challenge. generally the bending failure is ductile. it allows a redistribution of the stresses providing an early warning, whereas the rupture by shear is fragile and sudden which can lead to detrimental consequences for the structures. this research focuses on the repair of deep beams in reinforced concrete shear subjected to 4-point bending. after being preloaded at different levels of their ultimate loads, the beams are repaired by bonding a composite material made of an epoxy resin reinforced by glass fibers. the main objective of this study is to contribute to the mastery of a new method developed by the authors that consists by banding the cracks in critical zones in order to avoid fragile ruptures due to the shear force. this new technique led to better results in terms of mechanical properties when compared to conventional methods, notably the absence of the debonding of the composite found in the case of the repairs of the beams by bands or u-shaped composites. the feasibility, the performances and the behavior of the beams have been examined. the experimental approach adopted using this new technique has shown the influence of the type of loading on the fatigue behavior. in addition, the repair performed led to a considerable improvement in the fatigue durability of the preloaded beam. key words: deep beam, shear failure, preloading, composite, repair. 1. introduction during their lifetime, concrete structures can be subjected to different types of loading and environmental conditions. cracks produced and preload conditions are initial damage that can affect long-term structural behavior. these initial cracks and damage propagate and increase over time as a result of cyclic loading. in the case of deep bridge beams, for example, the structural elements are subjected in service to maximum values stresses of generally known but time-varying, most of which result from cyclic variations in stresses. generally a bridge is designed for a century, even in a regulatory way, their operating conditions turns out to change following the development not only of the size and load of vehicles but also road traffic. this leads to a reduction in their initial lifetime, sometimes causing catastrophic ruptures even when they are subjected to cyclic of modest maximum value stresses. the phenomenon involved in this is fatigue damage. it is characterized by irreversible deformations in the form of cracks that develop slowly over time without macroscopic signs. by accumulating, these can lead to a catastrophic rupture. indeed, the literature review shows clearly that experimental research and analytical studies on the fatigue behavior of reinforced concrete (rc) beams reinforced or repaired with frp are very limited. the majority of these studies relate to flexural reinforcement, while very few studies have been carried out on shear reinforcement (deep beams). mailto:messaoudabeb@yahoo.fr boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 85 meier et al. (1992) tested two rc beams reinforced with a hybrid glass/carbon composite. bames and mays (1999) conducted an experimental program to study the flexural behavior of reinforced rc beams using frp under fatigue stress. the reinforcement used is a unidirectional composite fabric based on carbon fibers (cfrp) bonded to the underside of the beam (tensile zone), which leads to the conclusion that the internal reinforcement rate affects the failure mode. shahawy and beitelman (1999) tested six beams of t shape under cyclic fatigue with a loading level between 0 to 25% of the ultimate load. papakonstantinou et al. (2001) also conducted fatigue tests in 4-point bending at a frequency of 2 or 3 hz on 14 reinforced rc, eight reinforced with glass fiber (gfrp), and six non-reinforced with different fatigue loading levels. on the one hand, they found that the fatigue failure of the reinforced beams is caused by the fatigue failure of the tensile steel armature reinforcements after their plastification and, on the other hand, the use of the frp increases the lifetime of the beams loaded at cyclic loading. masoud et al. (2001) also performed fatigue tests under 4-point bending with a frequency of 3 hz on rc beams, whose tensile steel armature are corroded, reinforced with a carbon fabric. the loading level is between 10% and 80% of the ultimate strength of unreinforced rc beams. the fatigue failure of reinforced beams is caused by the fatigue of the tensile armatures similarly to shahawy and beitelman (1999). in addition, some studies have also investigated a structural elements preloaded, reinforcement with composite materials in particular (arduini, 1997; choi et al.; de lorenzis and teng, 2007; boussaha, 2008; kreit, 2011; dong, 2013 and teo, 2017). the problems of premature failure associated with the complexity and incomprehension of the shear behavior of rc beams, under cyclic fatigue loading (loading/unloading) were the aim of this study. the main objective of this study is to elucidate, using an experimental investigations, the fatigue behavior of deep beams repaired by frp using a new technique. this technique was developed recently by the authors boumaaza et al. (2017) for static tests (non-cyclic). the deep beam, used in the present work, is tested under 4-point bending assuming that the shear failure mode is predominant, with cyclic loading. for this purpose, a beam is preloaded at 80% of its ultimate load and then it has repaired by composite materials using the new technique scr. after at list 15 days, resin polymerization time, the beam is cycled 19 times at 65 % of its ultimate load. 2. experimental protocol the aim of the experimental part is to investigate the fatigue behavior of the rc deep beams under cyclic loading (load/unload), repaired by glass fiber composites (gfrp) using the scr technique. the concrete beams were designed in accordance with astm c78-00, armed with two ha8 in tensile zone and two ha6 in compressed zone, and 6 frames used as transverse reinforcements spaced of 110 mm. fig. 1 shows the detail of the reinforcement in steel armatures of the beams. after at least 28 days, the manufactured beam is preloaded at 60% of its ultimate load. the beam is repaired using the scr technique which requires the preliminary work as follows: drilling the beam on each side at the vicinity of the diagonal cracks of the concrete by passing through it (figure 2a); before the glass fabric was inserted, a repair was carried out using the mortar fig. 2(b); the positions of the grooves, having 25 mm wide and 3 mm depth, were traced on the surface of the beam (figure 2c). then the grooves are subsequently cleaned of dust and concrete debris; 86 boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 fig 1. schematic layout of the specimen and steel reinforcement in accordance with astm 78-00. the unidirectional of 600 g/m2 surface density fabric is cut in pieces having a size of 1500x25mm and 1000x25mm. then the fabric, previously impregnated with the epoxy resin, is inserted into the grooves. scr repair involves introducing composite bands into holes in the shear zone in order to band the diagonal cracks (figure 2d). fig 2. repair of the beam (a) drilling of the holes (b) grooving (c) mortar reparation (d) cut of the unidirectional fabric (e) repair of the beam using scr technique. (a) (b) (c) (d) (e) boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 87 the tests were carried out in a bending machine (controls) in the architecture laboratory of the university of guelma. the frame of this machine is equipped with a load cell of 100 kn (figure 3). the vertical displacement was measured, in the middle section, using an lvdt sensor with a maximum stroke of 100 mm. the strains were measured using 3 strain gauges, where two are glued at the external surface of the composite bands and the third one in the tensile face in the middle of the beam (figure 2e). fig 3. machine test. 3. results and discussion 3.1. global behavior the stress/displacement curves versus the loading, of the control beam and the beam preloaded at 65% and then repaired by the gfrp composite using scr technique are represented in figure 4. the curves obtained show that, after the discharges (at zero loads), the presence of a permanent displacement due to inelastic behavior and therefore the existence of residual arrows which can be interpreted as an irreversibility due to the cracking of the concrete. these results are in agreement with the ones obtained by (boussaha, 2008) and (kreit, 2011). fig 4. stress/displacement of the beam ep_65% _prfv_e of the 19 cycles load/unload. 88 boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 the analysis of figure 5 shows that the evolution of the stress/displacement of the control beam is very close to that obtained at the first cycle (1st cycle), whereas the curve of the 19th cycle is distant from the previous one by approximately 1.64 mm (residual arrow) due to the plastification of the steel armature reinforcements of the tensile zone of the beam. fig 5. evolution of the stress versus displacement of the control beam and ep_gfrp_65%_test 1 and test 19. the results obtained, under fatigue loading, show generally that the displacements versus the cycling (load/de-load) number of the repaired beam are higher compared to the control one. however, the maximum displacements reached during the first three cycles of the repaired beam are lower than that obtained for the control beam (figure 6) and table 1. fig 6. evolution of the displacements versus the loading cycle numbers. 3.2. influence of the repair on the stiffness of the beams for the beam, preloaded and then repaired, bending stiffness was determined experimentally, which represents the slope of the linear part of the stress-displacement curve. the experimental results of the rigidities of the beams tested before and after the repair are presented in figure 7. a decrease of approximately 14.1% in the rigidity of the beam repaired with the gfrp is noticed for the 1st loading cycle compared to the control beam. however, in the second cycle, the boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 89 stiffness increased by about 17% and then slow decrease is observed while remaining greater than the rigidity of the control beam even for the 19th cycle. these results are in good agreement with the work of shahawy and beitelman (1999). fig 7. stiffness of the beams during the cyclic fatigue tests. 3.3. local behavior the stress/strain curves for the first loading cycle, plotted using the strain gauges (g1, g3 and g4), which their locations are illustrated in figure 10a, are shown in (figures. 8 and 9). the strains are measured in the middle of the tensile zone of the concrete beam using g1, while g3 and g4 at the cracks. table 1 recapitulates the obtained results of the strains gauges obtained by (g1, g3 and g4), displacements and rigidities of the control beam and the repaired one for the 19th tests. table 1. obtained strains using strain gauges (g1, g2 and g3), displacements and rigidities of the control beam and the repaired one for the 19th tests. n° of loading strains g1 (µm) strains g3 (µm) strains g4(µm) displacements (mm) rigidity control beam 385 3566 132 4.01 10,9 cycle 1 271 2553 2195 3.75 9,55 cycle 2 353 2412 2742 3.91 12,66 cycle 3 676 2303 1786 3.98 12,73 cycle 4 736 2268 1792 4.00 12,27 cycle 5 798 2228 1785 4.15 12,5 cycle 6 823 2210 1802 4.13 12,41 cycle 7 840 2156 1809 4.39 12,17 cycle 8 865 2122 1812 4.54 12,15 cycle 9 854 2119 1896 4.44 12,23 cycle 10 888 ----4.71 12,25 cycle 11 884 2107 1828 4.54 12,16 cycle 12 863 2074 1813 4.89 12,16 cycle 13 896 2092 1798 4.93 12,06 cycle 14 891 2118 181 4.77 12 cycle 15 893 2117 1790 5.12 12,03 cycle 16 882 2119 1781 5.27 11,74 cycle 17 866 2091 1784 5.2 11,91 cycle 18 862 2134 1796 4.88 11,82 cycle 19 864 2135 1766 5.07 11,79 90 boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 figure 8 and table 1 show the strains increases for the strain gauge (g1) from the 3rd cycle compared to the control beam, ie an increase of 1237% for the 19th cycle. fig 8. stress/strains obtained by strain gauge (g1) versus the cyclic loadings. it should also be noted that the recorded strains of the composite with the strain gauge g3 for the repaired beam have decreased for all cycles. the strains obtained for the control beam and the repaired one after the 19th cycle are respectively 3566 and 2135 μm, i.e. a decrease of 67% is noticed. while, increases for all loadings are recorded by the strain gauge (g4), ie approximately 1238% for the 19th cycle (figure 9, table 1). fig 9. stress/strain (g1) for 1st loading cycle of the beam (gfrp_65% _e) and the control beam. 3.4 fissuration figure 10a illustrates that the control beam subjected to 4-point bending has undergone a shear rupture, taking into account the type of cracking. the diagonal cracks were born on the lower supports and propagated towards the points of application of the upper load. boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 91 whereas the beam (ep_65% _e) was repaired by gfrp, under a load of fatigue in the service state, the rupture was not yet reached even after 19 loadings thus showing the effectiveness of the repair adopted in this work (figure 10b). moreover, no peeling of the composite was detected during the tests and the beam passed the fatigue test successfully. the ductile failure mode has not been distinguished for beams repaired under fatigue loading for a service level; this will be reached in static. fig 10. failure modes a) control beam b) beam preloaded at 60% then repaired by gfrp. 4. conclusions in this study, it was shown that the repair of beams using scr technique exhibited good fatigue behavior. the mode of failure of the repaired beam has not yet been reached even for 19th loading cycles. this result is very encouraging and must be confirmed by other tests in the future work. it is worth noticing that the presence of the composite in the shear zone not only reduced the potential crack propagation during fatigue cycles, but also stiffened the beams. therefore, this technique has a very good resistance to fatigue loading. acknowledgments the authors would like to acknowledge mr boudjehem h from the architecture laboratory of university of guelma having to facilitate the access to the experimental machine. 5. references arduini, m., nanni, a. (1997). behavior of precracked rc beams strengthened with carbon, frp sheets. asce journal of composites for construction, 63-70. barnes, r. a., mays g. c. (1999), fatigue performance of concrete beams strengthened with cfrp plates, asce, journal of composites for construction, 63 – 72. boumaaza, m., bezazi, a., bouchelaghem, h., benzennache, n., amziane, s. and scarpa. f. (2017). behavior of pre-cracked deep beams with composite materials repairs, techno press, structural engineering and mechanics 61(4), 575–583. boussaha, f. (2008). comportement en fatigue des poutres en béton armé renforcées en cisaillement à l’aide de matériaux composites avancés. thèse phd, école de technologie supérieure, montréal, canada., 144. choi y. w., lee h. k., chu s. b., cheong s. h, and jung, w. y. (2012). shear behavior and performance of deep beams made with self-compacting concrete. international journal of concrete structures and materials, 6 (2), 65–78. de lorenzis, l., teng, j. g. (2007). near-surface mounted frp reinforcement: an emerging technique for strengthening structures. composites: part b, 38, 119–143. dong, j., wang, q., guan, z. (2013). structural behavior of rc beams with external flexural and flexural– shear strengthening by frp sheets, composites: part b, 44, 604–612. kreit, a., mahmoud, f., castel, a., françois, a. (2011). repairing corroded rc beam with near-surface mounted cfrp rods. materials and structures 44, 1205–1217. (a) (b) 92 boumaaza et al., j. build. mater. struct. (2017) 4: 84-92 masoud s., soudki k., topper t. (2001), cfrp-strengthened and corroded rc beams under monotonic and fatigue loads, asce journal of composites for construction, pp.228 – 236. meier, u., deuring, m., meier, h., and schwegler, g. (1992). strengthening of structures with cfrp laminates: research and applications in switzerland. advanced compos. mat. in bridges and struct., k. w. neale and p. labossiere, eds. canadian society for civil engineers, montreal. papakonstantinou, c. g. (2000). fatigue performance of reinforced concrete beams strengthened with glass fiber reinforced polymer composite sheets.’’ ms thesis, university of south carolina, columbia, s.c. shahawy m., beitelman t.e. (1999). fatigue performance of rc beams strengthened with cfrp laminates, proceedings of 1st cddc international conference on durability of fiber reinforced polymer composite for construction, sherbrook, august, 169-178. teo, w., hing, k.l.m., and liew, m.s. (2017). interaction between internal shear reinforcement and external frp systems of rc beams: experimental study. the open civil engineering journal, 11, 143-152. wu, z.y. (2004). etude expérimentale du comportement des poutres courtes en béton armé pré-fissurées et renforcées par matériaux composite sous chargement statique et de fatigue. thèse lcpc paris, novembre. j. build. mater. struct. (2018) 5: 14-21 original article doi : 10.34118/jbms.v5i1.40 issn 2353-0057, eissn : 2600-6936 amelioration of mechanical and rheological characteristics of a ceramic slip by adding of bentonite hammadi l *, boudouaia w, belaid y laboratoire de rhéologie, transport et traitement des fluides complexes (lrttfc), faculté d’architecture et de génie civil, département d’hydraulique, université des sciences et de la technologie d’oran (usto mb) b.p. 1505 oran-el-m’naouar 31000, algérie * corresponding author: larbi.hammadi@univ-usto.dz or hammadi7280@yahoo.fr received: 29-01-2018 revised: 16-02-2018 accepted: 20-02-2018 abstract. this work is a contribution to the amelioration of the mechanical and rheological properties of a slip of ceramic used in the ceramic fabrication process. a study of characterization of slip of ceramic modified by bentonite has been accomplished chemically, physically, mechanically and rheologically. chemical analysis showed that the slip modified by bentonite consist essentially of silica with a ratio average equal to 3.5 and the ratio of clays (al2o3/sio2) is relatively stable with increasing percentage of bentonite in the slip, with an average 0.28. the mechanical and rheological tests showing that increasing the percentage of bentonite in base slip caused an increase in the mechanical resistance, the yield stress and rapid decrease in density of the slip. key words: amelioration, ceramic slip, yields stress, mechanical and rheological, density. 1. introduction the ceramic tile industry today is an important sector whose technological innovation and market trends have drawn a complex picture of products and processes. according to dondi et al. (2014) the production of ceramic tiles is growing worldwide at a rate of 300 million m2/year and has already passed 10 billion m2 in 2012. for this reason a many additives have been added to slip of ceramic such as the electrolytes (hayashi, 2012), polymers (mansur, 2008), sludge of wastewater treatment (martínez-garcía, 2012) in order to improve the quality of ceramic. the objective of this study is to ameliorate the mechanical and rheological properties of slip of ceramic by bentonite clay. it is noted that the bentonite is a natural clay whose mechanical properties (viscosity, fluidification, flow threshold, thixotropy) are widely used in the products of our daily life. its field of application extends from civil engineering (tan, 2014; besq, 2003), drilling fluid (hammadi, 2014; coussot, 2006), pharmacy and food application. the bentonite is also employed as a thickener in waterproofing of hydraulic structures (dams, large reservoirs, etc…). 2. materials and methods 2.1. materials and samples preparation the raw materials used in this study is from the "ceral" company of hassi -amer oran. this company uses clays at fixed percentages by adding deflocculants to facilitate mold release from the plaster molds. table 1 presents the various materials used by the company ceral for the manufacture of ceramics. table 1. the materials used by the company ceral for the manufacture of ceramics. materials percentage (%) schist 1 61 schist 2 10 sandstone 17 clay 12 mailto:larbi.hammadi@univ-usto.dz mailto:hammadi7280@yahoo.fr hammadi et al., j. build. mater. struct. (2018) 5: 14-21 15 in order to improve the physicochemical and mechanical characteristics of the slip of ceramic used by the company ceral we tried to replace the clay used by bentonite of maghnia without modifying the percentage of the other comps (schist 1, schist 2 and sandstone). the table 2 shows the percentage of mixtures. table 2. the percentage of mixtures used in this study. materials percentage (%) bentonite 0 3 6 9 schist 1 61 61 61 61 schist 2 10 10 10 10 sandstone 17 17 17 17 clay 12 9 6 3 2.2. experimental set up 2.2.1. mechanical characterizations the mechanical characterizations of the slip of ceramic and slip of ceramic with bentonite were carried out using the press (ceramic instruments srl) sassuolo-italy, the maximum pressure of this apparatus is 250 bar and a bending apparatus flexi 1000 lx gabtec, to the company ceramir from hassi amer oran. samples of 100 g were introduced into the press apparatus and a pressure of 80 bars was applied to make tiles with a thickness of 7.8 mm, a width of 100 mm and a width of 45 mm. then, tiles were introduced in a drying oven at 110° c for 2 hours. after completion of the tiles and drying, flexural tests were carried out. after 2 hours of drying at 110° c, the tiles of ceramic are placed in the oven at a temperature of 1140° c for 45 min to carry out the sintering tests. figure 1 shows the state of the tiles of ceramic after drying at 110°c. fig 1. the state of the tiles of ceramic after drying at 110°c. 2.2.2. rheological measurements the rheological measurements were performed by using a torque controlled rheometer (rs600 from thermo-fischer) connected to a temperature controlled water bath and equipped with a plate-cone geometry (diameter: 60 mm; angle: 2 degree; gap: 105 µm). a solvent trap was placed around the measuring device in order to minimize solvent evaporation. after the bending tests, the samples are recovered, ground and then passed through the 100 μm sieves in order to make granulometric tar compatible with the cone/plane geometry used for the rheological measurements. the slip in powder form is then dispersed with magnetic stirring for 3 hours in distilled water at a concentration of 58% by weight. the suspension obtained is left to stand for 24 hours. the creep and recovery tests after a rest time of 600 s, creep and recovery tests were performed by first applying a constant shear stress of 10 pa during 180 s to the samples of slip 16 hammadi et al., j. build. mater. struct. (2018) 5: 14-21 and then removing the shear stress during 180 s in order to obtain the time dependence of the compliance j. 3. results and discussion 3.1. chemical analysis chemical analysis of the samples was carried out at the laboratory of the lafarge company. the results are summarized in table 3. table 3. chemical analysis of slip modified by bentonite. elements (%) 0% of bentonite 3% of bentonite 6% of bentonite 9% of bentonite sio2 59.83 16.97 7.69 3.10 al2o3 60.68 17.36 7.62 2.49 fe2o3 60.93 16.26 7.37 2.27 cao 58.10 17.52 7.14 2.15 table 3 shows that the slip of ceramic modified by bentonite consists essentially of silica with average ratio of equal to 3.5. according to robert and tessier (1974), the values of the ratio are generally between 2 and 4 in clays, because of numerous substitutions. it is also observed that the clay ratio (al2o3/sio2) is relatively stable with the increase of bentonite content in the slip of ceramic, with an average of 0.28. the iron oxide content is quite high in the slip of ceramic modified by bentonite. it is also observed that the increase the quaintly of bentonite in slip of ceramic causes a decrease of cao. 2.1. amelioration of the mechanical characteristics of ceramic slip by bentonite 2.1.1. effect of bentonite on density of ceramic slip figure 2 shows evolution of the density of slip as a function of bentonite concentration added to slip. it can be observed that the density is decreased with the increase of the percentage of bentonite in slip of ceramic. this decrease can be explained by the increase in the volume of the slurry suspensions caused by the swelling of the bentonite. fig 2. evolution of the density of slip as a function of bentonite concentration added to slip of ceramic. 0 2 4 6 8 10 1420 1440 1460 1480 1500 1520 1540 1560 d e n si ty ( g /l ) bentonite (%) hammadi et al., j. build. mater. struct. (2018) 5: 14-21 17 3.2.2 effect of bentonite on mechanical resistance of slip the figure 3 shows the variation of mechanical resistance of slip as a function of the concentration of bentonite added to ceramic slip. we is it can be observed in the figure 3, an increase in the mechanical tensile bending strength with the increase in the amount of bentonite in the ceramic slip, this increase being of tensile bending strength can be explained by the increase in the silica content (sio2). fig 3. tensile bending strength as a function of bentonite concentration added to ceramic slip after baking at 110 ° c. 3.3. improvement of the rheological characteristics of the slip of ceramic by bentonite figure 4 shows the shear stress evolution as a function of shear rate for different concentration (0%, 3%, 6%, and 9%) of bentonite added in slip of ceramic. fig. 4. shear stress  as a function of the shear rate ̇ at different concentration of bentonite added in slip of ceramic. the solid lines correspond to the curve fitting to model of herschel-bulkley. 0 1 2 3 4 5 6 7 8 9 10 0 50 100 150 200 250 300 9 % bentonite 6 % bentonite 3 % bentonite 0 % bentonite r e ( m p a ) bentonite (%) 0 50 100 150 200 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 9% bentonite 6% bentonite 3% bentonite 0% bentonite model of herschel-bulkley s h e a r st re ss ( p a ) shear rate (s -1 ) 18 hammadi et al., j. build. mater. struct. (2018) 5: 14-21 from figure 4, it can be observed an increase of the shear stress of the modified slip is occurred with the increase of the concentration of bentonite added to the slip of ceramic. the variation of the shear stress  as a function of the shear rate ̇ at different concentration of bentonite added in slip of ceramic clearly shows a non-newtonian behavior after a yield stress. therefore experimental data were fitted to the classical model of herschel-bulkley with the coefficients of regression equal to 0.99 for all quantity of bentonite added in slip of ceramic: ̇ (1) where is the yield stress in pa, k the consistency index in pa.sn and n is the flow index. fig 5. yield stress as a function of bentonite added in silp of ceramic. fig.6. consistency index and flow index as a function of bentonite added in silp of ceramic. the fitted parameters of the model of herschel-bukley as a function of mass concentration of bentonite added to slip of ceramic are presented in figs 5 and 6. it appears that yield stress and consistency index increase with increasing mass concentration of bentonite added to slip of 0 2 4 6 8 10 5 10 15 20 25 30 35 y ie ld s tr e ss ( p a ) bentonite (%) 0 2 4 6 8 10 2 4 6 8 10 12 14 16 18 20 f lo w i n d e x ( -) c o n si st e n c y i n d e x ( p a .s n ) bentonite (%) k 0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 n hammadi et al., j. build. mater. struct. (2018) 5: 14-21 19 ceramic. concerning the flow index, it decreases with increasing mass concentration of bentonite in slip of ceramic. this increase on the yield stress, consistency index and the decrease of flow index can be explained by the increased interactions between the clay and bentonite particles. in addition to a hydrodynamic contribution, the bentonite particles thus provide an additional contribution in the form of a network of interactions, which modifies the mechanical and rheological behavior of the slip of ceramic. 3.4 effect of bentonite on creep and recovery of slip of ceramic figure 7 shows the values of compliance: , as a function of time, for the creep tests corresponding to the ceramic slip studied for mass concentration of bentonite range between 0 and 9% added in ceramic slip , in a time interval between 0 and 180s. for the interval time , we have represented the corresponding recovery. we observe on this figure a decrease of the elastic compliance with the increase of quantity of bentonite added to slip of ceramic. i.e., increase of the elastic modulus: , indicating an increase of the viscoelastic properties of modified slip. in other words, the creep deformation decreases with increasing the bentonite in slip and the time necessary to reach a constant deformation during recovery, after removal of the shear stress, decreases. this behavior could be explained by the interaction between the granules of the clays suspension. fig.7. compliance versus time in creep and recovery test for different content of bentonite added to ceramic slip. the solid lines correspond to the curve fitting to generalized kelvin-voigt model. the elastic properties were defined by correlating the results with the well-known viscoelastic models of burger model or generalized kelvin-voigt model (hammadi and ponton, 2017), comprising the association in series of the maxwell and the kelvin–voigt models. the creep curves are described by: ∑ ⌈ ( )⌉ (2) (3) whereas the recovery strain is given by: 0 40 80 120 160 200 240 280 320 360 0,0000 0,0005 0,0010 0,0015 0,0020 0,0025 0,0030 0,0035 0,0040 0,0045 recovery creep 9% bentonite 6% bentonite 3% bentonite 0% bentonite c o m p li a n c e j ( 1 /p a ) time (s) 20 hammadi et al., j. build. mater. struct. (2018) 5: 14-21 ∑ * ( ) + ( ) (4) where is the purely elastic contribution (or the instantaneous elastic compliance), is the purely viscous contribution, represented by the dashpot of the maxwell model, i.e., the uncoupled or residual steady-state viscosity obtained from the creep curve at long times when the compliance curve is linear, is the contribution to retarded elastic compliance, is the retarded time, is the retarded viscosity and is the time where the stress is applied for and removed at . the fittings in fig. 7 were performed with just one kelvin–voigt solid (n=1) and the fitting parameters are detailed in table 3. the column represents the instantaneous elastic modulus of the maxwell unit at t =0; that is, the instantaneous elastic response of the system and the column is the elastic modulus of kelvin–voigt. the latter represents the contributions of the retarded elastic region to the total compliance. the strong increase is observed in g0 and g1 when the quantity of bentonite added to slip of ceramic is changed between 0 and 9% is the manifestation of the shift from viscous to elastic behavior and an increase of the viscoelastic properties in that range of bentonite. table 3. fitting parameters of the creep–recovery data in fig. 7 , with n = 1 in eqs. (2) and (4). creep recovery bentonite (%) g0 (pa) g1 (pa) (pa.s) g1 (pa) (pa.s) (s) 0 1470 345 161615 2272 56468 26 3 1639 413 240173 3333 64016 38 6 2439 680 357729 4166 97617 44 9 4762 1266 454505 6666 163320 48 concerning let us mention that it has the meaning of viscosity of the system in the newtonian regime, whereas it shows a clearly increasing trend as the quantity of bentonite is increased in slip of ceramic. at high quantity of bentonite added to slip of ceramic, the applied stress of 10 pa is not sufficient to break weak particle-to-particle bonds, and the suspensions do not flow. for lower quantity of bentonite added to slip of ceramic such resistance to flow is not so large, and this explains the values of and in this case the retarded deformation, related to the breaking and reconstruction of weak links between the particles. the characteristic relaxation time associated with these breaking/reconstruction processes is . 4. conclusions addition of bentonite clay on slip of ceramic greatly changed the mechanical and rheological properties of slip. the degree of interaction between bentonite and slip particles depended on the bentonite concentration added to the ceramic slip. the effect of bentonite on stationary nonnewtonian flow behavior of slip of ceramic was successfully modeled using the herschel-bulkley model over the studied range of bentonite added to slip of ceramic. the yield stress and the consistency index of ceramic slip modified are increased by increasing the quantity of bentonite in ceramic slip. a strong increase of elastic modulus deduced from creep measurements fitted to generalized kelvin-voigt model with one element was observed when the quantity of benonite is increased between 0 and 9% added to slip of ceramic. the study has also shown an increase of mechanical resistance of ceramic slip with increase of quantity of bentonite added to ceramic slip. 5. references besq, a., malfoy, c., pantet, a., monnet, p., & righi, d. (2003). physicochemical characterisation and flow properties of some bentonite muds. applied clay science, 23(5-6), 275-286. hammadi et al., j. build. mater. struct. (2018) 5: 14-21 21 coussot, p., tabuteau, h., chateau, x., tocquer, l., & ovarlez, g. (2006). aging and solid or liquid behavior in pastes. journal of rheology, 50(6), 975-994. dondi, m., raimondo, m., & zanelli, c. (2014). clays and bodies for ceramic tiles: reappraisal and technological classification. applied clay science, 96, 91-109. hammadi, l., boudjenane, n., & belhadri, m. (2014). effect of polyethylene oxide (peo) and shear rate on rheological properties of bentonite clay. applied clay science, 99, 306-311. hammadi, l., & ponton, a. (2017). rheological investigation of vase of dam: effects of aging time, shear rate, and temperature. applied rheology, 27(1). hayashi, a., noi, k., sakuda, a., & tatsumisago, m. (2012). superionic glass-ceramic electrolytes for roomtemperature rechargeable sodium batteries. nature communications, 3, 856. mansur, a. a. p., nascimento, o. l. d., vasconcelos, w. l., & mansur, h. s. (2008). chemical functionalization of ceramic tile surfaces by silane coupling agents: polymer modified mortar adhesion mechanism implications. materials research, 11(3), 293-302. martínez-garcía, c., eliche-quesada, d., pérez-villarejo, l., iglesias-godino, f. j., & corpas-iglesias, f. a. (2012). sludge valorization from wastewater treatment plant to its application on the ceramic industry. journal of environmental management, 95, s343-s348.. robert, m., & tessier, d. (1974). méthode de préparation des argiles des sols pour des études minéralogiques. in annales agronomiques, 25 :859-882. tan, o., gungormus, g., & zaimoglu, a. s. (2014). effect of bentonite, fly ash and silica fume cement injections on uniaxial compressive strength of granular bases. ksce journal of civil engineering, 18(6), 1650-1654. j. build. mater. struct. (2017) 4: 50-57 original article doi : 10.34118/jbms.v4i2.31 issn 2353-0057, eissn : 2600-6936 the effect of building materials choice on the thermal comfort in the self-produced individual housing in biskra. latreche s*, sriti l department of architecture , university of biskra, bp 145 rp, 07000 biskra, algeria * corresponding author: sihem.latreche21@gmail.com abstract. the building envelope is the first barrier to protect against external climatic variations. generally, it consists of two types of walls: opaque walls (walls and roof) and transparent walls (windows). the design characteristics of the enclosure strongly affect the occupants' thermal comfort, as well as the building energy consumption. the constructive choices relating to structural elements, in particular, walls, roofing and openings are generally considered in the thermal exchanges between the building and its environment. in the present study, which is based on experimental analysis in the self-generated residential sector in biskra (algeria), where a warm and arid climate predominates, we aim to evaluate the thermal impact of certain architectural and constructive parameters that are specific to residential habitat self-produced in biskra. this paper summarizes the main results obtained from an in situ measurement campaign that evaluated the essential parameters of thermal comfort such as ambient and surface temperature, air velocity, and humidity. these parameters were used as indicators to measure the impact of the envelope material characteristics on its climatic adaptability. this paper also presents some recommendations for optimizing the choice of building materials specific to the self-produced residential in order to improve its thermal performance while preserving the essentials of its specificities. key words: construction materials, thermal comfort, individual housing self-produced, hot and arid climate, biskra. 1. introduction in algeria, there are several reasons for the evolution of the constructive system in the individual housing, in particular the appearance of new materials and construction techniques as well as new modes of architectural design. unfortunately, this revolution in architectural practice has ignored the specificities of the climate context, which has led to a rupture between the framework and its environment and an abusive and irrational exploitation of the resources energy. thus, electricity consumption in the residential sector in algeria represents 28% of the total consumption of electricity (aprue, 2015). this consumption is essentially, intended to cover the needs of artificial lighting, heating and air conditioning (figure. 1); it is experiencing a growing trend in particular for the residential sector (figure.2). fig. 1. distribution of energy consumption by sector in algeria (source: aprue, 2015). fig. 2. evolution of energy consumption by sector in tep (source: aprue, 2015). mailto:sihem.latreche21@gmail.com latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 51 the city of biskra, which is characterized by a hot and arid climate, illustrates the magnitude of this phenomenon. since a few decades, the built frame produced in this city has no relation with the climatic conditions, which drives the inhabitants to turn to the mechanical means to ensure a certain level of comfort whose cost is each year more high. in addition, it is to reduce this energy consumption and ensure optimum climatic comfort that must be taken on architectural design. as such, the design characteristics of the envelope strongly affect the thermal comfort of the occupants, as well as the energy consumption in the building. the climate and energy performance of the envelope depends on the constructive choices relating to the structural elements, in particular the walls, the roof and the openings generally considered as determining factors in trade between the building and its environment. the objective of this study is to evaluate the thermal impact of the structural and constructive elements of the envelope as they are used in the residential housing produced in biskra. the ultimate goal of our research is to improve the thermal performance of the architectural envelope of this type of habitat and thus reduce energy consumption through passive solutions. 2. the climatic characteristics of the wilaya of biskra the city of biskra is located in the south-east of algeria at a latitude of 34.80 ° north and longitude of 5.73 ° east (figure. 3). biskra belongs to a region classified arid, where a hot and dry climate with cold winters and hot summers predominates. the maximum temperature reaches 42c° during the month of july and the minimum temperature decreases to 7 c° in winter during the month of january. the average annual temperature is 21.7 c°, while the average annual humidity is 46%. very low precipitation is recorded with a maximum of 20 mm/year, and an annual average of about 8.8mm/year. the directions of prevailing wind is north-west in winter, south-east in summer at a speed from 6 to 10 m/s (figure.4). fig 3: situation of the wilaya of biskra (source: google earth) 52 latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 fig 4: climatic data of the city of biskra (source: weather station data biskra, 2000-2009) according to givoni (1978), to assure the hygrothermal comfort under a dry hot climate, the buildings must be adapted to the summer conditions and it assuming that a building where the comfort is assured in summer will satisfy the winter requirements. in this study, it will be limited to the presentation of the results obtained during the summer period. 3. the building envelope and thermal comfort from ancient times up to the present day, the man did not stop improving his housing environment to assure a protection always more effective against weather conditions and aggressive factors of the external environment. however, thermal comfort in a building depends mainly on the thermal behaviour of its envelope (fig. 5) more precisely are the building materials and the architectural and constructive characteristics of the structural elements (wall thickness, compositions, layout ... etc.), which determine the climatic adaptability of a construction. the outside envelope of the building is its first barrier of protection; it consists of two types of walls: opaque walls (walls and roof) and transparent walls (windows). the roof is responsible for 70.62% of the gains received while 27.11% of the thermal gains are transmitted by the four facades, and 2.27% by the windows (necib, 2016). a judicious treatment of the walls of the envelope according to the warm and arid climatic conditions (choice of construction materials with high thermal inertia for walls and roofing, reduction of the dimensions of windows, solar protections ... etc.) allows to guarantee an optimal comfort inside the building, even if the outside conditions are unfavorable (izard, 1979). latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 53 fig. 5: the outside envelope undergoes numerous aggressions of the local climate and the environment (source: hauglustaine, 2006) 4. experimental study our analytical work based on a survey in situ intended for the study of the structural and constructive parameters of the envelope influence on the thermal comfort. this one is measured from the ambient and surface temperature, the air speed, and the relative humidity. the measuring instrument testo was used to raise the variations of the previous three hygrothermal parameters while the surface temperature was measured with an infrared thermometer (figure. 6). the measures were made inside, outside of the room, and in various points, in particular the roof and the wall of facade (figure.7). to select houses to be studied, it was necessary to perform a typo-morphological analysis. an important corpus of contemporary individual self-produced in biskra was assembled. the houses were distributed in different planned subdivisions of the city and their choice was made according to the characteristics of the most recurring envelope (orientation, building materials, ratio of openings, number of levels ... etc.). in total, 15 variants of rooms were studied. the analysis of the climatic data of biskra allowed us to determine the period of overheating, which is approximately one week from the end of july to the beginning of august. the recording of the measurements took place at two times of the day from 14 pm to 16 pm in the afternoon and from 9 am to 11 am in the morning. fig. 6 : measuring instrument testo and infrared thermometer fig. 7: position of measurement points in the room 54 latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 in order to study the impact of the building materials used at the envelope level, several cases have been chosen. the sample includes 15 variants that illustrate the different constructive systems of exterior walls used in the biskra (table 1). in addition to the walls, two other parameters have been taken into account: the orientation and position of the room in the house is in the ground floor (unexposed roof, floor), or on the upper level (exposed roof, terrace). table 1: distribution of the 15 variants of the studied pieces distributions of the 15 variants of parts studied according to the construction material walls in hollow perpend ( 2 variants) walls in full perpend ( 1 variant) walls simple brickbuilt of 15cm (4 variants in the floor) walls brick-built double of 15cm x2 (2var. rdc, 3var. r+1) walls brick with blade of air (1var double. rdc, 2var. r+1) to illustrate the obtained results at the end of the campaign of measure, it was chosen to present some examples showing the parameters of thermal comfort (temperature, relative humidity, air velocity) measured in parts that differ according to three parameters: the physical and constructive characteristics of the walls, the orientation and the type of roofing (floor or terrace) (table 2). table 2: examples of results of the measures made in situ in rooms using various building materials for walls; wall in hollow brick (17cm), located on the floor, orientation south ambient temperature c ° morning afternoon max min moy max min moy temp inside 35.2 34.6 34.8 39 36.8 38 temp outside 39.1 33.1 37.8 44 40 41.5 thermal gap 4 1.5 3 5 3.2 3.5 surface temperature c ° temp surf insi wall 36.4 / 36.4 38.5 / 37.6 temp surf outs wall 40.6 / 40.1 46.9 / 45.6 thermal gap 4.2 / 3.7 8.4 / 8 temp surf insi roof 36.8 / 36.6 37.5 / 37.5 temp surf outs wall 42.6 / 42 41.6 / 41.2 thermal gap 5.8 / 5.4 4.1 / 3.7 relative humidity % humidity indoor 26.4 24.8 25.6 26.3 22.5 24.2 humidity outside 20.3 19.7 20 14 13 13.3 walls brick with blade of air 33cm located on the floor, orientation west ambient temperature c ° morning afternoon max min moy max min moy temp inside 41.3 33.3 32.5 36.6 34 36.3 temp outside 37.3 37.2 37 42.3 41 41.8 thermal gap 4 3.9 4.5 5.7 5 5.5 surface temperature c ° temp surf insi wall 37.7 / 37.6 38.5 / 38.1 temp surf outs wall 41.6 / 41.4 49 / 48.4 thermal gap 4 / 3.8 10.5 / 10.3 temp surf insi roof 38.4 / 38.1 39.6 / 39.3 temp surf outs wall 34.4 / 34.4 46.8 / 46.4 thermal gap 4 / 3.7 7.2 / 7.1 relative humidity % humidity indoor 25.9 24.7 25.4 20.6 20 20.3 humidity outside 21.8 20.6 21.2 13.9 13 13.3 latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 55 air speed m / s air speed inside 0,3 0 0,1 0,3 0 0,1 air speed outside 1,3 0,3 0.6 1,9 0,5 1.2 air speed m / s air speed inside 0.5 0 0.2 0.3 0 0.1 air speed outside 1 0.3 0.5 1.9 0.5 1.2 wall in hollow brick 15+15 (32 cm), located on the floor, orientation northwest ambient temperature c ° morning afternoon max min moy max min moy temp inside 35,3 35,3 35,3 38 37,6 37,8 temp outside 39,6 38 39,2 42,8 34,3 42,6 thermal gap 4.3 2.7 4 4.8 3.3 4.8 surface temperature c ° temp surf insi wall 35 / 34.1 38,5 / 38 temp surf outs wall 38.3 / 36.5 45,5 / 44,7 thermal gap 3.3 / 2.4 7 / 6.7 temp surf insi roof 38,4 / 38,4 38,8 / 38,7 temp surf outs wall 35,8 / 34,7 47,5 / 47,1 thermal gap 2.6 / 3.7 8.7 / 8.4 relative humidity % humidity indoor 30,7 26,7 29 26,7 20 21,8 humidity outside 23,2 20,4 21,6 15,4 14,8 15,5 air speed m / s air speed inside 0,3 0 0,1 0,3 0 0 air speed outside 1,9 0,3 0,7 0,5 0,3 walls in full perpend (20cm) located on the ground floor , orientation west ambient temperature c °° morning afternoon max min moy max min moy temp inside 37,4 37 37,1 40,3 40,1 40,2 temp outside 40 39 39,7 41.5 40,8 41 thermal gap 2.6 2 2.6 1.2 0.7 0.8 surface temperature c ° temp surf insi wall 36,4 / 37,1 42,1 / 41,7 temp surf outs wall 41,2 / 41 45,4 / 45 thermal gap 4.8 / 3.9 3.3 / 3.3 temp surf insi roof 37,1 / 37 44,7 / 44,3 temp surf outs wall 39,2 / 38,6 50,6 / 49 thermal gap 2.1 / 1.6 5.9 / 4.7 relative humidity % humidity indoor 31,1 24,2 26,1 21,4 19 19,6 humidity outside 21,8 21,6 21,7 19,4 17,5 18,2 air speed m / s air speed inside 0 0 0 0 0 0 air speed outside 1,4 0,4 0,8 0,5 0 0,3 walls in hollow perpend (22cm) located on the ground floor south-west orientation ambient temperature c ° morning afternoon max min moy max min moy temp inside 32,2 32 32,1 37,7 34,7 36,5 temp outside 34,8 34 34.3 41,1 38,4 37.5 thermal gap 2.6 2 2.2 3.4 0.5 1 surface temperature c ° temp surf insi wall 31,5 / 31,2 37,2 / 36.9 temp surf outs wall 35,8 / 35,4 45,7 / 45 thermal gap 4.3 / 4.2 8.5 / 8.1 relative humidity % humidity indoor 39,4 34,8 35,6 32,1 26,2 29,4 humidity outside 32,8 31,3 31,8 21,5 17,9 20 air speed m / s air speed inside 0.5 0 0,1 0,6 0,0 0,1 air speed outside 2.1 0.3 1 2,6 0,3 1 56 latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 5. interpretation of the results 5.1 air temperature according to bennadji (1999), the subtraction of the external average temperatures from those of the interior of the room allows to appreciate the temperature difference between the inside and the outside. in table 2, it is noted that there is a difference of 0.5 c ° to 2 c ° between these two temperatures in a house built in single wall (single partition). the maximum value of ambient temperature is recorded in houses built in hollow and full block; for these cases, the indoor temperature is in the order of 32 ° to 38 ° at the time when the outside temperature reaches the 40 °. this constructive choice is visibly inadequate for the warm and arid climate. for the rooms built on the floor the situation of discomfort is at its extreme, for example for a piece built in single 15 cm brick wall, the average temperature difference is in the order of 3 c ° to 3.5 c °. on the other hand, in the houses built in double partition, the temperature difference is more appreciable. as an example, for double brick walls of 15 cm, it is between 4 c ° to 4.5 c ° (the internal temperature reaches 23.5 c °, outside it is 26.5 c °). in the case of double walled walls with a blade of air, the thermal gap between the inside and outside is optimal in the order of 5 c to 5.5 c °. in conclusion, it appears that the highest indoor temperatures are recorded in simple walled rooms with low thermal resistance materials such as hollow and full block. on the other hand, the walls in double walls give more interesting results from the point of view of thermal comfort in the summer period. note that the ambient temperatures measured are also dependent on other factors such as orientation and external climatic fluctuations. 5.2. the relative humidity and the air speed when reading the results of the measurements, we can be said that the external relative humidity is low compared to the internal humidity, on the outside it usually varies between 15% and 19% and inside it is between 22% and 31%. these results can be explained by human metabolism vapor and domestic activities and also the lack of aeration in the house. according to liebard (2005), the air velocity that does not exceed 0.2 m/s in the habitat has an influence on convective heat exchanges. however, with respect to the parts tested, the air velocity was very low not exceeding 0.1 m/s due to the lack of transverse ventilation. 5.3. the values of the surface temperature according to szokolay (2004), the temperature of the external surface has great effects on the internal thermal conditions; moreover, it varies with the clarity of the color and the velocity of the air in contact with the surface. based on the results obtained, it appears that the temperatures of the internal surfaces are higher than the ambient temperature when the walls are exposed to solar radiation. thus, the higher the external surface temperature increases due to the lack of shading and the lack of solar protections at the level of openings, the higher the ambient temperature rises in proportion to the external surface temperature. the temperature of the air and the surface temperature are therefore linked both by the amount of the incident solar radiation and also by the thermo-physical properties of the building materials, which retard the transfer of the heat inside. latreche and sriti., j. build. mater. struct. (2017) 4: 50-57 57 6. conclusions through an experimental in situ study of a single-detached houses corpus in biskra, the influence of the structural and constructive choices of the architectural envelope on the inner thermal comfort was examined. this experiment has shown that a judicious choice of materials can positively influence the inner thermal comfort, especially thanks to the thermo-physical properties of the materials that allow regulating heat exchanges between the building and its environment. the double-walled walls offer some advantages from the point of view of thermal comfort during the summer period. moreover, the thermal operation of the enclosure can be optimized thanks to the integration of the solar protections according to the orientation of the façade. 7. references aprue, (2015). final energy consumption of algeria, key figure-year 2015; ministry of energy and mines. bennadji, a. (1999). climatic or cultural adaptation in arid zones: case of the algerian south-east. phd thesis. université d'aix-marseille1-université de provence. hauglustaine j.-m. (2006). the global conception of the envelope and the energy, a practical guide for architects; ministry of the walloon region; february 2006. givoni, b. (1978). man architecture and climate. editions le moniteur, paris, france, 460 p. izard, j. l. (1979). archi bio; editions parentheses; roquevaire, 1979. liebard, a. (2005). treatise on bioclimatic architecture and urbanism: design, build and develop with sustainable development. editions le moniteur, paris, france, 2005. necib, h (2016). improved thermal insulation of habitats in warm and arid regions. third international conference on energy, materials, applied energetic and pollution. icemaep 2016; constantine, algeria szokolay, v. (2004). introduction to architectural science, the basis of sustainable design. architectural press edition, edition an imprint of elsevier science, 348p. j. build. mater. struct. (2018) 5: 65-73 original article doi : 10.34118/jbms.v5i1.45 issn 2353-0057, eissn : 2600-6936 effect of glass addition on the properties of cements (cemi) morsli h1,*, chaid r1, molez l2, diouri a3 1 umb, boumerdes, algeria 2 insa, rennes, france 3 faculty of science, rabat, morocco * corresponding author’s e-mail: hamza_morsli@yahoo.fr abstract. the purpose of this study is to recover mineral residues as an additive in cementbased building materials. it is part of a sustainable development approach. the use of recovered and recyclable industrial residues in partial replacement of portland cement reduces greenhouse gas (ghg) emissions and results in the manufacture of cement with a lower environmental impact. using various experimental techniques, particular attention is paid to the behaviour of the glass powder finely crushed and chemically activated associated with portland cement. this study confirms the improvement in the physicochemical and mechanical properties of cements with the addition of glass powder, which augurs well for its use as a cement additive. key words: cement, glass, addition, activation. 1. introduction different mineral additions are currently used in cement. they are used as substitution to cement. the use of these supplementary cementitious materials provides to mortar a denser matrix that will be more resistant to aggressive environments such as sulphates, chlorides and other aggressive agents. the fineness of mineral additions, their chemical composition, their structure (glassy or crystalline), their pozzolanic activity and their solubility in alkaline medium govern their cementing properties in mortar. their content in amorphous phase is a key factor in the reactivity of the mineral additions (tagnit and nkinamubanzib, 2001). glass is obtained primarily from the fusion of silica sand (>99% silica) and hence could be a pozzolanic material. as the use of glass increases steadily, glass waste increases accordingly. there are many alternatives for glass reuse. according to some studies (kojima et al., 2000), most methods of reuse require preliminary preparation such as milling and hence could not be well developed and are unable to absorb the large quantities of waste glass. an alternative sustainable solution could be the reuse of waste glass in concrete (roz-ud-din and parviz, 2012). indeed, for economic and environmental reasons, the use of recycled glass in cement and concrete has attracted the interest of many municipalities which encouraged further studies (aci 116r-90, 2000). the development of using waste glass as coarse or fine aggregates or as cement replacement material was hindered because of the risk of alkali–silica reaction (asr) and other durability properties. however, de castro and de brito (2013) analyzed the effect of using fine and coarse glass aggregates on the durability performance of concrete and concluded that concrete with glass aggregates is completely feasible and that in most cases the glass aggregates do not alter the durability-related properties of concrete such as water absorption by capillarity and immersion, carbonation and chloride diffusion. oliveira et al. (2013) analyzed the effect of very fine glass aggregates in rendering and found that mechanical strength and durability properties are improved with the incorporation of up to 20% of fine glass aggregate. the incorporation of received: 09-02-2018 revised: 12-04-2018 accepted: 18-04-2018 mailto:hamza_morsli@yahoo.fr 66 morsli et al., j. build. mater. struct. (2018) 5: 65-73 fine glass waste aggregates improves the mechanical performance of mortar especially for replacement ratios around 20% (penacho et al., 2014). corinaldesi et al. (2004) found no detrimental effect of the glass particles (smaller than 100 mm) when they replaced 30 and 70% of the mass of sand with glass aggregates. shayan and xu (2006) and taha and nounu (2008) also concluded that there was no expansive reaction related to the incorporation of glass and powder to replace natural sand and cement, respectively. the glass powder led to changes in the concentration of hydroxide ions (oh−) in the matrix pores. this is considered to be the direct cause of the reduced risk of expansion due to asr. since the pozzolanic reaction occurs earlier than asr, the alkaline content of the paste is consumed in the creation of hydrated c–h–s gels, and there are not enough ions in the later stages of cement hydration. serpa et al. (2013) concluded that the incorporation of glass as cement replacement or even as aggregate can decrease the asr effects. its efficiency is related with the replacement ratio and size. glass can be used in substitution of natural, non-alkali reactive aggregates up to 20% ratio, particularly if limestone natural aggregates are involved. du and tan (2013) found that the asr expansion also decreased with smaller glass particle size due to pozzolanic reaction of fine glass particles. idir et al. (2010) observed that the finer the glass powder, the better it will perform in counteracting the asr expansion effects. this paper reports on a part of an ongoing research project on the reuse of mineral waste materials as an addition to cement for the development of sustainable cement. we discuss on naoh effect on physic-mechanical properties of cement mainly the results of an experimental study on the effect of finely crushed glass. 2. materials used 2.1. cement the cement used was a local portland cement type cem i 42.5n/sr5 without addition. the chemical and mineralogical compositions of the cement are summarized in table 1 and table 2 summarizes physical and mechanical characteristics of the cement. 2.2. standard sands the sand, of which a limited stockpile is maintained as reference material, is natural, siliceous sand consisting of rounded particles and has a silica content of at least 98 %. cen standard sand shall comply with the particle size distribution specified in table 3 as determined by sieve analysis on a representative sample of sand of total mass not less than 1345g. sieving shall be continued until the amount of sand passing through each sieve is less than 0,5 g/min. the moisture content shall be less than 0.2 % determined as the loss of mass of a representative sample of sand after drying at 105 °c to 110 °c to constant mass and expressed as a percentage by mass of the dried sample. other characteristics like sand equivalent, methylene blue test and finesse module are presented in table 3. table 1. chemical and mineral compositions of the cement. elements sio2 al2o3 fe2o3 cao mgo so3 k2o na2o ir free cao loi cl % 20.93 4.81 5.19 64.22 1.31 2.08 0.30 <0.05 0.74 0.474 0.740 <0.01 minerals c3s c2s c3a c4af free cao gypsum % 60 15 04 16 <0.01 05 morsli et al., j. build. mater. struct. (2018) 5: 65-73 67 table 2. physical and mechanical characteristics of the cement. physical characteristics mechanical characteristics initial setting time (mn) 190 age (days) flexure(mpa) compressive (mpa) final setting time (mn) 295 2 4.4 16.7 density (g/cm3) 3.2 7 6.4 34.4 specific surface (ssb) (cm2/g) 2900 28 6.6 55.3 table 3. particle size distribution of the cen reference sand. square mesh size (mm) 2.00 1.60 1.00 0.50 0.16 0.08 cumulative sieve residues (%) 0 7±5 33±5 67±5 87±5 99±1 sand equivalent (%) methylene blue test (g/kg) finesse module 90 0.0 1.3 2.3. glass powder the glass powder is obtained through grinding waste glass. the fineness of the glass was assured by air permeability method (blaine method). the physical and chemical characteristics of the powder are given in tables 4 and 5. the absence of peaks in the diffraction diagram of the glass powder (fig. 1) confirms its amorphous state and hence its pozzolanic activity. table 4. chemical composition of the glass powder. elements sio2 al2o3 fe2o3 cao mgo so3 k2o na2o p2o5 tio2 loi % 73.06 0.90 0.74 9.26 1.78 0.33 0.32 12.29 0.00 0.03 1.29 table 5. physical characteristics of the glass powder. density 2.55 (g/cm3) specific surface 8300 (cm2/g) colour white grey fig 1. x-ray diffraction of the glass powder. the simplest way to describe the pozzolanicity of a material is to evaluate the decrease of free lime in the system and also the kinetics of the reaction. generally, the parameters influencing the nature of the pozzolanic reactions are the nature of active phases and their proportions (lea, 2004). fig. 2(a) illustrates the volume of hcl necessary for the neutralisation of the solution of lime in the presence of glass powder over time. the stabilization is noted from the 18th day. fig. 2(b) shows the pozzolanic reactivity of glass compared with that of silica fume and fly ash. the 68 morsli et al., j. build. mater. struct. (2018) 5: 65-73 ratio of the combined lime by glass powder is identical to that of the fly ash. however, silica fume is the most reactive cementitious addition (chaïd et al., 2015). fig 2. (a) volume of consumed hcl; (b) pozzolanic activity of the glass powder. 2.4. sodium hydroxide derives from sodium carbonate; formerly named caustic soda. in ancient egypt, sodium carbonate was already mixed with lime to synthesize an alkali: the hydroxide ion ohin solution with the sodium ion na+. through the ages, several processes were developed to synthesize it, such as the solvay process in 1861. today, sodium hydroxide is mostly produced by the electrolysis of a solution of sodium chloride. in this study we used sodium hydroxide in pellets (fig 3) , before adding it to the cement mixture the soda is prepared by grinding it with a porcelain mortar, table 6 represents physical and chemical characteristics of sodium hydroxide. table 6. physical and chemical characteristics of sodium hydroxide. formula naoh molar mass 40 g.mol-1 colour white state solid fig 3. sodium hydroxide in pellets. morsli et al., j. build. mater. struct. (2018) 5: 65-73 69 3. experimental procedure 3.1. substitution and characterization of cement paste three mixtures with different proportions of glass powder 10%, 20%, 30% and one without addition to determine the standard consistence, initial and final setting time. we obtained the results presented in the figures 4 and 5. these tests shall be carried out in accordance with the terms of en 196-3. 3.2. preparation and characterization of mortars the same combination of cement is used with standardized sand and water for the preparation of mortar which is used to calculate mechanical strength at different age 2, 7, and 28 days and this serves to retain the best variant of substitution to activate it by sodium hydroxide, we obtained the results presented in the figures 6 and 7. these tests shall be carried out in accordance with the terms of en 196-1. 3.3. alkaline activation after selecting the best variant, the initial and final setting time are determined while adding (0.5, 1, 1.5 and 2%) of the sodium hydroxide calculated with respect to the level of the glass powder added to the cement mixture, at the end the variant which has the lowest initial setting is selected to determine the mechanical strength with the addition of a better percentage of sodium hydroxide add as solution form and as powder form to the mortar according to the terms of en 196-1. 4. results and discussion 4.1. standard consistence, initial and final setting according to fig. 4 that the addition of the finely grinding glass powder by substitution of cement increases the consistency value in a manner proportional to the percentage of the glass powder. the addition of 30% of glass powder by substitution of cement requires 2.5% water to have the same consistency as that without addition. the addition of naoh to the 10% glass powder variant reduces the consistency if the dosage is less than 1.5% naoh but in otherwise the water requirement increases for the same consistency. fig 4. standard consistence of the different variants. 70 morsli et al., j. build. mater. struct. (2018) 5: 65-73 fig.5. initial and final setting of the different variants. by adding 10% of glass powder by substitution of cement gave a 21 minute delayed initial setting with respect to that without addition, but that which had 30% of glass powder had an initial setting lower than those of 10% and 20%, this is due to the presence of na2o in the glass composition which is of the order of 12% (table 4), which is confirmed by the addition of naoh to the 10% variant (fig. 5). from figure 5 it can be said that the addition of 1.5% naoh gave the lowest initial setting which is an indication of an acceleration of the hydration kinetics. it is this embodiment which has been chosen for the determination of the mechanical strength by adding sodium hydroxide solution and powder in a mortar; these results are shown in the following figures. 4.2. mechanical strength without activation figures 6 and 7 are a column presentation of the values of the mechanical strength of compression and of flexion respectively at the different ages 2, 7 and 28 days for each variants it can be concluded that the addition of the glass powder by substitution of cement reduces the mechanical strength, but that the 10% glass powder variant gave a cement of 42.5 mpa class is a same as without glass adding and that of 20% is classed as cement of 32.5 mpa. fig 6. compressive strength of the different variants. morsli et al., j. build. mater. struct. (2018) 5: 65-73 71 the value of the compressive strength of mortar without glass powder is 55.3 mpa, but this value was 48.2 mpa two months before for the same cement bag, which is an indicator that the cement becomes more efficient if it is kept for a period before use away from moisture which is a cement hardener by hydration. fig 7. flexure strength of the different variants. the 10% variant of glass powder gave a value of 7 mpa less compared to the mortar poured the same day without addition, but an equal value than the mortar poured two months before. 4.3. mechanical strength with activation figures 8 and 9 are a column presentation of the values of the mechanical strength of compression and of flexion respectively at the different ages 2, 7 and 28 days. fig 8. compressive strength adding sodium hydroxide as solution and as powder. the results of compression and flexion by the addition of naoh as solution and as powder in the 10% glass powder variant at the different age shows that addition of naoh as solution to the mixture is easier than powder form because the naoh powder absorbs the moisture from the air and becomes liquid, so if naoh is used in cement it is preferable to add it with the mixing water according to the appropriate concentration. 72 morsli et al., j. build. mater. struct. (2018) 5: 65-73 fig 9. flexure strength adding sodium hydroxide as solution and as powder. we notice that there was an improvement in mechanical strength at 2 and 7 days compared with that without activator, which was not the case in compression at 28 days which was a slight decrease of 2.5 mpa, flexure strength has improved by 1 mpa with respect to a without addition of naoh. 5. conclusion this study focused on the effect of the addition of finely ground glass powder on the physical and mechanical properties of a cement (cem i) chemically activated by sodium hydroxide. it is noted that the addition of naoh accelerates the setting of the cement, this induces the improvement of the mechanical strengths at the first ages (2 and 7) days. these same resistances are reduced to 28 days, by about 5% with respect to the 10% variant of glass powder without activator. this leads us to say that sodium hydroxide has the same behaviour of an accelerating setting and curing accelerator. an improvement in bending strengths at different ages is recorded, ranging from 14.5% to 28 days for cement with 10% added activated glass powder compared to that without activation, which is favorable for the structural elements subjected to bending forces. the addition of 10% of glass powder to two main roles, the first one is economical, concerning the recovery of waste and the increase of the cement production, the second is ecological by the limitation of the emissions of the gases coming from the cement industry. in the end, the chemical activation of silica-rich cementitious additions is an area of current interest that attracts the intention of quite a few researchers. 6. references aci 116r-90. (2000). cement and concrete terminology, technical documents, american concrete institute. chaïd, r., kenaï, s., zeroub, h., & jauberthie, r. (2015). microstructure and permeability of concrete with glass powder addition conserved in the sulphatic environment. european journal of environmental and civil engineering, 19(2), 219-237. corinaldesi, v., gnappi, g., moriconi, g., & montenero, a. (2005). reuse of ground waste glass as aggregate for mortars. waste management, 25(2), 197-201. morsli et al., j. build. mater. struct. (2018) 5: 65-73 73 de castro, s., & de brito, j. (2013). evaluation of the durability of concrete made with crushed glass aggregates. journal of cleaner production, 41, 7-14. du, h., & tan, k. h. (2013). use of waste glass as sand in mortar: part ii–alkali–silica reaction and mitigation methods. cement and concrete composites, 35(1), 118-126. idir, r., cyr, m., & tagnit-hamou, a. (2010). use of fine glass as asr inhibitor in glass aggregate mortars. construction and building materials, 24(7), 1309-1312. kojima, t., takagi, n., & haruta, k. (2000). expanding characteristics of mortar in glass powder produced from waste bottles, 673–682. 11th international conference on alkali aggregate reaction. quebec, canada, june 2000, 673–1282. oliveira, r., de brito, j., & veiga, r. (2013). incorporation of fine glass aggregates in renderings. construction and building materials, 44, 329-341. penacho, p., de brito, j., & veiga, m. r. (2014). physico-mechanical and performance characterization of mortars incorporating fine glass waste aggregate. cement and concrete composites, 50, 47-59. roz-ud-din, n., & parviz, s. (2012). strength and durability of recycled aggregate concrete containing milled glass as partial replacement for cement. construction and building materials, 29, 368–377. serpa, d., silva, a. s., de brito, j., pontes, j., & soares, d. (2013). asr of mortars containing glass. construction and building materials, 47, 489-495. shayan, a., & xu, a. (2006). performance of glass powder as a pozzolanic material in concrete: a field trial on concrete slabs. cement and concrete research, 36(3), 457-468. tagnit, a., & nkinamubanzib, p.c. (2001). les ajouts cimentaires et le développement durable, journée d’étude technique, note trimestrielle d’information du centre d’etudes et de services technologiques de l’industrie des matériaux de construction, cetim, algérie. taha, b., & nounu, g. (2008). using lithium nitrate and pozzolanic glass powder in concrete as asr suppressors. cement and concrete composites, 30(6), 497-505. j. build. mater. struct. (2014) 1: 1-9 https://doi.org/10.34118/jbms.v1i1.3 issn : 2353-0057 mixture design approach to evaluate fresh properties of scc made with various sands bouziani t 1,*, bédérina m 1, makhloufi z 1 and hadjoudja m 2 1 structures rehabilitation and materials laboratory (sreml), university amar telidji, laghouat, algeria. 2 civil engineering laboratory, university amar telidji, laghouat, algeria. * corresponding author: t.bouziani@lagh-univ.dz abstract. the aim of the present paper is to provide a mixture design modelling to evaluate the effect of different sand types on fresh properties of self-compacting concrete (scc). a statistical approach was used to highlight the effect of river sand (rs), crushed sand (cs) and dune sand (ds) as proportions in binary and ternary systems in scc composition. the responses of the derived statistical models are sand packing density (spd), t500 and j-ring. the resulting mathematical models are used to illustrate the variation of different responses in ternary contours plots with respect to the proportions of rs, cs and ds. this offers flexibility to optimize rs, cs and ds blends with tailor-made of a given property that suit a particular recommendations. results indicate that spd of rs can be enhanced by a 40% of cs and 30% of ds proportions. moreover, it is shown that flowability, measured by j-ring, can be improved by the increase of cs and ds in rs-cs and rs-ds binary systems. results also indicate that passing ability measured with t500 decreased with the increase of cs proportion and increased with the increase of ds proportion in binary and ternary systems. key words: self-compacting concrete, fresh properties, river sand, dune sand, crushed sand, mixture design modeling. 1. introduction the main distinguishing of self-compacting concrete (scc) is to fill the forms and consolidate without the need of vibration (okamura, 2003). beside these characteristics, scc will enable a considerable reduction of the acoustic noise levels and the use of secondary raw materials. recently, there is an increasing attention on scc technology in algeria. the principal reasons for this interest are not only for the technical advantages of scc, but concern also the severe shortage of coarse aggregates, even though sands of different types and grading (such as dune sand and crushed sand) are available in large quantities (al-harthy, 2007; abidelah, 2009). in this regard, the development of new concretes that necessitate less coarse aggregates to be used, such as scc responds to some of the urgent needs of the construction sector. the limitation of coarse aggregates volume in scc is also one of the most factors affecting their passing and filling abilities while preventing segregation (ramge, 2010; zhu, 2005). on the other hand, several research works have investigated the use of sand as total or partial substitute of coarse aggregates to develop new concretes, which have mechanical properties comparable with conventional concretes (zhu, 2005; bédérina, 2005). due to the fineness of sand, scc requires a high water demand and a large cement content to achieve high fluidity. therefore, the use of superplasticizers and fine powders are thus two of the central aspects of self-compacting concrete mixture proportioning (albert, 2010; felekoğlu, 2008b; girish, 2010). sand from natural deposits or crushed rocks is a suitable material used as a fine aggregate in concrete production (al-harthy, 2007). bédérina et al. (2005) reported that dune sand is a useful component in optimizing particle size distribution of river sand and thereby improving workability and compressive strength of sand-concrete mixtures. kay et al. (1994) also investigated the potential of using dune sand as fine aggregates in concrete. results indicated that dune sand may provide a readily available alternative material for use as fine aggregate in concrete. crushed sand, produced from crushing rocks units, can has a large potential of applications in various fields of civil engineering (abidelah, 2009). the employment of crushed mailto:t.bouziani@lagh-univ.dz 2 bouziani et al. j. build. mater. struct. (2014) 1: 1-9 sand may be a second alternative source of filler and thereby can improve the cost effectiveness of scc, by reducing the demand for external filler addition (felekoğlu, 2008a). nowadays, some research results about the effect of sand type on the properties of flowable mixtures have been established, however, the related researches are focused on flowing sandconcretes and self-compacting mortars (bouziani, 2012; benabed, 2012). therefore, the effects of sand type and content on fresh and mechanical properties of scc needs more investigate. in this study, some fresh properties of scc made with different sand types have been investigated. these properties were introduced in this paper, in complementary of our recent investigation on the effect of sand type on fresh and hardened properties of scc (bouziani, 2013). a mixture design approach was used to highlight the effect of three types of sands proportions, river sand (rs), crushed sand (cs) and dune sand (ds) on these properties. 2. mixture design approach statistical modelling approaches are commonly used to identify the relative significance of primary mixture parameters and their coupled effects on relevant properties of scc (khayat, 1999; yahia, 2001; bayramov, 2004; sonebi, 2005; bouziani, 2012b; bouziani, 2013). for the present work, experiments were designed according to a mixture design approach. in contrast to classical non-mixture designs (factorial and response surface designs), all factors are constituent proportions of a mixture. since these proportions must always sum to 1, the last component proportion is dictated by the sum of all the others. in this mixture situation, the factors are not independent, which has consequences on the design process (goupy, 2007). a simplex-lattice mixture design was carried out, with three factors and five levels, to evaluate the effect of three types of sands (rs, cs and ds) on the properties of scc. all other scc components (coarse aggregate, cement, addition, superplasticizer and water) were kept constant. the simplex-lattice design is a space filling design that creates a triangular grid of combinations, as shown in fig. 1, where the number of combinations (c) is expressed by the flowing relation:     !1! !1    qm mq c (1) where, q is the number of factors and m the number of levels. with three factors and five levels, the number of combinations to be treated is 21. using this approach, a mathematical model describing the effect of three types of sands proportions and their blends on given property can be established. in this study, a second-degree model was used with three non-independent variables (proportions of rs, cs and ds) and five levels. the model is expressed as follows:      dscsbdsrsbcsrsbdsbcsbrsby  654321 (2) the model's coefficients (bi) represent the contribution of the associate variables on the response y. these coefficients are determined by a standard least-square fitting. analyses of variance are used to evaluate the significance of each term in the model. the residuals are used to calculate the variance of the coefficients, which is used to find the standard for testing whether a coefficient is significant or not (goupy, 2007). bouziani et al. j. build. mater. struct. (2014) 1: 1-9 3 fig 1. illustration of the simplex-lattice design with three factors (rs, cs and ds) and five levels. 3. experimental program 3.1. materials ordinary portland cement cem i 42.5 and marble powder lime-stone type were used in this study. the chemical and physical properties of cement and marble powder are presented in table 1. three types of sand (rs, cs and ds) and crushed limestone-type gravel were used. the particle size gradations obtained thorough sieve analyses method of selected sands and gravel are presented in fig. 2. the maximum sizes of aggregates are 10mm for gravel, 5mm for rs, 4mm for cs and 1.63mm for ds. physical properties of used aggregates are presented in table 2. the polycarboxylate-type high range water reducing superplasticizer, medaflow-30, fabricated by granitex, was used. the solid content, ph and specific gravity of the superplasticizer are 30%, 6 and 1.07 respectively. 3.2.mixture proportions a total of 21 scc mixtures were prepared for this investigation. in all the mixtures, the amounts of gravel, cement, marble powder, superplasticizer and water were kept constant. the mix proportioning has been designed according to afgc recommendations (afgc, 2008). in other words, the gravel/sand ratio was kept equal to 1 and the volume of paste was chosen 360 l/m3 (in the range 330 to 400 l/m3). table 1: chemical composition and physical properties of cement and marble powder. analysis (%) portland cement marble powder cao 65.9 55.6 sio2 21.9 0.6 al2o3 4.8 0.4 fe2o3 3.5 0.2 mgo 1.6 0.1 k2o 0.5 so3 0.48 caco3 90 na2o cl 0.1 0.1 loi 1.2 43 specific density 3.1 2.7 blaine surface (cm²/g) 2792 2126 4 bouziani et al. j. build. mater. struct. (2014) 1: 1-9 total sands content was 848 kg/m3, in which 21 combinations from different proportions of three sands (rs, cs and ds) were carried out using the mixture design plan (as presented in table 3). gravel content was 880kg/m3. cement and marble powder contents were 380kg/m3 and 199kg/m3 respectively. water to binder ratio was 0.4. the amount of superplasticizer was 1.6% by weight of cement. fig 1: particle size gradations of rs, cs, ds and gravel. table 2: physical properties of aggregates. property aggregate rs cs ds gravel specific density 2.65 2.7 2.67 2.75 fineness modulus 3.03 2.14 1 / sand equivalent 87.7 82.8 91 / absorption (%) 1.79 5.71 2.04 1.83 3.3.scc testing procedure in mixing, gravel, sands, cement and marble powder were blended first then high-range water reducing superplasticizer and water were added to the mixture. immediately after mixing, flowability and passing ability were evaluated using the following tests: t500 (s) and j-ring (cm). packing density (spd) test was also conducted on dry sands mixtures. 4. results and discussion 4.1.statistical models the test results of 21 scc mixtures are used to establish statistical models that can describe the effects of rs, cs and ds proportions as well as all possible interactions in binary and ternary systems, on the variation of each response. the coefficients of proposed models, as mentioned in relation (2), are evaluated basing on student's distribution, to eliminate non-significant (n-s) terms. in this study, the acceptance probability for the coefficients is set at a p-value less than 0.05. coefficients of derived models (coeff.), correlation coefficients (r2) and p-values for fresh properties responses are shown in tables 4. the final models of spd, t500 and j-ring can be written as: 0 10 20 30 40 50 60 70 80 90 100 0,01 0,1 1 10 sieve diameter (mm) p a s s in g ( % ) rs cs ds gravel bouziani et al. j. build. mater. struct. (2014) 1: 1-9 5      dscscsrsdsrsdscsrsyspd  4.037.033.06.15.15.1 (3)  dsrsdscsrsyt  252.199.37.4500 (4)  dsrsdscsrsy ringj  5.48434.645.72 (5) table 3: sands combinations of prepared scc mixtures. mix. n° sands combinations rs cs ds 1 0.8 0 0.2 2 0 0.8 0.2 3 0.2 0.6 0.2 4 0.4 0.4 0.2 5 0 0 1 6 0.2 0 0.8 7 0 1 0 8 0.2 0.4 0.4 9 0.2 0.2 0.6 10 0 0.6 0.4 11 0.6 0.4 0 12 0.2 0.8 0 13 0.4 0.2 0.4 14 0.4 0.6 0 15 0 0.2 0.8 16 0.6 0.2 0.2 17 0.4 0 0.6 18 1 0 0 19 0 0.4 0.6 20 0.6 0 0.4 21 0.8 0.2 0 table 4 indicates that the derived models have a good correlation coefficients, except for spd (r2=0.52). a negative coefficient indicates that the increase in associate factor results in a reduction of the response. table 4 : model parameters estimates of fresh properties responses. t e rm spd t500 (s) j-ring (cm) r2=0.52 r2=0.73 r2=0.86 coeff. p-value coeff. p-value coeff. p-value b1 1.5 <0.0001 4.7 0.0135 72.5 <0.0001 b2 1.5 <0.0001 3.9 0.0003 64.4 <0.0001 b3 1.6 <0.0001 19.1 <0.0001 43 0.0539 b4 0.37 0.0227 / / n-s 0.3572 b5 0.33 0.0403 -25 0.0152 48.5 0.0067 b6 0.4 0.0164 / / n-s 0.2275 however, it should be taken in account that the increase in a given factor, leads to a decrease in other factors, because the factors are constituent proportions of a mixture. the derived models have been established using the method of least squares that consists minimizing the sum of squares of residuals. the predicted-to-observed plots shown in fig. 3, indicate that the points seem to be distributed inside the confidence curves limits. 6 bouziani et al. j. build. mater. struct. (2014) 1: 1-9 fig 2: observed-to-predicted plots for: (a) spd, (b) t500 and (c) j-ring. 4.2.exploitation of models the established models can be used to present results in contour plots that illustrate the effect of rs, cs and ds proportions on sands compactness, flowability and passing ability of scc. ternary contour plot presented in fig. 3, illustrates the effect of rs, cs and ds proportions on spd. from this figure, it can be seen that the increase of cs and ds proportions in binary systems rs-cs and rs-ds or ternary system rs-cs-ds, increased spd until a maximum value (around 1.68) then decreased. the maximum spd value can be reached with the follow ternary proportions (approximately: 40% of cs, 30% of ds and 30% of rs). this can be explained by the filling effect of fine ds grains and the high filler content of cs. bouziani et al. j. build. mater. struct. (2014) 1: 1-9 7 fig 3: ternary plot of spd as function of rs, cs and ds proportions. fig. 4 illustrates the ternary contour plots of t500 flow time for scc mixtures made of rs, cs and ds. as illustrated in fig. 4, t500 time increased as the proportions of cs increased in rs-cs and cs-ds binary blends. this is apparently caused by the high filler content of cs. it can be also seen that t500 decreased as the proportions of ds increased in rs-ds binary system. fig 4. ternary plot of t500 (s) as function of rs, cs and ds proportions. the effect of different sands proportions on the j-ring slump diameter is plotted in fig. 5. results show that j-ring values increased for both cs and ds in rs-cs and rs-ds binary systems. 8 bouziani et al. j. build. mater. struct. (2014) 1: 1-9 fig 5. ternary plot of j-ring (cm) as function of rs, cs and ds proportions. 5. conclusions the mixture design approach developed in this experimental work is useful to evaluate the effect of three types of sand proportions (rs, cs and ds), in binary and ternary systems, on fresh properties of scc. using only 21 scc mixtures, this statistical design approach provides mathematical models that can be used to present results in ternary contour plots. such graphical representation offer a simple visual tool for optimizing rs, cs and ds proportions in binary and ternary systems, to meet different performances criteria of scc. based on obtained results, the following conclusions can be drawn: • sand packing density (spd) increased with the increase of cs and ds proportions in rscs and rs-ds binary systems and rs-cs-ds ternary system. sand mixture composed with approximately 30% of ds, 40% of cs and 30% of rs proportions, yielded scc mixtures with high packing density. • the passing ability, expressed by t500 flow time, increased with the increase of cs proportion in rs-ds binary mixture and decreased with the increase of ds proportion in rs-cs binary system. • the increase in ds and cs proportions with rs as binary or ternary systems, enhanced flowability and passing ability through j-ring bars. 6. references abidelah a, bouchair a, kerdal d, ayed k (2009). characterization of a self-compacting sand concrete using the quarry waste. canad j civil eng, 36: 1773-82. afgc, association française de génie civil (2008). recommendations for use of self-compacting concrete, scientific and technical documents, p n b@p. albert khk., ivan ytn (2010). improving performance and robustness of scc by adding supplementary cementitious materials, constr build mater, 24: 2260-66. al-harthy as, abdel halim m, taha r, al-jabri ks (2007). the properties of concrete made with fine dune sand. constr build mater, 21:1803–08. bouziani et al. j. build. mater. struct. (2014) 1: 1-9 9 bayramov f, taşdemir c, taşdemir m a. (2004). optimisation of steel fibre reinforced concretes by means of statistical response surface method. cement concrete compos, 26:665–75. bédérina m, khenfer mm, dheilly rm, quéneudec m (2005). reuse of local sand: effect of limestone filler proportion on the rheological and mechanical properties of different sand concretes. cement concrete res, 35:1172-79. benabed b, kadri e, azzouz l, kenai s (2012). properties of self-compacting mortar made with various types of sand. cement concrete compos, 34:1167-73. bouziani t (2013). assessment of fresh properties and compressive strength of self-compacting concrete made with different sand types by mixture design modelling approach. constr build mater, 49:308–14. bouziani t, bédérina m, hadjoudja m (2012a). effect of dune sand on the properties of flowing sand – concrete (fsc). inter j concrete struct mater, 6:59-64. bouziani t, benmounah a, bédérina m (2012b). statistical modelling for effet of mix-parameters on properties of high flowing sand concrete. j cent south univ, 19:2966-75. felekoğlu b (2008a). a comparative study on the performance of sands rich and poor in fines in selfcompacting concrete. constr build mater, 22:646–54. felekoğlu b, sarıkahya h (2008b). effect of chemical structure of polycarboxylate-based superplasticizers on workability retention of self-compacting concrete, constr build mater, 22:1972-80. girish s, ranganath rv, vengala j (2010). influence of powder and paste on flow properties of scc. constr build mater, 24:2481-88. goupy j, creighton l (2007). introduction to design of experiments with jmp examples. 3rd ed. cary, nc: sas institute inc. khayat kh, ghezal a, hadriche ms (1999). factorial design models for proportioning self-consolidating concrete. mater struct, 32:679–86. kay ea, frearson jph (1994). an investigation into the use of dune sand in concrete. in: fookes pg, party rhg, editors. proceeding of the 1st international symposium on engineering of arid soils. ballkema, rotterdam, pp.261-72. okamura h, ouchi m (2003). self-compacting concrete. j adv concr technol, 1:1–15. ramge p, proske t, kühne hc (2010). segregation of coarse aggregates in self-compacting concrete. in: khayat kh, feys d, editors. design, production and placement of self-consolidating concrete, rilem bookseries 1, pp.113-25. sonebi m, svermova l, bartos pjm (2005). statistical modeling of cement slurries for self-compacting sifcon containing silica fume. mat struct, 38:79–86. yahia a, khayat kh (2001). experiment design to evaluate interaction of high-rangewater-reducer and antiwashout admixture in high-performance cement grout. cement concrete res, 31:749–57. zhu w, gibbs j (2005). use of different limestone and chalk powders in self-compacting concrete. cement concrete res, 35: 1457-62. j. build. mater. struct. (2017) 4: 42-49 original article doi : 10.34118/jbms.v4i2.30 issn 2353-0057, eissn : 2600-6936 recycling of rubber waste in sand concrete guendouz m 1,*, boukhelkhal dj 2 1,* lme laboratory, university of medea, medea, algeria. 2 geomaterials laboratory, university of blida, blida, algeria. * corresponding author: guen12moh@gmail.com abstract. the large development in the consumption of rubber is observed in the recent years, which leads to an increase of the production of rubber related waste. rubbers are not hazardous waste, but they constitute a hazard for both environment and health, in case of fire in storage sites. so, recycling appears as one of the best solutions for disposing of rubber waste.this paper presents an experimental investigation dealing with the valorisation of rubber waste, specifically rubber obtained from old shoes sole waste. the waste rubbers are used form (0/5 mm) to mixes as addition at percentage (10%, 20%, 30% and 40%) in sand concrete. the physical (workability, bulk density), mechanical (compressive and flexural strength) and thermal properties are studied and analysed.the results indicate that the incorporation of rubber waste particles in sand concrete contributes to increase the workability and reduce the bulk density of all studied sand concrete. the obtained results show that mechanical performance (compressive and flexural strength) decreases when the rubber content increases. nevertheless, the presence of rubber aggregate leads to a significant reduction in thermal conductivity, which improves the thermal insulation performances of sand concrete. this study insures that reusing of recycled rubber waste in sand concrete gives a positive approach to reduce the cost of materials and solve some environmental problems. key words: rubber; recycling; sand concrete. 1. introduction the fraction of rubber waste in household wastes is large and increases with time. in each country the waste composition is different, since it is affected by socioeconomic characteristics, consumption patterns and waste management programs, but generally the level of rubber in waste composition is high. the large volume of materials required for construction is potentially a major area for the reuse of waste materials. recycling in concrete has advantages since it is widely used and has a long service life, which means that the waste is being removed from the waste stream for a long period. many authors have reported the properties of concrete with used tyre rubbers. their results indicate that the size, proportion, and surface texture of rubber particles affect the strength of used tyre rubber contained in concrete (khatib et al., 1999; fedroff et al., 1996; eldin and senouci, 1993; ali et al., 2000; rostami et al., 2000; topcu, 1995; fattuhi and clark, 1996; naik and singh, 1991; siddique and naik, 2004; lee et al., 1998; goulias and ali, 1998) . eldin et al (1993) conducted experiments to examine the strength and toughness properties of rubberised concrete mixtures. they used two types of tyre rubber, with different tyre rubber content. their results indicated approximately 85% reduction in compressive strength, whereas the splitting tensile strength reduced by about 50% when the coarse aggregate was fully replaced by chipped tyre rubber. a smaller reduction in compressive strength (65%) was observed when sand was fully replaced by fine crumb rubber. concrete containing rubber did not exhibit brittle failure under compression or splitting tension and had the ability to absorb a large amount of energy under compressive and tensile loads. a more indepth analysis of their results indicates that an optimised mixture proportion is needed to optimise the tyre rubber content in the mixture. in recent years, used tyre chipped rubber mailto:guen12moh@gmail.com guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 43 containing portland cement concrete for uses in sound/crash barriers, retaining structures, and pavement structures has been extensively studied (khatib et al., 1999; eldin and senouci, 1993; ali et al., 2000) . test results showed that the introduction of used tyre chipped rubber considerably increases toughness, impact resistance, and plastic deformation but in almost all cases a considerable decrease in strength was observed. khatib et al (1999) studied the influence of adding two kinds of rubber, crumb (very fine to be replaced for sand) and chipped (at the size of 10–50 mm to be replaced for gravel). they made three groups of concrete mixtures. in group a, crumb rubber to replace fines, in group b, chipped rubber to replace coarse aggregate, and in group c both types of rubber were used in equal volumes. in all, the three groups had eight different rubber contents in the range of 5–100% were used. they found that the compressive strength of concrete would decrease with increasing rubber content. for example, replacing 100% gravels by chipped rubber would decrease the compressive strength of concrete up to 90%. meanwhile, they showed that the rubberised concrete made with chipped rubber has less strength than concrete made with crumb rubber. this work focuses on the possibility of recycling rubber waste of shoes without any prior treatment as a partial replacement of natural aggregate in sand concrete, in order to minimize the cost of the final material. the influence of the proportion of rubber waste used on properties of the new material has been studied and analyzed. 2. experimental program 2.1. materials the sand used was a dune sand available in south of algeria, near the city of tamanrasset. the particle size distributions of the used sand are shown in figure 1 and the physical characteristics are presented in table 1. fig 1. particle size distribution of sand and rubber waste used. table 1. physical properties of used sand. properties sand standard bulk density (kg/m3) 1400 np en 1097-3 specific density (kg/m3) 2560 np en 1097-6 water absorption (%) 2.66 np en 1097-6 sand equivalent (%) 80.50 np en 933-8 fineness modulus 0.84 np en 933-1 compactness (%) 0.55 nf p 18-555 porosity (%) 0.45 nf p 18-555 thermal conductivity (w/m k) 1.3-1.4 nf en iso 8894-1 44 guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 an industrial portland cement cpj-cem ii/a of class 42.5 is used. the physical characteristics are the following: specific density 3100 kg/m3 and specific surface area 308 m2/kg, was used for all sand concrete mixtures. the use of fillers in sand concrete composition is essential (afnor 1994). their use is intended to complete the grading curve of sand in its finest part in order to obtain more compact concrete and reduce the cement content and therefore the cost of concrete. in this work the fillers used are the limestone powder. their specific density is 2660 kg/m3, and specific surface area 242 m2/kg. the rubber waste used in this work were obtained by the recycling the waste of shoes (figure 2) discharged into the nature after were collected, are washed, compressed, crushed and extruded in the form of grains, and added in the mass of sand concrete with percentage (10%, 20%, 30% and 40%).the sieve analysis results are given in figure 1, and the table 2 lists the set of physical and thermal properties. fig 2. particle size distribution of sand and rubber waste used. table 2. physical and thermal properties of used rubber waste. properties rubber waste standard bulk density (kg/m3) 1500 np en 1097-3 specific density (kg/m3) 800 np en 1097-6 water absorption (%) 1.28 np en 1097-6 fineness modulus 3.2 np en 933-1 compactness (%) 53 nf p 18-555 porosity (%) 47 nf p 18-555 thermal conductivity (w/m k) 0.15 nf en iso 8894-1 a polycarboxylate plasticizer (medafluid 104) produced by granitex group (algeria) with solid contents of 35% was used for all mixes. the mixing water used for the different mixes is the drinking water, free of impurities with a ph equal to 7. 2.2. mix design in this work, the optimal compositions of the sand concrete studied, without rubber waste, is based on the experimental method of project of sablocrete (sablocrete 1994). this gave for cement proportioning of 350 kg/m3, 1200 kg/m3 of sand, 250 kg/m3 of fillers, and a water/cement ratio of 0.85, a percentage of plasticiser of 1% of weight of cement. the rubber waste is added in sand concrete at dosages (0%, 10%, 20%, 30% and 40%). literary codes identify each mixture in a precise way:  csc: control sand concrete (without rubber).  scrw: sand concrete with rubber waste. all specimens were produced in laboratory environment with 20°c and 50% rh. after 24 h, they were removed from the molds and placed in water at 20°c and 100% relative humidity until the day of testing. this procedure was respected for all compositions and all tests. guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 45 2.3. test procedure the workability of concrete was measured in terms of slump according to nf p 18-451. the flexural strength was measured on 40×40 ×160 mm specimens at the ages of 28 days by a threepoint bending test, using a testing machine according to en 196-1.the half-samples resulting from this test were then submitted to compression test. the measurements of thermal conductivity led to the determination of the following parameters: thermal conductivity (λ), on three 40×80×160 mm samples using a ct-meter machine. 3. results and discussion 3.1. workability the slump of sand concrete as a function the content of rubber waste is sowed in figure 3. the use of rubber waste as addition in sand concrete contributes to increase the slump of sand concrete, probably due to the presence of more free water in the mixes containing rubber than in the concrete mix containing natural aggregate since, unlike natural aggregate, rubber aggregate has a lower absorption coefficient than dune sand, which is in concordance with the results of guendouz et al (2016). khatib et al (1999) investigated the workability of rubcrete and reported that there is a decrease in slump with increase in rubber content as a percentage of total aggregate volume. they further noted that at rubber contents of 40%, slump was almost zero and concrete was not workable manually. it was also observed that mixtures made with fine crumb rubber were more workable than those with coarse tire chips or a combination of tire chips and crumb rubber. siddique and naik (2004) have reported that mortars incorporating rubber shreds achieved workability comparable to or better than a control mortar without rubber particles it was also observed that mixtures made with fine crumb rubber were more workable than those with coarse tire chips or a combination of tire chips and crumb rubber. fig.3. slump of sand concrete as function of rubber waste content. 3.2. bulk density according to the results presented in figure 4, the use of rubber waste as addition in sand concrete contributes to reduce the bulk density, probably due to the lower density of the rubber compared with the dune sand, which is in concordance with the results of guendouz et al (2015). khatib et al (1999) concluded that because of low specific gravity of rubber particles, unit weight of mixtures containing rubber decreases with the increase in the percentage of rubber content. moreover, increase in rubber content increases the air content, which in turn 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 csc scrw 10% scrw 20% scrw 30% scrw 40% s lu m p ( c m ) 46 guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 reduces the unit weight of the mixtures. the decrease in unit weight of rubcrete is found to be negligible when rubber content is lower than 10–20% of the total aggregate volume. fig.4. bulk density of sand concrete as function of rubber waste content. 3.3. mechanicals strength the results of compressive and flexural strength of different sand concretes at 28 days of age are presented in figure 5 and 6 respectably. the results displayed in figure 5 and 6 show that compressive strengths of sand concrete decrease 15.7 % respectively for addition of 40% natural dune sand by rubber waste. event thing in the case of the flexural strengths, which indicates that the addition of 40 % of the rubber waste in a sand concrete represents decrease the performances of new materials. this trend may be related to a poor adhesion between the surface of the rubber aggregate and binder paste which is likely to have contributed to such a strong decay of mechanical properties. eldin and senouci (1993) compared the use of rubber as coarse aggregates and the use of rubber chips as sand. the reductions of up to 85% of the compressive strength were observed when the coarse aggregate was replaced by rubber. a smaller reduction in compressive strength (65%) was observed when sand was replaced by crumb rubber. it was further observed that rubber-containing concrete did not exhibit brittle failure under compression. the strength reduction can be attributed both to a reduction of the quantity of the solid load-carrying material and to stress concentrations (tensile and compressive) in the paste at the boundaries of the rubber aggregate. fig.5. compressive strength of sand concrete as function of rubber waste content. 0 250 500 750 1000 1250 1500 1750 2000 2250 2500 csc scrw 10% scrw 20% scrw 30% scrw 40% b u lk d e n si ty ( k g /m 3 ) 20,00 19,52 17,60 16,10 14,30 0 2 4 6 8 10 12 14 16 18 20 22 24 0 10 20 30 40 c o m p re ss iv e s tr e n g h t (m p a ) rubber waste content (%) guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 47 fig.6. flexural strength of sand concrete as function of rubber waste content. 3.4. thermal conductivity figure 7 give the thermal conductivity values of the specimens measured at 28 days. the thermal conductivity value of control sand concrete was 1.58 w/m k. this value decreased to 1.02 w/m k for dune sc when the replacement of rubber wastes into mixture with normal aggregate at a ratio of 40%. rubber waste aggregate addition into sc composites caused the reduction in the values of tc of the specimens. it is thought that, this situation caused by the lower thermal conductivity value of the rubber (0.15 w/m k) than natural aggregate (2 w/m k) iucolano et al (2013). so the decreasing thermal conductivity came also from the increase in porosity induced by the rubber waste. in fact the pores contain air which has a thermal conductivity value (0.024 w/mk) much lower than all the other components of the sc. similar results were observed by several authors in composite systems, for example hannawi et al. (2010) in a study on pf and pet in mortar composites, and it’s showed a decreased in value of thermal conductivity of mortar containing pet about 50% lower than a traditional mortar. akçaözog˘lu et al.(2013) find that the pet aggregate replacement with natural aggregate in mixture caused a reduction in the values of thermal conductivity value of the specimens. fig.7. thermal conductivity of sand concrete as function of rubber waste content. 3,00 2,60 2,30 2,10 1,90 0 1 2 3 4 5 0 10 20 30 40 f lu x u re l s tr e n g h t (m p a ) rubber waste content (%) 0 0.4 0.8 1.2 1.6 2 csc scrw 10% scrw 20% scrw 30% scrw 40% λ ( w /m .k ) 48 guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 4. conclusions this paper has presented the recycling and the use of rubber wastes as aggregate in sand concrete produced either from dune sand (ds). the results which could be summarized and concluded as: 1-these types of rubber wastes types can be used in sand concrete. 2-the workability of all sand concrete increases and the density decreases with the increase of rubber waste shoes content. 3-the compressive and flexural strength values of all waste rubber sc mixtures tend to decrease above the values for the reference sc with increasing the waste rubber ratio. but this result was acceptable for lightweight concrete. 4the addition of 40% of rubber waste in sand concrete caused a reduction (35%) in the values of thermal conductivity. this result is primarily due to lower thermal conductivity of the rubber waste, but also to the capacity of the aggregate rubber to facilitate the formation of micro voids which improves the thermal insulation performances of the sand concrete. the use of rubber waste of shoes as aggregates in sand concrete can most of the problems associated with their disposal as well as save natural resources related to aggregates mining. 5. references afnor. concrete – sand concrete. (1994).projet p 18-500 [in french]. akçaözoğlu, s., akçaözoğlu, k., & atiş, c. d. (2013). thermal conductivity, compressive strength and ultrasonic wave velocity of cementitious composite containing waste pet lightweight aggregate (wpla). composites part b: engineering, 45(1), 721-726. ali na., amos ad., roberts m.(2000). use of ground rubber tires in portland cement concrete. in: proceedings of the international conference on concrete. scotland (uk): university of dundee. eldin nn., senouci ab.(1993). rubber_tyre particles as concrete aggregates. asce j mater civil eng. 1993.478–96. fattuhi, n. i., & clark, l. a. (1996). cement-based materials containing shredded scrap truck tyre rubber. construction and building materials, 10(4), 229-236. fedroff, d., ahmad, s., & savas, b. (1996). mechanical properties of concrete with ground waste tire rubber. transportation research record: journal of the transportation research board, (1532), 6672. guendouz, m., debieb, f., boukendakdji, o., kadri, e. h., bentchikou, m., & soualhi, h (2016). use of plastic waste in sand concrete.j. mater. environ. sci. 7 (2) 382-389. guendouz, m., & debieb, f. (2015). formulation et caractérisation d'un béton de sable à base de déchets plastiques. in 33èmes rencontres universitaires de génie civil.". bayonne, france, p 1-8. goulias, d. g., & ali, a. h. (1998). evaluation of rubber-filled concrete and correlation between destructive and nondestructive testing results. cement, concrete and aggregates, 20(1), 140-144. hannawi k., kamali-bernard s., prince w.(2010). physical and mechanical properties of mortars containing pet and pc waste aggregates. waste management .30.2312–20. iucolano f., liguori b., caputo d., colangelo f., cioffi r.(2013). recycled plastic aggregate in mortars composition: effect on physical and mechanical properties. materials and design.52. 916–922. khatib zk. bayomy fm.(1999). rubberized portland cement concrete. asce j mater civil eng.11(3) .206– 13 lee hs., lee h., moon js.(1998). development of tire-added latex concrete. aci mater j.95(4):356–64. guendouz and boukhelkhal, j. build. mater. struct. (2017) 4: 42-49 49 naik tr., singh ss. utilization of discarded tyres as construction materials for transportation facilities. report no. (1991).cbu-02,uwm center for by-products utilization. milwaukee: university of wisconsin-milwaukee. sablocrete (1994). ’béton de sable : caractéristiques et pratique d’utilisation’. presse de l’ecole nationale des ponts et chaussées. rostami, h., lepore, j., silverstraim, t., & zundi, i. (2000). use of recycled rubber tires in concrete. in proceedings of the international conference on concrete (vol. 1993, pp. 391-399). london, united kingdom: thomas telford services ltd. siddique, r., & naik, t. r. (2004). properties of concrete containing scrap-tire rubber–an overview. waste management, 24(6), 563-569. topcu, i. b. (1995). the properties of rubberized concretes. cement and concrete research, 25(2), 304-310. j. build. mater. struct. (2017) 4: 68-75 original article doi : 10.34118/jbms.v4i2.33 issn 2353-0057, eissn : 2600-6936 behaviour of reinforced columns with e_glass fiber and carbon fiber bouchelaghem h1, 2, *, bezazi a2, boumaaza m3, benzanache n3, scarpa f4 1 department of mechanical engineering, faculty of science of technology, mentouri brothers university, constantine 25000, algeria. 2 laboratory of applied mechanics of new materials (lmanm), university 8 may 1945, bp 401 guelma 24000, algeria. 3 laboratory of civil and hydraulic engineering (lgch), university 8 may 1945, bp 401 guelma 24000, algeria. 4 department of aerospace engineering, university of bristol, bs8 1tr bristol, uk. * corresponding author: bouchelaghem_h@yahoo.fr abstract. externally bonded reinforcement using fiber reinforced polymer (frp) is a good response to the concern represented by the need for rehabilitation of concrete structures. these techniques are more and more attractive because of their fast and low labour costs, very good strength to weight ratio, good fatigue properties, and non-corrosive characteristics of frp. the present work is an experimental study investigating the mechanical behaviour under a uni-axial loading of short concrete columns reinforced by composite materials. these are constituted of glass fibers gfrp (bidirectional fabric of two surface densities 500 and 300 g/m2), carbon cfrp (unidirectional sheet of density per unit area of 230 g/m2) and polyester and epoxy resin respectively. the investigation aims at demonstrating the effectiveness of frp reinforcement through highlighting the effect of thickness (frp number of folds), the nature of the reinforcement (glass, carbon or hybrid), and the orientation of the fibers. the axial lengths shortening along with the radial expansion are measured using the strain gauges glued to the outer surfaces of the composite jacket via a wheatstone bridge. these measurements are saved to a pc through an acquisition card. the results obtained clearly show that the columns reinforced with cfrp folds allow an important increase in the compressive rupture stress in comparison with those reinforced with gfrp folds. the gains in compressive strength, in axial and in radial strains of the confined concrete with the different frps used are identified and quantified. it has further been demonstrated that the tested columns mechanisms depend strongly on the type of fiber reinforcements. key words: concrete columns reinforcement; uni-axial compression; frp; structure rehabilitation; fiber orientations. 1. introduction the durability of reinforced concrete structures depends on their behavior in relation to the climatic and environmental conditions that exist in the environments in which they are constructed. these structures are often exposed to numerous physico-chemical aggressions which they must satisfy, during their period of use, all the functions for which they were designed. when they can no longer resist these aggressions, disorders appear in the concrete of these structures. these disorders are generally due to design flaws, poor implementation or accidental causes, but these disorders can be also due to non-compliance with quality standards in manufacturing by certain companies. these behaviors, if not rectified, undermine the durability, resistance and stability of the structures and can lead to their degradation and then their ruin (ndzana akongo, 2007). fiber-reinforced polymer (frp) structural composite technology appeared for the first time in the mid-1930s as an experimental boat hull made of glass fiber and polyester resin. from military applications in the 1940s to the manufacturing and industrial sectors in the 1950s, frp composites have gradually become the preferred alternative to traditional repair techniques. mailto:bouchelaghem_h@yahoo.fr bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 69 their popularity was mainly due to their excellent strength-to-weight ratio and their superior strength, inherent in climatic conditions and the corrosive effects of salt media (mapei, 2015). numerous research and practical projects have demonstrated the effectiveness of the rehabilitation technique of buildings and structures by bonding frp elements used as external reinforcement (lam, 2009; karbhari, 2009; karbhari, 2004; mirmiran, 1997). an experimental and analytical study carried out by tamuzs et al. (2007) on the deformability and concrete reinforcement by steel bars, compared with the properties of concrete specimens externally confined by frp. they carried out experiments to estimate the participation of the steel bars reinforcement and the carbon/epoxy confinement of the concrete cylinders. the effect of composite confinement architectures (e glass /vinylester and carbon/epoxy) on the effectiveness of concrete columns reinforcement of the wrapped and then subjected to compression loading was investigated experimentally by zhang et al. (2000). moreover, these authors proposed evaluating the efficiency of each individual system by a cost index. shehata et al. (2002) carried out 54 tests on short columns to determine the strength and ductility gains of the concrete columns by covering them with carbon frp sheets. equations have been proposed to calculate the strength of the confined concrete and its ultimate specific deformation as a function of the lateral confinement stress. the present work is an experimental investigation carried out on a series of cylindrical columns of concrete subjected to uni-axial compression. two types of composite material confinement are used (gfrp and cfrp) and six stacks are made (see table 1). the aim of this study is to highlight the effectiveness of the reinforcement by frp through the study of the influence of the envelope frp staking sequence and the type of reinforcement (glass or carbon fiber) on the confined columns structural behavior. the strength, axial and radial strains gains are evaluated and analyzed, with identification of the failure and damage modes of the reinforced specimens. table 1. specimen’s classifications. description stack description stack concrete pilot not confined t500 3tr_t500 c2 (02/902) h1 2tr_h_t500 t300 c4 (902/02) h2 2tr_h_t300 t500 h3 2tr_h_t-mat 2. material study and experimental protocol 2.1. concrete columns preparations the concrete cylinders specimens having a size of 16 × 32 cm are prepared by a series of 50 samples by a company with a concrete plant (gesi-bat, algeria), thus obtaining the more or less uniform specimens. after 28 days, the surfaces of the concrete cylindrical specimens are brushed in order to obtain a rough and clean surface. in other words, the purpose of the surface preparation of the concrete is to remove any surface traces of oil, grease, formwork and other soiling in order to achieve a clean surface able to receive the resin. the cylindrical surfaces ends are ground with a stone to ensure the flatness of the contact surfaces and their perpendicularity to the cylindrical one. 2.2. frp external confinement the technical adopted in this work for confining the specimens by frp layers is the direct in-situ stratification technique. two types of resins are used for two different reinforcements, the first one is a polyester resin used for both types of bi-directional fabrics (t500) and (t300) and the 70 bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 mat (m300) made of glass fibers (t, h1, h2 and h3). however, the second is sikadur 330 epoxy resin used for a sika wrap hex 230 c carbon fiber unidirectional sheet for c2 and c4 confinements (fig. 1). fig 1. different types of reinforcements used. 2.3. compression test in order to evaluate the behaviour of wrapped concrete columns a strain gauges are glued to the center of each specimen vertically and horizontally. these strain gauges measure axial shortening and radial expansion using a wheatstone bridge. the specimens loading must be carried out without shock and continuously at a constant speed throughout the test. 2.4. preparation of the polyester resin the polyester resin used consists of three components (the resin, the hardener and the accelerator. their preparation is easy, the desired quantity of the resin is put into a plastic bowl and then 1.5% of hardener is added and then mixed until a pink color is obtained, and finally 1 % of the accelerator is added and mixed again until the mixture becomes dark green, so the resin is ready to be used. 2.5. preparation of the epoxy resin the epoxy resin sikadur 330 consists of two components, resin and hardener (fig. 2), which must be mixed shortly before application. the proportion by mass of the hardener represents 25% of the mass of the resin according to the recommendations of the supplier. the mixing was carried out for about three minutes until complete disappearance of the color streaks and obtaining a homogeneous mixture. fig 2. components of the epoxy resin used. 2.6. specimens frp wrapping two types of reinforcement are used, glass fiber reinforced polymer (gfrp), and cfrp (carbon fiber reinforced polymer). the fabric reinforcing bands (glass or carbon fibers) were measured t500 t300 mat carbon hardener epoxy resin the mixture bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 71 and then cut with a cutter and a metal ruler. the length of the confinement bands fold correspond to the perimeter (for a layer) or to n times for n layers. in addition, the outer layer is extended (overlapping in the longitudinal direction of the fibers) in order to ensure a ¼perimeter overlap which allows the full strength of the fibers to be developed without slipping or peeling the composite layer (fig. 3). the main advantage of dry fabric reinforcement is easy handling on site, without any heavy equipment to move. this technique allows in particular a perfect follow-up of the shape of the reinforced structure. fig 3. column wrapped models. 2.7. testing machine and instruments the simple compression tests were carried out with a constant loading speed until rupture in accordance with astm c39 / c39m-9a, using a hydraulic press with a capacity of 3000 kn "controls model 50-c55g2/ " equipped with a digimax plus (fig. 4). the data are transmitted to the automatic acquisition system via an interface. the tests are carried out within the laboratory of civil and hydraulic engineering (lgch) of the university 08 may 1945 of guelma. fig 4. testing machine and wheatstone bridge. 3. results and discussions 3.1. gfrp wrapped specimens effects the experimental tests results are graphically presented in the form of stress/strain curves in fig. 5. the curves of the stresses are plotted as a function of the axial and radial strains in the 72 bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 same reference frame. typically, these curves have an initial slope which follows that of the control concrete up to a point of inflection, followed by a zone of great plastic deformation. while, the second slope in the plastic area is much lower than the first. this characterizes the contribution of the reinforcement which depends on the orientation and the nature of the fibers of the composite envelope. the curves show the effect of the stacking sequence on the structural behavior of the confined specimens compared to that of the control concrete subjected to compression loading. the analysis of the results obtained shows that the specimens wrapped by t500 or h3 gives an increase of 65 and 60% in the resistance respectively. whereas, the hybrids h1 and h2 having the ultimate stresses equal to 39 and 37 mpa respectively, thus allowing an improvements of 43 and 41% respectively (table 2). fig 5. stress/strain behavior of stacks in gfrp. 3.2. cfrp wrapped specimens effects the mechanical behavior of columns confined by envelopes constituted by four cfrp plies having a staking sequence of c2 (02/902) and c4 (902/02) are illustrated in fig. 6. the confined columns are subjected to repetitive uniaxial compression loading until their final failure (i.e. until obtaining the load failure lower than the one of the control concrete). the stress/strain curves of specimens wrapped by cfrp (02/902) and (902/02) respectively show that the c2 resists up to seven loads whereas, c4 resists only two loads (figs. 6 and 7). the comparison of c2 and c4 for the first two loads showed bilinear behavior (fig. 7). c2 lead to have the best ultimate load capacity at the second loading where the stress reached 61.41 mpa, i.e. an increase of 136% compared to the control concrete. however, c4 present the best behavior from the point of view of repetitive loading with a maximum stress of 49.9 mpa obtained during the third loading to an increase of 89 %. the analysis of the c4 strains for the two loadings showed that the obtained axial and radial strains are practically identical and increase by (356%) and (1252%) respectively compared to the ones obtained for the control concrete. however, for c2, the axial and radial strains gains obtained are lower than those found for c4 and the both are equal to 23% (table 2). in general, the two stacking sequences of the cfrp composite used for the confinement of the columns show a high performance compared to the gfrp composite studied. this is in good agreement with previous works of bouchelaghem et al. (2011 a,b). 0 5 10 15 20 25 30 35 40 45 50 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 s tr e ss ( m p a ) radial strain (%) axial strain (%) concrete control 3tr_t500 2tr_t500-300 2tr_ht 300-500 2 tr_h tm bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 73 fig 6. stress/strain behavior of the repeated loading of the column wrapped by c2 (02/902). fig 7. comparison between the stress/strain behavior, first and second loading, of c2 (02/902) and c4 (902/02). table 2. mean values of the test results of confined columns.. config.de confin. fmax (kn) f'c (mpa) f'cc (mpa) f'cc/f'co ɛcc % ɛcc/ɛco ɛr, rup % ɛr, rup/ɛro concrete control 530.45 26.39 26.39 1.00 89.0 1.00 0.92 1.00 t 909.44 43.74 1.65 8.42 8.59 10.65 11.57 h1 759.27 37.83 1.43 1.74 1.77 8.75 9.51 h2 757.90 37.41 1.41 1.84 1.87 5.43 5.90 h3 858.72 42.30 1.60 8.21 8.37 13.39 14.55 c2 829.50 41.66 1.57 1.15 1.23 1.21 1.23 c4 1137.77 56.35 2.13 3.71 3.78 3.83 4.16 f’cc: axial compressive strength of confined concrete; ɛcc, ɛr,rup: axial and radial deformations respectively. 0 5 10 15 20 25 30 35 40 45 50 -4 -3 -2 -1 0 1 2 3 4 s tr e ss ( m p a ) axial strain (%) radial strain (%) test 1 test 2 test i 3 test 4 test 5 test 6 test 7 concrete control 0 10 20 30 40 50 60 70 -5 -4 -3 -2 -1 0 1 2 3 4 5 s tr e ss ( m p a ) axial strain (%) radial strain (%) test 1_c2(02/902) test 2_c2(02/902) test 1_c4(902/02) test 2_c4(902/02) concrete control 74 bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 3.3. failure modes of the columns confined by cfrp and gfrp the fig. 8 shows the fractures of the specimens confined by gfrp and cfrp. in the case of gfrp the damage is initiated by local delaminations between the frp envelope and the concrete which results in a change of color noted on the photos (the most damaged areas change its color and become white due to the delamination). then, a crack growth is obtained in the directions of the fibers (horizontal and vertical), whereas the total failure of the composite jacket is obtained by a dominate crack which occur in the vertical direction (i.e. in the direction of loading). the damage are located in the lower parts of the columns confined by the c4 (902/02) envelopes having the layer oriented at 0 in contact with the concrete. however, the cracks and breaks observed are located in the upper parts for the columns confined by c2 (02/902) envelopes having the layer oriented at 90 in contact with the concrete. fig 8. failure facies of the columns confined by the envelopes: a) gfrp t500, h1, h2, h3 and control concrete, b) cfrp (02/902) and (902/02). columns confined by frpc envelopes are generally characterized by fragile fracture obtained by explosion or brutal of the composite jacket; as is the case with stacking c4 (902/02) and (02/902). these phenomena are caused not only by the high strength of the carbon fibers but also by the rigid confinement due to a large number of folds (four plies) and their orientations. indeed, the fibres oriented at 0 are subjected to the tensile loading due to swelling of the test specimens during loading, while, the one oriented at 90 are loaded at compression. the use of gfrp composite materials in the repair and/or reinforcement of concrete structural elements (short columns), subjected to uni-axial compression have an acceptable efficiency in strength, axial and radial strains compared to those confined by cfrp. the fig. 9 clarifies the effectiveness of this technique and shows well the gains and increases obtained for each system. fig. 9. effectiveness of concrete reinforcement by frp in terms of stresses axial and radial strains. 0 2 4 6 8 10 12 14 16 in c re a se s ƒ 'c c /ƒ 'c o ; a x ia l st ra in s ɛ c c / ɛ c o a n d ra d ia l st ra in s ɛ r, r u p /ɛ ro f'cc/f'co ɛcc/ɛco ɛr, rup/ɛro c4 (902/02) c2 (02/902) t 500-300 t 300-500 h t-m bouchelaghem et al., j. build. mater. struct. (2017) 4: 68-75 75 4. conclusions according to the study of externally wrapped concrete columns subjected to uni-axial compression loading the main conclusions are: • the columns confined by the gfrp and cfrp composite subjected to a repetitive loadings, showed a more rigid compared to the concrete control; • the best gains in axial and radial strains are equal to 356% and 1252% respectively obtained for the column wrapped by c4 (902/02). while, for c2 (02/902), the axial and radial strains gains obtained are for the both only 23%; • the study of the columns confined by the hybrids adopted h1, h2 and h3 showed that their stress/strain behaviors follow the first folds i.e. the layers in direct contact with the concrete; however, their failure mode damage types follow the one of the external folds; • fractures of columns confined by cfrps are marked by a brutal rupture of carbon fibers. 5. references bouchelaghem, h., bezazi, a., & scarpa, f. (2011). compressive behaviour of concrete cylindrical frpconfined columns subjected to a new sequential loading technique, composite parte b, 42, 19871993. bouchelaghem, h., bezazi, a., & scarpa, f. (2011). strength of concrete columns externally wrapped with composites under compressive static loading, reinforced plastics and composites, 30 (19), 16711688. karbhari, v. m. (2004). fiber reinforced composite bridge systems–transition from the laboratory to the field, composite structures, 66, 5-16. karbhari, v. m., & ghosh, k. (2009). comparative durability evaluation of ambient temperature cured externally bonded cfrp and gfrp composite systems for repair of bridges, composite: part a, 40, 1353-1363. lam, l., & teng, j.g. (2003). design-oriented stress–strain model for frp-confined concrete, construction and building materials, 17, 471-489. mapei (2015). corporation, polymères renforcés de fibres (prf), siège social des amériques. mirmiran, a., & shahawy m. (1997). dilation characteristics of confined concrete, mechanics of cohesive frictional materials, 2, 237-249. ndzana akongo, & tchoumi, s. (2007). réhabilitation des ouvrages en béton armé dégradés par la corrosion des armatures, université de douala. shehata, l a. e. m., carneiro, l. a. v., & shehata, l. c. d. (2002). strength of short concrete columns confined with cfrp sheets, materials and structures, 35, 50-58. tamuzs, v., valdmanis, v., gylltoft, k., & tepfers, r., (2007). behavior of cfrp-confined concrete cylinders with a compressive steel reinforcement, mechanics of composite materials 43 (3). zhang, s. l., mai, ye y.w. (2000). a study on polymer composite strengthening systems for concrete columns, applied composite materials, 7, 125-138. j. build. mater. struct. (2018) 5: 55-64 original article doi : 10.34118/jbms.v5i1.44 issn 2353-0057, eissn : 2600-6936 the impact of facade materials on the thermal comfort and energy efficiency of offices buildings khadraoui m a 1,*, sriti l 2, besbas s 1 1,* department of architecture, mohamed khider university, bp 145 rp 07000 biskra, algeria. 2 laboratory of design and modeling of architectural ambiances and urban forms (lacomofa), mohamed khider university, bp 145 rp 07000 biskra, algeria. * corresponding author: makhadraoui@yahoo.com received: 04-02-2018 revised: 08-04-2018 accepted: 16-04-2018 abstract. in order to improve thermal comfort conditions of tertiary buildings through the facades of buildings, a research has been undertaken with the intention of developing a contextually appropriate and energetically efficient facade under the conditions of a hot and arid climate. the study has taken as its starting point the analysis of comfort conditions of a set of office buildings located in biskra. these buildings were distinguished from standpoints of the treatment of their facades and the materials used. the study proposes to evaluate the thermal functioning of the different materials of the facade, then to optimize their behavior by acting on their material characteristics and the walls composition. the facade, indeed, represents a place of interaction and exchange between the inside and the outside, the performance of which is due to factors that are formal, material and technical. this article presents the main results of the analytical work. the investigation is based on an empirical approach (measurements in situ on real cases) as well as on a parametric simulation study. the results show that the facade represents with excellence the place of interaction and exchange between the interior and the exterior, the performance of which is due to factors that are both material and conceptual. through a set of recommendations, this study tries to develop a material composition of high-performing facade that can respond optimally to the requirements of a tertiary building in a desert climate, while ensuring a pleasant thermal ambience and low consumption energy. key words: facade, material characteristics, thermal comfort, offices, simulation. 1. introduction the use of energy has always been a fundamental mean for man to improve his comfort (heiselberg, 2009; seoud, 2012; arnal, 2013). at the same time, the search for the control of thermal environments within the built environment, while minimizing energy consumption, continues to be considered as a challenge. the latter seems to be increasingly difficult to meet, especially with the current climatic and economic conditions in which the building represents an energy-intensive sector, responsible for increasing energy consumption. however, it is important not only to guarantee the quality of indoor environments, but also to minimize the amount of energy required for the operation of supplementary equipment (cantin et al., 2005). according to the aprue report (2007), the tertiary and residential sector are considered in algeria as energy intensive sectors, represents 41 % of total consumption (figure 1). indeed, it alone holds a significant rate of energy consumption, a large quantity of which is used mainly to meet the needs of thermal comfort (heating and cooling). this situation is the result of the irrational indifferent choices to the context and neglecting the climatic specificities during the conception. mailto:makhadraoui@yahoo.com 56 khadraoui et al., j. build. mater. struct. (2018) 5: 55-64 thermal comfort and energy efficiency are two crucial expectations for the building owner, with the development of technologies in the field of construction buildings, the building should also be undertaken under the sustainability concept (matthew, 2010). fig 1. final energy consumption in algeria by sectors according to aprue report. 2. the thermal behavior of the facade materials the thermal behavior of a building is complex and depends on the stresses to which it is subjected, notably the temperature of the outside air. the judicious choice of building materials contributes to the reduction of ambient air temperatures inside the building (mokhtari, 2008). the architecture should thus aim to integrate the climatic data of the site, to reduce energy consumption due to heating and cooling (benhouhou, 2012). the building envelope must be selected according to the loads and dynamic environmental conditions outside and inside (matthew, 2010). according to this research, it turns out that the choice of an envelope is a decisive decision in the architectural design given its complexity and its hyper-interfered aspects (khadraoui et al., 2017), because the proper design can limit the thermal impacts and obviously the energy consumption (giovanni et al., 2014). several studies have been carried out in order to optimize the thermal operation of the architectural envelope in a passive manner by acting on the vertical walls. the facade represents a separating shell that interacts between the interior space and the outside climatic conditions, its performance must be identical to that building. in this research, an attempt will be made to determine the impact of the material characteristics of the facade on the interior environment by taking measurements in situ as well as by parametric simulation. 2.1. the empirical study this research was carried out on administrative buildings and more precisely on office buildings, distinguished by the nature of their envelope. the buildings studied represent the most recurrent and representative facade types in the city of biskra (an algerian town in the south), which were selected after a thorough analysis according to previously selected criteria and the assigned objectives; the latter has given us four typologies of façade (figure 2). table 1 illustrates the composition of the facades in each case. table 1. the composition of the facades of the study cases. study case the composition of the facade from the outside to the inside thickness (cm) b1 ventilated facade in terracotta 1.6 cm cavity of air cement mortar 2cm brick 15cm air 5cm brick 10 cm plaster mortar 2cm 45 b2 curtain wall with single glazing 1 b3 cement mortar 2,5cm earthen brick of 45cm plaster mortar 2,5cm 50 b4 double skin facade in steel cavity of air cement mortar 2cm brick 15cm air 5 cm brick 10 cm plaster mortar 2cm 70 author et al., j. build. mater. struct. (2018) 5: 55-64 57 fig 2. photos of study corpus. building b1: administrative group with a ventilated facade, the b2 is an administration with a curtain wall facade. the b3 is a colonial-era building with a terracotta wall and the b4 is a relatively new construction with a double-skinned steel façade. the study context in the city of biskra, which is located in the south of algeria at a latitude of 34 ° 48 'north and a longitude of 5 ° 44' east. it rises to an altitude of 86 meters. the average monthly temperature under shelter in the town of biskra for about 15 years (between 2000 and 2015) illustrated in (figure 3). through the exploitation of the data of this graph, the coldest or the warmest period can be determined in order to calculate the "design day" and the "design week" of each period. fig 3. the average monthly temperature under cover of the city of biskra (biskra weather station, 2016). the measurements were taken during the winter period (december 13-14th, 2016) after the determination of the coldest week "design week" (figure 4) that is relatively connected with period of 15 years. this temperature (tout) was determined by the use of meteorological data and the calculation of the average daily temperature (hong, 1999). 58 khadraoui et al., j. build. mater. struct. (2018) 5: 55-64 fig 4. design week determination bi-hourly measurements were made under natural conditions during the winter period (december 2016). the measured temperatures are the ambient inside temperature (ta), the internal surface temperature (tis) and the temperature outside (tout). the instruments used are a "testo 480" thermometer and an infrared thermometer (figure 5). fig 5. the instruments used for taking measurements. we have measured the ambient temperature and the internal surface temperature, because in a simplified way the temperature of the comfort is calculated by the average of the temperature of the air and the surface temperature of the walls as shown by the formula (1) (herde, 2005). 2 surfaceair comfort tt t   (1) 2.2. modeling and simulation of the thermal behavior of the facade in order to predict the problems of the building, simulation tools should be used, for example to design a high-performance envelope, it is necessary to make an appropriate numerical simulation (tittelein, 2008; matthew, 2010). the simulation makes it possible to evaluate the thermal behavior of the facade throughout the year with the possibility of making corrections, therefore parametric improvements of elements with the possibility of determining the impact of each parameter. making a thorough rapid simulation of a design allows the architect to understand in a way the impacts of architectural choices and climate on the behavior of space. the simple action of testing a space using a design simulation creates an intuitive understanding of performance that author et al., j. build. mater. struct. (2018) 5: 55-64 59 can be used immediately; through subsequent design activities and future projects. while design simulation is often seen as a specialized engineer's tool to predict energy performance, the importance of this tool for architects is the freedom to play and develop ideas. instead of applying the generic sustainable strategies that the architect does not fully understand, design simulation allows for a quick assessment of assigned objectives (buratti et al., 2013; anderson, 2014). the software used is "energyplus v8-4-0", "open studio v1-9-0" and "sketchup 2015" (figure6). the software "enegyplus" is used as a calculation engine, this tool has been validated and has shown its performance (spitz, 2012; soudani, 2016). the 3d model was modeled on sketchup (graphical interface) and the "open studio" platform is used to link sketchup to energyplus. we have developed our own library of building materials and space use scenarios, while using the climate file of the city in question in "epw" format. we have created a virtual model (rm) as reference model, it is a small desk in rectangular form of 20 m² (4mx5m) with a height of 3m. it contains a single window oriented towards the south and occupies 12.6 % of the facade. fig 6. sketchup-open studio-energyplus simulation platform. according to the analysis of real cases, we found a random use of building materials without any relation to the climate context of the city. in this sense, we have developed the reference model (rm) which reflects a simple case with the material composition that is used in this region. in the second step, we have created an inertia model (im) and tested the impact of thermal inertia by the use of heavy materials with high thermal inertia. table 2 illustrates the thermal characteristics of the materials of the model produced. the type of glazing used is a simple glazing. table 2. the composition of the facades of the study cases. materials λ (w/m.k) c (j/kg.k) d (kg/m3) t (cm) cementmortar 0,80 850 1900 0,2 hollow-brick 0,39 1000 650 10-15 plastermortar 0,57 1008 1150 02 air 0,047 1000 1 05 concrete 1,75 1080 2500 10 60 khadraoui et al., j. build. mater. struct. (2018) 5: 55-64 3. results and discussion the results obtained after determination of the design week of the city of biskra. 3.1. discussion of the empirical study the graph (figure 7) illustrates the measurements obtained for buildings b1 and b3. it reveals that the indoor temperature is almost stable throughout the day with maximum amplitude of 5.6 °c at 8h. fig 7. graphs of the ambient temperatures measured in studied buildings b1 and b3. the composition of the facades for b1 and b3 prevents temperature fluctuations and ensures an internal temperature varying between 16.6 °c and 19.7 °c during the working period. it is also noted that these temperatures are quite comfortable with respect to the outside temperature, which reaches a minimum of 13.3 °c at 8 h. as for the graph (figure 8), which summarizes the measurements obtained for buildings b2 and b4, it is noted that the temperature inside the premises is less stable in comparison with b1 and b3. the large glazed surfaces of the facades b2 and b4 have caused an excessive increase in temperature, but only after a time of exposure to solar radiation, which generates more heat inside and allows the vertical walls to behave like a greenhouse. fig 8. graphs of the ambient temperatures measured in studied buildings b2 and b4. author et al., j. build. mater. struct. (2018) 5: 55-64 61 it is noted that the temperature at 10 h is in the order of 21.6 °c; it culminates at 16h in b4 and reaches 22.4 °c, which is considered as an annoying temperature (according to a personal observation and the opinion of the users). overall, it can be said that the best thermal behavior is that is in buildings b1 and b3, which ensures a stable temperature due to the material composition of the facade. whereas the worst cases are respectively b2 and b4 where we found an excess of heat in a cold period. figure 9 shows the measurements recorded for the outdoor temperature (tout) and the internal surface temperature (tis) during the week design. it is found that b1 and b3, (tis) is more stable unlike b2 and b4 where there is a significant increase in surface temperature. this is due to the physical characteristics of the materials composing if the facades, which are visibly climatically unsuitable (in b2 single glazing and in b4 double steel skin). fig 9. graphs of the outside temperature and the surface temperatures measured in studied buildings. thus, the materials used in building b3 have an impact on the stability of the surface temperature, followed by the ventilated facade (vf) of b1. on the other hand, the glass facade of b2 and the double skin facade (dsf) of steel of b4 negatively influence their thermal behavior through an increase of (tis). 3.2. results of the simulation figure 10 shows the thermal amplitude between the outdoor temperature and the operational temperature (to) simulated with the reference model for one year and allows simultaneous 62 khadraoui et al., j. build. mater. struct. (2018) 5: 55-64 viewing of the (isothermal) in order to determine the most unfavorable zone (overheating zones). fig 10. the thermal amplitude of the reference model. during the winter, the thermal amplitude is in the order from 3.4 °c and during the summer, it reaches 6.6 °c. the great amplitudes is during the summer period; where the maximum temperature can exceeds 40 °c during the month of july. the results of the thermal amplitude of the second model developed (inertia model "im") are shown in (figure 11). fig 11. the thermal amplitude of the inertia model. author et al., j. build. mater. struct. (2018) 5: 55-64 63 it is noted that there is an improvement in this model compared to the previous model by increasing the values of the thermal amplitude, generally throughout the year and especially during the summer (from 6.6 °c to 7.8 °c). thus, it can be seen that the thermal inertia influences the improvement of the thermal comfort conditions in the spaces, through these characteristics of attenuation of the heat flux with a delay in time (the time of the phase shift), which ignores the sudden change of the temperature and ensures comfort to the space users. figure 12 illustrates the thermal amplitude of the two models studied during a hot day (july). generally, it is noted that the best thermal behavior is the inertia model (im) all day long, this decrease in temperature is mainly dependent on the material characteristics of the facade of the model (im). fig 12. the thermal amplitude of the two models during a hot day. the thermal characteristics of the heavy materials used in the (im) facade have a major impact on the improvement of thermal conditions. in a hot and arid climatic conditions, thermal inertia in particular plays an important role in ensuring hygrothermal equilibrium. in summer, it reduces thermal fluctuations and extreme temperatures. in winter, it avoids too sudden falls in temperature and highlights the optimal management of heat inputs (medjelakh, 2008). the analysis and comparison between the two simulated models asserts the important impact of the physical characteristics of the facade on the thermal behavior and energy efficiency of the building as well as the comfort of the users. 4. conclusions this article presents the main results obtained from a study based on an empirical investigation (measurements taken in situ in existing buildings) as well as a parametric analysis by simulation. the objective of the investigation is to evaluate the impact of the material and conceptual aspects of the facade on the thermal comfort of office spaces in a hot and arid climate. the first part of the study is based on measurements confirmed the importance of mastering the physical characteristics of the building materials used on the facade. the importance of thermal inertia for a hot and arid climate and its impact on the thermal comfort was highlighted. the choice of building materials remains a determining factor in the thermal behavior of the facade. 64 khadraoui et al., j. build. mater. struct. (2018) 5: 55-64 the second part of the study was carried out using a simulation with the "energyplus" software using "open studio" as a platform. a parametric analysis was carried out and a preponderant factor of the thermal phenomena of the facade was studied (the thermal inertia). the results show that the increase in the thermal inertia of the facade materials has a positive influence on the thermal behavior of the building and the comfort of users of space. the results of this research open several avenues for future investigation. possibilities for studies and optimization related to the impact of the composition of the wall and the type of materials on thermal comfort and energy efficiency. 5. references anderson k. (2014). design energy simulation for architects, routledge publishing, first ed., new york. arnal, e. (2013). modélisation et commande hiérarchisées du bâtiment pour l’amélioration des performances énergétiques, thermiques et optiques, doctoral thesis, the national institute of applied sciences of lyon, france. aprue, (2007). rapport de la consommation énergétique finale de l’algérie, ministère de l’energie et des mines-agence nationale pour la promotion et la rationalisation de l’utilisation de l’energie. benhouhou, m.n., (2012). l’impact des matériaux sur le confort thermique dans les zones semi-arides, memory of magister, epau, algeria. buratti, c., moretti, e., belloni, e., & cotana, f. (2013). unsteady simulation of energy performance and thermal comfort in non-residential buildings. building and environment, 59, 482-491. cantin, r., & guarracino, g., (2005). complexité du confort thermique dans les bâtiments, vième congrès européen de science des systèmes, pp. 02-04. giovanni, z., & andrea, f. (2014). evolutionary optimisation of façade design a new approach for the design of building envelopes, springer, first ed., london. heiselberg, p. (2009). expert guide–part 1 responsive building concepts, université d’aalborg, first ed., danemark. herde a., & liebard a. (2005). traité d’architecture et d’urbanisme bioclimatiques, le moniteur et observ’er, 1st ed., france. hong, t., chou, s. k., & bong, t. y. (1999). a design day for building load and energy estimation. building and environment, 34(4), 469-477. khadraoui m.a., & sriti, l. (2017). facades’ thermal behavior of the office buildings in a hot and arid climate. algerian journal of engineering architecture and urbanism, 1(2), 28-38. matthew, r.h. (2010). materials for energy efficiency and thermal comfort in buildings, woodhead publishing, 1st ed., new delhi. medjelakh, d., & abdou, s. (2008). impact de l’inertie thermique sur le confort hygrothermique et la consommation énergétique du bâtiment. revue des energies renouvelables, 11(3), 329-341. mokhtari, a., brahimi, k., & benziada, r. (2008). architecture et confort thermique dans les zones arides application au cas de la ville de béchar. revue des énergies renouvelables, 11(2), 307-315. seoud, s. (2012). audit énergétique de bâtiments tertiaires, memory of magister, epau, algeria. soudani, l.c.l. (2016). modelling and experimental validation of the hygrothermal performances of earth as a building material. doctoral thesis, university of lyon, france. spitz, c., (2012). analyse de la fiabilité des outils de simulation et des incertitudes de métrologie appliquée { l’efficacité énergétique des bâtiments, doctoral thesis, university of grenoble, france. tittelein, p. (2008). environnements de simulation adaptés { l’étude du comportement énergétique des bâtiments basse consommation. doctoral thesis, university of savoy, france. j. build. mater. struct. (2018) 5: 86-94 original article doi : 10.34118/jbms.v5i1.47 issn 2353-0057, eissn : 2600-6936 effects of adding sisal and glass fibers on the mechanical behaviour of concrete polymer benzannache n1, *, bezazi a2, bouchelaghem h2, 3, boumaaza m1, scarpa f4, amziane s5 1 laboratory of civil engineering & hydraulics (lgch)/guelma university, algeria 2 laboratory of applied mechanics of new materials ((lmanm)/university of guelma, algeria 3 department of mechanical engineering/university of constantine1, algeria 4 advanced composites center for innovation and science (ccctb)/university of bristol, uk 5 department of civil engineering, polytech clermont ferrand/blaise pascal university, france * corresponding author: zanachenaziha@yahoo.fr, benzannache.naziha@univ-guelma.dz received: 07-02-2018 revised: 19-04-2018 accepted: 07-05-2018 abstract. in this study, we investigated the influence of the addition of sisal and glass fibres on the mechanical properties of polymer concrete (pc). these types of concrete are used in many modern civil engineering applications. the prismatic specimens sized according to astm c580-02 were elaborated with a pc constituted by 14% constant mass of polyester resin matrix, a granular skeleton based on sand and powder marble. the reinforcement with 60% sand and 26% marble powder adopted in this investigation is the best formulation found in previous authors work. this composition was reinforced by 1 and 2% of sisal and glass fibres, the first one having lengths of 6 mm or 12 mm, however, the second unidirectional cut into bands. these specimens were subjected to 3-point bending monotonic loading. the results obtained were discussed and compared with those obtained for control beams without fibres reinforcement. it is important to note that the incorporation of the glass fibre contributes to an increase of the ultimate load of the polymer composite material produced, however, the addition of the sisal fibre lead to its decreases. in addition, the incorporation of 2% of sisal fibre having 6 mm length leads to a reduction of 26% of the mass of the specimens. key words: polymer concrete, sisal and glass fibres, marble, resin, sand. 1. introduction polymer concrete (pc) is a material manufactured completely or partially by replacing the portland cement with a polymer. since the 1980s, research and development of polymer concrete and mortars have been growing rapidly in various western countries. the substitution of portland cement with a polymer results in a substantial increase in the cost of concrete, this should only be done if the cost of labour is lower or if the energy requirements for manufacturing and implementation are lower (blaga and beaudoin, 1985). at present, the pc can be used very efficiently due to its high strength and lightness, made of prefabricated elements in the building, such as: bridge decks, hazardous waste containers, industrial machine bases, floor tile manufacture with synthetic marble and stair panels, facade panels and panels of various structures and window sills (ohama, 2010). to improve the physical and mechanical properties, researchers have been interested in optimizing the pc formulation by reducing the resin mass fraction and/or replacing or adding part of the granular skeleton by other components (gorninski, 2004; haidar, 2011; elalaoui, 2012). as a result, the pc's qualities are improved while respecting economic requirements. moreover, the growing demand for environmentally friendly materials has led researchers to focus on the incorporation into the pc, industrial waste residue as reinforcement (fly ash, tire rubber, foundry sands, glass powder waste, marble powder etc...) to make one hand more powerful, lighter and less costly (bignozzi, 2000 ; ribeiro, 2013). castro et al.(2013), saribiyik et mailto:zanachenaziha@yahoo.fr mailto:benzannache.naziha@univ-guelma.dz benzannache et al., j. build. mater. struct. (2018) 5: 86-94 87 al. (2013) found that the incorporation of a 30% amount of glass powder waste into the pc leads to an increase in bending and compression stresses by 78 and 29% respectively. in order to reduce the cost of pc produced with synthetic fibres (ie carbon, kevlar, glass, etc.), the latter are replaced by natural fibres such as jute, sisal, flax, coco, banana, etc., which have gained considerable importance as reinforcements in polymer matrix composites. compared to synthetic fibre, natural ones issue from plants (lignocelluloses) has the advantage of being very light, issue from a renewable source, cheap and widely available in fibrous form. in a study conducted by reis (2006) using 2% of the coconut, bagasse (sugar residue) and banana fibres as addition in the pc. he concluded that coconut and bagasse fibres improve the mechanical properties of pc both its strength and its breaking energy, while banana fiber has only increased the breaking energy. in other words, coconut fibre proves to be an excellent reinforcement for pc thus increasing its ultimate bending strength by 25.1%. while, banana stem fibres is not a good choice for strengthening pc (reis, 2006). in another work, reis (2012) studied the effect of the incorporation of the treated and untreated sisal fibres with naoh and acetic acid into two polymeric mortars, based on epoxy and polyester resins respectively. the addition of a small quantity of sisal fibres contributes significantly to the improvement of the mechanical properties of the pcs. it has also been observed that polymer mortars reinforced with untreated sisal fibres have the highest ultimate strength and those reinforced with sisal fibres treatment with 10 % of naoh have the lowest properties. benzannache et al. (2018) have shown in an earlier study that the incorporation of marble waste has improved the mechanical and physical properties of polymer concrete. for this purpose, the main objective is to study the effect of the additions on the mechanical strength of the pc beams subjected to 3-point bending. the pc constituted of resin, marble powder waste, sand granulate as well as 1% or 2% additions of the glass fibre in the form of bands located at tensile zone precisely at 1/3 of the height of the beam. in addition, beams with the incorporation of sisal fibre cut in two different lengths (6 mm and 12 mm) and randomly distributed in the mass have been also studied. 2. experimental protocol 2.1. study materials previous work by the authors benzannache et al. (2018) revealed that the best flexural behaviour of the pc (designed as gc60 m26) was obtained with 14% of a polyester resin matrix, 60% of a granular skeleton (sand of particle size 1-3 mm, steamed at 105°) and 26% marble powder waste of particle size (0.02-1.4 mm). the present work consists of substituting 1 or 2% of the sand aggregate with glass fibre in the form of bands or sisal fibre cut into 6 or 12 mm lengths and randomly distributed in the mass. the characteristics of this type of glass fibre are determined in previous work, by bouchelaghem et al. (2011), done in the laboratory of applied mechanics (lmanm of the university of 8 mai 1945 guelma algeria). while, the sisal fibre are also characterised in laboratory lmanm by belaadi et al. (2013), (2014). the seven prepared formulations are shown in table 1. 2.2. preparation the seven formulations of pc can be classified into three groups: the first is a polymeric concrete control (pc_control), the second consists of four pcs formulations with 1% or 2% sisal fibre having a length of 6 or 12 mm. as for the last group contains two formulations pcg which is added 1 to 2% of glass fibre bands. 88 benzannache et al., j. build. mater. struct. (2018) 5: 86-94 concrete pc_control the constituents of the pc_control are weighted and dry-mixed and then a polyester resin, previously prepared with 1.5% hardener and 1% accelerator, is added to the mixture. the mixture thus obtained will be placed in prismatic moulds of dimensions 25×25×300 mm according to astm c580.02. table 1. formulations of the pc. formulation resin (%) sand (%) marble (%) sisal (%) glass fibre (%) average specimen weight m(g) decrease in weight df (%) density (kg/m3) pc_ control 14 60 26 0 0 419.60 0 2237.87 pcs_1%_6mm 14 59 26 1 0 355.60 15.25 1896.53 pcs_1%_12mm 14 59 26 1 0 336.97 19.7 1797.17 pcs_2%_6mm 14 58 26 2 0 320.94 23.5 1711.68 pcs_2%_12mm 14 58 26 2 0 310.50 26.0 1656.0 pcg_1% 14 59 26 0 1 413.26 1.5 2204.05 pcg_2% 14 58 26 0 2 388.37 7.3 2076.31 concrete pcs: for this type of concrete the sisal, having a length of 6 or 12 mm, has been incorporated and mixed well with the dry granulates. the prepared resin is then added gradually while mixing until the pcs is obtained, which is then poured into the mould may contain seven specimens (figure 1). fig 1. mould filled with pcs may contain seven specimens. concrete pcg: the same procedure for preparing the control concrete, only this time, 1 or 2% of sand is substituted by the glass fibre bands of size 25 × 300 mm impregnated with resin and spread out benzannache et al., j. build. mater. struct. (2018) 5: 86-94 89 at 1/3 of the height of each beam specimens, then continue until the mould is completely filled (figure 2). fig 2. filling of mould with the glass fibre band incorporations. 2.3. experimental setup the static 3-point bending tests were carried out on a zwick/roell z005 universal testing machine at a test speed of 2 mm/min. this machine is equipped with a load cell whose capacity is 20 kn (figure 3). fig 3. experimental setup. 3. results and discussion 3.1. bending behaviour of pcs the loads/displacements behaviour of the control beams presented in fig.4 occur in two phases: the first one is practically linear until reaching the ultimate load, while sometimes small staircase shapes are noted due to the detachment of sand grains (see figure 4, pc5_control). the second short phase is characterized by a sudden drop of force leading to the specimen failures. it is also important to note that at the beginning of the tests, a displacement with a small force is recorded before the actual response of the material starts. the average ultimate load is of the order of 800 n for an average displacement at failure of 0.80 mm. with the incorporation of the 90 benzannache et al., j. build. mater. struct. (2018) 5: 86-94 sisal fibre (figures 5a to 5d), the evolution of the load/displacement curves is similar to that obtained for the control concrete, nevertheless with more pronounced perturbations in the first phase with a less brutal drop in the load at the second phase. the addition of the sisal fibre provoke an absorption of resin, leading to an insufficient sticking between the grains, this causes more grain detachment which results in staircase perturbations in the response curves. the load is reduced for all the test specimens, for the incorporation of 1 or 2% of sisal fibre having lengths of 6 or 12 mm. the maximum recorded loads for the beams pcs_1%_6, pcs_1%_12, pcs_2%_6 and pcs_2%_12 are respectively 612, 583, 405 and 396 n and their corresponding to a reduction of 30 %, 37%, 97% et 102% comparatively to the control concrete. while, their displacements at failure are 1.24, 1.25, 1.22 and 3.03 mm respectively corresponding to an increase by 55%, 56%, 52% et 378% respectively. in other words, it was found that cut sisal fibre did not lead to improve the ultimate load on the contrary, it decreased it, however the displacement increased for the best case by 269% for the specimens containing 2% of sisal fibres having 12 mm length. it is important to note that the incorporation of the sisal fibres can lead to a decrease up to 26% of the specimen mass compared to the control one; this is obtained in the case of the addition of 2% of sisal having 12 mm length (see table 1). the load/displacement behaviour of the beams reinforced by unidirectional glass fibre bands is shown in (figures 5e and 5f). this behaviour, which occurs in three phases, is different from that of the control beams and those reinforced by sisal fibres because it has allowed to a considerable increases both in load and displacement. the first linear phase up to a force of about 800 n corresponding to that found for the concrete control. the second phase is also linear but with lower slope than the first phase and shows disturbances. the average ultimate loads and displacements at failure reached are 2040, 2740 n and 11.3, 10.5 mm respectively for the beams pcg_1% and pcg_2%. finally, a staircase is observed leading to a less brutal failure compared to those found for the control beams and the ones reinforced with sisal fibre. benzannache et al., j. build. mater. struct. (2018) 5: 86-94 91 fig 4. load/displacement of pc-control. fig 5. load/displacement of different pcs: a) pcs _1%_6 mm; b) pcs _1%_12mm; c) pcs_ 2%_6mm; d) pcs_ 2%_12mm ; e) pcg_ 1% ; f) pcg 2%. (a) (b) (e) 92 benzannache et al., j. build. mater. struct. (2018) 5: 86-94 the comparisons of the behaviour of the control pc with pcs reinforced by the sisal or glass fibres are shown in (figure 6). the analysis of the results shows clearly that the addition of the glass fibre bands leads to the best behaviour. indeed, the addition of 1 or 2% glass fibres allows to an average increase in ultimate load by 153 and 238% respectively and their corresponding displacements by 1281 and 1180%. fig 6. load/displacement curves of the pcs and pcg compared to the control concrete (pc_control). 3.2. pcs failure modes figure 7 shows the different failure modes of the pcs specimens where the cracks are initiated at the tensile zone (bottom surface). for the concrete control beams pc, the failure was brutal leading to divide the specimen in two parts (figures 7a and 7b). while, for beams reinforced with sisal fibre (pcs), the failure is less brutal and the crack initiated cannot reach the face application load (figures 7c to 7f). whereas, for the beams reinforced with 1% or 2% of glass fibre bands, the failure occurs on three steps following the load/displacement behaviour. the crack initiated in the tensile zone propagates until reaching the composite (step 1), this corresponds to the first phase of the curve load/displacement (figure 7g). the composite slows the failure propagation until it broke (step 2) where a new crack appear and develop until the top surface (step 3) leading to compression failure of the concrete. the step 2 and 3 are representing the phase two and three of the pcgs load/displacement behaviour (figure 7h). benzannache et al., j. build. mater. struct. (2018) 5: 86-94 93 fig 7. rupture facies : a) crack initiation of control beam, b) failure control beam ; c) eps-1%_6 ; d) eps1%_12 ;e) eps-2%_6 ; f) eps-2%_12 ; g) epv-1% ; h) epv-2%. 4. conclusions the study of the flexural mechanical behaviour of polymer concrete with the incorporation of 1 or 2% of sisal or glass fibre leads to the following points:  the addition of the sisal fibre cut and mixed randomly, allows a reduction in the mass of the specimens up to 26% compared to the control specimen. on the other hand, decreases in ultimate load with a slight increase in displacements are recorded.  the sisal fibre causes the absorption of the resin and therefore the 14% is not sufficient to agglomerate the grains, this causes the separation of the grains which leads to the appearance of the forms in staircase (abrupt decrease of load).  incorporation of the unidirectional glass fibre strips introduced at 1/3 of the height of the specimens allowed the improvement of the mechanical characteristics. indeed, the addition of 1 or 2% of glass fibre has increased the ultimate loads and displacements by 153, 238% and 1280, 1180% respectively. (a) (b) (c) (d) (e) (g) (f) (h) 94 benzannache et al., j. build. mater. struct. (2018) 5: 86-94 acknowledgments: the authors are great full to prof. redjel b. and prof. merzoud m. from the laboratory lgc university of annaba having to facilitate access to their machine for the experiment tests. 5. references belaadi, a., bezazi, a., bourchak, m., & scarpa, f. (2013). tensile static and fatigue behaviour of sisal fibres. materials & design, 46, 76-83. belaadi, a., bezazi, a., bourchak, m., scarpa, f., & zhu, c. (2014). thermochemical and statistical mechanical properties of natural sisal fibres. composites part b: engineering, 67, 481-489. benzannache, n., bezazi, a., bouchelaghem, h., boumaaza, m., amziane, s., & scarpa, f. (2018). statistical analysis of the 3-point bending properties of polymer concrete made of marble powder waste, sand grains and polyester resin. mechanics of composite materials, 53(6), 1123-1136. bignozzi, m. c., saccani, a., & sandrolini, f. (2000). new polymer mortars containing polymeric wastes. part 1. microstructure and mechanical properties. composites part a: applied science and manufacturing, 31(2), 97-106. blaga, a., & beaudoin, j. j. (1985). polymer modified concrete. canadian building digest, cbd-241. institute for research in construction. bouchelaghem, h., bezazi, a., & scarpa, f. (2011). compressive behaviour of concrete cylindrical frpconfined columns subjected to a new sequential loading technique. composites part b: engineering, 42(7), 1987-1993. castro, a. m., ribeiro, m. c. s., santos, j., meixedo, j. p., silva, f. j., fiúza, a., ... & alvim, m. r. (2013). sustainable waste recycling solution for the glass fibre reinforced polymer composite materials industry. construction and building materials, 45, 87-94. elalaoui, o., ghorbal, e., mignot, v. & ben ouezdou, m. (2012). mechanical and physical properties of epoxy polymer concrete after exposure to temperatures up to 250 °c. construction and building materials, 27, 415–424. gorninski, j. p., dal molin, d. c., & kazmierczak, c. s. (2004). study of the modulus of elasticity of polymer concrete compounds and comparative assessment of polymer concrete and portland cement concrete. cement and concrete research, 34(11), 2091-2095. haidar, m., ghorbel, e., & toutanji, h. (2011). optimization of the formulation of micro-polymer concretes. construction and building materials, 25(4), 1632-1644. ohama, y. (2010). concrete-polymer composites: the past, present and future. 13 th international congress on polymers in concrete (icpic), portugal, pp. 1-14. reis, j. m. l. (2006). fracture and flexural characterization of natural fiber-reinforced polymer concrete. construction and building materials, 20(9), 673-678. reis, j. m. l. (2012). sisal fiber polymer mortar composites: introductory fracture mechanics approach. construction and building materials, 37, 177-180. ribeiro, m. c. s., fiúza, a., castro, a. c. m., silva, f. g., dinis, m. l., meixedo, j. p., & alvim, m. r. (2013). mix design process of polyester polymer mortars modified with recycled gfrp waste materials. composite structures, 105, 300-310. saribiyik, m., piskin, a., & saribiyik, a. (2013). the effects of waste glass powder usage on polymer concrete properties. construction and building materials, 47, 840-844. j. build. mater. struct. (2019) 6: 32-38 original article doi : 10.34118/jbms.v6i1.66 issn 2353-0057, eissn : 2600-6936 analysis of static bending of plates fgm using refined high order shear deformation theory merdaci s1,*, boutaleb s2, hellal h2, benyoucef s2 1 structures and advanced materials in civil engineering and public works laboratory, university of sidi bel abbes, faculty of technology, civil engineering and public works department, algeria. 2 material and hydrology laboratory, university of sidi bel abbes, faculty of technology, civil engineering and public works department, algeria * corresponding author: slimanem2016@gmail.com received: 02-08-2018 accepted: 04-03-2019 abstract: this work deals with the analysis of the mechanical bending behavior of a rectangular plate simply supported on four sides (fgm), subjected to transverse static loading. the high order theory is used in this work, the developed models are variably consistent, have a strong similarity with the classical plate theory in many aspects, do not require correction to the shear factor, and give rise to variations transverse shear stresses such as transverse shear parabolically varies across the shear thickness and satisfies surface conditions without stresses. equilibrium equations are obtained by applying the principle of virtual works. the mathematical expressions of the arrow, the stresses are obtained using navies approach to solve the system of equilibrium equations. the influence of mechanical loading and the change of the parameter of the material on mechanical behavior of the plate p-fgm are represented by a numerical example. key words: fgm, rectangular plate, bending, high order theory rpt. 1. introduction in recent years, functionally graded materials (fgm) have attracted considerable attention in many applications in engineering. property gradient materials (fgms), a type of composite material produced by continuously changing the volume fractions in the thickness direction to obtain a definite profile, these types of materials, have received much attention recently in because of the advantages of reducing disparity in material properties and reducing thermal residual stresses (zhong & yu, 2007). the concept of “functionally graded materials” fgm was developed in japan national aerospace laboratory in 1984 by mr. niino and his colleagues in sendai (mostefa et al,. 2018). the idea is to produce materials used as thermal barriers in spatial structures and fusion reactors (koizumi, 1992). the fgm can be used for various applications, such as thermal barrier coatings for ceramic motors, gas turbines, optical thin films, etc. (nguyen et al., 2008). due to wide variations and applications of materials with gradient properties, the literature corresponding to the fgms in the constituents of the materials (shimpi & patel, 2006), fracture mechanics (wu & li, 2010; şimşek, 2010; lü et al., 2009; ying et al., 2009), have been rapidly increased in the past 15 years. many researchers have devoted their time to understanding the mechanical behavior and mechanism of fgm to provide an optimum profile to designers. composite plates made of metal and ceramic are widely used in aircraft, ship reactors, and other structural technology applications (merdaci et al., 2015; merdaci et al., 2016). understanding the mechanical behavior of an fgm plate is very important in estimating the safety of the plate (reddy,. 1984). (woo & meguid, 2001) have applied the karman theory for the large deformation to obtain the analytical solution for the plates and shells under a mechanical loading transverse and a field of temperature. (praveen & reddy, 1998) studied the static and dynamic responses of thick mailto:slimanem2016@gmail.com merdaci et al., j. build. mater. struct. (2019) 6: 32-38 33 (ceramic-metal) fgm plates using a finite element plate that takes into account the presence of transverse shear stresses, large rotations in the direction of von karman. this study deals with the analysis of the mechanical behavior at the static flexion of a rectangular plate of fgm functional gradient materials with the theory of refined shear deformation plates. it is assumed that the material properties of the plate change without interruption across the thickness, depending on the volume fraction of the constituent material according to a power-law function p-fgm. the results obtained show that the mechanical behavior of the rectangular plates fgm is different from those of the isotropic plates. changing the material parameter has a significant effect on the boom, the normal and tangential stresses. 2. refined plate theory (rpt) an efficient and simple refined plate theory (rpt) was initially introduced and implemented by (shimpi & patel, 2006) in order to deal with the problems of static and dynamic analysis of orthotropic plates. the refined theory can be classified among the third-order shear deformation theories. the development of the refined plate theory is based on the assumptions that the theory represents parabolic variations of shear strains and shear stresses throughout the plate thickness and also satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate. additionally, the theory can provide high accuracy in prediction plate behavior subjected to mechanical loadings without using the shear correction factor. based on the basic assumptions of the rpt (shimpi & patel, 2006), the displacement field of the rpt can be written as follows (merdaci,. 2017): 3 0 2 3 0 2 1 5 ( , , ) ( , ) 4 3 1 5 ( , , ) ( , ) 4 3 ( , , ) ( , ) ( , ) b s b s b s w w u x y z u x y z z z x xh w w v x y z v x y z z z y yh w x y z w x y w x y                         (1) the main differences between the improved tsdt developed by (shi, 2007) and the rpt are the middle terms of in-plane displacement functions. and the transverse displacement (w) of the rpt is composed of two components of the displacement due to bending (wb) and shear (ws).to apply the improved theory for analyzing plate problems (merdaci et al,. 2011), it is begun with the constitutive equations that take the form as, 11 12 12 22 66 0 0 0 0 x x y y xy xy q q q q q                               and 44 55 0 0 yz yz zx zx q q                          (2) or ( x , y , xy , yz , yx ) and ( x , y , xy , yz , yx ) are the stress and strain components, respectively. the stiffness coefficients ij q are expressed as follows:   11 22 12 44 55 662 2 ( ) ( ) ( ) , , . 2 11 1 e z e z e z q q q q q q            (3) 3. the solution method for fg plate analysis the governing equation or the total energy functional based on the improved rpt for fgm plate analysis derived from the energy approach can be solved using the navier solution in order to determine the static bending results. the total energy functional (π) of fgm plates for the static bending analysis can be written as the following, e e u v   (4) 34 merdaci et al., j. build. mater. struct. (2019) 6: 32-38 where ue is the virtual variation of the deformation energy and ve is the variation of work done by external forces can be expressed:   / 2 / 2 0 h x x y y xy xy yz yz xz xz h d dz q w d                               (5) the equilibrium equations can be written from the displacement gradients and put the coefficients 0 u , 0 v , b w  et s w  and equal to zero separately. thus the equilibrium equations related to the present shear deformation theory can be obtained. the boundary conditions, which are simply supported, are chosen to consider the analysis of the plate. 0 0, 0 b sb s b s x x x w w v w w n m m y y             and 0,x a (6) 0 0, 0 b sb s b s y y y w w u w w n m m x x             and 0,y b (7) the assumed in-plane displacements satisfying the conditions of simply supported in direction of x and y are: 0 0 1 1 cos( ) sin( ) sin( ) cos( ) sin( ) sin( ) sin( ) sin( ) mn mn b bmnm n s smn u u x y v v x y w w x y w w x y                                          (8) where mn u , mn v , bmn w and smn w are arbitrary parameters to be determined. we obtain the following equation:     k f  (9) where   and  f are column vectors        , , , , 0, 0, , . t t mn mn bmn smn mn mnu v w w et f q q     (10) 11 12 13 14 12 22 23 24 13 23 33 34 14 24 34 44 a a a a a a a a k a a a a a a a a                (11) 4. results and discussions a rectangular ceramic-metal fgm plate according to the p-fgm power-law distribution is considered in this section. the geometry of the fgm plate is shown in figure 1 in which the composition of the material on the upper surface is assumed to be the ceramic-rich surface and the compositions of materials are continuously varied at the metal-rich surface on the opposite side. fig. 1. the dimensions and the variation of the thickness of the rectangular plate fgm. merdaci et al., j. build. mater. struct. (2019) 6: 32-38 35 in this study, the bending analysis of the fgm plates by the present theory of trigonometric shear deformation is proposed. comparisons are made with the solutions available in the literature. in order to verify the accuracy of this analysis, some numerical examples are undertaken. the properties of the materials used in the present study are: metal (aluminium,al): em=70gpa ; 3.0 , ceramic (alumina,al2o3): ec=380gpa 3.0 . is taken the ratio a/h=10. various non-dimensional parameters used are: displacement:        2 , 2 10 0 4 3 ba w qa eh w c , axial stress:        2 , 2 , 2 0 hba aq h xx  , shear stress:        0, 2 ,0 0 b aq h xzxz  , coordinate thickness: hzz / . the fgm plate used is a symmetrical plate and has only two layers of equal thickness, there is no base layer. so, 0 21  hh . in this section, we propose to validate the proposed model through some standard tests known from the literature. it is essentially a question of evaluating its precision performance on the transverse displacements for different elongation ratios. in order to validate our model, an example of static flexion will be studied. the example treats the bending of a simply supported isotropic plate subjected to static loading varying linearly across the thickness. a comparison was made with the results of the method of (timoshenko & gere, 1972), the results of eulerbernoulli and (zenkour, 2004) will also be introduced in the comparison. table 1. effect of the ratio (a / b) of the elongation on the boom for an isotropic plate subjected to linear loading and (k = 2) for the different theory. a/b euler-bernoulli [timoshenko1972] [zenkour 2004] present study cpt fpt spt rpt 1/4 0.9832 1.0003 0.9969 0.99694 1/2 0.7103 0.7249 0.7220 0.72204 1 0.2774 0.2866 0.2847 0.28478 2 0.0443 0.0480 0.0473 0.04731 4 0.0038 0.0049 0.0046 0.00469 table 2. comparison between the different models of normal stress calculation of an isotropic plate subjected to linear loading. z/h eulerbernoulli [timoshenko1972] [zenkour2004] present study cpt fpt spt rpt 0.5 1.975764 1.975764 1.983924 1.995501 0.4 1.580611 1.580611 1.581429 1.582588 0.3 1.185458 1.185458 1.182452 1.178187 0.2 0.790305 0.790305 0.786469 0.781029 0.1 0.395152 0.395152 0.392663 0.389131 0 0 0 0 0 -0.1 0.395152 0.395152 0.392663 0.389131 -0.2 0.790305 0.790305 0.786469 0.781029 -0.3 1.185458 1.185458 1.182452 1.178187 -0.4 1.580611 1.580611 1.581429 1.582588 -0.5 1.975764 1.975764 1.983924 1.995501 36 merdaci et al., j. build. mater. struct. (2019) 6: 32-38 the results obtained from the deferent models (timoshenko & gere, 1972; zenkour, 2004) coincide with those resulting from the present method as illustrated in tables 1 and 2. displacements and normal stresses of an isotropic plate subjected to linear loading. table 3. value of displacements, and the effect of the volume fraction "k" with respect to the rectangular plate simply supported in fgm. theory w k = 0 k = 1 k = 2 k = 3 k = 4 k = 5 cpt 0.0737 0.1900 0.2774 0.3277 0.3554 0.3710 fpt 0.0779 0.1970 0.2866 0.3385 0.3673 0.3840 spt 0.0779 0.1960 0.284 0.3360 0.3645 0.3808 present study (rpt) 0.0779 0.1960 0.2847 0.3360 0.3645 0.3808 2 4 6 8 10 12 14 0,0 0,5 1,0 1,5 2,0 2,5 ceramic metal w h/a ceramic k=0.5 k=2 k=5 metal fig. 2. influence of thickness (h / a) for various values of "k" of fgm plate. in the figure 2, shows that the decrease is between those of the ceramic plates (al2o3) and the metal (al). it can be observed that the deflection of the metal-rich fgm plate is greater compared to the ceramic plate. this can be taken into account for the young module. -2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 -0,5 -0,4 -0,3 -0,2 -0,1 0,0 0,1 0,2 0,3 0,4 0,5 x z ceramic k=0.5 k=2 k=5 metal fig. 3. variation of the stress, through the thickness of fgm plate. merdaci et al., j. build. mater. struct. (2019) 6: 32-38 37 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 -0,5 -0,4 -0,3 -0,2 -0,1 0,0 0,1 0,2 0,3 0,4 0,5 z x z cceramic k=1 k=2 metal fig. 4. transverse shear stress across the thickness of the fgm plate. in figure 3, the stresses are tensile above the median plane and under compression below the median plane. the results demonstrate a non-linearity of the variation in the axial stress of sheet thickness for fgm plates. it is important to note that the maximum stress depends on the value of the exponent of the volume fraction "k". and n figure 4, the maximum value occurs at a point on the median plane of the plate, and its amplitude for an fgm plate is greater than for a homogeneous plate (ceramic or metal). 5. conclusion this work consists of demonstrating the theoretical plate solutions of fgm functional gradient materials under transverse loading developed using high order theory or refined theory (rpt). the numerical results obtained show that the variation of the modulus of elasticity plays an important role on the distributions of normal and tangential stresses as well as the transverse displacement of the fgm plate. the developed theories give a parabolic distribution of the transverse shear deformation and satisfy the boundary conditions and do not require a shear correction factor as in the case of (fpt). the accuracy and effectiveness of the present theory (rpt) has been demonstrated for the static bending behavior of the fgm plate. all comparative studies have shown that the arrows and stresses obtained using the new four-unknown deformation-shear theory (rpt) are almost identical to those of the other five-unknown theories (spt). the extension of the current theory is also provided for general boundary conditions and more general form plates. in conclusion, we can say that the proposed (rpt) theory is precise and simple to solve for the study of the behavior of the static bending of rectangular plates in fgm. 6. references koizumi, m. (1992). recent progress of functionally gradient materials in japan. in 16th annual conference on composites and advanced ceramic materials (vol. 13, p. 333). lü, c. f., lim, c. w., & chen, w. q. (2009). exact solutions for free vibrations of functionally graded thick plates on elastic foundations. mechanics of advanced materials and structures, 16(8), 576-584. merdaci, s. (2017). study and comparison of different plate theory. international journal of engineering research and advanced technology 3(8), 48-59. 38 merdaci et al., j. build. mater. struct. (2019) 6: 32-38 merdaci, s., belghoul, h., benyoucef, s., tounsi, a., adda bedia, e.a. (2016). étude à la flexion statique des plaques symétriques en fgm functionally graded materials. 9ème édition des journées d'etudes techniques jet'2016, hammamet, tunisie. merdaci, s., benyoucef, s., tounsi, a., adda bedia, e.a. (2015). analyse statique des plaques homogènes en matériaux à gradient variable (fgm) , 2nd international conference on aeronautical sciences i.c.a.s’02 , oran, algeria . merdaci, s., tounsi, a., houari, m. s. a., mechab, i., hebali, h., & benyoucef, s. (2011). two new refined shear displacement models for functionally graded sandwich plates. archive of applied mechanics, 81(11), 1507-1522. mostefa, a. h., merdaci, s., & mahmoudi, n. (2018). an overview of functionally graded materials «fgm». in international symposium on materials and sustainable development (pp. 267-278). springer. nguyen, t. k., sab, k., & bonnet, g. (2008). first-order shear deformation plate models for functionally graded materials. composite structures, 83(1), 25-36. praveen, g. n., & reddy, j. n. (1998). nonlinear transient thermoelastic analysis of functionally graded ceramic-metal plates. international journal of solids and structures, 35(33), 4457-4476. reddy, j. n. (1984). a refined nonlinear theory of plates with transverse shear deformation. international journal of solids and structures, 20(9-10), 881-896. reddy, j. n. (1984). a simple higher-order theory for laminated composite plates. journal of applied mechanics, 51(4), 745-752. shi, g. (2007). a new simple third-order shear deformation theory of plates. international journal of solids and structures, 44(13), 4399-4417. shimpi, r. p., & patel, h. g. (2006). a two variable refined plate theory for orthotropic plate analysis. international journal of solids and structures, 43(22-23), 6783-6799. şimşek, m. (2010). fundamental frequency analysis of functionally graded beams by using different higher-order beam theories. nuclear engineering and design, 240(4), 697-705. timoshenko, s. p., & gere, j. m. (1972). mechanics of materials. van nordstrand reinhold company. new york. woo, j., & meguid, s. a. (2001). nonlinear analysis of functionally graded plates and shallow shells. international journal of solids and structures, 38(42-43), 7409-7421. wu, c. p., & li, h. y. (2010). an rmvt-based third-order shear deformation theory of multilayered functionally graded material plates. composite structures, 92(10), 2591-2605. ying, j., lü, c. f., & lim, c. w. (2009). 3d thermoelasticity solutions for functionally graded thick plates. journal of zhejiang university-science a, 10(3), 327-336. zenkour, a. m. (2004). thermal effects on the bending response of fiber-reinforced viscoelastic composite plates using a sinusoidal shear deformation theory. acta mechanica, 171(3-4), 171-187. zhong, z., & yu, t. (2007). analytical solution of a cantilever functionally graded beam. composites science and technology, 67(3-4), 481-488. j. build. mater. struct. (2017) 4: 76-83 original article doi : 10.34118/jbms.v4i2.34 issn 2353-0057, eissn : 2600-6936 mechanical strengths of modified pet mortar composites in aggressive mgso4 medium: aci & b.s predictions kazi tani n 1,4*, benosman a.s. 1,2,3, senhadji y.3,5, taïbi h.2, mouli m.3 1 higher school of applied sciences (essa-t), bp 165, 13000 bel horizon, tlemcen, algeria. 2 faculty of exact and applied sciences, laboratory of polymer chemistry lcp, university of oran 1, oran, algeria. 3 department of civil engineering, labmat, enpo maurice audin, oran, algeria. 4,* lcge laboratory, faculty of mechanical engineering, usto-mb, oran, algeria. 5 department of civil engineering, university of mustapha stambouli, mascara, algeria. * corresponding author: kazitani_nabil@yahoo.fr abstract. composites mortars based on plastic aggregates are often considered as an innovative materials of the future because of their potential and the advantages they present. in this paper, a comparative study was carried out on the effect of magnesium sulfate mgso4 (5%) attack on the durability of composite mortars modified by recycled polyethylene terephthalate (pet). laboratory tests were accomplished on limestone sand and cement mortars where the blended portland cement was partially replaced by various volume fractions of pet plastic aggregates. mechanical properties measured on specimens were used to assess the changes in the compressive strengths of pet-mortar composites exposed to mgso4 attack at different ages, mainly the young modulus of elasticity. based on experimental compressive tests on selected specimens and there densities, the evolution of static young modulus of elasticity has been discussed in accordance to predicted models proposed by (aci-318) and (bs-8110) codes of practice. in addition, a comparative analysis has been carried out for corrosion resistance coefficients k of referenced mortar to those modified with plastic aggregates. it can be noted that, the corrosion resistance coefficients decrease as much as composite specimens are exposed to mgso4 corrosive medium. for the case of modified composites, the values of k based on predicted young modulus before and after immersion are better than the ones calculated for the unmodified mortar. therefore, aci 318 prediction model is recommended code for design and investigation works related to reparation mortars, screeds, pavements…etc. also, it can be concluded that adding pet plastic aggregates by volume to blend portland cement act to improve the corrosive resistance of this cement against mgso4 aggressive medium. key words: recycled polymer aggregates, composite mortars, mgso4 solutions, mechanical properties, sustainable materials. 1. introduction in the recent previous decades, polyethylene terephthalate (pet) is produced within large amount in industrial countries (planetoscope, html) and since waste pet is not biodegradable, then, it can remain in nature for hundreds of years and causes too many ecological problems. several research works were carried out recently by too many authors in the field of material science applied to building industries, such as (alfahdawi et al. 2016; benosman, 2013; gu and ozbakkaloglu, 2016; rahmani et al. 2013; sharma and bansal, 2016) in order to find ecologic and green ways to dispose and recycle polymer wastes. one of the main proposed technics by researchers is to introduce pet in the technology construction materials by substituting volumetric amount of cement (benosman et al. 2017a) and/or aggregates (azhdarpour et al. 2016; hannawi et al. 2010; zuccheratte et al. 2017) in concrete and mortars mix-design. mailto:kazitani_nabil@yahoo.fr kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 77 in this paper, the influence of magnesium sulfate attack on the durability of composites produced with waste polyethylene terephthalate (pet) is studied. experiments were accomplished on cement mortars and limestone sand where the blended portland cement was partially replaced by various volumetric fractions of pet particles (6%, 12% and 17%v). test solution used to provide the sulfate attack was 5% of mgso4 solution. tap water was used as the control medium. compressive strengths measured on specimens were used to assess the changes in the mechanical properties of modified mortars subjected to mgso4 attack at different ages, mainly the young modulus of elasticity. 2. raw materials 2.1. cement the cement used was a blended portland cement type cpj-cem ii/a42.5 supplied by zahana factory, located in western algeria, with 1022 kg/m3 bulk density; its compressive strength at 28 days was 42.5 mpa. the absolute density of the cement used was 3.15 g/cm3 and its specific surface area measured with the blaine method was 3532 cm2/g. its initial and final setting times were 170 and 245 min, respectively. mineralogical and chemical compositions of cement are listed in table 1. the chemical composition was obtained using an x-ray fluorescence spectrometer. table 1. the chemical and mineralogical compositions of cement (wt.%) c h e m ic a l co m p o si ti o n s sio2 20.91 al2o3 5.52 fe2o3 3.56 cao 63.50 mgo 0.64 so3 2.79 k2o 1.23 na2o 0.13 cao free 2.35 loi 1.19 m in e ra lo g ic a l co m p o si ti o n s c3s 49.39 c2s 22.97 c3a 8.61 c4af 10.83 2.2. sand the crushed natural limestone sand was obtained from the quarry of kristel, in oran, west algeria. the maximum size of sand grains was 5 mm. the absolute density and absorption coefficient of crushed sand were 2.53 g/cm3 and 0.5%, respectively. the grading of crushed sand is presented in table 2, according to standard nf p18-560 (afnor, 1990). 2.3. waste polyethylene terephthalate waste pet bottle granules (pet) used as particles were supplied by tramaplast pet bottle plant, in tlemcen, algeria. these particles were obtained by collecting the waste pet bottles and washing them; they are then crushed by granules into machines. in addition, they have an irregular shape and a rough texture surface, which enables the adherence of the particle-matrix. the bulk density of the wpet particles used was 401.4 kg/m3. 78 kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 after preliminary tests, pet particles of size lower than 1 mm were used in this study. the sieve analysis of pet particles was carried out according to standard nf p18-560 (afnor, 1990) and is presented in table 2. table 2. the sieve analysis of waste pet-particles and crushed limestone sand sieve size (mm) cumulative passing (%) pet sand 5 99.92 99.83 2.5 98.16 98.37 1.25 96.82 65.37 0.63 55.78 38.3 0.315 35.48 19.07 0.16 18.28 8.20 0.125 9.56 3.325 3. composite mixing conditions the mortar manufactured without wpet particles was first optimized on the basis of its mechanical criteria and was then used as a reference composite. the composites containing pet particles were produced in accordance with the results of the works of benosman et al. (2017b). a massic ratio of 3 between sand (s) and cement (c) was respected. four different mixtures were prepared (the control mixtures without plastic waste and three pet# mixtures including 6%, 12% and 17% waste pet particles by volume). mixture name of the different composites were: pet0 (without plastic waste), pet6, pet12 and pet17. the water to binder ratio was kept constant at 0.5. so, after pouring fresh material into the molds (en 196-1, 2005), the samples were stored in a room where hygrometry and temperature were controlled for 24 h (98% relative humidity, and 20 ± 1 °c). after removal from the molds, at 1 day of age, mortar specimens were cured in saturated lime water at 20 ± 1 °c, until the time of testing. 4. test methods of resistance to mgso4 attack the mortar specimens were cured in water saturated with lime at 20 ± 1°c for 28 days before being exposed to sulfate attack. three specimens of each mortar and composite mixes (40x40x160 mm3) were immersed in two types of solutions: fresh water (reference medium) and 5% magnesium sulfate (mgso4), figure 1. according to the standard astm c1012-04 (2004), the ph of the sulfate solution should be between 6 and 8 and the solution must be renewed each week, which requires huge amounts of magnesium sulfate. fig 1. immersion of the specimens in the aggressive solution for this, mehta’s method (1975) and that of siad et al. (2013) were adopted; they all recommend the control of the ph within a range of 6.0–8.0 by adding a suitable amount of sulfuric acid solution (0.1n h2so4), figure 2. the correction is performed daily during the first weeks of kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 79 immersion, and then becomes weekly, for the rest of the test. in addition, the aggressive solutions were totally renewed each 12 weeks. after immersion in magnesium sulfate solution (mgso4) for the required period of time, astm c1012-04 (2004), the specimens were tested for residual mechanical properties. the young modulus loss (yml%) is calculated as follows: 100(%)    cr cscr e ee yml (1) where ecr is the young modulus of the specimens before immersion (mpa) and ecs is the average young modulus of the specimens after immersion in magnesium sulfate solutions for the required period of time (180 days). fig 2. correction of the sulfate solution by adding small quantities of 0.1n h2so4, up to a ph equal to 6-8. 5. results and discussion 5.1. prediction models of mechanical properties the static modulus of elasticity e (young modulus) represents the one of the most important mechanical characteristics of construction materials (concrete, reinforced concrete, mortars, composites …etc). this intrinsic property is considering as the basic parameter for the computing strain-stresses in construction structures. various countries have been established their design codes based on this empirical relationship between static modulus of elasticity e, and compressive strength of plain concrete at 28 days of curing. the aci code (aci-318, 2005) defines the relationship between elastic modulus of concrete and compressive strength as: ec = w1.5 0.0043 f 0.5 (2) the british code of practice (bs-8110, 1997) recommends the following expression for static modulus of elasticity with cube compressive strength of concrete as: ec = w² 0.0017 fc0.33 (3) where, ec represents the static modulus of elasticity at 28 days in mpa fc : compressive strength at 28 days in mpa w : air dry density of mortar based on experimental compressive tests on pet-mortar composite specimens (benosman et al. 2013), and there densities, graphs in (figures 3, 4) bellow show the evolution of young modulus evaluated by empirical relationships in accordance to (aci-318) and (bs-8110) codes. the results of the young modulus loss using the specimens immersed in 5% mgso4 solutions (figure 5) showed that there are variations in time and group. however, a decrease in young modulus values of all specimens was observed when young modulus of elasticity is computed 80 kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 via aci-318 model. it was expected that the mechanical properties loss (yml%) values of modified mortars with pet plastic particles would be lower than those of unmodified mortar pet0, by 16.84%, 21.35% and 18.40% for pet6, pet12 and pet17, respectively for the case where the prediction model is bs-8110 and respectively by 12.00%, 18.30% and 13.40% when young modulus of elasticity is computed via aci-318 model. it can therefore be concluded that modified mortars by pet plastic particles are resistant to the magnesium sulfate aggressive exposure conditions often encountered in the field. fig 3. evolution of young modulus with volumetric pet rate and composite mortar ages via aci-318 code before and after mgso4 attacks fig 4. evolution of young modulus with volumetric pet rate and composite mortar ages via bs-8110 code before and after mgso4 attacks before immersion after immersion before immersion after immersion 28 56 90 180 28 56 90 180 kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 81 fig 5. young modulus loss (yml%) with volumetric pet rate and prediction codes (bs-8110 & aci-318) before and after mgso4 immersion 5.2. corrosion magnesium sulfate resistance furthermore, to compare, effectively, the corrosion resistance coefficients k of unmodified mortar (eq. 4) to those modified with pet particles, as it was used by benosman et al. (2017b) and jiang et al. (2004): k = eci / ecs (4) where eci is the young modulus of composite mortars immersed in corrosive magnesium sulfate solutions, ecs the young modulus of the normally cured composite mortars. the corrosion resistance coefficients of the specimens with and without pet plastic are given in table 3. it can be seen from table 3 that, for the composite immersed in a corrosive mgso4 solution, the corrosion resistance coefficients decrease with the increase of the immersion period. the corrosion sulfate resistance k based on young modulus before and after immersion of pet-mortar composites is better than that of the control mortar (pet0). table 3. the corrosion resistance coefficients of pet-mortar composites in 5% mgso4 mgso4 attacks k (bs.8110) k (aci.318) 90 days 180 days 90 days 180 days pet0 0.832 0.787 0.858 0.820 pet6 0.897 0.832 0.935 0.880 pet12 0.836 0.786 0.859 0.817 pet17 0.864 0.816 0.910 0.866 for all studied cases, corrosion resistance coefficients k computed via aci 318 are slightly higher than the ones evaluated by bs.8118 code of practice. therefore, in order to obtain a safe design using pet-modified mortar, aci 318 is the recommended code for design and investigation issues. also, it can be concluded that adding pet by volume fractions to blended portland cement renders this cement more resistant to the magnesium sulfate aggressive medium. (miletic, 1999) reported that the resistance of cement to sulfate aggression is also related to its content in c3a. 0% 5% 10% 15% 20% 25% bs-8110 aci-318 y o u n g m o d u lu s l o ss (y m l% ) young modulus prediction codes pet0 pet6 pet12 pet17 82 kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 consequently, using pet as cement substitutes reduces the energy consumption, contributes to save natural environment by reducing co2 emissions and is used to repair various reinforced concrete structures in magnesium sulfatic aggressive mediums. finally, the obtained results are in accordance with the ones reported by alqahtani et al. (2017) which stated that recovering plastic waste would reduce the co2 emissions by 3.8 million tons. the advantages of durability properties of modified mortar exposed to mgso4 attacks indicate longer life of the repaired structures by using this type of green composite repair materials. 6. conclusions the main conclusions based on results plotted above, can be drawn as follows: pet-mortar composites present a better behavior against aggressive medium such as magnesium sulfatic (mgso4) and it reduces significantly the consumption energy related to co2 emission. in mgso4 corrosive medium, unmodified mortar (pet0) and substitution volumetric rate of pet act to decrease the mechanical properties of pet-mortar composites, mainly, the static modulus of elasticity (computed by aci-318 and bs-8110 codes). in addition, prediction model proposed by aci-318 gives always the lowest values of elastic young modulus which can be recommended for structural design issues. the loss in static young modulus of elasticity (yml%) of modified mortars are lower than the ones of unmodified mortars. the optimal minimal values of (yml%) are given by aci-318 code of practice, mainly, for the case of pet-modified mortars within volumetric rate of 6%, 17%. the corrosion resistance coefficients k decrease with exposure time to mgso4 aggressive medium. acknowledgements the authors acknowledge financial support from the ministry of higher education and scientific research of algeria, under the grants cnepru b00l01un310120130068. 7. references aci 318. (2005). building code requirements for structural concrete (aci 318-05) and commentary (aci 318r-05), aci committee 318, american concrete institute, farmington hills, mi. afnor, (1990). granulats. analyse granulométrique par tamisage.. nfp 18-560, association française de normalisation. alfahdawi, i.h., osman, s.a., hamid, r., al-hadithi, a.i. (2016). utilizing waste plastic polypropylene and polyethylene terephthalate as alternative aggregates to produce lightweight concrete: a review, journal of engineering science and technology, 11(8), 1165-1173. alqahtani, f.k., iqbal khan, m., ghataora, g., & dirar, s. (2017). production of recycled plastic aggregates and its utilization in concrete, journal of materials in civil engineering, asce, 04016248, 29(4), 1. astm c1012-04. (2004). standard test method for length change of hydraulic-cement mortars exposed to a sulfate solution, c1012-04, annual book of astm standards. azhdarpour, a.m., nikoudel, m., & taheri, m., (2016). the effect of using polyethylene terephthalate particles on physical and strength-related properties of concrete; a laboratory evaluation, construction and building materials, 109, 55–62. benosman, a.s. (2013). performances, propriétés thermiques et durabilité des composites mortierpolytéréphtalate d’éthylène pet, dossier d’habilitation universitaire, université abou-bekr belkaid, tlemcen. benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2013). la durabilité des matériaux composites pet-mortier dans un environnements agressifs, in the kazi tani et al., j. build. mater. struct. (2017) 4: 76-83 83 proceedings of cimdd’2013, isbn : 978-9931-9090-1-9, université boumerdès, algérie, 06-09 mai 2013, 330. benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2017a). the chemical, mechanical and thermal properties of pet-mortar composites containing waste pet, environmental engineering and management journal, 16 (7), 1489-1505. benosman, a.s., taïbi, h., senhadji, y., mouli, m., belbachir, m, bahlouli, m.i. (2017b). plastic waste particles in mortar composites: sulfate resistance and thermal coefficients, progress in rubber plastics and recycling technology journal, 33(3), 171-202. bs 8110. (1997). structural use of concrete. code of practice for design and construction. british standards institution. en 196-1. (2005). methods of testing cement part 1: determination of strength, european committee for standardization, cen. gu, l., ozbakkaloglu, t. (2016). use of recycled plastics in concrete: a critical review, waste management, 51, 19-42. hannawi, k., prince, w. & kamali-bernard, s. (2010). effect of thermoplastic aggregates incorporation on physical, mechanical and transfer behaviour of cementitious materials, waste biomass valorization, 1, 251-259. http://www.planetoscope.com/petrole/989-production-mondiale-de-plastique.html jiang, l., liu, z., & ye, y. (2004). durability of concrete incorporating large volumes of low-quality fly ash, cement and concrete research, 34, 1467–1469. mehta, pk. (1975). evaluation of sulfate resisting cements by a new test method, journal of american concrete institute, 72(40), p 573–575. miletić, s., ilić, m., otović, s., folić, r., ivanov, y. (1999). phase composition changes due to ammoniumsulphate: attack on portland and portland fly ash cements, construction and building materials, 13(3), 117-127. rahmani, e., dehestani, m., beygi, m.h.a., allahyari, h., & nikbin, i.m. (2013). on the mechanical properties of concrete containing waste pet particles, construction and building materials, 47, 1302 -1308. sharma, r. & bansal p.p. (2016). use of different forms of waste plastic in concrete – a review, journal of cleaner production, 112, 473-482. siad, h., kamali-bernard, s., mesbah, h.a., escadeillas, g., mouli, m., & khelafi, h. (2013). characterization of the degradation of self-compacting concretes in sodium sulfate environment: influence of different mineral admixtures, construction and building materials, 47, 1188–1200. zuccheratte, a.c.v., freire, c.b., & lameiras, f.s. (2017). synthetic gravel for concrete obtained from sandy iron ore tailing and recycled polyethyltherephtalate, construction and building materials, 151, 859-865. http://www.planetoscope.com/petrole/989-production-mondiale-de-plastique.html j. build. mater. struct. (2018) 5: 212-217 original article doi : 10.34118/jbms.v5i2.59 issn 2353-0057, eissn : 2600-6936 sustainable utilization of plastic waste in concrete mixes a review kore s. d.* assistant professor, department of civil engineering, jspm narhe technical campus, pune india * corresponding author: sudarshankore123@gmail.com received: 24-05-2018 revised: 20-10-2018 accepted: 21-10-2018 abstract: plastic waste creates serious environmental problems, mainly owing to the inconsistency of the wastes streams. due to rapid population growth and its consistent necessity the use of plastic is increasing regularly. this creates a large, the quantity of garbage every day which is unhealthy and pollutes the environment. in present scenario solid waste management is a challenge in our country. this paper represents a collection of ideas of various studies done on the use of plastic waste materials in concrete mixes. conclusions are drawn based upon the respective results of all the mentioned research papers. key words: plastic waste, concrete, sustainability. 1. introduction one of the main goals of sustainable solid waste management is to maximize the ability of its recycling and reusing. the most common waste materials are metal and plastic which are available in enormous quantities in the world. the modern lifestyle, alongside the advancement of technology has led to an increase in the amount and type of waste being generated, leading to a waste disposal crisis (jaivignesh and sofi, 2017). the productive use of waste material represents a means of alleviating some of the problems of solid waste management (davis and cornwell, 1998) . therefore the use of this waste is very important from environment and sustainability aspects. this lead to saving of natural resources and resulting in decrease in environmental pollution. the wastes generated during various operations and their byproduct is one of major problem arising in the world today. plastic waste is one of the major contributing agent for polluting the environment. central pollution control board has estimated the generation of 15,342 tons per day of plastic waste in india. out of which 9205 tons were reported to be recycled and leaving 6137 tons uncollected (unep, 2009). in landfill or in environment plastic bags take up to 1000 years to degrade. the threat due to non-biodegradable materials like waste plastics may contaminate the soil and ground water. disposal of large quantity of plastic bag may cause pollution of land, water bodies and air. therefore to reduce these impacts on the environment these materials can be suitably used in other industries (hassani et al., 2005). concrete is one of the commonly and widely used construction material in the world (sudarshan and vyas, 2017). to reduce the burden on environment concrete industry conduct a lot of experiments to utilize these waste (singh et al., 2016). reuse of solid waste as partial replacement of aggregate in construction activities results in reducing the demand for extraction of natural raw materials as well as saving landfill space. thus utilization of plastic waste in concrete mixes reduces the demand of natural resources and as a result leads to sustainable development. mailto:sudarshankore123@gmail.com kore, j. build. mater. struct. (2018) 5: 212-217 213 2. state of art a study carried out by kou et al. (2009) revealed that: the workability, the compressive strength, and the tensile splitting strength of lightweight aggregate concretes that are prepared with recycled plastic waste were reduced. ghernouti et al. (2009) conducted a study on concrete mixes with the utilization of plastic waste as replacement of fine aggregate in different percentages 10%, 20%, 30% and 40%. it was reported that, the workability of concrete increased with increase in replacement of plastic waste this was due to plastic waste does not absorb water and excess water is available for lubrication. also, the bulk density decreases with increase of plastic bags waste. in case of flexural and compressive strength, appreciable reductions were observed. plastic waste increases the volume of voids in concrete which on other hand reduce the compactness of concrete simultaneously speed of sound in concrete is also decreased. strength reduction in concrete mix was prime concern and however they recommend 10% to 20% replacement of fine aggregate with plastic aggregate. ismail and al-hashmi (2010) studied the effect of replacement of fine aggregate by 5% plastic waste and 30%, 40%, 50 % iron fillings on mechanical properties of concrete mixes. in their study they investigated that, at all replacement levels decline in the slump was reported. this fact was attributed to heterogeneous distribution of waste material as well as the sharp and angular grain shapes of the waste particles compared to that of sand. the fresh and hardened density of concrete mixes prepared with iron filling and plastic waste showed increasing trend due to high density of waste iron. from the results of compressive strength it was reported that, the replacement of fine aggregate by iron filing and plastic waste improves the compressive strength by approximately 6%, 10% and 22% as compared to that of control mixes. this increase in strength was caused by the addition of polymeric material which leads to formation of polymer film during hydration resulting in co-matrix during which polymer is amalgamated with cement hydrate (van gemert et al., 2005). raghatate (2012) studied the feasibility of incorporation of plastic bags in concrete mixes in different percentages 0.2%, 0.4%, 0.6%, 0.8% and 1.0%. they reported that, incorporation of plastic bags in concrete reduces the compressive strength and tensile strength. but the reduction in strength was within 10% and it is acceptable as per bis 456-2000. they finally concluded that, more and detailed study is required to understand the behavior of concrete mix with the addition of plastic bags. other study conducted by mathew et al. (2013) reported the feasibility of utilization of plastic waste as a replacement for natural coarse aggregate in concrete mixes. the plastic coarse aggregate was obtained by crushing the boulder of plastic into the crusher. the concrete mixes was prepared with 20% to 100% replacement level with an increment of 20%. they reported that, the replacement of natural coarse aggregate by plastic aggregate enhances the compressive strength of concrete by approximately 10% at a replacement of 20% as compared to that of control concrete. as the percentage of replacement increased the concrete mixes showed loss in compressive strength. the decrease in strength was due to less specific gravity and crushing value as compared to that of natural aggregates. khilesh (2014) studied the impact of use of plastic waste and steel fiber addition on the properties of concrete. the fine aggregate was replaced by plastic waste at 0.2%, 0.4%, 0.6%, 0.8% and 1% by weight of cement and 0.1%, 0.2%, 0.3% 0.4% and 0.5% steel fibers were incorporated in concrete mixes. they observed that, replacement of fine aggregate by plastic waste in different percentages showed an increase in compressive strength whereas marginal reduction in slump as compared to that of control mix. on the other hand the mixture proportion of steel fiber and plastic waste also showed the same trend in compressive strength test. he summed up that, it was possible to use this plastic waste and steel fiber in concrete to produce a sustainable product. subramani and pugal (2015) reported that, the use of plastic waste as a replacement for conventional coarse aggregate improves the physical and mechanical properties of concrete 214 kore, j. build. mater. struct. (2018) 5: 212-217 mixes. it was reported that, the compressive strength, flexural strength and split tensile strength of concrete was increased by 8%, 5% and 3% as compared to that of control concrete at 15% replacement level. as the percentage of replacement increased beyond 15% all the properties of concrete showed downward trend. this fact was due to excess presence of water in the concrete mix because plastic waste has very low water absorption as compared to that of conventional coarse aggregate. chen et al. (2015) investigated the influence of plastic waste as a fine aggregate on concrete mixes. fine aggregate was replaced by plastic waste in different percentages 0%, 10%, 20%, 30%, 50% and 100%. they reported that, at 10% replacement level only 15% loss in strength was observed where as in other replacement level a notable reduction was observed as compared to that of control concrete mix. where as in case of tensile test, the concrete mixes prepared with 10%, 20% and 30% replacement level showed significant increase in the tensile strength of concrete mixes as compared to that of control mix. this increase in tensile strength was attributed due to addition of high-density polyethylene (hdpe) plastic which cause fundamental changes in the concrete. plastic is a byproduct of the shredding and pulverizing process which provides internal shear and tensile reinforcement. they also stated that, behavior of plastic is alike to that of the synthetic fiber which restricts the propagation of cracks and fractures in the concrete. they also reported that, the heat absorption and heat transfer of concrete modified with 10%, 20% and 30% replacement showed a significant decrease in heat absorption, and a minor decrease in heat transfer through the test slab. ahmed & raju (2015) conducted a study on the use of plastic waste as replacement for conventional coarse aggregate (at 10%) in concrete mixes with different water-cement ratios. they reported that, the workability and the dry density of concrete mixes prepared with plastic waste aggregate were reduced marginally. harini and ramana (2015) studied the influence of replacement of plastic waste and silica fume as fine aggregate and cement respectively in concrete mixes. the plastic waste was replaced in the percentage 5%, 6%, 8%, 10%, 15%, 20% by volume and silica fume 5%, 10%, 15% by weight in concrete. they reported that, the degree of workability was high in all the replacement levels. it was also stated that, in all the replacement levels of plastic waste as fine aggregate showed marginal reduction approximately 10% in compressive strength as compared to that of control mix. in case of silica fume replacement the compressive strength of concrete mixes increased by 13%, 20% and 23% at 5%, 10% and 15% respectively. tensile strength of concrete reduced marginally at 8% to 20% replacement and increased marginally at 5% and 6% replacement levels as compared to that of control mix. in a study conducted by aravind and john (2015) used crumb rubber and plastic waste as replacement for fine aggregate in concrete mixes with a percentage of 5%, 10% and 15%. they reported that, replacement of fine aggregate by crumb rubber and plastic waste in concrete reduces the workability of concrete due to variation in water absorption of the aggregates used. they also reported that, the mechanical properties of concrete such as compressive strength, split tensile strength and flexural strength was maximum at 5% replacement levels as compared to that of control concrete mix. at 10% and 15% replacement level the concrete prepared with plastic waste and crumb rubber as fine aggregate showed downward trend for all the values of strength as compared to that of control concrete mix. a combination of 5% crumb rubber and 10% plastic waste as fine aggregate showed lowest rate of water absorption as compared to all other concrete mixes. finely they concluded that, the optimum percentage for replacement of crumb rubber and plastic waste as fine aggregate in concrete was 10% for sustainability point of view. polyethylene terephthalate (pet) is most and common widely used plastics for soft-drink and packaging of food and other consumer goods (islam et al., 2016). it is estimated that, words annual consumption of pet drink is approximately 10 million tons and this number increase kore, j. build. mater. struct. (2018) 5: 212-217 215 every year by 15% as reported by frigione (2010). in particular recycled polyethylene terephthalate (pet), a packing material byproduct, was used as binder in the production of highperformance composite known as polymer concrete (marzouk et al. 2007). past researchers showed that, it is possible to use the pet ot plastic waste as construction material in concrete mixes. guendouz et al. (2016) investigated the impact of waste plastic [(polyethylene terephthalate (pet) and low density polyethylene (ldpe)] as a fibers and fine aggregates (powder) in sand concrete. the sand was replaced by plastic aggregates by volume fractions of sand (10%, 20%, 30% and 40%) and plastic fibers (0.5%, 1%, 1.5%, 2%) were introduced by volume in sand concrete mixes. it was reported that, the use of plastic waste as fine aggregate in concrete increases the workability by about 40%. this is probably due to the presence of more free water in the mixes containing plastic, on the other hand incorporation of plastic fibers in concrete reduces the workability. also the reduction in bulk density and air content was reported. they also reported that, compressive and flexural strengths of concrete prepared with plastic waste as fine aggregate increased by approximately 30% with 20% replacement and in case of concrete with plastic fibers it increased by 25% at 1.5% content. the authors have concluded that, the optimum percentage for replacement was 20% and 1.5% for plastic powder (ldpp) and plastic fibers respectively. mahesh et al. (2016) studied the behavior of concrete with the utilization of plastic waste as replacement for fine aggregate in concrete with 2%, 4% and 6% pulverized/non pulverized polyethylene material. they reported that, at all replacement levels the concrete prepare with plastic waste as fine aggregate showed marginal reduction (less than 10%) in compressive and split tensile strength as compared to that of control concrete. authors have concluded that, the use of plastic waste as a replacement for fine aggregate in concrete did not have any adverse impact on mechanical properties of concrete. jibrael and peter (2016) studied the mechanical properties of concrete modified by recycled plastic waste as a partial replacement of fine aggregate 1%, 3% and 5% by weight. two types of plastic waste were used, waste plastic bottle and bags for the production of fine aggregate. they observed that, the compressive strength, indirect tensile strength and modulus of rupture decreased when the replacement levels increased. the marginal reduction in all the values of strength was reported at a replacement level of 1% as compared to that of control mix. at 3% and 5% replacement level, the compressive strength, tensile strength and modulus of rupture of concrete prepared with plastic waste as fine aggregate showed average reduction of 16%, 27% and 27% as compared to that of control concrete. gaur et al., (2017) studied the impact of plastic waste as a replacement for fine aggregate at 5%, 10%, 15%, 25% by weight in concrete with incorporation of steel fibers 1% by volume. due to utilization of steel fibers the reduction in workability was observed. it was stated that, the use of plastic waste as fine aggregate results in reduction in compressive strength at all replacement levels as compared to control concrete mix. finally they stated that at 5% replacement levels the compressive strength was nearly close to that of control mix and this proportion was suggested as an optimum proportion for the replacement in concrete mixes. mechanical properties of concrete prepared with plastic waste as a replacement of fine and coarse aggregate at 10%, 15%, 20% and 15%, 20%, 25% was studied by jaivignesh and sofi (2017). in their study they reported that, the compressive strength of concrete was reduced by 9% at 10% replacement level where as at 15% and 20% replacement levels the compressive strength was reduced by 13 % and 17% respectively as compared to that of control concrete mix. a similar trend was observed in split tensile strength and flexural strength test. they concluded that, this reduction in strength is mainly due to poor bond strength between cement and plastic aggregate. this fact was also reported by various researchers in the past. ismail & al-hashmi (2008) used the plastic waste as partial replacement 10%, 15% and 20% for fine aggregate in concrete mixes and studied the mechanical properties of concrete. it was 216 kore, j. build. mater. struct. (2018) 5: 212-217 reported that, the slump values of concrete modified with plastic waste as fine aggregate were reduced by 68%, 88% and 95% at 10%, 15% and 20% replacement levels as compared to that of control mix. this reduction was due to irregular size and shape of aggregate which resulted in less fluidity. the fresh and dry density of concrete mixes prepared with plastic waste at above said replacement levels showed downward trend due to low density of plastic waste. the concrete prepared with plastic waste as replacement for fine aggregate showed reduction in compressive and flexural strength because of decrease in adhesive strength between the surface of the waste plastic and the cement paste. they also stated that, this reduction was due to hydrophobic property of plastic material which restricts the water required for the hydration during the curing period. from the load-deflection curves they reported that, the incorporation of plastic waste restrict the propagation of micro-cracks. they concluded that, all the values of concrete prepared with plastic waste as fine aggregate are higher that required for structural concrete b.s.1881, part 7. 3. conclusion based on the above studies on use of plastic waste it can be concluded that:  the utilization of 10% plastic waste as fine aggregate replacement gives satisfactory performance in concrete, which results in reduction cost of natural resources.  the use of plastic waste as replacement for fine aggregate maintains the mechanical properties of concrete.  the aggregate produced form plastic waste showed an improvement in the workability of concrete mixes where as some of the researchers reported the contradictory results. various researchers proposed economy in concrete production can be achieved by utilization of this plastic waste as fine aggregate. the studies reported by researchers, the various types of plastic waste were crushed to obtain desired gradation of fine aggregate and used in concrete mixes. when these plastic waste aggregates are used in concrete mixes as replacement for conventional fine aggregate, showed no adverse effects on quality of concrete but in turn enhanced to some extent the some mechanical performance of concrete. from the above studies, utilization of plastic waste achieved economy in concrete production with conserving natural resources as well as reduction in environmental hazards reported due to uncontrolled dumping of plastic waste. 4. references ahmed, m.m. & raju, s.s., (2015). use of waste plastic in the production of light weight concrete. international journal & magazine of engineering, technology, management and research, 2(april) 365–369. aravind, s. & john, e., (2015). replacement of fine aggregate by crumb rubber and plastic fines. international journal of engineering research & technology (ijert), 4(11),305–310. chen, c.c., jaffe, n., koppitz, m., weimer, w., polocoser a., (2015). concrete mixture with plastic as fine aggregate. international journal of advances in mechanical and civil engineering, 2(4), 49–53. davis, m.l., cornwell, d.a. (1998). introduction to environmental engineering third. wcb, ed., mcgrawhill. frigione, m. (2010). recycling of pet bottles as fine aggregate in concrete. waste management, 30(6), 1101-1106. gaur, k., arya, jyotsana, a.k. & singh, n.k. (2017). use of plastic as partial replacement of fine aggregate in fibre reinforced concrete. iosr journal of mechanical and civil engineering, 14(3), 71–74. ghernouti, y., rabehi, b., safi, b. & chaid, r. (2009). use of recycled plastic bag waste in the concrete journal of international scientific publications: materials, methods and technologies, 8, 480–487. kore, j. build. mater. struct. (2018) 5: 212-217 217 guendouz, m., debieb, f., boukendakdji, o., kadri, e. h., bentchikou, m., & soualhi, h. (2016). use of plastic waste in sand concrete. j. mater. environ. sci, 7(2), 382-389. harini, b. & ramana, k. v. (2015). use of recycled plastic waste as partial replacement for fine aggregate in concrete. international journal of innovative research in science, engineering and technology, 4(9), 8596–8603. hassani, a., ganjidoust, h., maghanaki, a.a. (2005). use of plastic waste (poly-ethylene terephthalate) in asphalt concrete mixture as aggregate replacement. waste management & research, 23, 322–327. islam, m. j., meherier, m. s., & islam, a. r. (2016). effects of waste pet as coarse aggregate on the fresh and harden properties of concrete. construction and building materials, 125, 946-951. ismail, z. z., & al-hashmi, e. a. (2010). validation of using mixed iron and plastic wastes in concrete. in second international conference on sustainable construction materials and technologies. ancona (pp. 393-403). ismail, z.z. & al-hashmi, e.a. (2008). use of waste plastic in concrete mixture as aggregate replacement. waste management, 28(11), 2041–2047. jaivignesh, b., & sofi, a. (2017). study on mechanical properties of concrete using plastic waste as an aggregate. in iop conference series: earth and environmental science (vol. 80, no. 1, p. 012016). iop publishing.. jibrael, m.a. & peter, f. (2016). strength and behavior of concrete contains waste plastic. journal of ecosystem & ecography, 6(2), 2–5. khilesh s. (2014). study of strength property of concrete using waste plastics and steel fiber. the international journal of engineering and science, 3(5), 9–11. kou, s. c., lee, g., poon, c. s., & lai, w. l. (2009). properties of lightweight aggregate concrete prepared with pvc granules derived from scraped pvc pipes. waste management, 29(2), 621-628. mahesh, m., rao, b.v.n. & sri, c.h.s. (2016). re-use of polyethylene plastic waste in concrete. international journal of engineering development and research, 4(4), 693–702. marzouk, o.y., dheilly, r.m. & queneudec, m., (2007). valorization of post-consumer waste plastic in cementitious concrete composites. waste management, 27(2), 310–318. mathew, p., varghese, s., paul, t., & varghese, e. (2013). recycled plastics as coarse aggregate for structural concrete. international journal of innovative research in science, engineering and technology, 2(3), 687-690. raghatate atul, m. (2012). use of plastic in a concrete to improve its properties. international journal of advanced engineering research and studies, 1(3), 109-111. singh, s., nagar, r., agrawal, v., rana, a., & tiwari, a. (2016). sustainable utilization of granite cutting waste in high strength concrete. journal of cleaner production, 116, 223-235. subramani, t., & pugal, v. k. (2015). experimental study on plastic waste as a coarse aggregate for structural concrete. international journal of application or innovation in engineering & management (ijaiem), 4(5), 144-152. sudarshan, d. k., & vyas, a. k. (2017). impact of fire on mechanical properties of concrete containing marble waste. journal of king saud university-engineering sciences. available at: http://dx.doi.org/10.1016/j.jksues.2017.03.007. unep (2009). converting waste plastics into a resource, united nations environment program industry and economics, osaka/shi. van gemert, d., czarnecki, l., maultzsch, m., schorn, h., beeldens, a., łukowski, p., & knapen, e. (2005). cement concrete and concrete–polymer composites: two merging worlds: a report from 11th icpic congress in berlin, 2004. cement and concrete composites, 27(9-10), 926-933. http://dx.doi.org/10.1016/j.jksues.2017.03.007 j. build. mater. struct. (2018) 5: 32-42 original article doi : 10.34118/jbms.v5i1.42 issn 2353-0057, eissn : 2600-6936 comparative study and optimization of the mechanical behavior of sandwich beams loaded in three point bending bourouis f *, mili f abstract: the sandwich material presents a certain interest in term of rigidity and specific resistance for the aeronautic structure design. the study of this material meets always the choice problem of their constituents (coating and core) in order to find the optimal mechanical characteristic. the aim of this work is to do a comparative study of the mechanical behavior of the sandwich beams loaded in three point bending. the structures considered consist of two skins of composite material with unidirectional fibers of six plies glass/epoxy, carbon/epoxy or kevlar/epoxy of stacking sequence [0°/90°]3s and [45°/45°]3s and the core is in alporas , corecel, pvc, or polyurethane foams. the different results obtained from the matlab code showed that the correct choice of the material of the coatings and of the core that improves the mechanical behavior of the sandwich beam. in order to increase the performance of sandwich beams, in three points bending, an optimization program based on the principles of genetic algorithms has been developed to maximize the tensile strength of face yielding and face wrinkling failure modes. the equations used to evaluate the individuals in population results from the classical laminate theory with transverse shear stresses and discrete variables. operators of genetic algorithms (selection, crossover and mutation) are applied to the children of a hundred generations. to achieve optimal solutions, the result appeared effective despite all the non-deterministic nature of genetic algorithms. but, to achieve maximum effectiveness, it’s important to choose smartly the parameters of genetic algorithms depending on the nature of the problem studied and the mechanical characteristics of the function to be optimized. key words: sandwich beam; three point bending; face wrinkling; face yielding; genetic algorithm. 1. introduction the importance of studying the bending behavior of beams is related to the use of beams as basic elements of structures, as well as to the mechanical characterization of laminates and sandwichs using test specimens in the form of beams (berthelot, 1996). a number of researchers have studied the mechanical behavior and optimization of sandwich structures in flexure. the static and fatigue behavior of acuum-assisted resin transfer molded sandwich panels has been experimentally investigated under flexural loading by jin and thomas (2003). two core materials, d-100 balsa wood and h 250 pvc foam, were used to study the effect of core material on static failure in 3-point and 4-point bending. a good similarity was seen between the static and fatigue failure modes for both short span and long span specimens. the comparison of sandwich was described by craig and norman (2004). a systematic procedure is presented to compare the relative performance of sandwich beams with various combinations of materials. the geometry of sandwich beams is optimized to minimize the mass for a required load bearing capacity in three-point bending. compression face wrinkling failures of sandwich columns under compression beams in three and four-point bending and cantilever beams under loading were investigated by gdoutos et al. (2003) the failure by wrinkling is prevalent in the case of low through-the thickness stiffness and long beam spans. in other cases, other failure modes including shear core failure, compressive facing failure, face sheet debonding or indentation university of mentouri brothers constantine 1, faculty of engineering science, laboratory of mechanics chaab ersas 25000 constantine, algeria. * corresponding author: famo006@yahoo.fr, mifauniversite@gmail.com received: 08-02-2018 revised: 24-03-2018 accepted: 08-04-2018 mailto:famo006@yahoo.fr mailto:mifauniversite@gmail.com bourouis and mili, j. build. mater. struct. (2018)5: 32-42 33 failure may occur. tahani et al. (2005) applied genetic algorithm (ga) for simultaneous costs minimization and frequency maximization. the proposed model is applied to a carbon/epoxy, glass/epoxy laminate and results are obtained for various aspect ratios and number of layers. many researchers have proposed modifications to the classical ga structure to take advantage of composite laminate characteristics and minimize the computational cost (hamidreza et al., 2012). the present paper reports on the static behavior and failure modes of sandwich beams under flexure. the structures considered consist of two skins of composite material with unidirectional fibers of six plies glass/epoxy, graphite/epoxy or kevlar/epoxy and the core is in alporas, corecel , pvc, or polyurethane foams. the objective of our work is to do an optimization study of fracture and damage of sandwich beams with composite laminated coating oriented at [+45°/-45°]3s and [0°/90°]3s , the optimal design of sandwich beams loaded in three point bending is treated by using algorithm genetic. two failure modes were studied face wrinkling and face yielding. 2. bending of sandwich beams the purpose of this section is to establish the equation for the mechanical behavior and the failure modes of sandwich beams loaded in three point bending. consider a sandwich beam loaded in three-point bending as sketched in (figure 1). let l be the beam length between the supports, b the width of the beam, h, the core thickness, and h1= h2 the face thickness. the beam is subject to a distributed load q. the load is given by equation (1): ⁄ (1) fig1. schematization of a sandwich beam loaded in three-point bending the mechanical characteristics face sheet and core materials are listed in the tables 1 and 2 (berthelot, 1996; ashby, 2000; zinker, 1995). table 1. properties of face laminate mechanical characteristics glass e/epoxy carbon hr/epoxy kevlar 49/epoxy vf 0.6 0.6 0.6 el (gpa ) 46 159 84 et (gpa ) 10 14.3 5.6 glt (gpa) 4.6 4.8 2.1 νlt 0.31 0.32 0.34 vf: fiber volume fraction, el: longitudinal young’s modulus. et: transverse young’s modulus, glt: longitudinal shear modulus. νlt :poisson ratio. 34 bourouis and mili, j. build. mater. struct. (2018) 5: 32-42 table 2. properties of core materials foams density (kg/m3) g13 (mpa) alporas 0.09 1.01 polyurethane 46 84 corecell a300 10 5.6 pvc h45 4.6 2.1 pvc h60 0.31 0.34 pvc h100 70 35 g13 (mpa): longitudinal shear modulus. 2.1. mechanical behavior of sandwich beams in three-point bending the equations of moments and transverse shear resultants are then given by: [ ] [ ] [ ] (2) and [ ] [ ] [ ] (3) the strains are then given: (4) (5) the symmetry of the problem loads permits to consider only half of beam. in the case of a three point bending the deflection including the transverse shear deformation is given by the equation: [ ( ) ] (6) the effective bending modulus of the beam: (7) the shear coefficient s defined by: ( ) (8) where given by: ( ) (9) (10) the stiffness constants are expressed as: ( ) (11) bourouis and mili, j. build. mater. struct. (2018)5: 32-42 35 we have: ∑ ( ) (12) and the coefficient are expressed as: (13) with: (14) and (15) : the transverse stiffness constants. ( ) + ( ) ( ) ( ) + ( ) (16) we consider the sandwich beam with two identical skins with orthotropy directions parallel to the directions x and y. the in plane stresses in layer k of the upper or lower skins are given by relations: ( ) (17) 2.2 failure modes of sandwich beams in flexure sandwich beams may fail by different competing mechanisms, such as face yielding; face wrinkling, core shear and indentation, depending on their geometries and material properties. the face yielding and face wrinkling failure modes together with the corresponding simplistic failure criteria are summarized below: face yielding fracture occurs when the normal stress in the face equals or exceeds the (yield) strength of the face material, in tension, such that: (18) fig 2. face yielding failure mode face wrinkling due to compression occurs when the normal stress in the face equals or exceeds the (yield) strength of the face material, in compression, such that: (19) 36 bourouis and mili, j. build. mater. struct. (2018) 5: 32-42 fig 3. face wrinkling failure mode the stresses in the face were calculated using maximum stress criterion and the simple beam theory, including transverse shear effect. 3. optimization process the maximum load of the sandwich beam in face wrinkling failure mode is equal to: ( ) (20) and the maximum load of the sandwich beam in face yielding failure mode is equal to: ( ) (21) the problem is formulated as: face wrinkling failure mode: face yielding failure mode: the optimization problem was solved using the algorithm genetic. the program can operate on many subpopulations ; number of subpopulation 5, number of chromosomes 20, number of genes 6, probability of mutation 0.2, probability of crossover 1. the selection is made by the rank method. the maximum number of generations is fixed to 100 and to seek the performance f(x) of the evolved individuals in this period. fig 4. optimization procedure based on a genetic algorithm bourouis and mili, j. build. mater. struct. (2018)5: 32-42 37 the aim of this part is to show how to model damage problems from genetic algorithms. this will then lead us to show the advantages of this tool compared to a resolution by an analytical method. we have considered sandwich beams loaded in three-point bending with two identical skins. the possible coatings orientations are around four distinct orientations: 0°, +45°, -45° and 90°. in order to respect the symmetry constraint, only half of the beams that are represented by independent variables. the representation of the laminates is made on the basis of the genetics concept. an individual is equivalent to a laminate and consequently, the population refers to a group of laminates. an individual can then be represented by one or more chromosomes. each chromosome contains a chain of genes of the same type representing the coded variables of the problem. let us take the example of a sandwich structure with laminate composite coatings consisting of six plies. when the ω domain comprises four discrete orientations 0°, 45°, -45 °, 90 °, it is necessary to use a coding of four alleles 1, 2, 3, 4. the table 3 gives an example of a six-ply laminate. table 3. encoding the discrete domain ωi domain variables /alleles (decoded 0° +45° 45° 90° (coded) 1 2 3 4 table 4. representation of a six-ply laminate representation variables /alleles coded 1 2 4 1 3 4 decoded 0° +45° 90° 0° 45° 90° we selected an initial population (p0) of ten individuals (n =10), represented by a chromosome ω’ = {1,2,3,4}. in this case, each gene takes aleatory value within the domain and each individual are evaluated in order to determine the values of their performance f(x). in this contribution, the crossing was chosen in two points. table 5. two-point crossover (x2p) coding-decoding variables /alleles coding a six-ply of individual p1 1 2 3 4 1 2 p2 3 2 1 3 2 1 c1 1 2 1 3 1 2 c2 3 2 3 4 2 1 decoding a six-ply of individual p1 0° +45° -45° 90° 0° +45° p2 -45° +45° 0° -45° +45° 0° c1 0° +45° 0° -45° 0° +45° c2 -45° +45° -45° 90° +45° 0° the simple mutation is applied to children in a probability pm. during the mutation, a vk gene of a child c is chosen at random. this gene is then randomly modified by a value other than vk belonging to the domain ω '. the third gene v3 is mutated and its value changes from 3 to 1. table 6. example of a simple mutation variables /alleles p1 1 2 3 4 1 2 p2 1 2 1 4 1 2 c1 0° +45° -45° 90° 0° +45° c2 0° +45° 0° 90° 0° +45° 38 bourouis and mili, j. build. mater. struct. (2018) 5: 32-42 the parameters of the genetic algorithm used during the generation of the results are given in table 7. table 7. genetic algorithm parameters. n nk crossover mutation stop criterion x2p simple tn 10 5 1,00 0.2 100 4. results and discussion 4.1 comparative study of the mechanical behavior of sandwich beams loaded in three-point bending in order to study the influence of the nature of the constituent materials of the sandwich structure; we considered thin beams 400 mm long, 50 mm wide and h=13 mm high. consisting of two identical skins of thickness h1 = h2 = 1.5 mm (figure 1). the structures considered consist of two skins of composite material with unidirectional fibers of six plies. the beams are subjected to a distributed load p = -70 n/m. fig5. variation of the deflection of a sandwich beam with different core materials and glass/epoxy coatings oriented at [45°/-45°]3s as a function of the distance x along its length. figs 5 and 6 show the influence of the core material on the mechanical behavior of thin sandwich beams with composite coatings oriented at [45°/-45°]3s loaded in three-point bending. pvc (h100) foams and corecell foams give high resistance to sandwich materials with carbon/epoxy and glass/epoxy coatings, while the alporas and polyurethane foams give poor behavior to the entire sandwich beam. the results obtained in fig 7 confirm the influence of the density on the mechanical behavior of sandwich beams loaded in three-point bending. pvc foam h 100 improves the behavior of sandwich structures with carbon/epoxy or glass/epoxy coatings with fiber orientation of [45°/-45°]3s . the pvc foam h45 gives a low resistance in the cases studied. 0,00 0,05 0,10 0,15 0,20 -2,0x10 -4 -1,5x10 -4 -1,0x10 -4 -5,0x10 -5 0,0 w (x ) (m ) l/2 (m) glass/epoxy/alporas glass/epoxy/polyurethane glass/epoxy/pvc(h100) glass/epoxy/corecell bourouis and mili, j. build. mater. struct. (2018)5: 32-42 39 fig 6. variation of the deflection of a sandwich beam with different core materials and carbon/epoxy coatings oriented at [45°/-45°]3s as a function of the distance x along its length. fig 7. variation of the deflection of a pvc core sandwich beam with different densities (h45, h60, h100) and with glass / epoxy and carbon / epoxy coatings oriented at [ 45°/ -45 °]3s as a function of the distance x along its length. fig 8 shows the influence of the thickness of the core on the mechanical behavior of sandwich beams. the three sandwich beams considered have the same pvc foam core material h100 of different thicknesses 6 mm, 8 mm, and 10 mm and with glass/epoxy coatings. the results obtained show that the sandwich material with the thicker core has a good resistance when it is loaded in three-point bending. 0,00 0,05 0,10 0,15 0,20 -1,8x10 -4 -1,6x10 -4 -1,4x10 -4 -1,2x10 -4 -1,0x10 -4 -8,0x10 -5 -6,0x10 -5 -4,0x10 -5 -2,0x10 -5 0,0 2,0x10 -5 w (x ) (m ) l/2 (m) carbon/epoxy/alporas carbon/epoxy/polyurethane carbon/epoxy/pvc(h100) carbon/epoxy/corecell 0,00 0,05 0,10 0,15 0,20 -2,6x10 -5 -2,4x10 -5 -2,2x10 -5 -2,0x10 -5 -1,8x10 -5 -1,6x10 -5 -1,4x10 -5 -1,2x10 -5 -1,0x10 -5 -8,0x10 -6 -6,0x10 -6 -4,0x10 -6 -2,0x10 -6 0,0 2,0x10 -6 w (x ) (m ) l/2 (m) glass/epoxy/pvc(h100) glass/epoxy/pvc(h60) glass/epoxy/pvc(h45) carbon/epoxy/pvc(h00) carbon/epoxy/pvc(h60) carbon/epoxy/pvc(h45) 40 bourouis and mili, j. build. mater. struct. (2018) 5: 32-42 fig 8. variation of the deflection of a sandwich beams with glass/epoxy coatings oriented at [0° / 90°]3s and [45°/-45 °]3s and pvc foam (h100) core at different thicknesses as a function of the distance x along its length. 4.2 optimization of sandwich beams in face yielding and face wrinkling failure modes in order to increase the performance of sandwich beams loaded in three-point bending, an optimization program based on the principles of genetic algorithms has been developed to maximize the failure load in face yielding and face wrinkling failure modes, depending on the orientation of the plies. fig 9. variation of the failure load of sandwich beams loaded in three-point bending under face wrinkling failure mode with different coating materials for 100 generations. the beams used are of length l = 180 mm and widths b = 50 mm, and heights h = 10 mm and thickness skins h1 = h2 = 3mm. the structures considered consist of two skins of composite 0,00 0,05 0,10 0,15 0,20 -6,0x10 -5 -5,0x10 -5 -4,0x10 -5 -3,0x10 -5 -2,0x10 -5 -1,0x10 -5 0,0 w (x ) (m ) l/2 (m) face sheet oriented at [45°/-45°] 3s : h=6mm h=8mm h=10mm face sheet oriented at [0°/90°] 3s : h=6mm h=8mm h=10mm 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 1,0x10 3 1,5x10 3 2,0x10 3 2,5x10 3 3,0x10 3 3,5x10 3 4,0x10 3 4,5x10 3 5,0x10 3 5,5x10 3 6,0x10 3 face wrinkling failure mode m a x im u m f a il u re l o a d ( n ) ( f it n e ss ) generation number carbon/epoxy glass/epoxy kevlar/epoxy bourouis and mili, j. build. mater. struct. (2018)5: 32-42 41 materials with unidirectional fibers of six plies: carbon/epoxy, kevlar/epoxy, glass/epoxy. their mechanical characteristics are summarized in table 1. fig 10. variation of the failure load of sandwich beams loaded in three-point bending under face yielding failure mode with different coating materials for 100 generations. analysis of the results obtained from fig. 9 shows that for the 10th first generations the beam sandwich with carbon / epoxy coatings appears to have a significantly the higher performance in compression than the other two materials. as of the 11th generation, the cost function deviates similar for sandwich materials with carbon/epoxy and glass/epoxy coatings up to the 55th generation. beyond that, the failure load of the carbon-epoxy sandwich beams becomes more important. the ag method gives an optimum value for carbon fiber stacks [0°/90°/-45°/ 0°/90°/+45°]. during the evolution of the 100 generations, the sandwich material with kevlar/epoxy coatings is the least resistant in compression failure mode. fig.10 shows that sandwich beams loaded in three point bending with carbon fibers are the best materials in the face yielding failure mode. the glass fibers promote the first generation to have higher child performance than the two other materials types. between 10th to 44th generation ga improves the tensile strength of sandwich beams with carbon/epoxy coatings especially from the 63th generation. the optimization program shows also that the sandwich material with kevlar/epoxy coatings is the better material from the 45th to the 62th generation. the ag converges to the optimum value at the 100th generation with carbon fiber orientated at [0°/+ 45°/ -45° /+ 45°/90°/90°]. 5. conclusions the objective of this article is to do a comparative study of the mechanical behavior of sandwich beams loaded in three-point bending. the structures are made of two unidirectional skins glass, carbon and kevlar fibers with epoxy resin which are symmetrical laminates oriented at [0°/90°]3s [45°/-45°]3s, and foam core with , alporas, corecel, pvc, or polyurethane. the different results obtained have shown that the good choice of the material of the coatings and the core improves the mechanical behavior of the sandwich beam loaded in three-point bending. improving the efficiency and reliability of the design of sandwich structures requires a thorough understanding and accurate modeling of damage to material. in order to optimize the failure load of sandwich structures, stochastic methods presented in the form of a genetic algorithm 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 2,5x10 3 3,0x10 3 3,5x10 3 4,0x10 3 4,5x10 3 5,0x10 3 5,5x10 3 6,0x10 3 6,5x10 3 7,0x10 3 7,5x10 3 face yielding failure mode m a x im u m f a il u re l o a d ( n ) (f it n e ss ) generation number carbon/epoxy glass/epoxy kevlar/epoxy 42 bourouis and mili, j. build. mater. struct. (2018) 5: 32-42 have been used which prove to be good optimization tools because of their capacity to out the local optima. after several combinations, it has been found that the number of generations has a very great influence on the search for the optimal solution. moreover, it has been observed that some adaptation functions sometimes have particularities that can put the genetic algorithm in difficulty, as in the case of the maximization of the load in face yielding failure mode. this function presents local maxima which make the task particularly difficult to the genetic algorithm. depending on the number of generations, a local maximum may be confused with the global maximum. the results of optimization in two failure modes face yielding and face wrinkling by the application of a probabilistic method based on the principles of genetic algorithms is acceptable. they confirmed the role of carbon fiber to maximized the failure load in three-point bending of the sandwich beam for stacks [0°/+ 45°/-45° /+ 45°/ 90°/ 90° ] under face yielding failure mode and [0°/90°/-45°/0°/ 90°/+45°] under face wrinkling failure mode. it is preferable in face yielding failure mode to change the rate of mutation probability over time to make the environment more stable, or to increase the numbers of the studied generations in order to achieve the best results. 6. references ashby, m.f., evans, a.g., fleck, n.a., gibson, l.j., hutchinson, j.w., & wadley, h. (2000). metal foams a design guide, butter worth heinemann. united states of america. berthelot, j.m. (1996). mechanical behaviour of composite materials and structures, masson., paris. craig, a.s., & norman, a.f. (2004). material selection in sandwich beam constructions. scripta materialia, 50, 1335-1339. gdoutos, e. e., daniel, i. m., & wang, k. a. (2003). compression facing wrinkling of composite sandwich structures. mechanics of materials, 35(3-6), 511-522. hamidreza, s., bahador s., hoseini ,f.a., & ahmadzadeh, m. (2012). use of genetic algorithms for optimal design of sandwich panels subjected to underwater shock loading. strojniski vestnik/journal of mechanical engineering, 58(3), 156-164. jin, d., thomas, h.h. (2003). flexural behavior of sandwich beams fabricated by vacuum-assisted resin transfer molding. composite structures, 61(3), 247-253. tahani, m., kolahan, f., & sarhadi, a. (2005). genetic algorithm for multi-objective optimal design of sandwich composite laminates with minimum cost and maximum frequency. in international conference on advances in materials, product design & manufacturing systems. zinker, d. (1995). an introduction to sandwich construction. emas solihull., united kingdom. j. build. mater. struct. (2019) 6: 10-19 original article doi : 10.34118/jbms.v6i1.64 issn 2353-0057, eissn : 2600-6936 development of high thermal stability geopolymer composites enhanced by nano metakaolin el nagar am *, khater hm housing and building national research centre (hbrc), 87 el-tahrir st, dokki, giza, p.o. box 1770 cairo, egypt * corresponding author: abdeenelnagar@yahoo.com received: 01-10-2018 accepted: 04-02-2019 abstract: this paper deals with study of thermal stability of geopolymer composites enhanced by nano metakaolin materials (nmk) and exposed to high firing temperature up to 1000 °c. the main geopolymer made up of water cooled slag having various kaolin ratios. the activators used are na2sio3 and naoh in the ratio of 3:3. the thermo-physical, microstructural and mechanical properties of the geopolymers before and after the exposure to elevated temperatures of 300, 500, 600 800 and 1000 °c have been investigated. the fire shrinkage of the geopolymer specimens increased by increasing temperature up to 1000 oc. also, the fire shrinkage increased slowly up to 500 °c. the mechanical strength of geopolymer specimens increased with temperature up to 500 oc. the good thermo-physical and mechanical properties for these geopolymer composites increase the possibility of vast application of these eco-friendly materials in construction sectors. key words: firing shrinkage, geopolymer composites, slag, kaolin, nano metakaolin. 1. introduction the geopolymerization technology introduced as an ideal and novel environmentally-friendly process for producing supplementary materials to ordinary portland cement (opc) in 1980s, by professor joseph davidovits that possessing higher mechanical and durability properties. the geopolymers synthesizing technology is based on the relatively simple alkaline activation of a source material which is rich in silicon (si) and aluminum (al) in amorphous form at relatively low temperature (davidovits, 1999). geopolymers have superior resistance to thermal shrinkage when exposed to temperatures up to 1000 °c compared to portland cements (palomo et al., 1999; duxson et al, 2005 ; duxson et al., 2007; rahier, 1996) very little attention has been given to the wider issue of ambient temperature drying shrinkage (barbosa & mackenzie, 2003a). unlike portland cement, water is not incorporated directly into the geopolymer gel product. only a small percentage of the mixing water remains as interstitial water in the geopolymer gel shrinkage (barbosa & mackenzie, 2003-b). this fact, combined with the high water requirement to mix geopolymer pastes, means that there is a large excess of unbound or free water, which can evaporate from the hardened paste under low relative humidity conditions at ambient temperature (rahier, 1996). despite the lack of chemically bound water, it still plays an important role in structural stability. excessive water loss under relatively normal environmental conditions can result in extensive shrinkage cracking of specimens (barbosa & mackenzie, 2003-a). the previous studies that investigated thermal properties of fly ash materials possessed low thermal shrinkage and good strength maintenance after exposure to high temperatures (bakharev, 2006; kong & sanjayan, 2008; kong & sanjayan, 2010; rickard et al., 2010). the fa geopolymers in these papers were directly heated from room temperature up to the elevated temperature of 800 ºc or further up to 1200 ºc, without studying the changes in the geopolymer phase composition and microstructure occurred at temperatures ranged from about 600-800 ºc. recently, these changes have been highlighted via dilatometric analysis el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 11 (rickard et al., 2012; provis et al., 2009). however, these studies were focused substantially on the effect of the silicate phase concentration exist in the fas sources and/or geopolymers which lacks to the micro-structural and mechanical analysis. also, all the designed alkali activated fly ash based systems, not depending on initial curing condition, displayed a higher resistance to high temperature with respect to traditional cementitious binders, which are affected by very high strength loss at high temperature such as 800 °c (messina et al., 2018). adding nano silica have good effect and improve residual compressive strength of both sodium and potassium activators synthetized geopolymers at elevated temperatures. the potassium activator synthetized geopolymers containing nano silica exhibited higher residual compressive strength at elevated temperatures above 400 °c than its sodium based counterparts (shaikh & haque, 2018). the main objective of the current study is to address the thermo-physical, mechanical and the macro/micro-structural changes that the geopolymer products experience after exposing to different elevated temperatures of 300, 500, 600, 800 and 1000 ºc to enhance the understanding about this new type of building materials. 2. geological setting of kaolin deposit the studied kaolin raw material was delivered from quarry of the middle east mining company (memco) (6 km west of gebel gunna in the central sinai, egypt). the kaolinitic sandstone beds in the quarry belong to the naqus formation of the early paleozoic age (el nagar, 2016). these rocks are partially covered in some parts by windblown sands and some gravel. these loose sands and detrital materials belong to the recent age. the studied quarry face section attains about 5.5 m thick (fig. 1). the quarry bed is completely composed of kaolinitic sandstone; whitish, very fine grain, compact and hard. the figure 1 illustrate the lithostratigraphic columnar section of the interface studied quarry of naqus formation, west of gebel gunna, sinai, egypt. fig. 1. lithostratigraphic columnar section of the interface studied quarry of naqus formation, west of gebel gunna, sinai. refers to the bed of samples collected. 12 el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 3. materials and methods 3.1 materials materials used in this work are kaolin collected from sinai, west of gebel gunna, egypt; water cooled slag also called ground granulate blast furnace slag (ggbfs) sourced from iron and steel factoryhelwan, egypt. commercially sodium hydroxide (naoh) with purity 98 % in the form of pellets and sodium silicate (na2sio3) are used as alkali activators. nano-metakaolin particles were prepared in the lab from the kaolin raw by firing at 800 ºc for 2 hr with heating rate of 5 ºc /min. the chemical composition of the starting raw materials are tabulated in table (1). also, the used dose of nmk was chosen at 3% from total weight based on the literatures (el nagar, 2016). table 1. chemical composition of the used raw materials (mass). material kaolin nano metakaolin ggbfs sio2 49.86 56.14 36.59 al2o3 34.10 38.21 10.01 fe2o3 0.30 0.38 1.48 cao 0.09 0.07 33.07 mgo 0.26 0.37 6.53 so3 0.59 0.18 3.52 k2o 0.02 0.00 0.74 na2o 0.03 0.02 1.39 tio2 0.88 1.14 0.52 mno2 0.01 0.00 3.44 p2o5 0.35 0.26 0.10 cl0.00 0.00 0.05 loi 13.44 3.13 0.00 total 99.92 99.89 99.69 notes bao=5.00 3.2 experimental 3.2.1 preparation of activator solution the alkaline solution was prepared by dissolving naoh pellets in water and then added to the required amount of water glass. after the solution was cooled down, the nano-kaolin powder was stirred for 15 minutes. the binders were first dry mixed together. then, the prepared activator solution was added on the powder and mixed for 5 minutes. 3.2.2. casting and molding the mix was poured in steal molds of 2.5 cm side length cube and vibrated for 30 second using a vibrating table. all mixes were left to cure at ambient temperature for 24 hours, and then subjected to curing temperature of 38 oc and 100% relative humidity in a controlled humidity chamber. compressive strength was measured at 28 days before firing. compressive strength tests were carried out using five tones german brüf pressing machine with a loading rate of 100 kg/min determined according to astm-c109-07 (2012), as follows: c = w/a where, c= compressive strength of the specimen, kg/cm2. w= total load at which failure occurs, kg. a= calculated area of the bearing surface, cm2. el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 13 as a confirmatory tool, thermo-gravimetric (tga) analysis was used. the thermal analyses were carried out using computerized dt-50 thermal analyzer (shimadzu co., kyoto, japan). the heating rate was 20 oc /min. the heating temperature was up to 1000 oc for tga under nitrogen atmosphere (30 ml/min). the microstructure of specimens was studied using sem inspect s (fei company, netherland). the studied mixes composition shown in table (2). table 2. the studied mix design of geopolymer composites specimens. mix kaolin, % slag, % nmk, % naoh, % na2sio3, % g1 50 50 3 3 3 g2 20 80 3 3 3 g3 100 3 3 3 3.3 fire shrinkage at the age of 28 days, the geopolymer specimens were dried at 105 °c for 24 hrs, then fired at temperatures of 300 °c, 500 °c, 600 °c, 800 °c and 1000 °c for 2 hrs with a heating rate of 5 °c/min. afterwards, the geopolymer specimens were left to cool inside the furnace to room temperature. then, fire shrinkage test for the fired specimens was measured according to the following equation. firing shrinkage% was calculated for each test specimen using the following formula norsker, 1987): average of firing shrinkage %= (dl-fl)/dl*100 where: dl means dried length and fl is fired length. 4. results and discussion 4.1. firing shrinkage fire shrinkage results of dried geopolymer specimens (g1, g2 and g3) fired at 300, 500, 600, 800 and 1000 °c are shown in (table 3) and plotted against temperature degrees in fig. (2). it can be seen that the firing shrinkage increases for the geopolymer specimens with temperatures higher than 300 °c and up to 1000 °c is which can be related to water evaporation from the geopolymer structure in a phenomenal called the ‘vapors effect’ as discussed elsewhere (abdulkareem et al., 2013). table 3. fire shrinkage of dried geopolymer specimens fired at 300, 500, 600, 800 and 1000°c. tempertaure degree °c fire shrinkage, % g1 g2 g3 300 0.016 0.013 0.005 500 0.018 0.017 0.016 600 0.042 0.040 0.021 800 0.044 0.045 0.024 1000 0.048 0.045 0.027 it is generally considered that there are three types of water exist in the hardened geopolymer products: physically bonded water, chemically bonded water and hydroxyl groups oh. the physical bonded water and chemically bonded water evaporate between 20 °c to 100 °c, and between100°c to 300 °c, respectively. when the temperature reaches above 300°c, the dehydroxylation of oh groups happens with the subsequent polycondensation into siloxo bond si-o-si, linking neighboring geopolymeric micelles. it is proven that more than 70% of the reactions water is physically bonded water, which evaporates below 100 °c without causing any internal stress and remarkable shrinkage. 14 el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 fig. 2. firing shrinkage of dried geopolymer specimens of various compositions exposed to 300, 500, 600, 800 and 1000°c. however, many micro pores will be produced owing to the empty space left by the water evaporation. the remaining 30% water, chemically bonded water and hydroxyl groups oh, accounting for up to 90% of the total shrinkage when the samples are heated from 20 °c to 500 °c (perera et al., 2007). above 500 °c further shrinkage takes place due to densification and/or volume changes as a result of crystallization and subsequent melting. davidovits estimated that the evaporation of the free water is not the cause of the damaging stresses except a very small shrinkage, although the free water contributes about 60% of the total water content in the geopolymer structure (davidovits, 1988). however, the remaining 40% of the water content evaporation is contributing about 90% of the total shrinkage at high temperatures. the main reason for the shrinkage when the samples are exposed to the 500 °c may be caused by the loss of the chemically bonded water and hydroxyl groups oh. it can be noticed from the pattern all mixes possess shrinkage values lower than 0.02 % for temperature lower than 600°c, also increase replacement of slag by kaolin results in the increase of shrinkage values due to the low reactivity of kaolin leading to the increase of physical water content. we can also notice that mix without kaolin has the lowest values of shrinkage due to the formation of dense structure that hinder the evaporation of water by all its type. 4.2 thermo-gravimetric (tga) analyses thermograms of geopolymer specimens at firing temperatures (0 oc, 500 oc and 1000 oc) are illustrated in fig. (3). comparing the tga patterns with firing temperatures, the geopolymer specimens (g1) gave a total weight loss of 13.91%, 7.20% and 1.10 % at 0 oc, 500 oc and 1000 oc, respectively. also, geopolymer specimens (g2) gave a total weight loss of 11.19 %, 5.32% and 0.34 % at 0 oc, 500 oc and 1000 oc, respectively. it is noticeable the geopolymer specimens (g3) gave a good stability and a lower weight loss of 11.68 %, 3.30 % and 0.81 % at 0 oc, 500 oc and 1000 oc respectively, as compared with g1 and g2 because of the lower intensity of the formed zeolite structure. el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 15 fig. 3. thermo-gravimetric graphs of geopolymer specimens of mixes g1, g2 and g3 fired at 0 oc, 500 oc and 1000 oc. 16 el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 4.3. scanning electron microscope from previous works a possible explanation for geopolymer shrinkage and cracking is the generation of high capillary pressures between wet and dry areas of the micro pore network, which has been reported to initiate crack propagation in the microstructure. attempts to avoid shrinkage and crack propagation have focused on modifying the pore structure to minimize capillary porosity, and controlling water loss during curing (perera et al., 2007; bell & kriven, 2008). the sem micrographs geopolymer composite fired at 1000 °c and having various ratios of kaolin are represented in fig (4), where as elucidated before from shrinkage data, the mix specimen which has high ratio of kaolin exposed to high deterioration as the lower reactivity of kaolinite material facilitate the evaporation of water and so increase the gaps and cracking between interacting particles fig (4a). on lowering the kaolin content to 20% results in somehow lower cracking depth as well as cohesion between geopolymer ingredient further increases in slag content g3 leads to extra enhancement and stability of the matrix against high temperatures leading to formation of dense structure where formed calcium silicate hydrate leads to formation of matrix free of wide cracks but only some micro cracks formed. fig. 4. sem micrographs of geopolymer specimens after exposure to 1000 °c. el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 17 4.4. compressive strength compressive strength of geopolymer specimens was increased with increasing firing temperature up to 500 oc. generally, this increasing is mainly related to the hydrothermal reaction and inter-autoclaving effect. the increase in strength is noticeable dramatically at 500 oc in both g2 (composed of 80% water cooled slag and 20% kaolin) and g3 (composed only of water cooled slag) as shown in fig. 5. the data presented in fig. (2) very closely reflect the trends in fig. (5), implying a strong correlation between firing shrinkage and changes in mechanical properties, so the firing shrinkage increase slowly up to 500 °c in the most specimens. on the other hand the compressive strength increase up to 500 °c, due to the microstructure is partially resisting further shrinkage. explanation for these observations is that the shrinkage mechanism causes a uniform physical contraction in the gel microstructure which, brings about an increase in strength (kuenzel et al., 2012). this result related to the increase of vitreous component in water cooled slag which enhance the geopolymer activation and so increase the yield of the reaction product. moreover, using 50% kaolin along with water cooled slag (g1) gave a higher fire shrinkage and low thermal stability as compared with other geopolymer specimens. however, the viscous sintering process occurred in the geopolymer matrix at the temperature range from 800 oc to 1000 oc led to strength gain (tai tran-thanh et al., 2016) especially in specimen g3. fig. 5. compressive strength of geopolymer specimens (g1, g2, g3) after exposure to 0°, 300°, 500°, 600°, 800° and 1000 °c. on the other hand, all specimens have promising mechanical properties up to 500 °c, which may be attributed to the effect of nano metakaolin filling the voids, producing denser geopolymer, and/or it may be attributed to the fact that the nano-composite specimens had higher amounts of geopolymer gel and amorphous content. 18 el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 5. conclusion 1the firing shrinkage increases of the geopolymer specimens after exposed to temperatures higher than 300 °c and up to 1000 °c. 2the firing shrinkage increase slowly up to 500 °c in the most geopolymer specimens, and possess lowest values for mixes without kaolin leading to the formation of dense compacted geopolymer. 3the micrographs showed the increasing of the voids content as well as wide micro cracks within in the paste microstructure with decreasing in slag content, while mix without kaolin has highest cohesive and denser structure at 1000 °c. 4compressive strength of geopolymer specimens increased with increasing firing temperature up to 500 oc, then strength decrease up to 1000 °c. 5the studied geopolymer mixes with their highly thermal stability favors their applications in construction sectors. 6. references abdulkareem, a. o., al bakri abdullah, m. m., kamarudin, h., & khairul nizar, i. (2013). alteration in the microstructure of fly ash geopolymers upon exposure to elevated temperatures. in advanced materials research (vol. 795, pp. 201-205). trans tech publications. astm c109. (2012). “standard test method for compressive strength of hydraulic cement mortars”. bakharev, t. (2006). thermal behaviour of geopolymers prepared using class f fly ash and elevated temperature curing. cement and concrete research, 36(6), 1134-1147. barbosa, v. f., & mackenzie, k. j. (2003-a). synthesis and thermal behaviour of potassium sialate geopolymers. materials letters, 57(9-10), 1477-1482. barbosa, v. f., & mackenzie, k. j. (2003-b). thermal behaviour of inorganic geopolymers and composites derived from sodium polysialate. materials research bulletin, 38(2), 319-331. bell, j.l. & kriven, w.m.. (2008). preparations of ceramic foams from metakaolin-based geopolymer gels. in: developments in strategic materials, ceramic engineering and science proceedings. davidovits, j. (1988). geopolymer chemistry and properties. geopolymer 88, first european conference on soft mineralurgy, compiegne, france, 1, 25-48. davidovits, j. (1999). chemistry of geopolymeric systems. in: terminology. geopolymer’99 second international conference, saint-quentin, france, 9–39. duxson, p. s. w. m., mallicoat, s. w., lukey, g. c., kriven, w. m., & van deventer, j. s. (2007). the effect of alkali and si/al ratio on the development of mechanical properties of metakaolin-based geopolymers. colloids and surfaces a: physicochemical and engineering aspects, 292(1), 8-20. duxson, p., provis, j. l., lukey, g. c., mallicoat, s. w., kriven, w. m., & van deventer, j. s. (2005). understanding the relationship between geopolymer composition, microstructure and mechanical properties. colloids and surfaces a: physicochemical and engineering aspects, 269(1-3), 47-58. el nagar, a. m. (2016). applied geological studies on some kaolin deposits and industrial wastes for production of nano geopolymer composites, egypt. ph d., al azhar university, faculty of science, may. kong, d. l., & sanjayan, j. g. (2008). damage behavior of geopolymer composites exposed to elevated temperatures. cement and concrete composites, 30(10), 986-991. kong, d. l., & sanjayan, j. g. (2010). effect of elevated temperatures on geopolymer paste, mortar and concrete. cement and concrete research, 40(2), 334-339. el nagar and khater, j. build. mater. struct. (2018) 6: 10-19 19 kuenzel, c., vandeperre, l. j., donatello, s., boccaccini, a. r., & cheeseman, c. (2012). ambient temperature drying shrinkage and cracking in metakaolin‐based geopolymers. journal of the american ceramic society, 95(10), 3270-3277. messina, ferone, colangelo, roviello, & cioffi. (2018). alkali activated waste fly ash as sustainable composite: influence of curing and pozzolanic admixtures on the early-age physico-mechanical properties and residual strength after exposure at elevated temperature. composites part bengineering, 132, 161-169. norsker, h. (1987). the self-reliant potter: refractories and kilns, friedr. braunschweig/wiesbaden: vieweg & sohn. palomo, a., blanco-varela, m. t., granizo, m. l., puertas, f., vazquez, t., & grutzeck, m. w. (1999). chemical stability of cementitious materials based on metakaolin. cement and concrete research, 29(7), 997-1004. perera, d. s., uchida, o., vance, e. r., & finnie, k. s. (2007). influence of curing schedule on the integrity of geopolymers. journal of materials science, 42(9), 3099-3106. provis, j. l., yong, c. z., duxson, p., & van deventer, j. s. (2009). correlating mechanical and thermal properties of sodium silicate-fly ash geopolymers. colloids and surfaces a: physicochemical and engineering aspects, 336(1-3), 57-63.. rahier, b. (1996). van mele, and j. wastiels,“low-temperature synthesized aluminosilicate glasses part ii rheological transformations during low-temperature cure and high-temperature properties of a mode/compound,”. j. mater. sci, 31(1), 80-85. rickard, w. d., riessen, a. v., & walls, p. (2010). thermal character of geopolymers synthesized from class f fly ash containing high concentrations of iron and α‐quartz. international journal of applied ceramic technology, 7(1), 81-88. rickard, w. d., temuujin, j., & van riessen, a. (2012). thermal analysis of geopolymer pastes synthesised from five fly ashes of variable composition. journal of non-crystalline solids, 358(15), 1830-1839. shaikh, f., & haque, s. (2018). effect of nano silica and fine silica sand on compressive strength of sodium and potassium activators synthesised fly ash geopolymer at elevated temperatures. fire and materials, 42(3), 324-335. tai tran-thanh. tuan le-anh. kwon hyug moon. (2016). alteration in the mechanical strength of fly ash based geopolymer mortar upon exposure to elevated temperatures. international journal of applied engineering research, v. 11, 21, p. 10433-10440. j. build. mater. struct. (2018) 5: 22-31 original article doi : 10.34118/jbms.v5i1.41 issn 2353-0057, eissn : 2600-6936 the thermal properties of mortars modified by the effect of combining polymers and scms belbachir b.1,2, benosman a.s.1,2,3*, taïbi h. 1, mouli m.2, senhadji y.2,4 1 faculty of exact and applied sciences, laboratory of polymer chemistry lcp, university of oran 1, ahmed benbella, bp 1524, el mnaouer, oran 31000, algeria. 2 department of civil engineering, laboratory of labmat, enpo maurice audin, oran, algeria. 3 higher school of applied sciences, essa-tlemcen, bel horizon, 13000 tlemcen, algeria. 4 department of civil engineering, university of mustapha stambouli, mascara, algeria. * corresponding author: amre20022000@yahoo.fr received: 29-01-2018 revised: 14-03-2018 accepted: 17-03-2018 abstract. the thermal performance of the building materials is relevant to any use of composite materials, especially in relation to constructions where it is desirable to have high specific heat, low thermal conductivity and slight or no decrease of stiffness upon heating. the thermal coefficients of composite mortars made up of mixtures of combining styrene polyacrylic spa latex and supplementary cementitious materials scms were measured at different ages (7, 14, 28, 60, 90 and 120 days). so, in order to determine the thermal conductivity, the calorific capacity and thermal diffusivity of scm-modified mortars, it seemed interesting to evaluate the influence of adding the spa latex (0.5%, 1% and 2%w) on the properties of these mortars when exposed to a quick thermal conductivity meter based on standard iso 8302-91. the highest thermal conductivity of 1.51 w.m-1.k-1 was observed with the samples containing only plain cement. it decreased with the increase of spa latex percentages. the lowest values of thermal coefficients were obtained with the samples prepared with spa polymer at 2% and scms. in this way, the results obtained highlight the beneficial effect of combining spa polymer and scm materials as thermal insulation in comparison with other insulation materials. in fact, using scms as cement substitutes reduces the energy consumption. these composite mortars address problems related to environmental pollution by co2 emissions, and can be recommended as materials for energy efficiency in buildings. key words: pozzolana, silica fume, latex, thermal coefficients, sustainable materials. 1. introduction the reduction of energy consumption in the building sector is a major challenge in order to cope with the scarcity of fossil energy resources and the problem of climate change (neville, 1996). today, the insulation of buildings has become a necessity; it is an efficient and cost-effective way to meet the challenge of reducing energy consumption. currently, in the cement industry, co2 emissions and raw material consumption are mainly targeted in order to reduce their environmental impact. the use of industrial mineral byproducts, such as silica fume (belbachir et al. 2016; hassan et al. 2012) or algerian natural pozzolana (belbachir, 2017; ghrici et al., 2006; kaid et al., 2009; senhadji et al., 2014; siad et al., 2013), in composite materials generally involves technological advantages and significant energy savings as well as co2 emission reductions. this should be consistent with the concept and objectives of sustainable development. for decades, polymer adjuvants have been widely used in civil engineering and are still increasingly used, due to the diversity of properties they can offer (ohama, 1995). in the modified formulations, the latex significantly improves the paste consistency, adhesion to the support and especially the mechanical properties of the cured material (ohama, 1997). thus, mailto:amre20022000@yahoo.fr belbachir et al., j. build. mater. struct. (2018) 5: 22-31 23 polymer-mortar composites based on mineral additions are necessary for energy efficiency in buildings (belbachir et al. 2016; benosman et al. 2015). the purpose of the present work is to study the impact of the combination of latex polymer (tekweld) and supplementary cementitious materials (scms) on the thermal response (thermophysical properties) of scm-based polymer-mortar composites. 2. experimental program 2.1 cement (c) the type of cement used is matine cemii/a, from lafarge cement plant, based in oggaz (wilaya of mascara, algeria). this cement has a fineness of 4220 cm2/g, relative density equal to 3.09 g/cm3 and a compressive strength equal to 48 mpa, at 28 days. the chemical and mineralogical compositions of the cement and its clinker are respectively given in tables 1 and 2. table 1. elementary chemical composition of cement, natural pozzolan and silica fume (%w). elt. c pz sf sio2 17.954 46.101 94.609 al2o3 4.071 16.442 0.320 fe2o3 2.750 9.140 1.212 cao 58.15 9.057 0.434 mgo 1.768 5.341 0.385 so3 2.428 0.059 0.104 k2o 0.661 1.338 0.527 na2o 0.205 2.257 0.113 p2o5 0.107 0.729 0.010 tio2 0.223 2.062 0.024 loi 10.720 7.110 1.980 loi: loss on ignition. table 2. mineralogical composition of clinker (%w) c3s c2s c3a c4af 64 15 8 12.16 2.2 natural pozzolan (pz) the natural volcanic pozzolan is extracted from the deposit of bouhamidi in the region of benisaf (north west of algeria). the natural pozzolan used in all tests is in the form of powder, resulting from crushed pozzolanic rock, previously steamed for 24 hours at a temperature of 50 °c, to remove moisture; they were then ground until the resulting powder can pass through a sieve with an 80-micron mesh (ghrici, 2006). the chemical composition of ground natural pozzolan is shown in table 1. 2.3 silica fume (sf) the silica fume used in our study is a ferro-silicon type additive for concrete in aggressive environments, from tecknachem company (sidi bel-abbes). its chemical composition is given in table 1. 2.4 polymer (tk) the polymer used (styrene polyacrylic “spa” latex), known as tekweld from tecknachem company, is a synthetic resin (latex) in the form of a high density aqueous solution, stable in an alkaline medium, and especially designed to be added to the mixing water of cement mortars or plaster. the main characteristics of the polymer used are summarized in table 3. 24 belbachir et al., j. build. mater. struct. (2018) 5: 22-31 table 3. characteristics of the polymer used characteristics shape color absolute density (g/cm3) ph polymer liquid white (milk) 1.050.01 6 2.5 sand in this experimental study, the silica sand used was of fraction 0/5, and came from the quarry of nedroma, 60km northwest of tlemcen. its principal characteristics are given in table 4. before use, a granular correction of this sand was conducted by sea sand in order to have a continuous granulometry, according to the granulometric analysis of standardized sand (figure 1). fig 1. particle size distributions of sand table 4. physical properties of sand used. designations values relative density (g/cm3) 2.63 fineness modulus 2.4 equivalent of sand (%) 72 absorption coefficient (%) 1.22 2.6 specimen preparation, curing and casting it was decided to produce composites based on mineral additives (scms) with different polymer contents, i.e. p/c = 0.5, 1 and 2%, where p is the soluble polymer tk and c the cement. the mineral additives used are silica fume and natural pozzolan which must necessarily be realized with percentages of (5% or 10%) natural pozzolan (laoufi, et al. 2016; makhloufi et al. 2015) and 5% silica fume (belbachir et al. 2016; senhadji et al., 2014; zhang et al. 2016). the mortar used in the present study, consists of the following proportions by mass: 1 cement and 3 sand, with a constant water to cement ratio w/c = 0.5 and superplasticizer/cement = 1.3% for all composites mortars (table 5). 0 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 c u m u la ti v e p a s s in g ( % ) particle size (mm) belbachir et al., j. build. mater. struct. (2018) 5: 22-31 25 table 5. the formulations of the different composite mortars code cement (%) scms (%) tk (%) sand (%) w/c sp (%) pz sf f0 (0;0;0) 100 100 0.5 1.3 f1 (5;0;0) 95 5 100 0.5 1.3 f3 (10;0;0) 90 10 0 100 0.5 1.3 f5 (0;5;0) 95 0 5 100 0.5 1.3 f6 (10;0;0.5) 89.5 10 0 0.5 100 0.5 1.3 f7 (10;0;2) 88 10 0 2 100 0.5 1.3 f8 (0;5;1) 94 5 1 100 0.5 1.3 f9 (0;5;2) 93 5 2 100 0.5 1.3 f0: control mortar; pz: pozzolan; sf: silica fume; tk: tekweld; sp: superplasticizer. mortars and/or composites were cast and compacted mechanically with a shock table (nf en 196.1, 2005). 1the molds containing the specimens were covered with a plastic film and stored in the laboratory environment. 2after this, the specimens were removed from the molds and they were kept in water saturated with lime for 1 day. 3afterward, the specimens were removed from the water and they were kept in an environment with a temperature of 20±2°c and a relative humidity of 60 ± 5%. 2.7 thermal coefficients a quick thermal conductivity meter (qtm 30) based on standard (iso 8302, 1991) guarded hot plate apparatus was used to measure the thermal conductivity, calorific capacity and thermal diffusivity of the sample at different ages. the measurement was performed after the specimens (40x40x160 mm3) were dried in an oven at 100 ± 3 °c. the thermal coefficients of composite mortars made up of mixtures of combining styrene polyacrylic spa latex and scms were measured at different ages: 7, 14, 28, 60, 90 and 120 days (figure 2). the experimental protocol of thermal test is carried out according to the recommendations of iso 8302 (1991). fig 2. device (quickline tm-30 thermal analyzer) with sample for thermal conductivity testing 3. results and discussion 3.1 thermal conductivity 3.1.1 effect of natural pozzolan and polymer (series i) the evolution of the thermal conductivity as a function of time is shown in figure 3. 26 belbachir et al., j. build. mater. struct. (2018) 5: 22-31 it is easy to note that at 7, 28, 60, 90 and 120 days, the reference mortar has a thermal conductivity that is close to that of natural pozzolan-based composite mortars. at all ages, adding natural pozzolan does not contribute to reducing the thermal conductivity of the composite mortars as compared to that of the reference mortar. however, there is a slight decrease in the conductivity values as a function of age, for different mortars. these results corroborates with those obtained by hamadache et al. (2014) and laoufi, (2015). note that at any age, the thermal conductivities of natural pozzolan-based composite mortars modified with the polymer are lower than that of unmodified mortar (reference mortar). therefore, the incorporation of the latex polymer into the cementitious mixture causes a significant decline in the thermal conductivity. the thermal conductivity of the composites (10; 0; 0.5) and (10; 0; 2), at 28 days, dropped by 18% and 47%, respectively, as compared with that of the unmodified mortar. this is certainly due to the formation of the tekweld polymer film. fig 3. evolution of thermal conductivity over time (series i) 3.1.2 effect of silica fume and polymer (series ii) figure 4 shows that the conductivity value of the silica-based mortar is slightly higher than that of the control mortar; it tends to remain constant beyond the young age. the addition of silica fume does not reduce the conductivity value. it can be assumed that the silica fume consists of silica nanoparticles that infiltrate into the matrix to act as filler. thus, the silica fume causes the cementitious matrix to be impermeable, since the number of pores will decrease over time until the stabilization of the cementitious hydration mechanism. on the other hand, it is observed that the values of this conductivity decrease slightly with age, for the different mortars. at 7 and 28 days, the conductivity of the composite containing 1% polymer (0; 5; 1) decreases by 28 % and 35%, respectively, as compared to that of the unmodified mortar; on the other hand, it can be noted that the conductivity decreases by 35% and 44%, respectively, relative to that of the control mortar for 2% of polymer (0; 5; 2). belbachir et al., j. build. mater. struct. (2018) 5: 22-31 27 in the longer term (90 and 120 days), there is a significant decline in the conductivity; it is of the order of 41% for a substitution rate of 2% of polymer and about 36% for a rate of 1% of polymer. this is due to the formation of the tekweld polymer film. the decrease in the thermal conductivity may be due to the effect of the latex on the total porosity, which decreases (belbachir, 2017). this porosity decline may be explained by the clogging of pores by the latex film. fig 4. evolution of the thermal conductivity over time (series ii) 3.1.3 effect of natural pozzolan, silica fume and polymer (series iii) figure 5 illustrates the variation of the thermal conductivity as a function of time. in the case of mortars with additions, i.e. the pozzolan and silica fume, it is found that, at all ages, the mineral additions do not contribute to the reduction of the thermal conductivity. on the contrary, an increase was recorded at the young age (7 and 14 days). the thermal conductivity values from this study are found to be slightly high for mineral-based mortars. it is found that the higher the densities of the mortars containing scms, the higher the thermal conductivity (see section 3.2). in addition, some studies (demirboga, 2003) have reported that the thermal conductivity increases with the density of the composite. the last mentioned findings support our results. the graphic illustration in the figure clearly shows the effect of the polymer on conductivity. it is noted that conductivity decreases when the substitution rate increases. it would therefore seem that polymer-mortar composites are poor thermal conductors since their conductivity decreases as the polymer content increases. these results could be attributed to the overall porosity of the cementitious matrix, to the density decline of the polymer-based composite (lightness of the composite mortar), and especially to the formation of the polymer film (belbachir, 2017). these results corroborates with those obtained by latroch et al. (2016). on the other hand, knowing that air has a thermal conductivity 25 times lower than that of water, it is clear that when the pores are filled with air (instead of water), the composite mortar will have a lower thermal conductivity (laoufi, 2015). the thermal conductivity decreases with age and polymer content; this is due to the reduction in the density of the composite and to the 28 belbachir et al., j. build. mater. struct. (2018) 5: 22-31 increase in its air content. benosman et al. (2017) reported that the increases in air content with increasing polymer particles reduce the thermal bridges in the matrix and contribute to improving composite insulation. for the different ages mentioned, the two mortars containing 2% polymer, i.e. (10; 0; 2) and (0; 5; 2), undergo very significant reductions in their thermal conductivities as compared to that of the control mortar and to those of mortars containing mineral additions, without latex. their thermal properties are therefore better. fig 5. evolution of the thermal conductivity over time (series iii) as a result, several authors (aattache et al., 2013; benosman et al., 2013; elalaoui, 2012a,b; fu et al., 1997; latroch et al. 2016) reported that the thermal conductivity decreases as the polymer content in the composite increases. because, the thermal conductivity of the polymer is lower than plain cement or scms. the findings of the present investigation are therefore consistent with those reported by the above mentioned authors. 3.2. correlation between thermal conductivity and density of the composite mortars the corresponding relationship between thermal conductivity and density of the composite is shown in figures 6 and 7. the thermal conductivity λ (w.m-1.k-1) decreases with decreasing apparent density (g/cm3). the derived correlation is of the linear type: λ = 1.438x 1.3476 (which yields a correlation coefficient r2=0.9907) for the series i and λ = 1.5419x 1.5421 (which r2=0.9986) for the series ii. the thermal conductivity of materials depends upon many factors, including their structure, material mixture proportioning, type of aggregate inclusions, density, porosity, etc (benosman et al. 2017; gouasmi et al. 2016). so, the decrease in thermal conductivity is also related to the less density of the tekweld polymer film content in the matrix that results in less density. consequently, this low density will allow the lightening of tekweldmodified mortar composites. the thermal insulating effect of latex polymer is most attractive and indicates a high and promising potential for development. these results corroborates with those obtained by latroch et al. (2016). belbachir et al., j. build. mater. struct. (2018) 5: 22-31 29 fig 6. relationship between thermal conductivity and density of composites (series i) fig 7. relationship between thermal conductivity and density of composites (series ii) 4. conclusions the results obtained allow us to draw the following conclusions: the thermal conductivities of mineral-based polymer-mortar composites, (10; 0; 0.5), (10; 0; 2), (0; 5; 1) and (0; 5; 2), are lower than those of mortars without polymer, hence the beneficial effect of tekweld polymer on the thermal properties. on the other hand, the thermal conductivity values are found to be slightly high for mineral-based mortars (without tk polymer). the thermal conductivity decreases as the styrene polyacrylic (spa) latex content in the composite increases. because, the thermal conductivity of the spa polymer is lower than plain cement or scms. the decrease in the thermal conductivity may be due to the effect of the latex “spa” on the total porosity, which decreases. this porosity decline may be explained by the clogging of pores by the latex film. the thermal conductivity decreases with age and polymer content; this is due to the reduction in the density. it is found that the smaller the densities of the spa polymerbased composite mortars, the lower the thermal conductivity. the correlations and coefficients indicate a good linear correlation between thermal conductivity and density in composites. thus, incorporation of tk polymer into the 30 belbachir et al., j. build. mater. struct. (2018) 5: 22-31 cement matrix reveals the ability of composites to provide a reliable level of thermal insulation. acknowledgments we would like to express our gratitude for the financial support of the algerian project cnepru b00l01un310120130068. we are also grateful to mr m.t. gouasmi and mr o. hasnaoui general director of hasnaoui companies group, the teknachem algeria. 5. references aattache, a., mahi, aek., soltani, r., mouli, m., & benosman a.s. (2013). experimental study on thermomechanical properties of polymer modified mortar, materials and design, 52, 459–469. belbachir, b. (2017). résistances mécaniques et durabilité des matériaux composites modifiés par ajout de polymères, thèse de doctorat es-science, université d’oran 1, ahmed benbella, oran, algérie. belbachir, b., benosman, a.s., taïbi, h. (2016). mineral-based composite materials for energy efficiency in buildings, key engineering materials (kem), 678, 123-134. benosman, a.s., latroch, n., belbachir, b., taibi, h., ayed, k., & mouli, m. (2015). matériaux composites mortier-polymère à bases des additions minérales : durabilité dans un environnement à tendance acide. rencontres universitaires de génie civil augc’15, 27-29 may, bayonne, france. https://hal.archives-ouvertes.fr/hal-01167753 benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2013). effect of addition of pet in the thermal properties of polymer-mortar composite materials, chemistry and materials research, 5, 21-26. benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2017). the chemical, mechanical and thermal properties of pet-mortar composites containing waste pet, environmental engineering and management journal, 16(7), 1489-1505. demirboga, r. (2003). influence of mineral admixtures on thermal conductivity and compressive strength of mortar, energy building, 35, 189-192. elalaoui, o. (2012a). optimisation de la formulation et de la tenue aux hautes températures d’un béton { base d’époxyde, thèse de doctorat en cotutelle, cergy-pontoise, france & université de tunis el manar, tunisie. elalaoui, o. ghorbel, e., mignot, v., & ben ouezdou, m. (2012b). mechanical and physical properties of epoxy polymer concrete after exposure to temperatures up to 250°c, construction and building materials, 27, 415–424. en 196-1. (2005). methods of testing cement part 1: determination of strength. european committee for standardization, cen. fu, x. & chung, d.d.l. (1997). effect of silica fume, latex, methylcellulose, and carbon fibers on the thermal conductivity and specific heat of cement paste, cement and concrete research, 27(12), 1799-1804. ghrici, m. (2006). etude des propriétés physico-mécaniques et de la durabilité des ciments à base de pouzzolane naturelle, thèse de doctorat d’état, ustmb d’oran, algérie. ghrici, m., kenai, s., mansour-said, m., & el-hadj kadri, a. (2006). some engineering properties of concrete containing natural pozzolana and silica fume, journal of asian architecture and building engineering, 5(2), 349–354. gouasmi, m.t, benosman, a.s., taïbi, h., belbachir, m., & senhadji y. (2016). the physico-thermal properties of mortars made of composite aggregates "pet-siliceous sand", journal of materials and environmental science, 7(2), 409-415. hamadache, m., mouli, m., bouhamou, n., chaib, o., benosman, a.s. & dif, f. (2014). he thermal properties of natural pozzolan and energy efficiency in buildings, journal of control science and engineering, 2(2), 120-127. https://hal.archives-ouvertes.fr/hal-01167753 belbachir et al., j. build. mater. struct. (2018) 5: 22-31 31 hassan, a.a.a., lachemi, m., & khandaker hossain, k.m.a. (2012). effect of metakaolin and silica fume on the durability of self-consolidating concrete, cement and concrete composites, 24 (3), 801–807. iso8302. (1991). thermal insulation, determination of steady-state areal thermal resistance and related properties--guarded-hot-plate apparatus. the international organization for standardization. on line at: https://www.iso.org/standard/15422.html. kaid, n., cyr, m., julien, s., & khelafi, h. (2009). durability of concrete containing a natural pozzolan as defined by a performance-based approach, construction and building materials, 23, 3457–3467. laoufi, l. (2015). comportement mécanique et structurel du béton dans un environnement agressif, thèse de doctorat es-sciences, enp-oran, maurice audin, algérie. laoufi, l., senhadji, y., & benosman, a.s. (2016). a study of natural pozzolan mortars exposed to sulfate as energy efficient building material, key engineering materials (kem), 678, 109-122. latroch, n., benosman, a.s., bouhamou, n., belbachir, b., senhadji, y., taïbi, h., mouli, m. (2016). testing of composite mortars based on supplementary cementitious materials: estimating durability and thermal properties, international journal of engineering research in africa, 27, 27-35. makhloufi, z., chettih, m., bederina, m., hadj kadri, e.l., & bouhicha, m. (2015). effect of quaternary cementitious systems containing limestone, blast furnace slag and natural pozzolan on mechanical behavior of limestone mortars, construction and building materials, 95, 647–657. neville, a.m. (1996). properties of concrete, fourth edition john wiley & sons, inc., new york, usa, 844. ohama, y. (1995). hand book of polymer-modified concrete and mortars: properties and process technology. building materials science series, noyes publications: usa, park ridge, n.j. p 236. ohama, y. (1997). recent progress in concrete-polymer composites, advanced cement based materials, 5, 31-40. senhadji, y., escadeillas, g., mouli, m., khelafi, h. & benosman, a.s. (2014). influence of natural pozzolan, silica fume and limestone fine on strength, acid resistance and microstructure of mortar, powder technology, 254, 314-324. siad, h., kamali-bernard, s., mesbah, h.a., escadeillas, g., mouli, m., & khelafi, h. (2013). characterization of the degradation of self-compacting concretes in sodium sulfate environment: influence of different mineral admixtures, construction and building materials, 47, 1188–1200. zhang, z., zhang, b., & yan, p. (2016). comparative study of effect of raw and densified silica fume in the paste, mortar and concrete, construction and building materials, 105, 82–93. https://www.iso.org/standard/15422.html j. build. mater. struct. (2019) 6: 20-31 original article doi : 10.34118/jbms.v6i1.65 issn 2353-0057, eissn : 2600-6936 microstructural studies of materials dd1 and kt2 by x-ray diffraction lakel a* laboratoire ttsm, université biskra, algérie. * corresponding author: lakel06@yahoo.fr received: 14-08-2018 accepted: 28-02-2019 abstract: in this work, we have studied two kaolin .kaolin dd1 which consists of two main phases (kaolinite and halloysite) and tamazert kaolin .kaolin kt2 whose main constituents are kaolinite, quartz and mica. our choice was set on the component that is kaolinite because of the existence of the latter in both kaolins. a correction of lorentz-polarization was carried out prior to the diffraction data, which has been achieved using lwl program dome. the true profile was extracted by this program. the methods used for the micro structural analysis of the present in the two kaolins are the warren averbach and the williamson – hall methods scherrer's relationship has been applied in cases where the compound is devoid of strains. the study revealed that the kaolin kaolinite dd1 is devoid of micro constraints. which similar analysis has shown that the kaolinite in kt2 incorporates the strains. this was confirmed by the williamson hall method as well as fourier analysis. the evaluation of strains in the kaolinite of kt2 has been dome the method of warren averbach and williamson – hall diagram. the average value of this constraint found by the first method us 0.15 and 0.21 by the second method gave. the average size of crystallites of the kaolinite in dd1 was found between 29 å and 230 å. by the method of warren averbach and about 118 å by the method of williamson hall. range the second kaolinite the kaolinite kt2, the size obtained was respectively 98 å and 130 å using to by methods. the study of the size distribution showed that the dominant size of kaolinite in dd1 and kt2 is about 40 å (42%) and 58 å (32%). respectively. key words: drx, lwl methods, crystallites size, microdéfomation, williamson-hall and warren & averbach methods. 1. introduction the microstructural parameters of a material (sizes, shape of the crystallites, external and internal stresses in the crystals) are generally obtained by first extracting the true profile of the sample using a deconvolution operation of profiles of diffraction lines for powdered compounds. for a microstructural study, the methods of rent, weigel and louboutin (lwl) and that of stokes are used in the deconvolution of the profiles of diffraction lines. these techniques are said to be rigorous because they do not make assumptions about the nature of the diffraction line profiles. nevertheless, they use the fourier coefficients to approximate the function of the 'true' profile of the diffraction peak. consequently, they are very sensitive to the number of these coefficients which implies the truncation effect (low number of coefficients) but also the cumulative error effect (large number of coefficients). for this reason, it is interesting to take into account the number of fourier coefficients concerning the x-ray diffraction peaks. the method best suited to this study, where there is a possibility of the presence of a double sizestress effect, is warren and averbach's method. the latter will be used in conjunction with the williamson-hall method (balzar, 1999; kamminga & seijbel, 2004; uvarov & popov, 2007; marinkovic et al., 2001; larson & von dreele, 2000; vives et al., 2002; williamson & hall, 1953; vives et al., 2004; rehani et al., 2006; mote, et al., 2012; langford et al., 1992; langford , 1978; wagner, 1966; rao & houska, 1986; klug & alexander, 1974). lakel, j. build. mater. struct. (2019) 6: 20-31 21 kaolins are part of the family of clays with montmorillonites, vermiculites, palygostites, the main phase constituting the kaolin is kaolinite or l’halloysite. often it is the older rocks, originally rich in feldspar, which decompose under the influence of reducing agents such as carbon dioxide, in kaolins and clays. all kaolin, formed by primary deposit contains beside hydrosilicate of alumina, kaolinite or halloysite, debris important rock undecomposed residue and non removed from the decomposition of which are essentially free quartz mica, magnetite, titanium minerals and other impurities hardly destructible. quality of kaolin depends on many other compounds that it contains kaolinite as well as the nature and concentration of impurities. often crude kaolins are directly usable in that state (in the case of kaolin-djebbel debbagh, eastern algeria), but they can also be enriched by kaolinite removal of all or part of the grading methods (case of kaolin tamazert, east algeria). 2. methods of analysis there are several methods to determine the microstructural parameters from the analysis of the peaks of x-ray diffraction. the methods based on the analysis of a single diffraction peak are constructed on fairly restrictive assumptions about the shape of the peaks and the contribution of the effects of size and shape. the warren-averbach method requires no assumption about the shape of the diffraction peaks, and it remains the most rigorous. however, it is very sensitive to the phenomenon of truncation profile and an overestimation of background noise. this method can lead to an error of 20-30% on the determination of the fourier coefficients and hence the microstructural parameters (ceretti, 2004). we have used this method in addition to one that is the williamson-hall (vives et al., 2006), which is used in case of presence of microstrain in the crystallites. 2.1. methods of evaluation of the size to calculate the average size, there are several methods in case the absence of micro strains in the sample. 2.1.1. relation of scherrer scherrer hasshownthatcuts her cristallites in the sample (when the latter does not contain of forced micro) vary in the opposite direction of the width of ray of diffraction. the relation enters those two sizes is given by (balzar, 1999): df = c λ ∕ β cos for widths specified in 2c is a coefficient which depends on the shape of the crystallites (langford et al., 1992) and can assume values between 0.8 and 1.39. for spherical particles, it is generally equal to 1. df = 1 ∕ β* for widths in units where reciprocal ɵ is the bragg angle, df is the average grain size, λ is the wavelength and β* is the integral width characterizing enlargement, expressed as the reciprocal lattice. 2.1.2. diagram williamson – hall this method applies to types of voightian or pseudo-voget profiles. it uses what is commonly called the willamson & hall graph (williamson & hall, 1953). this graph, to be a straight line, gives valuable information on the presence or absence of microstrain in the sample. the slope of the line indicates the presence of the latter (see figure 1). if the profiles are purely gaussian or purely voget, this method provides a very simple and fast way to evaluate the effects of constraint and size. for the other pseudo-voighal profiles, 22 lakel, j. build. mater. struct. (2019) 6: 20-31 approximations are necessary for the separation of these two effects (langford et al., 1992; langford, 1978; wagner, 1966). * =df + d* -df is the average grain size. d’ or: df = *d* fig. 1. diagram of shape williamson & hall. 2.1.3. method of warren averbach if the sample does not contain microstrain was: ad(l, s) = 0, therefore a(l , sn ) = as(l) =. the initial slope of the curve giving a(l , sn ) according to the length l columns is inversely proportional to the apparent size of the crystallites in a direction perpendicular to the plane (hkl) considered (see figure 2). this apparent size is given by the following equation (uvarov & popov, 2007): , or l = l with: ∆s = λ∕2 (sin2 sin1) 1 et 2are the values of the limit angles that define the profile. from the figure below, the point of intersection of the initial slope of the curve with the x-axis (l) provides the size df. fig. 2. fourier coefficients of as(l) as function of l. 2.2. measurement method constraints 2.2.1. method williamson – hall in the case of the presence of micro-stress, we use the following equation (williamson-hall), which allows to obtain the average crystallite size and an estimate of micro-stress (marinkovic et al., 2001): is the value associated with the constraint. 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8  d* *   0 ,   l n f dl slad d s 0 50 100 150 200 250 0,0 0,2 0,4 0,6 0,8 1,0)(la s f d l )/(sin)/1()/(cos  l f ed  le lakel, j. build. mater. struct. (2019) 6: 20-31 23 the diagram corresponding to this relationship (giving  * depending d *) is a straight line whose slope represents the average value of micro-constraints and whose intersection with the horizontal axis gives the average crystallite size. 2.2.2. method of warren – averbach the most valuable for the separation of the size effect and the effect of stress is that of warren averbach. recall that this method is based on the use of data in the form not of a single line but several lines corresponding to different levels of reflection of a family of plans. profile data are expressed in terms of fourier coefficients of real a (l, s) and the relationship between the average values of micro-stress and coefficient (larson & von dreele, 2000): i.e.: the coefficients as (l) which are obtained from this relationship, let be the average size of cristallites.la size s is equal to the reciprocal variable. we performed x-ray diffraction recordings on our kaolins advanced d8 diffractometer. for this, we follow the following steps. grinding the powder was done to make homogeneous grains. the powder is then deposited on the sample holder and pressed by a glass slide planar surface without too much pressure on the powder in order to avoid preferential orientations. it should be noted that the sample preparation is a critical parameter for obtaining quality results because the main information obtained from diffraction data are influenced by the sample. this information is: the position of the lines, the intensity of the lines, the line shape, the continuous background. once the powder deposited on the sample holder, it remains to start recording on the diffractometer. data recording is carried out on a predefined angular range with a pitch of 0.02 (2 and a counting time by less than three seconds. qualitative analysis by x-ray diffraction allowed from diffracting planes, highlighting the presence of kaolin dd1 main crystal phases as follows: table 1. diffraction planes of the two main phases of dd1. phase (hkl) 2 l’halloysite (010) (020) 12.36 29.28 la kaolinite (200) (300) (011) (201) 19.90 35.02 36.06 38.54 the same way as kaolin dd1, qualitative analysis by x-ray diffraction has highlighted the presence in kt2 kaolin, crystalline phases following table 2. table 2. plans diffraction phases present in kt2 phase (hkl) 2 kaolinite (100) (010) (200) (001) 12.40 19.88 24.94 38.52 quartz (201) 20.88 quartz+mica (101) 26.66 mica+kaolinite (011) 35.00 2222 2)(ln),(ln l s esllasl  22 21 2 122 )(2 ),(ln),(ln lss slasla e l     24 lakel, j. build. mater. struct. (2019) 6: 20-31 3. results and discussion application of the correction a few peaks our kaolin to see the effect of the application of lorentz-polarization correction, we chose to make the correction on a dozen peaks kaolins dd1 and kt2. we noticed that the peaks do not change significantly after correction for lorentz and polarization except for the first peak of each diffractogram which shows differences in a small part at the beginning of the peak. figure 3 shows the first peak (peak (010)), where we see the difference at the beginning of the peak and another peak (peak (100)) where we see the good superposition of the peak corrected and uncorrected peak. similarly, the same figure shows the first peak of the diffractogram kt2 (peak (100)) where the difference is visible in the early peak and a second peak (peak (020) where we see the significant effect of the correction lorentz-polarization. 10 11 12 13 14 0 2000 4000 6000 8000 10000 2 in te n s it y peak (010) of kaolin m1 corrected profile true profile 23.0 23.5 24.0 24.5 25.0 25.5 26.0 26.5 0 2000 4000 6000 8000 10000 2 in te n s it y peak (200) of m2 corrected profile true profile fig. 3. effect of correction lorentz-polarization peaks of some kaolins study corrects red black peak peak uncorrected. 3.1. diagram williamson – hall the williamson-hall diagram of kaolins m1 is given in figure 4. we represent the values of  /cos. *  as a function of  /sin * d . note that the curve is a straight line and the slope has a value that is negative. the negative value of this slope is probable due to the accuracy 23.5 24.0 24.5 25.0 25.5 26.0 26.5 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 2 in te n s it y peak (200) of kaolin m1 corected profile true profile 10 11 12 13 14 15 0 2000 4000 6000 8000 10000 2 in te n s it y peak (100) m2 corrected profile true profile lakel, j. build. mater. struct. (2019) 6: 20-31 25 of the data (obtaining the diffraction data, fitting, removal of the last point in the figure, ...). we therefore deduce that there are no substantial stresses in the kaolinite crystals. figure 5 shows the williamson-hall diagram of kaolin m2. note that the curve is a non-zero slope line. so there are micro-constraints in the sample. 0,30 0,35 0,40 0,45 0,50 0,55 0,60 0,65 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 d* b* fig. 4. wialliamson-hall diagram of kaolindd1. 0,0015 0,0020 0,0025 0,0030 0,0035 0,0040 0,0045 0,0050 0,10 0,15 0,20 0,25 0,30 0,35 kt2 b c d* b* fig. 5. diagram of williamson-hall of kaolin kt2. 3.2. evaluation of the microstrain of kaolin kt2 brut the relationships used in the warren & averbach method are: these relations can be used with harmonic lines. in our case, we have only two harmonics, they are: (001) and (002). we apply the method to the profiles of these two lines: 2222 2),(ln l d elssla  2222 2)(ln),(ln l s esllasl  26 lakel, j. build. mater. struct. (2019) 6: 20-31 for the peak (001) et : ( i ) for the peak (002) et l = 1 : the two previous relationships give the mean values of the size of the crystallites and of the micro-strain present in the sample: the estimated values for these strains are presented in table 3. the mean of the set is <el>= 0.15. table 3. : evaluation of the stresses exerted on the diffraction planes (hkl). l el 1 0,50 2 0,87 3 1,49 4 1,00 5 0,79 6 0,60 7 0,51 8 0,39 9 0,37 10 0,32 11 0,34 12 0,40 13 0,32 14 0,32 15 0,26 16 0,22 17 0,21 18 0,23 19 0,14 20 0,24 21 0,13 22 0,11 23 0,09 24 0,17 25 0,02 26 0,06 27 0,01 28 0,05 29 0,07 30 0,05 31 0,04 32 0,08 33 0,06 34 0,07 35 0,07 36 0,06 37 0,03 38 0,06 39 0,10 40 0,05 <el> 0.15 1l 2 1 2 )001( 2 )001( 2)1(ln),1(ln esasa s  2 1 2 )002( 2 )002( 2)1(ln),1(ln esasa s  )(2 ),1(ln),1(ln 2 )002( 2 )001( 2 )001()002(2 ss sasa e l     lakel, j. build. mater. struct. (2019) 6: 20-31 27 the williamson-hall diagram, shown in figure 4, provides the estimated value for these constraints : < el>= 0.21. 3.3. evaluation of size in kaolin kt2 brut from the relation 1 of warren and averbach, we find the values of the component as (l) of a (1, s). the values of these components are written in table 4. table 4. the value of the as component(l). l 1 30062 2 113961 3 211566 4 34602 5 45809 6 521 7 61602 8 77992 9 86551 10 980 11 103 12 1153 13 12161 14 1360 15 141611 16 15181 17 16302 18 17747 19 181 20 19587 21 20776 22 21993 23 225 24 2391 25 24681 26 251246 27 26751 28 27363 29 28499 30 29803 31 30133 32 31302 33 3259 34 3322 35 3486 36 35361 37 3683 38 371 39 3892 )(la s 28 lakel, j. build. mater. struct. (2019) 6: 20-31 fig. 6. variation of the fourier real coefficients a (l, s) as a function of l from this graph, we derive the value of the mean size of the crystallites in the kaolin m2. this value is: <df> = 92 å. evaluation of crystallite size in kaolin dd1 the average crystallite size of the kaolinite of m1 was calculated by the warren & averbach method 111 å. figure7 represents the variation of the coefficients of fourier based on l (harmonic number). fig. 7. variation of the fourier real coefficients a (l, s) as a function of l. 0 100 200 300 400 500 600 0,0 0,2 0,4 0,6 0,8 1,0 f d a s (l ) l 0 200 400 600 800 1000 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 f d a (l ,s ) l 0 500 1000 1500 2000 2500 3000 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 f d a (l s ) l (300) 0 100 200 300 400 500 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 f d a (l ,s ) l (201) -200 0 200 400 600 800 1000 1200 1400 1600 1800 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 f d a (l ,s ) l (011) lakel, j. build. mater. struct. (2019) 6: 20-31 29 table 5. the size of the crystallites of the kaolin dd1brut from the different diffraction peaks. the pics df (å) (200) 92 (300) 230 (011) 94 (201) 29 heightsiz<d> = 111 the average crystallite size of the kaolinite of dd1 was calculated by the scherrer125 å relation. table 6. the size of the crystallites of the kaolin dd1brut from the different diffraction peaks. the pics df (å) (200) 130 (300) 125 (011) 129 (201) 116 height size<df> = 125 å from the williamson-hall diagram, we derive the average values of crystallite size. the value found for this size is :d f = 118 (å). as can be seen, the three results obtained from the three methods are sufficiently close: by scherrer ' s relation: d f= 125 å. by the williamson hall diagram: d f= 118 å. by the method of warren & averbach: d f= 111 å. 3.4. size distribution of kaolinite present in dd1 the size distribution was estimated from the second derivative of the curveas(l)according to the harmonic number l. we used a second degree polynomial for the calculations. we give in the following table only the most common sizes (sizes dominant). table 7. size of the main phase dominant kaolin dd1. pics dominant size (å) (200) 32 (300) 35 (011) 40 (201) 42 3.5. size distribution of kaolinite present in kt2 and dd1 we calculated the size distribution of kaolinite in kaolin dd1. the value found for the dominant size is 40a. the distribution corresponding to this dominant size is of the order of 42%. the study of the size distribution of kaolinite in kaolin kt2 gave an average value of 58 å for the dominant size; it has a distribution of about 32% (lakel et al., 2013). 4. conclusion the methods for the determination of microstructural parameters from the analysis of the diffraction peaks were primarily developed for x-ray diffraction the warren-averbach method requires no assumption about the shape of the diffraction peaks and it is the most rigorous. 30 lakel, j. build. mater. struct. (2019) 6: 20-31 however, it is very sensitive to the phenomenon of truncation profile and an overestimation of background noise that can lead to an error of 20-30% on the determination of the fourier coefficients. in the method of sprauel, the fourier coefficients are determined by smoothing each diffraction pattern by a mathematical function (generally voigt), fitted to the experimental values by a least-squares optimization. in addition, this method allows to take into account the effects due to the heterogeneity of elastic deformations. the analysis is performed on two further orders of the same reflection. methods based on the analysis of a single diffraction peak based on fairly restrictive assumptions about the shape of the peaks and the contribution of the effects of size and shape. they are rather qualitative analysis methods, but quick and easy application. the results obtained in the simplest cases (isotropic cubic) are in agreement with those obtainable with the methods based on the analysis of two orders of reflection. 5. references balzar, d. (1999). voigt-function model in diffraction line-broadening analysis. international union of crystallography monographs on crystallography, 10, 94-126. ceretti, m. (2004). apport de la diffraction des neutrons { l’analyse des contraintes internes. habilitation à diriger des recherches, université de paris-sud, centre d’orsay, 7-17. kamminga, j. d., & seijbel, l. j. (2004). diffraction line broadening analysis if broadening is caused by both dislocations and limited crystallite size. journal of research of the national institute of standards and technology, 109(1), 65. klug, h. p., & alexander, l. e. (1974). x-ray diffraction procedures: for polycrystalline and amorphous materials. x-ray diffraction procedures: for polycrystalline and amorphous materials, 2nd edition, by harold p. klug, leroy e. alexander, pp. 992. isbn 0-471-49369-4. wiley-vch, may 1974., 992. lakel, a., bouyoucef, a., labii, t., guechi, n., guechi, i., boubertakh, a., & hamamda, s. (2013). microstructural study of some kaolin by warren-averbach and williamson-hall methods. first international conference on renewable energies and nanotechnology impact on medicine and ecology, icren 2013, algeria-constantine, february16-17, pp.169-177. langford, j. i. (1978). a rapid method for analysing the breadths of diffraction and spectral lines using the voigt function. journal of applied crystallography, 11(1), 10-14. langford, j. i., prince, e., & stalick, j. k. (1992). accuracy in powder diffraction ii. nist special publication, 846, 110-126. larson, a. c., & von dreele, r. b. (2000). report laur 86-748. los alamos national laboratory, new mexico, usa. marinkovic, b., avillez, r. r. d., saavedra, a., & assunção, f. c. r. (2001). a comparison between the warren-averbach method and alternate methods for x-ray diffraction microstructure analysis of polycrystalline specimens. materials research, 4(2), 71-76.. mote, v. d., purushotham, y., & dole, b. n. (2012). williamson-hall analysis in estimation of lattice strain in nanometer-sized zno particles. journal of theoretical and applied physics, 6(1), 6. rao, s., & houska, c. r. (1986). x-ray particle-size broadening. acta crystallographica section a: foundations of crystallography, 42(1), 6-13. rehani, b. r., joshi, p. b., lad, k. n., & pratap, a. (2006). crystallite size estimation of elemental and composite silver nano-powders using xrd principles, 44, 157-161. uvarov, v., & popov, i. (2007). metrological characterization of x-ray diffraction methods for determination of crystallite size in nano-scale materials. materials characterization, 58(10), 883891. vives, s., gaffet, e., & meunier, c. (2004). x-ray diffraction line profile analysis of iron ball milled powders. materials science and engineering: a, 366(2), 229-238. lakel, j. build. mater. struct. (2019) 6: 20-31 31 vives, s., gaffet, e., itié, j. p., & meunier, c. (2002). influence des conditions de broyage sur la nanostructure et le module de compression de poudres de fer. matériaux, 1-4 wagner, c. n. j. (1966). local atomic arrangements studied by x-ray diffraction. gordon and breach, new york, 219. williamson, g. k., & hall, w. h. (1953). x-ray line broadening from filed aluminium and wolfram. acta metallurgica, 1(1), 22-31. j. build. mater. struct. (2017) 4: 58-67 original article doi : 10.34118/jbms.v4i2.32 issn 2353-0057, eissn : 2600-6936 development of materials based on pet-siliceous sand composite aggregates gouasmi m.t.1,*, benosman a.s.1,2,3, taïbi h.1 1 faculty of exact and applied sciences, laboratory of polymer chemistry lcp, university of oran 1, ahmed benbella, bp 1524, el mnaouer, oran 31000, algeria. 2 higher school of applied sciences, essa-tlemcen, bel horizon, 13000 tlemcen, algeria. 3 department of civil engineering, laboratory of labmat, enpo maurice audin, oran, algeria. * corresponding author: m.t.gouasmi@hotmail.fr abstract. plastic waste recycling for the development of new building materials, such as cementitious composites, appears to be one of the best solutions to get rid of this type of waste. this operation has many economic and ecological advantages. the present study proposes some solutions for the recovery of plastic waste from pet (polyethylene terephthalate) bottles in order to obtain, after heat treatment at 290 °c followed by step cooling, a light composite material (pet-siliceous sand) with a hardness close to that of natural rock. the structure of the material obtained is characterized first; then the effect of this composite, with different substitution rates of natural aggregate, on the behavior of an industrial screed is studied. afterwards, some specific recommendations for the uses of this screed, and possibly of the composite itself, are given. although the main effects of certain polymeric additives on the mechanical properties of mortars are known, the mechanisms that are responsible for these effects are not yet well understood. techniques such ftir, xrd, sem and differential scanning calorimetry (dsc) are analytical tools that can be used for the characterization and expertise of this type of composites, particularly the industrial composite screeds. results from the present article enabled us to state that the composition of the materials obtained remains qualitatively unchanged and that no chemical interaction was observed between the mineral species and the waste pet lightweight aggregate (wpla) or the composite itself; in fact, no new compounds were formed. in addition, the differential scanning calorimetry (dsc) technique allowed us to conclude that the addition of wpla has an influence on cement hydration. the thermo-mechanical characterization of wpla made it possible to observe an excellent arrangement between the pet and siliceous sand. therefore, the development of wpla may be another solution for a number of applications in the field of eco-materials for construction and building. key words: green/eco composite; recycled materials; pet polymer; wpla (waste pet lightweight aggregate); microstructural analyses. 1. introduction in the field of construction, a screed is a mortar layer made of cement, resin or lime, applied on the ground and intended to flatten, level, come on a support and / or coat elements, such as a heating floor, and then to receive the upper layers, like tiles, a flexible floor, a floating or glued floor (fiches techniques g11, 2013). depending on the design and method of execution, two different types of screeds may be mentioned, namely the adhering screeds, which are incorporated or attached, and the floating screeds. the use of polymer waste in building materials has been evolving for decades. various kinds of screeds, composite mortars and concretes, plastic aggregates (alfahdawi et al. 2016; gu and ozbakkaloglu, 2016) and composite aggregates wpla (akçaözoğlu et al. 2013; choi et al. 2009; zuccheratte et al. 2017) have been formulated so far. these new applications came to respond to specific demands expressed by building and civil engineering professionals, in particular for the acoustic and thermal comfort and durability. gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 59 the aim of the present work is to present the results of a first experimental study on the characterization of the structure obtained using irtf, xrd, sem techniques as well as thermal analysis techniques, such as dsc, for building elements, like screeds made of composite aggregates (petsiliceous sand), which contain crushed pet waste. these composite aggregates are used as substitutes for natural aggregates in order to make an industrial composite screed. this represents an important contribution to sustainable development. some optimal substitution proportions have been studied as well in order to determine the feasibility limits, unlike what has been undertaken in previous works (alqahtani et al. 2014, 2017; choi et al. 2005, 2009; zuccheratte et al. 2017). in general, the wpla aggregate composites obtained seem to be inexpensive materials that could help solve some solid waste disposal problems, in addition to the energy gain they can generate. 2. experimental program 2.1 cement the type of cement used is matine 42.5 cpj cem ii/a, from lafarge cement plant, based in oggaz (north-west of algeria). this cement has a fineness of 4500 cm2/g, absolute density of 3.09 g/cm3 and average compressive strengths of 22 mpa at 2 days, and 48 mpa at 28 days. the chemical composition of cement, siliceous sand (ss) and calcareous sand (cs) as well as the mineralogical composition of clinker are given in tables 1 and 2, respectively. table 1. elementary chemical composition of cpj 42.5 cement, siliceous (ss) and calcareous (cs) sands, wt. % oxides cement ss cs sio2 17.40 83.29 11.76 al2o3 4.12 0.21 ‒ fe2o3 2.97 0.45 0.91 cao 61.15 7.03 44.35 mgo 1.16 4.2 ‒ k2o 0.66 ‒ ‒ so3 2.46 ‒ ‒ na2o 0.13 ‒ ‒ loi 8.85 ‒ ‒ cl0.017 ‒ ‒ caco3 ‒ 2.27 59.09 co2 ‒ 1.00 26 loi: loss on ignition. table 2. mineralogical composition of clinker (%w) c3s c2s c3a c4af 64 15 8 12.16 2.2 thermomechanical protocol for the preparation of the composite aggregate wpla (waste pet lightweight aggregate) it is a combination of a natural element, i.e. silica sand, and upgraded waste pet bottles. heat treatment followed by a stepwise cooling is required in order to have slices with hardness close to that of natural rock (figure 1a). these fragments undergo an industrial grinding, giving different granular fractions; the one used in this study is 0/0.3 (figure 1b). the chemical composition of silica sand used and the xrd analysis, mop picture of wpla microstructure are shown in table 1 and figures 1c.d, respectively. 60 gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 2.3 calcareous sand the calcareous sand (cs), which will be substituted by the composite aggregate wpla throughout this study, is a calcium-silicate sand from sech quarries of hasnaoui group, based at sidi ali benyoub (wilaya of sidi bel abbes, algeria). the chemical composition of the sand used, is shown in table 1. (a) (b) (c) (d) fig 1. (a) slices, (b) granular fractions, (c) xrd spectrum and (d) optical microscope picture (4.8x) of the wpla composite aggregate 2.4 test methods it was granular mixtures for the preparation of composite screed mortars were prepared from matine cement, and four combinations were obtained by partial and total replacement of the starting silico-calcareous sand by 25%, 50%, 75% and 100% by weight of the wpla composite aggregate previously prepared. for each formulation, the mixtures were prepared based on standard astm c109-11 (2011), in order to fabricate specimens with dimensions 5 × 5 × 5 cm3. these mixtures were composed of one third of binder (cement) and two thirds of aggregates with respect to the overall weight. these aggregates are calcareous sand and wpla. the water to cement (w/c) ratios used allowed for workability values between 85 and 105. the maneuverability of each type of the formulated mortars was measured according to standard astm c 1437 (2001), using the spreading table test. the molds containing the samples were covered with a plastic film and stored in the maturation cabinet of the laboratory. after 24 hours, the samples were unmolded and immersed in lime-saturated water (astm c511, 2006), for 28 days, at the temperature of 20 ± 2°c. the compression and flexural strengths of the samples were measured using a hydraulic press after 28 days (nfen 196-1, 2005). the characterization of the previous materials, conserved in water, was carried out using various analytical techniques, such as the differential scanning calorimetry (dsc) thermal analysis which was carried out in the laboratory of chiali group, located in the industrial zone of the town of sidi bel abbes. the apparatus used is a differential scanning calorimetric analyzer (dsc, netzsch dsc 200pc, with temperature rise ramps equal to 10 k / min, up to 600 °c, 0 10 20 30 40 50 60 70 80 0 500 1000 1500 2000 2500 3000 in te n s it y 2 theta scale composite wpla gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 61 under nitrogen flux).test samples of mortar, composite, siliceous sand and pet were analyzed according to linear heating, starting from ambient temperature up to 600 °c, with a heating rate of 10 k/min. the analysis of the samples was carried out on an attenuated total reflection (atr) patch, using a spectrum one perkinelmer ft-ir spectrometer. the ft-ir spectra were obtained by applying the ftir-atr infrared spectrometry technique to the samples for a few minutes. the sem and xrd analyses were performed using a hitachi tm-1000 apparatus and a bruker d8 advance diffractometer (cu-kα), respectively. 3. results and discussion 3.1 interpretation of ftir spectra of the composite aggregate and composite screed mortars the polymer pet is characterized by the presence of the following remarkable absorption bands (figure 2a): around 867.3 cm-1 (out-of-plane or para-disubstituted alternating cycle deformations), near 1095.8 cm-1, due to the vibrations of the -cobond, at 1577.9 cm-1 and 1616.1 cm-1, due to the vibration modes of the benzene ring, around 1715.8 cm-1, due to the grouping -coo-, at 2858.0 cm-1 and 2924.0 cm-1, characteristic of the bonds -ch2-, around 3002.2 cm-1, due to the valence vibrations ch of the benzene ring (figure 2a). it is important to mention that the amount of the valorized polymer (pet) is much less than that of silica sand in the wpla composite aggregate. this component (pet) is completely masked by the vibrations of the siliceous sand bonds. these vibrations are present in the spectrum of the wpla composite (in figure 2, presence of broad and intense absorption bands around 1200 cm1 1600 cm-1, and especially around 910 cm-1, which is characteristic of the si-o bond of silica, figure 2b). (a) (b) fig 2. (a) superposition of ftir spectra of pet and composite aggregate, (b) ftir spectra of siliceous sand. figures 3 and 4 display the superposition of ftir spectra of samples of pet, composite aggregate, wpla0 and wpla100. the spectra are distinguished by the presence of specific lines for pet, composite aggregate and wpla100. it is found that the characteristic lines of the waste pet lightweight aggregate (wpla) correspond exactly to those observed on the wpla100. the lines characterizing the pet are masked by those of the wpla composite, as shown in figure 4. 4000,0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 650,0 10,0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100,0 cm-1 %t pet composite pure 62 gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 fig 3. superposition of the ftir spectra of the samples wpla0, wpla100 and pet (gouasmi et al. 2017). fig 4. superposition of the ftir spectra of the samples wpla0, wpla100 and composite aggregate. all the spectra obtained for the composites showed the same lines, more or less intense, depending on the wpla composite aggregate content, as shown in figure 5. in view of the high number of results, it was necessary to reduce the number of spectra relating to samples wpla50 and wpla75. moreover, it was found that there is no chemical interaction between the inorganic compounds and the organic molecules, and therefore no new compounds were formed. this corroborates the results previously reported by benosman et al. (2012) and zuccheratte et al. (2017). fig 5. superposition of the ftir spectra of samples wpla0, wpla25 and wpla100. 3.2. scanning electron microscopy (sem) microstructural analysis the visualization of the microstructure of the pet-siliceous sand interface is illustrated in figure 6 (sem photo). the thermomechanical preparation of the wpla composite aggregates allowed having a good adhesion and an excellent arrangement between the plastic pet waste and siliceous sand, as shown in figure 6. fig 6. microstructure of the petsiliceous sand interface in the samples of the wpla composite using sem. 4000,0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 650,0 10,0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100,0 cm-1 %t 100%h2o 0 % h2o pet 4000,0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 650,0 10,0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100,0 cm-1 %t 100%h2o 0 % h2o composite pure 4000,0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 650,0 10,0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100,0 cm-1 %t 0 % h2o 25 % h2o 100 % h2o siliceous sand pet gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 63 3.3. differential scanning calorimetry (dsc) some research (kameche et al. 2009; nft01-021, 1974; platret and deloye, 1994) has reported the identification, by thermal analysis techniques, such as dsc, atd and atg, of cement hydration products such as c-s-h gel, portlandite, ettringite, gypsum and calcite. therefore, silva et al. (2002) used the atd analysis and showed the different changes resulting from the incorporation of ethylene vinyl acetate (eva) copolymer in composite materials. similarly, benosman et al. (2012) applied the atd technique and reported the different alterations resulting from the addition of polyethylene terephthalate (pet). the dsc curve (figure 7 a) relative to siliceous sand presents two peaks; one is endothermic, around 570 °c, and is due to the α-β phase transformation of quartz; the other one is exothermic and is found between 450 °c and 460 °c. polyethylene terephthalate (pet) is characterized by the three: vitreous, crystalline and melting phases corresponding to the three temperatures of 80 °c, 130 °c and 250 °c, respectively (figure 7 b). (a) (b) fig 7. dsc curves, with a heating rate of 10k/min, of: (a) siliceous sand, and (b) pet. the characterization of the wpla composite by the dsc technique (figure 8a) indicates the presence of pet, which is confirmed by the presence of an endothermic peak corresponding to the melting temperature around 250 °c and an intense exothermic peak between 460 °c and 520 °c (this peak is also observed in the case of siliceous sand). 64 gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 (a) (b) fig 8. dsc curves, with a heating rate of 10k/min, of: (a) wpla composite aggregate, and (b) wpla0 stored in fresh water. the dsc curves, obtained for all tests, are typical for hydrated cement pastes (figures 8b and 9). five major endothermic reactions occurred, during the sample heating, as follows: between 30 and 105 °c: free water and some of the adsorbed water escaped from mortar. it was completely removed at 105 °c, between 100 and 200 °c: various dehydration stages of c-s-h and ettringite were observed, at 140 °c: decomposition of gypsum caso4.2h2o, between 175 and 190 °c: hydration of calcium monocarboaluminate, between 470 and 500 °c: dehydration of portlandite ca(oh)2. gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 65 fig 9. differential scanning calorimetry (dsc) thermal analysis of wpla50 immersed in water. the incorporation of the wpla (pet-siliceous sand) composite into polyphase materials affects the dsc curve, as this can be seen in figure 9. peaks are observed: between 30 and 105 °c: free water and some of the adsorbed water escaped from mortar. it was completely removed at 105 °c, between 100 and 200 °c: various dehydration stages of c-s-h and ettringite were observed, an exothermic peak was found at 130 °c; it characterizes the crystallization temperature t°c of pet, around 140 °c: decomposition of gypsum caso4.2h2o, probably concealed by the peak of crystallization temperature tc° of pet, decrease in the intensity of the endothermic peak for the dehydration of calcium hydroxide ( 455 °c), the melting temperature of pet was observed at 255 °c, significant changes were noted on the dsc curve, for temperatures above 500 °c (an exothermic shoulder was detected between 510 and 520 °c). this is certainly due to the presence of the wpla composite, an endothermic peak was found around 565 °c, surely resulting from the transformation of the structure from quartz α into quartz β, indicating the presence of siliceous sand. these results confirm those previously reported by benosman et al. (2016). 4. conclusions on the basis of the above, the following conclusions can be drawn: analytical methods, such as ftir, xrd, sem and dsc, revealed that the composition of the materials studied remained qualitatively unchanged and that the chemical interactions between the mineral species and the wpla aggregate or the composite itself did not lead to the formation of new compounds. as part of a first attempt to evaluate an unknown material, the ftir spectrometry could provide a wealth of interesting information which was later confirmed by analytical means, better suited to the cases to be treated. from the thermogravimetric studies previously carried out, the results of which are illustrated by the dsc curves, it can be concluded that the addition of the pet-based wpla composite aggregate has an impact on the hydration of cement. 66 gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 the thermomechanical development of the wpla composite aggregates enabled us to obtain a good adhesion and an excellent arrangement between the pet plastic waste and siliceous sand. a rough surface of the composite aggregate was obtained; it exhibited better adhesion and a larger contact area between the wpla and the cementitious matrix (gouasmi et al. 2015a). thus, it can be said that the incorporation of pet lead to a densification of the cementitious matrix, and consequently a significant improvement in the durability of the material. the use of composite aggregates containing pet waste and siliceous sand in building materials seems to be feasible given the interesting results obtained during the analysis of their properties. positive results have been obtained by the author (gouasmi et al. 2015a,b, 2016) concerning the use of this composite aggregate in building materials. this study is certainly a valuable contribution to the pet waste recycling program and the reduction of pollution in order to preserve the environment. acknowledgments we would like to acknowledge the financial contribution within the framework of the algerian project cnepru b00l01un310120130068. the authors would also like to thank the hasnaoui group of companies, teknachem algeria and the late ahmed taleb. furthermore, the authors would like to warmly thank mr. m. benabadji for the proofreading and linguistic review of this paper. 5. references akçaözoğlu, s., akçaözoğlu, k., & atiş, c.d. (2013). thermal conductivity, compressive strength and ultrasonic wave velocity of cementitious composite containing waste pet lightweight aggregate (wpla). composites: part b, 45, 721–726. alfahdawi, i.h., osman, s.a., hamid, r., &. al-hadithi, a.i., (2016). utilizing waste plastic polypropylene and polyethylene terephthalate as alternative aggregates to produce lightweight concrete: a review. journal of engineering science and technology, 11(8) 1165-1173. alqahtani, f.k., ghataora, g., khan, m.i., & dirar, s. (2017). novel lightweight concrete containing manufactured plastic aggregate, construction and building materials, 148, 386–397. alqahtani, f.k., khan, m.i., & ghataora g. (2014). king saud university, synthetic aggregate for use in concrete. u.s. patent 8, 921, 463. https://www.google.com/patents/us8921463 astm c109/c109m. (2011). standard test method for compressive strength of hydraulic cement mortars (using 2-in. or [50-mm] cube specimens), astm, philadelphia, united states. astm c1437-01. (2001). standard test method for flow of hydraulic cement mortar, astm, philadelphia, united states. astm c511-06. (2006). standard specification for mixing rooms, moist cabinets, moist rooms, and water storage tanks used in the testing of hydraulic cements and concretes, astm, philadelphia, united states. benosman, a.s, mouli, m., taibi, h., belbachir, m., senhadji, y., behlouli, i., & houivet, d. (2012). mineralogical study of polymer-mortar composites with pet polymer by means of spectroscopic analyses. materials sciences and applications, 3(3), 139-150. benosman, a.s., taïbi, h., & mouli, m. (2016). performances mécaniques et durabilité des composites mortier-pet, recherche et développement dans la revalorisation et l’application des déchets du pet en génie civil. maison d’édition : editions universitaires européennes eue. choi, yw., moon, dj., chung, js., & cho, sk. (2005). effects of waste pet bottles aggregate on the properties of concrete. cement and concrete research, 35, 776-781. https://www.google.com/patents/us8921463 gouasmi et al., j. build. mater. struct. (2017) 4: 58-67 67 choi, yw., moon, dj., kim, yj., & lachemi, m. (2009). characteristics of mortar and concrete containing fine aggregate manufactured from recycled waste polyethylene terephthalate bottles. construction and building materials, 23, 2829-2835. fiches techniques, g11. (2013). les bétons : formulation, fabrication et mise en œuvre, ed, collection technique cimbéton, t.2, chap.1. pp. 22-25. gouasmi, m.t., benosman, a.s., taibi, h., & belbachir, m., & senhadji y. (2015b). effect of a composite aggregate on the durability of mortars. journal of chemistry and materials research, 3, 26–31. gouasmi, m.t., benosman, a.s., taïbi, h., belbachir, m., & senhadji y. (2016). the physico-thermal properties of mortars made of composite aggregates "petsiliceous sand". journal of materials and environmental science, 7(2), 409-415. gouasmi, m.t., benosman, a.s., taïbi, h., belbachir, m., senhadji, y., & mouli, m. (2015a). application des agrégats composites légers dans les mortiers : cas d’une chape industrielle. in proceedings of 2nd international symposium cimdd’2015, university m’hamed bougara boumerdes, algeria (910 nov.), (isbn: 978-9931-9090-6-2). gouasmi, m.t., benosman, a.s., taïbi, h., kazi tani, n., & belbachir, m. (2017). destructive and nondestructive testing of an industrial screed mortar made with lightweight composite aggregates wpla. international journal of engineering research in africa, 33, 140-158. gu, l., ozbakkaloglu, t. (2016). use of recycled plastics in concrete: a critical review. waste management, 51, 19-42. kameche, z.a., kazi aoual, f., semcha, a., & belhadji m. (2009). effets des hautes températures sur le comportement du béton: application au revêtement des tunnels. in the proceedings of the 1st international conference sbeidco, 1, 199, enpo oran, algeria, (12-14 oct.). (issn 2170-0095). nf en 196-1. (2005). methods of testing cement part 1: determination of strength, cen. norme nf t01-021. (1974). analyse thermique: vocabulaire présentation des résultats, décembre. platret, g., & deloye, f.x. (1994). thermogravimétrie et carbonatation des ciments et des bétons, acte des journées des sciences de l’ingénieur. 1, 273, giens, france (4-7 octobre). silva, d.a., roman, h.r., & gleize, p.j.p. (2002). evidences of chemical interaction between eva and hydrating portland cement. cement and concrete research, 32, 9, 1383-1390. zuccheratte, a.c.v., freire, c.b., & lameiras, f.s. (2017). synthetic gravel for concrete obtained from sandy iron ore tailing and recycled polyethyltherephtalate. construction and building materials, 151, 859-865. j. build. mater. struct. (2018) 5: 43-54 original article doi : 10.34118/jbms.v5i1.43 issn 2353-0057, eissn : 2600-6936 experimentation of a novel composite phase change material for thermal comfort improvement and energy saving in buildings boussaba l1*, makhlouf s2, foufa aa1 1 environment and technology for architecture and patrimonium laboratory, institute of architecture, saad dahleb university, blida 09000, algeria. 2 laboratoire de mécanique structure & energétique, faculty of construction engineering, mouloud mammeri university, tizi-ouzou 15000, algeria. * ccorresponding author: lisa.boussaba10@gmail.com received: 08-02-2018 revised: 24-03-2018 accepted: 08-04-2018 abstract. this study focuses on the preparation of a novel composite phase change material (pcm) for an application of latent heat thermal energy storage in buildings. the aim of this application is to improve thermal inertia in buildings. a good thermal inertia, involves the improvement of thermal comfort and energy saving. the experimented materials’ components are selected for their availability, safety and low cost. paraffin with a melting temperature range close to 30°c is selected as a pcm; it is composed of microcrystalline wax and liquid paraffin. the matrix is prepared from plaster, graphite powder and cellulose fibers. the pcm is introduced in the matrix following the immersion method. several samples are prepared; there after they are subjected to a thermal treatment at 50°c for 30 min on a filter paper. the purpose is to identify the performance of each sample to retain the pcm without leakages. thermal and physicochemical characterizations are performed to study the composites’ properties: scanning electron microscopy (sem) is used to observe its microstructure; x-ray diffraction (xrd) identifies the crystallographic structure of the composite-pcm while fourier transformed infrared spectroscopy (ft-ir) reveals the chemical compatibility between its different components. thermo gravimetric analysis (tga) and differential scanning calorimetry (dsc) are performed for thermal characterization. the thermal performance of the composite-pcm is verified experimentally using thermocouple measurements connected to a temperature recorder apparatus. the measurements are done simultaneously on two pellets; the first contains pcm while the second does not contain pcm. key words: composite-pcm, thermal inertia, buildings, thermal characterization, physico-chemical characterization. 1. introduction today, thermal comfort in buildings is mostly ensured using heating and air conditioning systems. however, the building sector becomes one of the leader consumers of fossil energies. it is also responsible for gas emissions which lead to greenhouse effect and global warming. thermal energy storage (tes) is known as a promising technique for energy supplying in the future. thermal energy may be stored as sensible heat or latent heat (garg et al., 1985). in buildings with massive masonry or concrete walls (voelker et al., 2008), the thermal comfort in the summer is ensured thanks to the high heat capacity of their massive components. in this case, the thermal comfort is obtained with the sensible heat storage (shs) concept. in contrast, the thermal comfort is not ensured with shs in lightweight constructions because of their low heat capacity. so, phase change materials (pcms) are used to ensure the thermal comfort with the latent heat thermal energy storage (lhtes) concept. unlike sensible heat storage, lhtes provides higher energy storage. researchers found that the use of pcms can provide a desirable alternative to rock storage (berroug et al., 2011) because in pcms systems, the heat is stored and mailto:email@email.com 44 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 released at a constant temperature (pasupathy et al., 2008). thus, the indoor temperatures in buildings are stabilized. for these reasons, the use of pcms for lhtes became a topic with a lot of interest within architects and engineers in the last decades (cabezaa et al., 2011) and recognized as an innovative energy saving strategy for a sustainable built environment (wahid et al., 2016). pcms are divided into three main groups: organic compounds, inorganic compounds and eutectics (sharma et al., 2009). the organic pcms include paraffin and fatty acids while the inorganic ones are salt hydrates. eutectics are mixtures of organic-organic pcms, inorganicinorganic pcms or organic-inorganic ones (pielichowska et al., 2014). each class of pcm has its own advantages and disadvantages. the organic pcms are the most used in the building industry because they are available in broad range of melting temperatures, chemically stable, non-corrosive and none supercooling but they have low thermal conductivity (sari and karaipekli, 2007). researchers have reported that there are three promising methods of incorporating pcms into the conventional building materials. these methods are: direct incorporation, immersion method and encapsulation (zhou et al., 2008); the first and the second methods are the simplest ones. in the present study, the immersion method of the experimented material in the melted pcm is followed. since the immersion consists of absorbing pcms into the internal pores of the building material, a composite material (based on mineral powder) for which the porosity is improved by the incorporation of cellulose fibers is prepared. it is known that wastes from industrial or agricultural productions lead the formation of pores when they are incorporated in building materials (bories et al, 2014). so in the present work, the incorporated fibers are obtained from recycling paper. the purpose is also to recover an organic waste material. the experimented material is then low-cost and environmentally ecofriendly. paraffin with a melting temperature range close to the temperature of human comfort (30°c) is chosen as a pcm for its safety and availability. despite its desirable properties, paraffin is an organic pcm which has low thermal conductivity (zalba et al., 2003). that is why graphite is added in order to improve the thermal conductivity. the prepared composite-pcm is characterized by a scanning electron microscopy (sem) to observe its microstructure. both x-ray diffraction (xrd) and fourier transformed infrared spectroscopy (ft-ir) are used for chemical characterization. the thermal characterization is done with differential scanning calorimetry (dsc) when thermo gravimetric analysis (tga) is used for the thermal reliability analysis. the thermal performance of the composite-pcm is verified experimentally on two pellets. the first contains the pcm while the second does not contain the pcm. the test is performed simultaneously on two samples using thermocouples measurement connected to a temperature recorder apparatus. 2. experimental 2.1. materials paraffin is an organic compound chosen as a pcm fig 1 (d) for its melting temperature range close to the temperatures of human comfort (30°c), its safety, availability and low cost. it is recovered from health facilities and pharmacies. a composite matrix composed essentially of plaster powder fig 1 (b) and cellulose fibers fig 1 (a) is prepared. graphite fig 1 (c) is added to the composite in order to improve its thermal conductivity. boussaba et al., j. build. mater. struct. (2018) 5: 43-54 45 table 1 displays the particle size parameters of the plaster used in the experiment and fig 2 shows its size distribution curve. the cellulose fibers are obtained from recycling of waste paper. it is introduced to the matrix in order to improve its porosity and its pcm absorption capacity. fig 1. the photographs of: a) cellulose fibers, b) plaster, c) graphite, d) paraffin. fig 2. the particle size distribution curve of plaster powder used in the experiment. table 1. particle size distribution parameters of plaster powder used in the experiment. sample d (0.1) d (0.5) d (0.9) s/g( m²/g) plaster powder values (ʯm) 0.707 5.186 43.699 2.9 2.2. preparation of the composite plaster/cellulose fibers/ graphite/ pcm before elaborating the composite-pcm, the matrix which supports the pcm is prepared first. so, components listed above (plaster powder, cellulose fibers and graphite) are mixed together. the purpose is to coat cellulose fibers with a thin layer of plaster powder and to make a regular distribution of graphite into the matrix. subsequently, the previous mixture is poured into the water. the resulting past is poured in a rectangular molded and a slight uniaxial compression is performed to form rectangular pellets. the pellets are dried in an oven at 100 °c for 24 hours. particle size distribution 0,1 1 10 100 1000 3000 particle size (µm) 0 1 2 3 4 5 v o lu m e ( % ) poudre de platre, jeudi 9 mars 2017 09:38:29 0 20 40 60 80 100 46 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 following the previous process, several samples with different mass fractions of components are prepared. the goal is to identify which matrix is able to contain the best rate of pcm without consequent leakages. the composite-pcm is prepared following the single face immersion method of the prepared pellets (the matrix) in the melted pcm. a thermal treatment is then performed on a filter paper at 50 °c for 30 minutes in order to test the performance of each sample to retain the pcm in its melted state. table 2 lists the absorption rates of the best pellets selected before and after thermal treatment. fig 3 (a) shows the pellet sample placed on a filter paper before the thermal treatment and fig 3 (b.1~b.5) shows the respective fat stains of pellets (compi~compv) obtained after thermal treatment on filter paper. table 2. pcm absorption rates of the selected samples. samples comp i comp ii comp iii comp iv comp v pcm absorption rate: before thermal treatment (wt %) 47.58 49.81 59.15 64.58 80.57 pcm absorption rate: after thermal treatment (wt %) 47.31 49.48 58.88 64.36 80.39 fig 3. photographs of: a) pellet sample before thermal treatment; b.1~b.5) the respective fat stains of compi~compv after thermal treatment. 2.3. characterization of the composite-pcm scanning electron microscopy (sem) is performed to observe the microstructure of the composite before and after its immersion in the pcm. the material is observed under different magnifications and 30 kv of tension acceleration. (fei quanta 650 sem) is used. both fourier transformed infrared spectroscopy (ft-ir) and x-ray diffraction (xrd) are carried out for chemical characterization. the ft-ir spectra of the different kbr pellets are recorded using (jasco ft/ir-4100 spectrophotometer) in a transmission mode under frequency range between 4000~400 cm-1. xrd pattern of the composite-pcm is obtained using (d2-phaser bruker x-ray diffractometer). the crystallographic structure analysis is done under cu-kɑ and (ʎ= 1.541874 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 47 å) irradiation. the thermal reliability of the composite-pcm is tested with thermo gravimetric analysis technique (tga); (sta pt 1600 of lienseis) thermo gravimetric apparatus is used for this purpose. the sample of 7mg is placed in an alumina crucible and tga test is performed from room temperature (20 °c) to 560°c with a heating rate of 10 °c/minute. (dsc q100 of ta instrument) apparatus is used for differential scanning calorimetry characterization (dsc). heating cycles are performed on both the pcm and the composite-pcm. (comp.v) is selected for the dsc test because of its best absorption rate of pcm. so, 8.4 mg of each the pcm and (comp.v) are placed in alumina crucibles and tested under nitrogen atmosphere (n2). dsc analysis is carried out with 5 °c/minute of heating rates from -10 °c to 60°c. fig 4 shows the schematic experimental protocol adopted for testing the difference in thermal performance between a sample which contains pcm and another sample which does not contain pcm. six thermocouples type k connected to the temperature recorder apparatus picolog tc08 are used. fig 4. procedure for measuring the thermal performance of the composite-pcm 3. results and discussion 3.1. morphology and microstructure of the composite fig 5 shows the esem photographs of the composite before the incorporation of the pcm, and the distribution of the pcm in the microstructure of this composite after the immersion process. fig 5 (a), (b), (c) show the morphology of the composite matrix under different magnifications (x9500, x2400, x100 respectively) before the incorporation of the pcm. as seen in fig 5, the matrix presents an accidental and rough microstructure. the adhesion of gypsum molecules to the cellulose fibers improves the roughness of the matrix. fig 5 (d), (e), (f) show the regular distribution of the pcm into the matrix and into the microstructure of cellulose fibers. the pcm is incorporated uniformly into the microstructure of its container. as a conclusion, the morphology of the composite matrix presents favorable properties for absorbing and containing the pcm in its microstructure. the pcm is absorbed and retained thanks to the capillary and surface tension forces of the matrix. 48 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 fig 5. esem photographs of: (a), (b), (c) microstructure of the matrix. (d), (e), (f) microstructure of the composite-pcm. a b c d e f boussaba et al., j. build. mater. struct. (2018) 5: 43-54 49 3.2. ft-ir for chemical compatibility analysis fig 6 shows the ir spectra of the composite-pcm and its components. ft-ir is performed in order to verify the chemical compatibility between the different components of the compositepcm. as seen from fig 6, cellulose fibers spectrum shows the presence of –ch2 bending peak at 1432cm-1. c6h10o5 is the chemical formula of cellulose (klemm et al., 2005). the peak reported at 1641 cm-1 corresponds to c-o bending. the bending peaks at 1100 cm-1 and 1500 cm-1 are related to c-h stretching vibrations. (hinterstoisser et al., 2001) studied ft-ir of cellulose fibers. the pcms’ spectrum displays characteristic absorption bands of alkanes at 2922 cm-1 and 2855 cm-1. the characteristic band reported at 1630 cm-1 corresponds to ch2 group. the peak at 1380 cm-1 refers to methyl groups which are hydrophobic groups. this result is confirmed by (peterson et al., 2008). it is observed in the composite-pcm spectrum the presence of specific peaks of c-h bands at 2847 cm-1 and 2914cm-1 wavenumbers. similar specific peaks are reported in the pcms’ spectrum at 2855cm-1 and 2922 cm-1 and at cellulose fibers spectrum. after comparison between the different obtained spectra, it is clearly visible that there is no shift in peaks of the compositepcm compared to those of its components. the result means that there is no chemical interaction between the different components of the composite-pcm. the combination is only physical. so, the material is chemically stable. 4000 3500 3000 2500 2000 1500 1000 500 0 10 20 30 40 50 60 t r a n s m it ta n c e % wavenumber (cm -1 ) pcm composite-pcm cellulose fig 6. ft-ir spectra of pcm, cellulose fibers and composite-pcm. 3.3. xrd for crystallographic structure analysis fig 7 shows the xrd pattern of the experimented composite-pcm. as can be observed from fig 7, the xrd pattern displays significant peaks at approximately all 3°, from 20°~32°. the peaks are reported at around (21°, 24°, 26°, 29°, 32°). the result can mean that the composite-pcm has a regular crystallization. the peaks become less distinguish than the first ones more than 32°. it can be related to the fact that the amount of the crystalline material decreased due to the melting of the pcm. so, the xrd peaks at (36°, 38°, 42°, and 48°) are caused by the plaster molecules. 50 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 fig 7. xrd pattern of the composite-pcm. 3.3. tga for thermal reliability analysis fig 8 shows the tga curve of the prepared composite-pcm. the curve displays weight loss stages of approximately 8 mg of the novel material as a function of temperature evolution. as can be seen from fig 8, the weight loss is really insignificant below 120 °c. the few weight loss reported at 100 °c corresponds to the evaporation of the water contained in the pores of the sample. the first stage of weight loss occurs between 180 °c~250 °c; it corresponds to the thermal degradation of paraffin. the weight loss reported at 260 °c to 340 °c is related to the deterioration of cellulose fibers. the last stage takes place more than 400°c and it corresponds to the deterioration of molecules of plaster. no weight loss of the experimented material is recorded below 100 °c. the result means that the material can be used for building applications without any risk of thermal degradation. as a conclusion, the composite-pcm is thermally stable in its working temperature range. 0 100 200 300 400 500 600 3 4 5 6 7 8 9 w e ig h t (m g ) temperature °c fig 8. tga curve of the composite-pcm. boussaba et al., j. build. mater. struct. (2018) 5: 43-54 51 3.4. dsc for thermal properties analysis fig 9 shows the dsc curves of the pcm and the composite-pcm. as can be seen from fig 9, two different peaks are distinguished on each curve of the pcm and the composite pcm. the first small peaks take place at around 10~15°c on both the dsc curve of the pcm and the compositepcm and they correspond to the solid-solid transformations of the pcm and the composite-pcm (srivastava et al., 1993). the second ones are more important than the firsts; they are reported at temperatures between 20°c to 40°c and they correspond to the melting peaks of the pcm and the composite pcm. as the pcm used is not a pure substance; there is no distinct melting point of the substance but a large band of fusion is recorded. the melting of the pcm starts at 21.75 °c and its fusion occurs at around 32.5°c with a latent heat of fusion of 183.99 j/g. the fusion of the composite-pcm begins at 23.05 °c and it takes place really at around 36°c with a latent heat of fusion of 130.57j/g. table 3 recapitulates the corresponding melting temperatures and the latent heat of fusion of both the pcm and the composite-pcm. table 4 compares the results of this study to those of other studies found in the literature. table 3. thermal properties of the pcm and the composite-pcm. samples melting points (°c) latent heat capacity (j/g) pcm (paraffin) 32.5 183.99 composite-pcm 36 130.57 table 4. comparison of thermal properties of the prepared composite-pcm with that of some other studies. samples melting points (°c) latent heats of fusion (j/g) references paraffin/montmorillonite/graphite. 45.3 112.79 kao et al. 2012 wallboard impregnated with methyl palmitate-stearate. 22.94 51.85 feldman et al., 1995 dodecanol/ montmonrillonite. 44.1 74.29 fang et al 2008 butyle stearate/ montmonrillonite. 26.5 79.25 fang et al 2006 composite plaster/ cellulose fibers/paraffin 32.5 130.57 this study… fig 9. dsc curves of the pcm and the composite-pcm. 52 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 3.5. thermal performance analysis of the composite-pcm fig. 10 shows the curves of temperature evolution inside two samples of the experimented materials: fig 10 (a) corresponds to the pellet which contains the pcm; fig 10 (b) is the curve of the pellet which does not contain pcm. the temperature evolution is measured using thermocouples placed in the same places of the two samples: the first thermocouples (1 and 6) are placed in the respective samples’ low faces which are in direct contact with the heat source. thermocouples (2 and 5) are placed in the middle layers of the samples (intermediate faces) and thermocouples (3 and 4) are placed on the samples (upper faces). as seen from fig 10, the temperatures of the three faces of the sample b (without pcm) exceed the temperatures recorded on the sample a (with pcm) with about 8°c. the temperature of the sample “a” is clearly lower than the temperature of the sample “b”. in addition, the temperature of the sample “a” remains constant over a fairly large time interval; it is due to the phase change process of the pcm from the solid state to the liquid state at a temperature of 32.5 °c. unlike the sample a, the stabilization of the temperature in the sample b at around 50°c is due to the action of the hotplates’ thermostat at 50°c. dsc analysis results confirm that the stabilization of temperature at 32.5°c in sample a is due to the phase change process. the result means that the incorporation of the pcm in traditional building materials improves significantly their thermal inertia. as a conclusion, the experimented composite-pcm has a good thermal inertia, so, it has the potential to be a good candidate for an application of improving thermal comfort in buildings and saving energy. fig 10. comparison of the temperature evolution into two samples: a) sample with pcm, b) sample without pcm. 4. conclusions this study encompassed the elaboration and characterization processes of a novel compositepcm for building applications. the composite-pcm is prepared from a matrix impregnated with paraffin (pcm) with a melting temperature range of 32.5°c. the matrix is composed of plaster, cellulose fibers and graphite. the pcm is incorporated in its matrix following the single face immersion process. esem micrographs show that the pcm is successfully confined in its matrix, it is uniformly distributed in the microstructure and it is retained thanks to the capillary and surface tension forces. the chemical characterization by ft-ir and xrd reveals that the novel composite-pcm is chemically stable. the result of thermal characterization by tga confirms that the material is 0 500 1000 1500 20 25 30 35 40 45 50 55 60 65 70 75 a) with pcm t e m p e r a tu r e ( ° c ) time (s) lower face intermediate face upper face 0 500 1000 1500 20 25 30 35 40 45 50 55 60 65 70 75 b) without pcm time (s) lower face intermediate face upper face boussaba et al., j. build. mater. struct. (2018) 5: 43-54 53 thermally stable above its working temperature range. the temperatures recorded on the novel composite-pcm compared to those recorded on the composite material without pcm after having exposed them simultaneously to a heat source; show that the composite-pcm has a higher thermal mass. 8°c of temperatures’ difference is recorded between the two samples; in addition the temperature of the composite-pcm remains constant over a time interval. as a conclusion, the ability of the composite-pcm to maintain the thermal comfort without air conditioning systems is evident and the energy needed for cooling may be saved. researches in this field may work to find other organic pcms as paraffin because of their excellent mixing properties with building materials. in addition, focused attention on searching the appropriate practical building applications of the composite-pcm must be made. 5. references berroug, f., lakhal, e. k., el omari, m., faraji, m., & el qarnia, h. (2011). thermal performance of a greenhouse with a phase change material north wall. energy and buildings, 43(11), 3027-3035. bories, c., borredon, m. e., vedrenne, e., & vilarem, g. (2014). development of eco-friendly porous fired clay bricks using pore-forming agents: a review. journal of environmental management, 143, 186196. cabeza, l. f., castell, a., barreneche, c. d., de gracia, a., & fernández, a. i. (2011). materials used as pcm in thermal energy storage in buildings: a review. renewable and sustainable energy reviews, 15(3), 1675-1695. fang, x., & zhang, z. (2006). a novel montmorillonite-based composite phase change material and its applications in thermal storage building materials. energy and buildings, 38(4), 377-380. fang, x., zhang, z., chen, z. (2008). study on preparation of montmorillonite-based composite phase change materials and their applications in thermal storage building materials. energy conversion and management, 49, 718–723. feldman, d., banu, d., & hawes, d. w. (1995). development and application of organic phase change mixtures in thermal storage gypsum wallboard. solar energy materials and solar cells, 36(2), 147157. garg h.p., mullick s.c., & bhargava a.k. (1985). solar thermal energy storage, d. reidel publishing company, dordrecht, holland. hinterstoisser, b., åkerholm, m., & salmén, l. (2001). effect of fiber orientation in dynamic ftir study on native cellulose. carbohydrate research, 334(1), 27-37. kao, h., li, m., lv, x., & tan, j. (2012). preparation and thermal properties of expanded graphite/paraffin/organic montmorillonite composite phase change material. journal of thermal analysis and calorimetry, 107(1), 299-303. klemm, d., heublein, b., fink, h. p., & bohn, a. (2005). cellulose: fascinating biopolymer and sustainable raw material. angewandte chemie international edition, 44(22), 3358-3393. pasupathy, a., velraj, r., & seeniraj, r. v. (2008). phase change material-based building architecture for thermal management in residential and commercial establishments. renewable and sustainable energy reviews, 12(1), 39-64. petersson, m., gustafson, i., & stading, m. (2008). comparison of microstructural and physical properties of two petroleum waxes. journal of materials science, 43(6), 1869-1879. pielichowska, k., & pielichowski, k. (2014). phase change materials for thermal energy storage. progress in materials science, 65, 67-123. sarı, a., & karaipekli, a. (2007). thermal conductivity and latent heat thermal energy storage characteristics of paraffin/expanded graphite composite as phase change material. applied thermal engineering, 27(8-9), 1271-1277. 54 boussaba et al., j. build. mater. struct. (2018) 5: 43-54 sharma, a., tyagi, v. v., chen, c. r., & buddhi, d. (2009). review on thermal energy storage with phase change materials and applications. renewable and sustainable energy reviews, 13(2), 318-345. srivastava, s. p., handoo, j., agrawal, k. m., & joshi, g. c. (1993). phase-transition studies in n-alkanes and petroleum-related waxes—a review. journal of physics and chemistry of solids, 54(6), 639-670. voelker, c., kornadt, o., & ostry, m. (2008). temperature reduction due to the application of phase change materials. energy and buildings, 40(5), 937-944. wahid, m. a., hosseini, s. e., hussen, h. m., akeiber, h. j., saud, s. n., & mohammad, a. t. (2017). an overview of phase change materials for construction architecture thermal management in hot and dry climate region. applied thermal engineering, 112, 1240-1259. zalba, b., marın, j. m., cabeza, l. f., & mehling, h. (2003). review on thermal energy storage with phase change: materials, heat transfer analysis and applications. applied thermal engineering, 23(3), 251-283. zhou, d., zhao, c. y., & tian, y. (2012). review on thermal energy storage with phase change materials (pcms) in building applications. applied energy, 92, 593-605. j. build. mater. struct. (2018) 5: 185-196 original article doi : 10.34118/jbms.v5i2.57 issn 2353-0057, eissn : 2600-6936 reaction kinetics of cassava starch graft anionic/nonionic-type polymer internal curing agents liu r j1,2,3*, sun zh 2, xiang wh1, chen p 1,3, zhou rz1 1 college of materials science and engineering, guilin university of technology, guilin 541004, p.r.c. 2 civil and environmental engineering department, university of louisville, louisville, ky 40292, u.s.a. 3 ministry-province jointly-constructed cultivation base for state key laboratory of processing for nonferrous metal and featured materials, guilin 541004, p.r.c. * corresponding author: liujin@glut.edu.cn received: 07-05-2018 accepted: 29-08-2018 abstract: internal curing can help to improve the durability of concrete by preventing and minimizing initial cracks due to autogenous shrinkage and plastic shrinkage. using a reliable internal curing agent is essential to the effectiveness of the internal curing process. this paper investigates the reaction kinetics of a starch graft anionic/nonionic-type polymer. the results demonstrate that initiator monomer concentration, and starch concentration are positively correlated with graft reaction rate rp. based on the research, the kinetics equation of this cassava starch graft anionic/nonionic-type polymer has also been developed, which coincides well with the law of free radical polymerization. the obtained rp equation is a firstorder dependence of the monomer concentration and the square root of the initiator concentration. and rp is further correlated to the reaction temperature based on a sigmoid function instead of a linear function. it is also found that the polymerization reaction is characterized by the coexisted disproportion termination and coupling termination. key words: free radical polymerization; graft reaction rate; kinetics; growth sigmoid curve; internal curing agent. 1. introduction concrete, as the most commonly used material, creeps and shrinks during its service life. concrete shrinkage, which causes volume change of the material, happens due to the loss of moisture (either internally or externally). it was found that the plastic shrinkage was the biggest reason for surface cracking of concrete pavements during the early age (mindess et al., 2003). early-age cracking is a predominant problem especially for high strength concrete/high performance concrete (hsc/hpc) due to the high autogenous shrinkage (self-desiccation) caused by its low water-to-cement ratio (w/c) and the usage of fine or ultra-fine mineral admixtures. these cracks would affect the durability and service life of concrete. therefore, concrete curing plays a vital role in guaranteeing the development of the mechanical properties and service life performance of concrete. in recent years, ideas of internal curing were proposed (philleo, 1991; weber & reinhardt, 1997; bentz & snyder, 1999; lura et al, 2014 ; jensen & hansen, 2001; jensen & hansen, 2002; igarashi & watanabe, 2006). internal curing is a process of providing concrete with additional water internally during the hydration process. this is done by using water absorbed in expanded shale, clay or slate (escs) lightweight aggregate(lwa)(weber & reinhardt, 1997; bentz & snyder, 1999; lura et al, 2014 ) to partially replace the conventional aggregates in the mixture; or by using superabsorbent polymers (sap) that would release water when needed during the selfdesiccation process (jensen & hansen, 2001; jensen & hansen, 2002; igarashi & watanabe, 2006). by compensating the moisture loss due to self-desiccation, cracking caused by early-age shrinkage can be minimized and the ongoing hydration can also be improved. 186 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 the effectiveness of internal curing is governed by the internal curing agents (ica) or internal curing materials (icm), such as lwa or sap that used. sap has been paid close attention to due to its high absorbency and its merit of swelling without dissolving in water. the present saps used in concrete are graft polymers made by starch, cellulose or the functional monomer such as acrylic acid, acrylonitrile, acrylamide (jensen & hansen, 2001 ; schröfl et al, 2012 ; assmann & reinhardt, 2014). controlling synthesis reaction is critical to acquire reliable icas. especially for starch graft type polymer ica, reaction kinetics strongly affects the stability of the reacting systems and the quality of the final icas. however, limited work has been done to report how to prepare stable and qualified starch graft type polymer ica through reaction controlling. lutfor et al. (2001) proposed several kinetics parameters and utilized ceric ammonium nitrate to investigate reaction kinetics of graft copolymerization of acrylonitrile and starch (rahman et al, 2000). they also deduced the graft copolymerization reaction rate and derived the relation formula for monomer concentration and graft rate. yu et al. (1999) studied the copolymerization kinetics of graft acrylonitrile onto starch by using benzoin ethyl ether as initiator, and derived the reaction rate equation and calculated the activation energy. they also deducted relative differential selective expression in the process of grafting under the experimental conditions. wang (2003), explored the relationship among the concentration of initiator, monomer, starch graft, and the reaction rate by utilizing butyl acrylate, starch, ammonium per sulfate and emulsifier sodium dodecylsulfate. he proposed a graft reaction rate equation at the beginning of the reaction when the concentration of initiator was low. similar research has been done by yang et al. (2006) who obtained a simplified kinetics equation for two parameter-type universal graft polymerization reaction with experimental data. these previous works on reaction kinetics mainly confine to binary starch graft copolymerization reaction system without considering the effect of temperature. recent research found that ternary starch graft system satisfies very well with the requirements of water absorbency, water retaining, and water releasing of icas because of its multiple functional groups (liu, 2003).therefore, knowing the reaction kinetics of the ternary graft system is useful to understand the relationship between the reaction systems and the quality of icas and is also helpful to control synthesis reaction. on the other side, temperature was also found to be a critical factor that closely related to molecular weight distribution, chain length, conversion of monomer, etc. (lipsa et al, 2013). therefore, temperature should also be included when modeling the reaction kinetics of a ternary starch graft system. in this study, a kind of ica called starch graft copolymer am-amps (stagaa) was developed. this ica uses cassava starch, acrylamide (am), and 2-acrylamide-2-methyl propyl sulfonic acid (amps) as the raw materials for the ternary system. based on the preparation of the stagaa, this paper attempts to further discuss how the related factors, such as concentration and temperature, affect the synthesis reaction. and the reaction rate equation for stagaa ternary graft copolymer was also developed in this study. this would serve the purpose to predict synthesis reaction with eligible explanation. 2. experimental details 2.1. raw materials there are four kinds of reagents used in synthesis process, which are starch, monomer, initiator agent, and crosslinking agent. the moisture content of the cassava starch, the skeleton of stagaa copolymer, was 11.2% and its side chain content was 83%. the molecular structure of the cassava starch is illustrated in figure 1. the amount of side chains plotted in figure 1a represents the amount of active graft sites. the higher content of the side chain would lead to more active chemical reaction with the monomer (moad & solomon, 2006).the c-c bond between c2 and c3 sites in the glucose ring is easy to break and then the hydroxide on c2 and c3 is easy to react (tong & zhang, 2005; zhang, 2001), as showed in figure 1b. rongjin et al., j. build. mater. struct. (2018) 5: 185-196 187 o o oh oh ch2 o oh oh ch2oh o o o oh oh ch2oh o oh oh ch2oh o o o o oh oh ch2oh o (a) structure unit o h h o o ch2oh oh oh h h 1234 5 6 (b) glucose ring fig 1. molecular structure of amylopectin cassava starch the used reagent monomers in stagaa synthesis process were of two kinds: acrylamide (am) that provides with nonionic amide group and 2-acrylamido-2-methylpropane sulfonic acid (amps) that provides with anionic sulfonic group. ammonium persulfate (aps) and n,n`methylenebisacrylamide (nmba) were used as an initiator agent and a crosslinking agent, respectively. 2.2. preparation of stagaa the stagaa copolymer was synthesized by aqueous solution method shown in figure 2. fig 2. flowchart of stagaa synthesis. first, the cassava starch was mixed and dissolved with distilled water, and then heated to 70~80 °c to gelatinize in a four-necked flask for about 30 minutes until the color turns colorless from white. then, the action temperature was lowered to 60~70 °c and aps was added for initiating for 30 minutes. next, am, amps and nmba were all dissolved in distilled water, and then dropped very slowly, and grafted and copolymerized for about 2 hours until a transparent or translucent gel-like substance was achieved. finally, the gel-like product was precipitated in alcohol, then filtered and washed with distilled water repeatedly, and dried at 105 ℃in a vacuum 188 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 oven to constant weight, then crushed and ground to the required fineness to obtain the stagaa powder. for the characterization purpose, part of the gel-like crude product was also put in a soxhlet extractor with isopropanoltoreflux and extract for 24 hours. the purified sample was subsequently dried to a constant weight to remove unreacted monomers. 2.3. determination of graft reaction rate in this study, the weight method was used to determinate the graft reaction rate, rp. firstly, a certain amount of the purified stagaa copolymer was put into concentrated hydrochloric acid by refluxing to fully eliminate the starch backbone. then, 1 mol/l sodium hydroxide solution was used to neutralize the residual hydrochloric acid and agno3 solution was used to be hydrochloric acid until the clis completely reacted. after that, the insoluble product was dried in a vacuum and its weight equaled the weight of monomer on the grafted side chain. the graft reaction rate, rp, can be calculated according to the following equation based on the side chain weight. (1) during the grafting reaction, several factors such as initiator concentration, monomer concentration, and starch concentration should be considered comprehensively, and rp can also be written as eq (2): [ ] [ ] [ ] a b c p r k a b c  (2) where k represents the rate coefficient; [a] is the initiator concentration (in mol/l); [b] is the monomer concentration (in mol/l); [c] is the starch concentration (in mol/l); a, b, and c are reaction orders, respectively. the logarithmic expression of the above mentioned eq (2) can be shown in the following equation: ln ln ln[ ] ln[ ] ln[ ] p r k a a b b c c    (3) according to the experimental data, there is a liner correlation between lnrpand ln[a], and the slope equals the coefficient a. similarly, when plotting the curve of lnrpversus ln[b] and ln[c] respectively, coefficient b and c can be obtained. given a certain temperature, reaction rate rp, reactants concentration [a], [b] and [c], reaction stages a, b, c, and the rate constant k can be obtained from eq (3). 3. results and discussion 3.1. ir analysis of stagaa in figure 3a, the absorption peak 3394.1 cm-1 presents the stretching vibration of alcohol oh group in cassava starch, while 2931.3 cm-1 marks saturated c h stretching vibration. peaks of 1421.3 cm-1, 1016 cm-1, and 1157 cm-1 represent asymmetric stretching vibration of c o c key symmetric in the glucose unit. in figure 3b, 3411.5 cm-1 shows that product retains the alcoholic alcohol oh group absorption peak but blueshifts; new "shoulder peak" 3208.8 cm-1 addresses the stretching vibration of imino group (= nh) in amps; for 1670.1 cm-1 and 1043.3 cm-1 , they are stretching vibration peak of carbonyl group c = o and s = o sulfonic group respectively. the above three characteristics are a clear indication that the monomer am and monomer amps were grafted onto the cassava starch and formed the anionic and nonionic polymer stagaa. grafted monomer weight onto side chain monomer molar mass reaction time ( / ) reaction volume p r mol l min     rongjin et al., j. build. mater. struct. (2018) 5: 185-196 189 fig 3. ir spectrograms of cassavastarch (a) andstagaa (b) 3.2. sem analysis of stagaa seen from figure 4a, cassava starch particles have spherical or hemispherical in shape and smooth surface, and its size varies widely. in figure 4b, stagaa obviously characterizes by wrinkled surface, and its assemble as a layered structure. its microstructure is clearly different from three-dimensional network of the common crosslinked sap (ren et al, 2012). according to the synthesis process and the surface morphology, the authors tentatively thought that the shape and its assemble state were formed as follows: the water-absorbed stagaas firstly lost internal water under the interaction with the environment, then the flexible strip or membrane stagaas gradually stacked, finally assembled as a special appearance of wrinkles. this kind of wrinkled surfaces and layered structure provides stagaas with a channel to absorb water and a lot of space to store water. 190 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 fig 4. morphology of cassava starch (a) and stagaa (b). 3.3. determination of early reaction time the monomer weight change grafted onto starch backbone has been recorded shown in figure 5. it shows that the mean monomer mass grafted onto starch backbone increases linearly with the increasing reaction time during the early 30minutes, but it increases slowly after that. this indicates that the reaction rate is approximately constant in early reaction time (30 minutes) and it can be considered as the initial reaction rate. rongjin et al., j. build. mater. struct. (2018) 5: 185-196 191 0 10 20 30 40 50 0.5 1.0 1.5 2.0 2.5 3.0 3.5 w e ig h t o f g ra ft in g s id e c h a in ( g ) reaction time (min) fig 5. curve of the grafted monomers weight changes with the reaction time 3.4. initiator concentration in the study, starch concentration [c] and monomer concentration [b] were first kept constant at 0.23 mol/land 1.5 mol/l. the material was reacted at 70 ℃ for 30minutes. the initiator concentration [a] was ranged from 0.01 mol/l to 0.012 mol/l. the fitting curve of lnrp is plotted in figure 6. it shows that the curve lnrp presents a positive linear correlation with ln[a] at early stage of the graft reaction. the linear correlation coefficient r2 was 0.998 using the least squares linear regression fitting. therefore, for the initiator, the reaction order (coefficient a in eq 3) was 0.509. 4.40 4.45 4.50 4.55 4.60 4.78 4.80 4.82 4.84 4.86 4.88 y = 2.53 + 0.509x r 2 =0.998 -ln[a] -l n r p fig 6. the relationship between -lnrp and -ln[a] it should be noted that when the initiator concentration increases, starch free radicals and monomer free radicals increase accordingly. thus, the number of graft reaction active center 192 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 increases, which accelerates the synthesis reaction. the chain termination process of the alkene monomers is controlled by the diffusion process (gugliemelli et al, 1972).when rp is proportional to the square root of the initiator concentration, it indicates that all the coupling reactions are terminated. however, it is difficult to realize the termination of all the coupling reactions because some free radicals are encased during the gel reaction process. in general, termination by disproportion and coupling coexist, and the graft reaction order of the initiator concentration ranges from 0.5 to 1.0 (0.5 for coupling termination, 1.0 for disproportionation termination). in this study, when the reaction order of initiator (coefficient a) goes up to 0.509, it means that both the disproportion termination and the coupling termination coexist and the latter takes a dominant position. 3.5. monomer concentration to find out the coefficient b in eq (3), the starch concentration [c] and the initiator concentration [a] were kept constant at 0.23 mol/l and 0.012 mol/l, respectively, and the material was reacted at 70 ℃ for 30 minutes. the monomer concentration [b] varied from 0.7 mol/l to 1.5 mol/l and the fitting curve of rp is presented in figure 7. -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 4.8 5.0 5.2 5.4 5.6 5.8 y = 5.35 + 1.13x r 2 =0.915 -l n [r p ] -ln[b] fig 7. the relationship between -lnrp and -ln[b] 3.6. starch concentration it can be seen that the curve of rp with [b] exhibits a positive linear correlation within the range that studied. the r2 is 0.915 and the reaction order (coefficient b in eq 3) is 1.135 for the monomer. this relationship indicates that low monomer concentration means monomer molecules have enough chance to cover the surface of the starch, so the active reaction center on the surface is relatively poor. within a certain range, the monomer amount caused by free radicals increases, thus rp increases significantly. in order to further study the relationship between rp and starch concentration [c], the monomer concentration [b] and the initiator concentration [a] were kept at 1.5 mol/l and 0.012 mol/l with the graft reaction at 70 ℃ for 30 minutes. the chosen starch concentration was changed from 0.03 mol/l to 0.23 mol/l. the correlation curve is shown in figure 8. it shows that the rp presents a good linear relationship with the starch concentration. with the r2 value of 0.999, the obtained reaction order is 0.506 (coefficient c in eq 3) for the starch. rongjin et al., j. build. mater. struct. (2018) 5: 185-196 193 1.5 2.0 2.5 3.0 3.5 4.8 5.0 5.2 5.4 5.6 5.8 6.0 y = 4.05 + 0.506x r 2 =0.999 -l n [r p ] -ln[c] fig 8. the correlation between -lnrp and -ln[c] this linear correlation is due to the fact that the reaction occurs mainly on the surface of starch molecules at first. then, with the increasing starch concentration, the active reaction sites on the surface of starch molecules will increase, which causes the significant increasing of rp. from the reaction orders of initiator concentration [a], monomer concentration [b], and starch concentration [c], the eq (2) of rp can be revised as follows:       0.509 1.135 0.506 p r k a b c  (4) 3.7. reaction temperature in order to investigate the influencing factors on the rate constant k, both the rp and k values are listed in table i when the reaction temperature t was changed from 50℃ to 80℃while the concentration of starch, monomer, and initiator constant were kept at 0.23 mol/l, 1.5 mol/l, and 0.012 mol/l, respectively. table 1. the relationship of the rp and k with t t (℃) 50 55 60 65 70 75 80 (k) 323.15 328.15 333.15 338.15 343.15 348.15 353.15 rp×103 1.079 1.576 2.988 5.01 7.905 8.295 8.412 k(min-1) 0.0136 0.0199 0.0377 0.0631 0.0997 0.1046 0.1061 the table indicates that both rp and k increase with the increasing reaction temperature. however, the rp value increases slowly when temperature increases from 50 to 55℃, it increases notably faster after that. this is due to the faster initiator (nh4)2s2o8 decomposition rate caused by the higher temperature. when the initiator produces more free radicals, the increased grafted monomer leads to the higher number of free radicals, causing graft reaction chain initiation and chain growth rate to increase correspondingly. at the same time, the higher temperature is beneficial to the starch gelatinization and the increase of active sites on the starch molecule surface, which makes the rp to increase in the end. 194 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 according to table 1, the relationship between the rate constant k and the temperature t (in kelvin) is plotted in figure 9. instead of a linear relationship proposed by lutfor et al. (2001) and wang (2003), it can be seen from the figure that the k-t relationship satisfies a sigmoid function. the rate constant, which should be called rate coefficient, increases slightly within the low and high temperature ranges, but it increases sharply during intermediate temperature section. this indicates that the copolymer reaction of starch-graft-am-amps is more complex than ordinary radical copolymerization. since a ternary starch graft system is easier to form gel for copolymerization, the reaction temperature of stagaa should not be limited to the range from 60 to 70℃. 320 325 330 335 340 345 350 355 0.00 0.02 0.04 0.06 0.08 0.10 0.12 k=0.10583-0.09462/(1+exp((t-337.298)/3.2769) ) r 2 =0.9888 k t (k) fig 9. the fitting curve of k with t this relationship can also be expressed by eq (5), where the correlation coefficient r2 is 0.9888.    / 1 0 337.289 / 3.276.10853 0.0 2 9946k exp t    (5) the final expression for rp (eq 4) can be rewritten as follows:            0.509 1.135 0.506 / 1 337.289 / 3.27690.10853 0.09462 p r exp t a b c     (6) as eq (6) includes the effect of temperature on starch graft reaction, it provides the production of such a starch graft copolymer with a solid background of the influence of processing condition on material reactivity in the future. this result is supported by the experimental data and can be used to verify the reaction kinetic related to the draft fractions of am and amps on cassava starch. 4. conclusion based on the represented research, following conclusions can be drawn. first, the developed reaction kinetics model for starch-graft-am-amps copolymer can be expressed as:            0.509 1.135 0.506 / 1 337.289 / 3.27690.10853 0.09462 p r exp t a b c     which agrees well with the law of free radical polymerization. the factors of initiator concentration [a], monomer concentration [b], starch concentration [c] are positively correlated rongjin et al., j. build. mater. struct. (2018) 5: 185-196 195 with rp. when the correlation between temperature and rp is considered specifically, it can be expressed with a sigmoid function instead of a linear function. the research also found that the synthesis reaction of stagaa copolymer is characterized by disproportion termination and coupling termination. both terminations coexist and the latter is the dominant reaction format. acknowledgements this research was financially supported by the national natural science foundation of china (51202039, 21566008), national science foundation of guangxi (2014gxnsfaa118314) and science and technology development plan of guangxi (1348011-2). the support from the civil and environmental engineering department at the university of louisville is also appreciated. 5. references assmann, a., & reinhardt, h. w. (2014). tensile creep and shrinkage of sap modified concrete. cement and concrete research, 58, 179-185. bentz, d. p., & snyder, k. a. (1999). protected paste volume in concrete: extension to internal curing using saturated lightweight fine aggregate. cement and concrete research, 29(11), 1863-1867. gugliemelli, l. a., doane, w. m., russell, c. r., swanson, c. l., arcand, c. g., & vullo, w. j. (1972). 2264201. starch-cerium (iv) complexes in aqueous media: formation, isolation, and stability. journal of polymer science: part b: polymer letters, 10(6), 415-421. igarashi, s. i., & watanabe, a. (2006). experimental study on prevention of autogenous deformation by internal curing using super-absorbent polymer particles. in international rilem conference on volume changes of hardening concrete: testing and mitigation (pp. 77-86). rilem publications sarl. jensen, o. m., & hansen, p. f. (2001). water-entrained cement-based materials: i. principles and theoretical background. cement and concrete research, 31(4), 647-654. jensen, o. m., & hansen, p. f. (2002). water-entrained cement-based materials: ii. experimental observations. cement and concrete research, 32(6), 973-978. lipsa, r., tudorachi, n., vasile, c., chiriac, a., & grigoras, a. (2013). novel environmentally friendly copolymers carboxymethyl starch grafted poly (lactic acid). journal of polymers and the environment, 21(2), 461-471. liu r. j. (2003). preparation and properties of organic-inorganic multiple concrete internal curing materials. ph.d. thesis. wuhan university of technology, wuhan. lura, p., wyrzykowski, m., tang, c., & lehmann, e. (2014). internal curing with lightweight aggregate produced from biomass-derived waste. cement and concrete research, 59, 24-33. lutfor, m. r., rahman, m. z. a., sidik, s., mansor, a., haron, j., & yunus, w. w. (2001). kinetics of graft copolymerization of acrylonitrile onto sago starch using free radicals initiated by ceric ammonium nitrate. designed monomers and polymers, 4(3), 252-259. mindess, s., young, j. f., & darwin, d. (2003). concrete, 2nd ed. upper saddle river: new york, pp.t22 moad g., solomon d. h. (2006). the chemistry of radical polymerization, 2nd ed. elsevier, amsterdam. philleo, r. (1991). materials science of concrete ii. american ceramic society, westerville, oh, usa, 1-8. rahman, l., silong, s., zin, w. m., rahman, m. z. a., ahmad, m., & haron, j. (2000). graft copolymerization of methyl acrylate onto sago starch using ceric ammonium nitrate as an initiator. journal of applied polymer science, 76(4), 516-523. ren, h., niu, z., wang, j., & ning, j. (2012). comparison of traditional methods and microwave irradiation method about amylum/acrylic acid/acrylamide polymerization. edited by ailton de souza gomes, 87. schröfl, c., mechtcherine, v., & gorges, m. (2012). relation between the molecular structure and the efficiency of superabsorbent polymers (sap) as concrete admixture to mitigate autogenous shrinkage. cement and concrete research, 42(6), 865-873. 196 rongjin et al., j. build. mater. struct. (2018) 5: 185-196 tong q. y., zhang g. w., (2005). graft polymerization of acrylonitrile and amps onto starch initiated by [mn(h2p2o7)3]3. polym. mater. sci. eng. 21(1), 106-109 wang, b. j. (2003) study on the synthesis and kinetics of starch-based graft copolymer. ph.d. thesis, nanjing university of technology, nanjing. weber, s., & reinhardt, h. w. (1997). a new generation of high performance concrete: concrete with autogenous curing. advanced cement based materials, 6(2), 59-68. yang, b., zhao, y. l., yang, w. m., & wang, j. y. (2006). kinetics equation of radiative graft copolymerization of starch and acrylamide. yunnan chemical technology, 33(3), 8-10. yu, f. q., yao, s., & liu, y. (1999). kinetics of graft copolymerization of an onto corn starch under uv light. polym. mater. sci. eng., 15(5), 62-65. zhang y. p., (2001). manufacture and application of modified starch. chemical industry press, beijing. j. build. mater. struct. (2019) 6: 39-49 original article doi : 10.34118/jbms.v6i1.67 issn 2353-0057, eissn : 2600-6936 effect of natural pozzolan and calcined paper sludge as pozzolanic additions on the physicals and mechanicals properties of heat treated self-compacting mortars ghernouti y*, safi b, rabehi b research unit: materials, process and environment, university m’hamed bougara of boumerdes. algeria. * corresponding author: y_ghernouti@yahoo.fr received: 26-01-2019 accepted: 16-03-2019 abstract: the aim of this research work was to investigate the effect of thermal treatment on strength development of self-compacting mortars (scms) based on two pouzolanic materials: natural pozzolan and calcined paper waste sludge, were used in the binders of scms. to evaluate the effect of heat treatment, a serial of the specimens were exposed to room temperature and another serial were exposed to heating regime (at temperature 60°c for a period of 14 h). the fresh and hardened properties of all mortars were evaluated. the obtained result show that the mechanical strength at 14 days of all mortar treated are almost similar or sometimes better to those not treated mortars tested at 28 days, which reduces the curing time for precast elements. key words: heat treatment, self-compacting mortars, pozolanic materials, calcined paper sludge. 1. introduction presently various types of by-product materials, such as fly ash, silica fume, rice husk ash, and others have been widely used as pozzolanic materials in concrete. their utilization not only improves concrete properties, but also preserves the environment. fly ash (fa), and silica fume (sf) are among the most effective mineral additives used in cement or concrete because of their cementitious or pozzolanic properties (barnett et al., 2004; aci 233r-03, 2003; bijen, 1996; escalante-garcıa & sharp, 2001). however, they exist other industrial by-products. recently, it was shown that the calcined silt of dam has a pozzolanic potential which gives it be used as additive. safi et al., (2011; 2012) showed that the introduction of 10% calcined silt (cs) of selfcompacting mortars with of ground granulated blast-furnace slag (ggbs) (30%) has a positive effect on the rheological behavior and the development of strength. based on the experimental work conducted by ahmadi and al-khaja (2001), it can be concluded that the sludge waste generated from the paper manufacturing industry can be successfully utilized as a replacement for mineral fillers in concrete mixes for non-structural masonry construction. banfill and frias (2007), studied the effects of calcined paper sludge as an alternative source of metakaolinon on the rheology and conduction calorimetry of cement pastes and compared to the effects of commercial metakaolin. the effects are similar and the results show that calcined paper sludge has the potential to be used as a supplementary cementitious material. frías et al., (2008), in their study shows the effect of calcination clay wastes from an art paper sludge for the use as supplementary cementing materials in blended cements. the starting clay sludge was calcined at 600, 650 and 700 °c between 2 and 5 h, kaolinite was transformed into amorphous metakaolinite. the study reveals that calcination at 650 °c for 2 h is recommended to obtain a good supplementary cementing material for manufacture of blended cements. lin et al., (2010), investigate the pozzolanic reactions and strength properties of waste brick-blended cements (wbbc) in relation to various replacement ratios (0–50%). the experimental results indicate that 10, 20, 30, 40 and 50% of cement can be replaced by waste 40 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 brick, which causes the initial and final setting times to increase. compressive strength development was slower in waste brick-blended cement (wbbc) pastes in the early ages; however, strength at the later ages increased significantly. also, the brick waste (gwb) was the subject of several studies. the results obtained by naceri, a., & hamina (2009), show that the addition of artificial pozzolan improves the setting times of the cement and the mechanical characteristics of mortar. in their work, a substitution of cement by 10% of waste brick increased mechanical strengths of mortar. in the manufacturing field of the precast elements, companies always tried to reduce the time of preparing these elements while maintaining the quality of concrete. so, to ensure a gain of time, and significantly reducing the setting time of concrete, the parboiling (drying) process is often used for this. due to high demand production of construction elements, the concrete industry has often resorted to use of temperature (erdoǧdu & kurbetci, 1998; neville, 2000). several methods are developed and applied in order to have a short period of realization and a sufficient resistance levels. a rise in temperature greatly accelerates the cement hydration reactions and affects advantageously the short term resistance. it also reduces the dormant period of hydrates and the overall structure of the hydrated cement paste is running at an advanced time. indeed, an initial rapid rate of hydration due to higher temperatures causes a no uniform distribution of hydrated products (verbeck, 1968; kjellsen, 1996). in the construction of large structural concrete elements where heat dissipation is slow, there can be a significant rise in temperature within the first few days after casting due to the exothermic. the main objective of this investigation is to valorise two various pouzolanic materials: natural pozzolan (np) and calcined paper waste sludge (cps) in the formulation of self-compacting mortars (scms) in order to investigate the effect of the drying temperature on the strength development of self-compacting mortars (scm) heat-treated at 60°c for 14 hours for every age. the results of these tests were compared with those obtained at 20°c (room temperature). 2. experimental investigations 2.1 materials used the cement used in this work is ordinary portland cement (pc) equivalent to cem ii 32.5r type. natural pozzolan (np) and a metakaolin as calcined paper sludge (cps) at 750°c for 5 hours obtained from a paper manufacturing industry are used as cementitious additions with particles sizes less than 80μm. the chemical compositions of all cementitious materials and mineralogical composition of cement are shown in table 1. natural ground sand of 3 mm maximum particle size was used as fine aggregate. the sand has a specific gravity of 2.65 g/cm3, a fineness modulus of 2.1 and its water absorption value is 5.1%. a polycarboxylate-based superplasticizer named “viscocrete tempo 12” was used to achieve the required workability of the (scms) mixes. table 1. chemical compositions of cementitious materials and mineralogical composition of portland cement portland cement (pc) natural pozzolan (np) calcined paper sludge (cps) sio2 21.1 32.4 21.7 al2o3 4.2 11 12.6 fe2o3 5.3 7 4 cao 61.8 16.6 22.8 mgo 2.3 5.3 4.3 so3 2.0 0.8 1.2 k2o + na2o 0.6 4.6 1.3 c3s 58 c2s 18 c3a 06 c4af 13 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 41 preparation of metakaolin after drying in an oven at 105°c, the paper sludge (ps) was crushed and sieved through dry. the calcination temperature is in the range of 750 °c for 5 hours. the the product obtained (calcined clay) was kept away from air and humidity. particles passing 80μm and represent more than 95% is recovered for later use in the preparation of scms. 2.2. mixture proportions and preparation the self-compacting mortars (scms) were established made using the design method of concrete equivalent mortar (cem) developed by schwartzentruber & catherine (2000). the comparative study of (scm) without addition and (scms) containing pouzzolanic materials was carried. three compositions of scms mixes were prepared, a reference self-compacting mortars (scm) without addition and two (scms) containing pouzzolanic materials as an additions. for all the mixtures, the total amounts of cement, sand, water and superplasticizer were all kept constant, there are in the order of 558kg/m3, 1349kg/m3, 276kg/m3 and 9.2kg/m3 respectively. for the two compositions of scms mixes with addition were prepared at the water–binder ratio is keep constant (w/b= 0.45) and the addition-cement ratio is also keep constant (a/c= 0.10). the notation of the scms mixtures are given as follows: scm: control mortar; scm (np): mortar with natural pozzolanic, scm (cps): mortar with calcined paper sludge. 2.3. mixing, casting, curing and testing specimens after mixing process scms, from each mortar mixture, thirty (30) specimens were cast in prismatic molds (40×40×160) mm3. the samples were used for the flexural and compressive strength tests at 3, 7, 14, 21 and 28 days of curing. before casting, a slump test was carried on each mortar mixture. one day after casting, fifteen (15) specimens were stored in a room temperature (under 21±1°c) and fifteen other specimens were heat treated. the total time of application temperature is 18 hours. the application of temperature involves three steps: a preheating step of 2h, after that, maintaining a constant intermediate temperature (60°c) for a period of 14 hours. the cooling is effected in the same way that the rise. it was noted that one day before each testing age, the specimens were subjected at this thermal treatment. after each treatment, a various tests and measurements were carried on mortars out in order to study physical properties (bulk density, weight loss) and mechanical properties (flexural and compressive strength), at different ages (3, 7, 14, 21 and 28 days). the mechanical strengths were determined on specimen’s heat treated and another that not heat treated and that in order to evaluate the influence of heat treatment (drying temperature) and the age of samples on the mechanical characteristics of scms based on various pozzolanic materials. 3. experimental results and discussions 3.1. pozzolanic reactivity of additions used the study of the pozzolanic reactivity of the additions used was inspired by the test chapel (chinjemelo & billong, 2004; bénoît, 1967). this test consists to determine the difference between the initial and final concentration of lime solution. it also allows determining the rate of cao fixed by the additions. the results of the pozzolanic reactivity of all additions are presented in figure 1. the pozzolanic reactivity is indicated by the amount of cao fixed by the additions. all results of the samples show a decrease of the concentration of cao in the lime solution of at least 74%. this decrease is more advanced in natural pozzolan (np) and calcined paper sludge (cps) is of the order of 76.3% and 74.5% respectively. the natural pozzolan is a material known by its reactivity with pozzolanic its contains amorphous silica that will react with the portlandite ca(oh)2 released during the hydration of cement. 42 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 metakaolin obtained from paper sludge, has a pozzolanic reactivity relatively high and which has the value closest to that of natural pozzolan. the calcination of clays at 750°c allows the departure of the water content (the dehydroxylation) and the formation of metakaolin (samet et al., 2007; michel, 1989) with an amorphous structure which makes it more reactive than the clay. this explains the strong decrease in cao concentration of the solution. the heat treatment causes the transition of the crystalline phase and orderly (kaolinite) in a disordered phase (metakaolin) by a collapse of the crystal structure. metakaolin is considered a good synthetic pozzolans, due to its particular reaction with lime in the presence of water to form compounds of the silicate and aluminate of calcium hydrates (wild & khatib, 1997; frıas etal., 2000; poon et al., 2001). fig. 1. pozzolanic reactivity of all additions. 3.2. fresh properties 3.2.1. workability the fresh properties of all studied mortars were evaluated by the slump test using a mini-cone. the slump value is the average diameter of spreading of mortar. the results of slump value of all scms mixtures are represented in the histogram of figure 2. in fluidity terms, all scms mixtures have a satisfactory slump flows which suitable for self-compacting concrete. the slump value is in the range of 28–32 cm which is a good deformability. the results indicate that the slump flows of all mixture mortars are similar. figure 3, presents the photography of the slump flow test off all scms mixtures. fig. 2. mini-slump for all scms mortars mixes. 76.3 74.5 0 20 40 60 80 100 np cps p o zz o la n ic r e a ct iv it y ( % ) 26 27 28 29 30 31 32 33 scm scm (np) scm (cps) m in isl u m p ( cm ) ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 43 fig. 3. photography of slump flow of various scms mortars mixes: (a) scm, (b) scm(np), (c) scm(cps). 3.2.2. bulk density fig 4, shows the bulk density evolution of all mortars. according these results, the recorded density is relatively high for mortars with additions compared to the control mortar (without additions). this is explained by the filling role the cementitious matrix by these additions. given they have a high finesse and are also added as binder in material matrix, fit into the gaps, they density the mortar skeleton resulting a reduction in voids and increase in density. fig. 4. bulk density of all scms mortars mixes. 3.3. hardened properties 3.3.1. flexural and compressive strength the mechanicals properties of the scms were studied by testing the (40x40x160) mm3 samples under 3 point flexural and uniaxial compressions, in accordance with standard nf en196-1 (2006). three samples were tested in flexure and the six half-samples obtained were tested in uni-axial compression on a hydraulic press with a capacity of 3000kn. the mechanical tests for the mortars were performed at 3, 7, 14, 21 and 28 days (curing at temperature room). the results obtained of all scms mixtures are given in figures 5 and 6. the figures present respectively the flexural and compressive strength of scms mortars with and without heat treatment. 2180 2200 2220 2240 2260 2280 scm scm (np) scm (cps) b u lk d e n si ty ( k g /m 3 ) 44 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 fig. 5. evolution of the flexural strength of all scms mortars with and without heat treatment. 0 2 4 6 8 10 0 5 10 15 20 25 30 f le x u ra l st re n g th ( m p a ) age (days) scm without treatment scm with treatment 0 2 4 6 8 10 0 5 10 15 20 25 30 f le x u ra l st re n g th ( m p a ) age (days) scm(np) without treatment scm(np) with treatment 0 2 4 6 8 10 12 0 5 10 15 20 25 30 f le x u ra l st re n g th ( m p a ) age (days) scm(cps) without treatment scm(cps) with treatment ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 45 fig. 6. evolution of the compressive strength of all scms mortars with and without heat treatment. 0 10 20 30 40 50 60 0 5 10 15 20 25 30 c o m p re ss iv e s tr e n g th ( m p a ) age (days) scm without treatment scm with treatment 0 10 20 30 40 50 60 70 0 5 10 15 20 25 30 c o m p re ss iv e s tr e n g th ( m p a ) age (days) scm(cs) without treatment scm(cs) with treatment 0 10 20 30 40 50 60 70 0 5 10 15 20 25 30 c o m p re ss iv e s tr e n g th ( m p a ) age (days) scm(cps) without treatment scm(cps) with treatment 46 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 it is clearly that the flexural and compressive strength increases for all curing age (3, 7, 14, 21 and 28 days). that is attributed to the hydration phenomenon of cement which causes the evolution of compactness with curing time. indeed, the hydration of the cement minerals (c3s and c2s), give birth of the calcium silicate hydrate (csh) which increases resistance of mortar. it is noted that, at 28 days the reference mortar presents a strength value slightly low comparatively with those of the scms mortars with additions. this difference is due mainly to the pozzolanic property of the additions having an (totally or partially) amorphous structure which in the ca(oh)2 presence released during the hydration of cement and water, gives birth new products (csh and cah), having same properties similar to those formed containing minerals of cement (wild, 1996 ; reinhardt & stegmaier, 2006). for flexural strength of mortars having undergone heat treatment, continuous improvement was observed compared to mortars up to 14 days without treatment, or it was found the opposite effect, this can be explained by the fragility of specimens from this age processing and ripening (figure 5), it has been proven in the work of safi et al., (2013). the temperature has a beneficial effect on the resistance of mortars. the results obtained show that mortars which have undergone heat treatment (figure 6), exhibit a better compressive strength as a function of age (3, 7, 14, 21 and 28 days), compared to those without treatment, which is probably due the effect of temperature. an improvement in the compressive strengths at 28 days is 7 mpa for the control mortar scm, 2 mpa for the scm (np) mortar and 3 mpa for the scm (cps). according to figure 7, the compressive strength values at 14 days, obtained for all mortar compositions having undergone thermal treatment, are almost similar or sometimes better than those obtained by non-heat treated mortars at 28 days, which reduces the curing time for precast elements. fig. 7. comparison of compressive strength of scms mortars thermally treated at 14 days and untreated at 28 days in order to see the strength development of mortars studied under the effect of heat treatment at each curing age, figure 8 has been established in this direction. indeed, this figure shows the improvements in compressive strength of mortars treated (at 60°c) compared to those untreated. so, it can be noted that an improvement in the compressive strengths at 28 days by the heat treatment (60°c) was less significant whatever the type of additives used. however, at 3 days of curing age a significant improvement of strength for all mortars. the heat treatment improved the compressive strength of mortars, especially at young age. indeed, at 3 days the strength gain was 67% for mortar without addition and 93% for mortar with natural pozzolan scm (np) or mortar with calcined paper sludge scm (cps). this can be explained also by 0 20 40 60 80 scm scm(np) scm(cps) c o m p re ss iv e s tr e n g th ( m p a ) with treatment at 14 days ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 47 accelerating of pozzolanic reactivity of these additions (naturel pozzolan and calcined paper sludge). fig. 8. compressive strength gain of the thermally treated scms mortars compared to untreated mortars. 3.3.2. evolution of weight to see the chosen additions effect on the weight (gain or loss) of mortars, the mass measurements was performed. the obtained results of the weight evolution during 28 days of hardening are given in figure 9. according this figure, it was recorded that a continuous increase in the weight of different mortars during to the curing age. it can be explained by due to the cement hydration reaction at short-time which giving thus the formation of new hydrates. it is also noted that weight changes of studied mortars with additions is almost similar to the control mortar (without addition) and in sometimes is better, for example, the mortar containing calcined paper sludge scm (cps) has a less weight about 28% compared to the reference mortar (figure 10). this explains by the beneficial effect of the pozzolanic reaction of mineral additives (barnett, 2004; safi et al., 2011). fig. 9. weight evolution of all scms mortars as function age. -50 -30 -10 10 30 50 70 90 scm scm(np) scm(cps) c o m p re ss iv e s tr e n g th g a in ( % ) gain / 3days gain / 14days gain / 28days 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 0 5 10 15 20 25 30 w e ig h t e v o lu ti o n ( % ) age (days) scm scm(np) scm(cps) 48 ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 fig. 10. loss weight of all scms mortars at 28 days compared to the reference mortar. 4. conclusion the aim of this study was the heat treatment effect on the strength development of selfcompacting mortars based on two (02) different types of mineral additions which are: natural pozzolan (np) and calcined paper sludge as metakaolin. it results that: 1the fluidity of all mortars, was acceptable for self-compacting concretes (28cm-32cm) giving a good flow stable and without vibration; 2the weight evolution of different mortars with additions was almost similar and in sometimes better compared to the control mortar (without addition). it was reported the mortar based calcined paper sludge (cps) has a less weight about 28% at 28 days compared to the reference mortar. 3the mechanical strengths (compressive and flexural strength) are significantly improved in the presence of the various pozzolanic materials: natural pouzzolan, and calcined paper sludge; 4comparatively to age 3 days, it can be also reported that an improvement in the compressive strengths at 28 days by the heat treatment (60°c) was less significant whatever the type of additives used. 5compared to reference mortar (without heat treatment at 28 days) significant improvements of the compressive strength of mortars studied heated thermally at age 14 days were recorded. they were sometimes similar, which is beneficial to use precast elements by mortars treated at the age of 14 days.. 5. references aci 233r-03 (2003). slag cement in concrete and mortar, report of aci committee 233, american concrete institute, farmington hills, mich. ahmadi, b., & al-khaja, w. (2001). utilization of paper waste sludge in the building construction industry. resources, conservation and recycling, 32(2), 105-113. banfill, p., & frias, m. (2007). rheology and conduction calorimetry of cement modified with calcined paper sludge. cement and concrete research, 37(2), 184-190.. 0 -13.5 -28.5 -30 -20 -10 0 s c m s c m (n p ) s c m (c p s ) lo ss o f w e ig h t a t 2 8 d a y s (% ) ghernouti et al., j. build. mater. struct. (2019) 6: 39-49 49 barnett, s. j., soutsos, m. n., bungey, j. h., & millard, s. g. (2004). fast-track concrete construction using cement replacement materials. special publication, 221, 135-152. bénoît, o. (1967). détermination de l’activité pouzzolanique d’une pouzzolane par voie chimique. bull liaison labo. p. et ch, (26), d1-d5. bijen, j. m. j. m. (1996). blast furnace slag cement for durable marine structures. stichting betonprisma. chinjemelo, u., & billong, n. (2004). activité pouzzolanique des déchets de briques et tuiles’. african journal of science and technology, 5(1),92-100. erdoǧdu, s., & kurbetci, s. (1998). optimum heat treatment cycle for cements of different type and composition. cement and concrete research, 28(11), 1595-1604. escalante-garcıa, j. i., & sharp, j. h. (2001). the microstructure and mechanical properties of blended cements hydrated at various temperatures. cement and concrete research, 31(5), 695-702. frıas, m., de rojas, m. s., & cabrera, j. (2000). the effect that the pozzolanic reaction of metakaolin has on the heat evolution in metakaolin-cement mortars. cement and concrete research, 30(2), 209-216. frías, m., garcía, r., vigil, r., & ferreiro, s. (2008). calcination of art paper sludge waste for the use as a supplementary cementing material. applied clay science, 42(1-2), 189-193. kjellsen, k. o. (1996). heat curing and post-heat curing regimes of high-performance concrete: influence on microstructure and csh composition. cement and concrete research, 26(2), 295-307. lin, k. l., chen, b. y., chiou, c. s., & cheng, a. (2010). waste brick’s potential for use as a pozzolan in blended portland cement. waste management & research, 28(7), 647-652. michel, v. (1989). la pratique des ciments, mortiers et bétons’. edition le moniteur. naceri, a., & hamina, m. c. (2009). use of waste brick as a partial replacement of cement in mortar. waste management, 29(8), 2378-2384. neville, a. m. (2000). propriétés des bétons. eyrolles, paris. nf en 196-1 (2006). cement. part 1: composition, specification and conformity criteria for common cements, afnor. poon, c. s., lam, l., kou, s. c., wong, y. l., & wong, r. (2001). rate of pozzolanic reaction of metakaolin in high-performance cement pastes. cement and concrete research, 31(9), 1301-1306. reinhardt, h. w., & stegmaier, m. (2006). influence of heat curing on the pore structure and compressive strength of self-compacting concrete (scc). cement and concrete research, 36(5), 879-885. safi, b., ghernouti, y., rabehi, b., & aboutaleb, d. (2013). effect of the heat curing on strength development of self-compacting mortars containing calcined silt of dams and ground brick waste. materials research, 16(5), 1058-1064. samet, b., mnif, t., & chaabouni, m. (2007). use of a kaolinitic clay as a pozzolanic material for cements: formulation of blended cement. cement and concrete composites, 29(10), 741-749. schwartzentruber, a., & catherine, c. (2000). la méthode du mortier de béton équivalent (mbe)—un nouvel outil d’aide { la formulation des bétons adjuvantés. materials and structures, 33(8), 475482. verbeck, g. j. (1968). structures and physical properties of cement paste. in 5th international congress on the chemistry of cement, 1968 (vol. 3, pp. 1-37), wild, s. (1996). observations on the use of ground waste clay brick as a cement replacement material. building research and information, 24(1), 35-40. wild, s., & khatib, j. m. (1997). portlandite consumption in metakaolin cement pastes and mortars. cement and concrete research, 27(1), 137-146. j. build. mater. struct. (2017) 4: 31-41 original article doi : 10.34118/jbms.v4i2.29 issn : 2353-0057, eissn : 2600-6936 strength and durability of low-impact environmental self-compacting concrete incorporating waste marble powder boukhelkhal a1,*, azzouz l1, benabed b1, belaïdi ase1 1 civil engineering laboratory, university of laghouat, 03000, algeria. * corresponding author: a.boukhelkhal@lagh-univ.dz abstract. this research studies the effect of waste marble powder (wmp) as substitute of portland cement on strength and durability of self-compacting concrete (scc) in order to produce scc with reduced impact environmental. for this purpose, five mixtures were designed in which four mixtures contained wmp at substitution levels of 5, 10, 15, 20%, and mixture included only the portland cement as control mix. the realized tests are compressive strength at 3, 7 and 28 days, water capillary absorption, water absorption by immersion and sulfate attack. the results show a reduction in the compressive strength with increasing wmp content. the use of wmp was found to increase both of the water capillary absorption and water absorption by immersion. scc containing wmp subjected to magnesium sulfate attack presented a lower expansion and higher resistance to sulfate aggressions. key words: self-compacting concrete, waste marble, environment, strength, durability. introduction self-compacting concrete (scc), self-consolidating concrete, self-leveling concrete, highlyflowable concrete or non-vibrating concrete are very fluid concretes that flow and compact under their proper weight without any effort of compaction or vibration even in highly reinforced structural elements or complex formwork (naik et al, 2012; kurita et nomura, 1998). scc was appeared and used for the first time in japan three decades ago, its use was not stopped because scc has special and interesting properties at fresh state such as flowability, passing ability and resistance to segregation. for achieving these contradictory properties, the formulation of scc needs the use of high portland cement content (450-600 kg/m³) and superplasticizer (sp). however, using high volume of portland cement causes many problems such as: increase in the consumption of cement environmental impacts due to co2 emissions consumption of energy and natural resources high production cost since the cement is the most expensive element in the concrete risk of cracking associate to the high heat of cement hydration in order to produce low-impact environmental, economic and durable scc, the cement is replaced by fine additive materials (fam) having large proportion of fine particles (<80 μm) such as slag, limestone, fly ash, rice husk ash…etc. the reuse of industrial by-products as fam is a good solution to ensure the equilibrium of eco-system, biological components of the environment and public health (sadek et al; 2016). another solution consists in the incorporation of industrial waste materials as fine or coarse aggregates, which can contribute effectively to sustainable development. using some types of fam were shown to reduce the mailto:a.boukhelkhal@lagh-univ.dz 32 boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 dosage of sp compared to scc with only portland cement. the characteristics of scc are strongly affected by the type, source, chemical, mineralogical, physical and mechanical properties of fam. the incorporation of fam in binary and ternary blended cement improves not only the fresh properties but also the hardened properties of scc (sonebi, 2004; belaidi et al, 2015; belaidi et al, 2012; boukhelkhal et al, 2016; safiuddin, 2008; uysal et yilmaz, 2011; boukhelkhal, 2012; boukhelkhal et al, 2012). previous studies found that the use of fam having different grain-size and morphology enhances the compactness and provides a better workability and cohesiveness by improving the grain-size distribution and particle packing. on other hand, this reduces the risk of cracking associated to the heat of hydration leading therefore to superior performance of scc at long-term (sonebi et bartos, 1999; boukendakdji et al, 2012). recycling waste powders of marble and granite in the production of scc was proved to be useful because the marble powder acts as filler, and granite powder acts as pozzolanic material despite its small pozzolanic activity (sadek et al, 2016). benabed et al (2016) have studied the effect of limestone powder as a partial replacement of crushed quarry sand on properties of self-compacting repair mortars, they concluded that the use of limestone powder at substitution rate of 10 to 15% is beneficial from rheological and strength properties. research conducted by chirici et al (2006), was demonstrated that including natural pozzolana (np) in cement mortars increases the strength at later ages and enhances its resistance to acid and sulfate attacks and chloride ion penetration. mortars with silica fume (sf), metakaolin (mk) and fly ash (fa) have shown an enhancement in compressive strength, dynamic modulus, ultrasonic pulse velocity, transport properties, sulfate resistance and freezing-thawing resistance (aghabaglouet al, 2014). pozzolanic fine additive materials such as sf, mk and fa are characterized by its high specific surface area and pozzolanic reaction in which additional calcium silicate hydrate csh forms by reaction between reactive silica and calcium hydroxide produced by the cement hydration. marble stone is locally available in some quarries in the east of algeria and is generally used in buildings for the preparation of slabs and tiles for decorative purposes. however, the process of cutting, shaping and lustrating of the marble stones generates a fine material know as waste marble powder which is not exploited and can pose a serious environmental problems. from this study, an attempt was conducted to produce a reduced impact environmental and durable scc by exploiting the waste marble powder and investigating its effect as a fine additive materials on the strength and durability properties of scc. experimental procedure 2.1. material properties the cement used in this study is an artificial portland cement (cemi) class 42.5. waste marble powder subject of this study is a waste powder resulting from cutting, shaping and lustrating of the marble stones. the chemical composition and physical properties of wmp and cement are given in table 1. from this table, the wmp is mainly consisted of lime (56.01%). as fine aggregate (fa), a river sand characterized by granular class of 0/5, and a continuous particles size distribution was used. for coarse aggregate (ca), two classes 3/8 and 8/15 were used. the physical properties of the aggregate are shown in table 2. the superplasticizer used is a polycarboxylates based high-range water reducers (hrwr). it has a specific gravity and ph of 1.07g/cm3 and 8, respectively. locally available potable water was used for mixing scc constituents. boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 33 table 1. chemical composition and physical properties of cement and waste marble powder. component (%) cement waste marble powder sio2 20.14 0.42 cao 63.47 56.01 mgo 2.12 0.12 al2o3 3.71 0.13 fe2o3 4.74 0.06 so3 2.67 0.01 k2o 0.47 0.01 tio2 0.21 0.01 na2o 0.69 0.43 p2o5 0.06 0.03 loss ignition 1.72 42.78 density 3.1 2.7 finesses (cm²/g) 3300 3600 table 2. physical properties of aggregates. aggregate fa 0/5 ca 3/8 ca 8/15 absorption coefficient (%) 0.59 1.56 2.26 density 2.60 2.61 2.54 water content (%) 0.03 0.17 0.13 in order to determine particle size distribution of wmp and cement, laser distribution analysis was realized and the results are illustrated in figure 1. the results indicate that wmp is relatively finer than the cement, and about 70% of particles of wmp have a diameter lower them 10 μm. fig 1. particle size distribution of cement and waste marble powder. 2.2. mix design five mixtures were designed to study the effect of waste marble powder on the strength and durability of scc. the binder content, water / binder ratio and dosage of superplasticizer were respectively equal to 470kg/m3, 0.4 and 0.9%. the control mixture contains only the portland cement as binder, while other mixtures include the wmp at different substitution levels 5, 10, 15 and 20 %. the mix proportions of different mixtures are presented in table 3. 0 10 20 30 40 50 60 70 80 90 100 0.1 1.0 10.0 100.0 1000.0 % p a ss in g particle size (µm) cement wmp 34 boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 table 3. mix proportions of scc. materials mixes 0wmp 5wmp 10wmp 15wmp 20wmp cement (kg) 470 446.5 423 399.5 376 wmp (%) 0 5 10 15 20 wmp (kg) 0 23.5 47 70.5 94 sand 0/5 (kg) 882.9 gravel 8/15 (kg) 553 gravel 3/8 (kg) 277 water (kg) 188 superplasticizer (kg) 4.23 w/b 0.4 2.3. test protocol 2.3.1. compressive strength compressive strength measurements of each mixture were made on six pieces of three prismatic specimens of 70×70×280 mm size that were previously crushed by flexion. the test was carried out using a hydraulic press with a capacity of 2000kn at concrete age of 3, 7 and 28 days according to the european standard (en 12390-3, 2001). 2.3.2. water capillarity absorption water capillary absorption was evaluated on concrete prismatic specimens of 70×70×280 mm size after initial water-curing of 28 days according to the french standards (nf p 18-502, 1989). the concrete specimens were firstly dried at 105 ± 5 °c for 72 hours before being sealed by waterproof material on the sides to ensure one direction of water flow, and stored in water on their cross section with a constant water height of 5 mm. the increase in specimen mass was measured regularly every 5 minutes until 90 minutes. the mass of water absorbed par unit area was plotted against the square root of time. the coefficient of water capillary absorption cc is determined using the following equation: √ (1) where m: mass of water absorbed at time t (g), a: exposed area of the specimen (cm2), t: elapsed time (min), cc : coefficient of water capillary absorption (g/cm2/min0.5). 2.3.3. water absorption by immersion in this test, three concrete prismatic specimens of 70×70×280 mm size from each mixture were cured in water for 28 days and dried after that at 105 ± 5 °c for 72 hours. the specimens were weighed m0 and immediately immersed in water at approximately 21 °c for not less than 48 hours before being weighed in accordance with astm c642-97 (1997). the coefficient of water absorption by immersion ai is given by the following equation: ( ) (2) where ms: saturated mass (g), md: dried mass (g), ai : coefficient of water absorption by immersion (%). boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 35 2.3.4 . sulfate attack the sulfate exposure testing procedure was conducted by immersing mortar specimens in sulfate solution after an initial water-curing period of 28 days. 25×25×285 mm prism and 50×50×50 mm cube specimens were prepared for sulfate resistance tests. the specimens were immersed in 5% magnesium sulfate solution at 23±2 °c according to astm c1012-04 (2004). the solution was renewed every 4 weeks to minimize the increase of ph due to the leaching 0h ions from the mortar specimen. the length changes of prism specimens were measured weekly for the first four months and monthly until six months, for cube specimens, the compressive strength was determined at 0, 28, 56, 90 and 180 days. the strength gain or loss of the mortar cube specimens was investigated by comparing the strength before immersion (0 days) and after immersion (28, 56, 90 and 180) in sulfate solution. visual control was performed on selected specimens. 3. results and discussion 3.1. compressive strength figure 2 shows the evolution of compressive strength with age of testing. the compressive strength of all hardened scc mixtures increases progressively with curing age. due to its high volume in portland cement, the control mix has for all ages the highest values of strength. with the same amount of the binder, the substitution of the cement by the wmp decreases the strength of scc. the compressive strength of 0wmp; 5wmp; 10wmp; 15wmp and 20wmp mixes at 28 days are 37.2; 36.7; 34.5; 28.8 and 26.1 mpa, respectively. scc with 5% of wmp has developed a similar compressive strength with scc control at 28 days (37 mpa) in comparison with the reference mixture, the compressive strength of 5wmp; 10wmp; 15wmp and 20wmp mixture decreased by 1.3; 7.3; 22.6; 30 and 36.6% at 28 days. fig 2. evolution of compressive strength. these results are in accordance with those reported by other researchers (güneyisi et al, 2009; bouziani et al, 2011). the decrease in compressive strength could be due to the use of a fine inert material having a fineness approximation similar to that of the portland cement (low filling effect), and to the reduction in the water/cement ratio by adding wmp. in addition, with introducing wmp, the cement paste was insufficient to coat all the sand particles, which consequently leads to a decrease in compressive strength (benabed et al, 2016). mixture containing 20% of wmp and a cement content of about 380 kg/m3 had developed at 28 days a 0 10 20 30 40 50 0 5 10 15 20 25 30 c o m p re ss iv e s tr e n g th ( m p a ) age of concrete (days) 0wmp 5wmp 10wmp 15wmp 20wmp 36 boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 similar compressive strength with ordinary concrete that is generally used in ordinary constructions (26mpa). the replacement of cement and sand by marble powder (mp) at substitution rate of 10% decreases the compressive strength of mortars, and mortars with mp substituted by sand performed better than mortar with mp substituted by cement (corinaldesi et al, 2010) 3.2. water capillary absorption the influence of wmp on the water capillary absorption is presented in figure 3. the obtained values show an increase in the water absorption with time for all mixtures. the increase in wmp content increases the water absorption. it should be noted that the reference mixture has the lowest water absorption value, while the water absorption value of mix including 20% of wmp is the highest. the coefficient of water capillary absorption (cc) of 0wmp; 5wmp; 10wmp; 15wmp and 20wmp mixes are 3.3x10-2, 3.6x10-2, 3.7x10-2, 3.9x10-2 and 4x10-2 g/mm2/min0.5. the values demonstrated that increasing wmp content from 5 to 20% leads to an increase in the coefficient of water capillary absorption from 9.7 to 22.6%. similar results were obtained in concrete containing slag at substitution levels of 15, 30 and 50%, with w/b ratio of 0.65, tested at 28 days (hadjsadoka et al, 2012). fig 3. effect of waste marble powder on water capillary absorption. 3.3. water absorption by immersion the durability of concretes is significantly influenced by their pore structure. this parameter can be evaluated by measuring water absorption by immersion. the variation of water absorption by immersion for all scc mixes is illustrated in figure 4. it is clear from the obtained results that the increase in the amount of substituted wmp leads to an increase in the water absorption. the water absorption values of mixtures containing 0, 5, 10, 15 and 20%of wmp are 4.67; 5.10; 5.11; 5.13 and 5.17%, respectively. this means that incorporation of wmp at substitution levels of 5, 10, 15 and 20% increases the water absorption rate by 9.26, 9.47, 9.9 and 10.9%, respectively. it was noted that all tested scc have low water absorption (less than 10%) (siddique, 2013), exception for mix that including 20% of wmp. in other hand, the obtained water absorption values are superiors to those found in mortar mixtures incorporated fly ash, silica fume and metakaolin (1.8 to 4.2%). these may be attributed to the use of inert material that having a low 0 0.1 0.2 0.3 0.4 0 2 4 6 8 10 w a te r ca p ii ll a ry a b so rb e d p e r u n it a re a ( g / m m 2 ) time (min0.5) 0wmp 5wmp 10wmp 15wmp 20wmp boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 37 filling effect because both the cement and wmp have approximately similar fineness (aghabaglouet al, 2014). similar effects was observed in scc made bottom ash in which increasing the amount of bottom ash increases water absorption by immersion (siddique, 2013). fig 4. variation of water absorption versus the substitution rate of waste marble powder. 3.4. correlation between compressive strength and water absorption by immersion correlation between compressive strength and water absorption by immersion is illustrated in figure 5. compressive strength decreases with increasing water absorption by immersion. it can be noted that there is a moderate linear relationship between these parameters. the coefficient of correlation was equal to 0.37. this relation suggests that with the increase in water absorption by immersion, scc is expected to have reduced compressive strength. fig 5. correlation between compressive strength at 28 days and water absorption by immersion. 3.5. correlation between compressive strength and water capillary absorption figure 6 presents the correlation between compressive strength at 28 days and coefficient of water capillary absorption of various scc mixtures. it is clear from the obtained results that the decrease in compressive strength is associated to the decrease of the water capillary absorption 0 1 2 3 4 5 6 0 5 10 15 20 w a te r a b so rp ti o n ( % ) substitution rate of waste marbe powder (%) y = -14.691x + 106.66 r² = 0.37 20 25 30 35 40 45 50 4 5 6 7 c o m p re ss iv e s tr e n g th ( m p a ) water absorption by immersion (%) 38 boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 coefficient. the results indicate that there is an excellent relationship between these parameters. the coefficient of correlation was found to be close to 1. fig 6. correlation between compressive strength at 28 days and coefficient of water capillary absorption. 3.6. effects of sulfate attack 3.6.1. expansion figure 7 depicts the evolution of the expansion of mortars with and without wmp. the expansion increases with increase of the immersion period in sulfate solution. it had been observed that there is an inversely proportional relation between the increase in wmp volume and the decrease in the expansion. fig 7. evolution of the expansion of mortar specimens immersed in magnesium sulfate solution. the results showed that the mix without wmp has the highest values of expansion, whereas the mix with 20% of wmp showed the lowest values of expansion. at 180 days, the expansion values of 0wmp, 5wmp, 10wmp, 15wmp and 20wmp mixes are 3.3x10-2, 2.3x10-2, 2.1x10-2, 2x10-2 and y = -32.917x2 + 223.78x 342.71 r² = 0.99 20 25 30 35 40 45 50 3 3.5 4 4.5 c o m p r e ss iv e s tr e n g th ( m p a ) coefficient of water capillary absorption 10² (g/mm2/min0.5) 0 0.01 0.02 0.03 0.04 0 50 100 150 200 e x p a n si o n ( % ) period of immersion ( days) 0wmp 5wmp 10wmp 15wmp 20wmp boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 39 1.9x10-2%. this means that the incorporation of wmp at substitution rate of 5, 10, 15 and 20% decreased the expansion by 30, 36, 39 and 42%, respectively. the increase in the expansion for all mixes is attributed to the formation of two voluminous products (gypsum and ettringite). the decrease in the expansion for mortars with wmp compared to mortar with plain cement is due to the reduction in the cement content which reduces the c3a content in the binder and the volume of the ettringite product (aghabaglouet al, 2014). 3.6.2. compressive strength figure 8 presents the evolution of the compressive strength of mixtures with and without wmp as a function to the period of immersion in magnesium sulfate solution. it can be seen from this figure that the reference mix shows a strength gain of about 24% at immersion period of 28 days. however, after this period the strength gain slightly decreases at immersion period of 56 and 90 days (18 and 17%), but considerably decreases at 180 days (1%). for mixes containing wmp, the strength gain increases until 180 days. the strength gain of 5wmp, 10wmp, 15wmp and 20wmp mixes is about 13, 26, 28 and 21% for immersion period of 28, 56, 90 and 180 days, respectively. this demonstrates that the inclusion of 10% of wmp by partial replacement of the cement is considered the optimum substitution rate. the strength gain might be attributed to the continuous hydration of anhydrated cement products and the reaction of mgso4 with ca(oh)2 to form two voluminous elements (gypsum and ettringite) which fill in the micro-pores leading to a denser structure. the reduction in strength gain is due to the expansion effect of the sulfate attack which leads to the formation of micro-cracks and softening of the cement matrix (ghrici et al, 2006). fig 8. evolution of compressive strength of mortar specimens immersed in magnesium sulfate solution. 3.6.3. visual control visual inspection on some selecting mortar specimens was carried out after 180 days of immersion in the magnesium sulfate solution to evaluate the visible signs of softening, cracking and spalling in the mortar specimens, the results are shown in figure 9. from this control, a low spalling deterioration was observed especially at the edges and corners of some specimens, in particular those of the control mortar. this is due to the fact that these places are exposed to two (edges) or three (corners) penetration flux of sulfate ions, which accelerates their degradation. 0 10 20 30 40 50 60 70 0 28 56 90 180 c o m p r e ss iv e s tr e n g th ( m p a ) period of immersion (days) 0wmp 5wmp 10wmp 15wmp 20wmp 40 boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 fig 9. visual control of mortar specimens. 4. conclusions this investigation was conducted to assess the strength and durability of reduced environmental impact scc made with waste marble powder. from the obtained results in this investigation, the following conclusions can be drawn:  scc made with waste marble powder at replacement level of 5% developed approximately similar compressive strength with control scc. at 28 days, compressive strength values ranging from 26 to 37 mpa were obtained. these results allow the use of different replacement levels of wmp for different concrete purposes. for example, scc containing wmp content of 10% can be used in a structure when the desired strength is about 35mpa.  concerning the water capillary absorption and water absorption by immersion, a slight increase in amount of water absorbed was observed when the cement is partially replaced by wmp.  correlations between compressive strength at 28 days and water absorption properties were found very good with a coefficient of correlation more than 0.9.  incorporating wmp in scc mixes immersed in magnesium sulfate solution was found to decrease the expansion and to improve the resistance to sulfate aggressions.  finally, it can be concluded that the exploitation of waste marble powder as fine materials in production of scc is very advantageous from technical, economical and environmental points of view. 5. references aghabaglou am, sezer gi, ramyar k. (2014). comparison of fly ash, silica fume and metakaolin from mechanical properties and durability performance of mortar mixtures view point. construction and building materials, 70, 17-25. astm c 642-97. (1997). standard test method for density, absorption, and voids in hardened concrete. american society for testing and materials, usa. astm c 1012-04. (2004). standard test method for length change of hydraulic cement mortar exposed to a sulfate solution. american society for testing and materials, usa. belaidi ase, kenai s, kadri eh, soualhi h, benabed b. (2015). effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes. journal of adhesion science and technology, 30, 247-261. belaidi ase, azzouz l , kadri e, kenai s. (2012). effect of natural pozzolana and marble powder on the properties of self-compacting concrete. construction and building materials, 31, 251-257. boukhelkhal a, azzouz l, belaïdi ase, benabed b. (2016). effects of marble powder as a partial replacement of cement on some engineering properties of self compacting concrete. journal of adhesion science and technology, 30(22), 2405–2419. boukhelkhal a. (2012). rheology, physical and mechanical characterization and durability of selfcompacting concrete made with marble powder. [msc thesis]. university of laghouat, algeria. p.170. boukhelkhal et al., j. build. mater. struct. (2017) 4: 31-41 41 boukhelkhal a, azzouz l, belaïdi ase, benabed b. (2012). effect of marble powder on the properties of self-compacting concrete at fresh state. in: proceeding of first international international conference on civil engineering, laghouat, algeria. boukendakdji o, kadri eh, kenai s. (2012). effects of granulated blast furnace salg and superplastizer type on the fresh properties and compressive strength of self-compacting concrete. cement and concrete composites, 34(4), 583–590. benabed b, soualhi h, belaidi ase, azzouz l, kadri e, kenai s. (2016). effect of limestone powder as a partial replacement of crushed quarry sand on properties of self-compacting repair mortars. journal of building materials and structures, 3,15-30. bouziani t, benmounah a, bederina m, lamara m. (2011). effect of marble powder on the properties of self-compacting sand concrete. the open construction & building technology journal, 5, 25-29. corinaldesi v, moriconia g, r. naik t. (2010). characterization of marble powder for its use in mortar and concrete. construction and building materials, 24(1), 113-117. en 12390-3. (2001). testing hardened concrete part 3: compressive strength of test specimens. european committee for standardization, bruxelles. ghrici m, kenai s, meziane e. (2006). mechanical and durability properties of cement mortar with algerian natural pozzolana. materials science, 41(21), 6965–6972. güneyisi e, gesoğlu m, özbay e. (2009). effects of marble powder and slag on the properties of selfcompacting mortars. materials and structures, 42, 813-826. hadjsadoka a, kenai s, courard l, michel f, khatib j. (2012). durability of mortar and concretes containing slag with low hydraulic activity. cement and concrete compsites, 34(5), 671–7. kurita m, nomura t. (1998). high-flowable steel fiber-reinforced concrete containing fly ash. in: malhotra vm, editor. proceedings, sixth canmet/aci international conference on fly ash, silica fume, slag, and natural pozzolans in concrete, sp-178. farmington hills, mi: american concrete institute. p. 159–179. naik r.t, kumara r, w. rammeb b, canpolatc f. (2012). development of high-strength, economical selfconsolidating concrete. construction and building materials, 30, 463-469. nf p 18-502 (1989). water capillary absorption. paris: afnor. sadek dm, el-attar mm, haitham aa. (2016). reusing of marble and granite powders in self-compacting concrete for sustainable development. cleaner production, 121, 19-32. sonebi m. (2004). medieum strength self-compacting concrete containing fly ash: modeling using factorial experimental plans. cement and concrete research, 34(7), 1199–1208. safiuddin m. development of self-consolidating high performance concrete incorporating rice husk ash. (2008). phd thesis, university of waterloo, canada, p.359 sonebi m, bartos pj. (1999, september). hardened scc and its bond with reinforcement. in: proceeding of first international rilem symposium on self-compacting concrete (pro 7), stockholm, sweden. siddique r. (2013). compressive strength, water absorption, sorptivity, abrasion resistance and permeability of self-compacting concrete containing coal bottom ash. construction and building materials, 47, 1444-1450. uysal m, yilmaz k. effect of mineral admixtures on properties of self-compacting concrete. (2011). cement and concrete composites, 33, 771–776. j. build. mater. struct. (2018) 5: 227-238 original article doi : 10.34118/jbms.v5i2.61 issn 2353-0057, eissn : 2600-6936 mechanical properties of concrete with partial replacement of coarse aggregates by coconut shells and reinforced with coconut fibre mandal b.1, tiwari s.1,*, ghimire s.1, tiwari a.2 1 department of civil engineering, pulchowk campus, institute of engineering, tribhuvan university, pulchowk , lalitpur , nepal 2 structural engineer,national society for earthquake technology – nepal (nset), nepal * corresponding author: tiwarisushant78@gmail.com received: 16-09-2018 revised: 01-12-2018 accepted: 18-12-2018 abstract: this paper centers around the study of physical and mechanical properties of concrete reinforced with coconut fibre and the coarse aggregates of which are partially replaced with coconut shells. american concrete institute (aci) method has been used to design m20 concrete wherein coconut shells (cs) replaced the coarse aggregates (ca) by 6%, 8%, 10%, 12% and 14% by volume. under each replacement of ca by cs, coconut fibres were added by 3%, 4% and 5% of cement content. compressive strength of concrete was found to comply with characteristic strength for certain mixes which avers that the replacements were justifiable for concrete production and thus, the optimum mix for the concrete prepared thereby, would have to be considered accentuating the tensile strength which was actually the one with 10% replacement of ca by cs in terms of volume and 3% addition of coconut fibre. the research vividly evinces a decrease in overall density of the concrete thus prepared. the authors suggest the use of coconut shell and fibre in the production of concrete not only because they impart themselves as viable materials, but their use would also assist to abate the amount of environmental waste. key words: coconut shell, coconut fibre, mechanical properties, non-conventional aggregate, concrete. 1. introduction pertaining to the massive growth in construction industry parallel to growth in population, the use of concrete has been escalating in various forms for infrastructure development. this assert that concrete is the 2nd most consumed material on earth after water and estimate that around 7.23 billion tons of concrete is produced every year (aggregate industries, h & s department, 2008). for developing economies like nepal, wherein infrastructure development calls for massive investments the use of concrete is certainly going to upsurge in the following years. concrete is a composite material abode of aggregates, cement and water held together to form a solid, strong mass that has been used as a robust construction material associating to its remarkable compressive strength, shear strength and pre-stressing properties. another significant advantage of concrete as a construction material is its ability to take in other materials which can be used to enhance the overall performance or result in decrease of cost related to production. a significant proportion of concrete is aggregate of which makes up 66-78 percentage of total volume. (vishwas & sanjay, 2013). the design of concrete is basically about deducing the relative proportion of different constituents as variation in proportion of constituents causes difference in strength and performance. a number of authors have employed this attribute of concrete to study the effect of replacement of conventional coarse aggregates with materials like palm shells and coconut shells on the strength and durability of concrete. however, the materials to be used for replacement must be pertinent to the function that they are expected to endow. on the grounds of literature study, the authors have used coconut shell (cs) as suitable material for partial replacement of coarse aggregate in concrete 228 mandal et al., j. build. mater. struct. (2018) 5: 227-238 which helps not only in economic production of concrete but also in the management of solid waste (gunasekaran et al., 2011). in addition, coconut shell fibers (cf) have been added to ameliorate the tensile and flexural property of concrete (ahirwar & joshi, 2015). light weight concrete (lwc) has procured remarkable attraction in the construction industry attributing to its features like lower density, lower self-weight and lesser foundation costs. besides, lwc is admired not only for the aforementioned properties but also for the abatement of disposal of agricultural solid waste like the cs which could be used as light weight aggregate for the production of lwc. thus, lwc is relevant not only for structural reasons but also in the view of curtailing environmental problems. although a number of research have already been conducted on cs concrete and concrete reinforced with coconut fibres (crcf) individually, the authors conducted a study using both the materials to observe how they deviated the physical properties of concrete from conventional concrete. for a nation like nepal situated in a highly seismic region, with a number of estimates available (center for disaster management and risk reduction technology, 2015) to expound the damage that earthquakes can inflict, it is intrinsic to study methods to optimize the performance of buildings among which the use of lightweight concrete to reduce the dead load of concrete structures which consequently leads to reduction in seismic forces can be a prominent option. objectives: i. to study the combined effect of use of the cs as aggregate and cf as reinforcing material in the physical and mechanical properties of concrete. ii. to assess the optimum proportion of cs and cf for strength. iii. to determine the decrease in density of concrete due to replacement of aggregate by cs. 2. literature review concrete as a construction material has a peculiar property that its properties can be altered as per requirement adding various other ingredients. even for the traditional concrete, its intrinsic properties like workability, colour, setting time can be changed by varying its constituents. however, researchers have been looking for materials other than conventional materials, literally, using agricultural wastes for production of concrete (mannan & ganapathy, 2004; mannan & ganapathy, 2002; olanipekun et al., 2006; alengaram et al., 2008) as they also contribute significantly in utilizing what could degrade environmental quality into construction material. olanipekun et al. (2006) investigated the comparative cost and strength of concrete produced using coconut shell and palm kernel shells as substitutes for coarse aggregates and concluded that concrete produced using coconut shell has better compressive strength though palm kernel shells are quite cheaper. however, the use of both these shells renders cheaper production with respect to conventional concrete. the strength to economy ratio establishes coconut shell over palm kernel shells as a suitable substitute for conventional coarse aggregate. chanap (2012) enlist the following properties of coconut shell which make it suitable to be used as coarse aggregate for concrete:  high lignin content that makes it more weather resistant  low cellulose content which causes it to absorb less moisture as compared to other agricultural waste.  non-biodegradable mandal et al., j. build. mater. struct. (2018) 5: 227-238 229  sugar in the coconut shell is not in a free sugar form because of which it has no effect on setting time and the strength of concrete.  high strength and modulus properties.  surface texture is smooth on concave and rough on convex surface. kanojia & jain (2017) observed the effect of partial replacement of coconut shell as coarse aggregate in concrete and assessed the additional quantity of cement required to be added to account for the strength loss due to replacement. they designed the conventional concrete first without replacement and started replacement of coarse aggregate with coconut shells by volume of 10%, 20%, 30% and 40%. in the next part, varying the proportions of coarse aggregate and coconut shells were taken and three different water-cement (w/c) ratio were considered and finally the w/c ratio for target strength was determined. they concluded that w/c ratio has to be reduced to get the required strength for increasing quantity of coconut shell. further, they also present that the density decreases by 7.5% for replacement by 40%. another major conclusion of this research was that no additional cement was required for 5 % replacement of coarse aggregates and 3.6% additional cement is required for 10% replacement. basri et al. (1999) depicted that wood based materials would not contaminate or leach to produce toxic substances once they are inserted in the concrete matrix as they are hard and have organic nature (basri et al., 1999). gunasekaran et al. (2011) studied the compressive, flexural, splitting tensile strength, impact resistance and bond strength of the coconut shell concrete. this research suggests the cement content under replacement that is required to meet the criteria of structural lwc as per astm, (minimum 28-days compressive strength should not be less than 17n/mm2). the authors also mention that individual shell strength plays an important role in the overall strength of concrete as they observed the breakage of cs aggregates. finally, the authors also conclude that cs endows better workability because of smooth surface on one side of shells. gunasekaran et al. (2012) mention that cs has higher water absorption value of around 24% compared to other conventional aggregate. thus, to prevent water absorption cs shells are to be used in saturated surface dry condition by immersing in water for 24 hours. nagathan et al. (2016) conclude that coconut shells exhibit more resistance against crushing and impact with respect to crushed granite aggregate. gunasekaran et al. (2013) conducted a study on reinforced lightweight coconut shell concrete beam under flexure and in 2014 gunasekaran et al. (2014) they conducted another study on reinforced lightweight coconut shell concrete beam behavior under torsion. ali et al. (2012) cited the work of munawar et al. (2007). which mentions coconut fibre is the toughest among all fibre and are capable of taking strain 4-6 times more than that of other natural fibres. (ramakrishna & sundararajan, 2005) investigated the loss of tensile strength for four fibers, namely coconut, sisal, jute and hibiscus cannabinus by alternate wetting and drying as well as continuous immersion for 60 days in water, saturated lime and sodium hydroxide and reported that it resulted in chemical composition of all fibres. they also suggest that continuous immersion lead to considerable loss of tensile strength and that coconut fibers were better in regard that they retained tensile strength better than other fibres. two types of coconut fibres are available namely brown fibre obtained from matured coconut shell and white fibre obtained from immature coconut shell. brown fibre being thick and strong unlike the weaker and smooth white fibre are mostly used for engineering purposes. ali et al. (2012). this research actually centered around the comparison on static and dynamic moduli of coconut fibre reinforced concrete (cfrc) for fibre content 1%, 2% ,3% and 5 % of cement 230 mandal et al., j. build. mater. struct. (2018) 5: 227-238 content and fibre lengths of 2.5cm, 5cm and 7.5cm and suggested that cfrc with a fibre length of 5cm and fibre content of 5% has the best properties. aziz et al. (1981) studied the properties of cement paste for varying lengths of coconut fibres and varying fraction of volume. the research demonstrated that highest mechanical properties were for 4% volume fraction and under 4% volume fraction itself they conducted tests on tensile strength for varying lengths of coconut fibres and reported that the optimum strength was for a length of 38mm. thus, coconut fibres with 4% volume fraction and 38mm length resulted in optimum properties of cement paste. john et al. (2005) studied the durability of coconut fibres in cement composites, whereby fibre reinforced alkaline cement mortar were taken from internal and external wall of a building 12 years old. the difference in lignin content from the internal and external wall was found to be inconsiderable. sivaraja et al. (2010) conducted tests on cfrc at an interval of 3 months for 2 years under alternate wetting and dry conditions after the specimens were cured for 28 days. comparing the compressive strength, splitting tensile strength and the modulus of rupture, all these properties escalated in magnitude parallel to the age which explicated the durability of fibres. filho et al. (2000) recommend that washed and boiled fibres effectively increase the fibre matrix bond strength. it was shown that in comparison to fibres without pre-treatment the internal bond between washed and boiled fibres and the cement paste is doubled. compared to chemical treatment soaked fibres have higher tensile strength and strain and in comparison to soaked fibres boiled fibres have still better results. boiled fibres have improved bond strength by 184% compared to soaked fibres. 3. methodology the literature review on coconut shell vividly elucidates that coconut shells can be adopted as replacement for conventional coarse aggregates but since the overall strength of concrete depends on properties of shells they need to be studied in detail. the determination of combined effects, on concrete due to partial replacement of ca with cs and reinforced with cf is involved destructive testing. thus, cubes of 100mm*100mm*100mm were used for determining the compressive strength and cylinder of 100mm diameter and 200mm height for the determination of splitting tensile strength of concrete thus produced. the methodology can be briefly articulated in the following points: i. coconut shells were washed and dried for 30 days. they were used in saturated surface dry condition in the concrete mix. ii. coconut shell fibres were extracted from the coconut shells and treated by boiling them for around 2 hours. the fibres were cut into lengths of 4cm. iii. m20 concrete as per aci method was designed wherein ca was replaced by cs by 6%, 8%, 10%, 12% and 14% in terms of volume. within each replacement of cs by volume, fibres in amount representing 3%, 4% and 5% of cement content were added. thus, the deviation of concrete produced using replacements from conventional concrete were studied. iv. also, the optimum mix for strength was determined. those mix which yielded to characteristic strength were only considered. v. a total of 144 cubes and 144 cylinders were prepared for the aforementioned purpose. vi. the cubes and cylinders were subjected to a controlled curing. mandal et al., j. build. mater. struct. (2018) 5: 227-238 231 vii. the cubes and cylinders were subjected to compressive test and splitting test respectively at 7 days, 28 days and 60 days to study the growth in strength. viii. the specimens were weighed under air dry condition to study the density of concrete and decrease in density due to replacement. chart 1. various possible mixes of cs and cf 4. materials used the basic ingredients of concrete that were used were: a. 43 grade ppc cement the use of ppc cement can be justified from the fact that it enhances the durability of concrete in regions of significant chloride and sulphate attacks. the specific gravity of cement is taken to be 3.15. b. coarse and fine aggregates table 1. properties of aggregates s.n properties value coarse aggregate 1 fineness modulus 4.33 2 nominal size 20mm 3 aggregate crushing value 24% 4 density 1650kg/m3 fine aggregate 1 fineness modulus 3.28 c. coconut shells the coconut shells that were used for partial replacement of coarse aggregate in concrete had the following properties. these shells were collected from the vendors around the temples in 232 mandal et al., j. build. mater. struct. (2018) 5: 227-238 kathmandu where coconuts are used in large quantities for religious purpose and the shells are openly disposed after use. table 2. properties of coconut shell s.n physical and mechanical properties values 1 maximum size 15mm 2 moisture content 4.51% 3 water absorption 18.62% 4 specific gravity 1.05-1.20 5 sat surface dry sp. gravity 1.4 6 impact value 6.77% 7 abrasion 2.10% 8 crushing strength 1.98% 9 bulk density 690 10 fineness modulus 7.10% 11 thickness of 10 shell 4.0-7.0 12 shape flaky 13 surface texture smooth in inner surface and rough outer surface fig 1. dumping of waste coconut shells. fig 2. preparation of coconut fibre. 5. tests performed 5.1. compressive strength test compressive strength tests were performed on cubes of dimension 100mm (is, 1959) at a loading rate of 150kn/minute. 3 cubes were tested for each mix and each age. the value of compressive strength is finally, taken as the average compressive strength of 3 cubes. however, the compressive strength of that cube, was discarded which varied significantly, precisely, by more than 20%, from the mean of the other two cube strength values which were close to each other. 5.2. splitting tensile strength the splitting tensile strength tests were performed on cylinders of dimension 100mm diameter and 200mm height (c 496/c 496m – 04, 1996) at a loading rate of 120kn/minute. min et al. (2014) showed that there is increase in strength by 15% for each unit increase in loading rates mandal et al., j. build. mater. struct. (2018) 5: 227-238 233 in kn/s. considering this the strength of cylinder should be divided by the factors of 1.2. three cylinders were tested for each mix and each age. the same method for taking the average as that described for compressive strength was used. 6. results and discussions 6.1. compressive strength the results for the compressive strength test for different mix for 7 days are represented in the following table which elucidates the strength obtained from the compression test on cubes with various contents of shell and fibres at 7 days, 28 days and 60 days. the table also shows clearly, the strength variation at different fibre content for same fraction volume of cs. table 3. variation of compressive strength with variation in cs and cf 7 days(mpa) 28 days (mpa) 60 days(mpa) cs% 6% 8% 10% 12% 14% 6% 8% 10% 12% 14% 6% 8% 10% 12% 14% c f % 3% 14.5 15.2 16.8 14.9 14.6 17.2 18.0 20.1 19.9 18.6 19.1 20.3 21.3 20.7 19.6 4% 16.8 16.8 18.2 16.2 15.9 19.6 20.0 22.1 21.6 20.0 21.6 22.0 22.5 22.2 21.1 5% 14.2 14.3 15.4 15.3 14.9 19.2 19.6 20.9 20.6 19.6 21.1 21.6 22.0 21.4 20.3 it can be clearly observed from the table that 7 out of 15 mixes meet the characteristic strength of 20mpa at 28 days. meticulous observation reveals that for all the mixes, under 28 days strength, addition of fibre by 4% of the cement content yields the best results which indeed substantializes the findings of aziz et al. (1981). thus, taking 4% addition of fibre as reference, a clear trend of increase up to 10% replacement of ca by cs in terms of volume can be observed while with further replacement in terms of magnitude leads to reduction in strength. thus, considering 28 days strength, the best results are obtained at the mix when, ca is replaced in terms of volume by cs by 10% and fibre is added by 4% of the cement content in terms of mass. also, for 10% replacement by cs, all cf additions meet the characteristic strength. however, even for 12% replacement of ca by cs shows that the characteristic strength has been adequately exceeded for 4% and 5% addition of fibre, which is even more economical. thus, with 12% replacement of ca by cs and addition of cf by 4% or 5% is justifiable both in terms of strength and economy. the calculations for 1m3 of concrete shows that 10 % replacement of ca by cs results in 2.11% economical mix while for 12% replacement with cs the mix is 2.53% economical for nepalese rates of price for materials. fig 3. test for compressive strength of concrete 234 mandal et al., j. build. mater. struct. (2018) 5: 227-238 moreover, the average compressive strength has been growing with age for 60 days as illustrated by the table on the basis of which it can be mentioned that the shells and fibres do not undergo decomposition as they are inserted in the concrete matrix which complies with what has been mentioned by basri et al. (1999). fig 4. variation of compressive strength with cs and cf. the above chart illustrates the 28 days compressive strength for all replacements of ca by cs and all addition of fibres under each replacement which shows 10 % cs replacement with 4% fibre addition as the best mix. the following chart also validates that 4% addition of fibre yields the maximum strength though after 28 days the increase in strength is at a lower rate than for 5% additions. fig 5. growth in compressive strength of cube with 10 % cs replacement for all cf with age. mandal et al., j. build. mater. struct. (2018) 5: 227-238 235 6.2. splitting tensile strength table 4. variation of splitting tensile strength with variation in cs and cf. 7 days (mpa) 28 days (mpa) 60 days(mpa) cs% 6% 8% 10% 12% 14% 6% 8% 10% 12% 14% 6% 8% 10% 12% 14% c f % 3.00% 2.0 2.3 2.1 1.7 1.6 2.7 3.4 3.1 2.7 2.6 2.9 3.8 3.4 3.2 3.2 4.00% 2.0 2.1 1.8 1.6 1.5 3.2 3.6 3.2 3.0 3.0 2.8 3.1 3.0 2.8 3.0 5.00% 1.8 1.8 1.8 1.9 1.8 2.9 2.6 2.8 3.1 3.1 3.1 3.0 3.2 3.3 3.2 the 28 days tensile strength showed the best results for 4% fibre addition for all cs replacements but, all 4% additions have a decrease in tensile strength at the age of 60 days though they have a higher value of tensile strength compared to conventional m20 concrete. this can be clearly observed in the following charts. fig 6. 28 days tensile strength of concrete for all cs replacements. the above chart shows the highest strength for 8% replacement of ca by cs and addition of fibre by 4% of cement mass. fig 7. growth in tensile strength of concrete with age for 8 % cs replacement. 236 mandal et al., j. build. mater. struct. (2018) 5: 227-238 however, the above chart shows that for 28 days the mix with 4% fibre replacement has the maximum strength but it unknowingly decreases for 60 days that is not the case for other percentage of cf. this behavior of 4% addition of fibres can be observed not only under 8% replacement of ca by cs but all other replacements which can be tallied from the table. thus, 4% addition of fibres is unsuitable with regards to splitting tensile strength. since, the 28 days splitting tensile strength values are exactly equal for 3% addition of cf under 10 % replacement by cs and 5% addition of cf under 12% replacement by cs, the best mix for tensile strength is derived from 60 days strength which clearly shows the mix consisting of 10% replacement of ca with cs and 3% addition of fibre having the highest tensile strength, the 28 days tensile of strength which is higher than the average value for normal m20 concrete by 30.25%. the tensile strength for normal m20 concrete was found to be 2.38n/mm2, which is valid as per oluokun’s (oluokun, 1991), for relation between tensile strength and compressive strength of concrete. moreover, the 8% replacement has not been considered as it does not comply with characteristic compressive strength. fig 8. test for splitting tensile strength of concrete the density for normal concrete is 2523 kg/m3 and the density for the mix of 10 % replacement of ca by cs with 3% addition of fibres 2248kg/m3 which is 10.9% lighter than normal concrete. (vishwas & sanjay, 2013). 7. conclusion the replacement of coarse aggregates by coconut shell in concrete along with addition of coconut fibre is justifiable in concrete as it meets the characteristic strength as well as results in increase of tensile strength. the optimum mix for the concrete thus prepared is one with coconut shells replacing coarse aggregates by 10 % by volume along with addition of fibre by 3% of the cement content. this also results in decrease in density of the concrete. moreover, during the destructive tests it could be observed that unlike normal concrete the concrete prepared with cs and cf did not undergo brittle failure to which the fibres contributed significantly. the concrete thus prepared not only provides itself as a building material but also helps to abate the environmental problems occurring due to the disposal of coconut waste. acknowledgement we would like to express our gratitude to the department of civil engineering, institute of engineering, pulchowk campus for providing us with ample workspace, environment and infrastructure for the research. mandal et al., j. build. mater. struct. (2018) 5: 227-238 237 8. references aggregate industries, h & s department, (2008). safety data sheet. ashbourne, derbyshire,: hullandward ward. ahirwar, e. a. k., & joshi, r. (2015). experimental analysis of fly ash & coir fiber mix cement concrete for rigid pavement. international journal of engineering research and applications, 5(4), 109-120. alengaram, u. j., jumaat, m. z., & mahmud, h. (2008). ductility behaviour of reinforced palm kernel shell concrete beams. european journal of scientific research, 23(3), 406-420. ali, m., liu, a., sou, h., & chouw, n. (2012). mechanical and dynamic properties of coconut fibre reinforced concrete. construction and building materials, 30, 814-825. aziz, m. a., paramasivam, p., & lee, s. l. (1981). prospects for natural fibre reinforced concretes in construction. international journal of cement composites and lightweight concrete, 3(2), 123-132. basri, h. b., mannan, m. a., & zain, m. f. m. (1999). concrete using waste oil palm shells as aggregate. cement and concrete research, 29(4), 619-622. c 496/c 496m – 04. (1996). american society for testing and materials, west conshohocken: astm international. center for disaster management and risk reduction technology. (2015). nepal earthquakes – report #3. germany: institut für meteorologie und klimaforschung (imk-tro). retrieved from https://www.cedim.de/download/cedim_impactsummary_earthquakenepal2015_report3.pdf chanap, r. (2012). study of mechanical and flexural properties of coconut shell ash, rourkela: national institute of technology, retrieved from: ethesis.nitrkl.ac.in/3398/1/rahulc_108me033.pdf filho, r. d., scrivener, k., england, g. l., & ghavami, k. (2000). durability of alkali-sensitive sisal and coconut fibres in cement mortar composites. cement and concrete composites, 22(2), 127-143. gunasekaran, k., annadurai, r., & kumar, p. s. (2012). long term study on compressive and bond strength of coconut shell aggregate concrete. construction and building materials, 28(1), 208-215. gunasekaran, k., annadurai, r., & kumar, p. s. (2013). study on reinforced lightweight coconut shell concrete beam behavior under flexure. materials & design, 46, 157-167. gunasekaran, k., kumar, p. s., & lakshmipathy, m. (2011). mechanical and bond properties of coconut shell concrete. construction and building materials, 25(1), 92-98. gunasekaran, k., ramasubramani, r., annadurai, r., & chandar, s. p. (2014). study on reinforced lightweight coconut shell concrete beam behavior under torsion. materials & design, 57, 374-382. is. (1959). is 516-1959. new delhi: bureau of indian standards. john, v. m., cincotto, m. a., sjöström, c., agopyan, v., & oliveira, c. t. a. (2005). durability of slag mortar reinforced with coconut fibre. cement and concrete composites, 27(5), 565-574. kanojia, a., & jain, s. k. (2017). performance of coconut shell as coarse aggregate in concrete. construction and building materials, 140, 150-156. mannan, m. a., & ganapathy, c. (2002). engineering properties of concrete with oil palm shell as coarse aggregate. construction and building materials, 16(1), 29-34. mannan, m. a., & ganapathy, c. (2004). concrete from an agricultural waste-oil palm shell (ops). building and environment, 39(4), 441-448. min, f., yao, z., & jiang, t. (2014). experimental and numerical study on tensile strength of concrete under different strain rates. the scientific world journal, article id 173531, 11 pages. munawar, s. s., umemura, k., & kawai, s. (2007). characterization of the morphological, physical, and mechanical properties of seven nonwood plant fiber bundles. journal of wood science, 53(2), 108113. https://www.cedim.de/download/cedim_impactsummary_earthquakenepal2015_report3.pdf 238 mandal et al., j. build. mater. struct. (2018) 5: 227-238 nagathan, s. j., jahagirdar, s., mulla, m., & katti, s. (2016). comparative study on coconut shell aggregate concrete with conventional concrete. international journal of civil and structural engineering research, 4(1), 198-202. olanipekun, e. a., olusola, k. o., & ata, o. (2006). a comparative study of concrete properties using coconut shell and palm kernel shell as coarse aggregates. building and environment, 41(3), 297301. oluokun, f. (1991). prediction of concrete tensile strength from its compressive strength: an evaluation of existing relations for normal weight concrete. materials journal, 88(3), 302-309. ramakrishna, g., & sundararajan, t. (2005). studies on the durability of natural fibres and the effect of corroded fibres on the strength of mortar. cement and concrete composites, 27(5), 575-582. sivaraja, m., velmani, n., & pillai, m. s. (2010). study on durability of natural fibre concrete composites using mechanical strength and microstructural properties. bulletin of materials science, 33(6), 719-729. vishwas, p. k., & sanjay, k. b. g. (2013). comparative study on coconut shell aggregate with conventional concrete. international journal of engineering and innovative technology, 2(12), 67-70. j. build. mater. struct. (2018) 5: 74-85 original article doi : 10.34118/jbms.v5i1.46 issn 2353-0057, eissn : 2600-6936 impact of passive cooling techniques on the thermal behavior of residential buildings in hot and arid regions -an experimental study athmani w 1,*, sriti l 2 1 phd student, lacomofa laboratory, college of architecture, mohamed khidher university, p.o box: 145 rp 07000 biskra – algeria 2 professor, lacomofa laboratory, college of architecture, mohamed khidher university, p.o box: 145 rp 07000 biskra – algeria. * corresponding author: athmani.wafa@gmail.com received: 05-02-2018 revised: 14-04-2018 accepted: 19-04-2018 abstract. the thermal performance of the roof is one of the most important factors for a comfortable environment. as 50% of the thermal loads received by a building come from the roof, this research seeks to find the roofing system that opposes the transmission of heat during the hottest days and promotes indoor thermal comfort. in this regard, this paper presents an experimental study carried out on four (04) testing cells constructed on a reduced scale and submitted to climatic external conditions. three (03) cells were used to test passive cooling strategies through the roof, namely: the cool roof, ventilated roof and a roof with inverted earth pots. the fourth cell that served as cell-reference, for its part, a conventional roof. the experimentation concerned the types of roofs most used in residential buildings in biskra, algeria. the measurements process was effectuated in an exposed field during the month of july, prevailing the metrological data of the hot and arid climate. the obtained results show that the use of the cool-roof technique makes it possible to record the lowest internal temperatures in comparison with the other systems. thus, the reflective coating technique is capable of reducing the internal temperature from 3.33 °c to 4.80 °c, also the internal and external surface temperature of the roofs from 5.31 °c to 10.18 °c, respectively. these experimental results confirm the effectiveness of the "cool roof" technique as an innovative and efficient solution that contributes to the achievement of the comfort conditions in a hot and arid climate by eliminating heat gains through the roof. key words: passive cooling, cool roof, thermal performance, scale-model testing, residential buildings. 1. introduction in hot and arid environments where climatic conditions are extreme, the thermal performance of buildings has become a curricular issue for designers, researchers, and occupants. however, in this type of regions, the excessive exposure of the building envelope to intense solar radiation is considered to be the major cause of the thermal discomfort felt in spaces (bencheikh, 2013). in this situation, the absence of building envelope that is climatically efficient, urges the occupant to seek, constantly, an improvement of their accommodations comfort by the use of mechanical cooling systems for longer periods of time. in recent decades, we attend in algeria a large urban extension and a production of energyconsuming constructions that are indifferent to the climate. today, the residential sector in algeria accounts for 40% of total electricity consumption. the building envelope such as the interface between the interior of the building and the outdoor environment serve as a thermal barrier. it plays an important role in determining the amount of energy needed to maintain a comfortable indoor environment relative to the external environment (madhumathi et al., 2014). as the horizontal element of the envelope, the roof is the most exposed to solar radiation; it receives sunlight for almost the entire day, which makes it responsible for 50% of the total heat gain in buildings (dabaieh et al, 2015). mailto:athmani.wafa@gmail.com athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 75 the undesirable storage of thermal energy through the roof is an important issue in desert regions where cement-based materials are commonly used in building constructions (nahar et al., 1999). moreover, this horizontal element of the envelope offers an important potential for passive cooling because of its large surface exposed to the sky. (santamouris et al., 2001, akbari et al., 2005). passive cooling roof systems play an important role in dissipating heat and thermal gains during the warm season and maintain the indoor air temperature close to the comfort zone (1827°c) at the same time, it is inexpensive, simple to operate and the materials are available in the trade (charde et al., 2013). givoni (1978) defines passive cooling as a strategy based on a sustainable approach to cool buildings by natural means. this strategy involves controlling the heat exchange with the environment in order to offer a lower ambient temperature than the outside and a low energy consumption. on this matter, a large number of studies in the scientific literature have largely dealt with the influence of passive roof cooling techniques on the thermal and energy performance of residential spaces. these techniques concern, in particular, passive cooling: by evaporation (tiwari et al., 1994; raeissi and theri, 2000), by radiation "cool roof" (gentle et al., 2011; kolkotroni et al., 2013; lee et al., 2008) and by shading roof (madhumathi et al., 2014). 2. purpose of work the main objective of this paper is to study the impact of different passive cooling techniques applied on roofs (the reflective membrane, ventilated roof inverted earthen pots) and to examine the possibilities of their use on roofs of typical houses in the hot and arid climate of the city of biskra. in this regard, an experimental study was envisaged by testing four (04) cells (scale models) constructed of concrete and submitted to real climatic conditions. for this experiment, it is about the evaluation of the three (03) techniques chosen, also, to demonstrate their advantage in minimizing the thermal stresses in buildings, implicitly, to reduce energy consumption and preserve the environment. 3. literature review: background the concept of "cool roof" is documented by numerous scientific researches and studies based on experimental analyses carried out on residential and nonresidential buildings. therefore, synnefa et al. (2007) demonstrated that the cool roof surfaces remain cooler than traditional materials during summer conditions. this characteristic makes these roofs effective in improving the thermal performance of buildings, reducing energy consumption and providing superior environmental benefits compared to very insulated standard roofs (bakhlah et al, 2012). for their part, akbari et al. (2005) in their research on hot climates showed that increasing the solar reflectance of a roof from 0.2% to 0.6% can reduce 20% of cooling energy of buildings. nahar et al. (1999; 2003) realized a comparative study of four different techniques (1reflective paint, 2thermal insulation, 3shallow ponds with movable thermal insulation, 4evaporative cooling) used to improve the thermal performance of roofs. the experiment was made on five identical test structures measuring 120cm x 60cm x 90cm in jodhpur (india). they found that the reflective paint technique recorded a difference of 7°c compared to the prototype control. nevertheless, the best results have been obtained for the evaporative cooling technique (10°c), but this system requires a large quantity of water 50 ml/m² per day (fig. 1). another experimental study was conducted by hamdan et al. (2012) involving several passive cooling techniques. four structures measuring 0.6 m x 1 m x 1 m were tested during a summer day in amman, jordan. these techniques are as follows: 1standard ceiling roof (concrete prototype) 8 cm thick, which is generally used in jordan, 2roof with white cement, 3roof with broken pieces of white glazed, 4a roof covered with a layer of clay (ep = 3 cm). the researchers 76 athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 showed that structure four (04) was the best cooling potential recorded in the hot and arid climate of amman. amer (2006) studied experimentally the effect of passive cooling techniques related to the roof, including 1roof with white paint, 2thermal insulation with a 5cm layer of glass wool, 3 roof with chimney solar, 4evaporative cooling. in addition to a reference cell (a standard concrete roof); four (04) cells each one was equipped with a cooling system built in the warm and dry climate of manouifia, egypt. through measurements of the indoor air temperature of each test cell, during a typical summer day, researchers showed that the average difference in air temperature between the passive test cells and the reference cell reached: 6.5 °c; 2 to 7 °c; 3 to 8.5 °c and 4 to 9.8 °c, respectively. lee et al. (2009) experimentally analyzed the effect of a ventilated and non-ventilated inclined roof on the energy and thermal performance of a prototype (2.0 m x 1.4 m x 0.4 m) with different cavity widths. fig 1. passive test structures installed in the field 4. passive cooling roof techniques 4.1. concept of the reflective roof: the « cool roof » according to parker et al. (1995) "cool roof" is a passive technique based on a typology of construction that helps to reduce energy and thermal requirements from the building envelope. this technique is based on the ability of the roof to reflect solar radiation and to emit heat, which allows it to be cooler than a conventional roof (pisello et al., 2013). on the other hand, urban and roth (2010) have shown that during hot days, when typical dark roof temperatures can reach 66 °c, a reflective roof is around 28 °c (al-obaidi et al., 2014) (fig.2). fig 2. temperature of dark surface vs temperature of cool roof "cool materials" are materials that do not significantly increase their surface temperature under solar radiation and minimize the absorption of sunlight. conforming to zinzi et al. (2010), high athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 77 solar reflectance and thermal emissivity are two key properties that determine the temperature and degree of freshness of a roof: 1. solar reflectance (sr): the high capacity to reflect the incident solar radiation on the material. the reflectivity varies from about 0.1 (black color) to 0.8 (white color). 2. thermal emissivity (ε): the high capacity to radiate heat in infrared wavelengths. it is between 0.8 and 0.9. therefore, several advantages are provided by the "cool roof" technology: on the urban scale, the reduction in the temperature of the outside air leads to the reduction in the amount of heat transmitted by the roofs to the urban environment (zinzi et al., 2009; 2010). it is also possible to reduce the impact of the urban heat island phenomenon. at the building level, the "cool roof" improves the thermal comfort of spaces, limits the use of air conditioners and reduces the consumption of electricity (pisello et al., 2013). it also helps extend the life of roofs. 4.2. ventilated roof in areas where solar radiation is high, the ventilation of construction structures minimizes the cooling load during the summer period and in fact reduces the energy requirements of buildings (lee et al., 2009). one of the advantages of ventilation is the reduction of the heat fluxes transmitted by the structures exposed to the solar radiation thanks to the combined effect of shading surfaces and heat evacuation by the air flow in the ventilated zone; the air flow in the cavity efficiently transports heat and moisture to the outside and maintains the temperature of the internal part of the roof (balocco et al., 2002) (fig.3). fig.3. mechanism of heat transfer in a ventilated roof 4.3. inverted earthen pot on roof (roof shading) a system used in traditional architecture, where, through empty earthen pots functioning as small air in inverted and arranged cavities on the surface of the roof. these pots are waterproof, and they act as a barrier to heat transfer, due to the microscopic porous structure of their surface (fig.4). 78 athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 fig.4. schematic section of roof with inverted earthen pots shading 5. methodology the main objective of this study is to evaluate the influence of the various passive cooling-roof techniques on the thermal comfort felt inside spaces. these techniques have been tested under the hot and arid climate conditions of biskra, to define the most appropriate solutions to this region. in order to achieve these objectives, four (04) test cells have been constructed with identical geometric and thermos-physical characteristics. only the treatment of the roof is modified. so, the four prototypes of tests were realized on a reduced scale and subjected to the external conditions. three (03) cells were used to test passive cooling strategies through the roofs, specifically: cool roof, ventilated roof and a roof with inverted earthen pots. the fourth cell is served as a control structure which has a conventional roof. 5.1. main steps of experimental work the main steps of the research are described as follows: 1. choice of the study case: a matrix has been developed regrouping the different types of roofs used in private residential constructions in biskra. 2. measurement period: the period of the experiment is fixed at the hottest month of the year, which corresponds to the month of "july". 3. the experimental framework: include the choice of cell dimensions, choice of materials, and realization of the prototypes. 4. measurement: temperatures were taken every 2 hours with instruments that measured surface temperatures at specific points. 5.2. choice of study corpus: typology of existing roofs the study is carried out on roofs of individual contemporary constructions in biskra. through an investigation, a corpus of houses was assembled and then a typo-morphological analysis of the roofs was accomplished. the houses chosen for the study were selected on the basis of the most recurring physical characteristics, in particular building materials and exterior roofing treatments. we restricted our study to the flat roofs. a matrix, showing the different roofs construction alternatives and their coatings, was developed (table 1). athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 79 table 1 presents the matrix of the different types of roofs and the coding system developed for the purposes of the study. after measuring of inside temperature of 12 houses, we found that tprc has a maximum interior temperature 40.85 °c, which means a situation of thermal discomfort for the occupants and a significant consumption of electrical energy. table 1. coding system used to identify the roofs 5.3. climatic analysis of biskra the city of biskra is located in the southeast of algeria. it is located in the northern part of the sahara at a latitude of 34.8 ° n, longitude 5.73 ° e, and an altitude of 87m. biskra belongs to a region classified aridly where predominates a hot and dry climate with cold winters and hot summers. the maximum temperature reaches 46 °c during the month of july, and the minimum temperature falls to 13 °c in winter during the month of january. the average annual temperature is 37.3 °c, while the average annual humidity is around 40%. very low precipitation is recorded with a maximum of 20mm/year. the directions of the prevailing winds are northwest in winter, south-east in summer at a speed of 4 to 10 m/s. 5.4. experimental set-up 5.4.1. cells description in this study, the tprc type is taken as a case study because it represents the worst case. on this topic, four (04) cells (c1, c2, c3, c4) of (1.20 x 0.80 x 1m) orienting along the east-west axis t re a tm e n t o f ro o fs i n b is k ra typology of roofs used in biskra cement screed rc slab in hollow block (tp) slab with brick (tb) tprc tbrc floor tile rt tprt tbrt 80 athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 were built on a site in a dense urban area (old biskra) which benefits all day long from the solar energy without any mask (fig.5). fig.5. experimentation: dimensions and disposition of cells fig.6. (a)the measurements points; (b) testo 480; (c) lazer liner thermospot independently from the treatment of the roof, the cells tested had the same dimensional and thermos-physical properties; the roofs were 20 cm thick, and the exterior walls were made of 10 cm hollow brick. the structures were coated with cement to limit air infiltration and thermal bridges. an opening of 15cm x 10cm covered with a polystyrene plate allows to open the cells at the time of the measurements and to record the surface temperature of the roof. the structures were raised on the ground by 15 cm on a wooden support. cell 1 (c1): a structure without any treatment (reference case). cell 2 (c2): ventilated roof with a 10cm air cavity width. cell 3 (c3): a roof with a reflective coating (planet supra) which help to reduces the infrared (heat) consumptively; solar reflectance (sr) = 94.6%, emittance (ε) = 0.90. cells 4 (c4): inverted earthen pots on the roof. the clay has a low thermal conductivity. athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 81 6. results and discussion 6.1. temperature profiles of exterior surface the experimentation was conducted under conditions of sunny sky. figure 7 shows the surface temperature average (ts) of the 4 test cells compared with the average surface temperature of reference case (control cell) measured in-situ. 6 8 10 12 14 16 18 20 25 30 35 40 45 50 55 60 t ( °c ) time (h) ts exterior (control cell) ts exterior (inverted earthen pots) ts exterior (cool roof) ts exterior (ventilated roof) external air temperature fig.7. profiles of average external surface temperatures of test cells during the month of july. the figure below shows that the values of exterior ts increase gradually from morning to reach a peak at 14: 00h when the sun is at the zenith, the rays are perpendicular to the surface of the roof. at that point, the surface temperatures of the roofs decrease to register their lowest value at 6: 00h. these temperatures variations, which range from 23.30 ° c in the early morning to 56.87° c in the afternoon, are due to the properties of the outside surface of the roof. according to the analysis of the results (fig.7), c3 (reflective coating) represents the best case compared to the control cell (base case) with an average variance of 10.18 °c, then, noting that c1 which corresponds to the types of roofs actually realized (reference case) represents the worst case. the structure (c3), shows a low average of surface temperatures (ts) from 6h to 10h with a difference of 3 °c to 7 °c and from 16h to 18h with a difference of 2 °c to 3 °c for (c2). this is due to the high thermal emissivity of the white membrane (ε = 0.90) which allows the structure to release the heat stored through the day during the night when the outdoor ambient t decreases. 82 athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 concerning (c4), the profile of the average outside surface presents a reduction less than the other systems especially during the day from 10h to 16h; this is due to the shape of the earthen pots that leave parts exposed to the sun which increases the absorption of the solar gains by the concrete. therefore, it is preferable to use a layer of clay that completely shades the surface of the roof. 6.2. temperature profiles of interior surface the interior surfaces temperature profiles of the cells shown in fig.8, show that c3 records the lowest internal surface temperature with a difference of 2.53 to 7.98 °c. therefore, an average difference of 5.31 °c compared to reference case (c1). c2 has an interior surface temperature 41.47 °c with a variance of 3.28° c in comparison with c1. 6 8 10 12 14 16 18 25 30 35 40 45 50 t s ( °c ) temps (h) ts exterior (control cell) ts exterior (inverted earthen pots) ts exterior (cool roof) ts exterior (ventilated roof) external air temperature fig.8. profiles of the mean lower surface temperatures of the test cells during the month of july. the thermal behavior of the roofs shown in fig.8 reveals that the interior surfaces temperature increases with the outside ambient temperature. however, at the end of the day, as the outside t°c decreases quickly due to the absence of direct solar radiation, the internal surface temperature continues to rise. this phenomenon is caused by the thermal inertia of the roof which decelerates the passage of the heat waves through the material; the heat absorbed during the day begins to propagate inside the structures which contribute to increase the interior surfaces temperature. hence, the application of the "reflecting coating" technique achieves a reduction in the surface temperature which confirming, once again, its effectiveness as a cooling strategy in a hot and arid region. athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 83 6.3 interior air temperature profiles the use of a high reflectance paint "cool paint" is an effective way to increase the level of comfort inside spaces. reading the air temperature profiles inside the structures (ambient t) during the hottest month of the year, exhibited a lowering of the indoor air temperature of c3 with a variance of 3.33 ° c at 14h and 4.80 ° c at 18h compared to base case c1 (fig.9). this situation is explained by a low diffusion of heat inside the cell resulting from the high reflectance (= 0.9) and high thermal emittance of material with high radiative properties that protects the roof. 6 8 10 12 14 16 18 30 32 34 36 38 40 42 44 46 48 50 52 54 t s ( °c ) temps (h) ts (control cell) ts ( inverted earthen pots) ts ( cool roof) ts (ventilated roof) external air temperature fig.9. profiles of mean indoor air temperatures of test cells during the month of july. examining the graph of the temperature curves shown in fig.9, it appears that the t°c reaches its maximum value 50.20 °c at 14h for c3, 53 °c for c2 and c4 at 16:00 h, when the outside air temperature reaches 38.48 °c, c1 records 54 °c. in fact, the heat stored inside takes a long time to begin to dissipate to the outside due to the absence of natural ventilation. the retained information from these results confirms that: the more the roof is reflective, the more the surface temperature is lower, and consequently, more the transfer of heat is slowed down. 7. conclusions it's agreed that the roof is one of the most difficult parts of the building to protect, because it's the most exposed to direct sunlight. this paper presents the main results of an experimental work consecrate to optimize the thermal performance of the individual houses by applying passive cooling techniques on the roofs under warm and arid climatic conditions of biskra. the study focused on the evaluation of: 1) the cool roof, 2) the ventilated roof and 3) the reversed earth pots as passive, innovative and inexpensive strategies. the research explored all means to apply these techniques according to the conditions and specificities of the context of the study. the results of the experiment carried out showed that the use of the "cool roof" technique on standard concrete roofs significantly reduced the surface temperature. in addition, the 84 athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 ventilated roof, for its part, presents acceptable results if combined with natural ventilation which promotes the fast cooling of the structure. to conclude, the results obtained have validated by experimentation, the investigations founding this research and demonstrated the effectiveness of the technique of the "cool roof" which has the advantage both of minimizing the thermal stress undergone in buildings and its detrimental effect on health and, at the same time, makes it possible to rationalize energy consumption and preserve the environment. 8. references akbari, h., levinson, r., & rainer, l. (2005). monitoring the energy-use effects of cool roofs on california commercial buildings. energy and buildings, 37(10), 1007-1016. al-obaidi, k. m., ismail, m., & rahman, a. m. a. (2014). passive cooling techniques through reflective and radiative roofs in tropical houses in southeast asia: a literature review. frontiers of architectural research, 3(3), 283-297. amer, e. h. (2006). passive options for solar cooling of buildings in arid areas. energy, 31(8-9), 1332-1344. bakhlah, m. s., & hassan, a. s. (2012). the effect of roof colour on indoor house temperature in case of hadhramout, yemen. american transactions on engineering & applied sciences, 1(4), 2229-1652. balocco, c. (2002). a simple model to study ventilated facades energy performance. energy and buildings, 34(5), 469-475. bencheikh, h. (2013). full scale experimental studies of a passive cooling roof in hot arid areas. international journal of renewable energy technology research, 2(6), 170-180. charde, m., & gupta, r. (2013). annual thermal performance of a hollow roof in combination with a cavity wall and static sunshade: experimental study of energy-efficient rooms. journal of energy engineering, 139(4), 281-289. dabaieh, m., wanas, o., hegazy, m. a., & johansson, e. (2015). reducing cooling demands in a hot dry climate: a simulation study for non-insulated passive cool roof thermal performance in residential buildings. energy and buildings, 89, 142-152. gentle, a. r., aguilar, j. l. c., & smith, g. b. (2011). optimized cool roofs: integrating albedo and thermal emittance with r-value. solar energy materials and solar cells, 95(12), 3207-3215. givoni, b. (1978). l’homme, l’architecture et le climat. paris, éditions du moniteur, 460 p. hamdan, m. a., yamin, j., & hafez, e. m. a. (2012). passive cooling roof design under jordanian climate. sustainable cities and society, 5, 26-29. kolokotroni, m., gowreesunker, b. l., & giridharan, r. (2013). cool roof technology in london: an experimental and modelling study. energy and buildings, 67, 658-667. lee, s., park, s. h., yeo, m. s., & kim, k. w. (2009). an experimental study on airflow in the cavity of a ventilated roof. building and environment, 44(7), 1431-1439.. madhumathi, a., radhakrishnan, s., & shanthipriya, r. (2014). sustainable roofs for warm humid climates—a case study in residential buildings in madurai, tamilnadu, india. world applied sciences journal, 32(6), 1167-1180. nahar, n. m., sharma, p., & purohit, m. m. (1999). studies on solar passive cooling techniques for arid areas. energy conversion and management, 40(1), 89-95. nahar, n. m., sharma, p., & purohit, m. m. (2003). performance of different passive techniques for cooling of buildings in arid regions. building and environment, 38(1), 109-116. parker, d.s, barkaszi, s.f., chandra, jr. s. & beal, d.j. (1995). measured cooling energy savings from reflective roofing systems in florida: field and laboratory research results, in proceeding of the thermal performance of the exterior envelopes of buildings. ashrae, clearwater, (4-8), 105– 115. athmani and sriti, j. build. mater. struct. (2018) 5: 74-85 85 pisello, a. l., thiemann, a., santamouris, m., & cotana, f. (2013, june). analysis of a cool roof system for reducing cooling loads and improving cooling system efficiency. in proceedings of clima2013 international conf. prague (pp. 16-18). raeissi, s., & taheri, m. (2000). skytherm: an approach to year-round thermal energy sufficient houses. renewable energy, 19(4), 527-543. santamouris m., ed. (2001). energy and climate in the urban built environment. james and james science publishers. london, uk,1, 409. santamouris. (2005). passive cooling of buildings. advances of solar energy, ises, james and james science publishers, london. suehrcke, h., peterson, e. l., & selby, n. (2008). effect of roof solar reflectance on the building heat gain in a hot climate. energy and buildings, 40(12), 2224-2235. synnefa, a., santamouris, m., & apostolakis, k. (2007). on the development, optical properties and thermal performance of cool colored coatings for the urban environment. solar energy, 81(4), 488-497. tiwari, g. n., upadhyay, m., & rai, s. n. (1994). a comparison of passive cooling techniques. building and environment, 29(1), 21-31. urban, b., & roth, k. (2010). guidelines for selecting cool roofs. us department of energy building technologies program and oak ridge national laboratory. zinzi, m. (2010). cool materials and cool roofs: potentialities in mediterranean buildings. advances in building energy research, 4(1), 201-266. zinzi, m., & fasano, g. (2009). properties and performance of advanced reflective paints to reduce the cooling loads in buildings and mitigate the heat island effect in urban areas. international journal of sustainable energy, 28(1-3), 123-139. j. build. mater. struct. (2018) 5: 1-13 original article doi : 10.34118/jbms.v5i1.39 issn 2353-0057, eissn : 2600-6936 influence of some industrial wastes as a heavy aggregate on durability of concrete upon utilization in the special constructions gharieb m 1,*, el-sayed h a 1, abo-el-enein s a 2, sakr k 3, ali a h 1, el-sokkary t m 1 1 housing and building national research center, dokki, cairo, egypt. 2 faculty of science, ain shams university, cairo, egypt. 3 atomic energy authority, hot laboratories center, cairo, egypt. * corresponding author: medo_20109129@yahoo.com received: 05-11-2017 revised: 18-02-2018 accepted: 20-02-2018 abstract. the aim of this study is to investigate the effect of some industrial wastes as a heavy aggregate on durability of the concrete after exposure to different effects. the coarse aggregates used to perform the concrete were dolomite (control) and lead slag, while fine aggregate were sand and lead slag aggregate. the physical and mechanical properties of use draw aggregates were determined also the physical and mechanical properties of different types of concrete were studied. the linear attenuation coefficients (μ) and half value layer (hvl) of gamma rays measurements have been carried out using γ-rays sources of cs173 and co60. effect of sea water on the mechanical properties of high performance concrete; in addition, corrosion behavior of reinforcing steel embedded in concrete incorporating different aggregates upon exposure to sea water were studied. it was found that, the compressive strength for all concrete mixes made with dolomite and lead slag coarse aggregates satisfy the requirements of compressive strength for high performance concrete (grade-m60) after 28 days of curing in tap water. the results indicate that, the compressive strength values and gamma radiation shielding properties of concrete mix containing lead slag aggregate enhances upon replacing sand by fine portion of lead slag aggregate. the concrete mixes made with lead slag coarse aggregate proved their high endurance and could sustain sea water exposure, achieving compressive strength values exceeding grade m-60 concrete even after 6 months exposure. lead slag concretein spite of its efficient durabilityrequires the incorporation of a corrosion inhibitor to counteract the hostile effect of the high sulfate concrete in the aggregate. key words: high performance concrete, heavy weight concrete, linear attenuation coefficients (μ), corrosion behavior of reinforcing steel. 1. introduction concrete is one of the most common and important materials used for radiation shielding in nuclear facilities, due to its high compressive strength and high durability (kharita et al., 2008). concrete shielding properties depending upon its composition. different types of special concretes have been developed by changing the aggregate used in concrete, depending on the available natural and artificial local materials. aggregates are the largest constituent (about 7080 wt. % of the total weight) of normal concrete. concretes with specific gravities higher than 2600 kg/m3 are called heavy weight concrete and aggregates with specific gravities higher than 3000 kg/m3 are called heavy weight aggregates according to (ts en 206-1, 2002). heavy weight concretes have been widely used as radiation shield materials in nuclear facility. the aggregate of concrete containing heavy elements plays an important role in improving concrete shielding properties and attenuation of photons and neutrons (el-sayed, 2003; akkurt et al., 2012). the density of heavy concrete based on the specific gravity of the aggregates and the properties of the other components of concrete. the aggregates and other components are based upon the exact application of the high density concrete. different experimental measures such as effect of radiation, marine environment and corrosion of reinforcing steel were examined to evaluate the mailto:email@email.com 2 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 durability of high performance concrete and its suitability for utilization in the constructions of nuclear facilities (ouda, 2014). in the design of a protective shielding, one of the key factors is preventing the penetration of the rays. the property of the shield material of the most significance in preventing this penetration is its density. gamma rays originate within the reactor core and attenuation of gamma rays is dependent upon the density of the shielding materials. (al-humaiqani et al., 2013), found that the compressive strength of heavy hpcs plays an important role in enhancing the attenuation of gamma rays. the high performance concretes (hpcs) density considerably affects the attenuation of gamma rays. with the increase in the density, the attenuation coefficient increases linearly. (atzeni et al., 1997) studied the possibility of using granulated slags resulting from the smelting of lead and zinc in partial, or total replacement of sand in mortars and concretes. the major components of these vitreous slags are ca, si, fe and al compounds with lead concentration of a few percent. the slag mortars and concretes studied yielded satisfactory mechanical strengths. (alwaeli, 2013) investigated the production of concretes containing granulated slag of lead and zinc industry as sand replacement mixed in different proportions. the results showed that, the concrete mixed with granulated slag of lead and zinc as a sand replacement has higher compressive strength. also, granulated slag of lead and zinc incorporation resulted in an increase of the attenuation coefficient of gamma radiation. in many cases, deterioration of concrete structures in nuclear facilities occurs by the surrounding marine environment since they are usually located near the sea to maintain a permanent source of flowing cooling water to the nuclear plant system. in a marine environment, the chloride ion penetrate into the concrete either from water or sea winds carrying salts ions which destroy the passivity of steel and lead to initiation of corrosion. on the other hand, the principal reason for the deleterious attack of sulfate on concrete is the formation of gypsum and a complex compound known as calcium sulphoaluminate (ettringite). both ettringite and corrosion products occupy greater volume after crystallization in the pores of concrete than the compounds they replace (maes and belie, 2014; wegian, 2010; mehta, 1986) found that the sulfate related expansion in concrete are associated with ettringite. corrosion of steel reinforcement in concrete is one of the major causes of premature deterioration of reinforced concrete structures leading to structural failure. steel in concrete remains in the passive state in alkaline solution, but various contaminates such as chloride ions and carbon dioxide have a detrimental effect on passivity of steel (ouda, 2015). this study investigates some especial concrete having maximum compressive strength (gradem60) (strength value of more 600 kg/cm2 after 28 days) and high density of about 3 ton/m3 to be used for nuclear radiation shielding (ts en 206-1, 2002). accordingly, it is necessary to use the high pozzolanic reactive cementitious material to make high performance concrete. silica fume better than the other pozzolanic materials when used as a high pozzolanic reactive cementitious materials and 10 % silica fume (sf) as a partial addition to ordinary portland cement in the mix has been to be the most successful supplementary cementing materials (scm) for heavy high performance concrete (elhakam et al., 2012; abo-el-enein et al., 2014; gharieb, 2014; ouda, 2015). 2. experimental 2.1. materials the materials used to produce heavy high performance concrete (hhpc m60 grade) to use as radiation shielding concrete and high durability upon utilization in the establishment of nuclear facilities are: el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 3 ordinary portland cement (opc cem142.5 n), supplied from suez cement company, suez, egypt. silica fume (sf), provided from ferro-silicon alloys company, edfo-aswan, egypt. the two types of coarse aggregates used are suitable for usage as a concrete component and satisfy the needed requirements for the construction of nuclear facilities: a. lead slag (ls), which is produced extensively as a by-product through lead production at the" lead production company, helwan, egypt. b. crushed dolomite [camg(co3)2], obtained from attaka area, suez, egypt. coarse aggregates were separated by manual sieving into various fractions of size (5-20mm), according to egyptian standard specification 1109 (2002) and astm c637(2009). the fine aggregate was local sand, washed at the site to remove deleterious materials and chloride contamination. in some concrete mixes, sand has been replaced by the fine fraction of lead slag to produce heavy density concrete according to ts en 206-1 (2002). the physical properties of coarse and fine aggregates are given in table 1. the chemical compositions of cement, silica fume, coarse aggregates and its fine portion shown in table 2, were evaluated according to the limits specified by the ess 1109 (2002) and astm c637 (2009). the values of alkali silica reaction of samples of dolomite and lead slag aggregates were evaluated according to the limits specified by the astm 1260 (2014). it is evident that the expansion reached upon utilizing any of the coarse aggregates, dolomite (0.053 %) or lead slag (0.080 %) is below the expansion limit specified by the standard specification (i. e. not exceeding 0.1 %) high performance concrete should have low water/binder ratio. hence, effective dispersion of the mix is necessary to achieve proper workability without increasing the unit water concrete. this has been achieved by using a high rang water reducing superplasticizer (sp)type (g) to concrete mixes, compatible with astm c494 (2011). 2.2. sample preparation the slump test according to astm c143 (2010) was performed for fresh concrete, steel moulds cubes of 10×10×10 cm were used, the concrete was considered to be fully compacted. following casting, concrete specimens were covered with a plastic sheet and kept in the laboratory at room temperature 23 ± 2ᵒc and relative humidity 100 % for 24 h. after de-molding, specimens were cured in water until the time of testing. curing was done according to astm c511 (2009). table 1 . the physical properties of coarse and fine aggregates. limits of coarse aggregates lead slag dolomite sand physical & mechanical properties. fine coarse fine coarse 3.57 3.51 2.79 2.60 2.65 specific gravity, (g/cm3) 2.61 2.12 1.79 1.46 1.62 unit weight, (ton/m3) ≤ 4(1) ≤ 10(3) 16.80 0.23 14.97 0.38 1.40 clay and fine materials (%) ≤ 2.5(1) 0.60 0.79 water absorption, (%) ≤ 25(2) 18.52 40.21 flakiness index, (%) ≤ 25(2) 22.02 20.38 elongation index, (%) ≤ 30(2) 13.10 crushing value, (%) ≤ 45(1) 25.01 12.01 impact value, (%) (1) according to egyptian standard specification no. 1109 (2002). (2) according to egyptian code of practice for reinforced concrete no.2032017). (3) according to astm c637 (2009). 4 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 table 2. chemical analysis of starting materials, (wt., %). oxides, (%) chemical analysis of starting materials opc sf coarse aggregates dolomite lead slag sand sio2 21.32 95.22 1.67 9.03 93.40 al2o3 3.99 0.32 0.07 1.29 2.03 fe2o3 3.15 0.85 0.01 64.57 0.98 cao 62.04 0.26 35.54 2.24 0.71 mgo 2.51 0.55 17.51 0.27 0.25 so3-2.70 0.20 0.13 17.99 0.30 cl0.01 0.05 0.08 na2o 0.26 0.37 0.04 0.69 0.38 k2o 0.22 0.51 0.02 0.05 0.64 tio2 0.01 0.23 0.17 bao 0.27 p2o5 0.06 0.01 0.15 0.06 mno 0.10 0.44 0.03 v2o5 pbo 1.98 cuo 0.32 zno 0.02 0.37 l.o.i 3.75 1.50 44.99 0.01 0.74 total 99.95 99.99 99.97 99.89 99.92 samples were tested for compressive strength after 7, 28 and 90 days of preparations. the crushed samples at each hydration time were first ground and then subjected to stopping of the hydration process using a mixture of acetone and methanol in the ratio of 1:1 by volume, followed by drying to 80 °c for 24 h to prevent further hydration and the dried samples were kept in a desiccators for further analysis (taha et al., 1981; khater, 2010). 2.3. mix proportion mixes proportions of high performance concrete were reached to comply to grade m60 that having a strength value of more than 600 kg/cm2 after 28 days, and by the addition of supplementary cementitious materials (10 % silica fume), to the total cement content are given in table 3. the free water content of all mixes has been limited by about 35 % of the total binders in addition to water content absorbed by both coarse and fine aggregates. a substantial reduction of quantity of mixing water and getting a high workability is possible only with the use of superplasticizer. a superplasticizer was used to maintain a constant slump of 10 ± 2 cm. table 3. mixes proportions of heavy-weight concrete per 1 m3. mixes concrete ingredients, (kg/m3) opc sf w fine aggregates coarse aggregates sp sand fine d l-slag ds 450 45 173 772 944 9.5 lss 450 45 173 902 1102 9.4 lsf 450 45 173 1041 1273 13.8 3. investigation 3.1. density the density of fresh and hardened concrete was determined according to bs en 123907 (2009) as follow: el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 5 where, : density of specimen, m: mass of specimen, v: volume of specimen, ma: mass of suspended specimen in air and mw: mass of suspended specimen in water. 3.2. compressive strength this test was performed for cubes after 7, 28 and 90 days of preparation. the maximum compressive strength values of tested concrete specimens were carried out using a 2000 kn compression testing machine with a loading rate of 0.6 mpa/s according to bs en 12390-3 (2001). 3.3. radiation attenuation tests the attenuation coefficient of gamma rays on concrete specimens were performed using sodium iodide activated with thallium nai(tl) scintillation detector connected with a computerized multi channel analyzer (mca). the utilized standard radiation sources comprised cesium-137 (cs137) and cobalt-60 (co60) radioactive elements with photon energies of 0.662 mev for cs137 and two energy levels of 1.173 and 1.333 mev for co60 with activities five micro curie (5 µ ci). specimens were dried at 105 :c for 2 hours as recommended by yilmaz et al. (2011), prior investigated. the attenuation coefficient of gamma rays was determined by measuring the fractional radiation intensity (ix) passing through the thickness (x) as compared to the source intensity (io). the linear attenuation coefficient (μ) has been obtained from the solution of the exponential beer–lambert’s law (kharita et al., 2008): 3.3. sea water exposure effects the concrete cubic specimens of dimensions 10×10×10 cm were cast in the laboratory. then, the specimens were kept at 23 ±1 :c and 90 % relative humidity for 24 hours. after demoulding, the concrete specimens were cured in tap water for 28 days (zero time) at room temperature, and then immersed in seawater tank for 1, 3 and 6 months. at each age of immersion, the specimens were subjected to compressive strength measurement and variations in the structure were studied using sem techniques with respect to the reference samples after curing in tap water up to 28 days. also, sea water has been renewed continuously to maintain the concentration of the immersion medium. 3.5. testing the corrosion of reinforcing steel in concrete 3.5.1. preparation of reinforcing steel the reinforcing steel used in the present investigation was mild steel bars with diameter of 8 mm. the steel rods were mechanically polished to remove the firmly adherent mill scales on the surface of steel and degreased with acetone, then coated with wax so that a predetermined area was always exposed between the waxed areas (el-sayed et al., 1998; el-sayed et al., 2000). 3.5.2. preparation of steel in concrete electrodes the reinforcing steel rods were centrally placed in cylindrical 5×10 cm steel moulds, and the active areas of the rods were completely covered by the prepared compacted concrete. the concrete specimens were cured for (24 hrs.) after casting at room temperature 27±2 :c, then demoulded and continuously cured for 28 days in sea water then tested in sea water, simulating the medium that will affect the concrete during actual service in the nuclear power plant. 6 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 3.5.3. electrochemical measurements. several electrochemical techniques can be employed to evaluate the corrosion risk of the reinforcing steel in concrete. among them are open circuit potential (ocp), linear polarization resistance (lp) and concrete resistivity measurement (andrade and alonso, 2004; millard et al., 2001; gonzalez et al., 1995; song and saraswathy, 2007; elshami, 2012). 4. results and discussion 4.1. density of tested concrete the density values of fresh and hardened concrete mixes made with dolomite and lead slag coarse aggregates and fine aggregate of local sand or replacing sand by the fine portion of the raw aggregates are given in table 4. the results show that, the concrete containing lead slag aggregate is higher density than that of the concrete containing dolomite aggregates by 18 %. this is due to lead slag aggregate has higher specific gravity value than the dolomite aggregates. the results indicate also that, the density of the concrete increases by about 20 % upon replacing sand by the fine portion of lead slag aggregate. table 4. physical properties of the concrete mixes. mixes physical properties slump, (cm) density, (ton/m3) fresh concrete hardened concrete ds 9 2.45 2.41 lss 10 2.84 2.84 lsf 8 3.45 3.41 4.2. compressive strength of tested concrete. the compressive strength results of concrete mixes are given in fig. 1. the results reveal that, the compressive strength of the all hardened concrete mixes increases with the increase of age. this is mainly due to the progress of hydration process with curing time and increase of the amount of cement hydration products which deposited in the open pore system of the hardened leading to a decrease in the total porosity as well as an increase in the total contents of binding centers in the specimens; this leads may be to an increase in the compressive strength. the results indicate that, for all concrete mixes made with dolomite and lead slag coarse aggregates and containing 10 % silica fume satisfy the requirements of compressive strength for high performance concrete (grad-m60) after 28 days of curing. this enhancement in the compressive strength is mainly due to the physical and chemical effects of silica fume with its fineness and high silica content provides a filler effect and a pozzolanic reaction, causing pore refinement process and further densification of the transition zone occurring due to the conversion of lime forming from the hydration of cement into additional binding materials through lime-pozzolanic reaction that lead to improve the mechanical performance of the heavy concrete. the results indicate also that, the compressive strength values of the hardened lead slag concrete containing lead slag as a fine aggregate are higher than those containing sand specimen by 27% and 24 % at 28 and 90 days, respectively. the improvement in compressive strength due to the concaved holes and micro-pores on the surface of crushed coarse aggregate are filled with mortar and hydrated cement paste which increases the interlocking and the mechanical bond between the aggregate particles and cement matrix in concrete. el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 7 fig. 1. compressive strength of concrete made with dolomite and lead slag aggregates cured in tap water up to 90 days. 4.3. radiation investigation the liner attenuation coefficient (μ) measurements has been carried out using a collimated beam of the point isotropic γ-rays source cs173, with one line of energy [e= 662 kev] and co60 with two lines [e1=1173 kev and e2= 1333 kev] are given in fig. 2. the results reveal that, the total linear attenuations coefficient (μ) of concrete mixes increases with an increase in concrete density (ρ). therefore, the concrete mix containing lead slag aggregate (ρ =2.84) shows the highest attenuation coefficient than that containing dolomite aggregate (ρ =2.41). the results indicate also that, the total linear attenuation coefficient (μ) increases upon replacing sand by the fine portions of lead slag aggregate (for energy of 0.662, 1.173 and 1.332 mev). this is mainly due to the concrete mixes made with fine portions of lead slag aggregate more density than concrete mixes made with local sand. whereas, the density of concrete made with fine lead slag aggregates increase by 20 %, than concrete made with local sand as fine aggregate. 4.4. effect of sea water on the mechanical properties of high performance concrete (hpc) 4.4.1. compressive strength the compressive strength values of hpc mixes made with dolomite and lead slag aggregates and fine aggregate of local sand or replacing sand by the fine portion of raw coarse aggregates and containing 10 % silica fume as a partial additive to opc, cured in tap water up to 28 days (zero time), then immersed in sea water for 1, 3 and 6 months are graphically represented in fig. 3. the results reveal that, the compressive strength values of the concrete made of lead slag aggregate incorporating their fine portions as the fine aggregate are higher than the concrete incorporating sand as the fine aggregate. this is due to the high fineness of the lead slag fine portions leading to high compaction of the concrete enhancing the resulting strength. however, all the recorded strength values satisfy the requirements of the high performance concrete (grade m-60) (i. e. exceeding 600 kg/cm2). the results reveal also that, the compressive strength of concrete mixes made with dolomite coarse aggregate exhibit a slight increase upon immersion in sea water for 1 month, then decrease upon increasing the immersion time in sea water. on the other hand, the compressive 8 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 strength values for the other concrete mixes decrease with the progress of the immersion time in sea water. the compressive strength increase at early immersion time is mainly due to the pozzolanic reactivity of silica fume, causing pore refinement process and further densification of the transition zone between the matrix and the coarse aggregates to give a more compact closed body structure. in addition to the existence of calcium chloride in sea water that accelerate the hardening process of concrete. this leads to compressive strength enhancement. the compressive strength decrease with increased immersion time in sea water up to 6 months may be due to the aggressive attack of chloride and sulphate ions present in sea water and formation of detrimental voluminous expansive compounds e. g. gypsum, ettringite and calcium chloroaluminate (freidel's salt). fig. 2. linear attenuation coefficients of the high performance concrete containing different coarse aggregates using cs137 and co60 sources. fig. 3. compressive strength of concrete containing different coarse aggregates, immersed in sea water up to 6 months. el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 9 4.4.2. scanning electron microscopy (sem) investigation the sem micrographs obtained for the high performance concrete made with dolomite and lead slag aggregates and fine aggregate of local sand or replacing sand by fine portion of lead slag aggregates and curing in tap water up to 28 days, then immersed in sea water up to 6 months are shown in fig. 4. fig. 4(a) shows the micrographs of dolomite concrete. the micrographs of the dolomite concrete cured in tap water for 28 days, indicates the growth of hydration products, and increase in the amount of csh phase which filled the available pores. after 6 months immersion in sea water fig. 4 (à), the dolomite concrete displayed the formation of micro-cracks spread throughout the concrete matrix particularly at the interfacial transition zone (itz) between the aggregate particles and cement paste. that caused the decrease in the compressive strength. fig. 4 (b, c) show the micrographs of lead slag concrete with fine sand (b), and lead slag concrete with fine lead slag (c). the sem micrographs showed a relatively dense and compact microstructure with curing in tap water up to 28 days. this is due to the pozzolanic reaction of amorphous silica of silica fume with ca(oh)2 produced from cement hydration to form additional amounts of csh gel which deposited in the pore system. after 6 months immersion in sea water (fig. 4 (b`, c`)), the lead slag concrete displayed the presence of little change in the micrographs throughout the concrete matrix particularly at the itz between the aggregate particles and cement paste. this is due to the ingress of sulphate and chloride ions from sea water into the cementitious matrix and reacts with hydrated cement produce and form expansive products that leading to slight decrease in the compressive strength. fig. 4. sem micrographs of dolomite concrete (a), lead slag concrete with fine sand (b), and lead slag concrete with fine lead slag (c) for 28 days in tap water, then immersing in sea water up to 6 months (à), (b`) and (c`), respectively. 10 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 4.5. corrosion behavior of reinforcing steel embedded in concrete incorporating different heavy aggregates upon exposure to sea water 4.5.1. open circuit potential (ocp) fig. 5 shows the variation of corrosion potential with time of reinforcing steel embedded in high performance concrete incorporating dolomite and leads slag coarse aggregates, and fine aggregates of local sand or replacing sand by the fine portion of the raw aggregates, immersed in sea water for 28 days. fig. 5 reveals that, the potential of steel in the dolomite concrete starts at -153 mv, then slightly shifts in the negative direction until reaching the steady state value of -238 mv. these results indicate that, the corrosion condition of steel in dolomite concrete is at intermediate corrosion risk. while, the corrosion potential values of reinforcing steel in lead slag concrete submerged in sea water starts at -183 mv, then increases in the negative direction until reaching the steady state value at -363 mv. this indicates that, the steel susceptibility to corrosion is high. the results indicate that, the potential of the steel in the lead slag concrete containing fine lead slag starts at -378 mv, then increases in the negative direction until reaching the steady state value at -442 mv, revealing a tendency to corrode. 4.5.2. linear polarization (lp) and polarization resistance measurements as can be seen from table 5, the polarization (electrical) resistivity of concrete is inversely proportional to the embedded steel corrosion rate. in other words, low concrete polarization resistance will facilitate the ingress and penetration of aggressive ions till reaching the embedded steel hence endangering its passivity and increasing the corrosion risk as appeared by the corrosion rate increment. table 5 presents the polarization resistance (rp), the corrosion current density (icorr.) and the corrosion rates of reinforcing steel embedded in high performance concrete incorporating dolomite and lead slag coarse aggregates and fine aggregate of sand or replacing sand by the fine portion of the raw coarse aggregates, immersed in sea water for 28 days. it can be seen that, lead slag concrete having sand or lead slag fine portion as the fine aggregate offer the lowest polarization resistance values and, consequently, the highest corrosion rate. on the other hand, dolomite concrete offers the highest polarization resistance values, the lowest corrosion rate values. fig. 5. open-circuit potential/ time curves of steel in high performance concrete containing dolomite and lead slag aggregates, immersed in seawater for 28 days. el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 11 table 5. corrosion risk for steel in high performance concrete containing dolomite and lead slag aggregates, immersed in sea water for 28 days. sample code polarization resistance, rp (kω.cm2) corrosion current density, icorr (µa/cm2) corrosion rate, (μm/year) ds 129 0.692 1.892 lss 82 0.988 2.679 lsf 63 1.302 3.821 5. conclusions 1. the slump values of the heavy concrete decreases while, the density increases upon replacing sand by the fine portion of magnetite and lead slag aggregates. 2. the compressive strength for all concrete mixes made with dolomite and lead slag coarse aggregates and containing 10 % silica fume satisfy the requirements of compressive strength for high performance concrete (grade-m60) after 28 days of curing in tap water. 3. the compressive strength values and gamma shielding properties of concrete mixes containing lead slag aggregate enhances upon replacing sand by fine portion of lead slag aggregate. 4. the concrete mixes made with lead slag coarse aggregate preferably with their fine portion as the fine aggregate proved their high endurance and could sustain sea water exposure, achieving compressive strength values exceeding grade m-60 concrete even after 6 months exposure. 5. lead slag concrete inspite of its efficient durability requires the incorporation of a corrosion inhibitor to counteract the hostile effect of the high sulfate concrete in the aggregate. 6. references abo-el-enein, s. a., el-sayed, h. a., ali, a. h., mohammed, y. t., khater, h. m., & ouda, a. s. (2014). physicomechanical properties of high performance concrete using different aggregates in presence of silica fume. hbrc journal, 10(1), 43-48. akkurt, i., başyigit, c., akkaş, a., kilingarslan, ş., mavi, b., & giinoglu, k. (2012). determination of some heavyweight aggregate half value layer thickness used for radiation shielding. acta physica polonica-series a general physics, 121(1), 138. al-humaiqani, m. m., shuraim, a .b. &hussain, r. r. (2013). γ-radiation shielding properties of high strength high performance concretes prepared with different types of normal and heavy aggregates, asian transactions on engineering, (ate issn: 2221-4267), 03,18-28. alwaeli, m. (2013). application of granulated lead–zinc slag in concrete as an opportunity to save natural resources. radiation physics and chemistry, 83, 54-60. andrade, c., & alonso, c. (2004). test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method. materials and structures, 37(9), 623-643. astm 1260, (2014). standard specification for alkali aggregate reaction for concrete. astm c143, (2010). standard test method for slump of hydraulic cement concrete. astm c494, (2011). standard specification for chemical admixtures for concrete. astm c511, (2009). standard specification for mixing rooms, moist cabinets, moist rooms and water storage tanks used in the testing of hydraulic cements and concretes. 12 el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 astm c637, (2009). standard specification for aggregates for radiation-shielding concrete. astm c637, (2009). standard specification for aggregates for radiation-shielding concrete. atzeni, c., massidda, l., & sanna, u. (1996). use of granulated slag from lead and zinc processing in concrete technology. cement and concrete research, 26(9), 1381-1388. bs, en 12390-3, (2001). testing hardened concrete part 3: compressive strength of test specimens. bs, en 12390-7, (2009). testing hardened concrete, density of hardened, concrete. egyptian code of practice 203, (2017). for reinforced concrete. egyptian standard specification 1109, (2002). concrete aggregates from natural sources. egyptian standard specifications no. 1109, (2002). concrete aggregates from natural sources. elhakam, a. a., mohamed, a. e., & awad, e. (2012). influence of self-healing, mixing method and adding silica fume on mechanical properties of recycled aggregates concrete. construction and building materials, 35, 421-427. el-sayed, a. (2002). calculation of the cross-sections for fast neutrons and gamma-rays in concrete shields. annals of nuclear energy, 29(16), 1977-1988.. el-sayed, h. a., ali, h. a., el-sabbagh, b. a. &hassan, h. m. (1998). role of an innovated waste product mix in promoting concrete characteristics: (a) strength and durability, 8th int. confr. on environmental protection is a must", alexandria, egypt. el-sayed, h. a., el-sabbagh, b. a., & hassan, h. m. (2000). role of an innovated waste product mix in promoting concrete characteristics: (b) corrosion protection of steel reinforcement, egyptian journal of applied sciences, 15(8), 1. elshami, a. (2012). efficiency of corrosion inhibitors used for concrete structures in aggressive environment, ph. d. thesis, in materials science for engineers, nantes university. gharieb, m. (2014). studied on the physico-chemical and mechanical characteristic of the hardened blended cement pastes containing some industrial wastes, b.sc. thesis faculty of science, alazhar university. gonzalez, j. a., andrade, c., alonso, c., & feliu, s. (1995). comparison of rates of general corrosion and maximum pitting penetration on concrete embedded steel reinforcement. cement and concrete research, 25(2), 257-264. kharita, m. h., takeyeddin, m., alnassar, m., & yousef, s. (2008). development of special radiation shielding concretes using natural local materials and evaluation of their shielding characteristics. progress in nuclear energy, 50(1), 33-36. khater, h. m. (2010). influence of metakaolin on resistivity of cement mortar to magnesium chloride solution. ceramics-silikáty, 54(4), 325-333. maes, m., & de belie, n. (2014). resistance of concrete and mortar against combined attack of chloride and sodium sulphate. cement and concrete composites, 53, 59-72. mehta, p. k. (1986). concrete-structures, properties and materials, prentice-hall, inc., englewood cliffs. new jersey, 105-169. millard, s. g., law, d., bungey, j. h., & cairns, j. (2001). environmental influences on linear polarisation corrosion rate measurement in reinforced concrete. ndt & e international, 34(6), 409-417. ouda, a. s. (2014). development of high-performance heavy density concrete using different aggregates for gamma-ray shielding, advances in civil, environmental and materials research, (acem 14), 24-28. ouda, a. s. (2015). development of high-performance heavy density concrete using different aggregates for gamma-ray shielding. progress in nuclear energy, 79, 48-55. song, h., & saraswathy, v. (2007). corrosion monitoring of reinforced concrete structures-a review, int. j. electrochem. sci., 2, 1-28. el-sayed et al., j. build. mater. struct. (2018) 5: 1-13 13 taha, a. s., el-didamony, h., abo el-enein, s. a., & amer, h. a. (1981). physicochemical properties of supersulphated cement pastes, zement-kalk-gips, 34(6), 351–353. ts en 206–1. concrete-part 1(2002): specification, performance, production and conformity t.s. ankara: turkey. wegian, f. m. (2010). effect of seawater for mixing and curing on structural concrete, the ies journal part a: civil & structural engineering, 3(4), 235-243. yılmaz, e., baltas, h., kırıs, e., ustabas, i., cevik, u., & el-khayatt, a. m. (2011). gamma ray and neutron shielding properties of some concrete materials. annals of nuclear energy, 38(10), 2204-2212. j. build. mater. struct. (2019) 6: 50-63 original article doi : 10.34118/jbms.v6i2.68 issn 2353-0057, eissn : 2600-6936 corrosion behavior of reinforcing steel in concrete elements in alkaline medium bourenane n1, *, sedira n2, hamlaoui y1 1 university of mohamed chérif messaadia, dept. process engineering, lpmr lab., rue d’annaba, bp 1553, 41000 souk-ahras, algeria 2 univ souk ahras. fac sci and tech. dept material sciences. rue d’annaba. bp 1553. 41000 souk-ahras. algeria * corresponding author: bourenane_nadjette1990@yahoo.fr received: 09-02-2018 accepted: 24-05-2019 abstract: corrosion of steel in reinforcement concrete is complex. when chloride ions and oxygen reach reinforcing steel, corrosion is initiated. the deterioration process starts with expansions of the bare steel substrate then after cracks in the concrete are developed. the aim of this work is to determine firstly, through the electrochemical technic, the critical concentration of chloride ions which are responsible for the initiation of the dissolution step. then, the effect of the external parameters on the rate of penetration of the chloride ions into the concrete are also evaluated. for this propose, the electrochemical behavior of the steel of construction “e24” is studied in carbonate medium without and with different concentrations of chloride ions. the effect of various parameters such as temperature, ions concentration and solution ph was also evaluated through the evolution of the open circuit potential, d.c polarization measurement and electrochemical impedance spectroscopy. the d.c polarization and eis results shows that the addition of 0.5m cacl2 (as critical concentration) to the saturated ca(oh)2 solution, brings to a rapid and a continuous dissolution of the substrate where after 3 hours of immersion time the whole surface of the substrate was covered the corrosion products. this is may be due to specific adsorption of cl-. key words: reinforcing steel, d.c polarization, sie, alkaline medium, chloride ions. 1. introduction the degradation phenomena and the damage of reinforced concrete structures depend on a large number of factors which intervene, not individually, but in a more or less complex relationship with each other: the nature and structure of the material, the environment and its chemical characteristics, the temperature, to which the material is subjected, the constraints imposed upon it. the coating concrete, or the mortar around an armature, offers the steels a double protection against corrosion. at first, it acts as a physical barrier that limits the penetration of aggressive agents and the access of oxygen to the framework. then, thanks to the composition of the interstitial solution and its high ph, between 12 and 13, the concrete offers a chemical protection against corrosion. indeed, at this ph level, the reinforcing steels do not corrode because they are covered with a passive film with a thickness between 10-2 and 10-1 μm, called "passive layer", most often formed with fe3o4-γ fe2o3. however, the porosity of the concrete is at the origin of the reduction of its capacity to isolate the steel from the aggressive substances of the external environment. thus, in the presence of water and oxygen, the passive film is destroyed by various agents such as chlorides and carbon dioxide. the corrosion is then possible; there is a reduction in the sections of the steel and the formation of rust, the volume of which is at least twice as great as that of the lost steel. the accumulation of these corrosion products leads to the swelling and deformation of the coating, which eventually cracks the concrete or causes it to burst. a saturated solution of calcium hydroxide is usually used as a synthetic solution representative of the interstitial solution of the concretes in order to study the bourenane et al., j. build. mater. struct. (2019) 6: 50-63 51 electrochemical behavior of metallic reinforcements (kosmatka et al., 2004). however, the interstitial solution also contains other cations such as ca2+, na+ and k+ and anions such as oh and so2-4. sodium and potassium ions come from alkali metal oxides, such as na2o and k2o, present in the cement. as for the sulphate ions, they can come from the gypsum (caso4. h2o) added during the cement manufacturing, agents of contaminants or the water used during the mixing (rosenberg, 1989). it has also been shown that the quality of the oxide film formed on the surface of the steel depends, on the ph and the temperature, on the chemical composition of the solution and particularly on the presence of sulfate ions. the purpose of this work is to study the electrochemical corrosion behavior of the structural steel e24, generally used as a constituent material of metal reinforcements in construction concrete using stationary and nonstationary electrochemical techniques. during this study, two solutions were used to allow us to study the corrosion behavior of the mild steel in a representative environment, the phenomena of carbonation of concrete and to simulate the phenomena of penetration of chloride ions: calcium hydroxide solution (ca(oh)2) saturated with a concentration of 3g/l). calcium hydroxide solution (ca(oh)2) with a concentration of 3g/l with different concentrations of cacl2 (the concentration of cacl2 changes when we study the influence of the chloride content). thus, the influence of the other parameters such as agitation speed, the ph of the medium on corrosion, is elaborated in order to understand and propose the mechanism involved in this corrosion. 2. materials the studied material is a mild steel e24, generally used as a constituent material of metal reinforcements in construction concrete. the composition of the major elements of the steel e24 is represented in the following table: table 1. chemical composition of e24 steel. element % max. carbon (c) 0.17 manganese (mn) 1.40 phosphorus (p) 0.045 sulfur (s) 0.045 nitrogen (n) 0.009 iron (fe) the rest 3. samples preparation the working electrodes e24 are machined in the form of a spherical cut with a surface area of 1.33 cm2. the samples are then coated in epoxy resin. only one side is active, and the other one is chemically covered with inert resin. in order to ensure electrical contact with the electrochemical assembly, a conductive wire has been welded to the end of the inactive surface. after that, the active surface of the electrode is polished to an abrasive grinding paper sic varying between 180 and 2500. the surface is then cleaned in an ethanol solution before being dried by a stream of hot air. the quality of this preparation is important because the electrochemical corrosion measurements or the coating deposition measurements are sensitive at the surface state (neville, 2000). in addition, it allows minimizing the presence of the surface heterogeneities. 4. electrochemical cell, aqueous synthesis solution the electrochemical tests are carried out in a conventional three electrode cell containing approximately 250 ml of solution (fig. 1) : a working electrode in ordinary steel e24, a saturated calomel reference electrode (hg / hg2cl2 / kcl sat) (e0ecs = + 0.241v / enh) and an auxiliary electrode or counter electrode of platinum with a surface area of 1cm². 52 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 fig. 1. working cell used for the electrochemical study. during this study, two solutions were used to allow us to study the corrosion behavior of the mild steel in a representative environment, the phenomena of carbonation of concrete and to simulate the phenomena of penetration of chloride ions calcium hydroxide solution (ca(oh)2) saturated with a concentration of 3g/l). calcium hydroxide solution (ca(oh)2) with a concentration of 3g/l with different concentrations of cacl2 (the concentration of cacl2 changes when we study the influence of the chloride content). 5. electrochemical characterization of the corrosion of structural steel e24 5.1 evolution of corrosion potential the electrochemical experiments were carried out using a potentiostat (bio-logic 150) piloted by the software eclab, version 10.40. the principle of this test is to immerse the electrode of the steel e24 in both ca(oh)2 solution and ca(oh)2 solution with 0.5m of cacl2 and to follow the spontaneous evolution of the corrosion potential as a function of time. this test may take several hours until the corrosion potential stabilizes (fig. 2). following the abandonment potential as a function of time (fig. 2), in both solutions, shows that they have different behaviors. indeed, we notice that: the ca(oh)2 solution: in the first hour of immersion, ecorr decreases slightly which means that there is an attack of the metal, but ecorr increases considerably more quickly with time and varies between -0.54v to -0.47v for an immersion time of 13h and reaches a stationary value after 18 h. this increase reflects the formation of a protective oxides layer on the surface of the steel which continues to evolve after 18 h. according to el haleem et al (2010-a) the value of the corrosion potential of a mild steel becomes increasingly noble (increasingly anodic value), reflecting the evolution in thickness and composition of the passive layer formed on the surface during the immersion time. the ca(oh)2 solution with 0.5m of cacl2: an optimization of the potential for the first two immersion hours, this behavior can be associated with the formation of a layer of surface protective corrosion product, at the end of the third immersion hour, a displacement of the potential towards more negative values in the simulating solution which stabilizes at -0.56v after 18h of immersion. this evolution of the potential is generally associated with a continuous dissolution of the material in the study medium (el haleem et al., 2010-b). bourenane et al., j. build. mater. struct. (2019) 6: 50-63 53 fig. 2. evolution of the corrosion potential in the two simulating solutions of concrete ca(oh)2 + ca(oh)2 with 0.5m of cacl2 5.2 influence of the agitation speed in ca(oh)2 solution 3.2.1 polarization curves in order to study the agitation effect of the medium on the electrochemical behavior of the steel e24, we have plotted polarization curves in the simulating solution ca(oh)2 (fig.3) with and without agitation in order to determine the electrochemical parameters such as the polarization resistance rp, the corrosion intensity (icorr), the corrosion potential (ecorr), the passivation step (q passivation) and the corrosion speed. fig. 3. polarization curves of the steel e24 in ca(oh)2 solution with and without agitation. 54 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 fig. 4. cyclic polarization in ca(oh)2 solution agitated and non-agitated. the test parameters are: scanning speed: 30 mv / min for the polarization resistance curves, 60 mv / min for the tafel curves and 120 mv / min for the cyclic polarization curves (these values correspond to the stationary state of the system). potential range (abscissa): -250 v to +250 v / ecs for the tafel curves. 100mv to 1200mv / sce for the cyclic polarization curves. the relative values for each case (without agitation, with agitation) are presented in table 2. table 2. electrochemical parameters determined from linear and cyclic polarization curves in the simulator solution. figs. 3 and 4 show the polarization curves for the steel e24 plotted in the ca(oh)2 solution agitated and non-agitated. in the cathodic domain, when the two curves are plotted from the corrosion potential ecorr, a pseudo-plateau is observed around -0.5 v / sce due to the reduction of oxygen. then, from: -0.5 v / sce, the cathode current density increases for both curves. this behavior can be explained by the contribution of the reduction of the oxide film formed during the tests (byfors, 1987). thus, we can say that during the cathodic plot the oxides are reduced and the surface becomes totally active for the reduction of the oxygen. in the anodic domain, a plateau of passivity is observed for both curves, but from the value of the rupture potential which is greater in the agitated solution than in the non-agitated solution and the increase in the density values of current for a more agitated solution than the increase in the non-agitated solution we can explain this behavior by the rupture of the passive film and the development of pitting in both cases (bertolini et al., 2004). but, the rupture is more rapid in the agitated solution, this shows that the corrosion products adhere hardly at the metallic surface for the agitated solutions and this is demonstrated by the value of the compaction index of the passive layer. electrochemic al parameters rp (ohm) ecorr (mv) icorr (µa/cm2) βa (mv) βc (mv) q (ma.v) ⁄ (v) without agitation 7590 -590,532 7,075 356,3 125 1,169 165,229 with agitation 12150 -591,077 28,166 670,9 181,3 1,949 69,196 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 55 5.2.2. electrochemical impedance measurement in our study, the impedance spectra were measured at the corrosion potential with a frequency sweep of 100 khz to 10 mhz at 10 points per decade and a modulation signal amplitude of 10 mv. the modeling of the spectra was carried out by the software "zview" using the equivalent electrical circuit (cee) method. the electrochemical impedance diagrams were plotted after the linear polarization resistance curves. fig. 5 (a) shows the diagram in the complex plane (nyquist diagrams) for an agitated and non-agitated ca(oh)2 solution. (a) (b) (c) fig. 5. impedance diagrams of the steel e24 in ca(oh)2 solution 3g/l, plotted in agitated and non-agitated solution. (a) nyquist diagrams, (b) bode representation of the phase and (c) imaginary part of impedance as a function of frequency. fig. 6 shows the equivalent circuit proposed to simulate the impedance diagrams in order to better understand the behavior of the steel. in this equivalent circuit, re and rf represent respectively the resistance of the electrolyte and the resistance of the passive film (the passive layer deposited on the surface of the electrode). the equivalent circuit is complemented by a constant phase element (cpe). it is often very difficult to match the model to the experimental 56 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 data. indeed, the acquisition of low frequency points is sensitive to variations in the potential, particularly related to the phenomena of passivation/repassivation of the steel. fig. 6. equivalent electrical circuit describing a metal-passive layer-electrolysis interface. the different diagrams obtained (fig. 5 (a)) have the same shape whatever the potential and they have a capacitive loop with a large diameter characteristic of a passive layer. all the diagrams overlap but show a slight slip in frequency when the solution becomes agitated. these results show that the electrochemical behavior of the steel is similar to ecorr and to an anodic potential belonging to the passive field. indeed, the diameter of the capacitive loop decreases in the non-agitated solution compared with the agitated solution, translating the less protective nature of the oxides layer formed, and the kinetics of dissolution of the metal. the bode representation of the phase (fig. 5 (b)) reveals the presence of a single time constant whatever the potential. the representation of the imaginary part of the impedance as a function of the frequency in logarithmic coordinates (fig. 5 (c)) is a straight line with a slope lower than 1 in absolute value in the low frequency domain and a stability in high frequencies, bringing out a cpe behavior. in the case of an oxide layer, the cpe behavior is generally attributed to a normal distribution of time constants induced by a significant variation in resistivity within the film (longuet p, 1973). for this purpose, we may say that the cpe parameters are related to properties of the oxide layer, which is translated by a reduction in the thickness of the protective layer in the non-agitated ca(oh)2 solution compared with an agitated solution. according to the results obtained in the ca(oh)2 solution with and without agitation we can conclude that the measurements are more reliable and significant in the agitated solutions better than in the nonagitated solutions. therefore, for our tests carried out to study the influence of the other parameters on the electrochemical behavior of the structural steel e24 are carried out with a moderate agitation speed of 40 rpm. 5.3. study of the effect of chlorides in this study, we added different levels of calcium chlorides in the calcium hydroxide solution. the tests were carried out in the presence of concentrations ranging between 0.01-0.5m of calcium chloride with a moderate agitation speed equal to 40 rpm. 5.3.1. polarization curves the effect of chlorides is more important. the corrosion potential is displaced to more anodic values (fig. 7), the anodic currents are higher and the hysteresis is increased with increasing chloride concentrations. in the case of a solution without addition of chloride, we notice that the hysteresis is very low; there is no attack of the metal when it is immersed in the solution, but we witness the formation of a very fine protective layer. however, the current densities (icorr) increase as the bourenane et al., j. build. mater. struct. (2019) 6: 50-63 57 concentrations of the chlorides increase with a decrease in the polarization resistance as well as an increase in the corrosion speed (table3), which explains the deterioration of the passive film formed at the surface of the electrodes and the high aggressiveness of the chloride ions (longuet, 1973; longuet et al., 1973). in the anode domain, it should be noted that the electrochemical process at the steel-solution interface is controlled by pure activation kinetics. the extrapolation of the tafel lines to the corrosion potential makes it possible to calculate the corrosion speed. the anodic plateau is more extensive when the amount of chlorides decreases. the cyclovoltamograms plotted in the range of -100 mv to 1200 mv /sce (fig. 7) show an increase in hysteresis with the increase in clcontent which indicates a strong degradation of the metal. the increase in the value of the oxidation peak current is due to the conversion of ferrous hydroxide (fe(oh)2) to ferric hydroxide (feooh). the mechanism of corrosion takes place according to the following reactions (ghods et al., 2009): • in the anode zone: • in the cathode zone: in the second step of the corrosion process, the dissolved metallic ion (fe2+) reacts with the hydroxyls to form a precipitate which covers the steel according to the reaction: in a sound concrete, which means if the ph> 11 and in the total absence of chlorides, we notice the formation of feooh protective layer according to the reaction? in the presence of the chlorides, the covering product no longer becomes leak-proof, and the steel corrodes following the sequence of the following reactions: when the concentration of chloride ions is lower than that of the hydroxyl ions, stable ferrous hydroxide is formed, on the other hand, when it is higher, the hydroxide formed is unstable. an intermediate compound is formed, which is green rust [ , feohcl, ], which converts to lepidocrocite (hydrated ferric oxide ) containing chlorine according to the reaction below (diamond, 1975) [ ] [ ] hydroxyde ii rouille verte i hydroxyde i this, explains the results observed on our polarized samples, a green product covers the surface of the steel and transforms into black. therefore, we can conclude that the addition of the different quantities of cacl2 in the solution increased the probability of corrosion initiation for structural steel e24. for the study the influence of chemical parameters on the electrochemical behavior to the corrosion of the structural steel e24 we use a ca(oh)2 solution with a concentration of 3g/l with 0.5m of cacl2. 58 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 the polarization and cyclo-voltamogram curves of the steel e24 in the calcium hydroxide (ca(oh)2) solution in the presence of the different quantities of cacl2 and the electrochemical parameters extracted from these curves are shown in figures and the table below: fig. 7. polarization curves of the structural steel e24 in the ca(oh)2 solution with different concentrations of cacl2. table 3. electrochemical parameters determined from linear and cyclic polarization curves with different concentration of cacl2 5.3.2. electrochemical impedance measurements the study of the corrosion mechanism of the reinforcing steel e24 in the saturated ca(oh)2 solution in the presence of different concentrations of cacl2 was carried out by electrochemical impedance measurements, with a free corrosion potential . the impedance diagrams recorded for these concentrations are shown in figs 8 and 9. electrochemical parameters rp ohm ecorr (mv) icorr µa/cm2 βa (mv) βc (mv) q (ma.v) ⁄ (v) concentrations of cacl2 without the addition of cacl2 7909 -522,104 4,335 435,2 148,1 1,989 458,824 with 0.01 of cacl2 4024 -582,213 10,895 263,7 107,6 5,16 473,611 with 0.1 of cacl2 1579 -577 18,714 264,7 127,6 109,32 5841,616 with 0.2 of cacl2 1446 -453,77 30,968 314,5 275,8 194,321 6274,897 with 0.3 of cacl2 715 -433,99 19,07 216,4 195,5 297,031 15575,826 with 0.4 of cacl2 520 -440,119 29,467 294,2 269,2 342,371 11618,794 with 0.5 of cacl2 446 -465 43,38 178,3 335,8 406,453 9369,594 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 59 fig. 8. impedance diagrams (nyquist plane) of the reinforcement steel e24 in a ca(oh)2 solution with different concentrations of cacl2 (a) (b) fig. 9. impedance diagrams (bode plane) of the reinforcement steel e24 in a solution of ca(oh)2 with different concentrations of cacl2. the diagrams are composed of two capacitive loops: one with a smaller diameter in high frequency (hf) and one with a larger diameter in low frequency (bf) (fig. 8). the size of the first loop increases progressively with the decrease in concentration of chloride ions, this loop corresponds to a charge transfer phenomenon which confirms a lot the aggressive effect of chloride ions. when the concentration of chlorides increases we notice the appearance of a second loop, which is attributed to the phenomenon of initiation of diffusion. on the bode diagrams (fig. 9a), we observe the presence of a resistive region at high frequencies. the polarization resistance rp decreases with the increase in chloride concentrations (table 03) but it decreases significantly at a concentration of 0.3m and higher. in this case we can say that at low concentrations the steel is able to resist and the oxide layer plays a little bit the role of a protective layer, but beyond the concentration of 0.2m there is an attack of chloride ions at the complete surface of the electrode and the corrosion resistance of the steel becomes very low for these concentrations. 60 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 as for the variation of the phase as a function of the frequency (fig. 9b), we notice that the phase angle reaches maximum values at high concentrations, so, for the different chloride concentrations two time constants have been observed. the interpretation of the electrochemical impedance spectroscopy (sie) diagrams makes it possible to determine the different processes that take place at the electrode (byfors et al., 1986). in some cases, especially when the time constants of the elementary steps are poorly decoupled, it is necessary to model the impedance of the electrochemical system by that of an equivalent electrical circuit. the analysis of the impedance data of figs. 8 and 9 from the equivalent circuit of fig. 10, using the z-view software, makes it possible to determine the cpe parameter values, the charge transfer resistance rt as well as the resistance of the electrolyte re. thus, the values obtained are presented in table 4 : fig. 10. modeled equivalent circuit of the electrode/electrolyte interface. table 4. electrochemical parameters deducted from impedance diagrams. cc de cacl2 re (ohm.cm²) rt (ohm.cm²) α q (ω-1 cm-2 sα) cpe (μf/cm²) 0.1m 13,06 1435 0.83 1.9x10-3 1075 0.2m 9,45 1317 0.82 1.6x10-3 1135 0.3m 10,23 985 0.71 1.2x10-3 1532 0.4m 8,73 743 0.71 1.2x10-3 1561 0.5m 6,81 684 0.71 1.2x10-3 1585 the impedance of a cpe is given by: it brings out two parameters, q and α, independent of the frequency. a cpe behavior can be attributed to a distribution of time constants either along the surface of the electrode (surface distribution) or along the normal axis to the electrode surface (normal distribution). a surface distribution may come from surface heterogeneities (grain boundaries, crystalline faces, etc.) or non-uniform distributions of current and potential induced by the electrode geometry, whereas a normal distribution can be generated by a porous electrode or a variation of conductivity within surface layers such as oxide films (rothstein et al., 2002). in the case of a r // cpe circuit, the parameters of the cpe α and q can be graphically estimated according to the method presented by orazem et al. (2006) α corresponds to the absolute value of the slope of the curve log | z | vs log f: | | | | bourenane et al., j. build. mater. struct. (2019) 6: 50-63 61 and q is obtained from α as follows: ( ) the values of α and q obtained by adjustment correspond to those usually measured for oxide layers ; the passive layer type (diamond, 1981). the value of q decreases as the concentration increases, which is consistent with an increase in the thickness of the dox oxide layer with an increase in concentration. similarly, in the case of cpe behavior, a decrease in q corresponds to an increase in dox. thus, the increase in the concentration of the clions leads to the decrease in the transfer resistance rt, which explains the decrease in the corrosion resistance. 5.4. study of the effect of the ph of the medium the polarization curves plotted in a carbonate medium with 0.5m of cacl2 for studying the influence of the ph are shown in fig. 11. the electrochemical characteristics deduced from these polarization curves by the tafel line plots and the linear polarization curves are summarized in table 5. the plotting of these curves at different ph values (ph varies from 06-08-10 and 11) was carried out with a sweep speed of 60 mv / min between ± 250 mv / sce. we should note that for all the tests a waiting period of 15 min after immersion corresponds to the time of formation and stability of the electric double layer was respected, while maintaining a continuous and moderate agitation of the medium throughout the test period (see paragraph 5.3.b). fig. 11. tafel curves deduced the influence of the ph of the medium. table 5. electrochemical parameters deducted from polarization curves. electrochemical parameters rp (ohm) ecorr (mv) icorr (µa/cm2) βa (mv) βc (mv) ph of the medium ph =6 361 -580,428 51,931 55,1 398,1 ph=8 474 -585,626 51, 480 94,2 269 ph=10 522 -597,821 26,726 166,8 144,6 ph=11 620 -630 38,113 121,3 154,1 hoar and hurlen in 1959 showed an influence of ph on the iron dissolution reaction and found that the kinetics of this reaction were of order 1 compared with the concentration 62 bourenane et al., j. build. mater. struct. (2019) 6: 50-63 of hydroxide ions (drouin et al., 2011). the numerous studies carried out subsequently led their authors to propose a mechanism of either catalytic or non-catalytic type (perier et al., 2013). after a first common hydrolysis step: the following steps diverge according to the mechanism: catalytic mechanism: non-catalytic mechanism: in our case, the examination of the polarization curves obtained for the reinforcing steel (fig.8) shows a displacement of the corrosion potential towards more cathodic potentials and, in contrast, a decrease in the density of the icorr current can be explained by an effect of the accumulation of corrosion products on the surface of the electrode. in fact, these corrosion products are more and denser and less soluble when the ph decreases. the corrosion speeds measured translating a greater corrosion at all ph values and clearly higher when the ph of the medium is low which indicates that the corrosion resistance decreases significantly when the ph of the medium reaches low values. we also notice that the rp values (table 4) increase as the icorr values decrease. these results are consistent because the resistance rp is inversely proportional to icorr and can be obtained via the stern-geary relation. these results are consistent with previous work by duprat and dabosi (dupart and dabosi, 1981) which show low corrosion resistance in this ph range. however, the observation of the surface state at the end of our electrochemical tests reveals an important layer of corrosion product with a deep attack under that one when the ph decreases, this examination would confirm an increase in corrosion when the ph decreases. 6. conclusion the consequences of the carbonation of concrete and the presence of chloride are frequently the cause of major degradations of concrete and reinforced concrete structures. this study shows the influence of calcium hydroxide solution ca(oh)2 used as a simulating solution alone and with different concentrations of cacl2 on the electrochemical corrosion behavior of reinforcing steel e24 using techniques electrochemical and stationary. the monitoring of the abatement potential as a function of time in the two solutions of saturated ca(oh)2 and ca(oh)2 in the presence of chloride ions after 18 hours of immersion shows that they behave differently, the ca(oh)2 solution observed an increase in the value of the ecorr and reached a stationary value after 18 h. this increase reflects the formation of a protective oxide layer on the surface of the steel by in the solution of lime in the presence of cacl2 we notice a displacement of the potential towards more negative values this evolution of the potential is generally associated with a continuous dissolution of the material in the study medium. thus, in order to study the influence of chloride ions and to determine the critical concentration of the latter responsible for the corrosion initiation of steel, we have drawn linear and cyclic polarization curves and electrochemical impedance curves, observed on our polarized samples, shows the appearance of a green product covering the surface of the steel and turns into black. therefore, we can conclude that adding the different amounts of cacl2 in the solution increased the probability of corrosion initiation for structural steel. thus the influence of the ph of the bourenane et al., j. build. mater. struct. (2019) 6: 50-63 63 medium on the corrosion of our steel samples is studied because it constitutes a very important parameter to better understand the reactions of the dissolution of iron the results obtained by the plot of the curves of linear polarizing in the solution of calcium hydroxide with 0.5m cacl2 watches when the ph of the simulating solution decreases there is a deep attack and the formation of a large layer of product for this purpose it can be concluded that the rate of corrosion increases when the ph of the medium decreases. 7. references bertolini, l., bernhard, e., pietro, p., & rob, p. (2004). corrosion of steel in concrete: prevention, diagnosis, repair. bedin: wiley—vch. byfors, k. (1987). influence of silica fume and flyash on chloride diffusion and ph values in cement paste. cement and concrete research, 17(1), 115-130. byfors, k., hansson, c. m., & tritthart, j. (1986). pore solution expression as a method to determine the influence of mineral additives on chloride binding. cement and concrete research, 16(5), 760-770. diamond, s. (1975). long-term status of calcium hydroxide saturation of pore solutions in hardened cements. cement and concrete research, 5(6), 607-616. diamond, s. (1981). effects of two danish flyashes on alkali contents of pore solutions of cement-flyash pastes. cement and concrete research, 11(3), 383-394. drouin, b., latour, g., & mohamed, h. (2011). more than 10 years successful field applications of frp bars in canada. in cdcc 2011, the 4th int. conf. on durability and sustainability of fiber reinforced polymer (frp) composites for construction and rehabilitation. duprat, m., & dabosi, f. (1981). corrosion inhibition of a carbon steel in 3% nacl solutions by aliphatic amino-alcohol and diamine type compounds. corrosion, 37(2), 89-92. el haleem, s. a., el aal, e. a., el wanees, s. a., & diab, a. (2010-a). environmental factors affecting the corrosion behaviour of reinforcing steel: i. the early stage of passive film formation in ca (oh) 2 solutions. corrosion science, 52(12), 3875-3882. el haleem, s. a., el wanees, s. a., el aal, e. a., & diab, a. (2010-b). environmental factors affecting the corrosion behavior of reinforcing steel ii. role of some anions in the initiation and inhibition of pitting corrosion of steel in ca (oh) 2 solutions. corrosion science, 52(2), 292-302. ghods, p., isgor, o. b., mcrae, g., & miller, t. (2009). the effect of concrete pore solution composition on the quality of passive oxide films on black steel reinforcement. cement and concrete composites, 31(1), 2-11. kosmatka, s. h., kerkhoff, b., panarese, w. c., macleod, n. f., & mcgrath, r. j. (2004). dosage et contrôle des mélanges de béton. bulletin d'ingenierie eb101, cement association of canada. longuet, p. (1973). la phase liquide du ciment hydraté, revue des matériaux de constructions et de travaux publics, section ciments. pp 35-41. longuet, p., peguin, p., rubaud, m., & zelwer, a. (1973). bases experimentales de l’etude electrochimique du comportement des metaux en presence di beton. corrosion tpe, 2(3), 155-159. neville, a. m. (2000). propriétés des bétons. eyrolles. orazem, m. e., pébère, n., & tribollet, b. (2006). enhanced graphical representation of electrochemical impedance data. journal of the electrochemical society, 153(4), b129-b136. perier, v., chataigner, s., & pruvost, a. (2013). comparaison de différentes armatures utilisées pour le renforcement du béton.. bulletin des laboratoires de ponts et chaussées, pp 5162. rosenberg, a. c. m. h. (1989). mechanisms of corrosion of steel in concrete. materials science of concrete, 1, 285-316. rothstein, d., thomas, j. j., christensen, b. j., & jennings, h. m. (2002). solubility behavior of ca-, s-, al-, and si-bearing solid phases in portland cement pore solutions as a function of hydration time. cement and concrete research, 32(10), 1663-1671. j. build. mater. struct. (2018) 5: 197-211 original article doi : 10.34118/jbms.v5i2.58 issn 2353-0057, eissn : 2600-6936 impacts of diatomaceous earth on the properties of cement pastes hasanzadeh b.*, sun z. dept. of civil and environmental engineering, univ. of louisville, louisville, ky 40292. * corresponding author: bashir.hasanzadeh@louisville.edu received: 10-05-2018 revised: 02-10-2018 accepted: 19-10-2018 abstract: fresh properties of concrete are closely related to operation and construction, such as transporting, placing, compacting, etc.; and they also have a great impact on the lifetime performance of concrete. in this paper, the influence of diatomaceous earth (de) as a natural pozzolan on fresh properties of cement pastes has been investigated. cement pastes with different water-to-binder ratios (w/b=0.4, 0.5 and 0.6) and 0%, 2%, 6% and 10% replacement levels of de by weight of cement were studied. viscosity, yield stress, flow diameter, bleeding, setting times, and the heat evolution of all cement pastes were measured. results showed that de has a significant impact on fresh properties of cement pastes. increasing de content in cement pastes resulted in higher viscosity and lower flow diameters. pastes with higher de replacement levels showed lower bleeding rate and shorter initial and final setting times. the isothermal calorimetry test also showed that, as a pozzolanic material, de lowered the heat of hydration, however, it advanced the appearance of the heat evolution peaks which was in agreement with the results from setting time tests. key words: fresh properties, diatomaceous earth, rheology, isothermal calorimetry, setting time, bleeding. 1. introduction diatomaceous earth (de), also known as kieselguhr, is a chalk-like, soft, very fine-grained, earthy, and siliceous sedimentary material (robert & crangle, 2013). it is finely porous, less in density, and essentially chemically inert with low thermal conductivity (robert & crangle, 2013; bakr, 2010). de consists of amorphous hydrous silica cell walls of dead diatoms (opal, sio2•nh2o), which are microscopic single-cell aquatic plants (algae). the diatom cells contain an internal, elaborate siliceous skeleton consisting of two valves (frustules), which fit together much like a pillbox (dolley, 1999). these skeletons vary in size from less than 1 m to more than 1 mm but are typically from 10 to 200 m (robert & crangle, 2013). there are many different types of de but almost all commercial des are composed of around 80% to 90% silica (sio2) (bakr, 2010; miller et al., 2010; jud sierra et al., 2010). united states’ production of diatomite in 2015 was estimated to be 925,000 metric tons, which was more than 40% of the whole world’s de production (jewell & kimball, 2016). there are wide ranges of applications for de. in 2015 in the us, 55% of diatomite was used in filter aids, 21% was used as cement additives, 14% was used as fillers, and 9% was used as absorbents. according to the united states geology surveys (usgs), using de as a cement additive has increased significantly from 14% in 2014 to 21% in 2015 and now it is the second largest de consumption in the us (jewell & kimball, 2016 ; jewell & kimball, 2015). de has been used thousands of years ago, as an addition to lime for binding limestone aggregates together in ancient egypt pyramids, to more recent years as a natural pozzolanic additive for concrete (miller et al., 2010; jud sierra et al., 2010). it is believed that replacing portland cement with de to some level can improve some properties of concrete. 198 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 being different from other commonly used pozzolanic materials, such as fly ash, silica fume, and slag, that have had more research conducted to investigate their influences on concrete properties, much less researches have been reported on the application of de in concrete. in recent years, due to the increased usage of de as a cement additive, some researches focused on mechanical properties have been reported (aydin & gül, 2007; degirmenci & yilmaz, 2009; ergün, 2011; fragoulis et al., 2005; kastis et al., 2006; stamatakis et al., 2003; yılmaz & ediz, 2008). separate studies by ergun (2010), fragoulis et al. (2005) and stamatakis et al. (2003) on different types of diatomaceous earth showed that replacing cement by de up to 10-15% increased compressive and flexural strength compared to control samples (almost at all different measured ages with highest increase at 10%). they concluded that samples with higher content of reactive silica and a higher blaine surface area showed a higher increase in compressive strength. also, studies by kastis et al. (2006) and yilmaz and ediz (2008) found that replacement levels up to 10% of cement content showed comparable compressive strength compared to the control samples, while samples with de content higher than 10% showed a significant drop in strength. on the other hand, studies by aydin and gül (2007) and degirmenci and yilmaz (2009) showed that for all replacement levels and all measured ages, the module of elasticity and compressive and flexural strength were lower than those of the control samples. however, they found that using de could improve both freeze-thaw durability and sulfate attack resistance. as these studies mainly focus on hardened properties of concrete, a comprehensive study on the impact of de on fresh properties of concrete is lacking. fresh properties of concrete, including setting, rheology, bleeding, and early hydration are closely related to operation and construction, such as transporting, placing, compacting, etc.; and they also have a great impact on the lifetime performance of concrete. therefore, this paper studies the influence of de as a partial replacement of portland cement on fresh properties of cement pastes. for this purpose, pastes with water-to-binder ratios (w/b) of 0.4, 0.5, and 0.6 were investigated. based on the findings of the aforementioned studies, only replacement levels up to 10% were considered. thus, for each w/b ratio, three replacement levels of 2%, 6%, and 10% of cement with de were used. the influences of de replacement on flowability, viscosity and yield stress, bleeding, setting time, and heat signature were studied systematically. 2. materials and experiment procedures 2.1. raw materials ordinary type i portland cement (from cemex, louisville plant (ky, usa)) was used in all the mixtures. the mean size of the cement particles was 11.4 m, determined through a laser particle size analyzer. the blaine surface area was 400.8 m2/kg. the chemical compositions of this type i cement were measured with xrf and they are listed in table 1. the mineral compositions for this cement are calculated based on the bougue’s equation (taylor, 1997) and are provided in table 2. table 1. chemical composition of type i portland cement and diatomaceous earth compound (%) type i portland cement diatomaceous earth sio2 19.70 93.5 al2o3 4.84 1.6 fe2o3 3.05 1.1 cao 62.62 0.4 mgo 4.00 0.05 so3 3.23 0.12 na2o 0.15 2.51 k2o 0.49 0.09 loi 1.21 0.35 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 199 table 2. mineral composition of type i portland cement compound wight, % c 3 s 59.1 c 2 s 11.9 c 3 a 7.67 c 4 af 9.3 de used in this study is a commercial pure diatomaceous earth, usually a powder, available widely on the market. the mean size of de particles is 19 m based on a laser particle size analyzer and the blaine surface area was 593 m2/kg. the chemical composition of de is also listed in table 1. 2.2. mixing procedures and testing matrix the details of mix proportions are listed in table 3, where “opc” indicates control samples with ordinary type i cement only, and “d” indicates the pastes with de replacement. three w/b ratios of 0.4, 0.5, and 0.6 were used. for each w/b ratio, three replacement levels of de were studied. table 3. mix proportions cement paste w/c de replacement level (%) cement (gr) de (gr) water (gr) opc-0.4 0.4 0 700 0 280 d2-0.4 0.4 2 686 14 280 d6-0.4 0.4 6 658 42 280 d10-0.4 0.4 10 630 70 280 opc-0.5 0.5 0 700 0 350 d2-0.5 0.5 2 686 14 350 d6-0.5 0.5 6 658 42 350 d10-0.5 0.5 10 630 70 350 opc-0.6 0.6 0 700 0 420 d2-0.6 0.6 2 686 14 420 d6-0.6 0.6 6 658 42 420 d10-0.6 0.6 10 630 70 420 when mixing the control pastes (opc-0.4, opc-0.5, and opc-0.6), water was gradually added to the cement over the first minute of mixing and then mixing continued for two additional minutes at a low speed of 136 rpm. the sample was then allowed to rest for two minutes, which was followed by another three minutes of mixing at a high speed of 195 rpm. for cement pastes with de replacement, cement powder and de were first dry mixed for one minute with a low speed of 136 rpm. then, the same mixing procedure used for control pastes was followed. mixing and all following tests were conducted at 25 °c. 2.3. rheological and mini-cone slump tests the rheometer (model: anton paar mcr 502) with a co-cylindrical cup-and-bob configuration (gap size of 1.13 mm) was used to measure the rheological properties of all pastes. for more information on the geometry of the co-cylindrical configuration see figure 1 and table 4. during the tests, the cement pastes were first pre-sheared at a shear rate of 600 s-1 for ten seconds to minimize the effects of shear history during mixing, so that all the samples can start from the same reference point. the paste then rested for three minutes. after that, samples were sheared based on a descending flow curve at six different shear rates (300, 250, 200, 150, 100, and 50 s1). samples were maintained at each shear rate for ten seconds and the corresponding shear 200 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 stresses were measured. the bingham model was applied to calculate the viscosity and the yield stress. fig 1. concentric geometry table 4. geometrical parameters of concentric cylinders geometrical parameters co-cylindrical configuration gap size (re ri) 1.130 mm re 14.460 mm ri 13.330 mm l 39.997 mm cone angle 120 previous studies showed that concrete flows during mixing and pumping can correspond to different shear rate. during mixing and casting, concrete may experiences shear rates of up to 60 s-1 (roussel, 2006). however, during pumping, especially high speed pumping, cement paste can be subjected to much higher shear rates especially at the lubricating layer, from 217 s-1 up to 924 s-1 (kim et al., 2017). therefore, in this study, 300 s-1 was used as the maximum shear rate applied to the pastes. the mini-cone slump tests were also conducted for all the paste samples to measure the flow diameter. the average of the flow diameter in two perpendicular directions was used to represent the flow diameter of the corresponding cement paste. all rheological and mini-cone slump tests were conducted 12 minutes after initial mixing. 2.4. bleeding test after mixing, the pastes were poured within 0.6 cm (1⁄4 inch) from the top of the 5 cm (2 inches) by 10 cm (4 inches) cylinders and then weighed. the containers were capped after weighing to prevent moisture loss. after 30 minutes elapsed, the cylinders were tilted 30° from vertical and bleed water was removed with a transfer pipette. caution was taken to prevent removing any of the paste with the bleed water. once no more visible bleed water remained on the surface, the cylinders were weighed and capped with a plastic lid. this process was repeated every 30 minutes until no further bleed water was observed. the reported value of weight loss and the weight loss rate is the averages of the three specimens (sun & young, 2014). l ri re hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 201 2.5. setting time the initial and final setting time of all cement pastes were determined by the vicat needle tests, which were carried out according to astm c191 (2008). when the needle penetrated the cement paste for 25 mm, the initial set was achieved. final setting was attained when there was no mark of the specimen surface with a complete circular impression (liu et al., 2014). 2.6. isothermal calorimetry the heat of hydration of all cement pastes was measured by the isothermal calorimetric test as defined by astm c1702 (2009). tam air, a commercial calorimeter, was adopted in this study. it was an eight-channel isothermal heat conduction calorimeter with the operating temperature range between 5°c and 60°c. before testing, the equipment was carefully calibrated based on the calibration procedures specified by the manufacturer. the energy change during hydration was collected and registered by an automated data acquisition program. the energy value was calculated based on the unit weight of the cementitious materials’ mass. 3. results and discussion 3.1. rheological and slump tests viscosity and yield stress of all different cement pastes were calculated based on the obtained flow curves and using the bingham model (banfill, 2003). figures 2 and 3 show the calculated viscosity and yield stress, respectively. it can be seen clearly that by increasing the de replacement level, the viscosity is increased for all the w/b ratios. the rheological properties of cement paste are highly related to its interparticle and non-contact surface forces (van der waals, double layer) (lootens et al., 2004; banfill, 1990). de particles, due to their high blaine surface and porous structure, tend to absorb the free water available in the paste. although this water will be released back to the cement matrix in later ages, in the early age, it causes a reduction in water content. it should also be noticed that the specific gravity of de is lighter than cement. when cement is replaced by de with the same mass, the solid volume fraction increases. the increased solid volume fraction together with the porous texture of de result in higher inter-particle interactions and consequently higher viscosity. fig 2. viscosity of cement pastes against de replacement levels 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 1 2 3 4 5 6 7 8 9 10 11 v is c o si ty ( p a .s ) de% 0.4 w/c 0.5 w/c 0.6 w/c 202 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 fig 3. yield stress of cement pastes against de replacement levels table 5 lists the solid volume fraction of each mix proportion. table 5. solid volume fraction of different mix proportions (cement density = 3.15 g/cm3, de density = 2.3 g/cm3 and de absorption capacity = 1.5 times its own weight) cement paste solid volume fraction opc-0.4 0.44 d2-0.4 0.46 d6-0.4 0.51 opc-0.5 0.39 d2-0.5 0.40 d6-0.5 0.44 d10-0.5 0.48 opc-0.6 0.35 d2-0.6 0.36 d6-0.6 0.39 d10-0.6 0.42 figure 3 depicts changes in yield stress by different replacement levels of de. it shows that for 0.5 and 0.6 w/b ratios, increasing the de replacement level in cement pastes constantly leads to a drop in yield stress. however, for 0.4 w/b ratio, increasing the replacement level at first does not change the yield stress significantly (it drops slightly from 25.75 pa for opc-0.4 to 25.42 pa for d2-0.4). while after that point, by increasing the de content from 2% to 6%, the yield stress increases considerably (from 25.42 pa for d2-0.4 to 30.32 pa for d6-0.4). to explain these changes in the yield stress of cement pastes with different w/b ratios and different de replacement levels, the change in their shear behaviors should be considered. shear thinning and shear thickening are typical for non-newtonian flow fluids, in which viscosity nonlinearly decreases or increases by an increase in shear rate (he et al., 2015; yahia, 2014). shearthinning is generally attributed to shear-induced deflocculation while shear-thickening is generally attributed to repulsive interactions between both colloidal and non-colloidal particles in the case of suspensions (bouras et al, 2012). figure 4 and figure 5 show the flow curves of cement pastes with a water to binder ratio of 0.6 and 0.4, respectively (0.5 w/b ratios had very similar flow curves as of 0.6). 0 5 10 15 20 25 30 35 0 1 2 3 4 5 6 7 8 9 10 11 y ie ld s tr e ss ( p a ) de% 0.4 w/c 0.5 w/c 0.6 w/c hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 203 fig 4. flow curve of cement pastes with 0.6 w/b ratio fig 5. flow curve of cement pastes with 0.4 w/b ratio it can be seen that the control cement paste (opc-0.6) with no additive shows a clear shear thinning behavior all along its flow curve while opc-0.4 first shows shear thinning at low shear rates and then shear thickening behavior at higher shear rates. this is in agreement with the findings of previous research which showed cement pastes with lower w/c ratios show more shear thickening behavior than pastes with higher w/c ratios at high shear rates (yahia, 2011). also, one can easily see that by increasing the de replacement level, flow curves from both w/b ratios (0.6 and 0.4) show more shear thickening behavior at higher shear rates. this can be explained by the porous structure and the high blaine surface of the de particles. according to he et al. (2015), the surface characteristics of dispersed particles significantly affect the rheological properties of the shear thickening fluids (stfs). they found that by dispersing porous particles (like porous silica fume) in polar liquids, the high specific surface areas and rough surface nature of the porous particles may influence the interfacial interaction between particles and dispersing medium to improve shear thickening behavior (he et al., 2015). 0 10 20 30 40 50 60 70 80 90 0 50 100 150 200 250 300 350 s h e a r s tr e s s ( p a ) shear rate (1/s) opc-0.6 d2-0.6 d6-0.6 d10-0.6 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 s h e a r s tr e ss ( p a ) shear rate (1/s) opc-0.4 d2-0.4 d6-0.4 204 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 from figure 4, it can also be seen that using de to partially replace cement not only changes the flow behavior from shear thinning to shear thickening at a high shear rate but also the higher the de dosage, the more obvious this transition would be. the flow diameter of cement pastes with different w/c ratios and de replacement levels are shown in figure 6. results show a consistent decrease in flow diameter by increasing the de content. this can be explained by a high blaine surface, porous structure, and the waterabsorbent nature of de particles that leads to lower water content in cement pastes. according to previous studies (ferraris et al., 2001; wallevik, 2006), there is a correlation between minislump flow diameter and yield stress. a lower yield stress corresponds to a higher spread in the minislump (ferraris et al., 2001). however, this research shows the slump flow can be related to both viscosity and yield stress. for the pastes with de replacement, the viscosity may dominate the flow diameter. fig 6. flow dia meter of cement pastes against de replacement levels it should be noted that paste d10-0.4 has very poor workability. due to its high water demand (miller et al., 2010; degirmenci & yilmaz, 2009; fragoulis et al., 2005; stamatakis et al., 2003; yılmaz & ediz, 2008; agullo et al., 1999), implementing rheological and mini-cone slump tests were not feasible for this cement paste. 3.2. bleeding test figure 7 plots the changes in weight loss due to bleeding against time. as it is clear from this figure, for pastes with 0.4 w/b ratio, by increasing the replacement level of the de in cement paste, the weight loss decreases for all time intervals. however, for 0.5 and 0.6 pastes, no clear pattern is observed. in the case of 0.4 w/b ratio, the bleeding water could be clearly identified and removed from the top of the specimen. while in 0.5 and 0.6 w/b, it is hard to differentiate the bleeding water and the diluted paste layer. some cement particles may be accidentally removed together with the water when the pipette was used. therefore, the trend line plotted with higher w/b ratios probably contains higher measurement errors. hence, the focus of the data analysis on bleeding will be on the 0.4 w/b pastes. 0 5 10 15 20 25 30 0 1 2 3 4 5 6 7 8 9 10 11 f lo w d ia m e te r ( c m ) de% 0.4 w/c 0.5 w/c 0.6 w/c hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 205 fig 7. weight loss of cement pastes against time figure 8 plots the changes in bleeding rates for all the pastes with w/b ratio of 0.4. one can see that for a given age, e.g. 30 minutes after mixing, the control specimen has the highest bleeding rate, and the rate decreases accordingly with the increase in de replacement. this indicates that adding de to cement paste can delay and reduce bleeding effectively. from the figure, it can also be noticed that bleeding for the d10-0.4 paste stopped earlier than any other pastes. this is another indication of minimizing the bleeding effect by using de. fig 8. weight loss rate of cement pastes against time for 0.4 w/b ratio, weight loss rate = (wt1-wt2)/wt1/(t1-t2) 3.3. setting time initial and final setting time of all cement pastes with different water to binder ratios and de replacement levels are provided in table 6. it is observed that for all the w/b ratios that were studied, increasing the de replacement levels causes decreases in both initial and final setting times, it also shortens the time difference between the initial and final settings for all the 0.4 and 0.5 pastes. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 50 100 150 200 250 w e ig h t lo s s ( % ) time (min) opc d2 d6 d10 0.6 w/b 0.5 w/b 0.4 w/b 0 0.00002 0.00004 0.00006 0.00008 0.0001 0.00012 0 20 40 60 80 100 120 140 w e ig h t lo s s r a te ( m l /m l /m in ) time (min) opc-0.4 d2-0.4 d6-0.4 d10-0.4 206 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 table 6. initial and final setting of cement pastes with different w/c ratios and de replacement levels cement paste initial set (min) final set (min) opc-0.4 226 350 d2-0.4 178 310 d6-0.4 166 255 d10-0.4 141 240 opc-0.5 268 450 d2-0.5 246 390 d6-0.5 234 375 d10-0.5 229 360 opc-0.6 340 570 d2-0.6 328 565 d6-0.6 300 555 d10-0.6 275 535 also, among cement pastes with the same de content, those with a higher w/c ratio have a longer initial and final setting time as expected. in addition, in cement pastes with lower w/b ratios, the rate of reduction in setting time (final setting) by increasing the de content is much higher than those with higher w/b ratios. for example, it took 110 minutes less for d10-0.4 to reach final set compared to opc-0.4, however, the final setting time has only been shortened by 35 minutes for 0.6 pastes when 10% of the cement is replaced by de. replacing cement with de reduces the concentration of cement particles in cement paste (i.e. reduces cement content) and is expected to prolong setting time. but on the other hand, de particles due to their porous structure and high blaine surface, can absorb some of the free water in the paste that lowers the free water content and improves diffusion of water in the cement matrix which shortens the time for water to reach the non-hydrated cement.. 3.4. isothermal calorimetry for all water to binder ratios, increasing the de content reduced the heat evolution of cement pastes on the first 70 hours. as an example, the heat evolution of pastes with 0.4 w/b ratio at different de replacement levels are shown in figure 9. fig 9. heat evolution of cement pastes with 0.4 w/b ratio 0.00e+00 5.00e+01 1.00e+02 1.50e+02 2.00e+02 2.50e+02 3.00e+02 3.50e+02 0 10 20 30 40 50 60 70 80 h e a t e v o lu t io n ( j /g ) hydration age (hours) opc-0.4 d2-0.4 d6-0.4 d10-0.4 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 207 figures 10 to 12 show the rate of heat evolution of all the cement pastes against time. it should be pointed out that these figures are cut and enlarged from hydration age 0.5 to 20 hours for better illustration of changes in peaks of heat evolution rate. the first peak in the figure is mainly associated with the hydration of c3s in cement paste and the second peak is mostly attributed to the hydration of c3a (rahhal & talero, 2009; pang et al., 2013; mostafa & brown, 2005). it is clear from these figures that an increase in de content results in a drop in the heat evolution rate of both peaks for all w/b ratios. as mentioned in the previous section, this is simply due to the decrease in clinker phases (cement content), which is caused by replacing cement with de. fig 10. heat evolution rate of cement pastes with 0.4 w/b ratio fig 11. heat evolution rate of cement pastes with 0.5 w/b ratio 0.00e+00 1.00e+00 2.00e+00 3.00e+00 4.00e+00 5.00e+00 6.00e+00 0 5 10 15 20 25 h e a t e v o l u t i o n r a t e ( m w / g ) hydration age (hours) opc-0.4 d2-0.4 d6-0.4 d10-0.4 0.00e+00 5.00e-01 1.00e+00 1.50e+00 2.00e+00 2.50e+00 3.00e+00 3.50e+00 4.00e+00 4.50e+00 5.00e+00 0 5 10 15 20 25 h e a t e v o lu t io n r a t e ( m w /g ) hydration age (hours) opc-0.5 d2-0.5 d6-0.5 d10-0.5 208 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 fig 12. heat evolution rate of cement pastes with 0.6 w/b ratio in addition, for all water to binder ratios, higher de content led to shifts (to the left) for both peaks. the higher the de content the larger the shift is (table 7). also, the shift with an increase in de content is observed to be more obvious for cement pastes with lower w/b ratios. table 7. hydration age of first and second peaks of heat evolution rate for all cement pastes cement paste first peak (h) second peak (h) opc-0.4 7.02676 8.69343 d2-0.4 -0.08975 -0.08976 d6-0.4 -0.43464 -0.35131 d10-0.4 -1.09506 -1.09506 opc-0.5 7.88261 8.96594 d2-0.5 -0.48359 -0.15025 d6-0.5 -0.81736 -0.23402 d10-0.5 -0.96151 -0.29484 opc-0.6 7.93628 9.01961 d2-0.6 -0.23428 -0.15094 d6-0.6 -0.52509 -0.19175 d10-0.6 -0.72741 -0.22741 these results fully support discussion in the previous section and research findings from the setting time test. the acceleration of peak appearance can be attributed to the absorption of free water to de particles that cause the increase of the solution of cement clinkers (like c3a) in water. this leads to the higher solubility of ions such as ca2+ (i.e. higher zeta potential). it, in turn, accelerates the formation of hydration products and shortens the setting time (yılmaz & ediz, 2008; nägele, 1985; plank & hirsch, 2007). kastis et al. (2006) pointed out that the pozzolanic nature of diatomite can form higher amounts of hydration products in the paste. based on the findings of rahhal and talero (2009), the hydration reactions may be stimulated by the positive and negative electrostatic charge acquired by the particles of pozzolans during mixing, and subsequently, by the zeta potential specially originated as portland cement hydration progresses (wallevik, 2006). therefore, de particles could play the role as nucleation sites (like seed crystals) for calcium hydroxide crystals to precipitate with accelerated setting (rahhal and talero, 2009). putting figures 10-12 together with table 6, one can see that the earlier the peaks appear, the quicker the paste would set. 0.00e+00 5.00e-01 1.00e+00 1.50e+00 2.00e+00 2.50e+00 3.00e+00 3.50e+00 4.00e+00 4.50e+00 5.00e+00 0 5 10 15 20 25 h e a t e v o l u t i o n r a t e ( m w / g ) hydration age (hours) opc-0.6 d2-0.6 d6-0.6 d10-0.6 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 209 4. conclusion findings of this paper show that using diatomaceous earth (de) as a partial replacement for cement has a significant influence on the fresh properties of cement pastes. the porous shape and high blaine surface of de particles make this natural pozzolanic additive of cement pastes highly water absorbent. de can impact fresh properties of cement pastes as follows:  increase in de content of cement pastes increased the apparent viscosity of cement pastes with w/b ratios of 0.4, 0.5, and 0.6. it can be due to the higher solid volume fraction of cement pastes with higher de content which leads to higher inter-particle interactions.  increase in de content changed the shear behavior of cement pastes from shear thinning to shear thickening behavior. this change in shear behavior is clearer in cement pastes with 0.5 and 0.6 w/b ratios.  increase in de content decreased the flow diameter of cement pastes at all water to binder ratios.  increase in de content of cement pastes reduced the bleeding rate of cement pastes with 0.4 w/b ratio.  increase in de content shortened both the initial and final setting times of cement pastes at all w/b ratios. de particles improve water diffusion, increase zeta potential, and accelerate the formation of hydration products which lead to shorter setting times.  increase in de content lowers the hydration heat of cement pastes at all water to binder ratios due to the lower cement content of cement pastes.  results from isothermal calorimetry show that an increase in the replacement level of cement with de hastens the hydration process in cement pastes with all water to cement ratios which is in good agreement with results from setting time test. acknowledgements the financial support from the national science foundation (cmmi-1265983, cmmi-1413031), kentucky science and engineering foundation (ksef-3242-rde-018) and the department of civil and environmental engineering at the university of louisville, are highly appreciated. the authors also appreciate the cemex technical center for cement chemical composition analysis. 5. references agullo, l., toralles-carbonari, b., gettu, r., & aguado, a. (1999). fluidity of cement pastes with mineral admixtures and superplasticizer—a study based on the marsh cone test. materials and structures, 32(7), 479-485. astm c1702. (2009). standard test method for measurement of heat of hydration of hydraulic cementitious materials using isothermal conduction calorimetry. astm international west conshohocken, pa. astm c191. (2008). standard test method for time of setting of hydraulic cement by vicat needle. astm international west conshohocken, pa. aydin, a. c., & gül, r. (2007). influence of volcanic originated natural materials as additives on the setting time and some mechanical properties of concrete. construction and building materials, 21(6), 1277-1281. bakr, h. e. g. m. m. (2010). diatomite: its characterization, modifications and applications. asian journal of materials science, 2(3), 121-136. 210 hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 banfill, p. (1990). rheology of fresh cement and concrete: proceedings of an international conference, liverpool, crc press. banfill, p. (2003). the rheology of fresh cement and concrete − a review. in international cement chemistry congress. durban. bouras, r., kaci, a., & chaouche, m. (2012). influence of viscosity modifying admixtures on the rheological behavior of cement and mortar pastes. korea-australia rheology journal, 24(1), 35-44. degirmenci, n., & yilmaz, a. (2009). use of diatomite as partial replacement for portland cement in cement mortars. construction and building materials, 23(1), 284-288. dolley, p. (1999). diatomite: minerals yearbook: volume i-metals and minerals. us geological survey, p. 1-4. ergün, a. (2011). effects of the usage of diatomite and waste marble powder as partial replacement of cement on the mechanical properties of concrete. construction and building materials, 25(2), 806812.. ferraris, c. f., obla, k. h., & hill, r. (2001). the influence of mineral admixtures on the rheology of cement paste and concrete. cement and concrete research, 31(2), 245-255. fragoulis, d., stamatakis, m. g., papageorgiou, d., & chaniotakis, e. (2005). the physical and mechanical properties of composite cements manufactured with calcareous and clayey greek diatomite mixtures. cement and concrete composites, 27(2), 205-209. he, q., gong, x., xuan, s., jiang, w., & chen, q. (2015). shear thickening of suspensions of porous silica nanoparticles. journal of materials science, 50(18), 6041-6049. jewell, s. & kimball, s.m. (2015). mineral commodity summaries 2015, in annual u.s. geological survey. jewell, s., & kimball s.m. (2016). mineral commodity summaries 2016, in annual u.s. geological survey: usgs. jud sierra, e., miller, s. a., sakulich, a. r., mackenzie, k., & barsoum, m. w. (2010). pozzolanic activity of diatomaceous earth. journal of the american ceramic society, 93(10), 3406-3410. kastis, d., kakali, g., tsivilis, s., & stamatakis, m. g. (2006). properties and hydration of blended cements with calcareous diatomite. cement and concrete research, 36(10), 1821-1826. kim, j. h., kwon, s. h., kawashima, s., & yim, h. j. (2017). rheology of cement paste under high pressure. cement and concrete composites, 77, 60-67. liu, f., sun, z., & qi, c. (2014). raman spectroscopy study on the hydration behaviors of portland cement pastes during setting. journal of materials in civil engineering, 27(8), 04014223. lootens, d., hébraud, p., lécolier, e., & van damme, h. (2004). gelation, shear-thinning and shearthickening in cement slurries. oil & gas science and technology, 59(1), 31-40. miller, s. a., sakulich, a. r., barsoum, m. w., & jud sierra, e. (2010). diatomaceous earth as a pozzolan in the fabrication of an alkali‐activated fine‐aggregate limestone concrete. journal of the american ceramic society, 93(9), 2828-2836. mostafa, n. y., & brown, p. w. (2005). heat of hydration of high reactive pozzolans in blended cements: isothermal conduction calorimetry. thermochimica acta, 435(2), 162-167. nägele, e. (1985). the zeta-potential of cement. cement and concrete research, 15(3), 453-462. pang, x., bentz, d. p., meyer, c., funkhouser, g. p., & darbe, r. (2013). a comparison study of portland cement hydration kinetics as measured by chemical shrinkage and isothermal calorimetry. cement and concrete composites, 39, 23-32. plank, j., & hirsch, c. (2007). impact of zeta potential of early cement hydration phases on superplasticizer adsorption. cement and concrete research, 37(4), 537-542. rahhal, v., & talero, r. (2009). calorimetry of portland cement with silica fume, diatomite and quartz additions. construction and building materials, 23(11), 3367-3374. hasanzadeh and sun, j. build. mater. struct. (2018) 5: 197-211 211 robert, d. crangle, j. (2013) diatomite, mineral yearbook 2013, in annual. u.s. geological survey: mineral yearbook. p. 22.1-22.5. roussel, n. (2006). a thixotropy model for fresh fluid concretes: theory, validation and applications. cement and concrete research, 36(10), 1797-1806. stamatakis, m. g., fragoulis, d., csirik, g., bedelean, i., & pedersen, s. (2003). the influence of biogenic micro-silica-rich rocks on the properties of blended cements. cement and concrete composites, 25(2), 177-184. sun, z., & young, c. (2014). bleeding of scc pastes with fly ash and ggbfs replacement. journal of sustainable cement-based materials, 3(3-4), 220-229. taylor, h. f. (1997). cement chemistry. thomas telford. wallevik, j. e. (2006). relationship between the bingham parameters and slump. cement and concrete research, 36(7), 1214-1221. yahia, a. (2011). shear-thickening behavior of high-performance cement grouts—influencing mix-design parameters. cement and concrete research, 41(3), 230-235. yahia, a. (2014). effect of solid concentration and shear rate on shear-thickening response of highperformance cement suspensions. construction and building materials, 53, 517-521. yılmaz, b., & ediz, n. (2008). the use of raw and calcined diatomite in cement production. cement and concrete composites, 30(3), 202-211. j. build. mater. struct. (2018) 5: 157-163 original article doi : 10.34118/jbms.v5i1.54 issn 2353-0057, eissn : 2600-6936 experimental case study on the effect of the urban morphology on urban microclimate and outdoor thermal comfort sedira s1, mazouz s 2,* 1 laboratory of design and modelling of forms and environments, department of architecture, university of mouhamed khider biskra,algeria. 2 department of architecture. university of larbi ben mhidi, oum bouaghi, algeria. * corresponding author: sedirasara@gmail.com received: 20-02-2018 revised: 28-05-2018 accepted: 03-06-2018 abstract. the present study aims at testing the influence of the urban morphology on the external weather conditions and the urban microclimate by treating quantitative aspects of the outdoor thermal comfort. this is based on a site investigation aims at studying the correlation between the geometry of the street, its orientation and the evolution of the physical variables: air temperature (ta), mean radiant temperature (mrt), relative humidity (rh), wind speed (ws).the measures were the subject of a campaign carried out in the urban fabric of the ksar of the red village in the wilaya of biskra in algeria. the objective is to define the most efficient urban geometry in term of summer thermal comfort by studying the real impacts of the urban form on the solar control and microclimatic conditions. the evaluation of the thermal comfort in these external spaces is carried out by analyzing physiologically equivalent temperature (pet) values calculated by rayman pro 2.1 software based on the measured microclimatic parameters. key words: urban morphology; urban microclimate; outdoor thermal comfort; warm and arid climate; mean radiant temperature. 1. introduction for several decades, the influence of climatological parameters on the comfort conditions at the urban scale has motivated a great deal of research. urban climatology specialists have sought to evaluate the thermal comfort in outdoor spaces, which has acquired its acclaim and becomes of similar importance to interior comfort, widely discussed (ali-toudert et al., 2005-a; ali-toudert et al., 2005-b; bourbia et al., 2004; johansson, 2006; stathopoulos et al., 2004). outdoor human comfort in an urban climate may be affected by a wide range of weather and human factors, including wind speed, air temperature, relative humidity, solar radiation, air quality, human activity, clothing level, age, etc . urban climatology has evolved research on the correlation between urban form, morphological characteristics, materials and the urban microclimate by accommodating specific and diversified methods. according to the different modes of adaptation of the human body, physical adaptation, physiological and psychological (ouameur, 2007). researchers specialized in urban climatology have developed a number of approaches and methods for evaluation, concluding that thermal comfort is not only influenced by physiological responses to the regulatory system via the microclimatic variables but also by the inevitable psychological and social adaptation, which shows the degree of adaptation of the users to the external conditions, considering that the adoption of the physiological approach alone is not sufficient for a convincing and reliable evaluation of the thermal comfort in an outdoor space (makaremi et al., 2012; louafi et al., 2013). in most outdoors thermal comfort studies, a purely physiological model has been used, involving a mathematical model of the thermoregulatory system employed for calculating the thermal comfort conditions, whereas the subjective responses have not been considered. thermal comfort in outdoor spaces is a complex and global notion because of the multiplicity of parameters that interact and influence its evaluation, taking into account both objective and mailto:sedirasara@gmail.com 158 sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 subjective factors, (nikolopoulou et al. , 2001) and translated by psychological factors such as: past experiences, perceived control, time of exposure, environmental stimulation, expectations and naturalness (nikolopoulou et al. , 2003). the effect of physical adaptation can be evaluated numerically. physical adaptation involves all the changes a person makes, in order to adjust oneself to the environment, or alter the environment to his needs. thus, physiological adaptation implies changes in the physiological responses resulting from repeated exposure to a stimulus, leading to a gradual decreased strain from such exposure. in the context of the thermal environment, this is called physiological acclimatization. the physical environment and psychological adaptation is argued to be complementary rather than contradictory, and consideration of this duality could increase the use of the outdoor spaces (nikolopoulou et al., 2003). 2. case study the dachra el hamra (the red village) is a traditional fabric of the pre-colonial era. it is the first nucleus of el kantara which, through its opening on the desert and by its richness in date palms (more than 50000), constitutes the portal of the transition between two regions whose climatic aspects are quite different: the north and the south of algeria. it is an oasis located in the wilaya of biskra to 50 km to the north of the city and in the southwest of the aures to 80 km of batna, (hamouda et al., 2013). the dachra el hamra is a compact entity characterized by a densely populated urban fabric with narrow, unpaved streets and a dominant type of habitat built in the saharan architectural style. the streets, the narrow streets, the deep canyons, cul-de-sac (darb), the covered passages (skifa), squares (rahba or batha) constitutes the elements of the structure designed according to the style of the old towns (ksour) the introverted model of the arab-islamic medina (hamouda et al., 2011). this region is characterized mainly by the aridity of her climate, high summer daytime temperatures, large diurnal temperature range, and high solar radiation. fig 1. the administrative card of algeria (in the left) and the localization of el kantara in the wilaya de biskra (in the right). sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 159 fig 2. the urban morphology of the dachra. 3. methods in order to determine the mean radiant temperature (mrt) required for the calculation of pet, the index adopted for the evaluation of thermal comfort in the study site, it is inevitable to examine the four main climatic parameters previously cited, of the instrument: "testo data logger 480" whereby the air temperature, relative humidity, wind speed and the temperature of a globe thermometer. fig 3. the localization of measured points. 160 sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 table 1. representation of geometrical characteristics of measured points. the investigations of this study are limited to the summer period of a meteorological data series (2006–2015), because climatic heat stress in the urban open spaces mainly occurs during this season. conversely, thermal cold stress only occurs in winter for a few days between 27 july and 04 august is where the thermal stress reaches its maximum values. during this period, 29 and 30 july were chosen for the elaboration of the investigation and considering the days with the typical summer conditions. the selection of measurement points is the result of a typo morphological analysis of the urban fabric of the case study, in order to identify the different typologies existing in the external space. these points were localized in (figure 3), presented and described in table 1. table 2. representation of geometrical characteristics of measured points. s ta ti o n 1 2 3 4 5 s o la r d ia g ra m s v f 0.277 0.006 0.016 0.104 0.151 ty p o lo g y dihedral street covered passage (skifa) covered passage (skifa) cul-de-sac (darb) deep narrow canyon s ta ti o n 6 7 8 9 10 s o la r d ia g ra m s v f 0.610 0.224 0.421 0.249 0.249 ty p o lo g y square dihedral street unobstructed street dihedral street dihedral street sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 161 4. results and discussion 4.1. impact of the urban geometry on mean radiant temperatures the mean radiant temperature reaches its maximum value in point six (06) where the lowest h/w ratio (the ratio: height of building / wide of street) was recorded with a considerable difference with the temperature of the air measured under the effect of the sunshine (figure 4). as well as recording low values in points with a high h/w ratio or in the covered passages where the graph begins to decrease, this difference relates to exposure to solar radiation, according to which points exhibits a small gap are the least exposed. fig 4. mean radiant temperature measured in different points at 29-30/07/2016. 4.2. impacts of the physiologically equivalent temperature the evaluation of the values of the physiological equivalent temperature presented in the graph (figure 5), we note the relationship between pet and mtr, the increase of mrt of which leads to an increase in pet values. it is also remarkable that the values of mrt and pet vary simultaneously with the variation in the values of the svf (presented above in table 1), the increase of which leads to an increase in the values of this index, the maximum value at point 06 with the highest svf. in addition, the minimum values for pet were recorded under the covered passages thanks to the shadow generated by the latter at the street level. the considerable difference between the svf of the two points 07 and 08 did not result in a large difference between the values of the pet recorded there, thanks to the solar orientation of the point 08 which presents the highest svf. the solar orientation also has a considerable effect when comparing the two points 09 and 10 which have the same svf and an apparent deviation from the values of the pet, finding that the point 10 oriented northwest. 0 1 2 3 4 5 6 7 8 9 10 11 0 10 20 30 40 50 60 t e m p measured points ta gt mrt h/w 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 h /w 162 sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 fig 5. the physiologically equivalent temperature calculated pet values measured in different points at 29-30/07/2016. 5. conclusion this study shows that a compact urban form with deep street canyons provides a good protection during the hot days of summer period, this typology of streets combined with covered passages provides shade for pedestrians during the warmest period of the day. the study of the above graphs in relation to the geometrical characteristics of the points studied, represented in table 1, and enabled us to reach a certain number of recommendations relating to urban design in hot regions. the analysis of the acquired results of the investigation allowed us to demonstrate the considerable effect of svf, the ratio h/w and the solar orientation on the thermal fluctuations in the street by affecting mainly the wind conditions that contribute to moderate air temperature, sun and shade in streets. in this study, narrow and covered streets, at the orientations north-south, north west south east, provide better shading by buildings, desirable at this region in summer, for pedestrians on sidewalks than wide streets, to ensure human thermal balance and guaranteed a level of thermal comfort, and the protection from the solar exposure is the more important objective related to the streets. this opening to the sun is defined by a controlled svf and an optimal h /w ratio combined with a controlled solar orientation, favoring the north-south, north-west-south-east orientation which offers acceptable conditions in terms of comfort compared with other solar orientations. although the level of thermal comfort is a quantifiable and measurable element, its evaluation also requires consideration of the psychological aspect required for the control of perceived thermal sensation, using observation techniques, questionnaire and surveys. 6. references ahmed ouameur, f. (2007). morphologie urbaine et confort thermique dans les espaces publics « étude comparative entre trois tissus urbains de la ville de québec». mémoire pour l'obtention du grade de maître en sciences. université laval, québec. 0 1 2 3 4 5 6 7 8 9 10 11 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 t e m p measured points svf mrt pet 0,0 0,2 0,4 0,6 0,8 1,0 s v f sedira and mazouz, j. build. mater. struct. (2018) 5: 157-163 163 ali-toudert, f., djenane, m., bensalem, r., mayer, h. (2005-a). outdoor thermal comfort in the old desert city of beni-isguen, algeria, climate research, 28(3): 243-256. ali-toudert, f., mayer, h., (2005-b), numerical study on the effects of aspect ratio and orientation of an urban street canyon on outdoor thermal comfort in hot and dry climate, building and environment, 41(2): 94–108. bourbia, f., awbi, h., (2004), building cluster and shading in urban canyon for hot dry climate, part 1: air and surface temperature measurements, renewable energy, 29(2): 249-262. boussoualim, a., (2002), contribution à la caractérisation de l’impact et de l’incidence du microclimat sur l’usage et les activités en espace public extérieur, etude de cas à blagnac, thèse de doctorat, universite de nantes. hamoud, a., abdou, s., (2013), approche d’une analyse syntaxique de l’habitat rural cas d’el kantara, courrier du savoir (16) : 27-36. hamouda, a., outtas, s., (2011), etude topologique et diachronique de l’habitat rural : cas d’el-kantara, biskra. sciences &technologie, d(34): 28-37. höppe, p., (1999), the physiological equivalent temperature – a universal index for the biometeorological assessment of the thermal environment. international journal of biometeorology, 43(2): 71-75. johansson, e., (2006), influence of urban geometry on outdoor thermal comfort in hot dry climate: a study in fez, morocco, building and environment, 41(10): 1326-1338. louafi, s., abdou s., (2013), benefits and well-being perceived by pedestrian in vegetated urban space in periods of heat stress, iacsit international journal of engineering and technology, 5(1):20–24. makaremi, n., salleh, e., jaafar, m.z., hoseini, a.h.g. (2012), thermal comfort conditions of shaded outdoor spaces in hot and humid climate of malaysia. building and environment, 48(1): 7-14. nikolopoulou, m, steemers, k, (2003), thermal comfort and psychological adaptation as a guide for designing urban spaces, energy and buildings, 35(1): 95-101. nikolopoulou. m, baker. n, steemers. k, (2001), thermal comfort in outdoor urban spaces: understanding the human parameter, solar energy, 70(3): 227-235. stathopoulos, t., wu, h., zacharias, j., (2004), outdoor human comfort in an urban climate, building and environment, 39(3): 297-305. j. build. mater. struct. (2018) 5: 102-109 original article doi : 10.34118/jbms.v5i1.49 issn 2353-0057, eissn : 2600-6936 influence of silica fume on the dynamic properties of concrete benmammar m *, boukli h s m e eole laboratory / civil engineering department, university of tlemcen, b.p. 230 chetouane, tlemcen 13000-algéria. * corresponding author: mohammed.benmammar@yahoo.fr received: 10-02-2018 revised: 27-04-2018 accepted: 07-05-2018 abstract. ultrasonic pulse velocity and resonance frequency methods are non-destructive tests that allow the evaluation and control of building materials. they have been used to determine the dynamic properties of concrete, which are used in the design and control of structures and which are the key elements of the dynamics of materials. in this study, we chose a non-destructive approach to quantify -in laboratory-, the influence of adding “silica fume” on ordinary concrete’s dynamic characteristics. however, several concrete mixtures have been prepared with limestone aggregates. the experimental plan used, allowed us to determine the dynamic elasticity modulus and the dynamic rigidity modulus of different formulated concretes. key words: concrete, non-destructive tests, dynamic elasticity modulus, dynamic rigidity modulus, additions, compressive strength. 1. introduction the non-destructive testing is a fundamental area of research, which allows obtaining the quality and the degradation state of building materials. some characteristics of concrete, such the ultrasonic pulse velocity test, which is standardized by astm c597–09 (2003) allows the control of the quality of the materials and makes it possible to estimate the mechanical properties. it is a method based on the propagation speed of elastic waves in a material. the speed measurement system according to certain steps makes it possible to calculate the speed of propagation of the longitudinal or compression waves, which are the fastest elastic waves and the longitudinal modulus of elasticity, compressive strength, porosity, etc., are essential in the design and control of structures. the dynamic modulus of elasticity is considered equal to the elastic modulus, tangent at the origin and determined in static testing. the dynamic modulus of elasticity can easily be measured by estimating the static modulus, which must be known to design concrete structures. in order to find the relationship between the static and dynamic moduli and confirm the influence of additions, such as silica fume (sf), a non-destructive approach, based on the measurement of the resonant frequency on cylindrical concrete specimens (16×32 cm2) was used (bouakkaz, 2012; astm c 597-02, 2003; dimitrios and shiotani, 2009; mirjana et al. 2014; fathollah and payam, 2012). the use of supplementary cementitious materials as sf, as part of binders for concrete, has increased worldwide. furthermore, their use as mineral additives, to partially replace cement, could somehow save non-renewable resources required for the production of cement, and may therefore contribute, in some way, to the durability of concrete structures (mehta and monteiro, 2006; baroghel-bouny, 2005; gesoglu and ozbay, 2007). this paper presents the results of the influence of supplementary cementing materials on the dynamic properties of ordinary concretes. the elastic modulus (longitudinal and transversal) of ordinary concrete, containing 05% sf, is compared with those of the reference concrete (rc) with similar mixing proportions but without supplementary cementing materials. in addition, mailto:mohammed.benmammar@yahoo.fr benmammar et al., j. build. mater. struct. (2018) 5: 102-109 103 the existing standards indicate that appropriate arrangements on the potential influence of additions on the estimation of the elastic modulus are actually lacking. 2. characterization of used materials the cement used in this study meets the algerian standard (na 44); it is of type (cpj cem ii/a 42.5) and comes from the national cement company in the town of benisaf, province (wilaya) of ain temouchent, algeria. to prepare different types of concrete, drinking water was used, from the public water supply network, from the district (daïra) of chetouane, in the city of tlemcen, algeria. the aggregates used are from the big quarry of the national company of aggregates (eng), in djebel abiod, in tlemcen, algeria, and silca fume (sf) is from the teknachem algeria (sidi bel abbes). the aggregates are marketed in various granular classes: sand 0/3 and gravels 3/8, 8/16 and 16/25. analysis on the chemical composition and physical properties of cement and sf are reported in table 1. the properties of the aggregates used were determined in our laboratory (boukli and ghomari, 2007; boukli et al., 2009; boukli, 2010). table 1. chemical compositions and physical properties of cement and sf. item cem ii sf sio2 22.17 95 al2o3 6.18 0.5 fe2o3 3.62 1 cao 59.45 0.5 mgo 1.05 1 so3 3.63 0 p2o5 0.18 0.01 tio2 0.43 1 loi 2.62 0 density 3.071 2.2 blaine specific surface (cm2/g) 3598 220000 3. experimental program and test methods 3.1 experimental program the concretes are formulated on the basis of optimized granular skeletons boukli (2010) with a w/c ratio equal to 0.5 and the percentage of silica fume 5% (table 2). eighty-four (24) cylindrical specimens (16×32 cm2) were prepared to determine the resonance frequency at different times (3, 7, 14 and 28 days), (24) other cylindrical specimens (16×32 cm2) for measuring ultrasonic pulse velocity at maturity (3, 7, 14 and 28 days). the concretes under study were prepared in accordance with the standards in use, afnor (2002a), afnor (2002-b) and algerian standards (1992). table 2. composition of rc boukli (2010). constituents quantities (kg/m3) cement cpj cem ii/a 42,5 350 gravel (16/25) 533 gravel (8/16) 432 gravel (3/8) 144 sand (0/3) 660 water 175 104 benmammar et al., j. build. mater. struct. (2018) 5: 102-109 3.2 test methods 3.2.1 measurement of dynamic characteristics the test apparatus used is the one required by astm c 215–02; the method ‘standard test method for fundamental transverse, longitudinal, and torsional resonant frequencies of concrete specimens’ was used. the equipment, which meets the astm requirements, was designed by various trade organizations. it includes an electromechanical transmitter placed at one end of the test tube, a receiver at the other end, and a device for measuring the resonant frequency of the medium, according to standard nf p18–414 (afnor, 2002-b). to measure the dynamic modulus of elasticity ed, the test seeks to evaluate the longitudinal resonance frequency of a cylindrical concrete specimen by placing the emitter and the receiver on the same longitudinal axis of the specimen, as shown in figure 1. fig 1. schematic diagram of the longitudinal resonance testing. this arrangement of the transmitter and receiver generates longitudinal vibrations, parallel to the main axis of the specimen. the dynamic longitudinal modulus of elasticity ed is obtained by the use of the theory of elastic wave propagation, assuming that the material is rigid and continuous, and exhibiting an elastic behavior. this method is used for homogeneous and isotropic materials, but can also be applied to a heterogeneous material, such as concrete, when the test tube dimensions are large compare to the size of the components (han and kim, 2004; khan, 2012; giner et al 2012). the frequency is varied until a resonant value is found. we have the following equation: √ (1) according to equation 1, we found e: (2) where, e is the dynamic modulus of elasticity, is the material density, l is the length of the sample, n is the resonance frequency, k is the radius of gyration of the section about an axis benmammar et al., j. build. mater. struct. (2018) 5: 102-109 105 perpendicular to the plane of bending and m is a constant (4.73 for the fundamental mode of vibration). the dynamic modulus of elasticity is calculated from the fundamental frequency of longitudinal vibration of the sample by the following equation: (3) the two equations (1) and (3) obtained are used to solve the differential equation of motion (hassan and jones, 2012). the dynamic shear modulus is calculated using the same way as the dynamic modulus of elasticity (equ.3), simply replacing nl by nt representing the transversal resonance frequency which is given by the following equation: (4) 3.2.2 measurement of ultrasonic velocities the fundamental idea of the method is based on recording the propagation of mechanical waves and preferably compression waves, because it is the fastest wave. an ultrasonic wave pulse in the concrete is generated at a point on the surface of the sample and the time required for the wave to travel from that point to the other surface is measured (fig 2). fig 2. schematic representation of an ultrasound test. the positioning of the sensors and the measurement of the distance are important. however, two-sided access is not required. knowing the distance between these two points, the pulse velocity can be determined. however, several factors affect the rate of impulse in concrete, such 106 benmammar et al., j. build. mater. struct. (2018) 5: 102-109 as the size, shape of large aggregates, water/binder ratio, degree of consolidation, condition of concrete curing and presence of reinforcement (malhotra et al., 2004). 4. results and discussion 4.1 influence of the silica fume on the longitudinal modulus of elasticity fig. 3 shows the influence of the additional addition on the dynamic modulus with a w/c ratio equal to 0.5. this figure shows that the greatest value of the dynamic modulus of elasticity is obtained from the concrete containing 5% of silica fume (sf) followed by the reference concrete (rc). the substitution of 5% sf give superior values to those of rc and this is during the curing period to the age of 28 days. in addition, the dynamic elasticity modulus obtained for the 5% sf5 concrete mix is higher than that of the reference concrete, throughout the duration of the hardening, because she has a very high finesse. 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 24 26 28 30 32 34 36 38 40 42 44 46 rc 5 % sfl o n g it u d in a l m o d u lu s o f e la s ti c it y ( g p a ) age (days) r 2 = 0,92 r 2 = 0,96 fig.3. influence of silica fume on the longitudinal modulus of elasticity 4.2 influence of the silica fume on the transversal modulus of elasticity fig. 4 is the same as fig. 3, shows the influence of the silica fume on the modulus of transverse elasticity for a w/c ratio equal to 0.5. this figure shows that the greatest value of the modulus of elasticity of stiffness is obtained from the concrete containing 5% of silica fume, followed by the reference concrete. benmammar et al., j. build. mater. struct. (2018) 5: 102-109 107 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 10 11 12 13 14 15 16 17 18 rc 5 % sft ra n s v e rs a l m o d u lu s o f e la s ti c it y ( g p a ) age (days) r 2 = 0,96 r 2 = 0,99 fig.4. influence of silica fume on the transversal modulus of elasticity the trend lines give a large scatter of points, which can be justified by the coefficients of determination which exceed 0.9 in all cases. the curves presented in figs. 3 and 4 can be represented by a type of exponential equation: (5) 4.3 influence of the silica fume on the ultrasonic pulse velocity the highest value of the upv of fig. 5 is obtained from the concrete containing 5% sf, followed by the rc, although this difference is not so important. for the concrete mixtures 5% sf, the upv values obtained are higher than those of the reference concrete during the entire curing period due to the formation of hydrates, in addition to the calcium silicates (c-s-h). the trend lines give a large scatter of points, which can be justified by the coefficients of determination that exceed 0.9. fig. 5 concerning the upv can be represented by a type of exponential equation: ( ) (6) 108 benmammar et al., j. build. mater. struct. (2018) 5: 102-109 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 3,75 3,80 3,85 3,90 3,95 4,00 4,05 4,10 4,15 4,20 4,25 4,30 rc 5 % sf u lt ra s o n ic p u ls e v e lo c it y ( k m /s ) age (days) r 2 = 0,97 r 2 = 0,998 fig.5. influence of silica fume on the ultrasonic pulse velocity 5. conclusions based on the results presented earlier in this document, the following conclusions can be made: the 05% silica fume of addition has a direct influence on the modulus of transverse and dynamic elasticity. the values of the dynamic and transverse modulus of elasticity of the concrete containing 5% of the silica fume are higher than those of the reference concrete. the substitution of silica fume tends to increase the values of dynamic, transverse elastic modulus and ultrasound pulse rate at young age up to the 28-day curing age. 6. references afnor (2002-a). concrete and its constituents. tome 1: specifications of concrete and its constituents. 5th ed. paris: french association of normalization. p. 431. afnor (2002-b). concrete and its constituents. tome 2: test methods of concrete. 5th ed. paris: french association of normalization. p. 510. algerian standards (1992). publishing and distribution by abou hamou moussa. algier: 192. astm c 215-02. standard test method for fundamental transverse, longitudinal and torsional. astm test designation c 597-02. (2003). standard test method for pulse velocity through concrete. annual book of astm standards. astm test designation c 597-09: (2003). standard test method for pulse velocity through concrete. baroghel-bouny v. (2005). new approach to concrete durability. methodology and examples. eng. tech. ed.;c2246:1–18. benmammar et al., j. build. mater. struct. (2018) 5: 102-109 109 bouakkaz, ma (2012). characterization of concrete using the resonant frequency method. magister thesis in civil engineering. tlemcen, abou bekr belkaid university. boukli h.s.m.a. (2010). contribution to the study of the characteristic resistance of concretes in the region of tlemcen, doctorat thesis in civil engineering, university of tlemcen. boukli h.s.m.a., & ghomari f. (2007). study of the compression resistance of local concretes. paper presented at: international colloquium on structural and geotechnical engineering, icsge; 12th annual colloquium. dec 3–6.cairo, egypt; 1005–1014. boukli hacene s.m.a., ghomari f., & khelidj a. (2009). compressive strengths of concrete formulated with algerian local materials. jordan j. civ. eng; 3: 103–117. dimitrios g, & shiotani t. (2009). experimental study of wave propagation through grouted concrete. aci mater. j.; 106: 19–24. fathollah s, & payam s. (2012). high-strength lightweight concrete using leca, silica fume, and limestone. arabian journal for science and engineering, 37(7), 1885-1893. gesoglu m, & ozbay e. (2007). effects of mineral admixtures on fresh and hardened properties of selfcompacting concretes: binary, ternary and quaternary systems. mater. struct.; 40: 923–937. giner vt, baeza fj, ivorra s, et al. (2012). effect of steel and carbon fiber additions on the dynamic properties of concrete containing silica fume. mater. des.34:332–339. han s.h, & kim j.k., (2004). effect of temperature and age on the relationship between dynamic and static elastic modulus of concrete. cem. concr. res; 34:1219–1227. hassan a. m. t. & jones s. w. (2012). non-destructive testing of ultra-high performance fibre reinforced concrete (uhpfrc): a feasibility study for using ultrasonic and resonant frequency testing techniques. construction and building materials, 35, 361-367. khan mi. (2012). evaluation of non-destructive testing of high strength concrete incorporating supplementary cementitious composites. resour. conserv. recycl. 61:125–129. malhotra, v. m., carino, n.j. et al. ( 2004). handbook on non-destructive testing of concrete, astm international, west conshohocken, pa, usa, 392 p. mehta pk, monteiro pjm. (2006). concrete – microstructure properties and materials. 3rd ed. mcgrawhill. mirjana m, vlastimir r, ivan l, et al. (2014).the effect of aggregate, type and quantity of cement on modulus of elasticity of lightweight aggregate concrete. arabian j. sci. eng.; 39:705–711. j. build. mater. struct. (2019) 6: 1-9 original article doi : 10.34118/jbms.v6i1.63 issn 2353-0057, eissn : 2600-6936 behavior of recycled asphalt to the fatigue bordjiba a1*, guenfoud h2 1 department of architecture, badji moukhtar university, annaba, algeria 2 department of civil engineering, 08 may 1945 , guelma, algeria * corresponding author: bordjibaabdelhak@gmail.com received: 23-03-2018 accepted: 22-01-2019 abstract: climatic and traffic effects are the causes of aging of the surface layer of asphalt, which leads to the necessary renovation of the latter. the use of waste from the tread layer provides a viable and beneficial solution for the environment and the economy. however, this solution must meet the requirement of sustainable development, which necessitates that a road has a very long lifespan. in this study we investigated the performance of recycled asphalt in terms of fatigue (as an element of life-cycle control). all the formulas were tested by the fatigue test in order to define the influence of the proportions of the asphalt aggregates, penetrability of the new binder used, and the manufacturing temperature. the results obtained showed the relationship between the contribution binder (reproduced between the new binder and the old binder) and the fatigue resistance under the influence of the parameters that we have mentioned above. at the end an optimization study has been carried in order to determine exactly the doses required to formulate recycled asphalt resisted to fatigue, the optimization seeks to maximize the asphalt aggregates and minimized the temperature of manufacture with a class of the binder compatible. key words: asphalt, fatigue, binder, environment, penetrability. 1. introduction surfaced roads age under the effects of traffic and climate, which lead to the end of their life, in increments that reflect the functions required by the regulations, or the needs envisaged by the employer, (abdelhak et al., 2016-a). in algeria, the asphalt aggregates for the maintenance of the rolling asphalt layer are recycled into nature or reused as a foundation layer for low-traffic roads, (pascal, 2017). however, after the rio summit in 1992, environmental awareness has emerged that sustainable development is the link between economic growth and environmental protection (kalantar et al., 2012). on applying the concept of sustainable development in the field of road construction, the latter requires minimizing the use of non-renewable natural raw material and the construction of a road surface that has a very long lifespan, (technical guides and general studiescttp, 2015). the logical answer to this problem is recycling, which imposes the valorization of the deposit of materials already existing in the surfacing, and limits the amount of new materials in the formulation of the new asphalt, (haddad et al., 2017). in this study we checked the effect of the penetrability of the contribution binder, asphalt aggregate dosing and the temperature of manufacturing on the resistance to fatigue of recycled asphalt. the formulated type of asphalt is bbsg 0/14 (semi-dense bituminous concrete), because this is the type most commonly encountered on algerian roads. the hypothesis in this work is that asphalt aggregates have a percentage of old binder which can cause fatigue for recycled asphalt, but that very precise control of the ‘contribution binder’ (old binder + new binder) of recycled asphalt can show us a new binder corresponding to the percentage of asphalt aggregates used. such close control also permits analysis of the temperature of manufacturing, such that the mixture (old binder and new binder) may take the form of a contribution binder compatible with the features of recycled manufactured asphalt. the asphalts were subjected to stresses of short durations, repeated over time. these represented the successive passages of the axles of 2 bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 vehicles, (kavussi & modarres, 2010). traction caused by bending phenomena occurs at the base of different layers of the surface, (kavussi & modarres, 2010). the induced stresses do not result in an immediate failure, but their repetition over time is at the origin of cracking by fatigue, (di benedetto et al., 2004). a program of fatigue tests was carried out to determine the resistance to fatigue of recycled asphalt formulated with binders of various degrees of penetrability. the asphalt aggregates comprised three percentages (15%, 45% and 75%) and the temperature of manufacturing included different temperatures. the fatigue test which we conducted involved samples of trapezoidal shape, being tested by bending at two points, (soltani & anderson, 2005). under review was the maximum deformation experienced by the extreme fiber of the test piece during a sinusoidal amplitude constant arrow application. this deformation was calculated from the arrow head, assuming linear and homogeneous material, (colbert & you, 2012). the fatigue in the laboratory test was to determine the deformation ε6 leading to the rupture of a specimen by fatigue under certain test conditions, (guthrie et al., 2007). 2. parameters of the study three parameters were controlled in this study in order to determine their influence on the resistance to fatigue of the asphalt recycled. 2.1. percentage of asphalt aggregate asphalt aggregate percentage is chosen to cover a range from the case of recycling at low rates (15%), achievable common with most existing asphalt central, until the case of recycling at high rate (75%) corresponding to the maximum capacity of recycling in the asphalt central with double drums dedicated to the production of asphalt recycled at high rate. the choice of these two values, maximum and minimum, requires an intermediate point to 45% of asphalt aggregate corresponding to the rate of recycling in the asphalt central with deported burner. 2.2. manufacturing temperature the minimum temperature of manufacturing is chosen equal to 120 ° c, this is the temperature to which the old binders start to be remobilized. used maximum temperature is fixed at 160 ° c, or above this temperature, it is in contradiction with the concept of sustainable development that requires a minimum consumption of non-renewable energy. the choice of these two values, maximum and minimum, requires an intermediate point to 140 ° c close to temperature of manufacturing of standard asphalt. 2.3. binder penetrability the penetrability is the measure of the pressing of a needle normalized in a binder maintained at a fixed temperature, after 5 seconds under a load of 100 g (abdelhak et al., 2016-b). in this study we used three binders have got different penetrability (42 m.m, 65 m.m and 90 m.m) to determine the influence of the latter with the old binder of the asphalt aggregates on the production of a contribution binder compatible with the recycled asphalt that we want to make it. 3. materials used 3.1. choices of new aggregates new aggregates choice must be done carefully because its characteristics play a very important role in the quality of the asphalt (lin et al., 2011). used aggregates in this study are the fractions 0/3, 3/8 and 8/14. the (figure 1) presents the results of the particle size analysis test. bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 3 fig. 1. particle size analysis of fractions 8/14, 3/8 and 0/3 the used reagent monomers in stagaa synthesis process were of two kinds: acrylamide (am) that provides with nonionic amide group and 2-acrylamido-2-methylpropane sulfonic acid (amps) that provides with anionic sulfonic group. ammonium persulfate (aps) and n,n`methylenebisacrylamide (nmba) were used as an initiator agent and a crosslinking agent, respectively. 3.2. new binders the characterization of the bituminous binder mainly reflects the consistency at ambient temperature. this information enables to classify the bituminous binders in rank. binders used in our study are 30-50, 50-65 and 65-100 classes. there characteristics are presented to the table 1. table 1. characterization of the new binders. sample penetrability at 25°c, (1/l0 mm) penetrability at 25°c, (1/l0 mm) moyen specifications sam 01 43 40 41.5 35-50 sam 02 64 64 64 50-65 sam 03 92 88 90 65-100 3.3. asphalt aggregate in this study asphalts aggregates used have an age of five years of utilization as layer of bearing. they are shown that recycled asphalt can reach 100% of asphalt aggregate if it is well calibrated (lin et al., 2011). for this reason that the asphalts aggregates used were spent in the sieve 14 mm to eliminate the upper elements to14 mm. after the selection of the elements less than 14 mm a particle size analysis was conducted as show on the figure 2. 4 bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 fig. 2. particle size analysis of asphalt aggregate 4. testing campaign 4.1. formulation of healthy asphalt the healthy asphalt made is a bbsg (semi-dense bituminous concrete). the choice of formula through the determination of a mixture having the best ability to compaction and which could give greater stability to the hydrocarbon mixture. marshal test results in the table.2 confirmed the percentages of fractions as well as the rate of the binder. the binder used in this formulation is 35-50 class, because this binder is recommended for the bbsg. this formula of healthy asphalt has been the subject of control by the fatigue test in order to determine its resistance to deformation. the results of the stress test showed that after 15000 cycles the healthy asphalt deforms fast and it begins to take the plastic state. therefore acceptable ultimate deformation equals 100 ε6 as represented on the figure 3. this ultimate deformation will be considered a limitation agreed for the recycled asphalts to they are going to be studied. fig. 3. fatigue test result on reference healthy asphalt bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 5 table 2. results of the formulation of healthy asphalt frac 8/14 45% norme frac 3/8 30% frac 0/3 25% tl 5.4 % ≈5.4% fluage marshal (f) 2.60 f<4 compactness (c) 96% c >95% 4.2. fatigue tests for asphalt recycled the table 3 contains formulations that have been programmed in this campaign tests, a control of fatigue as well as the penetrability of the contributions binder have been made for all mixtures of recycled asphalt. asphalt aggregates dosing protocol is based on the results of a particle size analysis of each fraction in the healthy mix asphalt, or must cancel the amount of healthy aggregate in each fraction and replace it with the asphalt aggregates. fatigue test is to apply for the test specimen at a fixed temperature (10 ° c) and a fixed frequency (10 hz). the fatigue test is also done in mode of deformation. a large number of cycles are applied up to the rupture of the test piece. to test the behavior to fatigue of a mix, at least 4 test tubes must be tested at different levels of deformation (boudlal et al., 2015). table 3. formulations programmed in this campaign tests 5. result and discussion from the results of this study, we can distinguish clearly the influence of the rate of aggregate asphalt, the temperature of the manufacturing and class of contribution binder (penetrability) on the resistance of asphalt recycled at the fatigue. for mixtures made with new binder class (35-50) and a temperature of manufacturing equal t ° = 120 °, resistance to fatigue, represented on the (figure 4), is low for mixes when asphalt aggregate rates of exceeds 25%, reflecting that the temperature was unable to transform the old binder to the presence of the new binder a contribution binder that has the characteristics required by regulation. the (figure 5) represents the results mixtures formulated in new binding class (50-65), when fatigue resistance is acceptable up to a rate of less than 50% of asphalt aggregate in temperature of the manufacturing equal 120°, this explains the class of the binding agent used to play a role in the cohesion of the components of the mixture and the increase in its resistance to fatigue. however for mixtures when used with new binder is class (65-100) and temperature of the manufacturing 120° as shown on the (figure 6), fatigue resistance is totally weak because of the contribution binder which is not compatible with the recycled asphalt manufactured bbsg and resistance to the fatigue desired because with a contribution binder of high penetrability n° test ae % t° class of bitume n° test ae % t° class of bitume 01 15 120 35-45 15 75 140 50-65 02 45 120 35-45 16 15 140 65-100 03 75 120 35-45 17 45 140 65-100 04 15 120 50-65 18 75 140 65-100 05 45 120 50-65 19 15 160 35-45 06 75 120 50-65 20 45 160 35-45 07 15 120 65-100 21 75 160 35-45 08 45 120 65-100 22 15 160 50-65 09 75 120 65-100 23 45 160 50-65 10 15 140 35-45 24 75 160 50-65 11 45 140 35-45 25 15 160 65-100 12 75 140 35-45 26 45 160 65-100 13 15 140 50-65 27 75 160 65-100 14 45 140 50-65 6 bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 cohesion becomes weak. mixtures made in a temperature of manufacturing equal t ° = 140 ° or t ° = 160 ° gave the results have deferential behavior with mixtures produced in a temperature t ° = 120 °. for an recycled asphalt manufacturing with binder class bitumen (35-50), fatigue resistance is undesirable when the asphalt aggregates rate exceeds 50%, see the (figure 6), this explains the rate of the old binder that influence the new binder to produce a contribution binder of very low penetrability and asphalt it becomes very stiff which causes a fast break. for mixtures made with a binder of class (50-65) the results gave acceptable resistance to fatigue for all formulas because the contribution binder reproduced by new binder and old binder has got a penetrability compatible with the recycled asphalt formulated (bbsg), presented in the (figure5). however for mixtures made with binder class (65-100), fatigue resistance becomes acceptable to mix them the rate of asphalt aggregate over 50%, this translated for a low rate asphalt aggregate contribution binder reproduced has very high penetrability, which causes a high flexibility and asphalt recycled it becomes fragile, but with a high rate of asphalt aggregates the old binder without the penetrability of the new binder to produce a contribution binder of desirable penetrability for the manufacturing of recycled asphalt bbsg type in the (figure 5). fig. 4. effect of the manufacturing temperature and the percentage of asphalt aggregates on the fatigue strength of recycled asphalt manufactured with new binder of penetrability 42 m.m fig. 5. effect of the manufacturing temperature and the percentage of asphalt aggregates on the fatigue strength of recycled asphalt manufactured with new binder of penetrability 65 m.m bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 7 fig. 6. effect of the manufacturing temperature and the percentage of asphalt aggregates on the fatigue strength of recycled asphalt manufactured with new binder of penetrability 90 m.m 5.1. optimization of a formulation of recycled asphalt resistant to the rutting following the results presented above, the tests performed by the classic method do not have the capacity to provide accurate results on the rate of ae and the degree of the manufacturing temperature and the class of the binder in the mixture as a function of the mechanical quality desired (fatigue), which has guided the study to the method of the plans of experience (anova). in this experimental plan three factors have been proposed, the answer find is the behavior of the recycled asphalt to fatigue and the influence of factors study on the response for each formula also the compatibility of binders with the performance wish. after operating the factorial experiment that we have chosen as a model of quality, the use of software minitab.17 we helped to program the necessary testing and the resolution of equations polynomial. the results obtained are the determination of the unknowns of the polynomial presented above in the equation (eq.1) which expresses the resistance of recycled asphalt to fatigue (response) in function of the parameters of the experience plan (factors) .this equation will allow us to determine the resistance to fatigue in function of these variables (factors). also this equation is a prior justification for the manufacturers of asphalt in the central of production of asphalt. fat = -453,9 3,021 ae + 6,049 t° + 6,584 pen 0,00884 ae2 0,02052 t°2 0,03595 pen2 + 0,02167 ae*t° + 0,01250 ae*pen 0,01719 t°*pen (eq.1) according to the results presented on the graph of parito in the figure.7, one finds that the interaction between the aggregates of asphalt and the penetrability of the binder plays a crucial role. the interaction between the three factors and the interaction between the temperature of the manufacturing process as well as the penetrability of the binder have shown their influence on the quality of recycled asphalt. these results have confirmed the classic tests performed or we have seen that the rate of aggregate of asphalt contains a percentage of the old binder which affects the mechanical performance of recycled asphalt also the temperature it has a direct relationship with the remobilization of old binder for the put him compatible with the mixture. 8 bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 fig. 7. the pareto chart of the standardized effects fig. 8. the desirable domain of the penetrability of contribution binder for manufacturing recycled asphalt resist to the fatigue 6. conclusion the mechanical behavior of recycled asphalt, in the areas of fatigue, has been studied in this work, and we conclude the following: 1. a rate of 100% of asphalt aggregate is possible if we can master the choice of a new binder which reproduces a contribution binder compatible with this maximum rate. 2. the temperature must be greater than 140° to ensure remobilization of the old binder and ensure the homogeneity of the contribution binder. 3. the penetrability or the class of the binder has shown that it plays a key role in the mechanical performance of recycled asphalt. figure 8. shows the field limit of the penetrability of the contribution binder to produce a recycled asphalt resistant to fatigue. this limit is 33mm inferior and 58mm superior. 4. the choice of binder must be made with caution because it is linked to the rate of asphalt aggregate tablets used. if the higher rate of asphalt aggregates is low, the penetrability of new bitumen used must be low, and the contrary for the high rates, in order to produce a contribution binder compatible with the percentage of used asphalt aggregates. term ab a c b bc abc ac 9876543210 a a e b t° c pen factor name standardized effect pareto chart of the standardized effects [4.20] bordjiba and guenfoud, j. build. mater. struct. (2019) 6: 1-9 9 5. the modeling by the use of the methods of the plans of experience allows you to determine the equation (eq.6.1) by which can estimate the fatigue for different rates of the factors studied. 6. this study we allow to control the preparation of the binder of intake as amended (old binder+ new binder) with the goal of having the same characteristics of the binder of recycled asphalt. this facilitates the manufacture of recycled asphalt with a high rate of aggregates of asphalt in central. 7. at low temperature the bitumen has a brittle behavior. 8. we can avoid the low-temperature cracking if one uses bitumen of high rank, that is to say, bitumen less "hard” and therefore less "brittle" at low temperature. 9. the bitumen ideal must therefore be both the less likely possible to the phenomena of the fatigue. 7. references abdelhak, b., abdelmadjid, h. c., hamza, g., & mohamed, g. (2016-b). influence of recycled aggregates on the resistance of bituminous concrete in the presence of additives. revista romana de materialeromanian journal of materials, 46(1), 89-94. abdelhak, b., abdelmadjid, h. c., mohamed, g., & hamza, g. (2016-a). effect of recycled asphalt aggregates on the rutting of bituminous concrete in the presence of additive. arabian journal for science and engineering, 41(10), 4139-4145.. boudlal, o., khattaoui, m., djemai, m., & medani, m. (2015). etude du comportement mécanique d'un mélange de granulats naturels et du verre pour une utilisation dans la construction routière (s25). in congrès français de mécanique. afm, association française de mécanique. colbert, b., & you, z. (2012). the properties of asphalt binder blended with variable quantities of recycled asphalt using short term and long term aging simulations. construction and building materials, 26(1), 552-557. di benedetto, h., de la roche, c., baaj, h., pronk, a., & lundström, r. (2004). fatigue of bituminous mixtures. materials and structures, 37(3), 202-216. guthrie, w., cooley, d., & eggett, d. (2007). effects of reclaimed asphalt pavement on mechanical properties of base materials. transportation research record: journal of the transportation research board, (2005), 44-52. haddad, k., haddad, o., aggoun, s., & kaci, s. (2017). correlation between the porosity and ultrasonic pulse velocity of recycled aggregate concrete at different saturation levels. canadian journal of civil engineering, 44(11), 911-917. kalantar, z. n., karim, m. r., & mahrez, a. (2012). a review of using waste and virgin polymer in pavement. construction and building materials, 33, 55-62. kavussi, a., & modarres, a. (2010). laboratory fatigue models for recycled mixes with bitumen emulsion and cement. construction and building materials, 24(10), 1920-1927. lin, p. s., wu, t. l., chang, c. w., & chou, b. y. (2011). effects of recycling agents on aged asphalt binders and reclaimed asphalt concrete. materials and structures, 44(5), 911-921. pascal r., (2017). national project mure day of exchange «contribution of regenerants in the recycling of asphalt mixtures» reminder of the european and french specifications and prescriptions on the use of (ae) aggregates of asphalt 15. soltani, a., & anderson, d. a. (2005). new test protocol to measure fatigue damage in asphalt mixtures. road materials and pavement design, 6(4), 485-514. technical guides and general studies developed by the cttp (2015). ministry of public works algeria. j. build. mater. struct. (2020) 7: 87-94 original article doi : 10.34118/jbms.v7i1.706 issn 2353-0057, eissn : 2600-6936 effect of cement types on carbonation depth of concrete merah a*, korichi y, khenfer m m ammar telidji university, civil engineering research laboratory, laghouat-algeria. * corresponding author: a.merrah@lagh-univ.dz received: 23-05-2020 accepted: 29-07-2020 abstract. reinforced concrete as a building material is the most used in civil engineering structures. this one is exposed to several attacks (physical, chemical and mechanical). among these attacks, we can cite the phenomenon of carbonation, which leads to corrosion of the reinforcements and consequently reduces the service life of reinforced concrete structures. in addition, this phenomenon generates additional repair costs, which can sometimes exceed the initial cost of the building. furthermore, it depends on the type and class of cement, two main classes of cement are used for the formulation of concrete in algeria, ordinary portland cements and cements with additions. this paper enters in the context of sustainable development, in order to study the behavior of these two types of cements against accelerated carbonation. for this purpose, two concrete compositions (based on ordinary portland cements and cements with additions) were formulated, from these two formulations, samples were made in order to subject them to accelerated carbonation in a chamber rich in co2 according to the recommendations of the afpc-afrem. the results obtained clearly show that concretes based on ordinary portland cements (opc) are less sensitive to the phenomenon of carbonation compared to concretes based on blended cements. key words: sustainability; reinforced concrete; opc cement; blended cement, durability, accelerated carbonation. 1. introduction reinforced concrete is widely used in the world for the realization of structures in all fields of civil engineering, the absolute need to protect this material against atmospheric aggressions is very necessary. among these attacks, we can mention the concrete carbonation. moreover, concrete as a cementitious material is highly sensitive to the phenomenon of carbonation, which is due to the penetration of atmospheric carbon dioxide through the porosity of the concrete surface. this gas reacts with the portlandite (ca (oh)2) by lowering the ph of the interstitial solution from 13 to 9. this decrease in ph causes the reserve of portlandite (component responsible for durability) to be consumed and once the coating of concrete is carbonated, the steel reinforcement initially protected may corrode. the damage associated with this phenomenon corresponds to cracks by the degradation of the concrete coating, by the formation of iron oxides and hydroxides on the reinforcements these consequences of carbonation can have an impact on the bearing capacity of structural elements. in addition, most of the civil engineering structures realized in algeria are made of reinforced concrete, these structures are mainly based on two classes of cements, ordinary portland cements opc and blended cement. many researchers have been interested in the effect of cement additions on the concrete carbonation, papadakis et al. (1992) developed a mathematical model that controls the evolution of carbonation in time with 50% relative humidity; this model has been extended to cover the case of carbonation of the coating system (lime cement) and concrete, this model has mailto:a.merrah@lagh-univ.dz 88 mearh et al., j. build. mater. struct. (2020) 7: 87-94 been validated for concrete based on ordinary portland cement (opc) and on blended cement with pozzolanic additions. elsewhere, dakhmouche chabil (2009) shows that the carbonation depth of concrete samples decreases if additions (silica fume and fly ash with a high and low calcium content) replace a quantity of aggregates and increases if additions replace a quantity of cement. moreover, dakhmouche chabil (2009) concludes that the carbonation depth in mortars based on blended cement is higher than the depth of carbonation mortars based on opc cements. in the same context, sisomphon and franke (2007) show that additions in volume (pozzolan materials) increases the carbonation rate with increasing w / c ratio, and concluded that the depth of accelerated carbonation (chamber riched of 3% co2) is 10 times higher than under natural exposure conditions. according to kulakowski et al. (2009), a rate higher than 10% additions in silica fume increases the potential for carbonation. moro et al. (2011) and phung et al. (2015) studied the effect of limestone fillers on the microstructure and permeability due to carbonation of cement pastes conditionally controlled co2 pressure, it shows that the carbonation samples (rh = 65%) is fast during the first hours while it decreases significantly if the relative humidity increases, this study shows that on the additional carbonation of portlandite, csh are also carbonated. moreover, morandeau et al (2015) and sideris et al. (2006) show that the fly ash additions (about 30%) to ordinary portland cement with a ratio of w / c in order of 0.6, the cement pastes develop coarse capillary pores which for extensive drying occur even if the total porosity decreases. this work inscribed in a sustainable development approach, which focus to study the behavior of concretes based on opc cement and blended cements (42.5 cem ii / b) produced in algeria, subjected to the accelerated carbonation. this work studies the effect of the class of cement on the evolution of the accelerated carbonation depth, two concrete formulations were made based on both classes of cement (opc cement 42.5 and blende cements cem ii / b) from the two concrete formulations, prismatic test samples 7x7x28 cm were made, and they were subjected to the accelerated carbonation test in a chamber enriched in co2 as recommended by afpc afrem (ollivier, 1997), carbonation depth measurements were carried out by spraying phenolphthalein at 4, 7,14, 28, 42 and 56 days for this study, the choice is oriented for the cements produced in algeria, the opc cement cem i and cement cem ii 42.5 / b. 2. experimental program 2.1. concrete formulation the cement used for the 1st concrete formulation is ordinary portland cement (opc) cem i 42.5, table 1 shows the chemical and physical characteristics of this cement. table 1. physical and chemical characteristics of the opc cement cem i 42.5 cemi 42.5 sio2 al2o3 fe2o3 cao mgo k2o na2o so3 s.s cm2/g 20-23 4.074.80 4.705.40 6265 0.711.22 0.350.50 0.07-0.18 1.001.45 25003263 *s.s : specific surface the used cement for the 2nd concrete formulation is the blended cement cem ii 42.5 / b, table 2 shows the chemical and physical characteristics of this cement. merah et al., j. build. mater. struct. (2020) 7: 87-94 89 table 2. chemical and physical characteristics of the blended cement cem ii/b cem ii/b 42.5 sio2 al2o3 fe2o3 cao mgo k2o na2o so3 s.s cm2/g 20.58 4.90 4.70 62.8 0.63 0.42 0.07-0.18 2.28 3700 *s.s : specific surface the used method for the two concrete formulations is the dreux gorisse method. two used classes of gravel were (3-8mm, 8-15 mm), with absolute density equal to 2700 kg/m3, and the used sand has an absolute density of 2400 kg/m3. the results of these formulations show that the cement content in concrete was 408 kg/m3 for the both concrete formulations, the slump cone was 11cm. the compressive strength at 28 days of the formulated concrete is 30mpa (the most used concrete in algeria). the w / c ratio is around 0.52. table 3. results of the concrete composition of the concrete formulation (opc cement cem i 42.5) sand (0-5) kg gravel 3-8 (kg) gravel 8-15 (kg) ciment cem i 42.5 (kg) water (l) w/c 708 115 933 408 211 0.52 table 4. results of the concrete composition of the 2nd formulation (cem ii 42.5 / b) sand (0-5) kg gravel 3-8 (kg) gravel 8-15 (kg) ciment cem ii 42.5/b (kg) water (l) w/c 708 115 933 408 211 0.52 the compressive strength at 28 days of the formulated concrete is 30 mpa, the w / c ratio is about of 0.57. figure 1: show the drx mineralogical composition of used limestone gravel fig. 1. mineralogical composition of used limestone gravel this analysis allowed to identify the nature of the component elements limestone gravel, they are all dolomite camg (co3)2 and some quartz elements sio2. 2.2. preparation of samples and conservations conditions for accelerated carbonation test the prismatic samples 7x7x28 cm were confectioned according the procedure recommended by afpc-afrem (ollivier, 1997). for both formulations, samples were made to undergo accelerated carbonation test, and they will be used for the carbonated concrete depth 90 mearh et al., j. build. mater. struct. (2020) 7: 87-94 measurements, other samples will be used to monitor evolution of the mass during the test. all these samples were cured in water for 28 days before initiating accelerated carbonation test, the procedure specified in afrem recommendations follow two phases: the first phase consist to saturate samples in the water. at the end of this phase, the samples will be weighed, dried for two days in an oven set at a temperature of 40 ± 2 c °, then they are still weighed, once before their introduction into the chamber of the accelerated carbonation. 2.3. accelerated carbonation test the test procedure adopted is the one recommended by the afpc afrem (ollivier, 1997) which consist to place (after 28 days of curing and drying) the prismatic samples 7x7x28cm (figure 2) of two concrete formulations in the chamber of accelerated carbonation (50 % co2+50 % air)( figure 3) , regulated at a temperature of 20 °c and a relative humidity of 65 ± 5%. all these samples were maintained in the chamber of accelerated carbonation for a period of 90 days. for each formulations, samples were removed from the chamber of accelerated carbonation at different ages: 4, 7, 14, 28, 42, 56 and 90 days, and they were sliced in two parts (figure 5) and a measurements of carbonation depth (by spraying the solution of phenolphthalein, (1% phenolphthalein in 70% ethyl alcohol) were executed with according to rilem recommendations cpc-18 (1988). carbonated depth corresponds to the distance between the outer surface of the concrete and the coloring front (figure 4), the uncarbonated concrete takes a pink color and the carbonated concrete is not colored (figure 5). this method is based on the change of the ph value, initially around 13 for the uncarbonated concrete and passes to 9 for the carbonated concrete, five distances are determined for each side of the test samples. the values of carbonation depth are given in mm. fig. 2. prismatic samples 7x7x28cm fig. 3. samples into the carbonation chamber fig. 4. method to measure of carbonation depth fig. 5. detection of the carbonated zone merah et al., j. build. mater. struct. (2020) 7: 87-94 91 3. results and discussions 3.1. drx test this technique essentially qualitative, used to differentiate varieties of the same crystallographic mineral such as portlandite and calcium carbonate (calcite). however, it does not identify the semi-crystalline or amorphous compounds such as amorphous portlandite or amorphous newly formed calcium carbonates. this method involves bombarding a sample (isotropic homogeneous powder consisting of tiny crystals welded together) with x-rays and recording the x-ray intensity which is redistributed according to the orientation in space. the scattered x-rays interfere with each other, the intensity then has maxima in certain directions. there is a diffraction phenomenon. the detected intensity is then drawn as a function of the beam deflection angle. the obtained curves are called diffractograms. figures 6 and 7, show diffractograms for an angle range (0 to 26 degrees), for the two types of carbonated concrete after 90 days in the carbonation chamber. fig. 6. drx analyzes on the carbonated (black)and uncarbonated (blue) samples for the 2nd concrete formulation (based on blended cement) fig. 7. drx analyzes on the carbonated (black)and uncarbonated (blue) samples for the 1st concrete formulation (based on opc cement) caco3 sio2 portlandite portlandite caco3 sio2 92 mearh et al., j. build. mater. struct. (2020) 7: 87-94 in order to confirm the measures of carbonation depth obtained with the method of the spraying phenolphthalein, the x-ray diffraction was used for the detection of the new formed products after carbonation and compared to controlled samples for the two concrete formulations. for both concrete formulations of carbonated samples, we observe that the reserve of portlandite was higher in the concrete made with opc cement compared to the samples of concrete made with blended cement. this can be explained that the concrete made with blended cement is more sensitive to carbonation compared with samples made with opc cement. this constating is caused that the opc cement has a high reserve of portlandite compared to blended cement. in another way, the composition of the two cements is different. 3.2. impact of the cement type on the accelerated carbonation figure 8 shows the results of the accelerated carbonation test for the test samples of the two concrete formulations. from this figure, it can be seen that the 1st concrete formulation based on the opc cement is less sensitive to carbonation phenomenon that the second one. 0 2 4 6 8 10 12 0 1 2 3 4 5 6 7 8 9 10 11 12 13 c a rb o n a ti o n d e p th i n m m f o r th e s e c o n d c o n c re te f o rm u la ti o n square root of time in days carbonation depth of concrete formulation based on opc cement carbonation depth of concrete formualtion based on blended cement fig. 8. : carbonation depth (concrete based on opc cement and concrete based on blended cement) the 1st concrete formulation gives a better protection for the concrete against the carbonation phenomenon compared with the 2nd concrete formulation. these results are in agreement with those obtained by sisomphon and franke (2007). in addition, for concrete samples of the 1st formulation, it was found that the depth of carbonation is low during the first days and increase from the 7th day, but it is still inferior to the depth of carbonation samples of the 2nd concrete formulation; this is due to the fact that during the first days the relative humidity is not stable within the chamber due to water exchange between the concrete and the relative humidity inside the chamber of accelerated carbonation. 3.3. evolution of mass during the accelerated carbonation test figure 9 shows the evolution of the mass during accelerated carbonation test for samples of the two concrete formulations. merah et al., j. build. mater. struct. (2020) 7: 87-94 93 0 10 20 30 40 50 60 70 80 90 100 3390 3400 3410 3420 3430 3440 3450 3460 m a s s i n g age in days mass gain for concrete based on opc cement mass gain for concreye based on blended cement fig. 9. mass gain during the accelerated carbonation test from this figure, it was found a mass gain in the early days of the test, especially for the samples of the 2nd concrete formulation; this can be explained by the fact that in the early days the relative humidity varies depending on the water exchange between the concrete and the atmosphere in the accelerated carbonation chamber. then the relative humidity stabilizes at a value of 65 ± 5%. moreover, this figure has the same form for the two concrete formulations, which agree with the results of afrem crossover tests. we also note that the mass gain during the accelerated carbonation test is less important for samples from the 1st formulation of concrete, this is due that the cement cemii / 42.5 b of the second formulation contains additions. these results confirm that the use of the 1st formulation of concrete based on cement cem i 42.5 opc gives a supplementary protection against the carbonation that the 2nd concrete formulation based on blended cem ii 42.5 /b 4. conclusion in the present work, a concrete composition b30 was made (2 fractions of gravel). samples from both concrete formulations were made and submitted to the accelerated carbonation test. we can draw the following conclusions: 1. the use of the opc cement for the confectioning of reinforced concrete structures minimizes carbonation depth compared to concretes based on blended cement cem ii / b 42.5. 2. it was found that a low mass change for concrete samples-based cements cem i / 42.5, compared to concretes-based cements cem ii / 42.5 b. 3. as regards the accelerated carbonation test, it was also found that the water exchange between the concrete and the atmosphere in the chamber do not stabilize after the 7th day. 4. the results show that the formulation of concrete-based opc cement is less sensitive to carbonation phenomenon compared to the concrete formulation based on cements cem ii / 42.5 b. 94 mearh et al., j. build. mater. struct. (2020) 7: 87-94 5. references dakhmouche chabil, f., z. (2009). carbonatation de bétons adjuvantés à base de ressources locales algériennes (phd thesis). orléans. cpc-18, r. r. (1988). measurement of hardened concrete carbonation depth. materials and structures, 21(126), 453-455. kulakowski, m. p., pereira, f. m., & dal molin, d. c. (2009). carbonation-induced reinforcement corrosion in silica fume concrete. construction and building materials, 23(3), 1189-1195. morandeau, a., thiéry, m., & dangla, p. (2015). impact of accelerated carbonation on opc cement paste blended with fly ash. cement and concrete research, 67, 226-236. moro, f. r., ghomari, f., boukli hacène, m. a., taleb, o., loukili, a., & rosière, e. (2011). la carbonatation des bétons aux fortes additions calcaires, xxixe rencontres universitaires de génie civil, tlemcen, algeria. ollivier, j. p. (ed.). (1997). essai de carbonatation accéléré, mesure de l’épaisseur de béton carbonate. durabilité des bétons, méthodes recommandées pour la mesure des grandeurs associées à la durabilité, 153-158. papadakis, v. g., fardis, m. n., & vayenas, c. g. (1992). effect of composition, environmental factors and cement-lime mortar coating on concrete carbonation. materials and structures, 25(5), 293-304. phung, q. t., maes, n., jacques, d., bruneel, e., van driessche, i., ye, g., & de schutter, g. (2015). effect of limestone fillers on microstructure and permeability due to carbonation of cement pastes under controlled co2 pressure conditions. construction and building materials, 82, 376-390. sideris, k. k., savva, a. e., & papayianni, j. (2006). sulfate resistance and carbonation of plain and blended cements. cement and concrete composites, 28(1), 47-56. sisomphon, k., & franke, l. (2007). carbonation rates of concretes containing high volume of pozzolanic materials. cement and concrete research, 37(12), 1647-1653. j. build. mater. struct. (2018) 5: 137-146 original article doi : 10.34118/jbms.v5i1.52 issn 2353-0057, eissn : 2600-6936 modeling of the interface between the concrete and the fibers grid in concrete slab bouzeboudja f *, ali ahmed c laboratory lamoms/university mouloud mammeri, tizi-ouzou, algeria, * corresponding author: bouzeboudjaf@yahoo.fr received: 14-02-2018 revised: 20-05-2018 accepted: 23-05-2018 abstract. abstract. fiber grid reinforcements are widely used in construction, especially in the rehabilitation of structures; short fibers are also used in concrete. however, reinforcing mortars with textiles (fiber gratings) which offers an improved concrete, and a wide variety of new and exciting architectural forms, is still a relatively new application that shows a need for research. tests on the use of glass fiber grids (gfg) and polypropylene grids (ppg) in the concrete matrix which can be an interesting solution to improve the bearing capacity and change the failure mode of slabs subjected to a load of punching have been realized. the results showed a significant increase in the bearing capacity, a better distribution of the cracks, as well as an improvement of the deflexion before failure; compared to unreinforced reference slabs. in order to understand the behaviour of the concrete-gfg interface of the tested slabs, a modeling of this latter was carried out using a constitutive law expressing the shear stress between the two materials as a function of the relative sliding between the surfaces in contact, taking into account the mechanical characteristics of both materials. the analysis of the bond-slip curve obtained has shown that the use of the glass fiber grid inside the concrete matrix allows a better behaviour of the interface between constituent materials with respect to the glued fiber-reinforced polymer (frp) plates on the surface of the slab. key words: concrete slab, reinforcement, grids, punching, interface stress, slip, modeling. 1. introduction new techniques that involve the use of composite materials in construction are currently being studied in different works (ait tahar and bouzeboudja, 2011). these methods are booming as these innovative materials have important advantages over traditional materials such as: lightness, mechanical and chemical resistance, freedom of shape and prolonged life. the use of textile reinforced concrete (trc) is a very effective method for strengthening reinforced concrete (rc) constructions. vast research on trc was carried out, so as to examine the use of trc for subsequently strengthening the bending load capacity of existing concrete or reinforced concrete elements (carozzi et al., 2016). frp (fiber reinforced polymer) is a composite material used in the rehabilitation of structures such as the reinforcement of beams, slabs and columns (neale et al., 2011). high modulus fibers can be used to improve stiffness and crack resistance. in order to greatly improve the structural strength, the high strength fibers can be used in conjunction with fibers having ductile behaviour, which exhibit some strain hardening until the high-strength fibers break (wang et al, 2010).the latter can be used to control the deformation of the elements of the structures. in addition, the service life can be increased by mixing high ductility fibers with high strength fibers. in the framework of this work, we have proposed a method of internal reinforcement of concrete slabs, by gfg and ppg grids, embedded in the concrete matrix at the level of the lower fibers and mailto:bouzeboudjaf@yahoo.fr 138 bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 top of the slab, to improve the bearing capacity and change the failure mode of these elements. this method consists of carrying out additional reinforcement to the traditional steel. indeed; an experimental study was carried out on reinforced slabs of gfg, and ppg, subjected to a progressive centered punching load. the bond between the fibers and the matrix has a considerable influence on this material behaviour and is very difficult to model because of the non-uniform stress distribution over a roving section (soranakom and mobasher, 2009). a study of the interfacial behaviour of the materials used for making the tested slabs, using an existing model in the literature to establish a relationship between the slip and the adhesion stress developed at the interface between the two materials is presented. 2. experimental program in order to demonstrate the advantage of reinforcement of concrete slabs with textiles against the loading of punching, the main objective of this experimental investigation consists in carrying out a characterization of the structural behaviour of bidirectional slabs armed with glass fibers and polypropylene, grids of large and small stitch. an experimental investigation was carried out, using slabs measuring 280 x 230 x 70 mm armed with two grids (see fig 2). two variants are considered: nine slabs reinforced by grids with small stitch and nine slabs reinforced by grids with large stitch. for each variant, a combination of grids is adopted to highlight the influence of the compatibility of the mechanical work of the grids, the influence of the position of the grid in the slab on the recovery of the applied load and on the mode of failure to ensure good reproducibility of the results, at least three specimens for each variant are tested. three unreinforced concrete slabs, considered as reference slabs, are also produced for the comparison of the results. to highlight the influence of grid mesh dimensions on the bearing capacity of the reinforced slab and especially on the failure mode, two types of mesh were considered in this study: small meshes and large meshes (figure 1). fig 1. grids of small meshes and larges meshes: a) gpg b) ppg fig 2. disposition of the grids in the slab bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 139 2.1. punching tests the slabs are tested under punching load (fig 3), applied using a hydraulic cylinder, through a rigid metal plate with 30 mm sides and a thickness of 1 cm. the slab is simply supported on a steel support device, consisting of four supposedly infinitely rigid sides. during the test, the value of the load and the vertical deflexion corresponding to the middle of the slab are read automatically. fig 3. ibertest test machine and support device. 2.2 results and discussion on fig 4 are confronted the curves load -deflection corresponding, to the slabs tested. fig 4. confrontation of the 'load-deflection' curves of the slab reinforced by two gfg / gpp grids and the reference slab. it can be seen that a considerable improvement in resistance and ductility is obtained with the reinforced slabs by the combination of gfg and ppg grids. indeed, unreinforced slab exhibits a fragile behaviour with an ultimate tensile load equal to 12.45 kn and a corresponding deflexion equal to 1.65 mm, on the other hand the rupture of the reinforced slab is obtained under an ultimate load of 25.42 kn and a corresponding deflexion of 3,07mm. this reinforcement of slabs has a gain in terms of bearing capacity of the order of 104.18% and of ductility estimated at 86.06%. the slabs reinforced with grids of small meshes have a better behaviour compared to the slabs armed with large meshes because the approximation of the mesh threads allows obtaining a 140 bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 homogeneous reinforcement of the slab and a better distribution of stresses around the most stretched fiber, as well as an increase in the percentage of reinforcement. the various results obtained highlight the interest of the internal reinforcement of concrete slabs by gfg and ppg grids; in fact, the gfg grid considerably increases the ultimate load and allows a better distribution of cracks in the tension zone, while the ppg grid allows the development of the flexional mechanisms in the slab, which leads to a more ductile mode of rupture compared to the reference concrete slabs. 3. aspect characterizing the bending behaviour of slabs the different aspects characterizing the flexional behaviour of the slabs were observed on the slab reinforced by the combination of gfg and ppg grids. indeed, during the loading, the behaviour of the reinforced slab passes through several successive phases, each one being characterized by a resistance to the peak and a corresponding deflexion. the first cracks create local discontinuities of the concrete matrix and a detachment of the concrete-gfg interface. when the different blocks are separated, the grids act as tie rods to secure and connect the blocks of the slab. when the ppg grid gives way, the slab is completely ruined. this behaviour is characterized by four phases as illustrated in fig. 5. fig 5. phases of the behaviour of the slab reinforced by 'gfg / ppg’ small meshes  phase i: this phase corresponds to the elastic behaviour of uncracked concrete, characterized by a rapid increase in load, up to 25.42 kn, corresponding to a deflexion of 3,07 mm. the first peak corresponds to the elastic limit value. at the end of this phase, there is a rapid drop in resistance due to the initiation and propagation of the first cracks;  phase ii: during this phase, cracks appear on the tensile face of the slab, and the deflexion increases more rapidly, the fall of the load is due to the peeling at the concretegrid interface gfg on both sides of the crack. the grid gfg then plays the role of tie-rod to secure and connect the "cracked blocks" of the slab. there was then a resumption of resistance;  phase iii: in this phase, a drop in the charge occurs suddenly, which corresponds to the breakage of the gfg grid. only the ppg grid continues to withstand the stresses developed by the applied load. this phase is very short because the ppg grid is weakly resistant to the applied load and deforms rapidly;  phase iv: this phase corresponds to the breakage of all the components of the slab. bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 141 4. behaviour of frp composite materials fig. 6 illustrates the idealized stress-strain curve of hybrid frp composites composed of three types of high modulus, strength and ductility fibers. fig. 6. idealized strain-strain curve of hybrid prf composites (wang et al, 2010) theoretical studies have shown that stiffness can be improved by fibers of higher modulus and the ductile behaviour can be obtained by hybrid fibers (wang et al, 2010). but the main problem often shown is the premature failure of the composites interface occurring due to the locally high stress concentration at the concrete-fiber interface. existing tear tests have shown that in the vast majority of cases and with the exception of cases where a very weak adhesive or a very strong concrete is used, the rupture of a frp-concrete interface is obtained by the development of cracks in the concrete layer adjacent to the adhesive layer, in case where this plate is narrower than the concrete block (neale et al, 2005) . during the load increase, the breaking plane propagates from the loaded end to the free end of the frp plate. a very important aspect of the behaviour of these bonded joints is the existence of an effective length of the adhesion beyond which an increase in the adhesion length l cannot improve the ultimate load. this constitutes a fundamental difference between an externally glued plate and internal reinforcement for which a sufficient anchorage length can always be found in order to ensure complete tensile strength of the reinforcement. since the behaviour of frp composites (fig 6) is similar to that of the slabs tested in our study (fig 4), an existing model characterizing the interface between the frp plate and the concrete will be used to establish bond-slip relationship characterizing the interface between the concrete and the textile used. 5. interface behaviour after the cracking of the concrete, the interface between the reinforcing fiber and the concrete has an important influence on the overall behaviour of the textile reinforced concrete. for that, several researchers are interested in the analytical modeling of the matrix fiber interface (carozzi et al., 2016) , others with the numerical simulation of the behaviour of this composite material, while some are interested in testing the pull-out of the textile from the concrete matrix (häußler-combe and hartig, 2007; lorenz, 2012). for our proposed internal reinforcement of the slabs, an analytical model will be used to characterize the interface between the gfg grid and the concrete matrix. 142 bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 5.1. grid removal mechanism in order to develop a law of the flexible and unified material, the constitutive law of the interfacial bond, the reaction of the wire to the longitudinal tensile stress, and the stress at the junction of the longitudinal and transverse wires are described as segmental linear functions (see fig. 7). figure 7.a shows a model of slip at the interface of the preand postmaximum shear stress  as a function of the slip s. figure 7.b presents a typical model of longitudinal tensile stress which could start with an initial release. finally, a nonlinear spring model, as shown in figure 7.c represents the additional stiffness gappearing at the junction (crossing) of the wires (soranakom and mobasher, 2008). fig.7. scheme of the grid removal mechanism; (a) interface link slip model; (b) of the longitudinal wire pattern; (c) spring model simulating the anchoring force at the junction cross wire; (d) the composite sample (soranakom and mobasher , 2008) with the use of multilinear segments to describe material behavior models and the use of intersection modules to control the behavior of the latter, the three models can be implemented as piecewise linear functions in the finite difference model. 5.2 stress slip relationship figure 8 illustrates the relationship between the tangential stress  and the slip s, this pace is the same for all interfaces., where τ (mpa) is the local bond (shear) stress, s (mm) is the local slip, τmax (mpa) is the local bond strength (i.e. the maximum bond/shear stress experienced by the interface), s0 (mm) is the slip when the bond stress reaches τmax (neale et al., 2005). fig. 8. lay of the constitutive law constraining of bond-slip (neale et al., 2005). bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 143 it is composed of a first linear elastic part, followed by a second part which becomes progressively non-linear as the slip increases. simultaneously, the plastic deformation in the interface increases to rupture. the post-rupture behaviour can be described by a reduction of the adhesion stress with the increase of the slip. schematically, this relationship can be represented by bilinear behaviour (fig 8), whose segments have the following characteristics: segment 1: elastic linear behaviour, going from s = 0 to s = s0, with: s0 being the slip corresponding to the end of the linear elastic domain, and to the maximum adhesion stress max. segment 2: locally linear behaviour, representing the inelastic and softening discharge, for s> s0. 5.3. model of lu and teng since it is difficult to obtain accurate bond–slip curves directly from strain measurements in a pull out test, lu et al. (2005) recently explored a numerical approach from which the bond–slip curve of any point along the interface can be obtained. the approach is based on the observation that debonding in a pull test occurs in the concrete, so if the failure of concrete can be accurately modelled, the interfacial shear stress and slip at a given location along the interface can be obtained from the finite element model. a simplified model without significant loss of accuracy can be readily obtained by noting that the initial stiffness of the bond-slip curve is much greater than the secant stiffness at the maximum point. based on this observation, the initial stiffness can be approximated as the infinite and the following simplified bond-slip model can be obtained by the relations (1a) and (1b) (lu et al., 2005) (1a) (1b) the shear stress τmax and the corresponding slip s0 are given by v (2) (3) w be calculated with equations: √ ⁄ ⁄ (4) bc width of concrete; b f width of renfort; the parameter α controls the shape of the descending branch of the curve, and is given by : (5) the interfacial fracture energy (gf ) can be expressed as : 144 bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 √ (6) where t is the tensile strength of concrete. 5.4. application of the simplified model of lu and teng to the case of slabs reinforced by grids to obtain the curve of bond slip between the concrete and the textile used (gfg),a study of the behaviour of the interface was undertaken using the simplified finite element model of lu et al. (2005),the different parameters taken into consideration in our case are the summarised in table 1: table.1. values of parameters characterizing the concrete interface – gfg grids parameters fc (mpa) ft (mpa) ßw u0 (mm) gf (mpa) ( values 34.8 2.69 1.5 1 0.052 0,505 4.035 after having programmed the different equations of the model and taking into account the real parameters characterizing the concrete-grids matrix interface, one obtains the curves illustrated by figures 9 and 10. fig.9. bond – slip curve of the concrete–gfg interface fig.10. illustration of the different domains of the bond slip curve of the concrete–gfg interface bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 145 results analysis from this curve, the following observations can be made: the shape of the curve is very close to the curves shown in figures 7 and 8. the bond-slip curve is composed of:  a rising branch corresponding to the elastic phase, for which a significant increase in the adhesion stress is observed, whereas the slip is not significant;  a descending branch, corresponding to the beginning of the rupture of the interface, for which it is observed that the adhesion stress tends to zero when the sliding is sufficiently large. the initial stiffness of the bond-slip curve is much greater than the secant stiffness at the point of maximum stress. this initial high rigidity, representing the rigidity of the completely linear elastic state of the interface, decreases rapidly with the appearance of microcracks in the concrete during the increase of the adhesion stress, finally, compared to the case of reinforcement by adhesive bonding of frp composite plates or, generally, the maximum adhesion stress max of the order of 3 mpa, in our case max = 4,035 mpa, which means that the adhesion of the gfg is greater than that of the frp with the concrete 6. conclusions the experimental results highlight the advantage of reinforcing the slabs with gfg and ppg grids. indeed, the gfg grid placed at the level of the stretched fiber increases considerably the ultimate load of the slabs subjected to the punching load, and confers a better distribution of the cracks. while the ppg grid allows the development of flexural mechanisms in the slab, which leads to a more ductile mode of rupture compared to the reference slabs. reinforcement with small mesh grids gives better results, because the increase in the number of roving per grid implies an increase in the percentage of the reinforcement in the concrete. the analysis of the curve of bond-slip obtained allowed us to observe that the use of gfg and ppg grids inside the matrix concrete leads to a better behaviour of the interface between the grid and the matrix concrete, the separation of the concrete-grid interface occurs only after numerous cracks in the concrete are encountered. nevertheless, a typical modelling of the gridconcrete interface should be established in order to have a more exact curve of bond-slip curve specific to this reinforcement case. these conclusions highlight the value of reinforcing the slabs with gfg and ppg grids. indeed, the gfg grid increases considerably the ultimate load of the slabs subjected to the punching and confers a better distribution of the cracks. 7. references ait tahar, k., & bouzeboudja, f. (2011). dalles en béton renforcées par des grilles composite. matériaux & techniques, 99, 281–289. carozzi, f. g., colombi, p., fava, g., & poggi, c. (2016). a cohesive interface crack model for the matrix– textile debonding in frcm composites. composite structures, 143, 230-241. häußler-combe, u., & hartig, j. (2007). bond and failure mechanisms of textile reinforced concrete (trc) under uniaxial tensile loading. cement and concrete composites, 29(4), 279-289. 146 bouzeboudja and ali ahmed, j. build. mater. struct. (2018) 5: 137-146 lorenz, e., & ortlepp, r. (2012). bond behavior of textile reinforcements-development of a pull-out test and modeling of the respective bond versus slip relation. in high performance fiber reinforced cement composites 6 (pp. 479-486). springer, dordrecht. lu, x. z., teng, j. g., ye, l. p., & jiang, j. j. (2005). bond–slip models for frp sheets/plates bonded to concrete. engineering structures, 27(6), 920-937. soranakom, c., & mobasher, b. (2009). geometrical and mechanical aspects of fabric bonding and pullout in cement composites. materials and structures, 42(6), 765-777. neale, k. w., ebead, u. a., abdel baky, h. m., elsayed, w. e., & godat, a. (2005). modelling of debonding phenomena in frp-strengthened concrete beams and slabs. proceedings of the international symposium on bond behaviour of frp in structures (bbfs 2005). international institute for frp in construction, university of sherbrooke. quebec, canada j1k 2r1. neale, k. w., godat, a., abdel baky, h., elsayed, w. e., & ebead, u. a. (2011). approaches for finite element simulations of frp-strengthened concrete beams and slabs. architecture civil engineering environment, 4(4), 59-72. wang, x., & wu, z. (2010). integrated high-performance thousand-metre scale cable-stayed bridge with hybrid frp cables. composites part b: engineering, 41(2), 166-175. j. build. mater. struct. (2018) 5: 164-173 original article doi : 10.34118/jbms.v5i1.55 study of architectural ceramics of the qal'a of bani hammad brahmi a *, hamiane m materials, processes and environment research unit (mpe-ru), city frantz fanon 35000 boumerdes, algeria * corresponding author: abla_arch@yahoo.fr received: 25-02-2018 revised: 04-06-2018 accepted: 13-06-2018 abstract. in order to define with precision, the physicochemical characteristics of the architectural ceramic exhumed from the qal'a of bani hammad’s site (inscribed on the unesco’s world heritage list in 1980), our study was conducted on a set of ceramics. the first analyses were focused on the color of the glazes, by optical absorption spectrophotometry (also called optical absorbance spectroscopy), on the texture by x-ray diffraction, and on the elemental composition of the various constituent stages of these glazes and their terra cotta, by scanning electron microscopy and x-ray fluorescence. indeed, the study combining optical absorbance spectroscopy and x-ray fluorescence enabled us to determine the origin of the monochromic green coloring of the glazes in some samples. this coloring can be attributed to the presence of the cu2+ chemical element; but these glazes darkened due to the high iron content they contain. this could be explained by an intentional addition of iron, in tin-opacified leaded glazes, baked in an oxidizing atmosphere and put on a limestone-rich marlacious paste. the chemical and mineralogical analyses of all shards show that their paste is calcareous. this dataset will be exploitable for re-creation experiments. it also represents a first exploitable referential system, for potential comparisons with other samples belonging to other algerian sites and different periods of time. key words: the qal'a of bani hammad; physicochemical characterization of ceramics; optical absorption spectrometry; x-ray fluorescence; x-ray diffraction. 1. introduction an ifriqiyan architecture took shape in the 9th century and the first elements of a ceramic art appeared in kairouan under the aghlabids dynasty. moreover, important urban centers such as mahdia, the qal'a of bani hammad, bougie, tunis, appeared and adopted this new industry. as for the qal'a of bani hammad, numerous records confirm that it was one of the most dynamic cultural and scientific centers of central maghreb in the 11th and 12th century. it played an important role of “relay place” after the decline of kairouan and before the founding of bougie (aissani and amara, 2014); and there is no doubt that local workshops definitely existed. golvin (1978) even assumed their exact location at the qal'a of bani hammad. the ceramic that we found in this site has an oriental style and continues the egyptian aghlabid and fatimid tradition (daoulatli, 1978). more specifically, the architectural ceramic is abundantly represented in the qal'a; the remarkable variety of its production techniques can only stir up regrets, regarding the fact that no systematic study using modern analysis processes has been undertaken, despite promising typological rating tests carried out a long time ago by george marçais (golvin, 1978) and refined by other archaeologists. although the site perfectly meets the criterion of authenticity defined by the world heritage chart, we defined specific objectives for this study by not selecting “all” the architectural ceramic varieties existing in the qal'a. indeed, the purpose of this work is to expose some varieties of the ceramic exhibited in our different museums, to provide a counterpoint regarding the analyzed mailto:email@email.com brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 165 ceramics and to contribute, on the first part, to the collection of analytical data supposed to promote historical, archaeological and architectural research, with a focus on the production techniques of the ceramics in question, as well as their diffusion and movement. 2. sampling and analytical methods a first study of the ceramic (collected from the qal'a of bani hammad’s site) took place in 1903 in works dedicated to the old city. it was led by a. roberto, who provided the reproduction of nine shards, among which eight were in color and mentioned them in the “collection of the archaeological society of constantine”. in 1906, georges marçais emphasized on the importance of this ceramic, in a comprehensive study on art in algeria. in 1908, m. saladin published and commented on paul blanchet’s notes, evoking architectural coatings and ceramic partitions found in the ruins. in 1909, general de bey lié put forward in his book on the qal'a, pictures and engraved drawings, and summarily analyzed this industry. in 1965, lucien golvin provided in his book « archaeological research at the qal'a of the bani hammad”, pictures and drawings of an important amount of ceramic, exhumed from the site in question. he also gave a descriptive approach on the production techniques used in the past. this same year 1965, rachid bourouiba published in a preliminary report about the excavations campaign led by himself, a number of plates about architectural ceramic and ordinary potteries exhumed from these excavations, that took place in september 1964. besides, seven samples of the architectural ceramic, used for the construction and the interior and exterior decoration of the qal'a’s palaces, were selected for this study. a quick examination of the physical characteristics of these samples enabled us to choose the appropriate investigation methods to solve the problem and, to define the analytical modes. these samples were submitted to the following tests: first, the surface of each shard was photographed and observed thanks to a binocular magnifier. then, millimetric chips removed from each shard were examined by using a scanning electron microscopy (philips.sem 505 model). in order to identify the chromogen agents responsible for the coloring of the glazes, at the level of the enameled samples, adouble-ray uv-visible optical absorption spectrometer (cary 500 de varian model) was used with the spread-reflection mode, directly on the sample for the glaze and in section for the terra cotta; the scanned spectral range vary between 350 mm and 800 mm. the study of the glaze’s elementary composition was performed by using the backscattering electron mode, thanks to the x-ray fluorescence paired up with the scattering energy scanning electron microscopy (jeol jsm6360lv model). results are in oxides mass percentage and the measures were carried out on cross-sections of glazes, previously polished and metallized with a thin carbon layer, on selected areas. the study of the terra cotta’s elementary composition was performed with an x-fluorescence spectrometer (srs 3400 – bruker – axs model). results are in oxides mass percentage and the measures were carried out on pearls, with a small amount of terra cotta. the study of the terra cotta’s mineralogical composition was performed with an x-ray diffractometer (panalytical: xpert-pro model). during the surface collection, the kbhec01 sample was found at the level of the lake palace, and kbhec06 was also collected from a ground paving made of terra cotta bricks; the whole of the bricks was put in opus picatum at the level of this same palace. nevertheless, the kbhec05, kbhec08, kbhec09, kbhec10 and kbhec12 samples were collected at the level of the manar palace. 166 brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 2.1. presentation of the studied material the kbhec01 sample: it represents a stalactite debris molded and enameled in opaque white on the four faces; the terra cotta is beige orange, compact and contains some thin and abundant inclusions. the piece has a parallelepipoid shape with four levels; on each side, we notice ribs. the kbhec05 sample: this one is a fragment from a rounded tile, produced by the modelling technique; the terra cotta is red-rosy, compact and contains a thick and abundant grog grease remover. the kbhec06 sample: it is a brick, produced by using the modelling technique, with a red color, compact and it contains a thick and abundant grog grease remover. the kbhec08 sample: it is a merlon debris molded in a leaf shape, which low surface is enameled in a dull green that has almost all disappeared. the paste of this shard is beige yellow, compact and contains some thick and abundant inclusions. this merlon represented a frieze element that decorated the hammadid palaces’ frontage. the kbhec09 sample: it presents a six-point star-shaped ceramic marquetery, molded and enameled in a bottle-green color on its superior surface. the paste of this marquetery is redrosy. the kbhec10 sample: this one is a fragment from a cross-shaped marquetery, used as ground paving, molded and enameled in white on its superior surface. the paste of this marquetery is beige yellow, compact and it contains some very thin and abundant inclusions. the kbhec12 sample: it represents a triangle-shaped ceramic marquetery debris, molded and enameled in green on its superior surface. the paste of this marquetery is beige yellow, compact and contains some very thin and abundant inclusions. all the samples indicated above are dated given the current state of knowledge, between the 5th and 6th hijri century (11th – 12th century after j.c). 3. experimental results and discussion 3.1. study of the surface’s states to the naked eye and by using the binocular magnifier, we notice that the surface state of these samples is characterized by a more or less significant loss of color. all these surfaces have some scratches caused by a mechanical degradation. one of the samples, kbhec10, also exhibited a "crazing". these cracks emerge in the glaze during the cooling, comingfrom traction pressures due to differences in terms ofthermal distention coefficient between the ceramic paste and the glaze. it is not uncommon to observe them on the surface of a glaze ( munier, 1957). all samples appear to be in good condition. they all have relatively homogeneous surfaces. with the exception of the kbhec08 sample, which almostlost all of its green glaze; the remaining part appears in a more advanced state of degradation. macroscopically, kbhec01 presents on its glazed part a defect of withdrawal. in the current state of knowledge, the glaze withdraws from the shard during the fusion and reveals spots where the clay is bared (fig. 1). this phenomenon can affect a glaze put on a poorly dusted biscuit. moreover, a frequent cause of this phenomenon is the crazing and cracking of the raw glaze. this case is more frequent in very matt glazes and viscous glazes during the fusion (rhodes, 1976). on a fresh break at the level of the terra cotta contained in the kbhec09 sample, we observe the presence of undecomposed limestone or gypsum in the shard’s pores (fig. 2). the observation under the binocular magnifier of a polished section at the level of the interface zone, between the glaze and the terra cotta support of the same sample, reveals the presence of a yellow border brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 167 (strip) (fig. 3),particularly visible at the level of the green glaze; which could correspond to devitrification crystals. this leads us to assume that the glaze was put on earth. at the level of the kbhec10’s terra cotta and on a polished section (fig. 4), the paste presents a beige color; it contains mauve luminescent grains, surrounded by a large amount of orange grains. this color could correspond to the respective presence of quartz crystals and undissolved calcite. the observation under the magnifier, at the level of the terra cotta contained in the kbhec12 sample reveals characteristics similar to those contained in the previous sample: the beige terra cotta contains mauve luminescent grains, surrounded by a large amount of orange grains. at this scale, no other characteristic is discernible. the observation using the backscattering electron mode shows the heterogeneity of the glaze contained in the kbhec08 sample, its thickness of about 350µm (fig. 5) as well as the presence of numerous variable-size bubbles. the bubbles were probably formed during the degassing phase of the terra cotta, or during the decomposition if the glazed mix during the baking. besides, khbec12 (fig 6) reveals on its glazed surface tiny needles, which could represent residues coming from a vegetal ash or from a contamination of the environment, such as biological microorganisms. 3.2. caracteristics of the glazes 3.2.1. measure of the glazes color the physicochemical origin of the coloring of the glaze is accessible analytically, by trying to identify metallic cations playing the role of chromogen agents. the registered optical absorption spectrum can thus be compared with reference absorption spectra. fig. 1. defect of withdrawal of fig. 2. observation on a fresh fig. 3 . the glaze/terra cotta the stalactite enamel kbhec01 break at the level of the terra interface zone, kbhec09 cotta, kbhec09 fig. 4 . polished section at the fig. 5 . micrography using the meb fig. 6 . micrography using the level of the paste of kbhec10 of the glaze/terra cotta interface meb of the glazed surface zone of kbhec08 of kbhec12 the spectra obtained on the white glaze contained in kbhec01 and khbec10 respectively present a low absorption between 350 and 410 nm and between 350 and 450 nm, which corresponds to the violet area. afterwards, the absorption is very low and constant between 450 168 brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 and 800 nm. the spectra show that the obtained color is not a perfect white but an off-white; and this, due to the absorption in the violets, as well as the beginning of the blues present in the glazes of the two samples. these spectra do not allow us to reveal the chromogen elements responsible for the coloring (richard, 2000). the optical absorption spectra of the khbec08, 09 and 12 show a first absorption strip between 350 and 500 to 520 nm (corresponding to the visible and blues area), and a second starting from 550 nm. a large strip varying from 550 and 800 nm is normally attributed to the cu2+ , which gives the glaze a green color when it gets leaded (rhodes, 1976). 3.2.2. elementary composition of the glazes for the white glazes contained in the kbhec01 and kbhec10 samples, they represent potassic alkaline-leaded glazes (table 1), which white opaque aspect is essentially due to the presence of tin (sno2 ꞊ 10.95 + 1.58 in kbhec01 and 17.13 + 1.58 in kbhec10), in the form of cassiterite crystals (sno2), highlighted by x-ray diffraction and performed on a sample of white glaze from the above samples. it is also possible that the unmelted quartz crystals in the white glaze reinforce the effect of the tin oxide in the opacification phenomenon. indeed, we know that the opacity of the pre-islamic glazes is sometimes related to the only presence of quartz crystals and feldspar (mason, 1997). we also observe the presence of iron in non-negligible content (fe2o3 ꞊2.55 % for kbhec01 and 4.49% for kbhec10), which may explain the white color with a yellow tendency of glazes contained in the two samples, because 1% of iron oxide is enough to dimly dye a glaze. besides, this high content in iron could also come from an intentional addition of it, in order to change few properties of the glaze. sometime a matt glaze will get bright and shiny by adding 2 to 3% of iron (picon, 1973). but the presence of lime in high content (05.56% in cao) minimized the effect of the iron oxide on the glaze’s color. on the other hand, the non-negligible content in aluminum (4.40 % of al2o3 for kbhec10) could explain that there was an intentional addition of aluminum as well, as alumina increases the viscosity of the glaze and the adhesion to the ceramic substrate. the elementary analysis of the green glazes from the kbhec08, kbhec09 and kbhec12 samples (table 1) show that they are leaded and that the tin (with the respective content of sno2꞊ 11.63%, 10.05% et 10.86%) explains the opacification of the glazes. table 1. qal'a of bani hammad. elementary analysis by scattering energy x-rays fluorescence, of the white and green glaze, converted in oxides mass percentage of studied samples. nd : not determined. oxides kbhec01 kbhec10 kbhec 08 kbhec09 kbhec12 white glaze white glaze green glaze green glaze green glaze sio2 51.32 32.77 36.44 21.57 23.93 al2o3 01.72 04.40 04.43 01.26 03.15 cao 02.59 05.56 05.85 02.03 03.44 mgo nd 03.75 01.00 00.23 03.08 na2o 00.84 00.59 00.73 nd 00.85 k2o 02.79 03.60 00.60 00.58 00.58 pbo 25.49 23.46 26.91 27.79 22.77 sno2 10.95 17.13 11.63 10.05 10.86 fe2o3 02.55 04.49 01.74 04.23 01.46 cuo nd nd 08.93 28.85 25.83 zno nd 00.90 nd nd nd p2o5 01.74 00.34 00.45 nd nd c nd 03.02 01.29 03.11 04.05 cl nd nd nd 00.30 nd brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 169 the optical absorption spectra at the level of the glaze from the three samples revealed the presence of the cu2+ ion as the chromogen agent responsible for the green color of these glazes, and the elementary analysis of the glaze confirm these data. the copper combined to the lead gives a green color when in an oxidizing atmosphere. furthermore, the presence of iron in high content (fe2o3 ꞊ 04.23 %) in the glaze of the kbhec09 sample, leads us to believe that it was intentionally added in order to darken and deepen the green color coming from the copper oxide (28.58% in cuo), which resulting color is dark bottle-green. finally, it is important to point out the presence of carbon impurities, in all studied glazes, due to the preparation of the samples, which glazed surfaces were covered by a thin carbon layer. 3.3 nature of the terra cotta 3.3.1 elementary analysis the results of the elementary analysis by x fluorescence, carried out on the terra cotta subsrate, are converted in weight oxides percentage (table 2). the terra cotta of the whole samples is calcique, the content in cao varies from 22.06 to 27.50%. the calcium in high content reveals that the ceramicist used an earth rich in calcium or that he added it intentionally, according to some authors. a substrate rich in calcium would be the most suitable to receive leaded glazes, due to their distention coefficient and their high porosity, that facilitates the adhesion of the glaze. we also observe the presence of iron in non-negligible content (between 5.48 and 6.12% in fe203); this element is almost always present in bedrocks. but, despite its presence, the color of the support contained in most of the samples remains light, certainly due to its calcique character (maniatis, 1983). 3.3.2 crystallographic analysis by using the x-ray diffraction (fig. 7), we highlighted the presence if the calcite (caco3), of quartz (sio2), gehlenite (ca2al2sio7) and albite (na al si3o8) in the paste contained in the studied samples (figure 9). besides, we notice the presence of the aluminous diopside, (ca (mg, fe , al ) ( si , al )2 o6), of the wadalite (ca6al5si2o16cl3 ) and the basanite (caso4(0.5h2o)) in the terra cotta of the kbhec01 sample. moreover, it is important to mention the presence of gypsum in the kbhec05 and kbhec08 samples, as well as the augite in kbhec05, 06, 10 and 12 and the orthose in kbhec08 and 12. table 2. qal'a of bani hammad. elementary analysis by x-ray fluorescence of the terra cotta, converted in oxides mass percentage of studied samples. oxides kbh01 kbh05 kbh06 kbh08 kbh09 kbh10 kbh12 sio2 42.20 41.29 35.50 38.92 39.76 44.41 43.85 al2o3 14.62 14.99 14.66 12.95 13.98 13.92 14.27 cao 24.71 22.06 27.50 26.84 24.32 22.94 23.61 mgo 2.86 2.26 1.91 2.20 2.17 2.56 2.57 na2o 0.94 1.65 1.32 1.00 1.60 1.20 1.16 k2o 1.02 1.61 0.83 0.88 1.52 1.13 1.26 fe2o3 6.03 6.12 6.02 5.56 5.59 5.48 5.69 tio2 0.85 0.85 0.87 0.76 0.80 0.79 0.80 p2o5 0.16 0.17 0.17 0.16 0.14 0.19 0.21 s 0.32 1.00 1.93 0.73 0.39 0.54 0.40 p.f 6.30 8.00 9.26 10.00 9.74 6.85 6.19 total 100 100 100 100 100 100 100 170 brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 (a) (b) (c) brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 171 (d) (e) (f) 172 brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 (g) fig. 7. qal'a des bani hammad, x-ray diffraction spectrum of terra cotta from the kbhec01(a), kbhec05 (b), kbhec06 (c), kbhec08 (d), kbhec09 (e), kbhec10 (f), kbhec12 (g) samples. the x-ray diffraction enables us to highlight the mineralogical composition and thus, it is possible to define temperature zones. the gehlenite (silico-aluminatecalcium) appears at about 800°c and reaches its maximum at around 900°c. the cohesion of the limestone pastes results from the formation of the gehlenite, when the baking does not exceed 900°c. however, at the highest temperature the cohesion role is mainly played by the anorthite. the diopside is formed after the gehlenite. but the fact that we discovered an important phase of unseparated calcite allows us to venture the hypothesis that the substrate would have been baked at around 850 to 900°c with a short length of baking time, which produced an incomplete separation of the calcite. it is important to mention as well that once baked, the shard shouldn’t contain calcite. the separation tension of the calcite is about 1 atmosphere at 900°c, but the separation becomes appreciable from 700°c in limestone clays (picon, 1973). nevertheless, it is not rare to discover calcite in archaeological ceramics. there could be three reasons: athe baking temperature remained at a lower level to bring the complete separation of the calcite, from which a part remained unchanged. bthe baking temperature, although it was high enough to lead to a complete separation of the calcite, was not maintained a sufficient time so the quicklime (cao) resulting from the decomposition of the carbonate (caco3) could get mixed with the other constituents of the paste. in these conditions there will remain a certain proportion of lime in the shard. but this lime, sooner or later, will come back to a carbonate by fixing the carbonic gas (co2) of the air (picon, 1973). c it results from a sediment (the action in a landfill place), which means that the calcite come from the water contained in landfill soils. 4. conclusions this study of characterization, that concerns few samples of architectural ceramic collected at the level of the qal'a of bani hammad, enables us to know the nature of clays in this region better and to conclude that: the ceramic material updated at the qal'a constitutes the major argument of a reasoning revealing the existence of an important handicraft of ceramic that developed in the area of this hammadid site. brahmi and hamiane, j. build. mater. struct. (2018) 5: 164-173 173 the similarity regarding the composition, between the samples of the analyzed ceramics, stipulates that the production workshops used the same baking method, which temperature can vary from 850 to 900°c. 5. references aissani, d. & amara, a. (2014). qalʽa des bani ḥammād : première capitale du royaume berbère des hammadides (xie siècle), 97547_enc_berbere_05.ind. daoulatli, a. (1978). la céramique ifriqiyenne du ixe au xve siècle. colloques internationaux du c.n.r.s n°584--la céramique médiévale en méditerranée occidentale xe-xve siècles, valbonne 11-14 septembre 1978, édition du c.n.r.s paris, 1980, p 197201. golvin l. (1978). les céramiques émaillées de période hammâdide qal'a des banû hammâd (algérie). colloques internationaux du c.n.r.s n°584-la céramique médiévale en méditerranée occidentale xe-xve siècles, valbonne 11-14 septembre 1978, édition du c.n.r.s paris, 1980, p 203. maniatis, y., simopoulos, a., kostikas, a. & perdikatsis, v. (1983). effect of reducing atmosphere on minerals and iron oxides developed in fired clays: the role of ca, in journal of the american ceramic society, 66, 11, 1983, p. 773781. marçais, g. (1913). les poteries et faïences de la qal’aa des beni hammad xie siècle ;contribution à l’étude de la céramique musulmane, constantine 1913. pp 417. mason. r (1997). m.s. tite the beginnings of tin-opacification of pottery glazes, in archaeometry, 39, 1, 1997, p. 41-58. munier. p (1957). technologie des faïences, m.p.de groote, france, 1957, p 25-209. picon, m. (1973). introduction { l’étude des céramiques sigillées de louzoux, publié par dessain et tolra, paris, 1973, p 16-73. rhodes, d. (1976). la poterie, terres et glaçures : les techniques de l'émaillage, dessain et tolra paris, p 43-175. richard, s. (2000). etude physique des carreaux glaçurés du palais des beys alger xviiexviiie siècle, sur la nécessité de connaître la texture et la nature des constituants (terre cuite, glaçure et décors en vue de recréations, mémoire de d.e.a de l’université de michel de montaignebordeaux 3, p16106. j. build. mater. struct. (2019) 6: 77-87 original article doi : 10.34118/jbms.v6i2.70 issn 2353-0057, eissn : 2600-6936 finite element modeling of strengthened beams using cfrp barour s*, zergua a department of civil engineering, university of frères mentouri-constantine 1. alegria. * corresponding author: baroure18@hotmail.fr received: 25-04-2019 accepted: 16-07-2019 abstract: deteriorating and damage of some structural elements influence negatively their strength and the bearing capacity. however, it is necessary to take some measures improve structural performance. in this context, the composite material is often used to strengthen the damaged parts. this paper presents a model to analyze the effect of carbon fiber reinforced polymer strengthening of beams under four point bending. finite element software ansys 12.0 has been used for modeling the beams by conducting nonlinear static analysis. the solid 65 and shell 181 elements have been used to, respectively; model the 3d concrete beams and the composite layer. constitutive properties of different components (concrete and frp) have been incorporated. the predicted finite element analysis results for the load-midspan deflection are compared to the measured experimental data. close agreement was found between the predicted and measured results at all stages of loading for both models developed. key words: finite element analysis, modeling, strengthened, frp. 1. introduction fiber reinforced polymer (frp) can be used to improve the shear and flexural capacities rc structural elements, (grace et al. 1999; bruno et al. 2007; arduini and nanni 1997; ross et al. 1999). increasing capacity depends on such factors as concrete strength, frp and steel mechanical properties and reinforcing steel and frp ratios. an et al. (1991), malek and saadatmanesh (1998) and ross et al. (1999) have done many studies. they have established analytical methods to evaluate the flexural capacity of reinforced concrete beam strengthened with frp laminates. santhakumar and chandrasekaran (2004 ) have studied the effect of cfrp on concrete beam with different fibre orientations. their results have been useful in tracking propagation of the crack. tăranu and bejan (2005) have studied mechanical modeling of composite aramide fiber. the carbon filaments have been observed to be more suitable in understanding the composite strips utilized for the basic restoration of strengthened solid twisted components. in the last decades, finite element analysis (fea) is also used to determine the overall behavior of the structure. (fanning, 2001), studied the experimental load-deflection response of ordinary and post-tensioned concrete beams with ansys. they have found that correlation of experiments and modeling depends on the values of the materials properties, such the young’s modulus of concrete and the yield strengths of the reinforcing bars. anthony (2004) have studied reinforced and prestressed concrete beams using finite element analysis. they concluded that the finite element package could well model the failure mechanism of the beams. dahmani et al. (2010) have conducted an investigation into the applicability of ansys software for analysis and prediction of crack patterns in rc beams and the advantage of performing numerical simulation instead of experimental tests. for this purpose, different phases of the behavior of the fe model of an rc beam was studied from initial cracking to failure of the beam. the entire load-deformation response produced correlated well with the analytical results. mailto:baroure18@hotmail.fr 78 barour and zergua, j. build. mater. struct. (2019) 6: 77-87 banu et al. (2012), have used ansys software to analysis the effect of frp material as an external layer to see the effect of it on load carrying capacity. they studied the numerical modeling of two-way reinforced concrete slabs strengthen with carbon fibers reinforced polymer strips. they have used soli65 element to model the 3d concrete beams while solid45 has been used to design the thick shells. they have conducted their results for load-deflection and ultimate carrying capacity. parandaman and jayaraman (2014), studied the finite element analysis of reinforced concrete beam retrofitted with different fiber composites using ansys. they have used three different composite layers. the load carrying capacity and the strength increase by using frp laminates. musmar et al.(2014), have studied a shallow reinforced concrete beams using ansys. they targeted their study towards the study of shallow reinforced concrete beam for transverse loading. they concluded that cracking initially occurs in the vertical flexural. it increases with increment in the load. the relationship between the load and deflection has been found to be linear elastic up to cracking moment strength then it inclines in horizontal plane. in this paper, four point bending analysis is carried out using concrete beam strengthened with externally bonded frp layers using ansys 12.0. load-deflection responses and the crack patterns at critical stages of loading are studied. in comparison to the experimental data, the numerical method was seen to satisfactorily predict the behavioral responses of the beams. 2. material properties 2.1. geometry and material data the geometry of the beam has a 1840 mm long and 120 mm width. the concrete strength was 21 mpa. a total of four types of beams are analysed depending on cfrp layers number (2 to 5) layers). table1 and table2 summarizes the material properties assumed for reinforced concrete as used by hawileh et al. (2015), in their experimental study. fig. 1. details of concrete beams by cfrp. hawileh et al. (2015). barour and zergua, j. build. mater. struct. (2019) 6: 77-87 79 table 1. experimental program details hawileh et al. (2015). group beams number of cfrp layers 1 ubs2 2 2 ubs3 3 3 ubs4 4 4 ubs5 5 table 2. mmechanical properties of the cfrp sheets and epoxy adhesive hawileh et al. (2015). material design thickness (mm) modulus of elasticity (gpa) ultimate tensile strength (mpa) elongation at failure (%) sikawra 300 c 0.17 230 3900 1.5 sikadur 330 4.5 30 0.9 3. samples preparation ansys computer program has been used for the finite element modelling ansys computer program has been used for the finite element modelling the finite element method is a numerical technique for obtaining approximate solutions to a wide variety of engineering problems. ansys is a software of finite elements modeling uses to solving a wide variety of problems, of which structural analysis (linear and nonlinear). the strengthening of concrete beams and cfrp had been analyzed using finite elements models by ansys 12. in this work, using the finite element models ansys12. multiple element types were used to model the five beams. 3.1. concrete properties solid65 (ansys12) is used for the three-dimensional modeling of solids with or without reinforcing bars. the solid is capable of cracking in tension, crushing in compression, creep nonlinearity and large deflection geometrical nonlinearity. here, the model without reinforcing bars was used. this element has eight nodes with three degrees of freedom at each node; translations in the nodal x, y, and z directions. stress strain relationship for concrete is shown in figure 2. figure 3 shows solid65 element in ansys fig. 2. concrete uniaxial stress-strain curve. 80 barour and zergua, j. build. mater. struct. (2019) 6: 77-87 fig. 3. solid65 element (ansys12). 3.2. composite layers for cfrp using elements shell181 (ansys12) it is an element of four-node with six degrees of freedom at each node:traductions in the x, y, directions and z, and rotations about the x, y, and z. shell181 is wellsuited for linear and large rotation, and/or large strain nonlinear applications. the geometry, node locations, and the coordinate system are shown in figure 4. modeling of composite layer has been done using shell181 element, presented in the figure 4. fig. 4. shell181 element (ansys12) 4. results the beam and cfrp layer were modeled using separate volumes. figures 5 and 6 show, respectively, the meshed beam and the meshed cfrp in ansys. the supports were modeled such that roller and the external loads were applied as concentrated forces distributed equally among the nodes. barour and zergua, j. build. mater. struct. (2019) 6: 77-87 81 fig. 5. the meshed beam. fig. 6. the meshed cfrp. 4.1. modeling validation one of the most important parameters in structures strengthening is bearing capacity, ductility and deflection. to validate the model, the results of ultimate load and deflection, obtained in mid span of beams, were compared with those of hawileh et al. (2015). they are presented in table 3. numerical results show an increasing in bearing capacities and decreasing in deflection with increasing of composite layers. the relative differences between the numerical and experimental results are not greater than 15.88% for load capacity and not greater than 18.7% for ultimate deflection. it can be concluded that numerical results are in good agreement with the experimental one. table 3. results between numerical modelling and experimentation. reinforced concrete beams load ( kn ) % difference ultimate deflection (mm) % difference exp fe a exp fea ubs2 24.056 28.600 15.88 7.1005 6.05461 14.72 ubs3 34.299 34.600 0.87 6.0075 5.2472 12.65 ubs4 34.042 36.600 6.98 5.6292 4.57632 18.70 ubs5 33.409 38.600 13.44 3.5166 3.76819 6.67 82 barour and zergua, j. build. mater. struct. (2019) 6: 77-87 4.2. comparison of the load-deflection curves for different beams comparison of load-deflection curves are shown in figure 7. firstly, it can be seen clearly that fe results are in good agreement with those of experiment. however, numerical curves are little stiffer, in linear zone, than those of experimental ones. the deflections and stresses in the beams were seen to increase with loading. comparison of the ultimate loads for strengthened beams according to the control beam has showed an increase of these loads, caused by the cfrp layer, ranging from 14 .89% to 1.46%. 0 1 2 3 4 5 6 7 8 9 0 5 10 15 20 25 30 35 40 l o a d ( k n ) deflection (mm) ubs2 ubs2(ansys) (a) case of 2 cfrp layers 0 1 2 3 4 5 6 7 8 9 0 5 10 15 20 25 30 35 40 l o a d ( k n ) deflection (mm) ubs3 ubs3(ansys) (b) case of 3 cfrp layers barour and zergua, j. build. mater. struct. (2019) 6: 77-87 83 0 1 2 3 4 5 6 7 8 0 5 10 15 20 25 30 35 40 l o a d ( k n ) deflection (mm) ubs4 ubs4(ansys) (c) case of 4 cfrp layers 0 1 2 3 4 5 6 7 8 9 0 5 10 15 20 25 30 35 40 l o a d ( k n ) deflection (mm) ubs5 ubs5(ansys) (c) case of 4 cfrp layers fig. 7. loaddeflection curves for different types of beams. comparison between experimental data and numerical results. having such a reliable and validated finite element model is advantageous over the experimentally measured data in many respects. the output of the experimental test are usually limited to that recorded by discrete number of strain gauges and lvdt at few points within the beam at specified time or load, while the finite element model provides predicted full deformation and stress results throughout the beam for the entire loading history. for instance, figure 8 shows the evolution stress in concrete 3rd principle stress (σ3) 84 barour and zergua, j. build. mater. struct. (2019) 6: 77-87 (a): case of 2 cfrp layers (b): case of 3 cfrp layers (c) : case of 4 cfrp layers barour and zergua, j. build. mater. struct. (2019) 6: 77-87 85 (d) : case of 5 cfrp layers fig. 8. response and stress distribution3rd principal stress (σ3). 4.3. distribution of cracks the numerical cracks distributions are illustrated in figures 9 and 10. fracture instability is affected by the layers number. the first crack in the fe model was a flexural crack in the mid span region of the beam. it appears at about 20% of the ultimate load. they are deeper in the beam with two layers than those of the beam with 5 cfrp layers. cracking also progressed with loading progress. they have been observed to increase in the constant moment region before they spread out towards the supports at last stages. at the end of loading, they have become more extended on the beam and denser than those observed in the first loading stage. fig. 9. cracks at load of 10.000 k n. case of 2 cfrp layers. 86 barour and zergua, j. build. mater. struct. (2019) 6: 77-87 (a) cracks at load of 10.000 kn. case of 5 cfrp layers (b) cracks prior to fracture. case of 5 cfrp layers fig. 10. crack distribution at two loading stages. case of beam with 5 cfrp layers. 5. conclusions in this study, the behavior of strengthened concrete beam was analyzed using finite element method. the results of load-displacement curves revealed that applying the cfrp layers, significantly improve beam performance. such that it increased beam bearing capacity. the deflections and stresses in the beams were seen to increase with loading. it has been seen that cfrp layers increase the ultimate load of the beam which depends on the cfrp layer numbers. the model allowed the tracking propagation of the cracks. the first crack in the fe model was a flexural crack. it appears at about 20% of the ultimate load. they are deeper in the beam with two layers than those of the beam with 5 cfrp layers. they also progressed with loading progress. they have been observed to increase in the constant moment region before they spread out towards the supports at last stages. at the end of loading, they have become more extended on the beam and denser than those observed in the first loading stage. 6. references an, w., saadatmanesh, h., & ehsani, m. r. (1991). rc beams strengthened with frp plates. ii: analysis and parametric study. journal of structural engineering, 117(11), 3434-3455. ansys. user manual, version 12. canonsburg (pa, usa). barour and zergua, j. build. mater. struct. (2019) 6: 77-87 87 anthony, j. (2004). flexural behavior of reinforced and prestressed concrete beams using finite element analysis, thesis report, marquette university. arduini, m., & nanni, a. (1997). parametric study of beams with externally bonded frp reinforcement. aci structural journal, 94(5), 493-501. banu, d., de barros, r. c., & taranu, n. (2012). numerical modeling of two way reinforced concrete slabs strengthened with carbon fibre reinforced polymer strips. in international conference on experimental mechanics (pp. 22-27). bruno, d., carpino, r., & greco, f. (2007). modelling of mixed mode debonding in externally frp reinforced beams. composites science and technology, 67(7-8), 1459-1474. dahmani, l., khennane, a., & kaci, s. (2010). crack identification in reinforced concrete beams using ansys software. strength of materials, 42(2), 232-240. fanning, p. (2001). nonlinear models of reinforced and post-tensioned concrete beams. electronic journal of structural engineering, 1(2), 111-119. grace, n. f., sayed, g. a., soliman, a. k., & saleh, k. r. (1999). strengthening reinforced concrete beams using fiber reinforced polymer (frp) laminates. aci structural journal-american concrete institute, 96(5), 865-874. hawileh, r. a., nawaz, w., abdalla, j. a., & saqan, e. i. (2015). effect of flexural cfrp sheets on shear resistance of reinforced concrete beams. composite structures, 122, 468-476. malek, a. m., & saadatmanesh, h. (1998). design equations and guidelines for reinforced concrete beams strengthened with frp plates. in second international conference on composites in infrastructure, national science foundation, university of arizona, tucson, ariz., 603–617. musmar, m. a., rjoub, m. i., & hadi, m. a. (2006). nonlinear finite element analysis of shallow reinforced concrete beams using solid65 element, arpn journal of engineering and applied sciences, 9(2), 85-89. parandaman, p., & jayaraman, m. (2014). finite element analysis of reinforced concrete beam retrofitted with different fiber composites. middle-east journal of scientific research, 22(7), 948-953. ross, c. a., jerome, d. m., tedesco, j. w., & hughes, m. l. (1999). strengthening of reinforced concrete beams with externally bonded composite laminates. structural journal, 96(2), 212-220. santhakumar, r., chandrasekaran, e., & dhanaraj, r. (2004). analysis of retrofitted reinforced concrete shear beams using carbon fiber composites. electronic journal of structural engineering, 4(1), 6674. ţăranu, n., & bejan, l. (2005). mecanica mediilor compozite armate cu fibre. editura cermi, iaşi. j. build. mater. struct. (2017) 4: 16-21 short communication doi : 10.34118/jbms.v4i1.27 issn 2353-0057 rehabilitation of existing building structure in expansive soils: a case study in laghouat, algeria ouai a engineer in national organization for the technical control of construction (ctc-sud), laghouat algeria. * corresponding author: ouai_aissa@yahoo.fr received: 14-09-2016 revised: 09-07-2017 accepted: 12-07-2017 abstract. this work presents results obtained from a case study conducted on m’kam neighborhood (600 housing social city) in laghouat, algeria. the bloc (j) in this location, suffering from damages that are attributed to the expansive clayey soil interaction with sewage disposal under foundations was the subject of rehabilitation in this study. the principal causes of observed structural damages were studied through diagnostic expertise (inspection-evaluation process) of the cracks and sewage disposal system of bloc (j). the results of this diagnostic investigation show that the main damages were mainly due to swelling of soil in presence of losses from sewage disposal. remedial actions were suggested to revise and repair all the sewage disposal system and strengthen the foundations of the building to avoid further damages. key words: expansive soils, sewage disposal system, damage, rehabilitation, repairing. 1. introduction expansive soils can exert, in presence of water, enough force on a building to cause severe damages. cracked foundations, floors, and basement walls are typical types of this damage. the occurrence of expansive soils in more pronounced in southern and arid regions such as the case of region of laghouat in south algeria (kamel et al., 2013; seco et al., 2011). due to important swelling and shrinkage potential of soils in arid region, it has become a severe problem to civil engineers. when a construction is realized on expansive soil under arid environmental conditions without the pre-understanding of their properties, the damage will be dramatically severe (kolay and ramesh, 2016). this paper presents a case study from an arid region (laghouat, algeria) characterized by a surficial formation of highly expansive soil. a social housing building (bloc j) with signs of distress and observable cracks was investigated to report the source and level of damages and propose rehabilitation measures. 2. state of the studied site the studied site is located in wilaya of laghouat, algeria (figure 1). laghouat is considered a semi-arid region, characterized by a hot dry climate in summer, followed by a cold rainy season. the studied site (m’kam city) is covered by an expansive clayey soil. the structure of studied bloc (j) is realized with reinforced concrete. the bloc (j) consists of sanitary basement, ground commercial floor and three floors for residential use as shown in figure 2. the visual inspection of the structure revealed evidence of cracking of external and internal walls of first and second floors. some photographs showing the current state of cracks inside and outside bloc (j) building are presented in figure 3. most of the cracks in the building were found to be at the internal walls of first and second floors. mailto:ouai_aissa@yahoo.fr ouai., j. build. mater. struct. (2017) 4: 16-21 17 fig 1. . map of algeria, situation of laghouat. fig 2. situation and general structure of bloc (j) building. 18 ouai., j. build. mater. struct. (2017) 4: 16-21 a) inside b) outside fig 3. state of cracks inside and outside bloc (j) building. 3. foundation and building sewer inspection the foundation of the studied building is of the superficial type, it is formed of insulated soles bonded by stringers. these soles are placed on a massive concrete. the foundation plan of the studied building is presented in figure 4. the main sanitary sewer system of the building is located in the basement and collects wastewater from the floors sewers. blockages in the building sewer can cause backups of sewage toilets, showers and floor drains. these types of blockages are sometimes referred to as basement backups, which can lead to disease, destruction of valuables and damage of building property. damages in the building sewers system have been located in the basement of the studied building, which causes infiltration of wastewater through cracked pipes (figure 5). 4. repair and remedial measures the type of any proposed repair or remedial measures undertaken on a damaged building depend on the following factors: the extent of the damage, the source causing the damage and the cost of remedial solutions (mughieda and hazirbaba, 2015). in this study the following remedial measures and building repair types were recommended: 4.1. building sewer repair the first step to repair the damages is repairing building sewers. the solution consist on performing an inspection of wastewater utility, prior any repair, to identify if there is a problem in floors sanitary sewer pipe system. after this preliminary inspection, the main sewer manhole located in the interior of building (in basement) is changed to the exterior, before the main sanitary sewer in the street, to avoid any wastewater infiltrations around the foundations (figure 6). ouai., j. build. mater. struct. (2017) 4: 16-21 19 fig 4. foundation plan of the building. fig 5. infiltration of wastewater through cracked pipes. 20 ouai., j. build. mater. struct. (2017) 4: 16-21 fig 6. main manhole sewers were moved completely outside the building. 4.2. building foundations reinforcement it is inspected that repairing wastewater utility and elimination of any infiltration of wastewater to the foundations specified in previous section, will restrict the problem of swelling and shrinkage of the foundation soil appreciably. if no further movement is detected after the implementing of the remedial measures of building sewers, foundations and crack repair may proceed. inspection and evaluation are the principal phase of any rehabilitation and repair of the building. inspection of the building is the process by which any damage in the building foundations is observed and recorded, while evaluation refers to all works to determine and assess the condition of the building based on the inspection step. it is intended to evaluate the general condition of the structure and identify any areas of deficiency. the followed repair work is largely based on the conclusions of the process of inspection and evaluation. fig 7. repairing of a concrete structure such as foundations means to replace, correct or strengthen damaged, faulty materials; components structure (idrissou, 2006). in order to improve the ouai., j. build. mater. struct. (2017) 4: 16-21 21 stability of the building and to correct the expansion joint openings caused by the differential movement of the foundations, reinforced concrete footings with peripheral sails were installed on both sides of each expansion joint along the total building basement height (figure 7). 5. conclusions a damaged social housing building due to an expansive soil was investigated in the form of a case study. diagnostic analyses of the damage were conducted through inspection and evaluation process. this finding of the followed process was significant in identifying the causes of differential movement of foundation and eventual cracking of the interior and exterior walls of the building. remedial measures were prescribed in the current study. the proposed remedial measures focused on revising and repairing the wastewater system of all floors and moving the main sewer manhole to the exterior of building to avoid any infiltration and isolate the foundations of the building from the wastewater so. we propose also a reinforcement of the foundations, to enhance the stability of the building and to rectify the openings at the expansion joints caused by the differential movement of the foundations, by using a reinforced concrete footings with peripheral sails were installed at both sides of each expansion joint along the total height of the building basement. 6. references idrissou, m. m. (2006). reliability in interpreting non-destructive testing (ndt) results of concrete structures (doctoral dissertation, universiti teknologi malaysia). kamel, g. m., idriss, g., & benchaa, b. (2013). effet de chaux, ciment et sel sur le potentiel de gonflement des argiles gonflantes des régions arides en algérie. european journal of environmental and civil engineering, 17(5), 315-328. kolay, p. k., & ramesh, k. c. (2016). reduction of expansive index, swelling and compression beha vior of kaolinite and bentonite clay with sand and class c fly ash. geotechnical and geological engineering, 1(34), 87-101. mughieda, o., & hazirbaba, k (2015). expansive clay soil-structure interaction: a case study. in: recent advances in mechanics, mechatronics and civil, chemical and industrial engineering, proceedings of the international conference on civil engineering. isbn: 978-1-61804-325-2, pp: 195-200. seco, a., ramírez, f., miqueleiz, l., & garcía, b. (2011). stabilization of expansive soils for use in construction. applied clay science, 51(3), 348-352. j. build. mater. struct. (2022) 9: 158-164 original article doi : 10.34118/jbms.v9i2.2798 issn 2353-0057, eissn : 2600-6936 tensile strength of multi-material bolted double lap joints under static loading bachi bensaad s 1,*, mazari m1, lahlali o 2 1,* department of mechanical engineering, djilali liabes – sidi belabbes, algeria. 2 department of mechanical engineering, faculty of science and technics – fés, morroco. * corresponding author: mailto:saoussanebachi@gmail.com received: 21-09-2022 accepted: 24-12-2022 abstract. this paper aims to study the mechanical behavior and failure mode of al 6082-t6 & polyvinyl chloride (pvc) in double-lap bolted joints. to accomplish this, the effect of geometric parameters was investigated using abaqus/standard. multi-material bolted assemblies have recently gained increasing attention in the aerospace engineering field, due to enhanced design possibilities and positive size effects with regard to decreasing ply thickness. in this paper, the mechanical behavior of polymer and aluminum alloy bolted joints with double‐lap bolted structure under quasi‐static loading was studied numerically. in general, double lap joints were found to have greater load carrying capacities than single bolt joints (by 40%–49%). also, double bolt joints with wider plates (increased width) can beneficially shift the failure mode from net-tension to bearing. the geometric parameters were found to play an important role in controlling the failure mode so that catastrophic failure modes of net-tension and shear-out can be prevented in bolted joint. key words: bolted joints, finite element analysis (fea), static behavior, multi-material assemblies. 1. introduction mechanically fastened joints are used widely in multi-material structures. in comparison with bonded joints, there are no surface preparation issues for bolted joints, there is the option of disassembly for routine inspection and they are relatively insensitive to environmental conditions. the major challenge with mechanically fastened joints is that the introduction of a hole into a composite/polymer plate leads to a stress concentration, which cannot be relieved by plastic flow in the way that is possible in a metallic material. standard static tests show that in terms of strength retention, a mechanical joint made of an aluminum alloy will largely outperform a polymer that was intended to replace it in structural applications. these assessments have not prevented the ongoing success of highly plastic materials over metal alloys counterparts in aeronautic applications. essentially, the top reasons for such success are the proven superiority of the long-term mechanical performance, if equal weight is considered, and the fact that fewer parts must be assembled, which reduces the final cost. the second reason is supported by the maturity and advances made in composite/polymer manufacturing, such as automatic fiber placement to produce massive complex composite structures in a single part (dirk et al., 2012). it was found that the mechanical properties of bolted joints such as ultimate load and failure modes are related to a few parameters. these include: i) design parameters, such as plate thickness, edge distance and end distance, bolt numbers and arrangement (kweon et al., 2006); ii) material parameters, such as grade of the connected plate materials (galos, 2020); iii) fastener parameters, such as clamping force (sihn et al., 2007). http://www.oasis-pubs.com/ mailto:saoussanebachi@gmail.com bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 159 the typical failure modes for steel bolted joints subjected to shear are bolt shear failure, net section failure, and bearing failure (wu et al., 2018). fiber reinforced polymer (frp) composites are promising construction materials consisting of polymer matrix and fibers. they have been increasingly used in engineering due to properties such as lightweight, high specific strength, and most importantly, high corrosion resistance to harsh environments (amacher et al., 2014). similarly, to steel bolted connections, the mechanical properties of bolted connections using frp plates and steel bolts have been studied in literature. four common failure modes for frp bolted connections tested in shear were identified and reported in the literature (wen et al., 2019), including net-tension failure, shear-out failure, cleavage failure and bearing failure. among the failure, modes of steel and frp bolted joints mentioned above, bearing failure is characterized by a progressive process, and capable of providing adequate warning before final failure. 2. finite element modelling according to structure sizes, a three dimensional model was generated using the commercial software abaqus (abaqus 6.13) in order to determine and to perform the analyses of stress field at contact zone. 2.1. material the materials used for modeling the component flat of double lap joint is aluminum alloy 6082t6, and polyvinyl chloride (pvc). there proprieties are taking from (yibo et al., 2013; (specialchem, 2017). the material for the bolt is high-strength and high-grade alloy steel (ajax steel bolt class 8.8 and unbrako steel bolt class 12.8). typical young’s modulus and poisson’s ratio for this material are 210,000 mpa and 0.3 respectively. 2.1.1. mechanical properties of aluminum 6082t6 strength properties of the aluminum plates: table 1. 6082-t6 aluminum alloy chemical composition si mg fe cu mn cr zn ti others al 0.7-1.3 0.6-1.2 ≤0.5 ≤0.1 0.4-1 ≤0.25 0.2 ≤0.1 0.15 balance table 2. 6082-t6 aluminum alloy mechanical properties alloy 𝛿ℎ 𝛿𝑝0.2 𝛿 6082-t6 310 260 8% table 3. tensile test condition setting. sample a a a a b b b b strain rate/s-1 0.001 0.01 0.1 1 10 20 50 100 2.1.2. mechanical properties of polyvinyl chloride (pvc) strength properties of the polymer chosen in this work (pvc): table 4. polyvinyl chloride (pvc) properties property ultimate tensile strength elongation at break elastic tensile modulus density poisson’s ratio value 52 mpa 50-80% 3.0-3.3 gpa 1.42-1.48 0.4 2.2. specimen details the figure 1 presents the geometry of the bolted assembly considered to this numerical analysis. (benhamena, 2010). 160 bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 fig. 1. the double lap geometry and dimensions in mm in this modeling the fasteners (screw, nut counter-nut discs), are regarded as rigid bodies in the finite element model. figure 3 shows the boundary conditions and the conditions of loading in statics. two contact pairs were established in the model. one was located between the polymer laminate and the aluminum metal plate, and the other was located between the polymer and bolt. a surface-to-surface discretization was employed for the contacts between bolts and plates, and a node-to-surface discretization was used for the contact between the plates to prevent element interpenetration at the edges of the parts. the contact between the hi-lite bolt and the inner surface of the hole was then simulated using a surface-to-surface contact type. the contact property was applied to the plate-plate and holebolt contacts. the polymer laminate was the master surface for the plate-to-plate contact, and the bolt was chosen the slave surface for the hole-to-bolt contact. the contacts were solved using the penalty method with hard contact, friction, small sliding and finite sliding. penalty contact was included between the aluminum alloy hi-lock bolt and the polymer laminate along the bearing surface with a coefficient of friction of 0.1, and the plate-to-plate contact was 0.2. the step time chosen for the simulation was 0.2 s, and final time is 1 s, in order to facilitate the analysis. fig. 2. boundary conditions and loading condition. bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 161 the theory of incremental plasticity is used to define the elastoplastic parameters of the used materials. the iterative method of newton–raphson is used as an approach to solve nonlinear equations by finite elements method. a typical 3d implicit finite element model for bolted joints is presented in fig. 3. the details of the finite elements model and the bolted assembly mesh are represented on fig. 4. one end of the plates was constrained and the tensile load was applied to the other end. bolt clamping force (preload) was applied using the bolt load option in abaqus. fig. 3. a typical fe model for double shear bolted joint with steel bolt fig. 4. finite elements detail model: the bolted assembly mesh the considered mesh consists essentially of c3d8r elements type: 8-node 3d continuum elements, with reduced integration. the choice of this element type was motivated by various numerical studies and given the fact that the accuracy/calculation time of this element type is suitable for the study. particular attention has been paid to the partitioning of the parts to have a mesh set and to have a continuity of the stress fields from one part to the other. 3. results and discussion the load-displacement curves of both geometries showed some interesting results. it was suggested that the load-displacement curves of the assembly exhibited three main stages. the load increased linearly at first arriving to a value of 2500n due to the joint load being reacted solely by static friction forces acting at the shear plane, then, a sliding occurred corresponding to that the large bolt-hole clearance was taken up and the bolt shank began to contact the laminates, when contact was established between the bolt and the laminates, the bolt started to transmit load and the load decreased causing the damage of the polymer. here, the typical force-displacement curve of the assembly was concluded in fig. 6. 162 bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 fig. 5. numerical result showing the deformation of the geometry fig. 6. relationship force-displacement for the whole assembly model along the load axes. it is found that the numerical models can run completely without convergence issues. transition stage begins with a value of 2500 n which is the maximum stress achieved in for this assembly, where the polymer laminate failure occurs. afterwards, the damage continues to evolve, an interesting amount of polymer tensile failure is recorded. the joint starts to lose its stiffness gradually due to damage accumulation. subsequently, a longitudinal tensile displacement of 50 mm was applied to the end of the middle plate through a quasi-static process. bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 163 the initiation of failure in the double bolt junctions occurred at the critical edge of the hole where there is a high stress concentration was almost 210mpa. fig. 7. numerical stress strain curve of the bolt joint. 4. conclusion a three-dimensional finite element model was developed to predict the tensile behavior of double lap bolted multi-material assembly of (al6082t6/pvc). this is vital for the optimization of multi-material structure designs and can be seen as the contribution of this paper. the following conclusions were obtained: the results obtained from the simulation were in total agreement with other experimental studies found in the literature. the maximum value of load went up to 2500n, along with a maximum elongation of 50mm. however the middle plate, clearly showed an interesting variation in the model due to its plasticity threshold the polymer/slave plate (pvc) went through a long plasticity phase, which explains why the aluminum plates didn't really show a remarkable transformation due to the highest rigidity of the al 6082t6 compared to the polymer (pvc). the damage and failure of the joints were dominated by the damage and failure of the pvc. the stress distributions in the bolt depends crucially on its rigidity. 5. references amacher, r., cugnoni, j., botsis, j., sorensen, l., smith, w., & dransfeld, c. (2014). thin ply composites: experimental characterization and modeling of size-effects. composites science and technology, 101, 121-132. benhamena, a. contribution à l’étude de l ‘endommagement en fretting fatigue des assemblages par fixation: cas des assemblages rivetés (contribution to the fretting fatigue damage study of assemblies by fixation: rivet assemblies case) (doctoral dissertation, phd thesis, sidi bel abbes, algeria 2010 (in french)). dirk, h. j. l., ward, c., & potter, k. d. (2012). the engineering aspects of automated prepreg layup: history, present and future. composites part b: engineering, 43(3), 997-1009. galos, j. (2020). thin-ply composite laminates: a review. composite structures, 236, 111920. kweon, j. h., jung, j. w., kim, t. h., choi, j. h., & kim, d. h. (2006). failure of carbon composite-toaluminum joints with combined mechanical fastening and adhesive bonding. composite structures, 75(1-4), 192-198. 164 bachi bensaad et al., j. build. mater. struct. (2022) 9: 158-164 sihn, s., kim, r. y., kawabe, k., & tsai, s. w. (2007). experimental studies of thin-ply laminated composites. composites science and technology, 67(6), 996-1008. specialchem, (2017). comprehensive guide on polyvinyl chloride (pvc). available online at: https://omnexus.specialchem.com/selection-guide/polyvinyl-chloride-pvc-plastic. wen, x., wan, m., huang, c., & lei, m. (2019). strength and fracture toughness of tc21 alloy with multilevel lamellar microstructure. materials science and engineering: a, 740, 121-129. wu, x., fuller, j. d., longana, m. l., & wisnom, m. r. (2018). reduced notch sensitivity in pseudo-ductile cfrp thin ply angle-ply laminates with central 0 plies. composites part a: applied science and manufacturing, 111, 62-72. yibo, p., gang, w., tianxing, z., shangfeng, p., & yiming, r. (2013). dynamic mechanical behaviors of 6082t6 aluminum alloy. advances in mechanical engineering, 5, 878016. j. build. mater. struct. (2014) 1: 30-39 https://doi.org/10.34118/jbms.v1i1.6 issn 2353-0057 a “new” design requirement: the mitigation of the progressive collapse of buildings under exceptional loading jaspart jp * and demonceau jf department argenco, liège university, belgium. * corresponding author: jean-pierre.jaspart@ulg.ac.be abstract. recent events such as natural catastrophes or terrorism attacks have highlighted the necessity to ensure the structural integrity of buildings under an exceptional event. according to the eurocodes and some different other national design codes, the structural integrity of civil engineering structures should be ensured through appropriate measures but, in most cases, no precise practical guidelines on how to achieve this goal are provided. at liège university, the robustness of building frames is investigated with the final objective to propose design requirements to mitigate the risk of progressive collapse considering the conventional scenario “loss of a column” further to an unspecified event. in particular, a complete analytical procedure has been developed for the verification of the robustness of steel or composite plane frames. for sake of simplicity, these first works have been based on the assumption that the dynamic effects linked to the column loss were limited and could therefore be neglected. more recently, complementary works have been carried out with the objective to address the dynamic effects. besides that, the extension of the static procedure to actual 3d frames is under investigation in liège. the present paper gives a global overview of the ongoing researches in the field of robustness at liège university; in particular, the global strategy to derive design requirements is detailed. key words: robustness, exceptional loading, loss of column. 1. adopted strategy the studies performed at liège university in the field of “robustness of structures” are mainly dedicated to the exceptional scenario “loss of a column” in a steel or steel-concrete composite building structure. the main objective is to derive guidelines for an appropriate design of the structure for the considered scenario. to achieve this goal, simplified analytical procedures are developed to predict the response of the structure further to a column loss; as an outcome, the way on how each structural parameter influences the structural behaviour may be described. the present section describes the global research strategy adopted by the authors. the loss of a column can be associated to different types of exceptional events: explosion, impact of a vehicle, fire… under many of these exceptional actions, dynamic effects may play an important role. however, it is first assumed that the column loss does not induce dynamic effects; so, the investigations of the structural response may be founded on static approaches. a building structure losing a column can be divided in two main parts, as illustrated in figure 1: the directly affected part which represents the part of the building which is directly affected by the column loss, i.e. the beams, the columns and the beam-to-column joints which are just above the failing column and; the indirectly affected part which includes the rest of the structure. the indirectly affected part is affected by the loads developing within the directly affected part; but obviously, these forces are themselves influenced by the response of the indirectly affected part. mailto:jean-pierre.jaspart@ulg.ac.be jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 31 fig 1. representation of a frame losing a column and main definitions. in figure 2, the curve representing the static evolution of the vertical displacement a according to the normal load nlo in the failing column (see figure 1) is illustrated: from point (1) to (2) (phase 1), the design loads are progressively applied, i.e the “conventional” loading is applied to the structure; so, nlo progressively decreases (nlo becomes negative as the column “ab” is subjected to compression) while a remains approximately equal to 0 during this phase. it is assumed that no yielding appears in the investigated frame during this phase, i.e. the frame remains fully elastic. from point (2) to (5), the column is progressively removed. indeed, from point (2), the compression in column “ab” nlo decreases until it reaches a value equal to 0 at point (5) where the column is considered as fully destroyed. so, in this zone, the absolute value of nlo progressively decreases while the value of a increases. this part of the graph is divided in two phases as represented in figure 2:  from point (2) to (4) (phase 2): during this phase, the directly affected part passes from a fully elastic behaviour (from point (2) to (3)) to a global plastic mechanism. in (3), the first plastic hinges appear in the directly affected part.  from point (4) to (5) (phase 3): during this phase, high deformations of the directly affected part are observed and second order effects play an important role. in particular, significant catenary actions develop in the bottom beams of the directly affected part. fig 2. evolution of nlo according to the vertical displacement at the top of the lost column. pha se 3 p h a s e 2 p h a s e 1  n (1) (2) (4) (5) (3) lo lo.design n 32 jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 it is only possible to reach point (5) if: resistance of the directly affected part is appropriate; the loads which are reported from the directly affected part to the indirectly affected part do not induce the collapse of elements in the latter (for instance, buckling of columns or development of a global plastic mechanism in the indirectly affected part); the different structural elements have a sufficient ductility to reach the vertical displacement corresponding to point (5). this global approach was first developed for steel and composite structures but may be applied to other typologies of structures, as given in table 1. table 1. steps to be crossed to derive design recommendations: (i: initiated, d: developed, tbd: to be developed). design recommendations tbd tbd tbd tbd tbd dynamic effects/type of exceptional actions i tbd tbd tbd tbd 3d behavior i i tbd tbd tbd 2d behavior d d tbd tbd tbd global approach d d d d d / steel structures composite structures concrete structures timber structures masonry structures in a first step, simplified analytical methods were developed to predict the response of 2d steel and composite frames further to the loss of a column with no dynamic effects; the latter are summarised in section 2. then, based on this first step, studies were initiated to take the 3d structural response and the dynamic effects into account; these two aspects are respectively addressed in section 3 and section 4. the final objective is to progressively complete table 1 with “d” indexes, what means that design recommendations would have been derived for most typologies of structures, with a similar global approach. 2. static behaviour of 2d frames further to a column loss luu (2008) has studied the static response of 2d frames further to a column loss during phase 1 and 2 (figure 2), while demonceau (2008) concentrates on phase 3 in which catenary effects develop. the adopted strategy to study phase 3 is presented in figure 3: step 1: an experimental test is carried out in liège on a substructure with the aim to simulate the loss of a column in a composite building frame; step 2: analytical and numerical fem tools are validated through comparisons with the experimental results; step 3: parametric studies based on the use of the models validated at step 2 are carried out; the objective is to identify the parameters influencing the frame response during phase 3; step 4: a simplified analytical method is developed with due account of the parameters identified at step 3 and validated through comparisons with the experimental test results of step1. in the present paper, part of the research works performed within steps 1 (section 2.1) and 4 (section 2.2) are reflected. more information is available in (demonceau, 2008, 2010) jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 33 fig 3. strategy followed to investigate phase 3. 2.1. experimental test on a substructure simulating the loss of a column a test on a composite substructure has been performed to simulate the loss of a column. the main objective of the test was to observe the development of catenary actions within a frame and the effect of these actions on the behaviour of the semi-rigid and partial-strength composite beam-to-column joints. indeed these joints are initially designed and loaded in bending, but have progressively to support tensile loads as a result of the development of membrane tying forces in the beams. to define the substructure properties, an “actual” composite building was first designed (demonceau, 2008) according to eurocode 4, so under “normal” loading conditions. as it was not possible to test a full 2-d actual composite frame within the project, a substructure was extracted from the actual frame (demonceau, 2008); it was chosen so as to respect the dimensions of the testing floor in the laboratory but also to exhibit a similar behaviour than the one in the actual frame. the tested substructure is presented in figure 4. as illustrated, horizontal jacks were placed at each end of the specimen so as to simulate the lateral restraints brought by the indirectly affected part of actual building when catenary actions develop. a specific loading history was followed during the test. first, the vertical jack at the middle was locked and permanent loads were applied on the concrete slab with steel plates and concrete blocks (“normal” loading situation). then, the vertical jack was unlocked and large displacements develop progressively at point a (figure 4) until the force in the jack vanished (free spanning of 8 m). finally, a downward vertical displacement was imposed to the system above the impacted column and was then progressively increased until collapse. the “vertical load vs. vertical displacement at point a” curve is reported in figure 5. fig 4. tested substructure. 34 jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 fig 5. “vertical load at the jack vs. vertical displacement at point a” curve. the first part of the test is represented by the segment “oa” of the curve presented in figure 5 and which represents the evolution of the vertical load acting on the beams at the middle of the substructure according to the vertical displacement under the “impacted” column. the vertical reaction in the lower column stub, before its removal, is equal to -33,5 kn (value of the load at point “o”). from figure 5, it can be seen that the structure remains globally elastic when “a” is reached. then, as previously explained, an increasing vertical displacement is progressively imposed until failure. during this stage, two “unloading-reloading” sequences are followed as illustrated in figure 5. from point “a” to “b” in figure 5, the substructure yields progressively to finally form a beam plastic mechanism at point “b” (development of plastic hinges in the joints). at that moment, the cracks in the concrete slab at the external composite joints are pronounced and yielding of some steel components of the joints is observed (column web and beam flange in compression). also, for the internal composite joint, a detachment of the end-plate and of the column flange is observed. from point “b” to “c”, a plateau develops, what means that the vertical displacements increase with a constant vertical load (equal to 30 kn). all along the plateau, the concrete cracks in the vicinity of the external composite joints continue to extend and yielding spreads further in the steel joint components. besides that, the concrete in compression close to the internal composite joint crushes. the horizontal jacks begin to be significantly activated at point “c” in figure 5; at this point, membrane forces start to develop as confirmed by the shape of the global displacement curve (part “cd”). at point “d”, the longitudinal rebars in the external composite joints suddenly fail; at that moment, the external joints work as steel ones. yielding also affects the different components of the internal and external joints. at point “d”, a loss of stiffness related to the failure of the rebars is observed; indeed, when these rebars fail, both flexural and tensile stiffness of the external joints decrease; but this not prevent the further development of catenary actions. indeed, it can be observed that the failure of the rebars does not lead to the failure of the substructure; after point “d”, the vertical load at the vertical jacks still increases with the imposed displacement (part “de” of the curve in figure 5). jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 35 this is possible as long as the steel connection is able to support, alone, the membrane forces developed in the system. in addition, associated to the loss of the rebars, the vertical displacements are increasing with a low variation of the vertical loads. these additional vertical displacements induce an increase of the membrane forces. so, the steel connection working alone has at the end to be sufficiently resistant to support these additional membrane forces and sufficiently ductile to support the additional rotations associated to the vertical displacement. the capacity of the steel connections, working alone, to support significant membrane forces has been confirmed by tests on joints in isolation performed at stuttgart university (kuhlmann, 2008). 2.2. prediction of the frame response during phase 3 in demonceau (2008), it was shown through numerical investigations that it is possible to extract a simplified substructure (see figure 6) composed of the beams and the joints just above the lost column and likely represent accurately the actual global response of full frame during phase 3. accordingly, a simplified analytical method based on a rigid-plastic analysis has been developed to predict the response of the so-defined substructure. also, as the deformations of the substructure are significant and influence its response, a second-order analysis has been conducted. fig 6. substructure to be investigated. the parameters taken into account in this process are illustrated in figure 6: p is the (constant) uniformly distributed load applied on the storey modelled by the simplified substructure and the concentrated load q is a concentrated load simulating the progressive loss of resistance of the column (=bnlo – nup see figure 1); l is the total initial length of the substructure; a is the vertical displacement at the concentrated load application point; k is the deformation of the horizontal spring simulating the lateral restraint provided by the indirectly affected part; n1 and n2 are the plastic elongations at each plastic hinge;  is the rotation in the plastic hinges at the beam extremities. in addition, the axial and bending resistances at the plastic hinges nrd1 and mrd1 for plastic hinges 1 and 4 and nrd2 and mrd2 for plastic hinges 2 and 3 have also to be taken into account (it 36 jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 is assumed that the two plastic hinges 1 and 4 and the two plastic hinges 2 and 3 (see figure 6) have respectively the same resistance curve for m-n interaction). so as to be able to predict the response of the simplified substructure, the stiffness k and the resistance frd of the lateral restraint have to be known; these parameters depend of the properties of the indirectly affected part (see figure 1). an analytical procedures have been defined to predict these characteristics (luu, 2008; huvelle, 2011). demonceau (2008) proposes an analytical expression for the q-q curve characterising the response of the simplified substructure. as a validation, the results obtained with the latter have been compared to the results of the experimental test performed on the substructure (see previous section). in figure 7, it is seen that a very good agreement is obtained between the analytical prediction and the experimental measurements. more details about the developed method are available in (demonceau, 2008). fig 7. comparison of analytical prediction vs. experimental results. 3. static behaviour of 3d structures further to column loss lemaire (2010) has investigated the behaviour of 3d structures made of steel beams and columns. two different structures have been considered, with same dimensions and constitutive elements (see figure 8); they just differ by the joint properties at the extremities of the secondary beams: pinned joints in structure 1 and fully rigid joints in structure 2. for both cases, the column which is considered to be lost is the central one, as illustrated in figure 8 (column “bx”). fig 8. investigated 3d structure. jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 37 for each structure, a simplified substructure (see figure 9) has been defined and extracted from the full 3d structure with the objective to check the possibility of this substructure to simulate with a sufficient accuracy the behaviour of the actual structure when significant membrane forces develop. the procedure followed for the definition of the substructure is the same as the one used for 2d frames (see section 2 and (demonceau, 2008)). this substructure is made of (i) four beams (two primary beams and two secondary beams) connected at the top of the failing column and of (ii) the joints at the extremities of these beams. fig 9. substructure extracted from the 3d structure. the influence of the rest of the structure (i.e. the part which is not directly affected by the column loss) is reflected by horizontal springs at the extremities of the so-defined substructure (see figure 6), with appropriate stiffness (kx and kz). in figure 10, a comparison between the predictions obtained (i) through a numerical simulation of the global 3d structure losing a column and (ii) through a numerical simulation of the sodefined substructure is given for the two considered structures. fig 10. comparisons between the results obtained through numerical simulations of the 3d structure and of the substructure. the graphs given in figure 10 represent the evolution of the axial load nlo in the failing column according to the vertical displacement at the top of this column. as the objective with the 38 jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 substructure is to predict the behaviour of the structure when significant membrane forces develop in the system, the predictions can only be compared from point a (see figure 10), i.e. when a plastic mechanism is formed in the structure and significant vertical displacements are reached. in figure 10, it can be observed that a very good agreement is obtained for structure 1 while it is not the case for structure 2. this observation can be explained as follows. the loss of the column is reflected in the substructure modelling through the application of a concentrated load q (see figure 9). in practice, this load q is equal to the difference between nlo and nup (see figure 1). for some structures, it was demonstrated through a parametrical study that, when significant membrane forces are developing in the directly affected beams, the value of nup can be assumed as a constant (luu, 2008). accordingly, the variation of q vs. the deformation of the substructure reflects the variation of nlo in the global structure. it is the reason why, for some 2d structure, it is possible to reflect the actual behaviour of the 2d frame with the substructure. for structure 1, nup remains approximately constant after the formation of the plastic mechanism and thus the substructure approach is valid. but for structure 2, nup is not remaining constant and, as a result, the variation of q according to the vertical displacement in the substructure modelling does not reflect the actual evolution of nlo in the 3d structure. the fact that nup is no more constant when significant membrane forces are developing is linked to the fact that a redistribution of forces takes place between the storeys located above the lost column; this aspect, which has to be explicitly considered in the model, has not been analytically characterised yet but is currently investigated. if the variation of the normal force in the column just above the failing one is introduced in the substructure model, it may be seen that the results are in good agreement with those obtained from the study of the actual full 3d structure. lemaire (2010) has also demonstrated that the analytical method initially developed for 2d frames by demonceau (2008) and able to predict the response of the “2d” substructure can be easily adapted to predict the response of the “3d” substructure defined in figure 9. accordingly, when a method will be available to predict the influence of the restraint provided by the upper storeys on the normal load in the column just above the failing one, it will be possible to predict analytically the behaviour of the global 3d structure through the substructure modelling. 4. dynamic behaviour of 2d frames further to a column loss comeliau et al. (2009, 2010) have studied the dynamic behaviour of 2d steel frames further to a column loss. in particular, a simplified model has been developed to predict the dynamic behaviour of the substructure defined in section 2. because of the limited allocation of pages, these works are not described in the present paper; for detailed information, the reader will refer to (comeliau, 2009, 2010, 2012). 5. conclusions at liège university, the exceptional scenario “loss of a column” in a building structure has been under investigation for a few years with the final objective to propose design requirements to ensure an appropriate robustness of structures under the considered scenario. the present paper gives a global overview of the adopted development strategy for this scenario, of the achievements in this field so far and of the ongoing research activities. in particular, simplified analytical methods have been developed to predict the static response of 2d steel and composite frames further to a column loss. investigations are presently in progress to extend these methods to 3d structures. besides, the dynamic behaviour of 2d structures has been investigated and a procedure has been developed to predict the dynamic response of a simplified substructure. there further validation and there extension to 3d structures have still to be developed further. jaspart and demonceau, j. build. mater. struct. (2014) 1: 30-39 39 6. references comeliau l (2009). effects of the dynamic behaviour of steel structures further to a column loss (in french)”. master thesis presented at liège university, 2009 (freely downloadable at http://hdl.handle.net/2268/32284). comeliau l, demonceau jf, jaspart jp (2010). robustness of steel and composite buildings under impact loading, proceedings of sdss rio-2010 international colloquium – stability and ductility of steel structures, rio de janeiro, pp. 393-400. comeliau l, rossi b, demonceau jf (2012). robustness of steel and composite buildings suffering the dynamic loss of a column. struct eng int, 22: 323-329. demonceau jf (2008). steel and composite building frames: sway response under conventional loading and development of membrane effects in beams further to an exceptional action. phd thesis presented at liège university, (freely downloadable at http://orbi.ulg.ac.be/handle/2268/2740). demonceau jf, jaspart jp (2010). experimental test simulating a column loss in a composite frame. adv steel constr, 6:891-913. huvelle c (2011). contribution to the study of the robustness of building structures: progressive yielding of the indirectly affected part further to an exceptional event (in french), master thesis presented at liège university. (freely downloadable at http://orbi.ulg.ac.be/handle/2268/127083) kuhlmann u, rolle l, jaspart jp, demonceau jf, vassart o, weynand k, ziller c, busse e, lendering m, zandonini r and baldassino n (2008). robust structures by joint ductility. final report of the rfcs project n° rfs-cr-04046. lemaire f (2010). study of the 3d behaviour of steel and composite structures further to a column loss (in french)”, master thesis presented at liège university. luu hnn (2008). structural response of steel and composite building frames further to an impact leading to the loss of a column. phd thesis presented at liège university, 2008 (freely downloadable at http://bictel.ulg.ac.be/etd-db/collection/available/ulgetd-01212009-095305/). http://hdl.handle.net/2268/32284 http://orbi.ulg.ac.be/handle/2268/2740 http://orbi.ulg.ac.be/handle/2268/127083 http://bictel.ulg.ac.be/etd-db/collection/available/ulgetd-01212009-095305/ j. build. mater. struct. (2018) 5: 147-156 original article doi : 10.34118/jbms.v5i1.53 issn 2353-0057, eissn : 2600-6936 fractal dimension of roughness: influence of grain size and granular class bouzeboudja h*, melbouci b, bouzeboudja a geomaterials laboratory, environment and development, mouloud mammeri university of tizi-ouzou, algeria * corresponding author: bouzeboudjah@gmail.com received: 15-02-2018 revised: 21-05-2018 accepted: 25-05-2018 abstract. the soil structure can be described as an assembly of elements of various sizes separated by a complex system of cracks and fractures, since the grains of the soil are differentiated by their shape, size and orientation. they are thus differently associated and related, their masses can form complex and irregular configurations which are in general extremely difficult to characterize in exact geometric terms. to understand the mechanical behavior of granular materials, it is then necessary to characterize the grains using the fractal dimension which is a characteristic that indicates the degree of irregularity and fragmentation of the latter. this experimental work consists in studying the influence of the parameters variation: granular class, grain size and normal stress applied during casagrande's direct shear tests on the roughness fractal dimension calculated with the method of box counting. the analysis of the results obtained at the end of a granulometric variation which caused a variation of the fractal dimension of grain roughness. this variation made it possible to analyze the level of fragmentation suffered by the sandstone grains during the various shear tests. this fragmentation produces fines that are the source of variations in the mechanical properties of the sandstone material. key words: fractal dimension, crushing, sandstone, direct shear. 1. introduction the behavior of granulate material is influenced by several parameters such as: granulometry, the size and shape of the grains, their hardness and applied stress, etc... an experimental study is essential for a better understanding of the influence of these parameters (ovalle, 2013). otherwise, to determine the grain size or the grain size variations during the shear test, we will use the notion of fractal dimension which is one of the main features of fractal geometry. its calculation is a theoretical tool for interpreting problems from the dimensions of the physical quantities involved. it has been used among others in the field of civil engineering. it describes well the irregularity of a grain of the granular material. so, several methods have been developed to calculate the fractal dimension of grains or grain samples. the most used techniques are the new theories of image analysis that are important after photographing the grains (sezer & al., 2008). they make it possible to quantify and study the crushing variation of the grains of the different granular classes studied by varying several parameters. 2. notion of crushing of grain granular materials may experience breakage or crushing under shear or compression effects. this phenomenon causes their fragmentation under different aspects. the evidence for this phenomenon has been published in several studies of granular materials subjected to mechanical testing (kim, 1995; lade & yamamura 1996; mac dowel & bolton 1998; melbouci 2002 & 2006a; 2006b; ovalle 2013; bouzeboudja & melbouci, 2016a; bouzeboudja & al., 2016b) mailto:bouzeboudjah@gmail.com 148 bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 these different studies have also shown that grain breakage is generally limited to contact points and can extend into the interior of the grain. when the grains are solid, hard and fairly rounded, they can withstand major constraints that require for example the use of heavy machinery or compactors in the construction of high dams earthen and rockfill to meet the requirements of high density. on the other hand, the angular-shaped grains of freshly quarried quarry materials undergo fragmentation due to breakage of the asperities under less severe stresses, and reach higher densities (ramamurthy, 1969). guyon and troadec (1994) classified grain failure in three ways: abrasion, flaking, and fracture (figure 1): fig 1. different modes of grain breakdown (guyon & troadec, 1994). abrasion: the result is a grain having substantially the same size as the original, but with a production of particles of very small sizes. chipping (or attrition): a grain breaks to become smaller, while giving several smaller grains. fracture: a grain breaks to give new ones that are substantially equal in size and smaller than the original grain. 3. generalities on the fractal dimension and definition of the method used the adjective "fractal" was proposed by mandelbrot in 1975 (mandelbrot, 1975). it comes from the latin word "fractus", from the verb "frangere" which means to break, to present irregularities, to fragment at all scales or to split up infinitely. a fractal object is a geometric structure that repeats, similar to itself, regardless of the scale at which it is observed; then we speak of internal similarity. mandelbrot defined it as a set that presents irregularities at all its scales of observation, both macroscopically and microscopically. the fractal dimension is a non-integer number (0 < df < 3) which measures the degree of irregularity or fragmentation of a geometric or natural object or measuring the roughness of a surface and this notion of fractal dimension is applied to scale invariant objects (fazzalari & al., 1996). it is possible to calculate it by various methods, in this work it is the method of counting the boxes that was used for the calculation of the fractal dimension (tyler & al., 1992). 3.1. method of box counting this is the most popular calculation method in practice. the fractal dimension calculated by this method gives us an idea of the dimensional distribution of the grains in the granular medium and its fragmentation process (russel & al., 1980). in fact, this method consists in dividing the image of a grain into a small square (or box) of the same dimension (meshing system), so the contour of the grain that passes through these boxes is counted, and the same operation is repeated with boxes of decreasing size until reaching the contour close to that of the real grain (figure 2). bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 149 fig 2. different steps of meshing of an image of a grain. this method is based on the principle that the image of the grain will correspond to the number of boxes according to its size and this relation is represented by formula (1): n( x) x df (1) x: size of boxes; x: linear dimension of the grains, greater than the dimension x; n (x> x): number of boxes; k: constant of proportionality; df: fractal dimension of roughness (huang & zhan, 2002; wang & al., 2006). by plotting the logarithmic graph of the number of boxes according to the box sizes, the fractal dimension is obtained according to the slope best suited to the line and can be calculated by the equation (2): df (2) m: is the exponent of the regression line of the scatter plot. fig 3. calculation of the fractal dimension by the box counting method of a grain of sandstone. 4. material of the study the material used in this study is a local material which is sandstone, a sedimentary rock of detrital origin, formed of grains agglomerated by a siliceous, calcareous or ferruginous natural cement, giving a hardness to the whole and with variable cohesion, but generally quite hard and compact, used especially as building and paving material or as sharpening stone. the grains obtained after crushing are characterized by their size and shape the chemical composition of sandstone is composed mainly of quartz. the material that binds the grains together is generally composed of silica, calcium carbonate or iron oxide. it is this y = 23,73x-0,95 r² = 0,999 1 10 100 1000 0.1 1 10 n u m b e r o f b o x e s dimension of boxes (mm) sandstone dfr = -m =0,95 150 bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 binder which gives the material its color, so iron oxide gives red or reddish brown sandstone and the others give white, yellowish or grayish sandstone. the sandstone breakage is characterized by the fracture of the cement but not the grains, which remain whole. fig 4. sandstone studied. the mineralogical compositions of the sandstone are grouped in table 1. table 1. the chemical compositions of numidian sandstones (alili & al., 1999). sio2(%) fe2o3 (%) al2o3 (%) cao (%) mgo (%) mno (%) na2o (%) k2o (%) paf (%) 91.57 at 98.64 0.10 at 1.8 0.04 at 3.60 0.10 at 1.05 0.02 at 0.21 0.01 at 0.05 0.05 0.01 at 0.51 0.29 at 1.35 the physico-mechanical properties of this rock are represented in tables 2 and 3. table 2. the mechanical characteristics of the material studied. characteristics fragmentability fr degradability dg micro deval mde los-angeles la [%] sandstone 118 1.04 91 92 table 3. the physical characteristics of the material used. characteristics optimal volumetric weight γopt [ n/ 3] optimal water content wopt [%] porosity n [%] volumetric weight of solid grains γs [ n/ 3] sandstone 17.6 8.33 24.5 26.3 sandstone is a fragmentable material with a fragmentation coefficient fr (nf p94-066) greater than 7. the coefficients micro-deval mde (nf p18-572) and los angeles la (nf p18-573) of the sandstone are very high, they are greater than 45; therefore this material is usable neither for the body of roadway nor for the layers of form. the degradability coefficient dg (nf p94-067) of the sandstone is less than 5, so it is not degradable. 5. apparatus and sampling the direct shear test makes it possible to quickly characterize the breaking behavior of the granular material. the necessary equipment and procedure are, however, much simpler. the 6 x 6 cm shear box was used (figure 5). the sample to be studied is placed between two half-boxes that can move horizontally relative to each other. a piston makes it possible to exert on the sample a determined normal stress (varying from 100 kpa to 400 kpa). the different samples prepared, as well as the direct shear test apparatus and the principle of the procedure followed are used according to french standards (afnor, 1994). bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 151 fig 5. apparatus for the direct shear test at the casagrande box. sampling three granular classes were studied: 3.15/5 mm, 5/8 mm and 3.15/8 mm. for each granular class (figure 6) a series of three samples are made which are subjected to shear tests by varying the normal stress of 100 kpa, 300 kpa and 400 kpa and for each sample five control grains of each diameter were stained and photographed before and after testing in order to better evaluate their fragmentation during crushing. fig 6. the granular classes used: 3.15/5 mm (a), 5/8 mm (b) and 3.15/8 mm (c). 6. test carried out the samples reconstituted in the laboratory are prepared in such a way as to be able to study the influence of the granular class and the size of the grains and the particle size distribution on the crushing phenomenon in order to be able to evaluate the fractal dimension of the grains after crushing. the samples are subjected, in the dry state, to the direct shear tests at the casagrande box, applying three shear stresses 100 kpa, 300 kpa and 400 kpa (afnor, 1994), these tests show that relative displacements occur between the grains, which result in friction at the points of contact and thus engender their crushing (figure 7). (a): before the testing and (b): after the testing. fig 7. example of a sample subjected to a stress test of 400 kpa. (a) (b) (c) (a) (b) 152 bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 the direct shear test is still widely used because of the simplicity of its implementation. it makes it possible to quickly characterize the rupture behavior of the different samples and to study the variation in crushing rate of the grains by comparing the fractal fragmentation dimension values calculated before and after each test with the box counting method used. 7. presentation and interpretation of test results the results obtained are presented in the form of stress-displacement curves. the behavior of granular materials is strongly influenced by the degree of crushing and breaking of grains. indeed, during the many tests, the samples suffered deformations and ruptures of their grains. the amount of fines produced increases with the increase of the intensity of the normal stress. we recall that the setting up of the samples is identical for all the tests and that each test has been repeated several times so as to systematically confirm the reproducibility of the results obtained and to better quantify the mechanical characteristics of sandstone. 7.1. curves constraints displacements the stress-displacement curves show the evolution of the tangential stress (τ [ pa]) as a function of the horizontal displace ents (δl [ ]) (τ = f (δl)), which allow to describe the evolution of the shear resistance of the samples according to the studied parameters for sandstone under different normal applied stresses (100, 300 and 400 kpa) (figure 8 (a)). during casagrande box shear tests, sample failure occurs along the plane between the half-boxes where the deformation is imposed. the shear stresses (τ) of the sa ples increase with the increase in the nor al stress (σ) applied, for the three granular classes (figure 8 (b)). fig 8. evolution of the curves efforts-displacements. the stress-displacement curves corresponding to the samples of the sandstone material have a resistance level for very low horizontal displacements. under high normal stresses (300 and 400 kpa), sandstone samples develop new strength after exhausting much of their shear strength. this can be explained by a new restructuring of the grains during their displacement and rotation, which has formed a new, denser matrix with a better reorientation of the grains, thus developing a new resistance. the angles of friction obtained vary according to the granular class (table 4) and according to the sharp edges of the grains favoring the friction between the grains. table 4. determination of the angle of friction of the different granular classes. granular classes sharp edges 3.15/8 13.82 5/8 15.37 3.15/5 23.89 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 ta n g e n ti a l st re ss τ ( k p a ) shifting (mm) 3.15/8 mm,100 kpa 3.15/8 mm,300 kpa 3.15/8 mm,400 kpa 0 100 200 300 400 500 600 0 2 4 6 8 10 12 t a n g e n ti a l s tr e s s τ ( k p a ) shifting (mm) 3.15/8 mm, 400 kpa 5/8 mm, 400 kpa 3.15/5 mm, 400 kpa (a) (b) bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 153 7.2. particle size distribution the particle size of the samples subjected to direct shearing at the casagrande box is measured before and after each test. the results are shown in the form of granulometric curves, varying the following parameters: the normal stress (100 kpa, 300 kpa and 400 kpa); the grain size class (3.15/5 mm, 5/8 mm and 3.15/8 mm). indeed, crushing of grains affects the characteristics of sandstone particularly on the spread of grain size curves. granulometric analysis before and after each test was performed and compared to the initial grain size curve (figure 9). fig 9. granulometric curves before and after shear for the three granular classes used; (a) 3.15/5 mm, (b) 5/8mm and (c) 3.15/8 mm. figure 9 shows the evolution of the granulometric spread for the three granular classes used (3.15/5, 5/8 and 3.15/ 8 mm) as a function of the increase in the normal stress. the higher the normal stress, the greater the crushing of the grains and the more significant the production of fines. this crushing leads to a reduction in the size of the grains and a modification of the shape and texture of the grains; therefore a modification of the value of the fractal dimension. granulometric spreading after the tests is evidence of grain fragmentation. the curves in figure 9 show that the 5/8 mm size class crushes more than the 3.15 / 8 mm class, which crushes more than the 3.15 / 5 mm class. the crushing of the grains after the test is shown in figure 10. (a): before the testing and (b): after the testing. fig 10. examples of the sheared grains under a normal stress of 400 kpa. 8. calculation of the fractal dimension of roughness and interpretation of results the fractal dimension of roughness df was calculated for the different samples studied before and after each run, using the matlab r2009b software, to facilitate the calculations, using an implemented program that processes the contour of a grain according to the same principle as the box counting method defined above. 0 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 c u m u la ti v e s ie v e s ( % ) diameters (mm) 3.15/5 mm, before testing 100 kpa 300 kpa 400 kpa 0 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 c u m u la ti v e s ie v e s ( % ) diameters (mm) 5/8, before testing 100 kpa 300 kpa 400 kpa 0 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 c u m u la ti v e s ie v e s ( % ) diameters (mm) 3.15/8, before testing 100 kpa 300 kpa 400 kpa (a) (a) (b) (b) (c) 154 bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 the results of the evolution of the fracture dimension of roughness df obtained after tests are analyzed, as a function of the applied shear stress, the granular class and the grain size. 8.1. study of the influence of normal stress on the evolution of the fractal dimension of roughness the following figures show the evolution of the fractal dimension of roughness of the grains of different classes used after the direct shear tests under different applied stresses. fig 11. influence of the normal stress on the evolution of the fractal dimension of roughness for the three granular classes used, (a) 3.15/5 mm, (b) 5/8 mm and (c) 3.15/8 mm. figure 11 shows that the variation of the fractal dimension of roughness increases with the increase of the applied normal stress. so the more the stress increases, the more the crushing rate increases, as the grains change shape and become more irregular and rough. the production of fines during the tests is greater in the case of grains of large diameters (8 and 6.3 mm) than in the case of grains of small diameters (4 and 3.15 mm). the 8 mm grains suffered a greater crushing, due to the rupture of angularities by abrasion; on the other hand for the small grains 3.15 and 4 mm, it is a rupture by peeling which caused the increase of the roughness of the grains. this result is explained by the fact that the smaller grains are stronger than the larger ones. indeed, the more the size increases, the more the probability of presence of the zones of weakness (or cracking) in the grain increases. 8.2. study of the influence of the granular class on the evolution of the fractal dimension of roughness fig 12. evolution of the fractal dimension df as a function of the size of the grains. the evolution curves of the fractal dimension of roughness df of the various granular classes (figure 12) show that: 0.04 0.06 3 4 5 6 f r a c ta l d im e n s io n o f r o u g h n e s s diameter (mm) 3.15/5, 100 kpa 3.15/5, 300 kpa 3.15/5, 400 kpa 0.05 0.07 4.5 5.5 6.5 7.5 8.5 f r a c ta l d im e n s io n o f r o u g h n e s s diameter (mm) 5/8, 100 kpa 5/8, 300 kpa 5/8, 400 kpa 0.055 0.075 3 5 7 9 f r a c ta l d im e n s io n o f r o u g h n e s s diameter (mm) 3.15/8, 100 kpa 3.15/8, 300 kpa 3.15/8, 400 kpa 0.04 0.05 0.06 0.07 0.08 0.09 3 4 5 6 7 8 9 f r a c ta l d im e n si o n o f r o u g h n e ss diameters (mm) 5/8, 400 kpa 3.15/8, 400 kpa 3.15/5, 400 kpa (a) (c) (b) bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 155 the highest fractal dimension deviation after crushing is obtained for the normal stress of 400 kpa and for the class 5/8 mm. this can be explained by the presence of angularities or cracks in the coarse grains which may possibly favor their crushing more than the small grains. this crushing causes the increase of the roughness of their surface parts, thus increasing the fractal dimension of roughness. the smallest fractal dimension after crushing is that of class 3.15/5 mm. this can be explained by the fact that small grains crash less so a lesser change occurs in their shape. this dimension df calculated increases with the increase of the size of the grains (diameter of the grains) of the sandstone and this regardless of the granular class. 9. conclusions the box counting method gives the fractal dimension of roughness df which indicates the degree of roughness with respect to a given grain sample. the results obtained after the direct shear tests showed that all the samples studied underwent appreciable crushing under maximum normal stress of 400 kpa, particularly for the granular class (5/8). the fractal dimension determined by the box-counting method clearly describes the irregularity of the grains of the granular material. this dimension increases after the shear tests. the greater the fragmentation, the greater the difference in the fractal dimension of roughness and the finer the production. these results lead to the conclusion that: micro cracks propagate when the grains are subjected to high loading, which gives us an important cause of grain breakage. indeed, the larger the size of the grain, the greater the likelihood of occurrence of areas of weakness. the phenomenon of crushing of the grains revealed the evolution of the fractal dimension. the grains may undergo crushing during shear, the extent of which depends on shear strength, roughness size, hardness, shape and grain surface. 10. references afnor (1994). essai de cisaillement rectiligne à la boîte, partie1: cisaillement direct. xpp 94-071-1, p16. alili, h., & amokrane, d. (1999). comportement mécanique des grés. mé oire d’ingénieur université mouloud mammeri, tizi-ouzou (ummto). bolton, m.d & mc dowell, g.r. (1998). on the micromechanics of crushable aggregates. géotechnique 48, n°5. bouzeboudja, a., & melbouci b. (2016a). study of the evolution of the fractal dimension of a granular aterial’s grains during echanical tests. bulletin of engineering geology and the environment, volume 75, issue 2,pp 821-839. bouzeboudja, a. , melbouci, b., & bouzeboudja, h. (2016b). characterization of aggregates fragmentation using the calculation of fractal di ension” 16th international conference on new trends in fatigue and fracture (nt2f16), may 24-27, 2016, dubrovnik, croatia, isbn 978-953-7738-39-6, pp. 211-213. fazzalari, n.l., & parkinson, i.h. (1996). fractal dimension and architecture of trabecular bone. journal of pathology. vol 178, pp.100-105. guyon, e., & troadec, j.p. (1994). du sac de billes au tas de sables. editions odile jacob sciences, paris. huang, g.h., & zhan, w.h. (2002). fractal property of soil particle size distribution and its application. acte pedologica sinica, 39, pp. 490-497. 156 bouzeboudja et al., j. build. mater. struct. (2018) 5: 147-156 kim, m.s. (1995). etude expérimentale du comportement mécanique des matériaux granulaires sous fortes contraintes. thèse de doctorat de l’école centrale de paris. lade, p.v., yamamuro, j.a., & al. (1996). significance of particule crushing in granular materials. journal de la technologie géotechnique, vol.122, n° 4, pp. 3109-3116. mandelbrot, b. (1975). les objets fractals : forme, hasard et dimension. editions flammarion, paris. melbouci, b., & hannachi, n. e. (septembre, 2002). etude de l’écrase ent des grains de peg atite { l’essai oedométrique. annales de btp, n°4., france. melbouci, b. (2006a). etude du phéno ène d’écrase ent des grains de schiste au co pactage. revue française de géotechnique, n° 117, 4° trimestre 2006. melbouci, b., & roth j.c. (juin., 2006b). etude du co porte ent des atériaux concassés { l’écrase ent. annales de btp, n°3., france. ovalle, c. (2013). contribution a l’étude de la rupture des grains dans les atériaux granulaires. mechanics of materials. ecole centrale de nantes (ecn), french. ramamurthy, t. (1969). crushing phenomena in granular soils. journal of the indian national society of soil mechanics and foundation eng. vol. 8. russel, d., hanson, j., & ott, e. (1980). dimension of strange attractors. physical review letters 45, 11751178. sezer, a., altun, s., & erdogan, d. (2008). correlation between cbr strength and fractal dimensions of sands. 12eme conference international de (iacmag), 1-6 october, goa indian. tyler, s.w., & wheatcraft, s.w. (1992). fractal scaling of soil particle-size distributions: analysis and limitations. soil sei. soc. am. j. 56: 362-369. wang, x., li, m.h., lui, s., & lui, g. (2006). fractal characteristics of soils under different land-usepatterns in the arid and semiarid regions of the tibetan plateau. china, geoderma, 134 (1-2), pp. 56-61. j. build. mater. struct. (2018) 5: 127-136 original article doi : 10.34118/jbms.v5i1.51 issn 2353-0057, eissn : 2600-6936 study of crushing of grains of limestone under the effect of cyclic loading with the fractal dimension bouzeboudja a1,*, melbouci b1, bouzeboudja o2 1 geomaterials laboratory, environment and development, university of tizi-ouzou, 15000, algeria. 2 laboratory of analysis and modeling of random phenomena, university of tizi-ouzou, 15000, algeria. * corresponding author: bouzeboudjaa5@gmail.com received: 15-02-2018 revised: 16-05-2018 accepted: 20-05-2018 abstract. the grains can be of very diverse nature (size, shape, mineralogy, etc), indeed even if each grain is a fairly simple object, the set of grains is a very complex system in which the geometrical and physical properties of the grains, their forces and their orientations play a crucial role in their mechanical behavior. the measurement of their shape in soil mechanics has historically required the use of standards and diagrams to which the different grains can be compared. however, these methods are approaches and remain insufficient and incomplete for the actual measurement of their form and the understanding of their behavior remains a task far from being completed. this work is in this context and proposes to analyze the shape and size of the grains with the fractal theory using the box counting method. it also makes it possible to study their influence on the crushing of the grains of the calcareous material under the effect of the cyclic loading-unloading during the oedometer test. the obtained results show that the variation of the fractal dimension, corresponding to the crushing effect of the grains, is strongly influenced by their shape, their size, their particle size distribution and the variation in the number of loading-unloading cycles. key words: cyclic loading, geometrical characteristics of grains, crushing, fractal dimension. 1. introduction the granular materials may undergo a rupture or crushing phenomenon under the effects of shear, compression or compaction and even under the effect of a small projectile. this phenomenon causes their fragmentation in different aspects. when the grains are solid, hard and fairly rounded, they can withstand high stresses which require, for example, the use of heavy equipment or compactors in the construction of high dams in earth and riprap to meet the requirements of high density. on the other hand, the angularly shaped grains of freshly extracted quarry materials undergo fragmentation due to the breakage of the asperities under lesser stresses and reach higher densities (ramamurthy, 1969). soil, which is both a fragmentary and porous medium, has a fairly complex structure where a same fractal representation may be particularly suitable. it is then necessary to characterize the shape of the grains using the fractal dimension (chen et al., 1996). 2. fractal dimension 2.1. definition to measure a length, a surface or a volume, a common method consists in covering these sets of blocks whose length, surface or volume are taken as units of measure. this is precisely what is done with the classical methods when calculating these quantities by means of the euclidean dimension. the fractal dimension is the complement which was lacking in the latter as well as in the crystal symmetry in order to obtain results very close to reality (falconer, 1990; mandelbrot, mailto:bouzeboudjaa5@gmail.com 128 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 1983). indeed, fractal geometry can be used for the characterization of the soil. to calculate the fractal dimension, image analysis techniques are important after photographing the grains (sezer et al., 2008). 2.2. box counting (bc) method this method was defined in the work of russel in 1980 (russel et al., 1980), is the most frequently used and most popular in practice. in the case of "fragmentation", the fractal dimension calculated by this method gives us an idea of the dimensional distribution of the grains in the soil and the fragmentation process. mandelbrot showed that the distribution of rock fragments is a fractal distribution. as he also suggested that fractal fragmentation could be measured by developing the fractal dimension of equation (1). this method consists in dividing the image of a grain into small squares of identical dimensions (making a mesh), thus the outline of the grain passing through these boxes is counted, and we do the same operation but this time with boxes of decreasing sizes and so on... this method is based on the premise that the image of the grain is the number of boxes based on their sizes, and this relationship is represented by the following formula: ( ) (1) x: size of the boxes; x: linear dimension of the grains greater than the dimension x; n (x> x): number of boxes; k: constant of proportionality; fdr: fractal dimension of fragmentation (huang & zhan, 2002; wang et al., 2006). by plotting these values; size boxes depending the number of boxes in a logarithmic graph, the fractal dimension is obtained according to the slope best suited to the regression line and can be calculated by the following equation: (2) m: the exponent of the line best suited to the scatter of points (figure 1). fig 1. calculating the fractal dimension of an angular limestone grain, size 6.3 mm, using the box counting method. 3. material studied the material used in this study is a local material, most encountered during the various civil engineering works (buildings, roads, bridges, dams, watertight barriers, etc.), which is limestone (figure 2) a mineral substance characterized by a chemical composition in which calcium carbonate (caco3) predominates, often of organic origin (limestones with foraminifers including chalk, shellstone limestones), but also of chemical origin (calcite, eolithic limestone, pisolithic, lithographic). y = 41,55x-0,97 r² = 0,999 1 10 100 1000 0.1 1 10 n u m b e r o f b o x e s dimension of boxes (mm) limestone fd = -m = 0.97 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 129 the limestone used is of jurassic age, extracted from a deposit located at a distance of 6 km from the city of bejaia (12 km west of the city on the coast). fig 2. limestone studied. the chemico-mineralogical compositions of the limestone are grouped in table 1. table 1. the chemico-mineralogical compositions of the material used. compounds quartz % calcium oxide % paf % limestone 1 à 5 55 à 63 35 à 42 the physico-mechanical properties of this rock are represented in tables 2 and 3. table 2. the physical characteristics of the material used. characteristics optimal volumetric weight γopt [kn/m3] optimal water content wopt [%] porosity n [%] volumetric weight of solid grains γs [kn/m3] limestone 21,6 5,1 9 27,4 table 3. the mechanical characteristics of the material studied. characteristics fragmentability fr degradability dg micro-deval mde los-angeles la [%] limestone 2 1.03 12.5 20 the samples were made in such a way that each test specimen is made up of a single form of grain. three forms of grains were visually selected (figure 3): the form-rounded (roughly rounded, with little angles and are very open), the angular shape (with several sharp edges) and the elongated shape (where the length of the grain is at least 1.5 times its width). (a) (b) (c) fig 3. forms used: (a) sub-rounded, (b) angular and (c) elongated. three particle size classes were chosen for this study: 3.15/5, 3.15/8 and 5/8 mm (figure 4). fig 4. granulometric curves before testing of the different classes for the material studied. 0 20 40 60 80 100 120 2 c u m u la ti v e s ie v e [ % ] sieve diameters [mm] 3.15/5 mm 3.15/8 mm 5/8 mm 130 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 five control grains of each diameter of the three classes were stained to better evaluate their fragmentation after crushing at odometric tests, which are shown in the figure 5. a good resolution camera was used to demonstrate better analysis of grain images before and after each test. the images are processed using matlab 7.9.0 (r2009b) software and the results of the fractal dimension obtained are interpreted using excel. (a) (b) (c) fig 5. different granulometric classes studied: (a) 3.15/5, (b) 3.15/8 and (c) 5/8 mm of the limestone used. 4. tests conducted the samples are subjected to oedometric tests (figure 6), applying loading cycles of up to 6400 kpa followed by unloading cycles up to 700 kpa (afnor, 1997). the tests are carried out using an automated geocomp corporation machine (ø = 63.5 mm). vertical deformations or settlements of the sample in the tests are measured using a comparator and recorded using software. fig 6. controlled odometric device, geocomp corporation type. 5. presentation and interpretation of test results 5.1. results and analysis this study is carried out with the aim of understanding the behavior and determining the mechanical characteristics and the influence of some parameters (namely the nature, shape and size of the grains and the applied load) by making oedometer tests on samples reconstituted in the laboratory using natural local material “limestone”; while taking account of the crush phenomenon in this trial. the results are presented as oedometer curves. the behavior of granular materials is strongly influenced by the degree of crushing and grain breakage. thus, the most important factor affecting the resistance to compressibility stresses is the phenomenon of fragmentation undergone by the granular body. actually, during our tests, the samples underwent deformations and ruptures of their grains. the amount of fines produced increases with increase of the load intensity. bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 131 we recall that the placement of the samples is identical for all the tests and that each test was repeated several times in such a way that confirm systematically the reproducibility of the results obtained and to quantify the mechanical characteristics of the granular materials. in our case, this test is used mainly to study the crushing of the grains of local material. the load is applied in stages of loading-unloading, with the presence of water. the deformations are almost instantaneous and the index of the voids decreases with the increase of the stress. if we represent the variation of the index of voids as a function of the effective stress σ’ applied on the surface of the sample, we obtain the curves called odometric curves of compressibility (figure 7). during the tests, the material are crushed increasingly with the increasing number of cycles ranging from 1 to 5 cycles (figure 7), regardless of the granular class and the shape of the grains. this creates a better compactness with optimum rearrangement of the grains and therefore a gradual decrease of the void ratio. indeed, with the increase in the content of fines, the volume of the voids decreases. the compressibility curves of all the samples studied have practically a lowslope portion at the start of loading, followed by a steep portion beyond the pre-consolidation constraint. fig 7. odometric curves of the angular class 3.15/8 mm, after 5 cycles of loading-unloading at 6400 kpa. when a granular mass is subjected to a compression load, the grains resist the load through a series of contacts there between. some grains may have more contacts than others, so they carry a greater load, which explains why they crash more than others. fragmentation begins when highly stressed grains can no longer resist, breaking after that into small pieces. some of these pieces move in the voids of the original structure of the material, which generates other chains of force and other assemblies of grains, by keeping high loads of microstructures appearing in the vicinity of the contacts of the grains, which can lead to a modification of the granular structure. note that the settlement under static loading is more important than the initial compactness is loose. thus, settlements occur very quickly in a coarse medium, so a sufficiently permeable medium. 5.2. particle size analysis grain crushing affects the characteristics of granular materials particularly on the spreading of granulometric curves. in order to quantify the breakage of the grains and to demonstrate this crushing phenomenon in the tests carried out, several quantitative measurements of the rupture rate have been proposed (lade et al., 1996 & einav, 2007a). the idea is to develop a quantitative parameter used to compare between various break levels, relative to a reference size. this reference may be the initial particle size, a supposed ultimate particle size or simply a given limit size. indeed, a 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 1 10 100 1000 10000 v o id r a ti o log (σ') angular limestone 3.15/8 5 cycles 0.35 0.36 0.37 0.38 0.39 0.4 0.41 0.42 1 10 100 1000 10000 log (σ') angular limestone 3.15/8 5 cycles 132 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 particle size analysis before and after each test was carried out and compared with the initial granulometric curve (figure 8). fig 8. particle size distribution curves of the elongated class 3.15/8 mm, after 5 cycles of loading-unloading at 6400 kpa. in addition, we observed that the higher is the number of loading/unloading cycles (figure 8), the more significant is the crushing. indeed, depending on the increase in the intensity of the stress. this crushing results in a reduction in the size of the grain with a modification of its shape and its surface state. what has been noticed even for limestone samples considered as a durable and hard material (figure 9). (a) (b) (c) fig 9. granulated crushing of the 5/8 mm classe of the elongated limestone after five (05) loading-unloading cycles at the oedometer test; (a) before the testing; (b) and (c) after the testing. it is interesting to note that the fragmentation took place at the contact points of the grains subjected to the various stresses. when crushing occurs, a production of fines ensues. thinner fragments begin to move the larger grains, as they can slip or roll without too much difficulty around other grains. 5.3. calculation of percentage of fines the figure 10 shows that the quantity of fines produced increases with the number of loadingunloading cycles applied to the oedometer test, regardless of the shape of the grains and the granular class. indeed, the number of crushed grains is a function of the number of cycles. this quantity is larger for the sub-rounded shape; also it is close to the level at first and second cycles of loadingunloading for the sub-rounded and angular shapes, the percentage of fines produced by the 0 20 40 60 80 100 120 0.01 0.1 1 10 a cc u m u la te d t a m is a ts [ % ] diameters [mm] elongated limestone 3.15/8, before testing elongated limestone 3.15/8, 1 cycle elongated limestone 3.15/8, 2 cycles elongated limestone 3.15/8, 3 cycles elongated limestone 3.15/8, 5 cycles bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 133 grains of the elongated form is smaller compared to that obtained from the two other forms, for class 3.15/8 mm (figure 10.a). the amount of fragments produced by the angularly shaped limestone grains is smaller compared to fines obtained from of the other two forms, the fines content is higher for the elongated form than for the other two forms, for classes 5/8 mm and 3.15/5 mm after the oedometric test (figures 10.b and 10.c). the angular structure of the limestone grains produces many fines at each stage of the crushing. (a) (b) (c) fig 10. percentage change of the fines based on the number of cycles for the three forms of limestone of classes 3.15/8, 5/8 and 3.15/5 mm under the oedometer test. 6. fractal dimension calculated before and after testing the introduction of fractal theory has improved the understanding of grain crushing and encouraged the application of fractal dimension in civil engineering work. the characteristics of the resistance at the oedometric test, as well as the different crushing rates observed during the tests, made it possible to understand the variations of the properties and the limitations of the studied granular material (bouzeboudja & melbouci, 2016a; bouzeboudja et al., 2016b; ovalle, 2013). for this method, the calculated fractal dimension is called the fractal dimension of roughness (fdr); it depends on the following parameters: the shape (sub-rounded, elongated and angular) and the size (large or small) of the grain studied; the scale of measurement, the larger the scale, the more precise the fractal dimension; the chosen face of the grain for imaging; the quality of the image taken (number of pixels). to calculate the fractal dimension of roughness of the grains of the different samples studied with the box counting method before and after crushing; a good resolution camera was used in order to have a better analysis of the contours of the five colored grains of each diameter; and the images were processed using auto-cad software. fig 11. calculating the fractal dimension of roughness with matlab r2009b by the box counting method. 20 22 24 26 28 30 32 34 36 0 1 2 3 4 5 6 p e rc e n ta g e s o f fi n e s [% ] number of cycles elongated 3.15/8 sub-rounded 3.15/8 angular 3.15/8 30 32 34 36 38 40 42 44 46 48 50 0 1 2 3 4 5 6 p e rc e n ta g e s o f fi n e s [% ] number of cycles elongated 5/8 sub-rounded 5/8 angular 5/8 30 33 36 39 42 45 0 1 2 3 4 5 6 p e rc e n ta g e s o f fi n e s [% ] number of cycles angular 3.15/5 elongated 3.15/5 sub-rounded 3.15/5 134 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 to facilitate fdr calculation, matlab r2009b software was used. by decreasing more and more the number of pixels of the calculation box, one gets closer to the actual contour of the grain. an example of the calculation is shown below (figure 11), which is of interest for an elongated limestone of ø = 8 mm and class 5/8 mm, after a loading-unloading cycle, to the oedometric test. after calculating fdr for the grains of different crushed samples, during the tests, under the different loads applied, the following results have been synthesized. due to the increase in the number of loading-unloading cycles (from 1 to 5 cycles), there was an offset of the curves in ascending order for all the samples studied in the oedometric tests. actually, the higher the number of cycles, the greater the crushing of the grains, which induces an increase in the fractal dimension of roughness (fdr). the results of grains of limestone of sub-rounded shape are presented in the figure 12. fig 12. variations of the fractal dimension roughness (fdr)of the class 5/8 mm, for the sub-rounded limestone, depending on the number of loading cycles. the figure 13 shows that the granulometric class 5/8 mm crushes more than class 3.15/8 mm, which crashes more than class 3.15/5 mm. the calculated fdr increases with increasing grain size (grain diameter), regardless of the granular class and the number of cycles. the production of fines during the tests is greater in the case of grains of large diameters (8 and 6.3 mm) than in the case of small diameter grains (4 and 3.15 mm). grain 8 mm underwent a greater crushing, due to rupture of angularity by abrasion; on the other hand for the small grains of 3.15 and 4 mm, it is a rupture by chipping which caused the increase in the roughness of the grains. this result is explained by the fact that the smaller grains are more resistant than the largest. indeed, the larger the size, the greater the probability of areas of weakness (or cracking) in the grain. (a) (b) (c) fig 13. variations of fdr as a function of the diameters analyzed, for the three granular classes: (a) elongated, (b) sub-rounded and (c) angular of the limestone, subjected to 5 cycles of loading-unloading to the oedometric test. 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23 4.5 5.5 6.5 7.5 8.5 f ra ct a l d im e n si o n f d r diameter [mm] sub-rounded 5/8, 1 cycle sub-rounded 5/8, 2 cycles sub-rounded 5/8, 3 cycles sub-rounded 5/8, 5 cycles 0.13 0.15 0.17 0.19 0.21 0.23 0.25 0.27 0.29 0.31 0.33 0.35 0.37 0.39 0.41 0.43 2 7 12 f ra ct a l d im e n si o n f d r diameter [mm] elongated 5/8 elongated 3.15/5 elongated 3.15/8 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23 0.25 0.27 2 4 6 8 10 f ra ct a l d im e n si o n f d r diameter [mm] sub-rounded 5/8 sub-rounded 3.15/5 sub-rounded 3.15/8 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23 0.25 0.27 0.29 0.31 2 4 6 8 10 f ra ct a l d im e n si o n f d r diameter [mm] angular 5/8 angular 3.15/5 angular3.15/8 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 135 the evolution of the fractal dimension of the elongated grains of limestone has higher values than those of sub-rounded and angular grain samples, regardless of the number of loadingunloading cycles and the applied stress. this can be explained by the crushing rate which is greater for the elongated form than for the other two forms studied (figure 14). the elongated shape has a rather large effect on the evolution of the fractal dimension for limestone (figure 14). (a) (b) (c) fig 14. variations of fdr as a function of the diameters analyzed, for the three forms limestone of classes : (a) 3.15/8, (b) 5/8 and (c) 3.15/5 mm, subjected to five cycles of loading-unloading. 7. conclusions it has been determined that with an increase in the content of fines the fractal dimension increases. the oedometric test generates more grain rupture, which leads to a large variation in the fractal dimension. this allowed us to relate the fractal dimension to the number of loadingunloading cycles. these ratios were compared according to the amount of fines produced, the granulometric class, and the size and shape of the grains. the variance of these last parameters (shapes, sizes and granular classes) significantly affects the rupture mode of the grains and their crushing; consequently, it increases or decreases the irregularities thereof. the three parameters mentioned above therefore affect their final fractal dimensions. the analysis of the fractal dimension of grain images seems to be a powerful tool for comparing the intrinsic characteristics of the granular materials associated with their fragmentation. so, the algorithms provide a satisfactory estimate of the fractal dimension of the grains. 0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3 0.34 0.38 2 4 6 8 10 f ra ct a l d im e n si o n f d r diameter [mm] sub-rounded 3.15/8, 5 cycles angular 3.15/8, 5 cycles elongated 3.15/8, 5 cycles 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 4 5 6 7 8 9 f ra ct a l d im e n si o n f d r diameter [mm] sub-rounded 5/8, 5 cycles angular 5/8, 5 cycles elongated 5/8, 5 cycles 0 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 3 3.5 4 4.5 5 5.5 f ra ct a l d im e n si o n f d r diameter [mm] sub-rounded 3.15/5, 5 cycles angular 3.15/5, 5 cycles elongated 3.15/5, 5 cycles 136 bouzeboudja et al., j. build. mater. struct. (2018) 5: 127-136 these results make it possible, on the one hand, to characterize and understand the behavior of granular materials, on the other hand, to choose the right materials according to the function to be ensured in the works and the progress of civil engineering (dams, roads, watertight barriers, ballasted columns, concrete, etc). it is recommended to improve this method of calculation and also to apply other methods of calculating the 3d fractal dimension of this material and other materials, subjected to various stresses to better understand the behavior of granular materials. 8. references afnor (1997). essai oedométrique. essai de compressibilité sur les matériaux fins quasi saturés avec chargement par paliers. xpp 94-090-1, p 24. bouzeboudja, a., & melbouci, b. (2016a). study of the evolution of the fractal dimension of a granular material’s grains during mechanical tests. bulletin of engineering geology and the environment, volume 75, issue 2, pp 821-839. bouzeboudja, a. , melbouci, b., & bouzeboudja, h. (2016b). characterization of aggregates fragmentation using the calculation of fractal dimension” 16th international conference on new trends in fatigue and fracture (nt2f16), may 24-27, 2016, dubrovnik, croatia, isbn 978-953-7738-39-6, pp. 211-213. chen, j., lo, k.y., leung, h., & litva, j. (1996). the use of fractals for modeling em waves scattering from rough sea surface. ieee transactions on geoscience and remote sensing, vol. 34, no. 4. einav, i. (2007a). breakage mechanics. part i: theory. j. mech. phys. solids 55(6), 1274-1297. falconer, k., chichester, wiley, j., & sons. (1990). fractal geometry: mathematical foundations and applications. 2e éd, poche (isbn 978-0 470-84862-3) (lccn 2004271361). huang, g.h., & zhan, w.h. (2002). fractal property of soil particle size distribution and its application. acte pedologica sinica, 39, pp. 490-497. lade, p.v., yamamuro, j.a., et al. (1996). significance of particule crushing in granular materials. journal de la technologie géotechnique, vol.122, n° 4, pp. 3109-3116. mandelbrot, b. (1983). the fractal geometry of nature. edition w.ii. freeman, san francisco, 461 pp. ovalle, c. (2013). contribution a l’étude de la rupture des grains dans les matériaux granulaires. mechanics of materials. ecole centrale de nantes (ecn), french. ramamurthy, t. (1969). crushing phenomena in granular soils. journal of the indian national society of soil mechanics and foundation eng. vol. 8. russel, d., hanson, j., & ott, e. (1980). dimension of strange attractors. physical review letters 45, 11751178. sezer, a., altun, s., & erdogan, d. (2008). correlation between cbr strength and fractal dimensions of sands. 12eme conference international de (iacmag), 1-6 october, goa indian. wang, x., li, m-h., lui, s., & lui, g. (2006). fractal characteristics of soils under different land-usepatterns in the arid and semiarid regions of the tibetan plateau. china, geoderma, 134 (1-2), pp. 56-61. http://fr.wikipedia.org/wiki/sp%c3%83%c2%a9cial:ouvrages_de_r%c3%83%c2%a9f%c3%83%c2%a9rence/978-0-470-84862-3 http://fr.wikipedia.org/wiki/num%c3%83%c2%a9ro_de_contr%c3%83%c2%b4le_de_la_biblioth%c3%83%c2%a8que_du_congr%c3%83%c2%a8s http://lccn.loc.gov/2004271361 j. build. mater. struct. (2020) 7: 130-139 original article doi : 10.34118/jbms.v7i2.712 issn 2353-0057, eissn : 2600-6936 conception of eco-friendly cement based on natural pozzolan to improve rheological behavior of concrete mansour sabria malika*, ghernouti youcef research unit: materials, process and environment, civil engineering department, university m’hamed bougara of boumerdes, algeria * corresponding author: s.mansour@univ-boumerdes.dz received: 27-06-2020 accepted: 31-08-2020 abstract. the pozzolan of benisaf region (north-west algeria) is a natural material of volcanic origin with the ability to react with cement hydration products and improve its properties. therefore, its use in the production of new cementitious materials will protect the environment. it will therefore be interesting to exploit this source as a partial cement substitution. in this work, a rheometric investigation was carried out to assess the performance of the natural pozzolan substituted to cement at variable rates ranging from 5%, 10%, 15% to 20% in order to obtain an ecological concrete. as the rheological behavior of concrete depends on the behavior of the cement paste, the effect of pozzolan on the latter was analyzed using static flow tests and dynamic creep and oscillation tests. the results of the rheometric tests have shown that in flow, the pozzolan improves the fluidity and in oscillation mode, it generates a viscous behavior of the cementitious pastes compared to elastic behavior of the control paste. furthermore, the transient study (creep / recovery) made it possible to highlight the liquid viscoelastic character of the cement pastes. with 10% of pozzolan, the rheological behavior of the paste is viscous liquid which seems to be the best. the use of pozzolan as cement substitution has significant environmental, economic and technical advantages, namely the development of natural pozzolan, reduction of co2 emissions during the manufacture of cement as well as energy reduction and finally improvement of the properties of fresh concrete. key words: rheology; flow; creep; oscillation; cement; pozzolan. 1. introduction the rheological behavior of cement paste and fresh concrete is a subject of considerable interest. fresh concrete is a fluid material and its rheological behavior affects the way it is treated, therefore the measurement and control of rheological parameters is very important in the production of quality concrete. much research (ferraris et al., 2001; park et al., 2005) has been carried out in order to improve the rheological and mechanical properties by using fine particles or mineral additions which can contribute to the improvement of workability in the fresh state, the microstructure densification of the cement matrix and the development of high mechanical properties due to their hydraulic or pozzolanic properties on the scale of concrete (tattersall & banfill, 1983). natural pozzolans have been used as a cementitious material for thousands of years. it is often used in concrete as a partial replacement for cement (lam et al.; 2018). the use of natural pozzolan and industrial by products in concrete as a partial replacement for cement has economic, environmental benefits by decreasing the gases emitted during cement production and technique by increasing the durability of concrete at later ages (sarker & mckenzie, 2009; lam et al., 2017). belaribi et al., (2003) studied influence of the beni-saf pozzolan on the mechanical characteristics of concrete. they have shown that substituting cement by 20% of pozzolan cement gives the concrete mechanical performances that equals, and surpasses those of the control concrete in the long term. khelifa et al. (2008) have shown that the pozzolan rock from beni-saf has pozzolanic properties. thus, it is used and marketed mainly to cement factories which use it as an active addition at rates of 15 to 20% in the manufacture of mailto:s.mansour@univ-boumerdes.dz mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 131 composite cements (kaid et al., 2009). moreover, research has been undertaken on the durability of mortars based on this pozzolan kept in aggressive environments (ghrici et al., 2006; ghrici et al., 2007). they found a gain in the compressive strengths of mortars stored in a 5% solution of sodium sulfates with the use of 20% and 30% pozzolan in the medium term (6 months). also, the study of the permeability to chlorine ions of concretes based on this natural pozzolan was limited to the measurement of the electric charge passing through the concrete sample. this result revealed a better permeability of concrete based on 30% pozzolan compared to that of a control concrete and a ternary concrete based on 20% natural pozzolan and 10% limestone filler. in addition siad (2010) studied the effect of this natural material on the mechanical properties and on the resistance in aggressive environments of mortars and concretes, either in substitution of part of the cement or in addition to concrete. in this work, the fines of the pozzolan powder are used as cement substitution. this substitution has advantages, both ecological by the reduction of greenhouse gases during the manufacture of cement and economic by reducing the manufacture of cement. the aim of this work is to seek the best replacement rate of natural pozzolan powder which generates the best rheological behavior of cement paste which reflects the behavior of concrete. for this, the effect of pozzolan (substituted to cement at 5%, 10%, 15% and 20%) on the rheological behavior of cement pastes was analyzed. this analysis was carried out under imposed stress thanks to the ar2000 rheometer by flow tests in static mode and creep and oscillation tests in dynamic mode. the rheological parameters (shear stress, viscosity, and compliance, mechanical properties such as storage and loss modulus) were evaluated. 2. materials and methods 2.1. materials cemi 52.5 cement conforming to european standard nf en 197-1 (2001) was preferably used because it contains a large amount of clinker (at least 95% by weight), has a high reactivity at an early age, and guarantees 28-days a minimum compressive strength of 52.5 mpa on mortars standardized according to standard nf en 196-1 (2006). as a cement substitution, pozzolan powder was used. this pozzolan is a material of volcanic origin extracted from the ghar ben brikhou deposit located 30 km south-east of the beni saf cement plant (north-west of algeria). it is a material with an ability to react with lime in the presence of water, and to form compounds with binding properties. this pozzolan is supplied in the form of crushed pumice and slag type rocks. the pozzolan was selected, homogenized, dried, crushed and reduced to powder using a micro-grinder (figure 1). fig 1. pozzolan powder 132 mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 fig 2. morphology of the pozzolan (sem, secondary electron mode) the morphological appearance of the pozzolan powder is shown in figure 2. the physical properties and the chemical composition of the cement and the pozzolan are given in table 1, table 2 and 3. the chemical analysis showed that the pozzolan contains a high percentage of silica, an average rate of aluminum, and a low rate of calcite and iron. on the other hand, the other minerals (mg, k, n) are in small percentage. high water-reducing superplasticizer based on modified polycarboxylate phosphonate and deionized water for preparing the cement blended were used. the x-ray diffraction diagram (figure 3) shows that the crystalline mineral phases of the pozzolan are cordierite al3mg2alsio5o18 in large quantity, the analcime naalsio6.h2o in average quantity, very little cristobalite sio2 and hematite as well as traces of illite (k, h3o) (al,mg,fe)2(si,al)4o10[(oh)2,(h2o)]. fig 3. x-ray diffraction diagram of the pozzolan (cu kα radiation ni filter) mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 133 table 1. physical properties of cement cemi 52.5 and pozzolan materials cement pz blaine specific surface (cm2/g) 4200 6200 specific gravity (g/cm3) 3.15 2.79 mineral activity mg ca(oh)/g 149.8 water demand (%) 27.4 27.6 table 2. chemical composition of cement cemi 52.5 and pozzolan. oxides % sio2 al2o3 fe2o3 cao mgo so3 k2o na2o pf cl‾ cement 19.85 4.80 2.75 63.60 1.45 3.45 0.90 0.15 2.20 0.002 pozzolan 44.78 16.53 9.01 10.97 4.59 0.17 1.15 3.42 6.55 0.014 table 3. mineralogical composition of cement cemi 52.5 (%). c3s c2s c3a c4af gypsum 62.0 10.2 8.1 8.4 5.0 2.2. preparation of cement pastes cement blended containing replacement rate of 5%, 10%, 15% and 20% of natural pozzolan have been developed. all the mixtures were prepared under the same conditions with w/c of less than 0.30 and 2% of superplasticizer. 2.3. testing samples the rheological measurements were carried out using ar2000 rheometer with imposed stress. the samples are kept at a temperature of 20 ° c by circulating water during the tests. the 14mm radius rotor with four blades turns in a hollow and fixed external cylinder of 15mm of radius. the air gap is 1mm. the samples are kept at a temperature of 20°c by circulating water during the tests. the cement pastes are prepared according to the following protocol: 2.3.1. flow test the water having a constant temperature of 19 ± 0.5 ° c and containing the superplasticizer is poured into the mixer. the cement is carefully added to the water and mixed for 1 minute at a low speed, then one minute at high speed. the mixer is stopped for 1 min 30 s, during which its walls are cleaned properly with a spatula. the cement blended is mixed for another one minute at high speed. the obtained paste is kept at rest 30s before placing it in the rheometer. the sample is kept at a constant temperature of 20 ± 1 ° c by an automatic controller during the test. the composition of the cement paste has been varied, in order to explore the influence of the dosage of the pozzolan on the rheological properties. a pre-shearing of 500s-1 of all cement pastes during 60s, followed by a rest period of 60s is retained for all the tests. then the cement pastes are sheared by applying an imposed stress whose interval is (0-200) pa for 120s. 2.3.2. creep/recovery test each paste was mixed by hand using 50g of cement to which is added the appropriate amount of water corresponding to the normal consistency containing the superplasticizer. after 90s of mixing, the paste is transferred to the rheometer. a pre-shearing of 500s-1 is applied for 240s, followed by a rest time of 60s. the rheological tests therefore begin 6 min 30s after mixing the cement and the water. this pre-shearing is carried out in order to put the structure of the paste 134 mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 in an irreversible state of rupture (tattersall & banfill, 1983). this procedure is performed before each creep measurement. during the creep measurements, the cement paste is subjected to a constant imposed stress of 0.03 pa during 40s and a deformation is measured (creep). then the stress is released and a deformation is measured again for another 40s (recovery). preliminary tests made it possible to determine the imposed stress of 0.03 pa, belonging to the field of linear viscoelasticity obtained by the stress scan test whose interval is (0.01-20) pa for a fixed frequency of 1hz. the number of identical samples to be tested is three for each mixture. concentrated suspensions often have a viscoelastic behavior and creep/recovery measurements can be used to characterize their behavior in flow. a stress is imposed and this, results in a deformation measured as a function of time. compliance j can be calculated from these measurements and its variation over time makes it possible to characterize the material as a viscoelastic solid or liquid. compliance (j) is defined as the deformation divided by the stress. solids or liquids behave like elastic solids, viscous liquids, viscoelastic solids and viscoelastic liquids under shear stress (struble and schultz, 1993). 2.3.3. dynamic oscillation test the dynamic test is carried out to study the viscoelastic behavior of cement pastes with additions. knowledge of viscoelastic properties can provide fundamental information about the physical state of a solid particle suspension system transforming to a viscous, semi-solid, fluid system and subsequently to a solid system (sun et al., 2006). during this test, the shear moduli of storage (elastic) g 'and of loss (viscous) g "of the cement paste can be measured directly by the application of an oscillatory shear stress according to a sinusoidal function and in measuring the corresponding shear deformation during the oscillation test, the controlled stress mode is used, a frequency sweep with a constant stress of 0.03 pa is applied. 3. results and discussion 3.1. flow test the rheological behavior of cement pastes changes with the replacement rate of pozzolan. the flow curves show that the shear stresses to which the cement pastes containing 5% and 10% of pozzolan pz are subjected are weak compared to those of the control paste without the pozzolan (0% pz) (figure 4). the rates of 15% pz and 20% pz have no positive effect on the flowability of cement pastes since they cause an increase in the shear stress compared to those of the control paste (0 % pz). the replacement rate of 10% pz seems to be the optimal rate for a better flow of the paste. this is confirmed by the decrease of viscosity of the cement paste by replacing the cement by the same rate (figure 5). furthermore, by modeling the flow curves, the herschelbulkley model seems to represent well the flow of the cement pastes. the law which describes this model is expressed by equation (1) (nehdi & rahman, 2004): n k    (1) where k is the consistency index or apparent viscosity, τ0 the yield stress which depends on the structural state of the dough, γ is the shear rate and n characterizes the behavior of the cement paste. mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 135 fig 4. flow curves of cement pastes containing pozzolan. fig 5. evolution of the viscosity of cement pastes containing pozzolan. 3.2. creeprecovery test the transient study made it possible to highlight the viscoelastic properties of cement pastes. those containing pozzolan behave like viscoelastic liquids, even better for the paste containing 10% pz where its behavior is viscous liquid considered to be the best (figure 6-b). moreover, the deformations undergone by the latter are the greatest compared to those other cement pastes. the large deformations are characteristic of weak interactions present in the microstructure of the pastes compared to the weak deformations generated in the control paste (figure 6-a) where the interparticle bonds are strong (zhang and han, 2000; cyr and legrand, 2000). 136 mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 (a) (b) fig 6. creep/recovery behavior of cement paste (a)without pz, (b)-with pz. 3.3 dynamic oscillation test oscillation tests provided information on the structure of the cement paste thanks to its mechanical properties g" and g’ from the first moments after the mixing of the cement paste. rheometric measurements show a parallel evolution of storage (elastic) modulus g' and loss (viscous) modulus g" as a function as frequency (figure 7). in addition, the shear moduli of cement pastes containing pozzolan are always lower than those of the control paste as shown in figure 7. in the case of pastes containing pozzolan, the rate of 10% generates the best behavior. the latter generates a viscous behavior (g" higher than g') which allows the flow of the paste at the first moments after mixing, compared to the elastic behavior of control paste (g' higher g") which characterizes the behavior of a solid. mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 137 fig 7. evolution of storage (elastic) modulus g’ and loss (viscous) modulus g″ of cement pastes containing pozzolan. 4. conclusions the major interest which was at the origin of this study is the possibility of replacing part of an industrial material which is the cement by a local and inexpensive mineral addition (pozzolan) in order to reduce the consumption of the cement in algeria and to improve the rheological behavior of cement pastes in the fresh state which reflects that of the concrete. the pozzolan has played its role in improving the fluidity of the flow of cement pastes. it was highlighted the existence of an optimal rate of 10% pz which generated the best fluidity, the best behavior in flow of the pastes and therefore a better flow of the concrete. the transient study made it possible to highlight the viscoelastic properties of cement pastes. the viscoelastic character decreases with the increase in the replacement rate up to an optimal pozzolan rate of 10%. in order to better understand the microstructure of cement pastes, a dynamic study has shown that pozzolan generates a viscous behavior of pastes compared to the elastic behavior of control paste. the results of the dynamic creep and oscillation tests are in agreement with those of the static flow tests, namely that the 10% replacement rate of pozzolan produces the best rheological behavior. the rheological study carried out on cementitious pastes has given promising results which further encourage the use of pozzolan as a component of a high performance concrete designated for industry in algeria, since it will help to improve the workability of concrete in a fresh state and the ease of its installation. 5. references belaribi, n. b., semcha, m., & laoufi, l. (2003). influence de la pouzzolane de beni-saf sur les caractéristiques mécaniques des bétons. canadian journal of civil engineering, 30(3), 580-584. 138 mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 cyr, m., legrand, c., & mouret, m. (2000). study of the shear thickening effect of superplasticizers on the rheological behaviour of cement pastes containing or not mineral additives. cement and concrete research, 30(9), 1477-1483. ferraris, c. f., obla, k. h., & hill, r. (2001). the influence of mineral admixtures on the rheology of cement paste and concrete. cement and concrete research, 31(2), 245-255. ghrici, m., kenai, s., & said-mansour, m. (2007). mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements. cement and concrete composites, 29(7), 542-549. ghrici, m., kenai, s., said-mansour, m., & kadri, e. h. (2006). some engineering properties of concrete containing natural pozzolana and silica fume. journal of asian architecture and building engineering, 5(2), 349-354. kaid, n., cyr, m., julien, s., & khelafi, h. (2009). durability of concrete containing a natural pozzolan as defined by a performance-based approach. construction and building materials, 23(12), 3457-3467. khelifa, r., brunetaud, x., chabil, h., & al-mukhtar, m. (2008). consequences mecaniques de l’attaque sulfatique externe sur les betons autoplaçants. sciences & technologie. b, sciences de l'ingénieur, 23-28. lam, t.v., bulgakov, b.i., aleksandrova, o.v., & larsen, o.a. (2017). possibility of using ash residues for the production of materials for construction purposes in vietnam. bulletin of the belgorod state technological university. vg shukhov, (6). doi: 10.12737/article_5926a059214ca0.89600468 (in russian language). lam, t.v., bulgakov, b.i., aleksandrova, o.v., & larsen, o.a., & anh, p. n. (2018). effect of rice husk ash and fly ash on the compressive strength of high performance concrete. in e3s web of conferences (vol. 33, p. 02030). edp sciences. nehdi, m., & rahman, m. a. (2004). estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction. cement and concrete research, 34(11), 1993-2007. nf en 196-1(2006). method of testing cement-part 1: determination of strength. afnor. nf en 197-1 (2001). cement-part 1: compostion, specification and conformity of cement. afnor. park, c. k., noh, m. h., & park, t. h. (2005). rheological properties of cementitious materials containing mineral admixtures. cement and concrete research, 35(5), 842-849. sarker, p., & mckenzie, l. (2009). strength and hydration heat of concrete using fly ash as a partial replacement of cement. in proceedings of the 24th biennial conference of the concrete institute australia. concrete institute of australia. siad, h. (2010). influence du type d'addition minérale sur le comportement physico-mécanique et sur la durabilité des bétons autoplaçants (doctoral dissertation, rennes, insa). struble, l. j., & schultz, m. a. (1993). using creep and recovery to study flow behavior of fresh cement paste. cement and concrete research, 23(6), 1369-1379. mansour sm and ghernouti y, j. build. mater. struct. (2020) 7: 130-139 139 sun, z., voigt, t., & shah, s. p. (2006). rheometric and ultrasonic investigations of viscoelastic properties of fresh portland cement pastes. cement and concrete research, 36(2), 278287. tattersall, g., & banfill, p.f.g. (1983). the rheology of fresh concrete, editions pitman, boston. zhang, x., & han, j. (2000). the effect of ultra-fine admixture on the rheological property of cement paste. cement and concrete research, 30(5), 827-830. j. build. mater. struct. (2018) 5: 174-184 original article doi : 10.34118/jbms.v5i1.56 issn 2353-0057, eissn : 2600-6936 structural characteristics of composite mortars and their evolution with pet substitution level for several specimens’ ages kazi tani n.1,4*, benosman a.s. 1,2,3, senhadji y.3,5, taïbi h.2, mouli m.3 1 higher school of applied sciences (essa-t), bp 165, 13000 bel horizon, tlemcen, algeria. 2 faculty of exact and applied sciences, laboratory of polymer chemistry lcp, university of oran 1, oran, algeria. 3 department of civil engineering, labmat, enpo maurice audin, oran, algeria. 4 lcge laboratory, faculty of mechanical engineering, usto-mb, oran, algeria. 5 department of civil engineering, university of mustapha stambouli, mascara, algeria. * corresponding author: kazitani_nabil@yahoo.fr received: 27-02-2018 revised: 13-06-2018 accepted: 14-06-2018 abstract. this present study aims to investigate the evolution of structural response of petmortar composite test with a short-beam specimen in three-point bending tests, with composite mortar ages and volumetric polymer rate and this, based on compression strength tests. the ultimate pet-mortar composite structural responses are calculated at the mid span of the short-beam by the mean of mechanics-of-materials theory basis. according to this theory, the distribution of bending moments and shear forces at any point of the composite short-beam specimen doesn’t depend on material mechanical properties especially the young modulus of modified mortar composite; so, the structural response analysis has been limited to investigate the evolution of ultimate deflection with several volumetric pet rates and composite mortar ages. in the other hand, we present a comparative study between experimental test results of splitting tensile and compressive strengths with the ones predicted by codale previsions (aci-363 and b.s) codes in terms of pet mortar ages and volumetric pet rates in order to recommend the most suitable design code for pet-mortar composite applications in construction industries. key words: green composites, waste polymer, mortar age, young modulus of elasticity, three point flexural test, short-beam lateral deflections. 1. introduction the production of a large amount of polyethylene terephthalate (pet) bottles has created an environmental problem of gigantic proportions, since these bottles are not recycled by the manufacturers and therefore are left as plastic waste, which do not decompose readily in nature (mahdi, 2007; hannawi, 2010; chowdhury, 2013). the effective solution to solve this problem is to recycle them (saikia, 2012; ozbakkalogulu, 2016). waste pet bottles had been reworked for drinking bottles by melting and fusion, which turned out to be too costly. the incorporation of pet waste in construction materials knows a very high evolution in the last couple years, and this due to the significant economic impact of this green materials used in construction industries where polymers are used as additives (sharma, 2016; pacheco, 2013) in order to reduce certain disadvantages such as hardening delay, low tensile strength, and the general drying shrinkage (yazoghli, 2007). actually, composite materials (yazoghli, 2007; benazzouk, 2007; cordoba, 2013; naik, 1996) are by now the subject of both theoretical and experimental investigations, motivated by a renewed interest for the use of polymer-mortar composites in the civil construction industry for different applications (cordoba, 2013; naik, 1996; benosman, 2015, 2017a,b). so, if waste pet bottles were reused as lightweight aggregates, positive effects are expected on the recycling of waste resources and the protection of the environment (ozbakkalogulu, 2016; sharma, 2016; ochi, 2007; de brito, 2013; kazi tani, 2017; gouasmi, 2017). considerable research and mailto:kazitani_nabil@yahoo.fr kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 175 development work on plastic waste modification for cement mortar and concrete has been conducted in various countries. as a result, many effective plastic waste modification systems for cement mortar have been used in various applications in the construction industry for its many excellent properties (latroch, 2018; chaib, 2017; ozbakkalogulu, 2016; sharma, 2016; de brito, 2013; batayneh, 2007; choi, 2005; rebeiz, 1996). these researches generally investigate the effect of incorporating pet waste on the properties of concrete and cementitious mortar. commonly, the results showed that granules or flakes of crushed pet post-consumer bottles can be used to replace sand to produce good quality concrete products. on the other hand, our previous work (benosman, 2008, 2013, 2015, 2017a) indicated that pet waste could reduce the apparent chloride ion diffusion coefficient of the composites, effectively enhance the reduced volume of large-sized pores and improve the resistance to the absorption of the test solutions (like acidic, basic, sulfatic solutions) as well as the thermal resistance and acoustic insulation with an increase in polymer–cement ratio. this current study concentrates on the waste materials without any further transformation beyond crushing, in order to minimize final material costs. certain key proportions are also studied, in contrast with what has been undertaken in previous work (benazzouk, 2007; benosman, 2011, 2015; ghernouti, 2012; safi, 2013; badache, 2018) in order to determine feasibility limits. particularly pet wastes are used as substitute for conventional materials, mainly cement as powder, in composites mixes. so, the main purpose of this present research work is to characterize in the first time the mechanical properties of this composite mortar for several pet-mortar ages and volumetric waste pet polymer rates in accordance to (aci-318) and (bs-8110) codes of practice and based on experimental compressive strength tests results. the second stage of this work consists to investigate the flexural behavior of modified petmortar specimen under three-point bending-tests in terms of elastic deflections based on predicted data base of experimental test results. the last part of this paper concerns the evolution analysis of tensile and compressive strength (ft/fc) ratio with early mortar ages and volumetric pet rates between experimental test results and predicted ratios suggested by the british code of practice bs-8007:1987 (bsi, 1987) and the aci-363 models (aci, 1992), in the aim to direct designers and researchers to the most suitable code for pet-mortar composite applications in the field of construction industries. 2. raw materials 2.1. cement the cement used was a blended portland cement type cpj-cem ii/a42.5 supplied by zahana factory, located in western algeria, with 1022 kg/m3 bulk density; its compressive strength at 28 days was 42.5 mpa. the absolute density of the cement used was 3.15 g/cm3 and its specific surface area measured with the blaine method was 3532 cm2/g. its initial and final setting times were 170 and 245 min, respectively. mineralogical and chemical compositions of cement are listed in table 1. the chemical composition was obtained using an x-ray fluorescence spectrometer. 2.2. sand the crushed natural limestone sand was obtained from the quarry of kristel, in oran, west algeria. the maximum size of sand grains was 5 mm. the chemical properties shown in table 1 were obtained by using an x-ray fluorescence spectrometer analysis. its principal characteristics are given in table 2. the grading of crushed sand is presented in table 3, according to standard nf p18-560 (afnor, 1990). 176 kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 table 1. the mineralogical compositions of clinker and the chemical compositions of cement and sand used (wt. %) chemical compositions constituent cement sand sio2 20.91 0.77 al2o3 5.52 0.11 fe2o3 3.56 0.36 cao 63.50 54.71 mgo 0.64 0.21 so3 2.79 nil k2o 1.23 na2o 0.13 cao free 2.35 chlorides nil loi 1.19 43.83 mineralogical compositions c3s 49.39 c2s 22.97 c3a 8.61 c4af 10.83 table 2. physical properties of sand used (benosman, 2011) designations values absolute density (g/cm3) 2.53 equivalent of sand (%) 84 fineness modulus 2.55 nature limestone absorption coefficient (%) 0.5 2.3. pet waste waste pet bottle granules (scheme 1) used as particles were supplied by tramaplast pet bottle plant, in tlemcen, algeria. these particles were obtained by collecting the waste pet bottles and washing them; they are then crushed by granules into machines. in addition, they have an irregular shape and a rough texture surface, which enables the adherence of the particle-matrix. the bulk density of the waste pet particles used was 401.4 kg/m3. after preliminary tests, pet waste particles of size lower than 1 mm were used in this study. the sieve analysis of pet waste particles was carried out according to standard nf p18-560 (afnor, 1990) and is presented in table 3. scheme 1. developed chemical formula of waste polyethylene terephthalate kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 177 table 3. the sieve analysis of waste pet-particles and crushed limestone sand (kazi tani, 2017) sieve size (mm) cumulative passing (%) pet waste sand 5 99.92 99.83 2.5 98.16 98.37 1.25 96.82 65.37 0.63 55.78 38.3 0.315 35.48 19.07 0.16 18.28 8.20 0.125 9.56 3.325 3. specimen preparation and experimental tests four pet-mortar composites mixtures were prepared to compare the effect of adding pet as a cement replacement material. first, the control sample was without pet waste. the other three polymer-mortar composite mixtures were made by replacing cement with 6%, 12%, and 17% of pet by volume as shown in table 4. the mortar mixes had proportions of 1 binder: 3 sand (by weight). the binder consisted of cement and pet waste. the water to binder ratio was kept constant at 0.5. the physical properties of the pastes of mortars were determined in accordance with en 196-3 (en196-3, 1995). the detailed mix proportions of the mortars are shown in table 4. for the mechanical properties, the compressive strength of mortars was determined in accordance with en 196-1 (en 196-1, 1995). the mortar was placed in 40x40x160 mm3 prismatic steel molds. after casting, specimens were left covered with a plastic sheet. after removal from the molds, at 24 h of age, mortar specimens were immersed in water saturated with lime at 20°c  2°c until the age of testing. compression and three point bending tests figure.1 were conducted at 3, 7, 14, 28, 56, 90, 180 and 360 days of age. the results reported are the average of three flexural specimens and six compression tests. fig 1. three point bending test equipment table 4. mix proportions and physical properties of pet-mortar composites mix design pet/c (% v ) binder: sand (by weight) water-cement ratio (%) water demand for standard (%) setting time (min) / / / / / initial final pet 0 0 1:3 50 24.5 120 200 pet 6 6 1:3 50 25 125 205 pet 12 12 1:3 50 25.5 130 210 pet 17 17 1:3 50 26 145 225 178 kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 4. results and discussion 4.1. mechanical characterization of pet-mortar composites the static modulus of elasticity e (young modulus) represents one of the most important mechanical characteristics of construction materials (concrete, reinforced concrete, mortars, composites …etc.). this intrinsic property is considering as the basic parameter for the computing deflections in construction structures. various countries have been established their design codes based on empirical relationship between static modulus of elasticity e, and compressive strength of plain concrete at 28 days of curing. fig 2. evolution of young modulus with volumetric pet rate and composite mortar ages via (a) aci-318 and (b) bs-8110 codes. the aci code (aci-318, 2005) defines the relationship between elastic modulus of concrete and compressive strength for calculating deflection as: √ (1) the british code of practice (bs-8110, 1997) recommends the following expression for static modulus of elasticity with cube compressive strength of concrete as: 15000 17000 19000 21000 23000 25000 27000 29000 31000 33000 35000 0 50 100 150 200 250 300 350 400 y o u n g m o d u li -a c i [ m p a ] composite mortar age [days] pet0-acipet6-acipet12-acipet17-aci(a) (b) kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 179 (2) where ec: the static modulus of elasticity (e) at 28 days in mpa fc: compressive strength at 28 days in mpa w: air dry density of mortar based on experimental compressive tests on pet-mortar composite specimens (benosman, 2011), and there densities, graphs in figures 2(a)-2(b) show the evolution of young modulus evaluated by empirical relationships in accordance to (aci-318, 2005) and (bs-8110, 1997) codes. the graphs plotted in the figures 2(a)-2(b) show that the elastic young modulus values predicted by the british code of practice (bs-8110) are in the higher side comparing them with the ones evaluated by (aci-318) code and this, for all studies cases regarding volumetric pet rates and mortar ages. in order to have an accurate prediction of the elastic young modulus of pet-mortar composite which is very important for structures and that required a strict control of deformability. international codes such as aci-318 and bs-8110 propose a wide variety of formulae which establish a relationship between modulus of elasticity and compressive strength. 4.2. flexural strain analysis as shown in figure 3, which illustrates three points bending test method, the pet-mortar composite specimen is supported by the reaction noses and the load p is applied at a constant speed through the loading nose. the stress and strain fields at any point in the short-beam section can be evaluated to a first approximation with mechanics-of-materials theory. this theory is based on the necessary conditions for static equilibrium, which pertains here because the rate of deformation is small. fig 3. three-point-bending test on pet-mortar composite specimens (40x40x160) mm3 the basic assumptions of the theory are as follows: • the external forces are applied at thin lines and not distributed over finite areas. • σy = σz = 0 (σy and σz are the transverse normal stresses). • σx = e εx (where σx is the longitudinal normal stress and e the elastic young modulus). • xy = 0, (xy is the in-plane shear stress). after the equilibrium conditions are applied for stresses σx and xz these two major components of the stress can be obtained. σx has its maximum tensile or compressive value at the lower or upper point of the specimen: (3) 180 kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 where p is the load and b is the width of the specimen. according to the euler-bernoulli theory, the maximum elastic deflection arising from a flexural stress in a rectangular beam max is: (4) where, i denotes the moment of inertia of the specimen section. in the following, we present a parametric study which can allow us to investigate the effect of waste pet additions in the construction mortars in terms of flexibility and flexural strain evolution. figures 4(a)4(b) bellow show the evolution of ultimate deflections computed by (aci-318) and (bs-8110) codes with composite mortar ages and this for different volumetric polymer rates. the obtained simulation results show that the most significant values of ultimate pet shortbeam specimen composite deflections are given when young modulus is evaluated by (aci-318) code, especially where composite mortar ages vary between 3 and 28 days. at long term of petmodified mortar ages, the results of ultimate beam responses seems the same for both evaluation cases of young modulus by (aci-318) and (bs-8110) codes. the volumetric rate of waste pet polymer has a significant impact of the flexural behavior of pet-composite mortar and this for short and long term of composite mortar ages. the increased rate of polyethylene terephthalate gives to composite mortar specimen more flexibility and then, pet-mortar composite became more ductile before to be brittle for the case of ordinary mortar. finally, it is important to notice that under the action of the same loads which correspond to the tensile strength of pet-mortar composite specimen, the highest volumetric rate of pet increases the values of ultimate deflection for both evaluation cases of young modulus by (aci-318) and (bs-8110) codes. the utilization of the pet waste as a binder instead of cement in the manufacture of such composites and as sustainable building materials in the construction industry helps to cleaner environment. therefore, the substitution of cement by the pet polymer waste is beneficial for energy efficiency and sustainability in buildings. (a) kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 181 fig 4. evolution of short-beam specimen ultimate deflections with volumetric pet rate and composite mortar ages: (a) aci-318 and (b) bs-8110 codes. 4.3. splitting tensile and compressive strengths ratio (ft/fc) the ratio between tensile and compressive strength (ft/fc) is an important material property of mortars and concrete. in this section, we investigate the evolution of the (ft/fc) ratio between splitting tensile strength and compressive strength with volumetric pet rate and early petmortar composite ages (07 and 28 days) and this, based on experimental test results (benosman, 2011). in the other hand, we present a comparative study between the experimental evaluation of splitting tensile strength and compressive strength ratio (ft/fc) and the predicted ratios given by the british code of practice (bs-8007,1987) and the (aci-363, 1992) models respectively as follows: (5) (6) fig 5. evolution of (ft/fc) with volumetric pet rates for 7 and 28 days short-beam pet0 pet 6 pet 12 pet 17 (b) 182 kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 the graphs plotted in the figure 5 above show that (ft/fc) ratio follow an increased slight evolution with volumetric pet rates and this ratio became more significant at early age of pet mortar composite (7 days) for the case of codal prediction. predicted ratio between tensile and compressive strength (ft/fc) suggested by aci-363 code is closer to the experimental (ft/fc) ratio. this prediction seems to be more realistic if we compare it to the model given by british standard code of practices bs-8007:1987. therefore, aci-363 code can be considered as the most suitable for the prediction of mechanical properties of pet-mortar composite material in its several applications in the field of construction industry. 5. conclusion this study of semi-experimentally obtained mechanical properties of pet mortar composites and its flexural strain analysis, led the following main conclusions: • the experimental measured values of compression and flexural strength of pet mortar composite specimen can be useful to predict the elastic young modulus through the corresponding codal previsions (aci-318 and bs-8110 codes). for all the mortar composite ages, the prediction of bs-8110 code values is in higher side compare with predicted young modulus values given by aci-318 code. • for all the studied cases, the pet volumetric rates have a significant effect of the mechanical properties of pet-mortar composite especially at the long term mortar age where young elastic modulus decreases significantly with the increasing pet volumetric rates of the composite mortar regardless of the code prevision (aci-318 and bs-8110). • flexural strain analysis of pet-mortar composite show that the incorporation of pet wastes in the mortar give more flexibility of pet-mortar composite, especially when the pet volumetric rate is relatively higher (%pet= 12 and 17). this can be explained by the increasing of the ultimate deflection specimen with pet volumetric rate and mortar ages. • unlike the case of young modulus codal prediction, predicted ratio between tensile and compressive strength (ft/fc) given by aci-363 code are closer to the (ft/fc) ratio evaluated by experimental test results. for all studied cases, the volumetric pet rates have a slight effect on (ft/fc) ratio especially at early age of pet-mortar composites. in this way, the obtained pet waste modified mortars would appear to be low-cost composite materials which would contribute to resolving some of the solid waste problems in addition to conserving energy. acknowledgements the authors acknowledge financial support from the ministry of higher education and scientific research of algeria, under the grants cnepru b00l01un310120130068. the authors would like to thank the anonymous referees for improving the quality of this manuscript. 6. references aci 318. (2005). building code requirements for structural concrete (aci 318-05) and commentary (aci 318r-05). aci committee 318, american concrete institute, farmington hills, mi. aci committee 363. (1992). state-of-the-art report on high-strength concrete (aci 363r-92). american concrete institute, farmington hills, mich. afnor, (1990). granulats. analyse granulométrique par tamisage. nfp 18-560, association française de normalisation. kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 183 badache, a., benosman, a.s., senhadji, y., & mouli, m. (2018). thermo-physical and mechanical characteristics of sand-based lightweight composite mortars with recycled high-density polyethylene (hdpe), construction and building materials, 163, 40-52. batayneh, m., iqbal, m., & ibrahim, a. (2007).use of selected waste materials in concrete mixes, waste management, 27, 1870–1876. benazzouk, a., douzane, o., langlet, t., mezreb, k., roucoult, j.m., & quéneudec, m. (2007). physicomechanical properties and water absorption of cement composite containing shredded rubber wastes, cement & concrete composites, 29, 732–740. benosman, a.s., mouli, m., taibi, h., belbachir, m., & senhadji, y. (2011). resistance of polymer (pet) mortar composites to aggressive solutions, international journal of engineering research in africa, 5, 1-15. benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2013). studies on chemical resistance of pet-mortar composites: microstructure and phase composition changes, engineering, 5(4), 359-378. benosman, a.s., mouli, m., taibi, h., belbachir, m., senhadji, y., bahlouli, i., & houivet, d. (2017a). the chemical, mechanical and thermal properties of pet-mortar composites containing waste pet. environmental engineering and management journal (eemj), 16(7), 1489-1505. benosman, a.s., senhadji, y., & mouli, m. (2015). application of polymer-mortar composites as a sustainable building material, key engineering materials, 650, 21-28. benosman, a.s., taibi, h., mouli, m., belbachir, m., senhadji, y. (2008). diffusion of chloride ions in polymer-mortar composites, journal of applied polymer science, 110, 1600-1605. benosman, a.s., taibi, h., mouli, m., senhadji, y., belbachir, m., bahlouli, i., & houivet, d. (2015). effect of addition of pet on the mechanical performance of pet-mortar composite materials. journal of materials and environmental science, 6 (2), 559-571. benosman, a.s., taïbi, h., senhadji, y., mouli, m., belbachir, m., bahlouli, m.i. (2017b). plastic waste particles in mortar composites: sulfate resistance and thermal coefficients. progress in rubber plastics and recycling technology journal, rapra, smithers, 33(3), 171-202. bs 8110. (1997). structural use of concrete. code of practice for design and construction. british standards institution. bsi. (1987). bs 8007: 1987 code of practice for design of concrete structures for retaining aqueous liquids. london: bsi. chaib, o., benosman, a.s., kazi tani, n., senhadji, y., mouli, m., taïbi, h., & hamadache, m. (2017). the evolution of shrinkage strain of pet-mortar composite eco-materials, journal of fundamental and applied sciences (jfas), 9(1), 136-152. choi, y.w., moon, d.j., chung, j.s., & cho, s.k. (2005). effects of waste pet bottles aggregate on properties of concrete, cement and concrete research, 35, 776–781. chowdhury, s., maniar, a.t., & suganya, o. (2013). polyethylene terephthalate (pet) waste as building solution. int. j. chem. environ. biol. sci. (ijcebs), 1, 2320-4087. cordoba, l.a., berrera, g.m., diaz, c.b., nunez, f.u., & yanez, a.l. (2013). effects on mechanical properties of recycled pet in cement-based composites. international journal of polymer science, 1-6. de brito, j., & saikia, n. (2013). recycled aggregate in concrete; use of an industrial, construction and demolition waste. (eds.), springer, london heidelberg new york dordrecht, pp. 431. en 196-1. (1995). methods of testing cement part 1: determination of strength. comité européen de normalisation (cen). en 196-3. (1995). methods of testing cement part 3: determination of setting time and soundness. comité européen de normalisation (cen). ghernouti, y., & rabehi, b. (2012). strength and durability of mortar made with plastics bag waste (mpbw), international journal of concrete structures and materials, 6(3), 145–153. 184 kazi tani et al., j. build. mater. struct. (2018) 5: 174-184 gouasmi, m.t., benosman, a.s., & taïbi, h. (2017). development of materials based on pet-siliceous sand composite aggregates. journal of building materials and structures, 4(2), 58-67 hannawi, k., kamali-bernard, s., & prince, w. (2010). physical and mechanical properties of mortars containing pet and pc waste aggregates. waste management, 30, 2312–2320. kazi tani, n., benosman, a.s., senhadji, y., taïbi, h., & mouli, m. (2017). mechanical strengths of modified pet mortar composites in aggressive mgso4 medium: aci & b.s predictions. journal of building materials and structures, 4(2), 76-83. latroch, n., benosman, a.s., bouhamou, n.-e., senhadji, y., mouli, m. (2018). physico-mechanical and thermal properties of composite mortars containing lightweight aggregates of expanded polyvinyl chloride. construction and building materials, 175, 77-87. mahdi, f., khan, a.a., & abbas, h. (2007). physiochemical properties of polymer mortar composites using resins derived from post-consumer pet bottles. cement and concrete composites, 29, 241-248. naik, t.r., singh, s.s., huber, c.o., & brodersen, b.s. (1996). use of post-consumer waste plastic in cementbased composites. cement and concrete research, 26, 1489-1492. ochi, t., okubo, s., & fukui, k. (2007). development of recycled pet fiber and its application as concretereinforcing fiber. cement and concrete composites, 29, 448-455. ozbakkaloglu, l., & gu, t. (2016). use of recycled plastics in concrete: a critical review. waste management, 51, 19–42. pacheco, t.f., & ding, y. (2013). concrete with polymeric wastes, eco-efficient concrete, a volume in woodhead publishing series in civil and structural engineering, book chapter 13, ed. by: f. pacheco-torgal, s. jalali, j. labrincha and v. m. john, 311–339. rebeiz, k.s. (1996). precast use of polymer concrete using unsaturated resin based on recycled pet waste, construction and building materials, 10, 215–220. safi, b., saidi, m., aboutaleb d., & maallem, m. (2013). the use of plastic waste as fine aggregate in the selfcompacting mortars: effect on physical and mechanical properties. construction and building materials, 43, 436-442. saikia, n., & de brito, j. (2012). use of plastic waste as aggregate in cement mortar and concrete preparation: a review. construction and building materials, 34, 385–401. sharma, r., & bansal, p. p. (2016). use of different forms of waste plastic in concrete a review. journal of cleaner production 112, 473-482. yazoghli-marzouk o., dheilly, rm., & quéneudec, m. (2007). valorisation of post-consumer waste plastic in cementitious concrete composites. waste management, 27, 310–318. j. build. mater. struct. (2019) 6: 64-76 original article doi : 10.34118/jbms.v6i2.69 issn 2353-0057, eissn : 2600-6936 predicting shear strength of rc columns using artificial neural networks said a 1,*, gordon n 2 1 architectural engineering department, the pennsylvania state university, 104 engineering unit a, university park, pa. 2 structural engineering division, tesla motors inc., las vegas, nevada. * corresponding author: aly.said@engr.psu.edu received: 01-01-2018 accepted: 08-06-2019 abstract. a primary objective in the seismic design of structures is to ensure that the capacity of individual members of a structure exceeds the associated demands. for reinforced concrete (rc) columns, several parameters involving steel and concrete material properties control behavior and strength. furthermore, it is unrealistic to simply consider the shear strength calculation as the sum of concrete and steel contributions while accounting for axial force when, in fact, all those parameters are interacting. consequently, it is challenging to reasonably estimate the shear capacity of a column while accounting for all the factors. this study investigates the viability of using artificial neural networks (ann) to estimate the shear capacity of rc columns. results from ann are compared with both experimental values and calculated values, using semi-empirical and empirical formulas from the literature. results show that anns are significantly accurate in predicting shear strength when trained with accurate experimental results, and meet or exceed the performance of existing empirical formulas. accordingly, anns could be used in the future for analytical predictions of shear strength of rc members. key words: reinforced concrete, neural network, artificial intelligence, shear, seismic, columns. 1. introduction in the seismic design of structures, it is essential to ensure that the deformation capacities of a structure and its components exceed the associated deformation demands. this concept is implicitly addressed in capacity-based design procedures, and is an explicit core requirement of displacement-based design procedures. thus, it is desirable that structures are designed with high ductility and large deformation capacities according to seismic provisions. shear failure of reinforced concrete (rc) members is inherently brittle, resulting in a significant drop in lateral load resistance at low deformation; this is highly undesirable in seismic design. several studies have demonstrated that the shear strength of rc members degrades substantially under cyclic loading when compared to the flexural strength of the member (ascheim et al., 1992; priestley et al., 1994; moehle et al., 2002; biskinis et al., 2004). accordingly, existing seismic design guidelines for rc structures require special reinforcement for zones where plastic hinges are expected to form in order to ensure that brittle modes of failure are avoided. nonetheless, in many cases, due to the complex interaction between the parameters that affect shear strength of a member, empirical equations formulated based on analytical reasoning are often proposed in order to predict the shear strength of these members. these empirical models have been continuously and significantly improved, as shown by biskinis et al. (2004). recent procedures issued by the u.s. federal emergency management agency (fema) for seismic evaluation of existing structures (fema-356, 2000) and for the seismic design of new structures (fema-368, 2000) involve member verifications explicitly in terms of member deformations. these procedures provide a strong motivation to develop an accurate, dependable quantification of load and deformation capacities of rc members. quantification of load and deformation mailto:aly.said@engr.psu.edu said and gordon, j. build. mater. struct. (2019) 6: 64-76 65 capacities of rc members is a difficult task due to their non-linear and complex behavior under seismic loading. accordingly, existing equations in the literature need to be reexamined and verified using a large amount of experimental data, the more recent information available in the literature, and modern analytical techniques. 2. objectives this study aims to improve upon existing empirical equations and models by implementing artificial intelligence algorithms to predict the shear strength of rc columns based on a number of different variables. artificial neural networks (ann) have been developed and trained to predict the shear resistance for rectangular and circular rc columns under axial load and cyclic lateral loading. a database has been compiled that consists of column specimens that have been loaded cyclically and failed in shear or in shear after flexural yielding (flexure shear). 3. experimental database the experimental database used was obtained from the pacific earthquake engineering research structural performance database (peer-spd). peer-spd was chosen because the hysteresis of load-displacement data was readily available for nearly all column specimens in the database. this was necessary to form the load-displacement envelopes in order to determine column displacement and lateral loads at yield and ultimate failure as well as to determine the experimental values for the shear resistance, vr. by applying a uniform approach for evaluating shear strength of rc columns, the authors believe that the database that was used will have a more consistent dataset. the experimental values of the shear resistance, vr, were obtained by analyzing the force-displacement data for the column, determining the maximum loading, and using a value of 75% of the maximum load. this 75% is an average determined by systematically analyzing the force-displacement loops; following the approach of elwood (2002), a yield point was defined as the corner point of a bilinear envelope of the first loading cycle on the loaddeflection diagram. the value of the force at this point was defined as vr by elwood (2002); however, for consistency and simple identification, an average of all specimens was taken at this point to be 75% of the peak resistance. software was written to automatically determine these points from the hysteresis; the source code is available upon request. 4. artificial neural networks artificial neural networks (ann) are powerful computational tools inspired by the understanding and abstraction of the structure of biological neurons and the internal operation of the human brain (haykin, 1994). the most important concept of anns is the way in which data is processed. each ann is composed of highly interconnected nodes or neurons used to process information. this structure allows anns to closely model the way that the human brain forms connections to solve problems and learn by example, or trial-and-error. a neural network must be “trained” for their specific application. this training process is accomplished by providing a network with a large amount of data to build connections between neurons. this is analogous to the same process that occurs in biological systems during the learning process. synaptic connections between neurons are built and reconfigured over numerous generations of training. increasingly, neural networks are applied to real-world applications where problems are too complex to solve by means of conventional methods or for problems where an algorithmic solution would be too complex or undefined. they also can be used where algorithmic solutions have been developed, but do not yield high accuracy in the results. many applications of anns have shown superior accuracy to empirical algorithms in these cases. several types of neural networks exist, the most common of which is the continuous multi-layer perceptron (cmp). this type of network is based on recursive generational evaluation, consisting of various layers of neurons passing information between each other. the first layer, called the ‘input layer’, has the same number of neurons equal to the number of variables. each 66 said and gordon, j. build. mater. struct. (2019) 6: 64-76 successive layer is called a ‘hidden layer’, and may contain more or less neurons than the preceding layer. a final layer, called the ‘output layer’, contains the same number of neurons as the number of outputs expected by the response. in the case of no hidden layers, a neural network can only act on linear tasks. all problems that are capable of a solution with a cmp can be solved with only one hidden layer; however, more layers can be used, and may result in more accurate responses. a sample of a neural network architecture is shown in figure 1. fig 1. an example of the structure of an artificial neural network (ann). each neuron in a hidden layer first creates a linear combination of the outputs of the previous layer and a bias to introduce variation. these combinations and biases are called the weights. the neurons in the hidden layer then create a non-linear function based on the inputs. the most commonly used function is called the logistic function. this function varies from 0 to 1, and maps to a real value that may be positive or negative as well as large or small. as a requirement of using this function, all input data must first be normalized into a range from 0 to 1. one of the methods of normalizing the data input is by using the following equation: ( ) ( ) (1) where xt is the scaled value of variable x, and xmin and xmax are the minimum and maximum values for the dataset, respectively. this normalizes any input data to a percentage value of the range of the data used. the training is based on making the mean squared error (mse) in the network as small as possible. this is done over many training cycles, because when the network is initially presented with a large seemingly random distribution, the mse will be very large. the training process modifies the ‘weights’ of each neuron in an attempt to decrease the mse of the net to a global minimum over each cycle. once the training process is complete, another set of testing data is presented to the network, and the results are compared with experimental results. in order to evaluate the performance of the ann model, the absolute average error (aae) of the ratio of the calculated shear capacity, vrcalculated, to the experimentally measured shear capacity, vrexperimental, was used to measure how accurately the network predicts the shear capacity relative to the experimental data. the aae was calculated using the following equation:     100 1 lxperimentae calculatedlxperimentae vr vrvr n aae (2) furthermore, to determine the coefficient of variation among the ratio of vrexperimental / vrcalculated, the following equation was used: said and gordon, j. build. mater. struct. (2019) 6: 64-76 67 )/( )/( calculatedlxperimentae calculatedlxperimentae vrvr vrvr cov    (3) where µ and σ are the mean and standard deviation, respectively. 5. existing shear strength models three previous models were evaluated for their accuracy in predicting the shear strength of cyclically loaded members. the models evaluated were the aci 318-14 (2014) shear strength model and the models developed by priestley et al. (1994), and moehle et al. (2002). the aci 318-11 (2011) model presents the same shear strength prediction model as has been provided by code standards in preceding versions. along with many of the other equations, this model recognizes a contribution to the shear strength by the steel (vs) as well as a contribution by the concrete (vc), as described in equations 11-2 (units: psi, in). (4) equations 11-5 and 11-6 (herein eqs. 5 and 6, respectively) provided a detailed approach to account for the moment and shear interaction and their effect on the concrete contribution as follows: √ √ √ (5) (6) (7) in the case that mm is negative, it is permitted to use the upper bound of vc as the concrete contribution. for spirally reinforced columns, vs is multiplied by (sin  + cos ), where  is the angle between inclined stirrups and longitudinal axis of the member. nonetheless, the most recent aci-318-14 (2014), eliminated accounting for mm as an optional additional step, while keeping mu instead. it also kept equation 22.5.6.1 (formerly 11-4), which accounts for the effect of axial load as follows: ( ) √ (8) priestley et al. (1994) presented a model that takes into account the displacement ductility, defined by the ratio of the ultimate displacement at failure to the displacement at yield. this ratio is used to define a modification factor that reduces the predicted shear strength of the column. priestley et al. (1994) divided the strength calculation into three parts: a concrete contribution, vc; a steel contribution, vs; and an axial load contribution, vp. these equations are presented as follows: (9) 68 said and gordon, j. build. mater. struct. (2019) 6: 64-76 √ (10) (11) (12) where k depends on the member displacement ductility level and the system of units chosen (megapascals or pounds per square inch) as well as on whether the column is expected to be subjected to uniaxial or biaxial ductility demand. in equation (10), the effective shear area is taken as ae = 0.8 ag for both circular and rectangular columns. figure 2, provided by priestley et al. (1994), is used to determine k values. in equation (12), d' is taken as the distance between the very outer peripheral loops or spirals of transverse reinforcement, center to center, or (d d)' by some notation. for circular columns, vs is multiplied by , and is taken as the overall diameter. fig 2. degradation of concrete shear strength with ductility (priestley, et al., 1994). the third model, evaluated for its capacity to predict shear strength, is a model recently proposed by moehle et al. (2002). this model also recognizes a degradation of shear strength as a result of cyclic loading. however, in contrast to the presentation by priestley et al. (1994), this model applies the shear degradation factor to both the concrete and steel contributions to shear strength. doing so results in a more accurate model, as is evidenced by the data. moehle’s equations recognize steel and concrete contributions as separate as well, with the axial load contribution taken into account in the concrete contribution term. ( ) (13) (14) √ (√ √ ) ( ) (15) said and gordon, j. build. mater. struct. (2019) 6: 64-76 69 (16) in circular columns, d' in equation 16 is taken as (diameter – 2 × cover). the above models were tested on a database of 120 columns consisting of 65 spirally reinforced circular or octagonal cross-sections and 55 rectangular sections. octagonal cross-section columns were approximated as circular sections, since the small difference in the concrete area is negligible. evaluation of the existing shear strength models for rc columns is shown in figures 3 through 5 as well as table 1. despite the fact that aci 318-11 does not account for shear degradation under cyclic loading, results are split fairly evenly between over-prediction of shear strength and a conservative prediction, as shown in figure. however, there are several cases where shear strength has been greatly over-predicted, for example, in the case of priestley et al. (1994), where the equations greatly over-predict the shear strength of almost all specimens, as shown in figure 4. this may be attributed to the lack of application of the shear degradation factor to the steel contribution or to the over-estimation of the concrete contribution to shear resistance. moehle’s return to the classical ritter-mörsch truss analogy of a 45-degree angle seems to be the most conservative, especially with the shear degradation factor applied to the steel contribution, as illustrated in figure 5. table 1. statistical performance of existing shear strength equations. rectangular columns circular columns vrexperimental / vrcalculated vrexperimental / vrcalculated method aae (%) average sd cov (%) aae (%) average sd cov (%) moehle et al. (2001) 46.6% 1.76 0.92 52.4% 42.1% 2.12 3.33 157.5% priestley et al. (1994) 99.3% 0.63 0.27 42.8% 82.4% 0.71 0.40 56.9% aci-318-14 eq. [22.5.6.1] 46.5% 0.85 0.35 40.5% 28.2% 1.14 0.35 30.5% fig 3. experimental vs. calculated column shear strength, according to aci 318-14 (2014) equation 22.5.6.1. 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 v r (c a lc u la te d ) vr (experimantal) rectangular circular 70 said and gordon, j. build. mater. struct. (2019) 6: 64-76 fig 4. experimental vs. calculated column shear strength according to the priestley et al. (1994) model. fig 5. experimental vs. calculated column shear strength according to the moehle et al. (2002) model. the statistical performance of the three approaches presented in this paper, shown in table 1, indicates that the aci approach is quite acceptable, taking into account that it is a design standard that needs to conform to a wide range of applications. 6. ann model hundreds of neural network architectures were created and tested, and the top performing networks for circular and rectangular columns were selected. selection criteria were based on the best fit to the data as well as the lowest absolute mean error. the networks were trained with a subset of the original data. this subset, chosen at random by a gaussian distribution function, consisted of half the specimens available in the database. the other half was reserved to test the performance of the network. figures 6(a) and 6(b) illustrate the networks for rectangular and circular columns, respectively. 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 v r (c a lc u la te d ) vr (experimental) rectangular circular 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 v r (c a lc u la te d ) vr (experimental) rectangular circular said and gordon, j. build. mater. struct. (2019) 6: 64-76 71 for rectangular columns, seven input variables were provided to predict the shear strength of the member. these variables are shown in table 2. table 3 illustrates relevant statistical data for each of the top ann models for rectangular columns. network nn-321 had the best correlation to the results, and an error mean that leaned more towards the conservative side of prediction, which is preferable. fig 6. ann model architecture for (a) nn-321 (rectangular columns) and (b) nn-149 (circular columns). for circular columns, the same input variables were used to train the networks, with the exception of bw and d, and the addition of the column diameter, d, bringing the total number of input variables for circular columns to six. table 3 illustrates the pertinent properties and information about the structure and statistical data of the top ann model for circular columns. the ann models used for predicting the shear strength of circular columns were not as robust and efficient, and did not achieve the same confidence in the results as did the rectangular anns. however, the confidence was still significantly greater than the previously presented empirical equations. table2. ann input variables for rectangular columns. input variable notation units comments column base length effective depth length distance from extreme compression fiber to centroid of longitudinal tension reinforcement axial load contribution √ unitless aspect ratio unitless displacement ductility unitless ratio of ultimate displacement at failure to displacement at yield longitudinal reinforcement ratio unitless area of longitudinal reinforcement divided by gross concrete area volumetric transverse reinforcement ratio unitless (b) (a) 72 said and gordon, j. build. mater. struct. (2019) 6: 64-76 ann model nn-149 performed the best out of a large number of evaluated ann models. however, nn-149 had trouble predicting shear strength for columns identified as high outliers. this is typical for many of the properties, especially in ann modeling, where confidence in the results becomes dependent on the number of test specimens from the database used for training within that range. for that reason, it is recommended that the models are only used within the range of parameters that they are used in training. table 3. ann properties and performance data for rectangular and circular columns. network nn-321 (rectangular columns) nn-149 (circular columns) data mean 158.74 253.68 data s.d. 113.26 130.08 error mean 2.325 2.133 error s.d. 14.703 29.609 abs e. mean 9.635 21.719 s.d. ratio 0.129 0.974 correlation 0.992 2 # of hidden layers 2 10 # hidden units, layer 1 15 7 # hidden units, layer 2 13 -- 7. results and discussion in the prediction of shear strength for rc columns under cyclic loading, neural networks prove to be a very valuable tool due to the extremely non-linear nature of the parameters involved contributing to shear strength and the complexity of their interaction. neural networks extend beyond the typical realm of empirically based equations, but have the important requirement of computing power and a meaningful database to predict the shear strength of columns. neural networks can be retrained when new data become available, and actually ‘learn’ how to predict the shear strength based on all available information, just as humans can. such capacity makes anns very beneficial in the seismic design of structures. 7.1. rectangular columns for rectangular columns, the best performing ann model was capable of predicting the shear strength of concrete columns significantly better than existing models in the literature. results displayed in figure 7 shows data points mostly around the 45 line; this is in clear contrast to the results shown in figures 3 through 5. results listed in table 3 show the capacity of the network to estimate the shear strength of columns accurately for the wide range of parameters studied. figure 8 shows the ratio of experimental to calculated column shear strength plotted against the range of several parameters. while most data points are close to the unity line, point clustering is quite common. accordingly, it is recommended that new tests target new values of parameters, thus improving the performance of ann models as well as other models in the literature. said and gordon, j. build. mater. struct. (2019) 6: 64-76 73 fig 7. experimental vs. calculated column shear strength according to the proposed ann model for rectangular columns. fig 8. ratio of experimental-to-calculated column shear strength for the nn-321 model (rectangular columns), plotted against the range of various parameters. 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 v r (c a lc u la te d ) vr (experimental) 0.5 1 1.5 0 0.2 0.4 0.6 0.8 1 v r e x p ./ c a lc . ( a n n ) b (m) 0.5 1 1.5 0 1 2 3 4 5 v r e x p ./ c a lc . ( a n n ) a/d 0.5 1 1.5 0 20 40 60 80 100 v r e x p ./ c a lc . ( a n n ) f'c (mpa) 0.5 1 1.5 0 2 4 6 8 v r e x p ./ c a lc . ( a n n ) μ 0.5 1 1.5 0 0.01 0.02 0.03 0.04 0.05 v r e x p ./ c a lc . ( a n n ) ρw (a) (b) (c) (d) (e) 74 said and gordon, j. build. mater. struct. (2019) 6: 64-76 7.2. circular columns for circular columns, the ann model performance was hindered by the limited number of data points provided. nonetheless, the ann model was able to outperform other formulas in the literature, as seen in figure 9. furthermore, figure 10 shows clustering of data for several parameters indicating that some parameters are repeatedly used at the same value, similar to rectangular columns. figure 10(c) illustrates the need for high strength concrete column testing, since most tested column are below 40 mpa. it is also noteworthy that the majority of the estimated results were an underestimation. fig 9. experimental vs. calculated column shear strength according to the proposed ann model for circular columns. 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 v r (c a lc u la te d ) vr (experimental) 0.5 1 1.5 0 0.2 0.4 0.6 0.8 v r e x p ./ c a lc . ( a n n ) d (m) 0.5 1 1.5 0 1 2 3 4 v r e x p ./ c a lc . ( a n n ) a/d 0.5 1 1.5 0 10 20 30 40 50 v r e x p ./ c a lc . ( a n n ) f'c (mpa) 0.5 1 1.5 0 2 4 6 8 10 12 v r e x p ./ c a lc . ( a n n ) μ (b) (a) (c) (d) said and gordon, j. build. mater. struct. (2019) 6: 64-76 75 fig 10. ratio of experimental-to-calculated column shear strength for the nn-149 model (circular columns) plotted against the range of various parameters. 8. conclusion in the prediction of shear strength for rc columns under cyclic loading, neural networks proved that it can be a very valuable tool due to the extremely non-linear nature of the parameters involved contributing to shear strength of rc columns. neural networks extend beyond the typical realm of empirically based equations, but have the necessary computing power to predict the shear strength of the column. neural networks can be retrained when new data become available, and can actually ‘learn’ how to predict the shear strength based on previous information, just as humans can. this makes anns very beneficial in the seismic design of structures. for the prediction of the shear strength of rectangular rc columns, the ann model nn-321 proved to be the best candidate with the best fit to the data, while ann model nn-149 was the best model for circular columns. both models outperformed the existing models in the literature examined in this study. nonetheless, neural networks have inherent limitation to their capability to predict shear strength of rc columns. ann models are most accurate within the range of parameters used to train the network and accordingly, they should be cautiously outside the ranges of parameters. 9. references aci committee 318 (2011). building code requirements for structural concrete (aci 318-11) and commentary (aci 318r-11). farmington hills, mich.: american concrete institute. aci committee 318 (2014). building code requirements for structural concrete (aci 318-14) and commentary. farmington hills, mich.: american concrete institute. ascheim, m. a. and j. p. moehle (1992). shear strength and deformability of rc bridge columns subjected to inelastic cyclic displacements. report ucb/eerc-92/04. berkeley, ca: university of california, earthquake engineering research center. biskinis, dionysis e., george k. roupakias and michael n. fardis (2004). “degradation of shear strength of reinforced concrete members with inelastic cyclic displacements.” aci structural journal v. 101.6: 773-783. elwood, k. (2002). “shake table tests and analytical studies on the gravity load collapse of reinforced concrete frames”. ph. d. dissertation, department of civil and environmental engineering, university of california berkeley. p. 419. federal emergency management agency, fema-356 (2000). “prestandard and commentary for seismic rehabilitation of buildings.” washington d.c. federal emergency management agency, fema-368 (2000),. “nehrp recommended provisions for new buildings and other structures.” washington d.c. haykin, s. (1994). neural networks. a comprehensive foundation. macmillan, new york, ny. 0.5 1 1.5 0 0.01 0.02 0.03 0.04 0.05 0.06 v r e x p ./ c a lc . ( a n n ) ρw (e) 76 said and gordon, j. build. mater. struct. (2019) 6: 64-76 moehle, j. p., k. j. elwood, and h. sezen (2002). “gravity load collapse of building frames during earthquakes.” aci sp-197. behavior and design of concrete structures for seismic performance: 215-238. priestley, m. j. n., r. verma and y xiao (1994). “seismic shear strength of reinforced concrete columns.” journal of the structural division, asce v. 120.8. j. build. mater. struct. (2019) 6: 97-106 original article doi : 10.34118/jbms.v6i2.72 issn 2353-0057, eissn : 2600-6936 effect of street morphology on buildings’ thermal storage in a hot and arid climate: case study of biskra (algeria) benamor k *, benabbas m laboratory lacomofa, department of architecture, university mohamed khider biskra, algeria. * corresponding author: kaouther61@gmail.com received: 25-05-2019 accepted: 12-09-2019 abstract: this work is an experimental study focusing on the relationship between street morphology and thermal storage in buildings. the first aim of this study is to reduce air conditioning usage in hot and arid areas, taking as example biskra city (algeria), during the long summer period (5 months), by reducing thermal storage. this leads to the reduction of carbon emissions to a level higher than the individual construction level in order to design a sustainable city, using measuring instruments (kimo hd 100 and cason ca 380), we measured outdoor air temperature, wall temperature, relative humidity and wind speed on three street morphologies ; the (canyon, dihedral and open streets). these streets are different in terms of morphological indicators such as sky view factor (svf) and albedo materials (a). we also applied mathematical equations across the thermal balance to calculate thermal storage. our second goal was to identify the morphological indicators of the streets affecting the thermal storage of buildings. in this context, the obtained results showed that svf was the most influential parameter on the heat storage. key words: street morphology, thermal storage, sustainable city, hot and arid climate, sky view factor (svf), albedo materials (a), air conditioning. 1. introduction according to the fourth report of the intergovernmental experts on climate change (iecc) in 2007, the temperature of the earth could rise from 1.1°c to 6.4°c by the end of the 21st century (coquillaud, 2015). furthermore, developing countries that have a hot and arid climate are the vulnerable ones to climate change. algeria is among the affected african countries because of the region's diverse climate with a mediterranean climate in the north and an arid climate in the south. this case study is conducted on the town of biskra which is located in the south-east of algeria in order to reduce the temperature in the city, also called the urban heat island (uhi) phenomenon and thus, to reduce the active air conditioning and co2 emissions, on a superior level than the individual construction (arantes et al., 2016). in this way, it is better to adopt an energy strategy in the design of efficient cities in the long term, by working on the urban form, through the morphological indicators of the streets (bouyer, 2009). at this level, there is an interaction between the external environment and the thermal comfort inside the buildings (nikolopoulou et al., 1999), as the street is a thermal regulator between the inside and the outside and a key factor that influences the heat storage in buildings (golany, 1996; adolphe, 2001), therefore, this article studies the effect of street morphology on the thermal storage of buildings in a hot and arid climate, in order to protect the environment and reach a sustainable city. 2. presentation of the case study the area that represents our case study is located in the east of the called river sidi zerzour (76 residential quarters), it is 2 km far from the city center (figure 1). 98 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 fig. 1. location of the 76 residential quarter. source: google earth (2016). this neighborhood was selected based on the following criteria:  urban geometry: morphological diversity.  the geographical situation: far from the center in order to neglect the impact of anthropogenic flux.  the absence of vegetation: in order to neglect the latent flux impact. this site is characterized by a morphological diversity which allowed us to neglect the impact of anthropogenic and latent heat fluxes that enter in the thermal balance calculation. these considerations allowed us to take into account only the criteria related to the morphology of the street and the thermal exchange of the mineral surface. 2.1. climate data of biskra town a large part of southern algeria is a sahara desert (2 million km2) representing about 85% of its all surface. the town of biskra which represents our case study is located in the south-east of the country (figure 2). fig. 2. location of biskra city source: wikipedia. according to biskra climate data of the ten years (2005-2015) (table 1), the average of the aridity index of de martonne (idm), is 5.64 which indicates that this city is located in the arid zone (table2). case study city center center river sidi zerzour https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 https://www.google.fr/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahukewjsrpxi0fdgahxm2oakhyuzap4qjrx6bagbeau&url=http://adrar-algerie.blogspot.com/2017/01/route-tindouf-adrar-sur-460-km-fin-2017.html&psig=aovvaw1k6qekdvfhqscpiw2hhxu-&ust=1552068880392460 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 99 idm = (1) where: idm : de martonne aridity index. p: annual total precipitation. t: annual mean temperature. the de martonne aridity index climate classification is given as follows: table 1. averages of annual precipitation and air temperature during 2005-2015 (biskra weather station, 2017). table 2. de martonne aridity index climate classification (guyot, 1999). idm value climatic conditions idm <5 hyper-arid 5 < idm <10 arid 10 < idm <20 semi-arid idm > 20 humid the climate of this region is characterized by two seasons, a very hot and dry climate in summer and a cold relatively wet winter, with a short period of comfort. the maximum temperature reaches 46.5 °c in july (summer) and the minimum temperature decreases to 1.67 °c during january (winter). the average annual temperature is about 23.31 °c, while the annual average humidity is 45.60%. a very low rainfall with a maximum of 29.85mm / year and an annual average of about 11.3 mm / year are recorded. the predominant winds are north-west in winter, at a speed of 40km / h, average, and south-east in the summer at a speed of around 20km / h. in spring and autumn, the winds are hot and dusty, blowing from south-west to south-east, reaching 80 km / h. (fig. 3 and 4). fig. 3. the temperature and humidity data of biskra city (biskra weather station, 2005-2015). 0 10 20 30 40 50 temperature (0c) minimum temperature maximum temperature average temperature 0 20 40 60 80 100 humidity % minimum humidiy % maximum humidity % average humidity % years 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 average p (mm) 14.74 10.94 16.38 14.73 10.17 7.68 1.10 2.05 22.27 29.85 14.47 average t (°c) 12.25 14.39 16.81 22.19 27.27 31.24 35.56 34.41 30.44 24.39 17.77 t+10 22.25 24.39 26.81 32.19 37.27 41.24 45.56 44.41 40.44 34.39 27.77 idm =p/t+10 0.66 0.45 0.61 0.46 0.27 0.18 0.024 0.046 0.55 0.87 0.52 p: precipitation, t: temperature. 100 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 fig. 4. average monthly precipitation and wind speed of biskra city (biskra weather station, 2005-2015). 3. methodology the adopted method was based on four measurements (wall temperatureoutdoor air temperaturewind speed and relative humidity). these measurements were collected at three types of streets (the canyon, the dihedral and the open streets) different in terms of the two morphological indicators: 1sky view factor (svf) and 2albedo materials (a). these measurements were collected using the measuring instruments (kimo hd 100 and cason ca 380) (table 3). table 3. the measuring instruments. instruments characteristics 1electronic thermohygrometer hd 100 source : www.kimo.fr is used to measure three climatic parameters, that of the air temperature in (° c, ° f, k), the relative humidity (%), and the dew point (° c, ° f, k) on beaches measurements ranging from -20 ° c to + 80 ° c for air temperature and dew point, and 5 to 95% for rh. while the resolution is (0.1% rh, 0.1 ° c). 2lv 100 anemometer source : www.kimo.fr the instrument is used to record the flow of air in circulation, the measuring ranges are limited to: 0.2 m / s to 3.1 m / s 3.1 m / s to 35 m / s. the resolution of the anemometer shows a difference of 0.01 m / s to 0.1 m / s. 3the cason thermometer ca 380 source : www.aliexpress.com measures the surface temperature of the materials composing the built mass by means of an infrared ray. measurements were taken during critical hours, in the afternoon (16.00 h where the facades are very exposed to solar radiations) and before sunrise (04.00 h), during a typical summer day 0 5 10 15 20 25 30 35 average precipitation (mm) average precipitation (mm) 0 1 2 3 4 5 6 average wind speed (m/s) average wind speed(m/s) http://www.aliexpress.com/ benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 101 (july 17th, 2016). this day is the hottest one, where the sky is clear and the wind is very weak, this makes the best local thermal conditions. once the microclimatic measurements are complete, we calculated the thermal storage, which was done through the thermal balance. 3.1. placement of measuring stations to locate our stations, we chose the east-west axis because of significant access to solar radiation in the west facades (figure 5 and 6). fig. 5. the measurement points in the streets (scale: 1/1000). (a) (b) fig. 6. a) urban section, scale: 1/1000 . b) stations’ situation. h = 9 w=4.30 w=10.00 w=7.30 h = 6 h = 7. 5 102 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 the three streets in particular differ in terms of: the opening to the sky, exposure to solar radiation, and the nature of materials and the height of adjacent buildings …etc the morphological indicators calculations of this study are based on the mathematical process, as shown in the equations below, this seems to be appropriate for determining the thermal exchanges in the street. all these indicators are summarized in (table 4).  sky view factor (svf) the svf was calculated according to the equation of oke and cleugh (1987). ψsky = (1-2 ψwall) (2) ψwall = 0.5 (sin2 θ + cosθ -1) (3) θ = (h/0.5 w)  materials’ albedo (a) the albedo of materials was calculated according to a visual analysis of the percentage of occupation of each material in the facade (ahmed ouameur, 2007). table 4. morphological features of three streets. (benamor, 2017). streets morphological indicators sky view factor (svf) percentage occupancy of the albedo on the west façade % albedo material (a) canyon street (s1) 0.25 red bricks: 30 concrete bricks wall : 65 ceramic : 5 0.35 0.25 0.30 0.28≈0.30 dihedral street (s2) 0.45 red bricks: 30 concrete bricks wall: 60 wall coating: 10 0.35 0.25 0.45 0.30 open street (s3) 0.65 red bricks: 30 concrete bricks wall: 70 0.35 0.25 0.28≈0.30 4. thermal balance (thermal storage) the system (urban environment, neighborhood, green space, infrastructures, buildings, streets, etc.) acts as an environment that can store heat during the day and releases it during the night time (parmentier, 2010). according to masson et al. (2002), the thermal balance can be written according to the following equation: q* + qf = qh +qe +δqs (w/m2) (4) q*: net radiation (w/m2) qf: anthropogenic heat flux (w/m2) qh: sensible heat flux (w/m2) qe: latent heat flux (w/m2) qg: conductive heat flux (w/m2) benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 103 in our case, we have neglected the impact of anthropogenic heat flux and latent flux since the site is far from the city center and does not have any green space, in this way, our thermal balance will be defined by the equation: q* = qh + qg (5) so the formula for calculating the thermal storage in buildings can be written as follow: thermal storage = q* qh qg (6) 4.1. sensible heat flux (qh) the sensible heat flux was calculated using the equation: qh = hc (tair – t wall) (7) ta = temperature of the outside air (°c) t wall = wall temperature (°c) hc = 0,5 + 1,2 √ hc: coefficient of thermal convection 4.2. conductive heat flux (qg) the conductive heat flux was defined by oke and cleugh (1987) as it follows: g= k (∆t/∆x) ≈ k (∆t/ )) (8) ∆t = coldest and hottest temperature (k) e = level of ∆t (m) k: thermal conductivity of wall = 0.12w/m/k 4.3. net radiation (q*) according to colombert (2008), the urban surfaces were exposed to direct solar radiation from the sun and diffused solar radiation (due to multiple reflections from the sky and the soil). the net radiation can be written according to the equation below: q * = q direct solar radiation received on the wall + q diffuse solar radiation (multiple reflections) (9) direct solar radiation and diffuse radiation are defined according to masson et al. (2002), by the following equation: 4.3.1. direct solar radiation received on the wall qdirect solar radiation received on the wall= q direct (sun) ( ) + tan ( )]) (10) h = height of street w= width of street solar altitude 104 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 solar azimuth angle qdirect (sun) = a. exp (perrin de brichambaut) (11) with a, b and c as the empirical constants that depend on the nature of the sky with their values as: a = 1230, b = 3.8, c = 1.6 in normal clear sky conditions. 4.3.2. diffuse solar radiation according to masson et al. (2002), diffuse solar radiation between walls is expressed by the following: qdiffuse solar (multiple reflections) = . qdiffuse sky (12) = √( ) (13) qdiffuse sky = e. (sin h)0.4 (perrin de brichambaut) (14) the value of the empirical constant e is 125 for normal clear sky conditions. 5. results and discussion the figures 7 show that the value of albedo (a) is fixed at 0.30 in all the measurements of the stations, because of the same construction materials used in the facades (brick and concrete). however, the qh, qg, and q* values are variable fig. 7. relationship between albedo material (a) and sensible heat flux (qh), conductive heat flux (qg) and net radiation (q*). this means that the albedo indicator is not the only cause that can influence the energy balance of the facades and thermal exchange at the street level, but there is also the effect of sky view factor (svf) (fig 8). benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 105 fig. 8. relationship between svf and the sensible heat flux (qh), conductive heat flux (qg) and net radiation (q*). before sunrise (4.00h) and afternoons (16.00h) : the figure 9 and table 5 show a relation between the sky view factor (svf) and thermal storage, this means that if svf increases (open space) the energy storage also increases, since the facade is exposed to the sun. fig. 9. relationship between svf and the thermal storage before sunrise and afternoon. table 5 . thermal storage in the afternoons and before sunrises in the three types of streets svf3=0.65 svf2=0.45 svf1=0.25 street -155 -140 -90 thermal storage before sunrises 04.00h (w/m2) 225 100 80 thermal storage in afternoons 16.00h (w/m2) 70% 40% 10% percentage of real thermal storage (w/m2) 6. conclusion the obtained results show that the (svf) has a significant impact on thermal storage in buildings. the percentage of thermal storage in the case of canyon street (svf=0.25) is 10%, while in the case of dihedral street (svf=0.45) it is 40%. in the case of open street (svf=0.75), the value is 70%. in order to improve the performance of urban energy and reduce the storage of heat in buildings and active air conditioning, it is necessary to act on morphological indicators of the streets. for 106 benamor and benabbas, j. build. mater. struct. (2019) 6: 97-106 hot and dry climate, the sky view factor for the streets (svf) should be between 0.25 and 0.45, which means that the urban fabric should be dense; this fabric shape seems to be the most appropriate morphology to reducing the heat storage, when varying in the svf interval mentioned. 7. references adolphe, l. (2001). modelling the link between built environment and urban climate: towards simplified indicators of the city environment, building simulation, proceedings of ibpsa (international building performance simulation association), pp. 679-684. ahmed ouameur, f. (2007). urban morphology and thermal comfort in public spaces: comparative study between three urban forms of the city of quebec, thesis of the master, university of laval, quebec. arantes, l., marry, s., baverel, o., & quenard, d. (2016). energy balance in the urban built environment: a" morpho-energetic" optimisation tool, cybergeo-european journal of geography. benamor, k. (2017). l’impact de la morphologie urbaine sur la demande énergétique dans les zones arides-cas d’un tissu urbain éparse, cité 76 logements à biskra. magister dissertation, university mohamed khider–biskra, algeria. bouyer, j. (2009). modeling and simulation of urban microclimates: study of the impact of urban development on the energy consumption of buildings, doctoral thesis, university of nantes, france. colombert, m . (2008). contribution to the analysis of the taking into account of the urban climate in the various means of intervention on the city, doctoral thesis, university paris-east. coquillaud , s. (2015). climate change : nature reserves of france, (3rd ed.), france: impro, montreuil. golany, g. s. (1996). urban design morphology and thermal performance. atmospheric environment, 30(3), 455-465. masson, v., grimmond, c. s. b., & oke, t. r. (2002). evaluation of the town energy balance (teb) scheme with direct measurements from dry districts in two cities. journal of applied meteorology, 41(10), 1011-1026. nikolopoulou, m., baker, n., & steemers, k. (1999). thermal comfort in urban spaces: different forms of adaptation. proc. rebuild 1999: shaping our cities for the 21st century. oke, t. r., & cleugh, h. a. (1987). urban heat storage derived as energy balance residuals. boundary-layer meteorology, 39(3), 233-245. parmentier, a . (2010). development of a decision support tool to mitigate urban heat island phenomenon, thesis of the master, superior technology school, university of quebec. j. build. mater. struct. (2017) 4: 22-30 review article doi : 10.34118/jbms.v4i1.28 issn 2353-0057 biocomposite bridge malschaert d the netherlands, the hague university of applied sciences, civil engineering, antea group b.v. * corresponding author: david.malschaert@gmail.com received: 11-07-2017 accepted: 11-08-2017 focus and restrictions. this paper focuses on the structural application of the material biocomposite in bridge building. no experimental tests were executed during this research. this paper is the result of two underlying reports: literature research and applied research. these underlying reports are not published and are in possession of the author of this paper, the hague university of applied sciences and antea group b.v. abstract. biocomposite materials are becoming more interesting to use in infrastructural projects due to their biodegradable, renewable, recyclable and sustainable properties. with a relatively low density, it is an interesting building material regarding a bridge deck. when designing with biocomposite the following factors are important to consider: material design, fibre treatment, coating and manufacturing technique. a pla-bamboo biocomposite was applied to an existing design of a bridge deck made out of synthetic composite. due to its randomly oriented fibres and its equally designed lamellae, the cross section was considered homogeneous and the stresses were calculated according to ‘hooke’s law’. the unity checks were performed according to ‘cur 96’ with an own devised material factor of 5,69. this factor was calculated in this study for biocomposites with untreated fibres. the calculations showed that the original material (synthetic composite) was not directly replaceable by the pla-bamboo biocomposite. an alternative design of the deck (deck height of 1 meter and doubled thicknesses of the skins and web plates, 40and 10 mm) showed better results. this design complied for the unity checks for strength. key words: biocomposite, biofibre, bioresin, biobridge, biobased structural application. 1. introduction at this moment, most of the bridges in the world are made out of the traditional materials: wood, steel and reinforced concrete. developments in ‘composite bridges’ started roughly two decades ago. this new material has proven itself to be a strong and eco-friendly material. another interesting material, when sustainability is an important factor, is biocomposite. currently, there is no bridge in the infrastructure which is made out of biocomposite (according to the definition set out in this paper, see below). this brings up the following question: is biocomposite a good alternative material for structural application regarding a small bridge? antea group b.v. is interested in new and innovative materials for infrastructure with the circular design taken into account. with these design considerations, knowledge is gained about what is possible now and perhaps in the future. in this paper the following definition is used in terms of biocomposite: a composite where all of the elements of the construction (fibres, resins and optional core materials) exist out of 100% organic material, apart from a coating and fibre treatment. 2. methodology this research is based on a literature review. no experimental tests were done during this research as mentioned in ‘focus and restrictions’. the literature used for this research is mainly mailto:david.malschaert@gmail.com malschaert, j. build. mater. struct. (2017)4: 22-30 23 adapted from published papers. with the knowledge of this literature review, an applied research was carried out. in this applied research, biocomposite was applied on a design of a synthetic composite bridge deck. the outcome of the calculations showed if biocomposite can be used on this design and where the weak spots are in the material regarding this application. 3. pros and cons due to the use of biological materials, biocomposite is biodegradable, renewable, recyclable and sustainable. these are important benefits in regards to the growing environmental awareness (satyanarayana, 2009; mohanty, 2000). with an eye on the increasing scarcity of other materials (e.g. oil for synthetic composites), biocomposite can be an alternative material in the future. next to this biocomposite has a relatively low density and low coefficient of thermal expansion which reduces loads on the structure (kalia, 2009). the relatively low density makes biocomposite an interesting building material for bridge decks. this reduction in weight could result in less deep foundation piles or even a shallow foundation. biocomposite also has a wide range of materials (nijssen, 2015). this variety gives the designer the opportunity to find the materials for his/her biocomposite which are most favourable for the project (low costs on raw materials, high mechanic properties, etc.). a great disadvantage of biocomposite is the poor adhesion between fibre and matrix. this poor adhesion results in low mechanical properties of the biocomposite (kalia, 2009). because biocomposite is, in general, a hydrophilic material, it absorbs water. this water absorption significantly reduces the mechanical properties (singh, 2000). the mechanical properties can also differ in respect to the climate of origin, harvest method, weatherand soil conditions (kalia, 2009). 4. important factors multiple important factors when designing a bridge out of biocomposite are discussed in this chapter. 4.1. material design when considering the design of the biocomposite the fibre orientation and fibre volume fraction are important aspects which can have a great positive impact on the mechanical properties of the biocomposite. (shalwan & yousif, 2013). in comparison with woven or randomly oriented fibres, unidirectionally oriented fibres (bundles) have a significantly higher tensile strength and stiffness in the axial direction. in this case, the strength and stiffness in the radial direction are determined by the resin (nijssen, 2015). when concerning a bridge deck, the forces in the transverse direction are significantly lower than in longitudinal direction. another option is to use different orientations for each layer in the biocomposite. in this case, the strength and stiffness in the axial and radial direction of the laminate can be influenced. the fibre volume fraction is the ratio of the fibre content of the biocomposite. this fibre volume fraction can also be modified to gain a stronger biocomposite. a higher fibre volume fraction results in general in an increase in mechanical properties of the biocomposite; therefore, a high fibre volume fraction can be favourable when the biocomposite has a structural application (shalwan & yousif, 2013). 4.2. fibre treatment the use of natural fibres in a composite, results in poor adhesion with the matrix. fibre treatment can clean and modify the surface of the fibre and thus improve the surface roughness. this treatment results in better adhesion with the matrix and ultimately higher mechanical properties of the biocomposite (kalia, 2009). 24 malschaert, j. build. mater. struct. (2017) 4: 22-30 previous research shows that the chemical treatments organosilane and alkali increase the mechanical properties of the biocomposite considerably. thermal-, plasmaand corona treatment (physical treatments) also have a strong positive influence on the mechanical properties of tensile strength and young’s modulus (faruk, 2012). 4.3. coating biocomposite is, in general, a hydrophilic material. due to this, biocomposite is likely to absorb moisture. this moisture absorbance decreases the mechanical properties significantly (singh, 2000). the effect of moisture absorbance on the strengths of a jute fibre composite is shown in figure 1. a hydrophobic coating on the biocomposite could prevent the absorption of moisture. the coating needs to resist moisture, uv-light, corrosion and lowand high temperatures in order to be applicable on a bridge. polyesters are widely used as a coating material because they often have these properties. fig 1. the effect of humid conditions on strengths of a jute composite (singh, 2000). 4.4. manufacturing techniques biocomposite can be manufactured using traditional composite manufacturing techniques, e.g. compression moulding, vacuum infusion, pultrusion and mixing (faruk, 2012). of these techniques mixing has a low quality as result, contrary to the others mentioned (nijssen, 2015). vacuum injection or compression moulding is best when the bridge consists of a small number of parts. figure 2 illustrates the process of vacuum infusion. pultrusion can be used to make piles for deep foundation or structural profiles. in the latter case, the structure is constructed out of many parts which increase building time. when a core material is used (in the case of a sandwich biocomposite) wet lay-up, prepreg layup or the adhesive bonding method can be used (karlsson & aström, 1996). malschaert, j. build. mater. struct. (2017)4: 22-30 25 fig 2. vacuum infusion proces (gent, 2014). 5. bridge deck design to test the structural application of the biocomposite material, it was applied to an existing bridge deck design. this design was originally made out of glass fibre reinforced polyester resin (synthetic composite). 5.1. geometry the deck is made out of a sandwich structure with 20 mm thick skins. the deck has a length of 16 meters and has 5 mm thick (centre distance 200 mm) web plates in both longitudinaland transverse direction. the cross section of the deck is illustrated in figure 3. fig 3. cross section deck. where: b=4500mm, h=460mm. 5.2. materials extensive research was done on the mechanical properties of different biocomposites. there was only one biocomposite to apply to this design. this biocomposite exists out of a pla resin with bamboo fibres. the fibres are untreated and the fibre volume fraction has a value of 38% (fibre weight fraction=30%). the properties, except the shear strength and the interlaminar shear strength (ilss), were extracted from ‘ces edupack 2016, sheet: pla(30% natural fiber)’. the shear strength was calculated according to ‘von mises’ theory (τmax=σy/√3) (anderson, 2005). the ilss of a pla-bamboo biocomposite or any other biocomposite, could not be adopted from the available literature. this value was adapted from a synthetic composite (glass fibre reinforced polyester), knowing that the actual value can be much lower. an assumption could not be made for this value due to the missing of research in this area. this makes the calculations in this research incomplete. table 1erreur ! source du renvoi introuvable. presents the used properties in this study of a pla-bamboo biocomposite. research has shown that the adhesion between core material and skins is poor. the core material is therefore not included in the calculations. the function of the core material is only 26 malschaert, j. build. mater. struct. (2017) 4: 22-30 practical (mould in manufacturing). balsa wood can be used as core material. this and the plabamboo biocomposite is shown in figure 3. table 1. properties pla-bamboo biocomposite. property value unit fibre orientation random [-] fibre volume fraction 38.0 [%] density 1.30 [g/cm3] tensile strength 57.0 [mpa] compressive strength 88.9 [mpa] shear strength 32.9 [mpa] interlaminar shear strength 20.0 [mpa] young’s modulus 5.23 [gpa] shear modulus 1.89 [gpa] poisson’s ratio 0.39 [-] glass temperature 53.0 [°c] 5.3. calculation method it has been proven that the traditional ‘rules of mixtures’ (rom) are not directly applicable on biocomposite (facca, kortschot, & yan, 2006) (facca, kortschot, & yan, 2007). the calculated values differ significantly from the experimental values. because of this, the use of experiments for determining the mechanical properties of a biocomposite is inevitable. the next problem in designing with biocomposite is to calculate the occurring stresses. three methods where considered. 5.3.1. classical laminate theory the ‘classical laminate theory’ (clt) is a theory that calculates the elongations and stresses in lamellae individual. the fibre orientations may differ from one another. for the use of the clt, the thickness in the cross section must remain the same. this is not the case in the design of the deck (figure 3). in addition, the shear forces are not included in the clt (nijssen, 2015). due to these reasons, the classical laminate theory cannot be used for this research. 5.3.2. inhomogeneous cross section because the cross section of biocomposite exists out of two different materials with different strength and stiffness properties, it can be considered an inhomogeneous cross section. the adhesion between fibre and matrix must be perfect for this method. this is because the strength and stiffness of the materials are taken into account separately. the interaction between fibre and matrix is not included. the adhesion between fibre and matrix is very unpredictable for biocomposites (faruk, 2012). because of this unpredictability, the method based on a inhomogeneous cross section is not a good method to calculate the stresses in a biocomposite. 5.3.3. homogeneous cross section in this method it is assumed that the properties in the entire cross section of the structure are equal. in order to ensure this, the lamellae must be equal to each other as well. this includes, fibre volume fraction and fibre orientation. when a material has a homogeneous cross section, ‘hooke’s law’ can be applied. in order to calculate according to hooke’s law, a linear relation is needed in the stress-strain curve of the material (welleman, 2011). studies have proven that the stress-strain curve of a biocomposite increases linearly to a maximum fibre volume fraction of 50% (ochi, 2007; akil, 2011; shin, 1989). a biocomposite is manufactured in lamellae, due to this the adhesion between these lamellae needs to be strong enough. these lamellae are not included in the design of a homogeneous cross section but the adhesion will be checked according to cur 96 (see table 4, interlaminar malschaert, j. build. mater. struct. (2017)4: 22-30 27 shear stress). for these reasons, the method based on a homogeneous cross section is a good method to calculate the stresses in a biocomposite. this method was used for this study. 5.3.4. standards several standards where used for calculating the structural safety of the deck. the ‘eurocodes’ where used for the design of the loads and the safety factors. the unity checks where performed according to ‘cur 96’. this is a recommendation (not a standard) for designing structures with glass fibre reinforced synthetic resins (cur, 2003). the reason that cur 96 was used is because of the absence of a standard (or recommendation) on biocomposite and the absence of a standard on synthetic composite. for this study, the material factor was adapted for the use of cur 96. this factor was distracted from differences between calculated values of the tensile strength and young’s modulus according to the rom and the experimental values. the highest calculated factor in table 2 has a value of 5.69 and counts for all biocomposites with untreated fibres which are produced according to the following methods: vacuum injection, compression moulding, prepregs and pultrusion. calculating the inverse of this factor gives a 0.18 strength correction factor. table 2. determination material factor (graupner, 2009; ochi, 2007). property measured calculated unit factor tensile strength 41 224 mpa 5.46 tensile strength 58 330 mpa 5.69 tensile strength 53 241 mpa 4.55 young’s modulus 4242 4740 mpa 1.12 young’s modulus 8064 5990 mpa 0.74 young’s modulus 7139 6369 mpa 0.89 tensile strength 131 178 mpa 1.36 tensile strength 211 297 mpa 1.41 6. results 6.1. stresses and unity checks table 3 presents the occurring stresses in the deck by position (see figure 4). table 3. stresses in deck. position σn,max [mpa] σm,1,max [mpa] σm,2,max [mpa] τv,max [mpa] τw,max [mpa] 1 0.11 30.39 0.70 0.00 0.12 2 0.11 0.00 0.73 7.28 0.12 where: σn = stress as a result of axial force σm,1 = stress as a result of a moment in axial direction σm,2 = stress as a result of a moment in radial direction τv = stress as a result of shear force τw = stress as a result of torsion 28 malschaert, j. build. mater. struct. (2017) 4: 22-30 fig 4. positions in deck (heester, 2015). the stresses in table 4 must be checked according to cur 96 (cur, 2003). table 4. unity checks (cur, 2003). uc position [1] tensile stress in fibre direction 1 [2] compression stress in fibre direction 1 [3] tensile stress perpendicular to fibre direction 2 [4] compression stress perpendicular to fibre direction 2 [5] shear stress in cross section 2 [6] interlaminar shear stress 2 [7] combined stress (tensile) 1 [8] combined stress (compression) 1 table 5 shows the calculated uc-values of each unity check. only the maximum uc-values are given for each unity check. table 5. unity checks by design. h t1 t2 unity check [mm] [mm] [mm] [1] [2] [3] [4] [5] [6] [7] [8] original design 460 20 5 4.23 2.71 0.10 0.06 1.75 2.88 17.92 7.37 alternative design 1000 40 10 0.89 0.57 0.02 0.01 0.43 0.70 0.79 0.33 due to the randomly oriented fibres the stresses are checked in longitudinal (1 and 2) and transverse (3 and 4) direction of the deck. with a highest calculated unity check of 17.92, the original design of the bridge deck does not comply when a pla-bamboo biocomposite is used as material. the values of the unity checks can decrease when a different biocomposite is used or when fibre treatment is applied. this increases the mechanical properties and gives an opportunity to apply a lower material factor. 6.2. alternative design an adjustment on the design of the cross section of the deck can decrease the occurring stresses. for this study the thickness of the skins and web plates where doubled (40and 10 mm) and the height of the deck was increased up to 1.0 meters (+ 117%, see table 5 and figure 5). the design of the biocomposite remained unchanged due to the lack of information about the properties of biocomposites. the highest unity check of 0.89 was calculated. this shows that this biocomposite can be applied, but extreme adjustments must be done to the design. a different biocomposite may show better mechanical properties and results in which no (extreme) adjustment to the design of the cross section are necessary. 7. conclusions several conclusions have been made during this research on the structural application of biocomposite on a bridge. malschaert, j. build. mater. struct. (2017)4: 22-30 29 1. in comparison with synthetic composite, biocomposite has lower mechanical properties (tensile strength biocomposite: ca. 60 mpa, synthetic composite: ca. 200 mpa). the unity checks in the deck complied for strength with an adjustment, when the synthetic composite was replaced by a pla-bamboo biocomposite. the geometry of the deck (height and thicknesses) needed to be doubled (height + 117%, thicknesses + 100%) in the reference design. 2. biocomposite has a linear stress-strain curve up to a maximum fibre volume fraction of 50%. 3. with a safety factor of 5.69, cur 96 can be used as recommendation for designing with biocomposites with untreated fibres. 4. in comparison with other building materials (steel, concrete, synthetic composite etc.), biocomposite is eco-friendlier, biodegradable and it does not deplete other materials like iron and oil (in synthetic composite). the relatively low density (ca. 1.3 g/cm3, steel: ca. 7.9 g/cm3) makes biocomposite an interesting building material for bridge decks. due to these benefits, biocomposite can be a good alternative building material. 5. the design of the biocomposite (fibre orientation and fibre volume fraction) and fibre treatment are important factors regarding the mechanical properties of the biocomposite. biocomposite can be manufactured using traditional composite manufacturing techniques like vacuum infusion, compression moulding and pultrusion. 8. recommendations there are four recommendations made based on mechanical properties, material design, calculation method and time-dependent properties: 1. there is still too little knowledge about the properties of biocomposites. most research currently done is about the tensile strength and young’s modulus of biocomposite. when designing a bridge, properties such as compressive strength, (interlaminar) shear strength, shear modulus and poisson’s ratio are also important. more research on these properties is needed. with more research and thus knowledge about the mechanical properties of the biocomposite, it can also be possible to reduce the material factor calculated in this research. 2. the fibres flax, nettle, hemp, abaca and silk with a pla resin can be a biocomposite with high mechanical properties. an organosilane-, alkali-, thermal-, coronaor plasma fibre treatment show good adhesion between fibre and matrix and thus results into higher mechanical properties of the biocomposite. the mechanical properties of these combinations must be studied. 3. more research on calculation the occurring stresses in biocomposites is needed. the ‘classical laminate theory’ can be applied but has its limitations (shear strength and thickness in the cross section). a method based on a homogeneous cross section can only be used when the properties for each lamellae are equal to one another. a bridge is mostly designed for numerous years. because of this, the time-dependent properties are important. more research is needed to the creepand fatigue behaviour of biocomposite. also the effect of time on the young’s modulus must be studied. 9. references akil, h., omar, m. f., mazuki, a. a. m., safiee, s. z. a. m., ishak, z. m., & bakar, a. a. (2011). kenaf fiber reinforced composites: a review. materials & design, 32(8), 4107-4121. 30 malschaert, j. build. mater. struct. (2017) 4: 22-30 anderson, t. (2005). fracture mechanics fundamentals and applications. boca raton: taylor & francis group. cur. (2003). aanbeveling 96, vezelversterkte kunststoffen in civiele draagconstructies. cur. facca, a. g., kortschot, m. t., & yan, n. (2006). predicting the elastic modulus of natural fibre reinforced thermoplastics. composites part a: applied science and manufacturing, 37(10), 1660-1671. facca, a. g., kortschot, m. t., & yan, n. (2007). predicting the tensile strength of natural fibre reinforced thermoplastics. composites science and technology, 67(11), 2454-2466. faruk, o., bledzki, a. k., fink, h. p., & sain, m. (2012). biocomposites reinforced with natural fibers: 2000– 2010. progress in polymer science, 37(11), 1552-1596. gent, u. o. (2014). organizing your composite workshop. retrieved from university of gent: http://www.composites.ugent.be/home_made_composites/organizing_your_composite_worksho p.html graupner, n., herrmann, a. s., & müssig, j. (2009). natural and man-made cellulose fibre-reinforced poly (lactic acid)(pla) composites: an overview about mechanical characteristics and application areas. composites part a: applied science and manufacturing, 40(6), 810-821. heester, b. (2015). definitief ontwerp. brug over de kleine dommel te eindhoven. antea group. kalia, s., kaith, b. s., & kaur, i. (2009). pretreatments of natural fibers and their application as reinforcing material in polymer composites—a review. polymer engineering & science, 49(7), 1253-1272. mohanty, a. k., misra, m., & hinrichsen, g. (2000). biofibers, biodegradable polymers and biocomposites: an overview. macromolecular materials and engineering, 276(1), 1-24. nijssen, r. (2015). composieten basiskennis. vereniging kunstofcomposieten nederland. ochi, s. (2008). mechanical properties of kenaf fibers and kenaf/pla composites. mechanics of materials, 40(4), 446-452. satyanarayana, k. g., arizaga, g. g., & wypych, f. (2009). biodegradable composites based on lignocellulosic fibers—an overview. progress in polymer science, 34(9), 982-1021. shalwan, a., & yousif, b. f. (2013). in state of art: mechanical and tribological behaviour of polymeric composites based on natural fibres. materials & design, 48, 14-24. shin, f. g., xian, x. j., zheng, w. p., & yipp, m. w. (1989). analyses of the mechanical properties and microstructure of bamboo-epoxy composites. journal of materials science, 24(10), 3483-3490. singh, b., gupta, m., & verma, a. (2000). the durability of jute fibre-reinforced phenolic composites. composites science and technology, 60(4), 581-589. welleman, j., dolfing, a., & hartman, j. (2011). basisboek toegepaste mechanica. amersfoort: thieme meulenhoff. http://www.composites.ugent.be/home_made_composites/organizing_your_composite_workshop.html http://www.composites.ugent.be/home_made_composites/organizing_your_composite_workshop.html j. build. mater. struct. (2021) 8: 32-44 original article doi : 10.34118/jbms.v8i1.1005 issn: 2353-0057, eissn : 2600-6936 study of the mechanical behavior of dune sand treated by hydraulic binders: application in the road geotechnical field smaida a 1 * , haddadi s 2, nechnech a 2 1 civil engineering department, university of djelfa, 17000 djelfa, algeria 2 laboratory environment, water, geomechanics and structures, (leego), usthb, algeria * corresponding author: smaidaali@yahoo.fr received: 18-11-2020 accepted: 25-02-2021 abstract. the purpose of this work consists of valorizing a local sand dune which is found in abundance in the region of djelfa (algeria); for use in pavement foundations. for this investigation a method of formulation has been proposed, which based on the stabilization of this material using a mixture of two hydraulic binders. various mixtures were subjected to classification tests, tests grain size distributions, tests of compaction with modified proctor, shear strength, tests of bearing pressure (cbr unsoaked and soaked), compressive strength and tensile strength. the results obtained have shown that some mixtures are of high mechanical characteristics and could be then used in road foundations. keywords: dune sand, hydraulic binders, valorization, pavements. 1. introduction the roads undergo excessive deformation at the level of their various layers. this implies the use of often very expensive maintenance work. the search for economy in projects, as well as the need to properly exploit natural resources leads to trying to make the best use of all local materials available on site. in algeria the dune sand constitutes a huge deposit almost 60% of the territory of algeria. the current trend of nowadays research is the exploitation of local materials. this has prompted us to perform the present contribution aiming to the valorization of local materials, in particular the dune sand, in the foundations of pavements (mehrpazhouh, 2019); (shalabi, 2021) and (salour, 2017). the modern pavements are made up of three parts, subgrade, base course, and surface layers. the role of pavement foundations is essential to take up the vertical forces and to distribute the resulting normal stresses on the support ground. previous studies done on this subject have shown that the materials used must have certain specifications in terms of their bearing capacity and their fine material content. many studies have been carried out with the aim of improving the mechanical characteristics of the different materials used in road construction by adding binders (cement, clay, lime, pozzolan, fly ash ...) (grzegorz, 2006; setra, 2008; tran, 2009; segui, 2011; ghrieb et al., 2014; azadegan et al., 2013; cherrak et al., 2015; rios r et al., 2016 and tataranni et al., 2018). in the present work, we report on the improvement of the physical and mechanical characteristics of dune sand used for road construction. it is shown that by adding a mixed hydraulic binder all the investigated features are found to be improved. 2. identification of used materials 2.1 dune sand the studied sand comes from the region of djelfa located about 300 km from algiers to the centre of algeria. besides, both centre and south of algeria are known by their huge sand dunes that constitute an important fraction of the surface of the country. using this dune sand in the road domain is of great interest from the economic, technical and environment friendliness points of view. mailto:smaidaali@yahoo.fr 33 smaida et al., j. build. mater. struct. (2021) 8: 32-44 according to the gtr 2000 soil classification (setra-lcpc.gtr, 2008), dune sand belongs to the d1 class. it is characterized as permeable, incoherent, and poorly graded soil. this suggests that dune sand alone will not be sufficiently compact, and subsequently its immediate bearing index is not adequate (reddy and gupta, 2008; haach et al, 2011). therefore, a treatment of this sand with hydraulic binders as correctors will be essential. it is clear from the chemical analysis summarized in table 1, that our sand is siliceous, formed of a large quantity of sio2 (silica), with the presence of some traces of calcium and magnesium species. x-ray analyzes reveal the presence of quartz with a high percentage, and traces of illite and calcite. table 1. chemical composition of dune sand oxyde sio2 co2 fe2o3,al2o3 caso4,h2o nacl caco3 mgo p.f h2o % 93.56 1.49 1 traces 0.29 3.39 0.07 1.73 0.24 the physical properties of dune sand are summarized in table 2. table 2. physical properties of the dune sand. 2.2 lime the lime used in the present study comes from the west of algeria. it is a slaked lime which has a low concentration of oxides such as sio2 (silicate) < 2.2% and mgo (aluminate) <0.4% and a high concentration of basic elements such as cao (free lime) < 67.4% and 73.25%, with more than 90% passing through 80μm sieve. its absolute density is 2.559 g / cm3, and its specific surface area is 11053 cm2 / g. table 3 summarizes the chemical composition of the lime. table 3. chemical composition of the lime. 2.3 natural pozzolan the used natural pozzolan is of volcanic origin extracted from the bouhamidi deposit (western algeria). this pozzolan consists mainly of well-stratified slate and pumice stones, ranging in color from red to black. the natural pozzolan used in all tests is in the form of a powder resulting from the crushing of pozzolanic slags; steamed for 24 hours at a temperature of 50 ° c to remove their moisture, and then crushed until the resulting powder can pass through a sieve mesh of 80 µm (figures 1 and 2). x-ray diffraction of this pozzolan shows that it consists of crystalline minerals rich in silica, alumina, iron and magnesium. the chemical composition of natural pozzolan after grinding is shown in table 4. it is noted that the blaine specific surface of natural pozzolan is 4330 cm2/g with an absolute density of 2.45 g/cm3. coefficient of uniformity cu 1.87 norme nf p18-560 coefficient of curvature cc 1.09 apparent density (g/cm3) 1.48 norme nf p18-554 absolute density (g/cm3) 2.54 norme nf p18-555 visual sand equivalent (%) 82 norme nf p18-598 sand equivalent with the piston (%) 68 blue value for 100g 0.07 norme nf p94-068 fineness modulus 0.9 norme nf p18-540 cao mgo fe2o3 al2o3 sio2 so3 co2 caco3 >67.4% <0.4% <2% <1% <2.2% <1% <5% <10% smaida et al., j. build. mater. struct. (2021) 8: 32-44 34 fig 1. slags of natural pozzolan before grinding. fig 2. powder of natural pozzolan after grinding < 80 µm. table 4. chemical composition of natural pozzolan. 3. test methods the stabilization of the studied dune sand is carried out by adding mass substitutes to act on the physical and mechanical behavior: physical stabilization: correction of the grading by adding 10 %, 15%, 20% and 25% of fine elements (pozzolan+lime), where those percentages are chosen according to the recommendations of the standards of road networks (setra-lcpc, 1998). mechanical stabilization: densification by compaction operation. the mixtures are denoted by ds-pz-li; where ds is the dune sand, pz the percentage of pozzolan, li the percentage of lime respectively. details of the mixtures proportions are given in table 5. table 5. mixtures proportions. mixtures % of dune sand % of natural pozzolan % of lime % of (pozzolan+lime) ds 100-0-0 100 0 0 0 ds 90-8-2 90 8 2 10 ds 85-12-3 85 12 3 15 ds 80-16-4 80 16 4 20 ds 75-20-5 75 20 5 25 4. evolution of the physical and mechanical characteristics 4.1. grain size distributions figure 3 shows the grain size distributions of the mixtures according to the standard nf p18560. there is a slight upward shift of the curve. this shift becomes more accentuated as the percentage of additive (pozzolan+lime)) is increased. this can indicate an increase in the fraction of fine elements in favor of a decrease of larger elements (ismael, 2006; tataranni, 2018) especially those less than 0.2mm. dubois (2006) has reported that the fraction of fines (% of particles whose diameter is less than 63 μm) in the mixture is more critical for providing adequate bearing capacity. the fine fraction was limited to 20% in its mixtures. schlosser (1988) has set two criteria as for respecting uniformity of curvature. these two criteria are expressed as, cu = d60/d10 > 6; cc = d30²/ (d60×d10); cu and cc are in between 1 and 3. cao sio2 al2o3 fe2o3 so3 k2o na2o mgo cl caco3 12.36% 42.95% 16.32% 9.49% 0.01% 1.39% 3.00% 4.20% 0.00% 10.75% 35 smaida et al., j. build. mater. struct. (2021) 8: 32-44 accordingly, two among our mixtures (ds 80-16-4 and ds 75-20-5) do fulfill these criteria; with a small advantage for the last mixture fig 3. grain size distribution. 4.2 evolution of the proctor characteristics these mixtures studied have been first compacted at different water contents in order to determine the optimal water content along with the maximal dry density via the modified proctor test according to the nf p94-093 normalization. by inspecting figure 4, one can see that the dry density of the mixtures is increased with a notable shift of the proctor curve to the right, and hence towards higher water contents. this is because of the binders absorb a part of the available water to their hydration resulting thus in the diminution of the water proportion acting as lubricant. furthermore, hydraulic binders are fine particles that can help to obtain an improved granulometric distribution by reducing voids. fig 4. modified proctor cure according to the percentage of pozzolan+lime. smaida et al., j. build. mater. struct. (2021) 8: 32-44 36 the sand incorporation has permitted to densify the material by increasing its density from 1.72 g/cm3 à 1.87 g/cm3 and its optimal water content (figure 5) from 5% to 11%. our results show that the incorporation of pozzolan + lime tends to improve the compaction optimal characteristics of the mixtures as compared to those of the dune sand with no adding. fig 5. optimum water content and maximum dry density according to the percentage of pozzolan + lime. 4.3 evolution of direct shear strength the studied mixtures are statically compacted at the proctor optimum prior to placement in the straight shear box. the test mode is conditioned by a fast speed of 1 mm / min corresponding to an unconsolidated undrained test (uu) according to the standard nf p 94-071-1. figure 6 shows the variation of the shear strength as a function of the normal stress. fig 6. intrinsic curves for the mixtures. 37 smaida et al., j. build. mater. struct. (2021) 8: 32-44 the cohesion of a soil represents the internal forces of attraction defined between the particles, allowing to hold firmly between them and to ensure a physical coherence. so, for a sand, the cohesion of the grains is considered to be zero (c = 0kpa). from figure 6, we note that the shear strength improves with the increase of the dosage of the hydraulic binder. this evolution is usually accompanied by an increase of the cohesion and a decrease of the angle of friction (figure 7). fig 7. evolution of cohesion and angle of friction for the mixtures the mixtures showed that the cohesion steadily increases from 0.02 bars for dune sand untreated (incoherent material) to a maximum value of 0.79 and 0.97 bars, respectively for the mixture ds 80-16-4 and ds 75-20-5. therefore, the friction angle decreases from 36.65° to 19.6° for the ds 80-16-4 and from 36.65° to 22.88° for the mixture ds 75-20-5. 4.4 evolution of bearing capacity cbr (%) the cbr test was carried out according to the standard nf p 94-078, where cbr (unsoaked) is determined immediately, just after compaction, or after four days of immersion (cbr soaked). the test consists of punching test specimens made at different compaction energies (10 blows per layer, 25 b / l and 55 b / l) in the cbr mold and at water contents corresponding to the optimum of the modified proctor test. figure 8.a illustrates the piston pressure as a function of penetration. the cbr is determined for each compaction energy, which is used to represent the variation of the dry density as a function of the cbr, and then the cbr is determined. it corresponds to 95% of the maximum of dry density obtained in the modified proctor test (figure 8.b exp: ds 75-20-5). smaida et al., j. build. mater. struct. (2021) 8: 32-44 38 fig 8. a) evolution of pression according to its penetration. b) evolution of maximum dry density according to the cbr (%). figure 9 shows the added binder (pozzolan + lime) dependent evolution of the immediate load bearing has a steep slope in the range 0-25% of added binder. the unsoaked cbr increases from 8.28% up to 41.8% whereas the soaked cbr increases from 6.45% for untreated dune sand to 12.51% for ds 75-20-5 showing a slower slope. 39 smaida et al., j. build. mater. struct. (2021) 8: 32-44 fig 9. evolution of cbr (%) at 95% of opm according to the mixtures. 4.5 evolution of compression and tensile strength a series of cylindrical specimens with dimensions (φ = 100mm, h = 100mm) was prepared according to the standard en 13286-53, for the different mixtures. the mixture is put in a single layer in a double piston mold and then statically compacted, at the dry density and the water content of the proctor modified according to en 13286-41. after that the specimens were preserved in bags at a temperature of 20 ± 2 ° c until the date of the test. these tests were performed at age of 7, 14, 28, 60 and 90 days for the compressive tests; while the tests tensile were measured by the indirect tensile strength according to the standard en 13286-42 after preparing the specimens by the same way they were preserved in bags at the same temperature until the test date of 60 days. figure 10 illustrates the evolution of the compressive strength as a function of the percentages of the binder for different curing times and figure 10.b represent the evolution of the tensile strength as a function of the added binders. figure 10 shows that the compressive strength increases very significantly and follows a linear function with the increase of the quantity of (pozzolan+lime). the effect of the added binder becomes more significant beyond 15% of (pozzolan+lime). note that compressive strength corresponding to a cure time of 90 days is greater than that corresponding to the others cure times. smaida et al., j. build. mater. struct. (2021) 8: 32-44 40 fig 10. evolution of the compressive strength according to the percentage of pozzolan+lime. fig 11. evolution of the tensile strength according to the percentage of pozzolan+lime. in a similar way to compressive strength, figure 11 confirms an increase of the tensile strength with the proportion of added pozzolan + lime. this quantity ranges from almost zero in the case of untreated dune sand to 0.28 mpa for 10% of binder (ds 90-8-2) giving thus a very clear idea of the effectiveness of our added binder. this is the case for all mixtures up to a maximum value of 0.71 mpa for the mixture (ds 75-20-5). 41 smaida et al., j. build. mater. struct. (2021) 8: 32-44 5. classification of optimal mixtures the standard nf 14227-1 states that there are 6 resistance classes from t0 to t5 and that t2, t3 and t4 are recommended for use in road layers base. table 6 summarized the mechanical characteristics of the mixtures. table 6. the mechanical characteristics of the mixtures. mechanical characteristics ds 90-8-2 ds 85-12-3 ds 80-16-4 ds 75-20-5 optimum water content (%) 8 9.8 9.9 11.7 maximum dry density (g/cm3) 1.79 1.81 1.86 1.87 cbr unsoaked at 95% of opm (%) 23.4 26.5 37 41.8 cbr soaked at 95% of opm (%) 7.57 10.35 11.1 12.55 cohesion c (bars) 0.42 0.44 0.79 0.97 friction angle (degree) 33.94 35.77 19.6 22.88 compressive strength at 60 days (mpa) 2.671 3.439 5.255 6.790 tensile strength at 60 days (mpa) 0.28 0.48 0.58 0.71 elastic modulus (mpa) 3123 4021 4533 7066 the classification is based on the tensile strength-modulus of elasticity (rt, e). the modulus of elasticity e was measured according to the standard nf 13286-43. for this classification, the curing times were considered is 60 days. the values rt360, e360 corresponding to a duration of one year are estimated from the ratio rt60 / rt360 and e60 / e360 which are respectively equal to 0.78 and 0.82 according to standard nf en 14227-5. the standard en 14227-1 recommends that materials whose torque (rt, e) is under the zone of class t2 are not used in foundation road. fortunately, our materials are located at least in the zone t2 as shown in figure 12 and therefore usable as a layer of seats. it is noted in particular that the mixture ds 75 – 20 – 5 is visibly much better than the other two because it is located in the t3 zone. fig 12. classification of mixtures according to en 14227-1. smaida et al., j. build. mater. struct. (2021) 8: 32-44 42 6. conclusion the objective of this work is to valorize dune sand in the layers of pavement foundations; this abundant material is known for its poor geotechnical properties: poorly graded, incoherent, porous, without fine elements and low bearing capacity. the improvement of these physical and mechanical properties was made by the addition of percentages of hydraulic binders (pozzolan + lime). the experimental results were very encouraging, and show that all the mixtures have resulted in sufficient mechanical characteristics to valorize this material in layers of pavement foundations, which according to these results draws the following conclusions: the incorporation of the pozzolan + lime percentages allowed to have mixtures with a spread and graduated curves. the maximum dry density and optimum water content increase proportionally to the percentages added, and therefore have a denser (compact) material. the mixed hydraulic binder (pozzolan + lime) improve mechanical characteristics: bearing capacity (cbr (%), unsoaked and soaked), shear strength, compressive strength and tensile strength. the modulus of elasticity increases in proportion to the percentage of binder added; which always confirms the effectiveness of binder (pozzolan + lime) used. the classification of our treated material shows that all the mixtures can be used in pavement foundations with an advantage for the both mixtures ds 80 16 4 and ds 75 20 – 5. 7. references afnor 1994, nf p94-071-1. sols ; reconnaissance et essais – essais de cisaillement rectiligne à la boîte partie 1 : cisaillement direct. afnor 1990 nf p18-555. granulats –mesures des masses volumiques, du coefficient d'absorption et de la teneur en eau des sables. afnor 1990, nf p18-554. granulats – mesures des masses volumiques, de la porosité, du coefficient d'absorption et de la teneur en eau des gravillons et cailloux.. afnor 1990, nf p18-560. granulats – analyse granulométrique par tamisage. afnor 1990, nf p18-598. granulats –equivalent de sable. afnor 1994, nf p94-093. sols : reconnaissance et essais détermination des références de compactage d'un matériau, essai proctor normal — essai proctor modifié. afnor 1997, nf p18-540. granulats – définitions – conformité et spécifications. afnor 1997, nf p94-078. sols : reconnaissance et essais indice cbr après immersion-indice cbr immédiatindice portant immédiat. afnor 1998, nf p94-068. sols : reconnaissance et essais mesure de la capacité d'adsorption de bleu de méthylène d'un sol ou d'un matériau rocheux détermination de la valeur de bleu de méthylène d'un sol ou d'un matériau rocheux par l'essai à la tache. afnor 2003, nf en 13286-41. mélanges traités et mélanges non traités aux liants hydrauliques partie 41: méthode d’essai pour la détermination de la résistance à la afnor 2003, nf en 13286-42. mélanges traités et mélanges non traités aux liants hydrauliques partie 42: méthode d’essai pour la détermination de la résistance à la traction indirect des mélanges traités aux liants hydrauliques. 43 smaida et al., j. build. mater. struct. (2021) 8: 32-44 afnor 2003, nf en 13286-43. mélanges traités et mélanges non traités aux liants hydrauliques partie 43: méthode d’essai pour la détermination du module d’élasticité des mélanges traités aux liants hydrauliques. afnor 2005, nf en 13286-53. mélanges traités et mélanges non traités aux liants hydrauliques partie 53 : méthode de confection par compression axiale des éprouvettes de matériaux traités aux liants hydrauliques. afnor 2005, nf en 14227-1. mélanges traités aux liants hydrauliques partie 1: mélanges granulaires traités au ciment. afnor 2005, nf en 14227-5. mélanges traités aux liants hydrauliquesspécifications partie 5: mélanges granulaires traités au liant hydraulique routier. azadegan, o., yaghoubi, e., & li, j. (2013). evaluation of the performance of lime and cement treated base layers in unpaved roads. the electronic journal of geotechnical engineering, 18, 1593-1602. cherrak, m., morsli, m., boutemeur, r., & bali, a. (2015). valorization of the use of calcareous tuff and dune sand in saharan road design. journal of civil engineering and architecture, 9, 665-676. dubois, v. (2006). etude du comportement physico-mécanique et caractérisation environnementale des sédiments marins–valorisation en technique routière, doctoral dissertation, université d’artois. ghrieb, a., mitiche-kettab, r., & bali, a. (2014). stabilization and utilization of dune sand in road engineering. arabian journal for science and engineering, 39(3), 1517-1529. grzegorz k. (2006). etude de comportement mécanique des mélanges sable/argiles. doctoral dissertation, institut national des sciences appliquées de lyon, france. haach, v. g., vasconcelos, g., & lourenço, p. b. (2011). influence of aggregates grading and water/cement ratio in workability and hardened properties of mortars. construction and building materials, 25(6), 2980-2987. ismael, n. f. (2006). influence of fines on the properties of arid climate sand deposits. in unsaturated soils, pp. 1617-1626. mehrpazhouh, a., tafreshi, s. n. m., & mirzababaei, m. (2019). impact of repeated loading on mechanical response of a reinforced sand. journal of rock mechanics and geotechnical engineering, 11(4), 804814. reddy, b. v., & gupta, a. (2008). influence of sand grading on the characteristics of mortars and soil – cement block masonry. construction and building materials, 22(8), 1614-1623. rios, s., da fonseca, a. v., & bangaru, s. s. (2016). silty sand stabilized with different binders. procedia engineering, 143, 187-195. salour, f., & erlingsson, s. (2017). permanent deformation characteristics of silty sand subgrades from multistage rlt tests. international journal of pavement engineering, 18(3), 236-246. schlosser f. (1988). eléments de mécanique des sols, presses de l’ecole nationale des ponts et chaussées, isbn 2-85978-104-8, 276p. segui, p. (2011). elaboration de liants hydrauliques routiers à base de pouzzolane naturelle ou de cendre volante de papeterie. doctoral dissertation, université de toulouse, université toulouse iii-paul sabatier. setra. (2008). technical guide. treatement of soils with lime and / or hydraulic binders –application to the construction of pavement base layers. smaida et al., j. build. mater. struct. (2021) 8: 32-44 44 setra-lcpc. (1998). assises de chaussées – guide d’application des normes pour le réseau routier national en graves non traitées et matériaux traités aux liants hydrauliques. setra-lcpc. gtr. (2000). guide technique pour la réalisation des remblais et des couches de forme. editions du setra-lcpc, fascicules i & ii, 98 p. et 102 p. shalabi, f. i., mazher, j., khan, k., amin, m. n., albaqshi, a., alamer, a., ... & alshuaibi, o. (2021). influence of lime and volcanic ash on the properties of dune sand as sustainable construction materials. materials, 14(3), 645. tataranni, p., sangiorgi, c., simone, a., vignali, v., lantieri, c., & dondi, g. (2018). a laboratory and field study on 100% recycled cement bound mixture for base layers. international journal of pavement research and technology, 11(5), 427-434. tran n.t. (2009). valorisation de sédiments marins et fluviaux en technique routière. doctoral dissertation, université d’artois, france. j. build. mater. struct. (2020) 7: 95-104 original article doi : 10.34118/jbms.v7i1.710 issn 2353-0057, eissn : 2600-6936 properties of sandcrete block produced with coconut husk as partial replacement of sand ubong williams robert1, sunday edet etuk2, okechukwu ebuka agbasi *, 3, sylvester andrew ekong1 1 department of physics, akwa ibom state university, ikot akpaden, mkpat enin, nigeria 2 department of physics, university of uyo, uyo, nigeria 3 department of physics, michael okpara university of agriculture, umudike, nigeria corresponding author: agbasi.okechukwu@gmail.com received: 20-06-2020 accepted: 19-08-2020 abstract. sandcrete block is the most popular building material in construction industry. however, with the high and increasing cost of building materials experienced nowadays, it has been difficult to achieve affordable housing especially in developing countries. also, significant dredging of sand for block production and the large amount of coconut husk thrown away as waste have increased the level of concern due to their adverse effect on environment. this work, therefore, sought to produce solid core sandcrete blocks in which sand component is partially replaced with coconut husk and investigate the suitability of using such blocks for building designs. the block samples produced using untreated and also treated coconut husks at various levels of sand replacement were subjected to bulk density, water absorption and compressive strength tests at 7 days and 28 days of curing. it was found that sand replacement with 20% of untreated coconut husk or 30% of treated coconut husk could yield a solid core sandcrete block suitable for non-load bearing walls of satisfactory performance. since coconut husk is cheaply available, sustainable, and recyclable, utilising such promising material in this case can enhance production of costeffective and optimally performing sandcrete blocks for building purposes. this will in turn help to boost the development of housing, minimise loss of agricultural lands, and reduce environmental pollution level, and so on. key words: alkalisation; bulk density; compressive strength; curing; water absorption. 1. introduction in recent decades, the drive for economic diversification has resulted in greater emphasis on coconut (cocos nucifera) production, especially, in developing countries. report by burton (2018), shows that indonesia is the largest global producer of coconut with 18,300,000 tons, followed by philippines (15,353,200 tons) and then india (11,900,000 tons). also, vanguard newspaper report published on october 17, 2019 had it that nigeria produced 364,000 metric tons of coconut yearly across 22 states out of which lagos state contributed the highest amount being 257,000 metric tons. for inculcating all the resources required by man for his survival, coconut is regarded as a must-grown tree. several benefits that can be derived from coconut include, among others, the use of its trunk for interior building insulation (etuk et al., 2005) and application of the water from its fruit (coconut water) for health purposes (prades et al., 1998; campbell-falck et al., 2000; harini, 2010). notably, coconut tree is a member of palm family called arecaceae and is known to produce between 30 and 75 fruits annually if planted on a fertile soil. each coconut fruit yields 40% husks containing 30% fibre with dust making up the rest. chemically, the husks consist of cellulose, lignin, pyroligneous acid, gas, charcoal, tar, tannin, and potassium (zafar, 2020) and they encompass 80% to 85% of the weight of coconut fruit with very high content of lignin (bolivar-telleria et al., 2018). due to the fact that priority is given to the economic and medicinal values of coconut fruits, less value is usually placed on the husks. as such, the husks are simply thrown away as waste. this practice is dangerous as a large 96 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 amount of the waste sent can reach water table and impose a great environmental risk during decomposition. there is, therefore, need to consider recycling such wastes into value-added products for use by man. one of the basic needs of humans is an affordable housing that has aesthetic value and durability. nowadays, various grades of materials can be used to build a house. in the construction industry, a mixture of sand, cement, and water in prescribed quantities yields sandcrete block, which as remarked by ojo (2015), is the most popular building material. research reports have shown that in nigeria, over 90% of walling units in houses and even physical infrastructure are constructed using sandcrete blocks (baiden and tuuli, 2004; oladeji and awos, 2013). the use of sandcrete blocks for non-load bearing and partition walls helps to control moisture infiltration and wind action, and also provides buildings with aesthetic value. as opined by omoregie (2012), such uses constitute utility value that is responsible for wide application of sandcrete blocks for building purposes within tropical rainforests where a considerable amount of precipitation and high average temperatures are predominant. another notable advantage is that sandcrete blocks neither rust nor decay unlike in the case with some other building materials. the building code of federal republic of nigeria (building code, 2006) stipulates that aesthetics, durability, functionality, character and affordability of housing must be achieved through the application of all materials and components used in construction of buildings. however, such achievement has been hampered in recent times because construction industry relies heavily on conventional building materials. the high and increasing cost of those materials, consequently, cramp the development of housing as well as other infrastructural facilities, thereby hindering compliance with the said building code. also, it has been observed that due to suitability of dredged sand for production of masonry units (akinpelu and adekanmbi, 2017), its many uses have led to significant dredging. this has eventually raised environmental concerns over fish depletion, flooding, landslides, losses of agricultural lands as well as damage to buildings. obviously, the search for alternative and cheaply available materials that can perform effectively, if utilised for building purpose, is inevitable. attempts so far made in this regard by researchers revealed that substituting high-density polyethylene for sand (ali et al., 2017), replacing fine aggregates with shredded plastic (akinyele and toriola, 2018), and partially replacing cement with eggshell ash (afolayan et al., 2017) yielded sandcrete blocks with impressive compressive strength. not only that, even concrete produced with dolomite sand waste was reported to have a set of properties very close to traditional concrete filled quartz sand (korjakins et al., 2009). in this work, coconut husk is considered for use as partial replacement of sand in the production of solid core sandcrete blocks. the major tests, such as water absorption and compressive strength, required by nigerian industrial standard for verifying the quality of sandcrete blocks (robert et al., 2019) and also bulk density required by british standard institution for the same purpose will be performed. it is hoped that the findings from this work will be useful to researchers, manufacturers/fabricators, practising engineers and designers. 2. experimental perspective 2.1 materials and their description cement (manufactured by lafarge africa plc with certification mark nis 444 – 1:2018 cem ii bl 32.5r on the product bag), potable water (free from salts, oil contaminations and suspended particles), white river sand, and brown coconut husks (in lump form) were obtained within akwa ibom state, nigeria and used as basic materials in this research work. in addition to being clean and sharp, the sand was free from dirt, loam, clay and organic matter. it was of specific gravity 2.66 and coefficient of uniformity 2.95. moreover, the coconut husk contained cellulose (24.72%), hemicelluloses (12.26%), lignin (40.13%), and tannin. ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 97 2.2 method 2.2.1 materials processing the as-received coconut husks were cut into smaller pieces using knife and then processed into two kinds, namely, untreated and treated coconut husks as described elsewhere (robert et al., 2019). in this case, the chemical modification of the husk particles was done by soaking them in 2m freshly prepared solution of sodium hydroxide for 18 hours. the sand and processed husks were sun-dried completely (figure 1 shows the dry forms of the untreated and treated coconut husks used). then after, five trial runs of sieve analysis were performed for the sand and coconut husks based on the standard procedure outlined in astm c136 / 136m, (2019). also, each of the dried materials was screened using mesh no. 10 of us sieve and the quantity that passed through the sieve was used for production of solid core sandcrete block samples in this work. fig. 1. dry forms of the (a) untreated coconut husks (b) treated coconut husks 2.2.2 production and testing of the solid core sandcrete block samples under laboratory conditions, the cement was thoroughly mixed with the sand and this was followed by addition of water when an even colour was attained consistently. all the constituents of the mixture were batched by volume method. the cement to sand ratio adopted was 1:6 and water –cement ratio of 0.5 was maintained throughout the production process. also, the resulting mixture was quickly cast in a steel mold of dimensions 100mm x 100mm x 100mm. on reaching half of the depth of the mold, a tamping bar was used to tamp the mixture with 40 strokes over the cross-section of the mold. then after, more quantity of the mixture was added and tamped as well until the mold was completely filled to its brim. the tamped mixture was demolded as fresh block sample. in this work, such sandcrete blocks produced at 0% level of sand content replacement with coconut husk served as control samples. other block samples were similarly produced but at 10%, 20%, 30%, and 40% partial replacement levels of the sand content with the untreated coconut husk, and then with the treated coconut husk. after 24 hours, all the block samples produced were kept in a shade and cured by splashing water on them twice daily (morning and evening). at curing ages of 7 days and 28 days, the block samples were tested. for each intended test at a particular curing age, three block samples were produced per formulation and used. the bulk density of each block sample was calculated as the ratio of mass to bulk volume, expressed mathematically as (1) where d= bulk density, m = mass, and v = bulk volume. for water absorption test, the mass of the block sample was determined before the block was soaked in cold water at 28oc for 24 hours. after removal of the block from the water, its mass was determined and the percentage water absorption, w.a was computed using the formula ( ) (2) 98 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 where = mass of the block sample before soaking, and = mass of the sample after soaking in water. compressive strength test was conducted by means of compression testing machine. the data obtained for the cross-sectional area and crushing force of the block sample were used to determine the corresponding compressive strength according to the equation (3) where = compressive strength of the block sample at a particular curing age, = minimum force required to crush the block sample and = cross-sectional area of the block. the mean values of the results obtained for each of the tests were determined with their standard error and tabulated. 3. results and discussion the results of the sieve analysis of the sand and coconut husk used in the production of the block samples are recorded in table 1. also, the results of the tests performed on the block samples at different curing periods for various levels of sand partially replaced with coconut husk are presented in table 2. the aggregates distribution curves of the sand and coconut husks are illustrated in figure 2. as can be seen, the grading curves for the sand and coconut husks fall within the grading limits for zone one of bs 882 aggregates (bs 882, 1992). this signifies that the sand and coconut husks are well graded and therefore, suitable for use as fine aggregates in sandcrete block production. it can be seen from table 2 that for a particular sand replacement level, the mean values of bulk density at 28 days of curing are greater than the results obtained at the curing period of 7 days irrespective of whether uch or tch is used. this may be attributed to the effect of hydration and it implies that increase in curing duration enhances higher degree of compaction by allowing proper hardening of the blocks. also, it can be observed that at a particular curing age, block samples containing the tch have greater mean values of bulk density than their counterparts in which the uch is used as partial sand replacement material. this is obviously due to alkalisation of raw coconut husk with sodium hydroxide solution to obtain the tch used in this work. in other words, the alkaline treatment given to raw coconut husk to get the tch leads to the removal of light and dusty particles that characterise uch. as such, tch is denser than uch and consequently, block samples produced with a particular proportion of the tch become denser than those with the uch content of same proportion. with respect to the minimum bulk density of 1500 kg m-3 specified in bs2028 (1975) for blocks made with lightweight aggregates, it can be deduced that the least mean values of bulk density obtained in this work exceed the standard lower limit requirement by not less than 5.03%. this means that partial substitution of the sand with 40% of the uch or tch can yield solid core lightweight sandcrete blocks that are suitable for interior building design. table 1. results of sieve analysis of the sand used sieve size (mm) percentage passing (%) lower limit mean ± std. error upper limit sand coconut husk 4.750 90 99.04 ± 0.09 99.86 ± 0.07 100 2.360 60 87.60 ± 0.02 87.67 ± 0.05 95 1.180 30 65.73 ± 0.03 65.80 ± 0.03 70 0.600 15 27.78 ± 0.02 26.61 ± 0.05 34 0.300 6 17.76 ± 0.02 14.73 ± 0.04 20 0.150 1 2.28 ± 0.01 1.51 ± 0.02 10 0.075 0.1 0.44 ± 0.01 0.28 ± 0.01 1 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 99 table 2. results of the tests performed on the block samples curing age of the samples sand replacement material level of sand replaced with the material (%) mean (with standard error) values of the test properties bulk density, d (kgm-3) water absorption, w.a (%) compressive strength, cs (n/mm2) 7 days uch 0 2032.68 ± 2.39 2.23 ± 0.07 4.35 ± 0.03 10 1817.18 ± 3.12 2.49 ± 0.04 2.78 ± 0.03 20 1779.42 ± 1.98 2.88 ± 0.01 2.49 ± 0.03 30 1708.24 ± 2.38 3.34 ± 0.04 1.97 ± 0.01 40 1575.40 ± 3.75 3.97 ± 0.07 0.98 ± 0.03 tch 0 2032.68 ± 2.39 2.23 ± 0.07 4.35 ± 0.03 10 1978.44 ± 3.88 4.28 ± 0.02 3.96 ± 0.05 20 1922.75 ± 3.42 5.43 ± 0.05 3.55 ± 0.04 30 1814.45 ± 2.74 5.78 ± 0.03 2.76 ± 0.03 40 1749.66 ± 2.94 6.28 ± 0.04 2.25 ± 0.03 28 days uch 0 2077.92 ± 3.62 2.45 ± 0.03 4.67 ± 0.05 10 1915.22 ± 5.09 2.90 ± 0.04 3.49 ± 0.04 20 1804.56 ± 5.04 3.10 ± 0.03 2.67 ± 0.04 30 1727.15 ± 2.90 3.72 ± 0.04 2.12 ± 0.03 40 1612.23 ± 4.02 4.25 ± 0.04 1.27 ± 0.05 tch 0 2077.92 ± 3.62 2.48 ± 0.03 4.67 ± 0.05 10 2009.27 ± 2.12 4.79 ± 0.03 4.18 ± 0.03 20 1979.44 ± 2.62 5.63 ± 0.04 3.96 ± 0.04 30 1858.27 ± 2.93 5.90 ± 0.05 3.07 ± 0.04 40 1753.86 ± 4.28 6.29 ± 0.05 2.32 ± 0.04 uch = untreated coconut husks; tch = treated coconut husks figure 3 shows that for both curing durations, the bulk density of the block samples decreases with increase in the proportion of either uch or tch used. fig. 2. plots of sand and coconut husks gradation and limits of zone 1 aggregates to bs 882:1992 this simply portrays the fact that coconut husk is lighter than sand. thus, the more the added quantity of uch or tch is, the lower the bulk density of the block samples becomes. it can be deciphered from the plots that with the use of the uch, the initial decrease in the mean values of 100 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 the bulk density is more pronounced than in the case of utilising the tch in the production of the block samples. this observation therefore confirms the verity of the finding that tch is denser than uch as asserted above. fig. 3. variation of bulk density with coconut husk level in the block samples in the case of water absorption, the results registered in the table show that the mean values of percentage water absorption vary directly with the age of curing for each proportion of sand replaced with the coconut husks. it could be suggested that since hydration proceeds with the presence of evaporable water, increase in age of curing may affect the pore structure of the block samples in such a way that it enhances greater tendency for water permeability from the surface into interior part. from the results presented, it can be observed that there is a marked increase in the mean values of percentage water absorption at a particular curing period of the block samples when sand is partially replaced with the tch unlike when the uch of same proportion is used. this clearly indicates that the use of uch enhances water repellent capability of the block samples whereas sand replacement with tch does the opposite as a result of its nature. meanwhile, the cell wall of uch is covered with highly hydrophobic impurities like lignin, hemicelluloses, tannin, and so on. the removal of a great amount of such materials from the raw coconut husk yields the tch which is mainly cellulose with rougher surface, increased hydrophilicity and high porosity. hence, at a particular age of curing, the amount of water absorbed by block samples in which sand component is partially replaced with the tch is greater compared to the case of blocks made with the uch material of same proportion. in other words, the alkaline treatment employed changes the morphology of the raw coconut husk and increases water absorption capability of the resulting tch. this finding resonates with the submission of faola et al., (2013). statistically, assessing the water absorption test results at 0.05 level of significance using one-way analysis of variance between the use of the uch and application of the tch gives calculated f-values of 5.35 and 5.34 for 7 days and 28 days curing periods respectively. when comparing the critical f-value (5.32) with the calculated values obtained, it shows that a significant difference is established in the instant case. in this work, the highest recorded mean value of percentage water absorption (6.29 ± 0.05) % is observed to be about (5.17 ± 0.05) % less than the maximum value of 12% stipulated in nis 87, (2007). this shows that with up to 40% content of the uch or tch, solid core sandcrete blocks can be produced to have water absorption capacity that satisfies the standard requirement for building design. the trend in the variation of percentage water absorption with the proportion ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 101 of coconut husk used to replace sand in the block samples is illustrated in figure 4. observably, there is increase in the percentage water absorption with added proportion of either the uch or tch at both curing ages. this indicates that the coconut husk materials (untreated and treated) have greater water absorption tendency than the sand used in producing the block samples. at the age of 28 days, the plots show that the percentage water absorption of the block samples tends to stabilise when 10% to 20% of the sand content is replaced with the uch. in the case of using the tch, such behaviour is exhibited between 20% and 30% levels of partial sand replacement. fig. 4. variation of water absorption with coconut husk level in the block samples furthermore, the results presented reflect that the compressive strength of the block samples vary in consonance with the age of curing. this observation is fully supported by the report of dashan and kamang (1999). the possibility of it may be due to hydration since such chemical reaction leads to reduction in the porosity of cement used while the evaporable water ensures gain in the strength of the block samples. when comparing the uch with the tch in terms of their degree of influence as sand partial replacement materials in the block samples, the results obtained show an appreciable improvement with the use of the tch at either age of curing. as a matter of fact, the presence of hydroxyl and polar groups in the uch leads to weak interfacial bonding, which implies ease of crushing of block samples containing it (that is, the uch). on the contrary, the chemical treatment with sodium hydroxide solution employed to produce the tch from raw coconut husk increases the surface adhesion and enables the tch to have a greater bonding ability than the uch. based on the results recorded, it can be argued that when up to 20% content of the uch or 30% component of the tch is used, the block samples produced meet the minimum requirement of 2.5n/mm2 according to nis 87, (2007) for nonload bearing walls. however, since 3.5n/mm2 is also the minimum value recommended for load bearing walls, it is important to mention here that in addition to block samples made with 0% content of coconut husk, only those containing up to 10% sand partial replacement with the uch and cured for 28 days or others similarly developed with at most 20% content of the tch and cured for at least 7 days can give satisfactory performance as well (even though they contain light weight aggregates). the graphical depiction of decrease in compressive strength of the block samples as the proportion of the uch or tch increases (figure 5) confirms that bulk density has influence on the compressive strength of the blocks. there is no doubt that after the chemical treatment process, the number of dead air cells present in uch is very much reduced in 102 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 the tch. eventually, cell wall densification is increased with improvement of adhesion in the tch, thereby increasing the bulk density and compressive strength of the block samples in which it is used. but due to the refractory nature of coconut husk, adding more quantity of the uch or tch brings about decrease in compressive strength. by testing the results obtained at 0.05 level of significance using pearson’s product moment correlation, the coefficients reveal that there exists a very high positive relationship between bulk density and compressive strength of the block samples. fig. 5. variation of compressive strength with coconut husk level in the block samples 4. conclusion untreated and treated coconut husks were separately utilised at the same proportions to partially replace sand in the solid core sandcrete block samples produced and tested at curing periods of 7 days and 28 days in this work. at both ages of the block samples, the experimental verdicts showed increase in percentage water absorption but decrease in bulk density and compressive strength with increasing proportions of either the untreated or treated coconut husks used. also, for a particular age of curing, all the properties examined were found to be of higher value in the case of block samples containing the treated coconut husk compared to their counterparts with untreated coconut husk component. based on the requirements stipulated by nigerian industrial standard and british standard institute for solid core sandcrete blocks, it was observed that the block samples produced by partially replacing sand content with up to 40% of coconut husk (either untreated or treated) and cured for at least 7 days are lightweight with water absorption capacity suitable for non-load bearing walls. however, it was evident that if emphasis is solely on compressive strength, then sand replacement with 20% of untreated coconut husk or 30% of treated coconut husk should be the ultimate choice for satisfactory performance of the developed sandcrete blocks in building designs. 5. references afolayan, j. o., oriola, f. o. p., moses, g., & sani, j. e. (2017). investigating the effect of eggshell ash on the properties of sandcrete block. international journal of civil engineering, construction and estate management, 5(3), 43 – 54. akinpelu, a.t. & adekanmbi, j. (2017). comparing compressive strength of sandcrete blocks made with sand from different sources. researchjournali's journal of civil engineering, 3(4), 2 – 6. ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 103 akinyele, j. o., & toriola, i. o. (2018). the effect of crushed plastics waste on the structural properties of sandcrete blocks. african journal of science, technology, innovation and development, 10(6), 709-713. ali, n., din, n., khalid, f. s., shahidan, s., abdullah, s. r., samad, a. a. a., & mohamad, n. (2017). compressive strength and initial water absorption rate for cement brick containing high-density polyethylene (hdpe) as a substitutional material for sand. series: materials science and engineering, 271, 012083. astm c136/136m, (2019). standard test method for sieve analysis of fine and coarse aggregates, astm international, west conshohocken, pennsylvania. baiden, b. k., & tuuli, m. m. (2004). impact of quality control practices in sandcrete blocks production. journal of architectural engineering, 10(2), 53-60. bolivar-telleria, m., turbay, c., favarato, l., carneiro, t., de biasi, r. s., fernandes, a. a. r., santos, a.m.c. & fernandes, p. (2018). second-generation bioethanol from coconut husk. biomed research international, article id 4916497, 20 pages. bs 2028, (1975). british standard institute, precast concrete blocks. london. bs 882, (1992). british standard institutions, specification for aggregate from natural sources for concrete. london. building code, (2006). federal republic of nigeria: national building code, first edition. burton, j. (2018). the world leaders in coconut production, www.worldatlas.com last accessed: april 19, 2018. campbell-falck, d., thomas, t., falck, t. m., tutuo, n., & clem, k. (2000). the intravenous use of coconut water. the american journal of emergency medicine, 18(1), 108-111. dashan, i.i. & kamang, e.e.j. (1999). some characteristics of rha/opc concretes: a preliminary assessment. nigerian journal of construction technology and management, 2(1), 22 – 28. etuk, s. e., akpabio, l. e., & akpabio, k. e. (2005). determination of thermal properties of cocos nucifera trunk for predicting temperature variation with its thickness. the arabian journal for science and engineering, 30(1a), 121-126. faola, a. e., oladele, i. o., adewuyi, b. o., & oluwabunmi, k. e. (2013). effect of chemical treatment on water absorption capability of polyester composite reinforced with particulate agro-fibres. chemistry and materials research, 3(13), 106-112. harini, s. (2010). coconut water. american society for nutrition. https://nutrition.org/coconut-water/ last accessed: june 21, 2020. korjakins, a. śahmenko, g. bajare, d. gaidukovs, s. & pizele, d. (2009). producing of concrete by using a dolomite waste as an alternative filler. ěpitǒanyag-journal of silicate based and composite materials, 61(2), 44 – 47. nis 87, (2007). nigerian industrial standard: standard for sandcrete blocks, standard organisation of nigeria, lagos. ojo, o.j. (2015). post project review of lumber used for construction of building projects in osun state, nigeria. international journal of scientific research and innovation technology, 2(4), 39 – 49. oladeji, o. s., & awos, o. a. (2013). assessment of materials and process variables on regulatory compliance of sandcrete blocks: a case study of ogbomoso, nigeria. international journal of engineering research and applications, 3(6), 793-799. omoregie, a. (2012). impact of vibration time on compressive strength of hardened sandcrete building blocks. buildings, 2(2), 153-172. prades, a., dornier, m., diop, n., & pain, j. p. (2012). coconut water uses, composition and properties: a review. fruits, 67(2), 87-107. 104 ubong williams robert et al., j. build. mater. struct. (2020) 7: 95-104 robert, u. w., etuk, s. e., umoren, g. p., & agbasi, o. e. (2019). assessment of thermal and mechanical properties of composite board produced from coconut (cocos nucifera) husks, waste newspapers, and cassava starch. international journal of thermophysics, 40(9), 83. zafar, s. (2020). uses of coconut wastes, www.bioenergyconsult.com last accessed: january 18, 2020. j. build. mater. struct. (2020) 7: 76-86 review article doi : 10.34118/jbms.v7i1.707 issn 2353-0057, eissn : 2600-6936 analysis of autoclaved aerated concrete (aac) blocks with reference to its potential and sustainability mohammad arif kamal arhitecture section, aligarh muslim university, aligarh india. corresponding author: architectarif@gmail.com received: 11-06-2020 accepted: 14-07-2020 abstract. the traditional bricks are the main building materials that are used extensively in the construction and building industry. autoclaved aerated concrete blocks are recently one of the newly adopted building materials. the autoclaved aerated concrete (aac) is a product of fly ash which is mixed with lime, cement, and water and an aerating agent. the aac is mainly produced as cuboid blocks and prefabricated panels. the autoclaved aerated concrete is a type of concrete that is manufactured to contain lots of closed air voids. the aac blocks are energy efficient, durable, less dense, and lightweight. it is manufactured by adding a foaming additive to concrete in different sizes of molds as per requirement, then wire-cutting these blocks or panels from the resulting ‘cake lump’ and ‘heating them with steam. this process is called as autoclaving. it has been observed that this material is an ecofriendly building material that is being manufactured from industrial waste and is composed of non-toxic ingredients. in this paper, an overview of aac blocks with reference to its potential and sustainability as a novel building material has been presented. the paper also presents a comparative cost analysis of aac blocks with the red clay bricks and its suitability and potential use in the construction in the building industry. key words: aac blocks; performance, potential, walling system; sustainability. 1. introduction the traditional bricks are the main building materials that are used extensively in the construction and building industries in india. due to the rapid urbanization and expanding interest for development materials, block furnaces have quickly developed which have legitimately or in a roundabout way caused a progression of ecological and medical issues. at a worldwide level, ecological contamination from block making activities adds to the wonders of an earth-wide temperature boost and environmental change. the different kinds of blocks can be utilized as an option in contrast to the red blocks, to diminish natural contamination and global warming. aac blocks might be one of the answers for block substitution. like froth concrete, autoclaved aerated concrete (aac) is one of the confirmed green structure materials, which can be utilized for business, modern and private development. it has the basic properties required for use as a structured segment. because of the lightweight and high solidarity toweight proportion of circulated air through solid items, their utilization brings about an obvious economy in the auxiliary individuals, and along these lines spare concrete and steel support. fig. 1 shows an aac block, (brand name as aerocon blocks). fig 1. aerated autoclaved concrete (aac) blocks. mailto:architectarif@gmail.com kamal arif m., j. build. mater. struct. (2020) 7: 76-86 77 the autoclaved aerated concrete (aac) was created and developed in 1924 by the swedish architect dr. johan axel eriksson, along working with professor henrik kreüger at the royal institute of technology (rajan, 2013). it is an eco-accommodating structural material that originates from modern waste and is produced by using non-poisonous and non-toxic ingredients. with aac, the development procedure can be around 20 percent quicker. it weighs just around 50 percent of a standard solid square and has high warm protection and is acousticsaccommodating. it additionally has preferable imperviousness to fire over fly debris and is nonburnable. it's non-hypersensitive and henceforth keeps up the nature of air inside a structure without changing its properties after some time. with aac, the development procedure can be around 20 percent quicker. it weighs just around 50 percent of a standard solid block and has high thermal insulation and acoustical properties. it's non-unfavorably susceptible and consequently keeps up the nature of air inside a structure without changing its properties after some time. the utilization of aac block can lessen development costs by about 2.5 percent for structures, for example, schools and medical clinics, and diminish the running expenses of lodging and places of business by to 30 to 40 percent after some time. fig. 1 shows an aac block, (brand named as aerocon blocks).as indicated by one report, aac now represents over 40% of all development in the united kingdom and over 60% of development in germany (schnitzler, 2016). 2. raw materials used in manufacturing of aac blocks as compared to most other concrete building applications in the construction industry, aerated autoclaved concrete (aac) is created utilizing no total bigger than sand. quartz sand, calcined gypsum, lime (mineral) as well as concrete and water are utilized as a coupling specialist. in certain nations, similar to india and china, fly debris produced from thermal power plants and having 50-65% silica content is used as an aggregate. there are many raw materials which are used in the manufacturing of aac blocks. the aerated autoclaved concrete (aac) comprises of flyash or sand as the major component. the percentage proportion of fly ash is 65-70% and coarse sand is 55-65%. the percent proportion of cement 53 grade opc with flyash is 6-15% and with sand is 10-20 %, the percent proportion of lime with flyash is 18-25% and with sand 20-30 %, the percent proportion of gypsum with flyash is 3-5% and with sand is 2-3 %. the percent portion aluminium powder paste (600 kg/m3) is 8 % or 0.05%–0.08% by volume (contingent upon the pre-indicated thickness). the water percent with flyash is 0.6 and with sand is 0.65 %. 3. specifications and performance summary of aac blocks the product specification and its performance summary of aac blocks are summarized as below (kamal, 2016): 3.1. appearance the autoclaved aerated concrete (aac) is light-hued and contains numerous small voids that can be observed when taken a gander at intently. the gas used to 'froth' the solid during the manufacturing process is hydrogen from the chemical reaction from the aluminum paste with alkaline soluble components in the cement concrete. these air pockets add to the material's protecting properties. in contrast to stonework, there is no immediate way for water to go through the material; be that as it may, it can suck up dampness and a suitable covering is required to forestall water infiltration. 3.2. size and density the autoclaved aerated concrete (aac) blocks are made of 625 mm length, 250 mm tallness, and of different thicknesses: 100, 125, 150, 200, 225, 250, 300 mm with a resistance of ±1.5 mm. the thickness of the block is 600 to 650 kg/cum, though the blocks have a thickness of 1750 to 2000 78 kamal arif m., j. build. mater. struct. (2020) 7: 76-86 kg/cum. the density of wet blocks is around 800 kg/cum as compared to that of red clay bricks (2400 kg/cum). 3.3. structural capability the compressive quality of autoclaved aerated concrete (aac) blocks is excellent. the compressive quality is from 35 to 50 kg/cm2 (according to is: 2185). although it is one-fifth the thickness of typical solid it despite everything has a large portion of the bearing quality, and loadbearing structures up to three stories high can be securely raised with aac blockwork. the aac is 3-4 times lighter than traditional bricks, therefore, easier and cheaper to transport. usage reduces the overall dead load of a building, thereby allowing the construction of taller buildings. entire building structures can be made in aac from walls to floors and roofing with reinforced lintels, blocks, and floor, wall and roofing panels available from the manufacturer. aac floor panels can be used to make non-loadbearing concrete floors that can be installed by carpenters. lightweight blocks diminish the mass of a structure, along these lines diminishing the effect of tremor on a structure. 3.4. thermal mass the thermal mass performance of autoclaved aerated concrete (aac) is dependent on the climate in which it is used. with its mixture of concrete and air pockets, aac has a moderate overall level of thermal mass performance. its use for internal walls and flooring can provide significant thermal mass. the temperature moderating thermal mass is most useful in climates with high cooling needs. 3.5. insulation the autoclaved aerated concrete (aac) has very good thermal insulation qualities relative to another masonry. a 200mm thick aac wall gives an r-value rating of 1.43 with 5% moisture content by weight. with a 2–3mm texture coating and 10mm plasterboard internal lining it achieves an r rating of 1.75 (a cavity brick wall achieves 0.82). a texture-coated 100mm aac veneer on a lightweight 70mm or 90mm frame filled with bulk insulation achieves a higher r rating than an otherwise equivalent brick veneer wall (see insulation; lightweight framing). relative to their thickness, the thermal conductivity of aac blocks is 0.16 kw/m°c against 0.70 of bricks, thus recurring energy cost is reduced in air conditioning. aac panels provide less insulation than aac blockwork, e.g. a 100mm blockwork aac wall has a dry state r-value of 0.86, and a 100mm aac wall panel has a dry state r-value of 0.68. 3.6. sound insulation with its closed air pockets, autoclaved aerated concrete (aac) can provide very good sound insulation. it has superior sound absorption qualities due to the porous structure of blocks. combining the aac wall with an insulated asymmetric air cavity system gives a wall excellent sound insulation property. aac offers sound attenuation of about 42 db, blocking out all major sounds and disturbances. the sound reduction index is 45 db for 200 mm thick block walls (against 50 for 230 mm thick wall). it is ideal for schools, hospitals, hotels, offices, multi-family housing, and other structures that require acoustic insulation. 3.7. fire and vermin resistance autoclaved aerated concrete (aac) is inorganic, incombustible and does not explode; it is thus well suited for fire-rated applications. depending on the application and the thickness of the blocks or panels, fire ratings up to four hours can be achieved. aac is non-combustible and fireresistant up to 1600° c. it can withstand up to 6 hours of direct exposure. due to the structure of kamal arif m., j. build. mater. struct. (2020) 7: 76-86 79 blocks, aac cannot be damaged or infested by termites and other pests. it does not attract rodents or other pests nor can it be damaged by such. 3.8. durability and moisture resistance the purposely lightweight nature of autoclaved aerated concrete (aac) makes it prone to impact damage. with the surface protected to resist moisture penetration, it is not affected by harsh climatic conditions and does not degrade under normal atmospheric conditions. the level of maintenance required by the material varies with the type of finish applied. the porous nature of aac can allow moisture to penetrate to depth but the appropriate design (damp proof course layers and appropriate coating systems) prevents this happening. aac does not easily degrade structurally when exposed to moisture, but its thermal performance may suffer. several proprietary finishes (including acrylic polymer-based texture coatings) give durable and waterresistant coatings to aac blockwork and panels. they need to be treated similarly with acrylic polymer-based coatings before tiling in wet areas such as showers. 3.9. water absorption in autoclaved aerated concrete (aac) curing takes place at a high temperature and high pressure in saturated steam. during curing, part of the siliceous material (flyash) reacts chemically with the calcareous ingredients such as lime liberated by the hydration of cement to form a micro-crystalline structure of tobermorite with much lower specific surface and is characterized by pores formed by the release of h2 gas during casting-rising stage of production. 3.10. toxicity and breathability the aerated nature of aac facilitates breathability. there are no toxic substances and no odor in the final product. however, aac is a concrete product and calls for precautions similar to those for handling and cutting concrete products. it is advisable to wear personal protective equipment such as gloves, eyewear, and respiratory masks during cutting, due to the fine dust produced by concrete products. if low-toxic, vapor-permeable coatings are used on the walls, and care is taken not to trap moisture where it can condense, aac may be an ideal material for homes for the chemically sensitive. 3.11. constructability, availability, and cost although aac is relatively easy to work, it is one-fifth the weight of concrete comes in a variety of sizes and is easily carved, cut and sculpted, it nevertheless requires careful and accurate placement: skilled trades and good supervision are essential. different sizes of blocks help reduce the number of joints in wall masonry. lighter blocks make construction easier and faster. it reduces construction time by 20%. they are easy to install. aac sets and hardens quickly. blocks can be easily cut, drilled, nailed, milled, and grooved to fit individual requirements. thickbed mortar is more forgiving but is uncommon and not the industry preferred option. it also simplifies hydro-sanitary and electrical installations, such as pipes or ducts, which can be installed after the main construction is complete. the construction process with aac produces little waste as blockwork offcuts can be reused in wall construction. 4. autoclaved aerated concrete (aac) block walling system the aac blocks are generally used in the wall masonry. the process of laying and construction of a complete wall unit is summarized in the following steps (majumdar, 2019). 80 kamal arif m., j. build. mater. struct. (2020) 7: 76-86 4.1. laying of blocks in laying aac blocks, the procedure is the same as that for conventional half brickwork except that the block should be slightly wet with a sprinkler before use and not soaked as in case of bricks. a. before laying the first course the alignment of the wall is marked over the dpc. b. the blocks for 1st course should first be laid dry without mortar along a stretched thread between properly located corners of the wall to determine the correct position of the blocks, including those of cross walls joining it and also to adjust their spacing within the wall length. c. when the blocks are set in a proper position, the two corner blocks are removed. a specified mortar bed is spread for the required bed thickness (10mm). d. the blocks are laid back in place with true level and plumb. e. the thread is then stretched tightly along with the faces of the two corner blocks and the faces of the intermediate blocks are adjusted to coincide with the thread line. f. each intermediate block is removed and re-laid with mortar. g. after every three or four blocks, layers are laid, their correct alignment level and verticality are checked. h. in the vertical joints, the mortar is applied only on the face of the blocks. 4.2. electrical and plumbing installations electrical and plumbing installations in aac masonry are placed in routed chases. care should be taken when laying out chases to ensure that the structural integrity of the aac elements is maintained. do not cut reinforcing steel or reduce the structural thickness of the aac elements except where permitted by the designer. in vertically spanning aac elements, horizontal routing should be permitted only in areas with low flexural and compressive stresses. in horizontally spanning aac elements, vertical routing should be minimized. 4.3 exterior finishes unprotected exterior aac deteriorates when exposed to cycles of freezing and thawing while saturated. to prevent such freeze-thaw deterioration, and to enhance the aesthetics and abrasion resistance to aac, exterior finishes should be used. they should be compatible with the underlying aac in terms of thermal expansion and modulus of elasticity and should be vapor permeable. many different types of exterior finishes are available. polymer-modified stuccos, paints, or finish systems are the most common exterior finish for aac. they increase the aac’s water-penetration resistance while allowing the passage of water vapor. heavy acrylic-based paints containing aggregates are also used to increase abrasion resistance. there is generally no need to level the surface, and horizontal and vertical joints may be chamfered as an architectural feature or may be filled. 4.4 interior finishes interior finishes are used to enhance the aesthetics and durability of aac. they should be compatible with the underlying aac in terms of thermal expansion and modulus of elasticity and should be vapor permeable. a. many different types of interior finishes are available. interior aac wall panels may have a thin coat of a mineral-based plaster to achieve a smooth finished surface. lightweight interior gypsum-based plaster may provide a thicker coating to level and straighten walls, and to provide a base for decorative interior paints or wall finishes. interior kamal arif m., j. build. mater. struct. (2020) 7: 76-86 81 plasters have bonding agents to enhance their adhesion and flexibility and are commonly installed by either spraying or troweling. b. for commercial applications requiring high durability and low maintenance, acrylicbased coatings are often used. some contain aggregates to enhance abrasion resistance. c. when ceramic wall tile is to be applied over aac, surface preparation is normally necessary only when the aac surface requires leveling. in such cases, a portland cement or gypsum-based parge coat is applied to the aac surface before setting the ceramic tile. the ceramic tile should then be adhered to the parged wall using either a cement-based thin-set mortar or an organic adhesive. in moist areas such as showers, only a portland cement-based parge coat should be used, and the ceramic tile should be set with cementbased, thin-set mortar only. 4.5 service lines for concealed or piping, a block wall can be chased using hand or electric router. depths of vertical chases should be limited to one-third of the wall thickness and horizontal chases to onesixth of the wall thickness. holes in a block wall can be made with a standard hand or electric drill. the chases shall be refilled with a leaner mortar and chicken mesh shall be applied to that area and cured. 4.6 lintels precast or cast-in-situ concrete lintels can be used in block masonry, over all openings. lintels shall always rest on a full block with a minimum bearing as under. below the openings, the rcc band should be provided with reinforcement to avoid diagonal tension cracks. the bond beam to be extended up to 300 mm from window corners both sides. 4.7 plastering followings are the points that should be considered while plastering the aac walls: a. do not soak the wall before plastering. the wall shall be moistened evenly before applying the plaster. a fog spray is recommended for this purpose. b. for external plastering has to be carried out in two coats, apply sbr coating with sand on the block surface will enhance the bonding and minimize the thickness of plastering. c. it is recommended to use cement mortar 1:6 for internal & external plastering works and preferably use ppc cement for masonry and plastering works to minimize shrinkage cracks. d. plastering thickness can be minimized to 10 mm and 15 mm for internal and external walls. 4.8 precautions while laying the aac masonry blocks the cracks occurring in block masonry and plastering are of any structural problem involving stability and safety to the structure. but it is advised to minimize the same to have good appearance and maintenance-free. a. do not store the blocks on an unleveled surface b. do not use wet blocks for masonry construction c. do not make the holes on block masonry for scaffolding supports d. do not soak the blocks before use e. do not hammer the block masonry for service lines, chases, etc. f. do not completely wet the block masonry before plastering works g. do not chase the blocks back to back for lesser thickness blocks. 82 kamal arif m., j. build. mater. struct. (2020) 7: 76-86 5. advantage of autoclaved aerated concrete (aac) block autoclaved aerated concrete (aac) has many advantages as compared to other cement concrete materials. the basic advantage is that it is cost-efficient and eco-friendly with having a low environmental impact. in the manufacturing of aac blocks, the topsoil of the earth's surface is not used; therefore it emits very low carbon dioxide as compared to red clay bricks. since aac blocks are an industrial product manufactured with machines, the quality of the end products is very good, uniform, and consistent. the blocks are even and well finished from all sides, therefore the thickness of wall plaster is reduced. due to its lightweight, there will also be a reduction of dead weight in the structural system, which will lead to the saving of steel and concrete. also this lead to construction more stories or taller buildings. the economy is achieved in multistoried, especially buildings by using aac blocks as compared to red clay bricks due to a significant reduction in the dead weight of the structure; and hence it reduces the cost of the rcc framed structure. the aac blocks have a lot of pores and voids; hence it provides better sound absorption and insulation as compared to red clay bricks or concrete blocks. the aac blocks have a low thermal conductivity which is approximately 0.24 kw-m/°c, which results in the saving of electricity costs by 30%, which is required for heating and cooling of the house. the manufacturing process of aac blocks is non-polluting. the by-product from the manufacturing industry is only steam. all the ingredients to manufacture the aac blocks are non-toxic and safe. the aac blocks are fire resistant and non-combustible. they can tolerate up to 6 hours of direct exposure to fire. the aac blocks have air voids and hence have better fire-resisting property compared to red clay bricks. the melting point of the aac blocks is over 1600 °c more than twice the typical temperature in building fire 650 °c. the aac blocks are easy to work with i.e they can be easily cut nailed and drilled and can be fitted to the individual requirements which give more design flexibility. it cannot be rotten easily since it is pest and termite-proof. the aac walling system has a simplified hydro-sanitary and electrical installations, such as pipes or ducts, which can be installed after the main construction is completed. it also has low maintenance and it reduces the operating and maintenance cost by 30% to 40%. the chemical mortars can be used for joining the aac blocks in masonry work; hence this reduces the material consumption for cement mortar and also there is no need for the curing. the aac blocks are suitable both for non-load bearing strictures and also for reinforced cement concrete structure in partition walls. 6. disadvantage of autoclaved aerated concrete (aac) block there are many advantages of using aac block, which has made this material a very suitable and sustainable material in the building and construction sector. but there are also a few disadvantages of using aac blocks. it has been observed that the aircrete cracks after installation in the rainy season, which can be avoided by reducing the strength of the mortar and ensuring the blocks, are dry during and after installation. the aac blocks should be handled carefully then as compared to red clay bricks to avoid breakages since it is little brittle. due to its brittle nature, it requires long thin screws when fitting cabinets and wall hangings. the initial cost of the manufacturing industry is a bit high. there are not many factories, which are producing aac blocks; therefore it is not very easily available. kamal arif m., j. build. mater. struct. (2020) 7: 76-86 83 7. comparative analysis of aac block, clay brick and clc block the comparative analysis of autoclaved aerated concrete (aac) blocks, red clay bricks, and cellular light weight concrete (clc) blocks are summarized in table 1: table 1. comparison of aac block, clay bricks, and clc blocks (kulbhushan et al, 2018). s. no parameter aac blocks clay red bricks clc blocks 1 raw materials cement, fly ash, water, and air entraining agents locally available clay cement, lime, specially grinded sand, foam 2 size 400-600mm x 200mm x 150mm – 300mm 225mm x 75mm x 100/150mm 400-600 x 200 x 100/150/200 mm 3 variation size 1.5 mm (+/-) 5 mm (+/-) 5 mm (+/-) 4 compressive strength (as per is codes) 3-4 n/mm2 3.5 n/mm2 2 -2.5 kg/cm2 5 dry density (as per is codes) 550-650 kg/m3 its one-third of the weight of clay brick which makes it easy to lift and transport 1800 kg/m3 800 kg/m3 6 cost-benefit for high rise buildings, there will be a reduction of deadweight which leads to saving in concrete and steel quantities. as easily available in the local market hence it is beneficial for low rise structure. for high rise buildings, there will be a reduction of deadweight which leads to saving in concrete and steel quantities. 7 fire resistance (8″ wall) up to 4 hours around 2 hours around 4 hours 8 quality of end product factory-made product. so the quality of the end product is consistent and good locally made products. quality depends on various parameters like quality of raw materials used, the process of manufacture, etc., the quality of the end product depends on the foam used and degree of quality control 9 sound insulation better sound absorption /insulation as compared to bricks normal better sound absorption /insulation as compared to bricks 10 energy saving low thermal conductivity (0.24 kw-m/c) helps in saving electricity costs 30% for heating and cooling of the house high thermal conductivity (0.81 kw-m/c). so no significant cost savings low thermal conductivity (0.32 kw-m/c) helps in saving electricity costs 30% for heating and cooling of the house 11 environmental friendliness in aac block there is no topsoil consumption and it emits very low carbon dioxide as compared to red clay one sq ft of carpet area with clay brick walling will consume 25.5 kg of topsoil (approx.). it damages the environment in clc block there is no topsoil consumption and it emits very low carbon dioxide as compared to red clay 84 kamal arif m., j. build. mater. struct. (2020) 7: 76-86 bricks while manufacturing bricks while manufacturing. 12 internal and external plaster as these bricks have dimensional accuracy, the internal and external plaster thickness can be reduced requires thick plaster surface as there are variations in the dimensions as these bricks have dimensional accuracy, the internal and external plaster thickness can be reduced 13 cost of construction 1 cum costs – rs. 4200/ 1 cum costs – rs. 2440/ 1 cum costs – rs. 4000/ 14 joining process chemical mortars can be used for joining the brick. this reduces the material consumption for cement and avoids curing process the traditional mortar needs to be used and the brickwork should be cured at least for 7 days before plastering chemical mortar can be used for joining the brick. this reduces the material consumption of cement & avoids the curing process. 15 availability the factory setup cost is high. not many factories, so availability is a concern. available locally in all cities and villages. the factory setup cost is low as compared to aac. it also takes a long time to produce if steam curing is not used. timely availability is a concern. 16 thermal insulator aac blocks are good thermal insulator if cooling is a major component, monthly expenses it will save cost for an entire lifetime it has low thermal insulation as compared to aac and clc block clc blocks are good thermal insulator if cooling is a major component, monthly expenses it will save cost for an entire lifetime 17 tax contribution contributes to government taxes in form of central, excise, and vat no tax contribution contributes to government taxes in form of central excise and vat 18 cylindrical structures for cylindrical structure, these blocks are not much useful cylindrical manholes need small size of bricks so that the curvature can be formed hence red clay bricks are useful for cylindrical structure, these blocks are not much useful 19 water absorption absorb 1215% by the total volume of aac blocks absorb 17 -20% by the total volume of red clay brick absorb 12-15% of water by the total volume of block 20 range of application they are suitable for non-load-bearing or rcc structure in the partition wall they are useful in both load-bearing and non-load bearing structure they are suitable for non-load-bearing or rcc structure in the partition wall 8. cost comparative analysis of aac block, clay brick and clc block the cost comparative analysis of brickwork in masonry and plaster for aac blocks, red clay bricks, and cellular light weight concrete (clc) blocks are summarized in table 2 and table 3 respectively (jain et al., 2018). kamal arif m., j. build. mater. struct. (2020) 7: 76-86 85 table 2. cost comparative analysis for aac blocks and clay brick masonry for 1 m3 [1:4] s. no. parameters clay red bricks aac blocks 1 quantity analysis 200mmx 100mm x 100mm 600mm x 200mm x 200mm 2 no. of bricks / blocks 500 37 3 mortar quantity 0.2766 m3 0.1344 m3 4 no. of begs of cement 1.65 1.0 5 quantity of sand 0.221 m3 0.1075 m3 6 quantity of water 31 litres 16 litres 7 rate analysis 5252.00 rs./ m2 (as per mp pwd sor building work 2014 clause no.6.3) 5052.00 rs. / m2 (as per mp pwd sor building work 2014 clause no.6.27) table 3. cost comparison for plasterwork for aac blocks and clay brick for 1 m3 [1:4] s. no. parameters clay red bricks aac blocks 1 the volume of mortar for plaster 1.8 m3 1.0 m3 2 the volume of mortar by 25% for wastage and frog filling 2.25 m3 1.25 m3 3 quantity of cement 0.45 m3 0.25 m3 4 no. of begs of cement 13.5 7.5 5 quantity of sand 1.8 m3 1.0 m3 6 quantity of water 236.25 liters 131.25 liters 7 rate analysis 171.00 rs./ m2 (as per mp pwd sor building work 2014 clause no.13.6) 91.10.00 rs./ m2 (as per messor building work 2010 item no.14001) 9. environmental benefits of aac blocks the autoclaved aerated concrete (aac) is an eco-friendly material that has many environmental benefits. the weight of the aac block is around one-fourth to one-fifth that of concrete based on volume. the manufacturing of aac blocks has the same greenhouse gas environmental impact and has the same embodied energy as that of concrete block. the aac blocks or panels have lower embodied energy per square meter than a concrete alternative building material. the aac block and panels have more insulation value and thus it has low energy usage for heating and cooling loads requirement. the total energy used in manufacturing the acc blocks is around 50% less than that of manufacturing other prefabricated building components and products. as compared to regular cement concrete building products, aac reduces around one-third of the environmental waste. the autoclaved aerated concrete (aac) blocks and panels have proven to be more durable, provide thermal insulation and structural requirements, and also have major economic and environmental benefits as compared to other traditional building components and products. thus autoclaved aerated concrete can be said to a suitable and potential eco-friendly building material, which is beneficial for the environment, which fulfills the requirement for the construction of sustainable architecture and construction (andrews, 2019). 10. conclusions the autoclaved aerated concrete (aac) is a novel and one of the most suitable and sustainable building materials in the present building construction industry. aac blocks are a result of 86 kamal arif m., j. build. mater. struct. (2020) 7: 76-86 productive use of recycled industrial waste i.e. fly ash, hence this material can be classified as a sustainable building material. the production price of aac blocks at the manufacturing unit is from rs. 3200/to rs. 3600/ per cubic meter as per the rates in india in the year 2019. the inherent properties of aac blocks result in fast and efficient construction techniques. hence the autoclaved aerated concrete (aac) has become an efficient building construction material which is being used in a wide range of residential, commercial and industrial buildings and it has been used in the gulf countries for the last 40 years and in europe for since 70 years, and in australia and south america for the past 20 years. according to a report, the aac blocks are used more than 60% of construction in germany, and in england approximately 40% of all construction industry (andrews, 2019). since the aac blocks use readily available raw materials in the manufacturing process, have excellent durability, are energy efficient, are cost-effective, and also can be recycled, therefore autoclaved aerated concrete (aac) can be said to be a green and sustainable building material. 11. references andrews a. (2019). global autoclaved aerated concrete market outlook: trend and opportunity analysis, competitive insights, actionable segmentation and forecast 2023, research report, energias market research, buffalo, usa. jain u., jain m., & mandaokar s., (2018). comparative study of aac blocks and clay brick and costing, international journal of research in engineering, science and management, 1(9), 539-543. kamal arif m. (2016), autoclaved aerated concrete (aac): a sustainable building material [online] available from http://www.masterbuilder.co.in/autoclaved-aerated-concrete-aaca-sustainable building-material/, accessed on 10 may 2020. kulbhushan k., kumar s., chaudhary r., ahmad s., gupta s., & chaurasia r. (2018). a contextual analysis of the advantages by using lightweight concrete blocks as substitution of bricks, international research journal of engineering and technology (irjet), 5(2), 926-931. majumdar b. (2019). new building materials and technologies, vol. iv, compendium of new building technologies, indian building congress, new delhi, india. rajan n. (2013). five green building blocks, [online] available from http://www.thehindu.com/features/homes-and-gardens/5-green-building blocks/article4813910.ece, accessed on 20 may 2020. schnitzler s. (2016), autoclaved aerated concrete as a green building material, uc davis extension, switzerland. http://www.masterbuilder.co.in/autoclaved-aerated-concrete-aaca-sustainablehttp://www.thehindu.com/features/homes-and-gardens/5-green-building j. build. mater. struct. (2020) 7: 19-31 original article doi : 10.34118/jbms.v7i1.74 issn 2353-0057, eissn : 2600-6936 comparative design procedures of stone columns for liquefaction stabilization messafer t1,*, hassak m2, abzar a2 1 research unit: materials, processes and environment, m’hamed bougara university of boumerdes, algeria 2 civil engineering department, m’hamed bougara university, boumerdes, algeria, * corresponding author: tmessafer@hotmail.co.uk received: 17-11-2019 accepted: 18-01-2020 abstract: soil liquefaction is one of the most important and complex phenomena of soil dynamics. it is a loss of résistance of loose granular soils under a seismic shock. the aim of this work is to study the improvement made on a liquefiable soil using a stone column solution by several methods namely observational, static and dynamic solutions. the site used for this application is located in a terminal port container in algiers. the analysis was carried out using the test results of standard penetration and cone penetrometer tests completed during a site investigation. a comparative study between the methods was carried out to determine the most suitable method. the results of the 3 methods showed that the sizing by taking into account the earthquake, the mesh of stone columns is denser. it was deduced that it is important to analyze by the dynamic method in seismic zones and by static or observational techniques in areas of no or low risk of liquefaction. recommendation for further research was put forward to develop new tools in order to improve current design methods. key words: liquefaction, stone columns, keller, dynamic, analysis, container terminal. 1. introduction ports are works that are built to create zones of extension on the seas and rivers. most of these are natural deposits of sand and gravels. this type of material is likely to liquefy because of its grain size and due to the high and variable hydraulic gradient depending on the mechanical and hydraulic load. these are already two favorable conditions for triggering the liquefaction phenomenon when a cyclic or monotonous solicitation manifests itself (seed and idriss, 1971). limited availability of adequate land for construction has prompted engineers to consider improvement techniques for strengthening weak soils. techniques such as dynamic compaction, vibro-compaction, preloading, vibro replacement, compaction grouting, permeation and jet grouting have been used (sarker and abedin, 2015). stone columns have had a proven record of success due to their easy use and economy. they have been used in many areas such as increasing the bearing capacity of soils, reducing settlement of structures, accelerating the rate of consolidation (han and ye, 2002) and to increase the resistance to liquefaction (kumari et al, 2018). the method of construction of stone columns consists of replacing the weak material with compacted granular material. this creates a flexible structure compared to concrete piles and allows the draining of groundwater and dissipation of water pressure and increasing the bearing capacity of the weak soils which improves the resistance to liquefaction (babu et al, 2013). several types of granular fill were studied (samuel thanaraj et al, 2019). the many applications of stone columns have allowed this solution to be chosen as a primary alternative to other mitigation measures. following the evolution of international trade at port level near algiers, development work has begun with the construction of a container terminal. earthworks comprised placing of a 20 messafer et al., j. build. mater. struct. (2020) 7: 19-31 hydraulic embankment from oued el-harrach during the 1990s. this material was placed in a loose state. an extensive program of laboratory and in situ tests indicated the fill needed stabilization prior to letting the site being used as a vital terminal port container. in particular in situ tests showed that the liquefaction potential was high and therefore improvement of the site with stone column method was analyzed. several methods of designing a stone column solution were assessed and the more appropriate was recommended. 2. investigation works the container terminal of the port of algiers covers an area of almost 18 hectares, located west of the bay of algiers and in the south-eastern part of algiers port on the mediterranean sea. different boreholes and in situ tests (figure 1) carried out on the site have revealed an anthropogenic soil, composed of a granular fill up to 12 meters thick, above marls and marly clay surmounted in places by a layer of fractured sandstone (figure 2). fig. 1. location of boreholes and field tests. fig. 2. layers encountered on site messafer et al., j. build. mater. struct. (2020) 7: 19-31 21 laboratory tests on samples of granular fill have shown that the amount of fine contents vary between 9 and 43%. the grading curves are within the grading zones delimiting the area of most liquefiable soils (faccioli and resendiz, 1976). 3. mechanical characteristics of the anthropic soil standard penetration (spt) and static cone penetration tests (cpt) results carried out are plotted on figures 3 and 4 below: fig. 3. spt test results (anthropic soil) fig. 4. cpt test results (anthropic soil) the results show that the fill is in a loose state and the natural soil beneath the fill is denser. 22 messafer et al., j. build. mater. struct. (2020) 7: 19-31 4. mechanical characteristic of the bedrock (marl) spt) and cpt results carried out are plotted on the bedrock are summarized on figures 5 and 6 below: fig. 5. spt test results in the marl layer fig. 6. cpt test results in the marl layer analysis of the geotechnical properties obtained from the laboratory and in situ tests of the embankment material and the layer of marl make it possible to highlight the following points: messafer et al., j. build. mater. struct. (2020) 7: 19-31 23  embankment materiel is loose, compressible with low density. in addition the water table was detected at around 2.3m depth.  the marl layer located between 7.65 and 15m depth has very good geotechnical characteristics 5. analysis of the liquefaction potential by empirical methods liquefaction potential is assessed by comparing the rate of shear resistance (crr) calculated for a site with the rate of shear stress (csr) induced by the earthquake. the safety factor fs being the ratio between crr and csr. the empirical equation of seed and idriss (seed and idriss, 1971) is used to estimate csr. the maximum acceleration is taken as 0.4g according to the recommendations of the algerian seismic regulation (rpa, 2003) and the coefficient rd is determined by the expression of blake (blake, 1997). 5.1. analysis based on spt tests the crr indices were calculated by the method of idriss and boulanger (idriss and boulanger, 2006). the results obtained (figure 7) show that the risk of liquefaction is high in the zone up to 10 to 12 meters in depth as the values of fs are low and do not exceed the limit (1.25). fig. 7. variation of fs with depth 5.2. analysis based on cpt tests the crr indices were calculated using the method developed by robertson and wride (robertson and wride, 1998). the results obtained (figure 8) show a risk of liquefaction up to 10 to 12 meters depth, the values of fs are low and do not exceed the limit (1.25). a modified cpt based method for the liquefaction assessment which is a function of the modified cone bearing and the mean grain size can also be used to predict the cyclic stress ratio (τl/σ’vo), (robertson and campanella, 1985). 24 messafer et al., j. build. mater. struct. (2020) 7: 19-31 fig. 8. variation of fs with depth 6. analysis of liquefaction potential with numerical methods shake 2000 software [ordonez, 2012] was used to calculate the safety factor for liquefaction fs with the spt and cpt test data. 6.1. comparison based on spt results the results obtained show that the study area is exposed to the risk of liquefaction from the surface up to 10m depth. fig. 9. variation of csr and crr with depth for borehole s9 messafer et al., j. build. mater. struct. (2020) 7: 19-31 25 6.2. comparison based on cpt tests it is clearly shown that the risk of liquefaction is highly probable by both calculation methods, especially in the two zones whose depth varies from 2 to about 12m. through the results obtained, we have shown that empirical results are in accordance with the results obtained by the shake2000 software (ordonez, 2012). fig. 10. variation of csr and crr with depth for cpt 13 7. simulation during the evaluation process, we designed an application by excel. this application is used to calculate the safety factor fs, by selecting the method of calculation and the principal values of the data entry (z, nspt, qc, σ𝑣). the following flow chart summarizes the operating steps : fig. 11. operating steps of the application 26 messafer et al., j. build. mater. struct. (2020) 7: 19-31 empirical and numerical methods predict liquefaction with similar safety factors. 8. stabilization with stone columns stone columns are one of the methods used for stabilizing soft soils. their use makes it possible to increase the bearing capacity of the soil, reduce its compressibility and also accelerate the consolidation by reducing the drainage path. in addition they have shown that they can reduce the liquefaction potential of the soil during the earthquakes. several types of materials exist to form the stone columns such as sand, gravel, fly ash, recycled aggregates, tire chips, etc... (zukri and nazir, 2018), some of these applications are still at the research stage but the materials generally used are aggregates. despite the widespread use of these columns, current design methods are largely empirical. in what follows we will calculate the diameter and spacing of the columns following 3 simplified approaches, namely keller's method, static method and dynamic method. conclusions and recommendations will be developed from the results. 8.1. keller’s method (cfms, 2011) the method used by keller is based on experience and site testing and control. keller installed the stone columns using the wet method to a depth of 7 to 12 m. a diameter of 80 cm of the columns was chosen with a triangular mesh. the implantation of the columns is hexagonal with a desired substitution rate of 18.7%. a total of six (6) test zones were made in the site to define the final conditions of implementation in order to achieve the expected results. the positions of the test are shown in figure 12. fig. 12. location of test benches in the areas to be stabilized messafer et al., j. build. mater. struct. (2020) 7: 19-31 27 8.1.1. control during installation a) control of materiel supplied the constituent material of the stone columns comes from the quarry of el m'hir (bordj bou arreridj). the control is done by laboratory tests to confirm the criteria of the cfms (2011) and the results are as follows: table 1. results of tests realized in the laboratory on the ballast tests granular class results wet microdeval (%) 25-50 5.25 % los angles (%) 25-50 30.56 % flatness coefficient (%) 25-50 0.93 % these values meet the recommendation criteria of the cfms (2011). b) system execution parameters (diameter, depth) from the volumes of gravel introduced, the equivalent diameter obtained in each of the columns is determined. for its determination, a reduction factor of 1.4 on the volume of the materials incorporated is considered to take into account the losses at the execution, as well as the compaction of the material in the column according to the recommendations of the cfms (2011). the results obtained in the test zones are as follows: table 2. results of control checks in the tests areas area no test bench 1 column no average depth (m) equivalent average diameter (m) average volume corrected volume (m3) spacing between axes (m) substituti on rate (%) 4 1 28 7,45 0,86 5,87 4,28 1,7 18,7 1 2 23 12,17 0,92 11,47 8,2 1,85 19,1 1 3 27 11,84 0,92 10,5 7,5 1,85 19,1 2 4 28 13,22 0,86 11 7,5 1,85 18,7 3 5 27 8,97 0,80 6,5 4,5 1,8 18 2 6 25 12,07 0,92 11,5 8 1,85 18,7 8.1.2. control after treatment the controls shown in figure 13 are performed in the test zones after treatment. fig. 13. location of controls carried out after treatment 28 messafer et al., j. build. mater. struct. (2020) 7: 19-31 a) loading tests load tests were performed using 4 comparators. a service load (qs) was applied on the column, whose value will vary according to the mesh adopted, and it will be necessary to reach a value of 1,5qs. the measured settlement curves have shown that column settlements for service loads are generally smaller than 5 cm, which is the permissible limit value (table 3). table 3. loading test results loading tests 65.9 load qs (bars) 86,40 measured settlement (cm) 0,6-1,58 b) control of soil density and column continuity the objective of the cpt test between columns is the control of soil densification due to the inclusion of gravel columns, while the test on the columns is for the control of the column continuity and density. most of the stone columns showed shallow refusal at the top of columns with peak resistances greater than 10 mpa. the results obtained from cpt tests between columns before and after treatment were compared and a marked improvement of the resistance at the tip (figure 14) was obtained. fig. 14. variation of qc with depth – comparison between treated and untreated soils 8.2. analysis with static method (balaam and booker, 1981) the container terminal area has been divided into four areas (figure 13). in our case the construction of the columns is supposed to be by the wet method and a column diameter of 80cm was assumed. the substitution rate is given by: a = δ dr(%) =dr2 dr1 messafer et al., j. build. mater. struct. (2020) 7: 19-31 29 according to the results of the cpt test, the curves show an average value of qc of the order of 2.5 mpa, with an average effective stress of 100 kpa on the entire container terminal. table 4. results of relative densities qc average (mpa) σ’v average (kpa) dr1 (%) substitution rate 2,5 100 20 20 relative densities indicate that the embankment material is loose. since we want to obtain a relative density dr2 = 40% for the material to become compact, the desired substitution rate is given in table 4. table 5. results of stone column analysis in the areas 1, 2, 3 and 4 with static method area mesh a (%) ø (m) ac (m2) am (m2) e (m) de (m) total surface (m2) column no depth (m) 1 triangular 20 0,8 0,5 2,5 2,41 2,53 35625 14250 12 2 triangular 15 0,8 0,5 3,35 2,78 2,92 27500 8209 12 3 triangular 15 0,8 0,5 3,35 2,78 2,92 19000 5672 10 4 triangular 15 0,8 0,5 3,35 2,78 2,92 34125 10187 8 the arrangement of the columns is shown in the figure below. fig. 15. stone column details with static method 8.3. analysis with dynamic method (seed and booker, 1977) data for the boumerdes earthquake were considered (mw = 6.8) and therefore the equivalent number of uniform stress (ns) of 30, the number of cyclic stress application cycles (ni) of 12 and a duration of the earthquake (td) of 46s were assumed. the properties of the surface layer, namely the coefficient of permeability in the horizontal directions (kh) of 2.10-5 (m/s), a volume compressibility coefficient (mv3) of 3.105 (m2/kn) and an average ratio of interstitial pressure of 0.6 were considered. the normalized time factor (tad) is: after calculation, we get tad = 19.54 30 messafer et al., j. build. mater. struct. (2020) 7: 19-31 for ns /ni = 2.5, we obtain rd / re = 0.27, with rd: radius of the column. re: spacing between the columns. as a column diameter of 0.8 m was chosen, a mean re of 1.5m can be adopted (figure 16). table 6. results of stone column analysis in the areas 1, 2, 3 and 4 with dynamic method area mesh ø (m) ac (m2) am (m2) re (m) total surface (m2) column no depth (m) 1 triangular 0,8 0,5 0,97 1,5 35625 36727 12 2 triangular 0,8 0,5 0,97 1,5 27500 28351 12 3 triangular 0,8 0,5 0,97 1,5 19000 19588 10 4 triangular 0,8 0,5 0,97 1,5 34125 35180 8 fig. 16. stone column details with dynamic method 9. comparison between the results the results showed that the spacing between the columns obtained by keller's method and the static method is higher than the spacing obtained by the dynamic method. as a result, the number of columns obtained by the dynamic method is greater. this is predictable because the dynamic method takes into account the seismic loading. this highlights the error made by certain companies that uses observational techniques to design stone columns in areas at risk of liquefaction. in such areas dynamic method are required. the above results are based on simple empirical analysis methods and need to be confirmed by methods based either on small scale models and/or develop numerical models that take into account the heterogeneity of materials, dissipation of interstitial pressures and dynamic stresses. 10. conclusions diameter and spacing of stone columns were assessed using 3 methods and it was noticed a difference between the results. the method used by keller is mainly observational. it clearly showed that the soil was improved and compacted based on post-treatment trials. however it has been used to reduce the settlement problem only while the soil has been confirmed to be potentially liquefiable as well. the results of the 3 methods have shown that if we size by taking into account the dynamic solicitations, the mesh of stone columns is denser. therefore it is recommended to analyze by the dynamic method in seismic zones and by static or observational techniques in areas of low or no risk of liquefaction. however, it is useful that stabilization results be confirmed by methods based on small scale models to verify the findings of the empirical dynamic method. messafer et al., j. build. mater. struct. (2020) 7: 19-31 31 11. references babu, m. d., nayak, s., & shivashankar, r. (2013). a critical review of construction, analysis and behaviour of stone columns. geotechnical and geological engineering, 31(1), 1-22. balaam, n. p., & booker, j. r. (1981). analysis of rigid rafts supported by granular piles. international journal for numerical and analytical methods in geomechanics, 5(4), 379-403. blake, t. f. (1997). summary report of proceedings of the nceer workshop on evaluation of liquefaction resistance of soils. youd tl, and idriss im. eds., technical report nceer 97-0022. cfms, (2011). recommandations sur la conception, le calcul, l’exécution et le contrôle des colonnes ballastées sous bâtiments et sous ouvrages sensibles au tassement, comité français de mécanique des sols. faccioli, e., & resendiz, d. (1976). soil dynamics behavior including liquefaction in seismic risk and engineering decisions, lomnitz and rosenblueth, eds, elsevier scientiific publishing co. , new york, pp. 71-140, chap 4. han, j., & ye, s. l. (2002). a theoretical solution for consolidation rates of stone column-reinforced foundations accounting for smear and well resistance effects. international journal of geomechanics, 2(2), 135-151. idriss, i. m., & boulanger, r. w. (2006). semi-empirical procedures for evaluating liquefaction potential during earthquakes. soil dynamics and earthquake engineering, 26(2-4), 115-130. kumari, s., sawant, v. a., & mehndiratta, s. (2018). effectiveness of stone column in liquefaction mitigation. proceedings of geotechnical earthquake engineering and soil dynamics v. 207-216. ordóñez, g. a. (2012). shake2000: a computer program for the 1-d analysis of geotechnical earthquake engineering problems. geomotions, llc, lacey, washington, usa. robertson, p. k., & campanella, r. g. (1985). liquefaction potential of sands using the cpt. journal of geotechnical engineering, 111(3), 384-403. robertson, p. k., & wride, c. e. (1998). evaluating cyclic liquefaction potential using the cone penetration test. canadian geotechnical journal, 35(3), 442-459. rpa99 (2003), règles parasismiques algériennes, centre national de recherché appliqué en génie parasismique. samuel thanaraj m., freeda christy c., brema j. (2019). analysis on the performance of stone columns with different materials in soil stabilization, international journal of engineering and advanced technology (ijeat), 8(3s), 148-153. sarker, d., & abedin, m. z. a review on ground improvement techniques to improve soil stability against liquefaction., international journal of science and engineering investigations, 4(40):53-55. seed, h. b. & idriss, i. m. (1971). simplified procedure for evaluating soil liquefaction potential, journal of soil mechanics and foundation division, asce, vol. 107, no sm9, 1249-1274. seed, h. b., & booker, j. r. (1977). stabilization of potentially liquefiable sand deposits using gravel drains, journal of the geotechnical engineering division, asce, vol. 103, no. gt7, 757-768. zukri, a., & nazir, r. (2018). sustainable materials used as stone column filler: a short review. in iop conference series: materials science and engineering, vol. 342, no. 1, p. 012001. iop publishing. j. build. mater. struct. (2019) 6: 88-96 original article doi : 10.34118/jbms.v6i2.71 issn 2353-0057, eissn : 2600-6936 effect of thickness stretching on the natural frequencies of laminatefaced sandwich plates using a new layerwise model belarbi mo1,*, tati a1, khechai a2 1 laboratoire de génie energétique et matériaux, lgem. université de biskra b.p. 145, r.p. 07000, biskra, algeria. 2 laboratoire de génie civil, lrgc. université de biskra b.p. 145, r.p. 07000, biskra, algeria. * corresponding author: belarbi.m.w@gmail.com received: 30-04-2019 accepted: 17-07-2019 abstract: the current work investigates the effect of thickness stretching on the natural frequencies of laminate-faced sandwich plates using new layerwise finite element model. the proposed model assumes higher-order displacement field for the core and first-order displacement field for the face sheets. thanks for enforcing the continuity of the interlaminar displacement, the number of variables is independent of the number of layers. the consistent mass matrix and the element stiffness matrix are derived using the hamilton’s principle. the performance and reliability of the proposed formulation are demonstrated by comparing the author’s results with those obtained using the three-dimensional elasticity theory, analytical solutions and other advanced finite element models. key words: layerwise, finite element, sandwich plates, free vibration. 1. introduction composite sandwich structurers provide high performance and reliability due to their low weight, high stiffness and high strength properties. as a result, composite structures, such as sandwichs plates, will continue to be widely used for many years in the engineering fields such as civil, naval, aerospace and construction industries. despite the many advantages of sandwich structures, their behavior becomes very complex due to the large variation of rigidity and material properties between the core and the face sheets. different plate theories have been proposed to study the behavior of sandwich structures. these plate theories may be grouped as equivalent single layer (esl) approach (where all the layers are referred to the same variables) and layerwise (lw) approach. the esl approach can be divided into three major theories, namely: (1) the classical laminated plate theory (clpt); (2) the first order shear deformation theory (fsdt); and (3) the higher order shear deformation theories (hsdt). however, esl approach fail to capture precise the local behavior of sandwich structures. this drawback in esl was circumvented by the layerwise theories in which the displacements are assumed at the mid surface of each laminate and maintaining the continuity of the displacements at the layer interface (pandey & pradyumna, 2015). in the finite elements (fe) development, many researchers have adopted the lw approach for the sake of a good description of sandwich structures (belarbi & tati, 2015; belarbi et al., 2016; belarbi & tati, 2016). on this topic, we can distinguish the work of nabarrete et al. (2003), where a 3d layerwise fe model is developed for free vibration analysis of sandwich plates. they used the fsdt to model the face sheets and the hsdt was adopted to model the core. desai (desai et al., 2003) developed an eighteen-node layerwise mixed brick element with 108 degrees-of-freedom (dofs) for the free vibration analysis of multi-layered thick composite plates. later, an eight nodes quadrilateral element having 136 dofs was developed by araújo et al. (2010) for the analysis of sandwich laminated plates with a viscoelastic core and laminated anisotropic face layers. the construction of this element is based on layerwise approach where belarbi et al., j. build. mater. struct. (2019) 6: 88-96 89 the hsdt is used to model the core layer and the face sheets are modeled according to a fsdt. elmalich & rabinovitch (2012) have undertaken an analysis on the dynamics of sandwich plates, using a c0 four-node rectangular element. the formulation of this element is based on the use of a new layerwise model, where the fsdt is used for the face sheets and the hsdt is used for the core. more recently, pandey & pradyumna (2015) presented a new higher-order layerwise plate formulation for static and free vibration analyses of laminated composite plates. a high order displacement field is used for the middle layer and a first-order displacement field for top and bottom layers. the authors used an eight-noded isoparametric element containing 104 dofs to model the plate. the goal of this work is to propose a new 2d layerwise fe formulation for free vibration analyses of multi-layered sandwich plates. unlike layerwise models, the number of variables in the present model is independent of the number of layers. the results obtained from this investigation will be useful for a more understanding of the free vibration behavior of sandwich laminates plates. 2. mathematical formulation sandwich plate is a structure composed of three principal layers as shown in fig.1, two face sheets (top-bottom) of thicknesses ( ) t h , )(h b respectively, and a central layer named core of thickness  hc which is thicker than the previous ones. total thickness  h of the plate is the sum of these thicknesses. the plane  , x y coordinate system coincides with mi-plane plate. fig 1. geometry and notations of a sandwich plate. in the present model, the hsdt is adopted for the core layer. hence, the displacement field is written as a third-order taylor series expansion of the in-plane displacements in the thickness coordinate, and as a constant one for the transverse displacement: 2 3 0 2 3 0 0 c c c c x x x c c c c y y y c u u z z z v v z z z w w                (1) where 00 0 , and u v w are in-plane and transverse displacement components at the mid-plane of the sandwich plate, respectively. and c c x y   represent normal rotations about the x and y axis respectively. the parameters , , and c c c c x y x y     are higher-order terms the taylor’s series expansion. 2.1. strain–displacement relations the kinematic relations for the core are given by: 90 belarbi et al., j. build. mater. struct. (2019) 6: 88-96 2 30 2 30 2 30 0 20 2 3 c c c c x x x xx c c c y y yc yy c c cc c c y y yc x x x xy c c c c yz y y y c c xz x u z z z x x x x v z z z y y y y u v z z z y x y x y x y x w z z y                                                                                                  20 2 3 c c x x w z z x        (2) 2.2. displacement field of the face sheets the face sheets are modeled using the fsdt. the compatibility conditions as well as the interlaminar displacement continuity (face sheets/core), leads to the following improved displacement fields: top face sheet 2 3 0 2 3 0 0 2 4 8 2 2 4 8 2 c c c tc c c c t x x x x c c c tc c c c t y y y y t h h h h u u z h h h h v v z w w                                                              (3) bottom face-sheet 2 3 0 2 3 0 0 2 4 8 2 2 4 8 2 c c c bc c c c b x x x x c c c bc c c c b y y y y b h h h h u u z h h h h v v z w w                                                              (4) 2.3. strain –displacement relations the kinematic relations for the top face sheet can be written as follows: 2 3 0 2 3 0 0 0 ( ) 2 4 8 2 ( ) 2 4 8 2 c c c t t c x c x c x c x c c c t y y y yt c c c c t t c t xx t yy t xy u u h h h h z x x x x x x v v h h h h z y y y y y y u v u v h y x y x                                                                                                   2 3 0 0 2 4 ( ) 8 2 , c cc c y yx c x c tc t y yc x c x t t y x t t yz xz h y x y x h h z y x y x w w y x                                                                 (5) belarbi et al., j. build. mater. struct. (2019) 6: 88-96 91 the same steps are followed to elaborate the strain-displacement relationships of the bottom face sheet. 2.4. constitutive relationships in this work, the two face sheets (top and bottom) are considered as laminated composite. hence, the stress-strain relations for kth layer in the global coordinate system are expressed as:       11 12 16 21 22 26 44 45 54 55 61 62 66 0 0 0 0 ,0 0 0 0 0 0 0 0 f f xx xx f f yy yy f f yz yz f f xz xz f f xy xy k k kq q q q q q f top bottomq q q q q q q                                                             (6) the core is considered as an orthotropic composite material, and the stress-strain relationships can be defined as follows: 11 12 16 21 22 26 44 45 54 55 61 62 66 0 0 0 0 0 0 0 0 0 0 0 0 xx xx yy yy y yz xz xy xy z xz q q q q q q q q q q q q q                                                            (7) the efforts resultants of the core are obtained by integration of the stresses through the thickness direction of laminated plate. hence, the constitutive equations can be written in the following contracted form:                                               0 0 1 1 2 2 3 , s s s s s s s s s s s s n a b d e a b dv m b d e f s b d e d e f gn r d e f e f g hm                                                                                                   (8) where the components of the reduced stiffness matrices of the core are defined by:         2 2 3 4 5 6 2 2 2 3 4 2 , , , , , , 1, , , , , , ( , 1, 2, 6) , , , , 1, , , , ( , 4, 5) c c c c h ij ij ij ij ij ij ij h h s s s s s ij ij ij ij ij h ij ij a b d e f g h z z z z z z dz i j a b d e f z z z z dz i j q q         (9) according to the theory fsdt, the constitutive equations for the face sheets are: 0 0 0 0 f f f m f f f f f c f c f f f a b d a n m t b                                (10) 92 belarbi et al., j. build. mater. struct. (2019) 6: 88-96 3. finite element formulation in the present study, a c0 four-node isoparametric element, named qsft52 (quadrilateral sandwich first third with 52-dof), with thirteen dof per node has been developed. each node contains: two rotational dof for each face sheet, six rotational dof for the core, while the three translations dof are common for sandwich layers (figure 2). fig 2. geometry and corresponding degrees of freedom of the qsft52 element. the displacements vectors at any point of coordinates (x, y) of the plate are given by: where   t c c c c c c t t b b i i i i xi yi xi yi xi yi xi yi xi yi u v w           is displacement vector corresponding to node i ( 1, 2, 3, 4i  ). the generalized strain vector for three layers can be expressed in terms of nodal displacements vector as follows:     ( ) ( ) i k k i b      (12) 3.1 governing differential equation in this work, hamilton’s principle is applied in order to formulate governing free vibration problem, which is given as:   2 1 0 t t t u dt     (13) where t is the time, t is the kinetic energy of the system and u is the potential energy of the system. using the standard finite element procedure, the governing differential equations of motion can be rewritten as:       0t tm k   (14) where  tm and  tk denote the element mass matrix and the element stiffness matrix, respectively, for the three layers sandwich plate.       1 1 1 1 d et t t t t t t c c c b b b e k b d b b d b b d j d db                                     (15) and the element mass matrix can be written as:                 1 1 ( ) ( ) ( ) 1 1 det t t tt c b e m n m n n m n n m j dn d                  (16) belarbi et al., j. build. mater. struct. (2019) 6: 88-96 93 now, after evaluating the stiffness and mass matrices for all elements, the governing equations for free vibration analysis can be stated in the form of generalized eigenvalue problem.      2 0t tk m    (17) 4. numerical results and discussions 4.1 free vibration analysis of square sandwich plate having three-ply laminated stiff sheets in this problem, a seven-layer simply supported square sandwich plate is studied. two sandwich plates with various lay-ups on face sheets [0/90/0/core/0/90/0] and [45/-45/45/core/45/45/-45] are considered. the core is made of herex-c70.130 pvc foam and the face sheets are made of glass polyester resin. the mechanical properties of the sandwich plate are presented in table 1. the geometrical properties of the plate are (a/h = 10, a/b = 1, hc/h = 0.88) where h is the total thickness of the plate. table 1. material properties for laminated sandwich plate. material elastic properties (gpa) e11 e22 g12 g13 g23 ν12 ρ (kg/m3) faces 24.51 7.77 3.34 3.34 1.34 0.078 1800 core 0.1036 0.1036 0.05 0.05 0.05 0.32 130 the convergence of the non-dimensional results of natural frequencies, for the first four modes, is shown in table 2 with different mesh sizes. the comparison was made with the analytical solutions based on lw approach (jam et al., 2010; rahmani et al., 2010), the 3d-finite element models also based on lw approach (fem-3d-lw) given by burlayenko et al. (2015). it is clear, from the table 2, that the results of developed element are in excellent agreement with numerical results found in the literature. these results show clearly the performances and convergence of the proposed layerwise formulation. the non-dimensional results of frequencies are expressed as: 2 c c a e h    . table 2. non-dimensional natural frequencies for a square multi-layered sandwich plate with various lay-ups on face sheets. references fe models various lay-ups on face sheets frequencies (hz) mode 1 mode 2 mode 3 mode 4 present element (6×6) present element (8×8) present element (10×10) present element (12×12) present element (14×14) present element (16×16) burlayenko et al. (2015) rahmani et al. (2010 jam et al. (2010) qsft52 qsft52 qsft52 qsft52 qsft52 qsft52 fem-3d-lw analytical-lw analytical-lw cas 1 14.736 14.583 14.513 14.477 14.452 14.440 14.620 14.270 15.040 28.207 27.499 27.173 26.999 26.893 26.826 26.800 26.310 26.733 28.802 28.115 27.796 27.626 27.524 27.456 27.400 27.040 27.329 37.584 36.627 36.167 35.954 35.777 35.706 35.550 34.950 35.316 present element (6×6) present element (8×8) present element (10×10) present element (12×12) present element (14×14) present element (16×16) burlayenko et al. (2015) jam et al. (2010) qsft52 qsft52 qsft52 qsft52 qsft52 qsft52 fem-3d-lw analytical-lw cas 2 15.674 15.536 15.473 15.437 15.419 15.405 15.420 15.786 28.756 28.069 27.754 27.587 27.485 27.417 27.170 27.316 28.756 28.069 27.754 27.587 27.485 27.417 27.460 27.316 38.363 37.478 37.053 36.805 36.698 36.592 36.240 36.216 * cas1: [0/90/0/c/0/90/0], cas 2: [45/-45/45/c/-45/45/-45] 94 belarbi et al., j. build. mater. struct. (2019) 6: 88-96 moreover, the same sandwich plate was analyzed for different thickness ratios (a/h) and aspect ratios (a/b) keeping the same ratios hc/hf = 0.88. from figure 3, it is found that the nondimensional natural frequencies increase with increasing in thickness ratios, whatever the aspect ratios. this can be explained by the fact that the frp sandwich plates are not assumed to be infinitely stiff through the thickness. fig. 3. effect of a/h ratio on the fundamental frequencies of a simply supported square laminated sandwich plate (0/90/0/c/0/90/0). 4.2 free vibration analysis of sandwich plate having un-symmetric laminated face sheets in this problem, a simply supported square sandwich plate with un-symmetric laminated face sheets (0/90/c/0/90) is considered to assess the performance of our model to the thin as well as thick plate. the mechanical properties of the sandwich plate are presented in table 3.the thickness ratio (a/h) is considered to vary from 2 to 100, where the ratio of thickness of core to thickness of face sheet hc/hf is considered as 10. the first six mode shapes obtained for simply supported square laminated sandwich plate with a/h =10 are shown in figures 4. the non-dimensional results of frequencies are expressed as: 2 22c f b h e   the comparison of natural frequencies, considering mesh size (12×12), are shown in figure 5, with those obtained by the 3d-elasticity solution (rao et al., 2004), the analytical results based on hsdt (kant and swaminathan, 2001), and those obtained with the fem-q8 solution based on global-local higher order shear deformation theory (glhsdt) (zhen et al., 2010). it can be seen, from the figures 4 and 5, that the present fe model gives more accurate results than the other models which confirm the good performance and robustness of the proposed formulation. table 3. material properties for laminated sandwich plate. material elastic properties (gpa) e11 e22 g12 g13 g23 ν12 ρ (kg/m3) faces 131 10.34 6.9 6.9 6.9 0.22 1627 core 0.0069 0.0069 0.0034 0.0034 0.0034 10-5 97 belarbi et al., j. build. mater. struct. (2019) 6: 88-96 95 mode 1 mode 2 mode 3 mode 4 mode 5 mode 6 fig. 4. first six mode shapes of simply supported square laminated sandwich plate (0/90/c/0/90) with a/h =10. fig. 5. effect of the thickness ratios (a/h) on the non-dimensional fundamental frequencies of a simply supported sandwich plate having un-symmetric laminated face sheets. 5. conclusion in this paper, a new layerwise finite element model was proposed for the natural frequency analysis of multilayer sandwich plates. the developed model is based on a proper combination of higher-order and first-order, shear deformation theories. these combined theories satisfy interlaminar displacement continuity. the results obtained by our model were compared with those obtained by the analytical results and other finite element models found in literature. the comparison showed that the element has an excellent accuracy and a broad range of applicability. 96 belarbi et al., j. build. mater. struct. (2019) 6: 88-96 the effects of degree of length-to-thickness ratio (a/h) plate and aspect ratio (a/b) upon the fundamental frequencies are discussed and the results reaffirm that these effects plays an important role in the free vibration frequencies of laminated sandwich plates. 6. references araújo, a. l., mota soares, c. m., & mota soares, c. a. (2010). finite element model for hybrid activepassive damping analysis of anisotropic laminated sandwich structures. journal of sandwich structures & materials, 12(4), 397-419. belarbi, m. o., & tati, a. (2015). a new c0 finite element model for the analysis of sandwich plates using combined theories. international journal of structural engineering, 6(3), 212-239. belarbi, m. o., & tati, a. (2016). bending analysis of composite sandwich plates with laminated face sheets: new finite element formulation. journal of solid mechanics, 8(2), 280-299. belarbia, m. o., tatib, a., ounisc, h., & benchabane, a. (2016). development of a 2d isoparametric finite element model based on the layerwise approach for the bending analysis of sandwich plates. structural engineering and mechanics, 57(3), 473-506. burlayenko, v. n., altenbach, h., & sadowski, t. (2015). an evaluation of displacement-based finite element models used for free vibration analysis of homogeneous and composite plates. journal of sound and vibration, 358, 152-175. desai, y. m., ramtekkar, g. s., & shah, a. h. (2003). dynamic analysis of laminated composite plates using a layer-wise mixed finite element model. composite structures, 59(2), 237-249. elmalich, d., & rabinovitch, o. (2012). a high-order finite element for dynamic analysis of soft-core sandwich plates. journal of sandwich structures & materials, 14(5), 525-555. jam, j. e., eftari, b., & taghavian, s. h. (2010). a new improved high‐order theory for analysis of free vibration of sandwich panels. polymer composites, 31(12), 2042-2048. kant, t., & swaminathan, k. (2001). analytical solutions for free vibration of laminated composite and sandwich plates based on a higher-order refined theory. composite structures, 53(1), 73-85. nabarrete, a., m. de almeida, s. f., & hansen, j. s. (2003). sandwich-plate vibration analysis: three-layer quasi-three-dimensional finite element model. aiaa journal, 41(8), 1547-1555. pandey, s., & pradyumna, s. (2015). a new c0 higher-order layerwise finite element formulation for the analysis of laminated and sandwich plates. composite structures, 131, 1-16. rahmani, o., khalili, s. m. r., & malekzadeh, k. (2010). free vibration response of composite sandwich cylindrical shell with flexible core. composite structures, 92(5), 1269-1281. rao, m. k., scherbatiuk, k., desai, y. m., & shah, a. h. (2004). natural vibrations of laminated and sandwich plates. journal of engineering mechanics, 130(11), 1268-1278. zhen, w., wanji, c., & xiaohui, r. (2010). an accurate higher-order theory and c0 finite element for free vibration analysis of laminated composite and sandwich plates. composite structures, 92(6), 1299-1307. j. build. mater. struct. (2014) 1: 10-22 https://doi.org/10.34118/jbms.v1i1.4 mix proportioning and performance of a crushed limestone sandconcrete makhloufi z 1,*, bouziani t 1, bédérina m 1 and hadjoudja m 2 1 structures rehabilitation and materials laboratory (sreml), university amar telidji, laghouat, algeria. 2 civil engineering laboratory, university amar telidji, laghouat, algeria. * corresponding author: z.makhloufi@mail.lagh-univ.dz abstract. satisfying the ever-growing demand of concrete aggregates poses a problem in many parts of the world due to shortage of natural sand. moreover, to conserve natural resources and protect civil engineering infrastructures, there is a need to find alternative materials. crushed stone sand has been identified as a potential substitute material for natural sand in making good quality concrete. the main objective of the present investigation is to determine an adequate mix design method and evaluate engineering properties of crushed limestone sand concrete mixtures in both the fresh and hardened sates. more than thirty concrete mixtures were examined. the results indicate that water demand and cement paste content in crushed sand concrete are generally higher than that used in similar conventional concrete. good mechanical properties were obtained for concrete using crushed limestone sand as fine aggregates with a superplasticizer. however, a higher than normally used dosage of superplasticizer is required in these concrete mixtures and the optimum dosage of the superplasticizer needs to be determined for each cement and sand content. key words: crushed stone, fine aggregate, limestone, mix proportioning, fresh concrete, performance, mechanical properties. 1. introduction a guaranteed continuous supply of sand to produce the ever-growing amount of concrete needed for economic development poses a problem in many parts of the world due to the shortage of natural river sand. therefore, to preserve natural resources and to maintain a sustainable construction, alternative resources are needed. in algeria where the amount of sand needed annually is estimated at more than 25 million tons, crushed rock sand may constitute a viable substitute to natural river sand. crushed sand, with particle size less than 5 mm, is a byproduct obtained in the process of rock crushing to manufacture gravel or coarse aggregates. thus, many of the sand properties (chemical and mineralogical compositions …etc.) are related to the source rock. however, crushed rock sand differs from the usual river sand in particle shape, grading, surface texture, and particularly in the content of fines or dust. fines are defined as the part of sand passing a determined test sieve. the standards bsi (1992), astm (1996), afnor (1997) and cen (2002) recommend respectively the sieves 75m, 80m and 63m for determining fine content. the bsi standard allows a dust content of 16% by mass of sand for crushed rock fine aggregate whereas the corresponding limit in the astm (1996) standard is only 7%. however, in the nfp18-540 standard (afnor, 1997), the maximum amount of allowed fines is set to 12%. these restrictions are aimed at limiting the adverse effects on the properties of fresh and hardened concrete that the dust is thought to have. in fresh concrete, high percentage of dust increases the fineness and the total surface area of aggregates, and thus leads to an increase in the amount of water needed to obtain a suitable workability (celik, 1996; ahmed, 1989). obviously, this higher demand of water will adversely affect the strength and shrinkage properties of hardened concrete (neville, 1995). durability properties may also be affected by the presence of dust as it acts on the nature of the paste-aggregate interface by coating the aggregate surface (ahmed, 1989; makhloufi, 2012a; makhloufi, 2012b). moreover, the use of crushed sand may be an alternative source of filler, which help to achieve an adequate mailto:z.makhloufi@mail.lagh-univ.dz makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 11 workability (donza, 2002). the research results reported by celik and marar (1996) and ahmed and elkourd (1989) seems to suggest that the optimum amount of dust may lie between 5 and 10% of the quantity of crushed sand. this perceived risk associated with crushed sand together with the lack of data has contributed to skepticism and the reluctance to use crushed sand. it also led some aggregates manufacturers to invest on costly processing equipment to screen off or remove the fines (benabed, 2012; gschaider, 2001). the shape of crushed sand together with the mineralogical properties of the dust associated with it depends on the nature and the degree of stratification of rock deposit. moreover, the quality of fresh and hardened concrete is greatly influenced by the properties of crushed sand such as shape, size of particle and the surface texture (donza, 2002; taylor, 1996). the amount of additional paste content needed in the case of crushed sand depends also on the shape, texture and grading of the sand (donza, 2002). on the other hand, water demand seems to be primarily dependent on the particle shape of the sand (nichols, 1982; bharatkumar, 2001). nevertheless, crushed sand with no or a relatively small percentage of dust content (less than 3%) is reported to be an adequate substitute material for natural silica sand in producing good quality concrete and is more suitable for the production of high strength concrete than natural sand (nichols, 1982; lecomte, 1995; celik, 1996; taylor, 1996; cen, 1997; donza, 2002; park, 2012). while it is important to control the dust content in the aggregate, it may be more objective that limits are set on the basis of the source and mineralogical properties of the dust. higher limits can be set when the dust is clean and is essentially a by-product of the fracture of rocks. in contrast tighter limits are set when this dust contains a considerable amount of deleterious substances such as clay or shale (lecomte, 1995; nichols, 1982). this seems to be the reason that the cen standard (cen, 2002) was reluctant in fixing precise limits on the amount of fines allowed in crushed sands. furthermore, a considerable enhancement in the properties of fresh and hardened concrete could be achieved by adding clean and properly graded fines to the concrete mix. these fines act as filler and help to reduce the total voids content in concrete which in turn decreases water permeability and improves the quality of concrete (celik, 1996). they also contribute in cement hydration during the early age by acting as a nucleation sites for the hydration products (donza, 2002; bosiljkov, 2003; pipilikaki, 2009b). furthermore, the packing of fine particles is improved by the addition of fillers. as a result the stability and workability of fresh concrete are enhanced and the concrete density is increased (bosiljkov, 2003). improvement in concrete strength is also obtained due to better aggregate-paste interface (donza,. 2002; bosiljkov, 2003). the main objective of this paper is the proportioning and the evaluation of the performances of a crushed limestone sand-concrete with and without superplasticizer. the experimental program reported herein was carried out to document and evaluate engineering properties of crushed limestone sand-concrete mixtures in both fresh and hardened states. these properties were then compared to traditional concrete mixtures made with natural silica sand to expand the beneficial use of crushed limestone concrete and underline its potential applications. two series of concrete mixtures using crushed limestone sand have been investigated during this study; the first mixture (series a) did not contain any admixtures while in the second one (series b) a superplasticizer (sp) was incorporated into the concrete mixtures. 2. mixture design approach all the aggregates used in this research were quarried from a turonian limestone rock deposit of the mesozoic era in the region of laghouat (south algeria). three granular fractions were considered in the concrete mixtures. the first fraction (0/5mm) was a crushed sand while the two other fractions (5/15 and 15/25mm) were combined to make the mixture coarse aggregate. the main physical characteristics of these aggregates are summarized in table 1 while figure 1 shows their particle size distributions. the surface texture of the sand was rough and its 12 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 gradation fell within the limits prescribed by both the bs and afnor standards. the content of fines in the sand is higher than the limit proposed by the astm standard (astm, 1996), but is lower than that proposed by the bsi and the afnor standards (bsi, 1992; afnor, 1997). figure 2 shows the x-ray diffraction of fine crushed sand content, where it is noted that the main components of the fines is caco3 in the form of calcite. therefore, most of the fine material contained in the sand can be considered as clean limestone filler. the particle size distribution of this filler, obtained by using the sedimentation test method, is shown in figure 3. the shape of the coarse aggregates was mainly angular with a rough surface texture. table 1: physical characteristic of crushed sand and gravels. characteristics symbol unit sand 0/5 gravel 5/15 15/25 absolute density s kg/m3 2700 2680 apparent density  kg/m3 1530 1270 real density r kg/m3 2610 2590 absorption abs % 2.5 1.42 porosity  % 3.33 3.36 fig 1: particle size distribution curves of the limestone sand and gravel a portland composite cement designated cem ii 32.5n, which properties are shown in table 2, was used in this investigation. a sulphonated naphthalene superplasticizer type (sp) in aqueous form was incorporated in the second series of the mixes. the solid content and the ph values of used sp are respectively 33.5% and 6.5. as stated before, the present investigation was intended to assess the effect of various controlling parameters on the performance of crushed limestone concrete. to achieve such objective, more than 30 concrete mixtures were made and both workability and strength were determined. all the concrete mixtures were carried out in a tilting drum type mixer machine. the mixing sequence of concrete without sp consisted of homogenizing at first the aggregates with cement, and then water was added. for concrete with sp, after the homogenizing phase, makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 13 water and a third of the sp were first added and mixed and then the rest of sp was added to achieve the required workability. the overall mixing time was about two and a half minutes. fig 2: x-ray diffraction of the fine crushed sand content. table 2: chemical composition and physical properties of cement. chemical composition oxides % sio2 21.04 al2o3 4.97 fe2o3 3.91 cao 63.80 mgo 1.08 k2o 0.62 na2 o 0.08 so3 0.96 physical properties loss on ignition 0.57 absolute density 3 g/cm3 blaine specific surface 3678 cm2/g cement class (σ28) 37.10 ± 0.62 mpa two workability-control tests were considered during this study; the slump test and the lcl test (afnor, 1998). standard procedures were followed in performing both tests. the lcl apparatus, like the remoulding test, determines the time it takes for concrete to flow into a new form. immediately after measuring the workability, the test specimens were made. no significant loss in workability was noted over this time. six cylinders of 160x320mm were cast from each concrete mixture. the steel moulds were filled in three layers and compacted using a small internal vibrator. the specimens were kept in their moulds and covered with plastic to prevent water evaporation until the following day when they were demoulded and putted in water at 24°c for approximately one week. after this period, the specimens were left to cure in the laboratory. the compressive strength of prepared concrete mixtures made was determined 14 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 by testing three cylinders at 28 days. the remaining ones were used to determine the splitting tensile strength of concrete at the same age. fig 3: the particle size distribution of limestone filler 3. mixture proportions the mix proportioning of concrete is rather a complicated task (neville, 1995; al-ghahtani, 1998; sriravindrarajah, 2012) as it involves many parameters such as the properties of the ingredients and the specifications of the construction job which are usually given in term of workability, strength and durability. once most of these parameters are specified, the procedure consists then of finding for a particular gradation of aggregates, a first approximations of mix proportions; water to cement ratio (w/c), total aggregate to cement ratio ((s+g)/c) or fine to coarse aggregate ratio (s/g). this first approximation is further adjusted until it meets the initial specifications. a number of mix proportioning methods exist and, despite various attempts to develop computer or manual methods aimed at determining the exact mix proportions; these have invariably been adjusted empirically. since dreux mix proportioning method (dreux, 1998) is widely used in algeria and is reported to yield the required workability for the ingredients presently available there, it was adopted in the present study to get the first approximation of the concrete mixture proportions. the dreux method makes use of bolomey equation to estimate the strength of concrete at 28 days (bolomey, 1935): where: rc28 = average or nominal compressive cylinder strength of concrete at 28 days. g = empirical constant used to take into account the aggregate nature and gradation. σc28 = cement class (table 2). c/w = cement to water ratio.  5.0/  wcc28c28 gr  (1) makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 15 methods based on the bolomey equation are reported to be adequate for conventional concrete and provided that the particle size distribution of the concrete mixture follows closely a reference curve which is thought to give a higher concrete compactness (lecomte, 2001). for a targeted characteristic strength of concrete (rc28=25mpa) with a medium workability (slump=60mm), the dreux method yielded a w/c of 0.5, the cement content was 400 kg/m3 and the total volume aggregates (vagg) was 658.67 l. the volume of aggregates comprised the volume of sand (vs=41.4%) and the volume of coarse aggregates (vg=58.6%) with a sand to coarse aggregate ratio (s/g) of 0.71. the coarse aggregate volume was a combination of 5/15mm (vg1=39%vg) and 15/25mm (vg2=61%vg). the water quantity (w=200 l) is the effective or free water (we), which is necessary to achieve the required workability and ensure the hydration of cement (neville, 1995). the aggregates are therefore supposed to be in a saturated and surface-dry area condition when they are introduced into the mix, and adjustment to the mixing water (wm), needs to take into account the actual moisture content and the absorption of the aggregates. the mixing water, wm, together with the total water in the mix (wt) are given by the following relation (lecomte, 1995): where: ggssc ggssabs mωmωw mkmkw   ωandk, m, are respectively weight, absorption, and water content of the aggregate. the subscripts (s) and (g) refer to the sand and the coarse aggregate respectively. the computed mixing water, wm, was 15.5% higher than the effective water we, which confirms the findings of other researchers (ahmed, 1989; celik, 1996; donza, 2002) that crushed sand concrete mixtures tend to require more water than conventional concretes. in order to reduce the number of variables affecting the concrete mix, a preliminary investigation was carried out to determine the optimum s/g ratio, and subsequently the optimum aggregate packing (al-ghahtani, 1998; lecomte, 2001). to achieve this, the baronlesage method was used (baron, 1976). for constant volumes of paste and aggregates, the method consists of varying the proportions of sand and coarse aggregate to find the optimum s/g ratio that gives the lowest concrete flow time, measured by the lcl apparatus and hence the optimum workability. this optimum workability corresponds to the best apparent viscosity of the mix and to the highest packing of the aggregate in the mix (lecomte, 2001). only a slight increase in water demand (w/c=0.52) was needed to get the initially specified workability (slump=60mm) thus validating the approach used in estimating the mixing water (eq. 2). thereafter, seven different concrete mixtures were investigated to identify the optimum s/g ratio. the results of this phase are presented in figure 4, whereby the optimum s/g was found to be 0.68 (close to 0.71 establish by dreux) and the weights of the aggregates needed to achieve this are given in table 3. cmt cabsem www wwww   (2) (3) 16 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 fig 4: variation of lcl-flow time according to s/g ratio. table 3: weights of aggregates according different cement contents and we/c ratios. cement (kg/m3) we/c sand dry g1 dry g2 dry (kg) 250 0.66 791 452 726 0.71 779 445 716 0.73 773 441 710 0.81 753 430 692 0.89 731 417 671 350 0.50 745 425 684 0.51 741 423 681 0.57 720 411 661 0.66 690 394 634 0.71 670 382 615 450 0.41 700 400 643 0.43 690 394 634 0.46 680 388 625 0.49 666 380 612 0.54 639 365 587 once the optimum s/g was found, the following step was to investigate the performance of crushed limestone sand-concrete with a fixed granular matrix. this means that the weights of the aggregates with a ratio s/g=0.68 (table 3) were kept constant and only the cement and the water contents were varied during this investigation. three cement contents, 250, 350 and 450 kg/m3 were considered. for each dosage of cement, five concrete mixtures were carried out with different w/c ratios to achieve a range of chosen workability. as stated before, the performance of crushed limestone sand-concrete with sp was also investigated in this research. the concrete mixtures used were the same as those used above: the weights of aggregates are shown in table 3 (with s/g=0.68), three cement contents 250, 350 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 17 and 450 kg/m3 were considered, and five w/c ratios were surveyed for each dosage of cement. prior to this, a preliminary study was undertaken to identify the optimum dosage of the sp. the testing procedure consisted of making several concrete mixtures that incorporate increasing proportions of the sp and measuring the slump for each mixture (baalbaki, 1990; kismi, 2012). self-evidently, in the calculation of the mixing water, due allowance was made for the volume of the liquid sp content. the results of this investigation are shown in figure 5 and the optimum sp dosages in terms of cement content are shown in table 4. the determined dosages are higher than those proposed by the manufacturer (1.5% in liquid form), and seem to depend on the cement content. moreover, the determined dosages appear to confirm results reported elsewhere by donza et al. (2002), which indicate that a high dosage of sp is needed in concretes made with crushed and for each type of sand and cement content the optimum dosage need to be studied. however, high dosage of sp aimed at reducing the water content to a very low value is undesirable as the effectiveness of the sp depends on temperature, cement chemistry and fineness (bharatkumar, 2001). fig 5: variation of slump as function of sp dosage, according different cement contents. table 4: optimum sp dosages in terms of cement content. cement (kg) saturation dosage dry extract (%) 250 4.25 1.42 350 2.50 0.84 450 2.25 0.75 4. results and discussion 4.1.fresh concrete properties results of the workability tests together with details of the concrete mixes considered during the investigation are given in figure 6. as expected, this figure shows that for any value of the cement content, the slump increases almost linearly with the increase in we/c. for a given slump, the we/c required is higher for leaner mixes. however, water demand (quantity of we) in the concrete mixtures tends to be higher for richer mixes. therefore, for mixes with high cement content, both the relatively high amount of water and the increase in cement paste contribute in enhancing the workability of the concrete mixture. fresh concrete density decreases upon an increase in either the we/c ratio or the slump. this may be ascribable to the fact that voids in 18 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 concrete that are initially packed with filler become progressively filled with water (substance lighter than filler) as the slump or water in the mixtures increases. consequently, for a given we/c ratio, the richer concrete mixtures tend to have the lowest fresh density due to the greater amount of water present in them. fig 6: variation of the needed we/c ratio according to slump. the inclusion of the sp into concrete mixtures resulted in both a reduction of water quantity and an improvement of the workability. the deflocculation of cement particles by the sp produces a much more efficient binder which leads to better workability, hydration, and strength (neville, 1995; pipilikaki, 2009a; menadi, 2009; aquino, 2010). the average reduction of water in the mixes was 30% which is much higher than the 15% stated by the manufacturer for conventional concretes. moreover, the workability as well as the deformability of fresh concrete was enhanced by the incorporation of the sp. for a given we/c, workability improves from low in the case of series a mixtures to medium in the case of series b mixtures. the use of sp increased also the density of fresh concrete, thus denoting an enhancement in the packing of concrete. however, as reported by researchers (donza, 2002), all series b mixtures displayed a considerable loss in workability after 20min. 4.2.hardened concrete properties the compressive as well as the tensile strengths of concrete for various mixes are presented in table 5. the obtained 28-day compressive strengths varied from 6 to 33mpa for series a mixtures whereas series b strengths are ranged from 29 to 54mpa. the corresponding tensile strength ranged from 1.6 to 3.8 mpa for series a and from 3.0 to 5.0 mpa. the failure of the majority of series a test specimens occurred at the aggregate-paste interface. however, in series b specimens, the excellent aggregate-paste bond resulted in a predominance of fractured particles. since the ratio we/c is the principal factor in concrete mixture proportioning for strength and durability (neville, 1995; al-ghahtani, 1998), the variation of the concrete compressive strength with c/we (bolomey equation) is shown in figure 7. the best fits for series a and series b as shown in figure 7, are respectively given by the following relations: 24.1269.1628  e c w c r (4) makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 19 the relation between compressive and tensile strengths is depicted in figure 8 for the considered series. table 5: compressive and tensile strengths results (mpa) cement (kg) series a series b we/c rc28 rt28 rc28/rt28 we/c rc28 rt28 rc28/rt28 250 0.56 12.91 2.38 5.42 0.40 33.89 3.60 9.41 0.66 11.29 2.24 5.04 0.43 33.21 3.53 9.41 0.71 10.50 2.18 4.82 0.49 28.64 3.11 9.21 0.73 8.42 2.00 4.21 0.51 27.72 3.03 9.15 0.81 6.43 1.84 3.49 0.53 27.15 2.97 9.14 350 0.89 20.82 3.04 6.85 0.34 42.33 4.28 9.89 0.50 20.18 2.99 6.75 0.37 41.52 4.20 9.89 0.51 16.85 2.71 6.22 0.39 39.41 3.99 9.88 0.57 13.22 2.41 5.49 0.42 35.22 3.59 9.81 0.66 11.26 2.24 5.03 0.46 32.39 3.34 9.70 450 0.71 28.04 3.65 7.68 0.28 49.25 4.85 10.15 0.41 26.15 3.49 7.49 0.32 47.99 4.72 10.17 0.43 24.31 3.34 7.28 0.35 45.65 4.48 10.19 0.46 22.12 3.15 7.02 0.39 39.81 3.92 10.16 0.49 18.44 2.84 6.49 0.42 37.78 3.73 10.13 the inclusion of the sp in concrete mixtures increases the strength by enhancing both the compactness of concrete through a reduction of water, air and the paste-aggregate interface bond. the gain in strength seems to be more significant (44 to 130%) for leaner mixes or mixes with excess of water (we/c  0.5). for concrete mixture with low we/c (0.5) the increase is relatively moderate (20 to 44%). however, the addition of sp did not alter with the same proportions the tensile strength of concrete. fig 7: evolution of the compressive strength according to the c/we ratio 75.063.1528  e c w c r (5) 20 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 the relation between rc28 and rt28 for the two series is similar to those found for conventional concretes. however, the tensile strengths of series a seem to be higher than what is traditionally found in concrete with the same rc28 as clearly indicated in table 5 (ratio rc28/ rt28) and figure 8. this may be attributed to the contribution of the limestone filler contained in the sand to the hydration of cement (cen, 2002; makhloufi, 2012a) by acting as a nucleation site. fig. 8 relation between compressive and tensile strengths for series a and b mixtures. 4.3 comparison with conventional concrete in order to identify the potential use of the concrete studied herein, a comparison between its properties (series a) and those of conventional silica sand-concretes was attempted. the conventional concrete results used in this comparison were obtained from the literature (dreux, 1998). comparison of the fresh behaviour of the concretes is captured in figure 8, whereby it can be observed that the two concretes have similar trend of behaviour; an increase in slump increases we/c. for a given workability and in the case of low workability or in leaner mixes (<450kg/m3), the we/c required for crushed limestone sand is lower than the corresponding value for conventional concrete. consequently crushed sand appears to have a better fresh concrete behaviour than conventional concrete in this range. this may be due to the lubricant action of the filler particles (particles size  150m) present in the crushed sand (neville, 1995). in richer mixes, the high amount of cement present in the mix tend to provide sufficient particles of the size indicated above to lubricate the concrete mix, and the fines of sand become less required. moreover, for a given water content and a chosen slump, crushed sand-concrete requires therefore more cement than conventional concrete (lower we/c). if eq. (1) is applied to natural sand-concrete made with the same coarse aggregates and cement as the crushed sand concrete studied herein, it will yield: natural sand 5.18 25.9 25.95.18 28 28   c ee c r w c w c r crushed sand 7.16 24.12 24.127.16 28 28   c ee c r w c w c r makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 21 it can be clearly seen from the above relations that for a given strength of concrete, crushed sand-concrete (series a) needs a higher c/we (lower we/c) ratio. this can only be realistically achieved with an increase in the amount of the paste. 5. conclusions the following conclusions can be drawn from this study: • mixture proportioning of concrete elaborated with crushed limestone sand can be adequately determined using standard mixing methods provided that the mixing water is properly estimated. • it appears that higher limits on the quantity of fines content in the crushed sand could be allowed for provided that the fines are clean and properly graded. • crushed limestone concrete required more mixing water than conventional silica sand concrete to achieve a specified fresh behaviour. a higher amount of paste is also needed for crushed sand concrete to acquire medium range strength. • similar or better mechanical strength than conventional natural sand concrete can be produced using crushed limestone sand as fine aggregate with a sp. however, to overcome the adverse effect of crushed sand such as texture and shape, a higher than normally used dosage of sp is required. the optimum dosage of sp needs to be determined for each cement and sand content. the inclusion of sp reduces the water content which in turn reduces the cement content for a specified w/c. consequently the saving of cement can compensate the extra cost of the sp. 6. references ahmed ea, elkourd aa (1989). properties of concrete incorporating natural and crushed stone very fine sand. aci mater j, 86: 417-23. afnor (1997). granulats définitions, conformité, specifications. french standard (nf p18-540), paris, 1997. afnor (1998). bétons mesure du temps d'écoulement des bétons et des mortiers aux maniabilimètres. french standard (nf p18-452), paris. al-ghahtani hj, abassi agf, al-amoudi osb (1998). concrete mixture design for hot weather: experimental and statistical analyses. mag concrete res, 50:95-105. aquino c, inoue m, miura h, mizuta m, okamoto t (2010). the effects of limestone aggregate on concrete properties. constr build mater, 24:2363–68. astm (1996). concrete aggregate. annual book of astm standards, standard specification c33-04(02), astm, west conshohocken, pennsylvania. baalbaki, m (1990). façon pratique d’évaluer le dosage en superplastifiant : la détermination du point de saturation. séminaire sur les superplastifiants, centre de recherches inter universitaire sur le béton, université de sherbrooke, pp.69-79. baron j, lesage r (1976). la composition du béton hydraulique, de laboratoire au chantier. rapport de recherche lcpc, no.64. benabed b, kadri eh, azzouz l, kenai s. (2012). properties of self-compacting mortar made with various types of sand. cement concrete comp, 34:1167–73. bharatkumar bh, narayanan r, raghuprasad, bk, ramachandramurthy ds (2001). mix proportioning of high performance concrete. cement concrete comp, 23:71-80. bolomey j (1935). granulation et prévision de la résistance probable des bétons. travaux, 19:228-32. bosiljkov vb (2003). scc mixes with poorly graded aggregates and high volume of limestone filler. cement concrete res, 33:1279-86. 22 makhloufi et al. j. build. mater. struct. (2014) 1: 10-22 bsi (1992). specification for aggregates from natural sources for concrete. british standard (bs882), london. celik t, marar k (1996). effects of crushed stone dust on some properties of concrete. cement concrete res, 26:1121-30. cen (2002). aggregates for concrete. european standard (en12620), london. donza h, cabrera o, irassar ef (2002). high strength concrete with different fine aggregate. cement concrete res, 32:1755-61. dreux g, festa j (1998). nouveau guide du béton et de ses constituants. 8ème edition, eyrolles, paris, p.409. gschaider hj, kalcher a (2001). improving the quality of crushed sands by screening off very fine materials. min proc ext met rev, 42:328-335. kim jk, lee cs, park ck, eo sh (1997). the fracture characteristics of crushed limestone concrete. cement concrete res, 27:1719-29. kismi m, saint-arroman jc, mounanga p (2012). minimizing water dosage of superplasticized mortars and concretes for a given consistency. constr build mater, 28:747–58. lecomte a, delarrard f, mechling jm (2001). résistance à la compression des bétons hydrauliques au squelette granulaire non optimisée. bulletin du lcpc, 234:89-105. lecomte a, masson l, remillon a (1995). formulation des bétons courants avec des granulats calcaires lorrains 0/6 et 6/20. annales de ibtp, 539:1-24. makhloufi z, kadri eh, bouhicha m, benaïssa a (2012a). resistance of limestone mortars with quaternary binders to sulfuric acid solution. constr build mater, 26:497–504. makhloufi z, kadri eh, bouhicha m, benaïssa a, bennacer r (2012b). the strength of the limestone mortars with quaternary binders: leaching effect by demineralized water. constr build mater, 36:17181. menadi b, kenai s, khatib j, aït-mokhtar a (2009). strength and durability of concrete incorporating crushed limestone sand. constr build mater, 23:625–33. neville am (1995). properties of concrete. fourth edition, longman, england, pp.844. nichols fp (1982). manufactured sand and crushed stone in portland cement concrete. concrete int, 4:5663. park s (2012). study on the fluidity and strength properties of high performance concrete utilizing crushed sand. int j concrete struct mater, 6:231-37. pipilikaki p, katsioti m (2009a). study of the hydration process of quaternary blended cements and durability of the produced mortars and concretes. constr build mater, 23:2246–50. pipilikaki p, katsioti m, gallias jl (2009b). performance of limestone cement mortars in a high sulfates environment. constr build mater, 23:1042–49. sriravindrarajah r, huai wang nd, wen ervin lj (2012). mix design for pervious recycled aggregate concrete. int j concrete struct mater, 6:239-46. taylor mr, lydon fd, barr bi (1996). mix proportions for high strength concrete. constr buildi mater, 10:445-50. j. build. mater. struct. (2023) 10: 27-39 original article doi : 10.34118/jbms.v10i1.2884 issn 2353-0057, eissn : 2600-6936 the influence of mineralogical composition and alkali reactivity for utilization of some egyptian crushed granites as a concrete aggregate maged e. el-fakharany 1, *, ahmed a. omar 1, mahmoud l. abdel latif 2 1 researcher, housing and building national research center (hbrc), egypt. 2 associate professor, housing and building national research center (hbrc), egypt. * corresponding author: geomagedmg@yahoo.com received: 31-01-2023 accepted: 05-06-2023 abstract. egyptian eastern desert is rich in many areas that contain granites masses throughout the geological era; some of them show good characteristics of the rock hardness, durability, density and mineralogy. this current research aims to utilize three main types of granite aggregates based on their mineralogical composition and alkali reactivity with cement during concrete production. the studied granite aggregate can be also classified into red younger granite aggregate, white older granite aggregate and grey older granite aggregate. evaluating these granite rocks as aggregate used in concrete mixture is interesting by produced three mixes using the three studied granite aggregate symbolized (red ga), (white ga) and (grey ga), tested mechanically to give a more detailed for the obtained results to be not restricted for only studied granite aggregate criteria but also to follow the actual reaction of this studied granite aggregate with cement. it was obtained that all studied granite aggregates within acceptable limits of concrete aggregate by following egyptian code (ecp203) although their variation on its mineralogical composition. some reflections produced from change in mineralogical composition between the three studied granite aggregates exhibited by relative regression in the average physico-mechanical values for both (white and grey ga) than (red ga). on the other hand, slight reactive for (red ga) than others at the age of 28 day. in addition, all produced (red ga), (white ga) and (grey ga) mixes were acceptable mechanically with limits of (ecp-203) giving benefit for using all of the studied granite aggregate after their detailed study involving its mineralogical composition and alkali aggregate reactivity (aar). key words: aggregates, granite, mineralogical composition, alkali reactivity, compressive strength. 1. introduction generally, aggregate encompasses a wide variety of naturally occurring or manmade materials of different sizes and physical properties (langer, 1993). engineering definition of aggregate considered as particles of rock which when brought together in a bound condition form units of engineering structure, (neville, 2011). nature aggregate type essentially refers to the geological origin of the aggregate under investigation. the main distributed aggregate types could be classified into igneous, sedimentary, and metamorphic rocks as discussed by many authors (tsado, 2013; shahien et al., 2014; petrounias et al., 2018; el-fakharany et al., 2019). locally, igneous aggregates are further subdivided on the basis of their mineralogy to granite and basalt according to the egyptian specification. aggregate should be selected for adequate durability and workability for concrete application. limited resources and huge demand of local aggregates needed to investigate an alternative to other locally traditional aggregates such as basalt, limestone and dolomite (abd-allah et al., 2018; http://www.oasis-pubs.com/ mailto:geomagedmg@yahoo.com 28 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 masoud et al., 2020). granite aggregate is very hard rock mainly of granular structure and angular shape due to the crushing preparation. it is wide distribute on earth forming most of the igneous basement rocks. soundness properties of granite rocks acquired their aggregate a good compressive strength with the concrete mix and make it serve as an adequate building material (ubi et al., 2020; sharma et al., 2016). it is regarded as the best aggregate for high grade concrete by szczesniak et al. (2019). mineralogical and chemical composition of aggregate can affects the quality of concrete and its reactivity (shahien et al., 2014; el sayed et al., 2014; antolik & niedzwiedzka, 2021). feldspars, quartz and mica crystals are the main minerals content of granites which reflect the soundness and stability of the concrete (rutkauskas et al., 2017). since aggregate filled most of the conventional concrete volume. it is inevitable that the physical characteristics and chemical compositions of such a large percentage of occupying mass should contribute important properties to both the fresh and hardened product. (jackson & dnir, 1991; kabir et al., 2019). concrete strength found to depend on the quality, type, surface and internal structure of the aggregates besides the properties of interfacial transition zone close to aggregate surface (beshr et al., 2003; sorensen & kristensen, 2007). reactive siliceous aggregate with high alkali content of cement may cause the alkali silica reaction (asr) as documented by shahien et al. (2014). it was known that the mechanism of asr proceeds first through the hydrolysis of reactive silica from harmful minerals impurities by oh ions from sodium and potassium hydroxides in presence of moisture of the surrounding media (rutkauskas et al., 2017). then formation of a hygroscopic gel involves absorption of water which increases the concrete volume and finally causes a type of concrete deterioration and damage (ramachandran, 1998; wakizaka, 2000). granites rocks are widely distributed in egypt deserts all over the egyptian shield, constituting approximately 60% of its plutonic assemblage (el ramly, 1972). the igneous rocks especially granites could be a good source of concrete aggregate. the recent research focused on evaluation the role of mineralogical composition and alkali reactivity of the crushed granites as a concrete aggregate, particularly in some areas such as the egyptian eastern desert where rare other aggregate sources. although the high cost of quarry-crushed granite due to high energy consumption during rock blasting and transportation as discussed by nduka et al. (2018), but locally it is still highly preferable in case of the excavated granites did not used as ornamental stone and considered as useless rock masses. from this stand point, the available crushed granite aggregate will be used as an alternative and investigate its behavior with cement paste. 2. sampling and experimental program different samples of granites were collected to evaluate the possibility of using some types of crushed granite as a concrete aggregate and the influence of their mineralogical composition on aggregate properties. the studied samples represent three types of local granite (red, white and grey granite) spread in egyptian eastern-desert quarries (fig.1). in the recent research, the studied samples of crushed granites chosen carefully to achieve the aim of the current research. the studied crushed granite samples can be divided to two different main geological origin, red granite originated to younger granites while on the other hand, older granites is represented by the grey and white colored granites, based on the classification of the previous egyptian geological studies (el ramly, 1972; el gaby, 1975; greenberg, 1981; gharib & obied., 2004). all studied samples were crushed by using a laboratory jaw crusher to prepare granite aggregates (ga) with a maximum size of 10mm. while natural quartz sand with a maximum size of 4.75 mm was used as fine aggregate. portland cement type ii was used for all concrete mixes in this study (portland cement-cemii-rank42.5n, suez cement company, egypt) with 3.15 specific gravity that fulfils the requirements of egyptian standard (es 4756, 2009). el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 29 fig 1. location map of the different studied granitic aggregates (ga) analyzing by x-ray diffraction [xrd (model x’pert prophillips mpd– panalytical manufacturing b.vco., netherlands iso 9001/14001 kema, 0.7516) provided with (cu) anode at 40 kv&30 ma with a scanning speed of 2o /minute), axios (pw4400) wd-xrf sequential spectrometer (panalytical, netherland)] with the aid of petrography to identify crushed granitic aggregates composition. the three main types conducted to polarizing microscope to investigate not only the main mineralogical composition and crystals relations (texture), but also to help in identifying the presence of any altered minerals which may cause detectable effect on the main alkali silica reactivity of the studied different granites. alkali silica reaction (astm c1260-21), also some physico-mechanical tests water absorption (astm c127-15), aggregate crushing value (acv) and aggregate specific gravity are performed on ga samples to know their suitability for use in concrete meet the astm c33 specification. the concrete mix design according to (ecp 203, 2017) is followed. the proportion by mass 1:1.8:2.9 (cement: sand: aggregate) of the concrete mix with 0.45 w/c ratio was used. the representative samples then casted in 0.1x0.1x0.1 m cubes to determine its compressive strength at ages of 14 and 28days according to the egyptian code (ecp203, 2017). 3. results and discussion 3.1 x-ray diffraction analysis the xrd analyses of the aggregate elaborated with the studied granites are illustrated in fig. 2. the predominant minerals within granitic aggregate types are quartz, plagioclase, and k-feldspars with minor amounts of biotite and traces of actinolite minerals. quartz mineral showed the highest intensity between all minerals in all the granitic samples especially the white and grey granite samples. the three granitic aggregates show minor variables between feldspars content. red ga gray ga white ga 30 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 relatively red granite shows the highest intensity of the total feldspars (both plagioclase and kfeldspar) than grey and white granite samples, although the red granitic aggregate type showed relatively the lowest biotite mineral content between all samples. there is not an indication of any mineralogical alteration within the studied granite aggregates except traces of kaolinite within the grey granite indicated begin of hydrolysis type of feldspars. traces of actinolite mineral were also detected within the studied grey granite sample. fig 2. xrd patterns of the different studied ga 3.2 petrographic analysis in the recent research three main types of granites which can be divided into two main groups : the first one includes younger granites that represented by red ga while on the other hand, the second is older granites that represented by the grey and white colored ga. petrographically, not only investigate the main mineralogical composition and the texture of the three main types but also to help in identifying the presence of any altered minerals which may cause detectable effect on the main reactivity of the studied different granitic aggregates. firstly, the petrographic investigation of the studied red granite showed that spread and presence of microcrystalline quartz crystals between crosshatched microclne and perthite (fig.3). slightly to moderatly altered plagioclase(albite) surrounded by quartz crystals. the studied red granite shows relative increase in alkali feldspare (microcline) than the other studied granitioids. the (white and grey) exhibited similar mineralogical compostion which differs than the red as: biotite mineral more apperared in (white and grey). thin section photomicrograph of grey granite aggregate showed simple altered coarse plagioclase crystals associated with biotite and surrounded by quartz grains (fig.3c). the white granite showed quartz grains with medium biotite minerals intersected the coarse lamellar plagioclase crystals (fig.3d). 10 20 30 40 50 red ga grey ga white ga 2q in te n s it y ( a .u ) qtz : quartz ab: albite bt: biotite mc: microcline k: kaolinite ac: actinolite bt ab qtz ab mc qtz ab mc ab ab mcqtz qtz mc qtz k ac el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 31 fig 3. photomicrographs of the three ga types, (a) the presence of microcrystalline quartz between crosshatched microcline and perthite of (red ga). (b) slightly to moderatly altered plagioclase (albite) surrounded by quartz crystals. (c) moderate altered coarse plagioclase crystals associated with biotite and surrounded by quartz grains (grey ga). (d) quartz grains with medium biotite minerals intersected the coarse lamellar plagioclase crystals in (white ga) thin section. [qtz:quartz, fsp:feldspare, mi:microcline, pl:plagioclase, bt:biotite]. 3.3 chemical characteristics the xrf analysis of oxides content in granitic aggregates is shown in table 1. it can be noticed that sio2 content values vary between 67.41% (white ga) and 69.82% (red ga). the higher value in red granite may be related to the abundance of more feldspars and quartz minerals than others. aluminum oxide content of red and white samples are slightly similar reached to 14.78% than the least al2o3 value in grey granite sample (11.73%). both of the red and white granites characterized by enrichment in alkalis (k2o+na2o) content which attributed to the relatively higher contents of alkali feldspars. the percents of iron oxide (3.5, 4.0 and 4.9%) for (red, white and grey ga) respectively with approximately 1% of magnesium oxide indicate to presence of biotite mineral especially in the white granite aggregate. there is a direct relation between increasing of calcium oxide content and increasing of loss among all studied aggregate samples. to some extent the relatively high value of the loss on ignition as in case of grey granite aggregate (a) (b) (c) (d) p l q tz q tz f s p q tz p l p l b t b t b t q tz mi p l 32 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 since it reached to 4% loss may be related to the water loss of altered minerals. the used cement show high percent (58.71%) of calcium oxide and insoluble residue reach 0.82%. also, the sodium equivalent calculated from portland cement oxides content equal 0.54 which considered in limits of the astm c1260 (2021) requirements. table 1. chemical composition of the used materials oxide content (wt,%) cement red ga grey ga white ga sio2 21.21 69.82 68.51 67.41 al2o3 5.42 14.00 11.73 14.78 fe2o3 5.65 3.50 4.89 4.01 cao 58.71 1.50 5.00 2.00 mgo 2.17 1.06 1.30 1.39 so3 2.76 0.20 0.12 0.10 na2o 0.41 3.37 1.53 4.10 k2o 0.20 3.82 2.42 3.10 tio2 0.44 0.48 0.27 0.67 p2o5 0.17 0.18 0.13 0.18 mn2o3 0.23 0.08 0.06 0.04 loss of ignition (loi) 2.47 1.98 4.00 2.20 total 99.94 99.99 99.96 99.98 ins.res 0.82 na2oeq 0.54 c3a 4.81 c3s 25.33 c2s 41.79 c4af 17.18 3.4 water absorption (wa) there is affinity for wa values of the studied granite aggregates as shown in fig. 4. it varies between 0.13 and 0.18% for red and white aggregate samples respectively where white ga shows relatively the highest percent between the studied granitic aggregate. that may attribute to abundance of biotite mica than other samples. to achieve durable concrete mix, aggregate with low water absorption classification (less than 0.2%) should be used besides avoid aggregate with high abundance of biotite mica as mentioned by ahmad et al. (2016). increase of wa percent will not be more safely in concrete due to the mechanical adherence with high water absorption may be weakening as discussed by el-fakharany et al. (2019). el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 33 fig 4. water absorption (wa) values of the studied ga. 3.5 aggregate crushing value (acv) the acv gives a relative measure of the resistance of the aggregate applied to erosion or friction effect. from the results, the acv is ranged between 18.98 and 23.11% (fig. 5). it was noticed that there was an increase in loss percent (as detected by xrf) within increasing of acv. grey granite showed the highest value and therefore the lowest resistance aggregate between the studied granitic aggregates. the highest value may be related to the presence of friable clay mineral (kaolinite) or the high percent of elongated shape biotite mineral as detected from the xrd analysis of this aggregate sample. however, these acv results were considered acceptable in normal concrete (the maximum limit is 30%) and in especial concrete which exposed to the friction (the maximum limit is 25%) according to the egyptian code for concrete (ecp-203, 2017). fig 5. aggregate crushing values (acv) of the studied ga. 3.6 specific gravity the specific gravity of all the studied granitic aggregate ranged between 2.59 and 2.64 gm/cm3 with an average equal 2.62 gm/cm3 (fig.6). white granite sample showed the lowest value 34 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 between those granitic aggregates (2.59 gm/cm3) however, that value is considered reasonable to good concrete with normal weight. all values are within the acceptable limits which ranged between 2.50 and 2.75 gm/cm3 for the natural aggregate according to(ecp-203, 2017). fig 6. specific gravity values of the studied ga. 3.7 alkali silica reaction the tested granite aggregate samples contain few reactive silica/silicate minerals because the linear expansion after 14 curing testing days did not exceed 0.1 % (0.002 % for grey granite mix, 0.007 % for white granite mix and 0.03% for red granite mix) as the result curves showed in figure 7. therefore, the studied samples can be considered as non alkali-reactive aggregate (if expansion after14 days < 0.10 %) according to astm c1260 test method. in case of soaking the mixes for the long period of 30days the expansion results of granitic aggregates showed slightly difference and still within the limits (expansion after 30 days < 0.2 %). the determined insignificant difference between the tested samples (0.004 % for grey granite mix, 0.041 % for white granite mix and 0.102% for red granite mix) is expected due to the similarity of the predominant minerals content as identified by mineralogical composition. however, red granite can be distinguished to some extent expansible from others tested granitic aggregates. that noticed tendency of expansion may attribute to the high alkali feldspars content than others in addition to the texture behavior of such minerals. the expansion gel may be formed within microcrystalline quartz also associated to its microcracks, in addition to expansion can be more accused if the granitic aggregate contains perthite texture (torres et al., 2010). el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 35 fig 7. the alkali silica reaction curves of the studied ga mixes 3.8 characterization of granite aggregate (ga) mixes compressive strength at 14and 28-days interval was evaluated by testing four moulded concrete cubes of each ga type. there is a simple variation in strength between all ga concrete samples (fig. 8). this may relate to specific physical difference and mineralogical composition of the applied granitic aggregate. the strength ranges between 28.63 and 32.24 mpa in 14 days interval. then strengths increase to the range between 40.91 and 50.38 mpa in the age of 28days. according to the egyptian code that strength values are considered acceptable within the limit of traditional concrete after 28days. the strength of red ga still the highest between the three ga concrete types till the later age, however its ability for more alkali silica expansion than (grey and white ga). the relative high strength value in both early and later ages of the (red ga) mix than studied mortars may due to the properties of crushed granite aggregate with lower content of biotite mineral give good performance within the concrete. the weak bond present between the cement paste and the soft crumble surface of flaky biotite particles, also their irregularity in shape was responsible for poor workability and lowering the compressive strength as reported by (wakizaka et al., 2005). 36 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 fig 8. correlation between 14 and 28 days compressive strength of the studied ga mixes it showed that by mineralogical analysis the composition of casted concrete is influenced by the type and content of its aggregates in case of blended ga with portland cement. quartz and feldspars minerals are present in the form of fine and coarse aggregates added to the cement paste in addition to the cement phases of portlandite, and calcium silicate hydrate (fig.9). the intensity of cementitious minerals has approach result between the studied samples and gives relatively poor diffractograms after 28 day. further examination with the aid of stereo-microscope, the photomicrograph of the red ga mortar reflects good compaction and gives dense appearance as noticed in (fig.10). that indicates the high strength gained by red ga mix between other studied ga mixes. therefore, the strength quality of the concrete mix elaborated with the studied granitic aggregate cannot be judged from xrd analysis alone without petrography investigation under the polarizing and stereo-microscopes. 29,563 28,635 32,244 42,845 40,908 50,381 0 10 20 30 40 50 60 white ga grey ga red ga c o m p re ss iv e s tr e n g th ( m p a ) 14 days 28 days max limit (28d) el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 37 fig 9. xrd patterns of the different studied ga mixes. fig 10. photomicrograph of the studied red ga mix (agg:aggregate, f.agg:fine aggregate, c.p:cement paste). 10 20 30 40 50 red ga mix grey ga mix white ga mix 2q in te n s it y ( a .u ) bt qtz p ab qtz qtzmcmcqtzqtz ab ab csh ab mc qtz : quartz ab: albite bt: biotite mc: microcline csh: calcium silicate hydrate p: portlandite 38 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 4. conclusions depending on the obtained outcomes of the recent study it can be concluded that: all of the studied crushed granitic aggregate achieved the requirements of the physicomechanical average values for its using as a concrete coarse aggregate based on documented egyptian code (ecp-203, 2017). the impact of mineralogical composition as important parameters in the evaluation and differentiation between the studied granite aggregates should be taken in to consideration during aggregate selection. mineralogically, there is a similarity between white and grey granitic aggregates while red granitic aggregate shows excess of alkali feldspar mineral (microcline). the negative effect of the presence altered minerals (kaolinite and actinolite) in the studied older granite aggregates (white and grey ga) besides mica (biotite) as all those minerals led to slight increase in water absorption average value associated with slight regression in the other different studied physico-mechanical values than younger granite aggregate (red granite aggregate). the second important parameter within the current study is alkali silica reaction of the different studied granitic aggregate by which it can be concluded that; all of the studied granite aggregates are non-reactive up to the curing time 14 day. on the other hand, only the red granite aggregate show relatively raises in linear expansion curve up to 28days with a tendency to be in the slow reactive zone most likely to be as a reason for its excess of alkali feldspar mineral (microcline) and its specific texture described by the petrography examination. however, the standard method for identification asr (astm c1260) classifies the studied three types of local egyptian granitic aggregate as a non reactive aggregate. although granitic aggregate show some extent similar mineralogical and chemical composition but it may show differences in the behavior within cement paste. characteristics of the studied granite aggregate play an important role in its possibility of their utilization as a concrete coarse aggregate. granitic aggregate with excess presence of mica minerals may accompanied with slightly decrease of compressive strength. moreover, granitic aggregate with higher altered minerals content or perthitic texture should be avoided and take into consideration in selection a high quality igneous aggregate. the results clearly showed the need to study the changes in the mineral composition of the granite aggregate and its relationship to the alkali reactivity of it in concrete mixtures, as the mineral changes, even if they were slight have repercussions on the alkali activity of it and thus the quality of the concrete product elaborated with granite aggregate. 5. references abd-allah, a. m, baghdady, a.r., and dawood, y.h. (2018). adequacy of carbonate aggregates as an alternative for chert aggregates in concrete manufacture, construction and building materials, 181, 94–105. ahmad, m., ansari, m., singh, r., sharma, l., singh, k., prashant, singh, t. n., (2016). mineralogical control on the water absorption of few igneous and metamorphic rocks. indorock2016 proceeding mashud, 520-531. antolik, a., niedzwiedzka, d. (2021). assessment of alkali silica reaction in granitic rocks, construction and building materials, 295, 12. astm c127, (2015). standard test method for density, relative density (specific gravity), and absorption of coarse aggregate, astm international, west conshohocken, pa, www.astm.org http://www.astm.org/ el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 39 astm c1260, (2021). standard test method for potential alkali reactivity of aggregates (mortar-bar method), annual book of astm standards, 04 (02), concrete and aggregates, astm international, west conshohocken, pa, www.astm.org astm c33, (2018). standard specification for concrete aggregates, astm international, west conshohocken, pa, www.astm.org astm c642, (2013). standard test method for density, absorption and voids in hardened concrete, astm international, west conshohocken, pa, www.astm.org beshr, h., almusallam, a.a., maslehuddin, m. (2003) effect of coarse aggregate quality on mechanical properties of high strength concrete. construction and building materials, 17, 97-103. ecp-203, (2017). egyptian code for the design and implementation of concrete structures, manual of testes, copy2017, hbnrc, giza, egypt es 4756–1 (2009) cement part: (1) composition, specifications and conformity criteria for common cements. egyptian organization for standardization and quality, egypt el-fakharany, m. e., ezzat, m., gad, a., abdel-ghafour, n. g., baghdady, a. r. (2019) performance of dolomitic cementitious mortars as a repairing material for normal concrete in egypt, építő anyag – journal of silicate based and composite materials, 71 (2), 33–42. el-gaby, s. (1975) petrochemistry and geochemistry of some granite from egypt. n. jb. mineral. abh., 125, 147189. el-ramly, m. f. (1972) a new geological map for the basement in the eastern desert and southwestern desert of egypt, ann. geol. surv. egypt, 2, 1-18. el-sayed, m. i., shahien, m. g., abdel-ghafour, n. g., gharieb, s. e., abou bakr, a. (2014) mineralogical assessment of the coarse carbonate aggregates of gabal ataqa to predict their alkali reactivity behavior, suez, egypt. egyptian journal of applied sciences, 29 (6) , 194-205. gharib , m. e. and obied,m.a., 2004. geochemistry and evaluation of the neoproterozoic granitoids magmatism in the wadi shiekh-gabal saint katherine area, southwestern, sinai. 7th int.conf.,geology of the arab world, cairo univ.,egypt, 53-73. greenberg, j. k. (1981) characteristics and origin of egyptian younger granites, summary. bull. geol. soc. am., 92, 224-232. jackson, n., dnir, r. k. (1991) civil engineering material, (4th ed). addison wesley longman’s limited edinburgh gate, england kabir, n., aliyu, s., nasara, m., chinade, a., shehu, a. (2019) characteristics of different type of coarse aggregate on properties of high performance concrete, sustainable structure and materials, 2 (1), 88-96. langer, w.h. (1993). natural aggregates of the conterminous united states, u.s. geological survey bulletin, second printing, 1-3, 1553-1560. masoud, m. a., rashad, a. m., sakr, k., shahien, m. g., zayed, a. m. (2020) possibility of using different types of egyptian serpentine as fine and coarse aggregates for concrete production materials and structures, 53, 1-17. nduka, d. o., fabgenle, o. i., joshua, o., ogunde, a. o., omuh, i. o. (2018) comparative analysis of concrete strength utilizing quarry-crushed and locally sourced coarse aggregates, international journal of mechanical engineering and technology, 9(1), 609–617. neville, a.m. (2011). properties of concrete, pearson education limited. edinburgh gate, (5th ed) england. petrounias p, giannakopoulou p, rogkala a et al. (2018) the impact of secondary phyllosilicate minerals on the engineering properties of various igneous aggregates from greece. minerals, 8, 329. ramachandran, v.s. (1998). alkali-aggregate expansion inhibiting admixtures, cement and concrete composites, 20 (2-3), 149-161. http://www.astm.org/ http://www.astm.org/ 40 el-fakharany et al., j. build. mater. struct. (2023) 10: 27-39 rutkauskas, a., nagrockienė, d., skripkiūnas, g., barkauskas, k. (2017). determining reactivity level of granite aggregate for concrete, construction science, 20, 33–37. shahien, m.g., el sayed, m.i., abdel ghafour, n.g., and el-fakhrany, m.e. (2014). effect of mineralogical composition of some egyptian wadi wash aggregate on the alkali aggregate reactivity. egyptian journal of applied sciences, 29 (4),194-205. sharma, a. s., vinoth kumar, n., harish j., and sathish, a. (2016). utilisation of granite chips as a supplementary coarse aggregate material. indian journal of science and technology, 9 (2), 1-4 sorensen, e. v., kristensen, l. f. (2007). sea dredged gravel versus crushed granite as coarse aggregate for compacting concrete in aggressive environments, nordic concrete research, 7 (1-2), 9-18. szczesniak, a., siwinski, j., stolarski, a. (2019). experimental study on the use of granite as fine aggregate in very-high-strength concrete. iop conf. series: materials science and engineering, 471, 1-8 torres, a. alaejos, p. soriano, j. (2010) comparative study of the alkali silica reaction (asr) in granitic aggregates, estudios geol, 66 (1), 105-114. tsado. a, (2013). a comparative analysis of concrete strength using igneous, sedimentary and metamorphic aggregate as coarse aggregate, zeszyty naukowe politechniki częstochowskiej.19 (169), 179-191. ubi, s.e, nkra, p.o, agbor, r.b, ewa, d.e, nuchal, m. (2020) efficacy of basalt and granite as coarse aggregate in concrete mixture, international journal of engineering technologies and management research , 7 (9), 1-9. wakizaka, y. (2000). alkali-silica reactivity of japanese rocks, engineering geology, 56 (1–2), 211-221. wakizaka, y, ichikawa k, nakamura y, anan s (2005). deterioration of concrete due to specific minerals, environ econ, 2, 331–338. j. build. mater. struct. (2020) 7: 105-118 original article doi : 10.34118/jbms.v7i1.709 issn 2353-0057, eissn : 2600-6936 dynamic analysis of a multi-span simply supported prestressed concrete bridge with restrainers and seismic isolation devices ouanani m 1,3 *, sandjak k2,3 , tiliouine b3 1 université de djelfa, faculté des sciences et de la technologie, djelfa, algeria. 2 département de génie civil, faculté des sciences de l’ingénieur, université m’hamed bougara, 35000, boumerdes, algeria. 3 ecole nationale polytechnique, département de génie civil, laboratoire de génie sismique et de dynamique des structures, 10 avenue des frères oudek, hassen badi, bp. 182, 16200, el harrach, alger, algérie dynamics, alger, algeria * correspondingauthor:mouloud.ouanani@g.enp.edu.dz ,m.ouanani@univ-djelfa.dz received: 16-06-2020 accepted: 24-08-2020 abstract.the nonlinear f.e. code structural analysis program (sap) in which the primary nonlinear characteristics of bearings, impact elements and steel restrainer cables considered herein in order to investigate the dynamic analysis of a multi-span simply supported msss prestressed concrete bridge, equipped with steel restrainer cables and lead rubber bearings lrb devices includingsoil structure interaction (ssi) effects. a msss bridge with restrainer cables and lead rubber bearings at the two abutments and intermediate bents located in north algeria is selectedaccording to rpoa for seismic design category 1 is considered in this study.a detailed 3d nonlinear analytical model of study bridge subjected to three components identical seismic excitation includingpounding elements, restrainer cables and bearing devices at expansion jointsis developed. the nonlinear characteristics of theses boundary elements are represented by bilinear hysteretic models. under strong seismic excitations, the large longitudinal displacementsresult the collision between bridge decks or even unseating of these decks at expansion joints of msss bridge. finally,the study reveals among others that in order to prevent deck unseating resulting from restrainer failures and subsequent bridge collapse, particular attention should also be given to proper design of nonlinear characteristics of restrainers and bearing devices. key words: nonlinear f.e., soil structure interaction, pounding elements, restrainer cables, lead rubber bearings 1. introduction the multi-span simply supported msss prestressed concrete bridgesare frequently used in highway bridgesrepresenting an essential component of transportation networks. this categorie of bridges presentsvarious advantages such as, fast construction, convenient manufacture and installation and their adjacent bridge decks are connected at expansion joints in order to accommodate temperature and deformations induced by shrinking and creep of prestressed concrete. unfortunately, the expansion joints between adjacent decks or between deck and abutment become vulnerable components under severe ground motions, because of the superstructure pounding which may induce the local failure of the deck itself and unseating damage. however, the msss highway bridge damages due to pounding impact at the expansion joints of girders and abutments and unseating have been particularlyobserved in several seismic events, (e.g. wenchuan earthquake (hung et al., 2008), boumerdes earthquake (afps, 2003), chi–chi earthquake (uzarski and arnold, 1999), kobe earthquake (chouw,1995) and northridge earthquake (todd et al., 1994)). in particular, the chi-chi earthquake (1999) in taiwan revealed hammering at the expansion joints in some bridges which resulted in damage to shear keys, bearings and anchor bolts (uzarski and arnold, 2001). based on these observations, pounding mailto:mouloud.ouanani@g.enp.edu.dz mailto:m.ouanani@univ-djelfa.dz 106 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 can cause crashing and spalling of concrete at the impact locations, result in damage to column bents, abutments, shear keys, bearing pads and restrainers, and possibly contribute to the collapse of deck spans. many previous works have been conducted to investigatethe fragility of highway bridges under uniform ground motions (shinozuka et al., 2003; desroche and muthamar, 2004; hong et al., 2019) and non uniform ground motions (yang et al., 2018), they corroborated that the multispan simply supported msss prestressed concrete bridges are most vulnerable to pounding damage due to the discontinuity in the superstructure at multi-column bents. in particular, hong et al. (2019) investigated the effect of the nonlinear impact on the longitudinal response of multi-span simply supported bridges under strong earthquakes and they concluded that the collision parameters affect the responses of the multi-span simply supported beam bridge subjected to ground motions. further researches by bi et al. (2013) and yang et al. (2018) have also studied extensively the impact of spatially varying ground motions on the seismic response of bridges when pounding was either considered or not considered. in addition to above pratical justifications, the damage data of bridges have also illustrated thatthe bridge components structural performance may be very sensitive to 3d components of ground motions (tiliouine and ouanani, 2012) and foundation soil flexibility including abutment–backfill soil (ouanani and tiliouine, 2017). this paper presents some results from an exhaustive investigation carried out on the dynamic analysis of amulti-span simply supported msss prestressed concrete bridge equipped with retrainers and seismic isolation devices at expansion joints and abutments including soil structure interaction (ssi) effects. in this context, the nonlinear time history analyses using detailed 3d finite element model fem of a msss bridge located in north algeria are performed to assess the performance of the steel restrainer cables and lead rubber bearing devices lrb under the 3d components of severe seismic excitation. nonlinear characteristics of the impact and restrainer elements at expansion joints and bearing devices at the seat-abutments and intermediate bents of study bridge are represented by nonlinear hysteretic models. these nonlinear properties are considered in the dynamic analysis of amulti-span simply supported concrete bridge. these considered nonlinearities include the width of expansion joint, the impact stiffness of colliding spansand the longitudinal stiffness of the bearing device in the seismic analysis in order to predict or to avoid the collision damages in bridge structures. in order to include the ssi effects, the effective stiffness, foundation soil damping at the base of the spread footings have been evaluated using procedure guidelines (fema, 2000). 2. description and 3-d nonlinear analytical modelind of msss prestressed concrete bridge 2.1. description of msss prestressed concrete bridge fig. 1 shows details of typical mssspre-stressed concrete girder bridge located on the east-west highwayjoining the bouiracity in eastern algeria. the bridge consideredin this study isstraight with slope of 4.60% and consists of a three discontinued decksreinforced concrete of 13.1 m wide and equal length of 35.85m (figures. 1(a), 1(b))and supported by seven prestressed concrete t girders (figure 1(c)). the bridge with an overall length of 107.77m is supported on multi-column bents of equal height of 19.3m and two seat-type abutments.each column has a circular cross-section with 1.8 m diameter (figure 1(d)). the bridge consists of four expansion joints in steel of type wd110, located on the two multicolumn bentsand the two abutments. each pre-stressed concrete t-shaped girder is supported at abutments and bents by the lead rubber bering device lrb. https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-1 ouanani et al., j. build. mater. struct. (2020) 7: 105-118 107 fig 1. general description of msss prestressed concrete bridge. 2.2. 3d nonlinear analytical modeling of msss prestressed concrete bridge the msss bridge with steel restrainer cables and lead rubber bearings at two abutments and intermediate bents considered in this study is analytically modeled as a lumped mass system. thus, a 3d nonlinear analytical model of a bridge is developed using the nonlinear f.e. code (csi bridge, 2015). the superstructure and multi-columns bents of bridge are modelled as elasticbeam elements, while bridge additional connecting components such as the expansion joints that represent pounding elements aremodelled by linear spring elements, while the lead rubber bearings and restrainer cables are modelled by nonlinear springelements accounting the energy dissipation under strong motion. pre-stressed expansion concrete girder joint 107.77m ex : expansion joint lrb : lead rubber beraing b: bent abut: abutment restrainer (src) abut.2 abut.1 b.3 b.2 lrb 6 lrb 5 lrb 4 lrb 3 lrb 2 lrb 1 ex1 ex4 ex3 ex2 35.85m 35.85m 35.85m 1 9 .3 m (b) elevation view: longitudinal direction a a multi-column bent (c) bent elevation: transverse direction column superstructure (deck + prestressed girders lrb bearing s 1.8m (d) column section a-a pre-stressed concrete girders backfill soil 13.10 m (a) plan view 108 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 2.2.1 analytical modeling of restrainer cables elements restrainer cable elements are devices which permitthe limitation of the deck longitudinal displacement and relative hinge openings in order to prevent unseating of bridge spans, or as fail-safe mechanisms to support bridge decks in case of unseating. they are often employed in bridges with insufficient seat widths and placed at the hinge locations at the deck abutment and deck-bent cap interfaces in the (msss) bridge considered herein. in general, the restrainer cables are employed in order to avoid unseating of the superstructure at the expansion joints.the restrainers alter the behavior of adjacent spans by transferring forces as the span opening exceeds the slack in the cable. three types of restrainers are used in order to assess the seismic performanceofamsss bridge: the steel restrainer cables (src), the shape memory alloy (sma) bars in tension (sma-t), and the sma bars in bending (sma-b) (desroches and delemont, 2002; tazarv and alam, 2018). for the considered bridge, the src devicesconnecting the adjacent spans at the expansion jointsas shown in fig. 1(b) are used herein in order to investigate the dynamicanalysis of a multi-span simply supported msss. 2.2.2 analytical modeling of pounding elements two analytical methods are available for simulating the highly nonlinear behavior of pounding at the interfacesspan-abutment and span-span; the stereo mechanicalmethod and that of the contact element. the latter is activated when the collision occurs between decks/abutments and deck/deck of the bridge.the spring stiffness of pounding elementsis fixed proportionally to the axial stiffness of the neighboring structural segments, sometimes in combination with a damper (kawashima and shoji, 2000; hong et al., 2019), the spring stiffness, kgap is expressed as: where ea represents the axial stiffness of the cross-section of the superstructure, l is the length of the superstructure’s element, and is the ratio of impact spring stiffness to that of the superstructure. the gap provided at the expansion joint is 11cmand adjacent spanscollision develop compressive forces when the relative displacement exhausts this gap width. it is modelled by the kelvin model with stiffness kgap = 45.87x106 kn/m. the compressive forces ( ) for this model are expressed as follows (desroche and muthamar, 2004; hong et al., 2019): ( ̇) otherwise, is given as. ; ̇ ̇ ̇ where and are the displacements of nodes i and j respectively, gap is separation between these nodes, ̇ and ̇are the velocities of nodes i and j respectively. the dashpot constant of the kelvin model is calculated using these formulas √( ) ouanani et al., j. build. mater. struct. (2020) 7: 105-118 109 √( ) where m1 and m2are the masses of the two impacting bodies, the constant (e) is the coefficient of restitution, for which the value is 1 for completely elastic impact and 0 for completely plastic impact (e.g. anagnostopoulos and spiliopoulos, 1992). 2.2.3 analytical modeling of lr bearing devices bridgesseismic isolation with lead rubber bearings (lrbs) devices is an effective technique to passively reduce the seismic responses of the bridge. the lrb devices have a nonlinear behavior which may be idealized by a hysteretic bilinear model (see figure 2). fig 2. characteristic curve of the lrb system: hystereticbilinear model. the principal parameters that characterize the lrb analytical model are the elastic stiffness k1, corresponding to combined stiffness of the rubber bearing and the lead core, the stiffness of the rubber k2, and the yield force of the lead core fyield. the characteristic strength, q can be accurately estimated as being equal to the yield force of the lead core.flim and dlimare respectively maximum force and maximum bearing displacement, keff is effective stiffness of the lrb. as a rule of thumb for lead-rubber isolators k1is taken as 10k2, (fema, 2000; xu chena and chunxiang, 2020). the table 1 reportes the parameter values adopted in this study of the lrb analytical modelin the longitudinal and lateral directions for a design displacement equal to 0.08m. table 1. parameters of the bilinear model for lrb 2.2.4 analytical modeling of dynamic soil structure interaction the complex dynamic impedance z of the soil foundation is expressed as (e.g. gazetas, 1991; wolf, 1997): direction k1 (kn/m) k2 (kn/m) keff (kn/m) q (kn) fyield (kn) c longitudinal and lateral 1634 163.4 357.65 15.50 85.33 q fyiel keff k2 k1 k1 displacement , (d) dlim flim force, (f) 110 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 where k and are real and imaginary parts of the dynamic impedance complex function, the damping coefficient c expresses the radiation that arise from waves emanating away from the foundation soil. table 2 summarizes the relationships expressing the static stiffnesses of springs and damping coefficients corresponding to the six degrees of freedom at the base of the supports of bridge piers. (e.g. ouanani and tiliouine, 2015; gazetas, 1991). table 2. dynamic impedance complex function of foundation soil in table 2, , , , , and are equivalent radii forarectangular foundation with dimensions l and b (l: long side dimension; b: short side dimension) (e.g. fema 273, 1997; gazetas, 1991; wolf, 1997; yohchia, 1997). represents the poisson’s coefficient, whereas and designate the effective shear modulus and the effective shear wave velocity consistent with soil type and pga design value. the 2d-fenonlinear analytical modelin the longitudinal direction of msss bridge modelled as lumped massas well as its connection components are detailed in figure 3. fig 3. detail’s2d-fe non linear analytical model in the longitudinal direction of the mss bridge and its components 3. modal analysis of amsss prestressed concrete bridgefoundation soil system for free vibration response analysis of a msss prestressed concrete bridge-foundation soil systems, the soil structure interactionis essentially controlled by foundation soil flexibility which in turn is dependent onproperties of foundation soil. in this study,the soil corresponding to the actual condition site construction for the considered bridge issoil type s2 (firm site) in accordance with rpoa (2008); the weight density  = 21kn/m3; poisson’s ratio  = 0.40 and initial shear wave velocity vs = 400m/s. degrees of freedom stiffness of foundation soil damping coefficient longitudinal direction lateral direction direction vertical direction rocking about the longutudinal, x-axix rocking about the lateral, y-axix torque lr b abutme nt soil spring pounding and hook elements pier soil spring elasti cfram es lumpe d masses lr b ouanani et al., j. build. mater. struct. (2020) 7: 105-118 111 moreover, the equivalent stiffness and damping coefficients of foundation soil are determined under a simulated accelerogram with pga equal to 0.275g. the pga consistent reduction factors for the effective shear modulus g/go and the effective shear wave velocity are determined using a computer program (shake) for earthquake response analysis of horizontally layered sites schnabel et al. (1976). the associated values of coefficients of stiffness and viscous damping foundation soil have been evaluated for soil type s2 (firm site) with g/go = 0.55 and = 0.55. table 3.effective stiffness and effective damping constants of foundation soil. in this study, numerical techniques (e.g. wilson, 2002; chopra, 2011) have been performed in order to identify the dynamic characteristics of the msss prestressed concrete bridge. table 4 lists the first eleven modal periods and the modal participation factors as well as the corresponding mode types denoted herein by l for lateral, lg for longitudinal, v for vertical directions and t for torsional vibrations for the coupled bridge structure-foundation soil system. in addition, the first 3-d modal characteristics of lateral, vertical, longitudinal and torsional vibrations of both symmetrical (s) and unsymmetrical (as) higher modes of the bridge have been identified. a 3-d graphical representation of the corresponding mode shapes is presented in figure 4. table 4. modal periods and participation factors vibration modes from table 4, it is clearly observed that the first three modes of vibration are longitudinal, which leads to a dynamic analysis in the longitudinal direction (i.e. in the most critical direction) of a multi-span simply supported msss prestressed concrete bridge equipped with restrainers and seismic isolation devices at expansion joints and abutments including soil structure interaction (ssi) effects. rectangular spraed footings translational stiffness (kn/m) rotational stiffness kn /rd) l(m) b(m) e(m) 3 2 1 3 2 1 13.2 6.4 1.8 9277264 9055319 9717088 299229684 101021483 259074216 translational damping (kn.s/m) damping rotationnel (kn.m.s/rd) 63027 63027 109612 848832 199542 629024 modal orders period (sec.) particiaption factors(%) mode types x-x y-y z-z r-x 1 3,445 64,8 0 0 0 first-order symmetric (s) longitudinal vibration (lg) 2 3,398 0 0 0 0 first anti symmetric (as) longitudinal vibration (lg) 3 3,373 6,7 0 0 0 second-order symmetric (s) longitudinal vibration (lg) 4 3,184 0 57,2 0 0,1 first-order symmetric (s) lateral vibration (l) 5 2,518 0 0 0 0 first-order antisymmetric (as) lateral vibration (l) 6 0,504 0 0 56,4 0 first-order symmetric (s) vertical vibration (v) 7 0,502 0 0 0 0 first-order antisymmetric (as) vertical vibration (v) 8 0,500 0 0 0,1 0 second-order symmetric (s) vertical vibration (v) 9 0,476 0 10,1 0 0,1 coupling modes of l and t vibrations 10 0,473 0 0 0 0 first-order antisymmetric (s) torsional vibration (t) 11 0,468 0 0,8 0 3,2 first-order symmetric (as) torsional vibration (t) 112 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 fig 4. 3-d graphical representation of the mode shapes of both symmetrical (s) and unsymmetrical (as) fundamental modes of vibration of the msss bridge mode 1 lg, 1 (s) mode 2 lg, 2 (as) mode 4 l 1 (s) mode 5 l 1 (as) mode 6 v 1 (s) mode 7 v 1 (as) mode 10 t 1 (s) mode 11 t 1 (as) ouanani et al., j. build. mater. struct. (2020) 7: 105-118 113 4. dynamic analysis of a msss prestressed concrete bridgefoundation soil system in the second part of this study, the previous work is now extended to assesthe dynamic analysis of a msss prestressed concrete bridge with restrainers and seismic isolation devices including foundation soil flexibility subjected to a stochastically simulated earthquake based on the design spectrum for the soil type s2 (firm site) in accordance with rpoa(2008). figure 5 show the simulated ground motion compatible with a design spectrum rpoa(2008) scaled by a factor of 2 (i.e. pga = 0.55g). fig 5. (a) simulated ground motion, (b) response spectra and design spectrum rpoa(2008) of the simulated ground motion for time history analysis of the study bridge response, the mass and stiffness proportional rayleigh damping coefficients were determined considering the first two modal periods assuming a 5% viscous damping ratio. the dynamic equations of motion are solved numerically using newmark’snumerical method (zienkiewicz and taylor, 2005; newmark, 1962). 4.1. effect of pounding on the gap relativedisplacement the absolute maximum gap relative displacements of expansion joints at abutments and at intermediate bentsof the msss bridge with and without completely elastic pounding are determined in the longitudinal direction (i.e. in the most critical direction). the results obtained are reported in table 5. table 5. effect of pounding on the absolute maximum gap relative displacements (m) of the girders. from table 5 it is clear that the absolute maximum gap relative displacement is larger at abutment expansion joints, especially in the corner girder. by comparing the pounding effects, we can also see that the absolute maximum gap relative displacements are reduced at abutments and amplified at bents when the pounding effects are considered. for illustration purposes, the time history responses of bridge in term of relative displacements without and with pounding are depicted in figures 6(a) for expansion joints of abutments and in 6(b) for expansion joints of intermediary multi-column bents of the study bridge. locations abutment expansion joints multi-column bents girders locations corner intermediary central corner intermediary central without pounding 0.2054 0.2036 0.2000 0,0301 0,0252 0,0175 with pounding 0,1108 0,1029 0,1015 0,0389 0,0347 0,02553 time (sec.) a cc e le ra ti o n (m / s2 ) spe ctr (b) 114 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 it observed that the pounding effects generally lead to a decrease in gap relative displacements at the joint expansions of abutments (see figure 6(a)) and an increase at the expansion joints of bents (see figure 6(b)). 4.2. effect of pounding on the peak lrb shear strain the maximum shear strains in the longitudinal direction of lead rubber bearings lrb located at abutments and multi-column bents of the msss bridge with and without pounding are given in table 6 below. table 6. effect of pounding on the maximum shear strain of lead rubber bearings (in %) it is seen that the maximum values of bearings shear strain located on abutments and multicolumns bent are more prounced when the pounding effects are negleted. moreover and for the purpose of illustration, figures 7(a) and 7(b) below show the time-history response in the longitudinal direction of lrb seismic isolation devices at abutment back wall and multi-column bents. fig. 7. time history response of shear strain response of lrb seismic isolation device at abutments (a) multicolumns bent (b) of bridge model. 4.3. effect of restrainer on the relative displacement of expansion joints the restrainers used in seisimic design of the study bridge are steel cables. the latters are modelled as a multi-linear model with strain hardening andthe axial forces are generated when restrainers get engaged by loosing the initial slack of 15mm. the yield force of restrainers is locations abutment expansion joints multi-column bents girder locations corner intermediary central corner intermediary central without pounding 413 409 377 442 440 435 with pounding 244 241 303 245 248 252 time (sec.) fig 6. time history response of absolute maximum relative displacement; (a) expansion joints of abutments, (b) expansion joints of intermediate multi-column bents s h e a r st ra in ( in % ) time (sec.) ouanani et al., j. build. mater. struct. (2020) 7: 105-118 115 2640 kn/m and initial modulus of elasticity is equal to 69000 mpa. the initial stiffness of the restrainers of 30 kn/mm and a strain hardening of 5% is assumed. figure 8 below, depict the temporal variations of relative displacements of expansion joints at abutments and intermediate multi-column bents of the msss bridge with and without restrainers. fig 8. time history response of absolute maximum relative displacement; (a) expansion joints of abutments, (b) expansion joints of intermediary multi-column bents from figure8(a) it is seen that the values of relative displacements of expansion joints of abutments are reduced (indicated by the dash-dotted line) when using the restrainers combined with pounding elements and seismic isolation bearings.similar trends are observed in the expansion joints of intermediary multi-column bents (see figure 8(b)). we can summarize that the restrainers could control the expansion joint opening deformation and secure the unseating of the bridge deck on the expense of the increase of shear and moment seismic demand of the supporting pier at the expansion joint. 4.4. effect of restrainer on the shear strain response of lrb seismic isolation device in order to understand the influence of restrainer cables on the lrb seismic isolation device response in the longitudinal direction for study bridge under simulated earthquake, shear strains time variations for these isolators at abutments and bents are plotted in figure 9. fig 9. time history response of shear strain response of lrb seismicisolation device of bridge model (a) at abutments (b) at multi-columns bent. from figure 9(a) it is observed that, there is a significant reduction of lrb isolators shear strains at abutments due to the application of restrainer cable system. the bearing peak shear strain at abutment locations is found to be 240% for bridge without the restrainer cables, while it is equal to 132% for bridge with restrainer cables which corresponds to significant decreases of 45% when the restrainer cables system is considered. similar conclusions can be drawn for lrb isolators shear strainsat multi-columns bents figure 9(b). therefore, the restrainer cables tend to reduce the earthquake forces induced in the seismicisolation system of a multi-span simply supported bridge. under extreme seismic r e la ti v e d is p la ce m e n t (m ) time (sec.) time (sec.) s h e a r st ra in ( in % ) time (sec.) time (sec.) 116 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 excitations, the maximum bearing shear strain is a quantity of prime interest in the seismic design of bridge structures because if it exceeds certain limits, the bearings may fail resulting into the bridge collapse. 4.5. effect of restrainers on pounding forces the gap element is provided to take care of pounding effects between the abutment-deck and deck-deck. the initial gap provided in the gap element is 0.10 m and pounding develops the compressive forces at the interfaces when the relative displacement exhaust this initial gap width. it is modeled by introducing a linear spring with stiffness kgap = 3790622 kn/m at abutments and equal to 1895511 kn/m at bents. to investigate the effect of restrainer cables on the pounding response at deck-abutment and deck-deck interfaces of msss bridge, the temporal variations of the pounding forces without and with restrainers are presented in figure 10. fig 10. time history response of pounding forces of bridge model(a) at abutments (b) at multi-columns bents. from figure 10 (a), it can be noticed that the restrainer cables reduce significantly the values of pounding forces at the interface of abutment-deck of study msss bridge. the maximum pounding force is found to be 41064kn for bridge without restrainers, while it is equal 18646kn when the bridge spans are connected with restrainer cables system. similar conclusions can be drawn for pounding forces at multi-columns bents (see figure 10(b)). from the same figure, it is seen that, there is a substantial 23% reduction in the peak pounding forces at multi-columns bents due to restrainer cables effects. it can be concluded that the maximum pounding force at expansion joints of a multi-span simply supported msss concrete bridge is obviously reduced using restrainer cables system. 5. summary and conclusions in this paper, an extensive numerical investigation on the dynamic analysis of a multi-span simply supported msss prestressed concrete bridge with expansion joints and lead rubber bearing devices including foundation soil flexibility effects are presented. in this context, the 3d finite element model fem of a msss bridge subjected to a 3d components of severe seismic excitation is performed in order to assess the performance of steel restrainer cables and lead rubber bearing devices lrb. the nonlinear hysteretic models characterizing the seismic behavior of various bridge components (including expansion joints and bearing devices) are considered. the effects of restrainer cables and pounding forces on the msss bridge behavior are discussed, and the following conclusions are drawn: 1. the first three dominant modes of the bridge are in the longitudinal directions which to assess a dynamic analysis in this direction (i.e. in the most critical direction). 20445kn 26515kn 18646kn 41064kn ×10 -3 time (sec.) pounding forces (kn) ouanani et al., j. build. mater. struct. (2020) 7: 105-118 117 2. pounding effects generally lead to a decrease in gap relative displacements at abutment joint expansions and increase at bent expansion joints. 3. the computed maximal shear strainsof lrb in the longitudinal direction are more prounced when the pounding effects are negleted. a comparative assessment of behaviour of expansion joints, lead rubber bearing devices and steel restrainers components showsthat under this study: i. the restrainers could control the expansion joint opening deformation and secure the unseating of the bridge. ii. the steel restrainer cables tend to reduce the earthquake forces induced in the seismic isolation devices lrb of a multi-span simply supported bridge. iii. under extreme seismic excitations, the peak shear strain at bearing devices is a quantity of prime interest in the design of bridge structures because if it exceeds certain limits, the bearings may fail resulting into the bridge collapse. iv. the maximum pounding forces at expansion joints of a multi-span simply supported msss concrete bridge are obviously reduced using restrainer cables system. it follows that in order to ensure an acceptably safe structural performance of amsssprestressed concrete bridge with expansion joints and seismic isolationsystem lrb at abutments, due consideration should be given at design stage to:  sound evaluation of distortion limits of seismic isolation bearings lrb at expansion joints and the restrainers components capacities at expansion joints.  using restrainers combined with the seismic isolation systems at bridge expansion joints could be an effective method of reducing the large pounding forces and preventing unseating damage. 6. references anagnostopoulos, sa. & spiliopoulos, kv. (1992) an investigation of earthquake induced pounding between adjacent buildings. earthquake eng. struct dyn., 21, 289–302. association francaise de génie prasismique afps (2003). séisme de boumerdes du 21 mai 2003: rapport préliminaire de la mission afps organisée avec le concours du ministère de l’habitat. bi, k.m., hao, h. &chouw, n. (2013). 3d fem analysis of pounding response of bridge structures at a canyon site to spatially varying ground motions. advances in structural engineering, 16 (4), 619640. chopra, a. k. (2011). dynamics of structures: theory and applications to earthquake engineering. prentice-hall, new jersey, usa. chouw, n. (1995). effect of the earthquake on 17th of january 1995 on kobe. in proceedings of the d-a-ch meeting of the german, austrian and swiss society for earthquake engineering and structural dynamics, university of graz, austria, pp. 135169. csi bridge 2015 v 17.2.0 . computer and structures inc. sap2000 (nonlinear version 15), nonlinear user’s manual reference. usa. desroches, r. & delemont, r. (2002). seismic retrofit of simply supported bridges using shape memory alloys. engineering structures, 24, 325–332. desroches, r. & muthukumar, s. (2004) implications of seismic pounding on the longitudinal response of multi-span bridges—an analytical perspective. earthquake engineering and engineering vibration, 3, 57–65. fema 273 nehrp (1997).guidelines for the seismic rehabilitation of buildings, federal emergency management agency.washington d.c, usa. https://link.springer.com/article/10.1007/bf02668851#auth-1 https://link.springer.com/article/10.1007/bf02668851#auth-2 https://link.springer.com/journal/11803 https://link.springer.com/journal/11803 118 ouanani, m. et al., j. build. mater. struct. (2020) 7: 105-118 fema-356 (2000). prestandard and commentary for seismic rehabilitation of buildings, federal emergency management agency, washington, dc, usa. gazetas, g. (1991). foundation vibrations: chapter 15, in foundation engineering handbook, h-y fang hy, van nostrand reinhold, new york. hong, y.j., xian, l.l., nan l., jian, y., shi-xiong, z. & chao, z. (2019). nonlinear pounding analysis of multispan and simply supported beam bridges subjected to strong ground motion. shock and vibration, 1-11. hung, c. j. lin, h., liu, y. & chai, j. (2008, october). reconnaissance report of 0512 china wenchuan earthquake on bridges. in proceedings of the 14th world conference on earthquake engineering, beijing, china. kawashima, k. & shoji, g. (2000, february). effect of restrainers to mitigate pounding between adjacent decks subjected to a strong ground motion. proceedings of 12th world conference on earthquake engineering, auckland, new zealand. newmark, n. m. (1962). a method of computation for structural dynamics,” trans. asce, 127. ouanani, m. & tiliouine, b. (2015). effects of foundation soil stiffness on the 3-d modal characteristics and seismic response of a highway bridge. journal of civil engineering ksce, 19(4), 1009-1023. ouanani, m. & tiliouine, b. (2017). progressive seismic failure of a highway bridge, including abutment– backfill interaction. current science, 112(2), 355-363. rpoa (2008). règles parasismiques applicables au domaine des ouvrages d’art. document technique règlementaire, ministère des travaux publics, alger, algeria. schnabel, p. b., lysmer, j. & seed, h.b. (1976). a computer program for earthquake response analysis of horizontally layered sites (shake), report (eerc 72 12), earthquake engineering research center, university of california, berk'eley. shinozuka, m., murachi, y., dong, x., zhou, y. &orlikowski, m. (2003) effect of seismic retrofit of bridges on transportation networks. earthquake engineering and engineering vibration , 2, 69–179. tazarv, m. & alam, s. (2018, june). shape memory alloy for bridge columns. proceedings of the eleventh u.s. national conference on earthquake engineering, ca, usa. tiliouine, b.&ouanani, m. (2012, september). 3-d nonlinear earthquake response of r.c. box girder bridges with expansion joints and bearing devices. 15th world conference on earthquake engineering, lisbon, portugal. todd, d., carino, n., riley, m., chung, h. s., andrew, w., william, d., james, d., and roland, n. (1994). the northridge, california, earthquake of january 1994: performance of structures, lifelines, and fire protection systems. national institute of standards and technology (nist), usa. uzarski, j. & arnold, c. (2001). chi-chi, taiwan, earthquake of september 21, 1999: reconnaissance report. earthquake spectra, supplement, taiwan. wilson, e. l. (2002). three-dimensional static and dynamic analysis of structures: a physical approach with emphasis on earthquake engineering. computer and structure, inc. berkeley, california, usa. wolf, jp. (1997). springs-dashpots-mass models for foundation vibration. earthquake engineering and structural dynamics, 26, 931-949. xu chena, b. & chunxiang, lib. (2020) seismic performance of tall pier bridges retrofitted with lead rubber bearings and rocking foundation. engineering structures, 212, 1-15. yang, z., kun, c & chouw, n. (2018, december).impact of spatial variation of ground motions on the seismic performance of a bridge structure. 25th australasian conference on mechanics of structures and materials (acmsm25), australia. yohchia, c. (1996). modeling and analysis methods of bridges and their effects on seismic responses: i theory. computers and structures, 59(1), 81-89. https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-1 https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-2 https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-3 https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-4 https://link.springer.com/article/10.1007/s11803-003-0001-0#auth-5 https://link.springer.com/journal/11803 https://www.researchgate.net/profile/mostafa_tazarv?_sg%5b0%5d=wydhdvpaumw8d_5kuutk-y6dcfvno9i8vadzl-ifh5en2sdvpsra2ixidz1gza7ckzetbci.moe_peg-o_l0sifvtleitkjwr7mcshurlsneh18d78mdug2qov3kxesjbs92lzefezfbvth-jczz9bnev5xo6a&_sg%5b1%5d=xumbm8a3rviaqocrddmkdikpfpc0mkjmxd0nia8uu6no047u-og5cvmuwdbquv2zphbq_w0.d5-yrmemjsz82m4_f2hbbeyb3tw_6pmtyx5j6pwi3ekifl2ew4_khd0l9zzy8ndjprozdenqottszkbd4beouq https://www.sciencedirect.com/science/journal/01410296 https://www.sciencedirect.com/science/journal/01410296/212/supp/c ouanani et al., j. build. mater. struct. (2020) 7: 105-118 119 zienkiewicz, o.c. & taylor, r.l. (2005). the finite element method, solid mechanics. upper saddle river, new jersey, usa. j. build. mater. struct. (2018) 5: 110-126 original article doi : 10.34118/jbms.v5i1.50 issn 2353-0057, eissn : 2600-6936 mechanical behavior and durability of latex modified mortars benali y *, ghomari f eole laboratory, faculty of technology, university abou bekr belkaid, tlemcen, algeria. * corresponding author: benaliyacine_gc@yahoo.fr received: 10-02-2018 revised: 15-05-2018 accepted: 19-05-2018 abstract. this article summarizes the results of an experimental program developed on latex-modified mortars. fluidity tests, compressive strength tests, flexural strength tests, water absorption tests, adhesion tests on clay bricks and cementitious substrates were carried out. the test bodies were prepared by the pre-wetting method with different latex contents while partially substituting portland cement by two types of latex: styrenebutadiene (sbr) and styrene acrylic (sa). in addition, samples of ordinary mortars are made in parallel as references. the experimental results showed that the substitution of cement in mortars produced a notable improvement on fluidity and adhesion. in the case of clay substrates, a cohesive failure in the support above 10% substitution has been reported; whereas the rupture is always at the interface for all the mixtures tested on cementitious substrates. an improvement was also noted on the flexural tensile strength beyond 60 days. on the other hand, the compressive strength of the polymer mortars decreased with the substitution rate of cement for all the maturities studied. as for the absorption of water, the results show a clear reduction in the percentage of water absorption by increasing the substitution rate. key words: latex modified mortars, fluidity, absorption, strength, adhesion. 1. introduction synthetic polymeric additives such as latexes, redispersible polymer powders, water-soluble polymers, and liquid resins have been introduced into cement mortar to obtain the polymermodified mortars. the use of these materials for repair work, restoration, facade coatings, tile adhesives, sealing coatings, decorative coating and external thermal insulation are increasing more and more since the 1960 s (said, 2016). the latex polymers, which are usually manufactured by emulsion polymerization technique (very successful process from the technical and environmental point of view, because water is used as a solvent and also the amount of volatile organic compounds (vocs) released during their preparation and application is negligible, etc.) erdmenger et al. (2010), amaral (2004), thickett and gilbert (2007), prove to be the most commonly used polymers (benali and ghomari, 2017; diab, 2014; xu, 2016). they are marketed as very small (0.05–5 pm in diameter) polymer particles dispersed in water, often milky white (al-zahrani, 2003). the literature shows that there is a variety of types of latex, depending on the kind of monomers or polymers used to manufacture them. the choice of a type of latex depends on the specific properties required for the application (benali and ghomari, 2017; balayssac, 2011). styrenebutadiene rubber (sbr) and styrene-acrylic (sa) are most widely used latex (eren, 2017; benali and ghomari, 2017). from the beginning, the mix proportions of modified systems has always been based on a simple combination of cement, water, sand and latex, associated with a polymer/cement ratio, generally ranging from 5 to 20% of dry latex extracts, depending on the weight of cement in the mixture. mailto:benaliyacine_gc@yahoo.fr benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 111 (benali and ghomari, 2017; aci committee 548, 2003). the various formulations are used not only to improve the properties of conventional mortars by the formation of latex network and membranes, but also as an admixture to reduce the water content into the mixture (al-zahrani, 2003; diab, 2013), due to the presence of high range super plasticizer agent on latex constituents (diab, 2013). during the curing time, the evaporation of the mixing water from the cement paste-latex emulsion system along with the cement hydration leads to film and co-matrice formation (benali and ghomari, 2017; eren, 2017). these two elements fill the open and capillary pores of the matrix, thus improving the cohesion between the aggregates and the cement paste at the interface, and increasing the compactness of the hardened material. this will therefore ameliorate its flexural and tensile strengths, its adhesion to different substrates as well as its durability, while slowing down its permeability to water and also the diffusion of aggressive species, such as carbon dioxide, chlorides, and sulfates. moreover, latex-modified cementitious materials have better water retention, sufficient entrainment of air, and also a better fluidity (benali and ghomari, 2017; parghi and alam, 2016; diab, 2013; ramli and tabassi, 2012b). this investigation aims to study the effect of using two types of synthetic latex: styrene butadiene (sbr) and styrene acrylic (sa), as materials replacing portland cement at the proportions of 0, 2.5, 5, 10, 15 and 20 % (by weight). the main objective is to highlight the influence of these materials on the mechanical properties, adhesion, and durability of conventional mortars, though the properties of cement mortars can be improved by the addition of latex as a water reducer plasticizer. the modification mechanism, through the replacement of portland cement by latex (because its production is energy-hungry and it is responsible for several environmental damages), is not clear yet; and a lot of research work needs to be performed. our hope is to use them for repair works and to manufacture protective mortars and coatings as well. 2. experimental program 2.1. materials used a portland cement compound of type cpj cem ii / a 42.5, meeting the algerian standard na 44, from the cement plant of beni-saf, in the wilaya of ain temouchent, was used. its main constituents are clinker, natural pozzolan of volcanic origin from the deposit of bouhamidi (beni-saf, algeria), and gypsum. the chemical composition of this cement is given in table 1, and its physical characteristics are summarized in table 2. table 1. chemical composition of cement. compounds (%) sio2 22.17 al2o3 6.18 fe2o3 3.62 cao 59.45 mgo 1.05 so3 2.63 k2o 0.49 na2o 0.19 cl 0.004 p2o5 0.18 tio2 0.43 loi 2.62 112 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 table 2. physical characteristics of cement. test result bulk density (t/m3) 1.01 specific gravity (densitometer le chatelier) (t/m3) 3.02 blaine’s specific area (cm2/g) 3597 the sand used is crushed limestone sand 0/3 mm, from the quarry of djebel abiod of (eng ), sidi abdelli, in tlemcen (algeria). this choice was made because it is the main quarry that supplies the entire region. the characteristics of this sand are summarized in table 3 and fig 1. the quarry of jebel abiod produces clean sand 0/4 mm. this sand was passed through a 3.15 mm mesh sieve. the choice of sieving is dictated by the fact that sand 0/3 is the most frequently type used in the literature for the preparation of mortars. no washing or size correction has been performed for the formulation of various mortars. table 3. identification of physical properties of sand. test result bulk density (t/m3) 1.43 absolute density (t/m3) 2.50 sand equivalent (%) 84.5 percentage of fines (%) 15.7 fineness modulus 3.01 fig 1. granulometry of sand used. clay bricks, with horizontal perforations and grooves in the coating, of dimensions (100 × 200 × 300 mm3), were used as substrates for the adhesion tests (see fig. 2.). these substrates have a bulk density equal to (1.41 t /m3), and water absorption equal to (13.55%). this test was performed according to the standard astm c373-88 (2006). concrete substrates of dimensions (300 x 300 x100 mm3), with grooved in surfaces were made (fig. 3.) in order to see the influence of a different substrate that the brick on the adhesion by pull off. these concrete have the same composition as the reference concrete that we use in the benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 113 research team "granular materials" of the laboratory eole (boukli, 2009). it is characterized by w/c ratio of 0.5, a bulk density equal to 2471 kg/m3, slump (abrams cone) equal to 6 cm, and water absorption of 6.3%. two latex polymers, i.e. styrene-butadiene (sbr) and styrene acrylic (sa) manufactured respectively by sika el djazaire and technalab, were used. their physical characteristics are reported in table 4. fig 2. clay bricks used. fig 3. concrete substrate used. table 4. physical characteristics of latex used. name of product sikalatex d-70 nature styrene-butadiene rubber (sbr) styrene-acrylics (sa) color and form viscous milky white viscous milky white odour low low properties of the film not clear, flexible clear, hard density (t/m3) according to the manufacturer at (20°c) 1.02 measured in the laboratory at (19°c) 1.01 1.07 viscosity (cps, 30°c) (brookfield rvt 20 rpm) 1.5 – 1.6 total bulk solids (%) according to the manufacturer 50 (50±1) measured in the laboratory 45 50 ph according to the manufacturer 7.5 measured in the laboratory at (19°c) 9.65 7.90 particle size (µm) 0.1-0.3 minimum temperature of film forming (mfft), ° c 17 glass transition temperature (tg), ° c +16 type of surfactant nonionic 2.2. method of preparation of samples and tests performed 2.2.1. mixes and cures our experimental program consisted in replacing amounts of cement by latex proportions ranging from 2.5 to 20% of dry extract. the results obtained were compared with reference mortars with similar composition, where cement is the only binder. 114 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 the cement to sand ratio (c/s) used was 1/3. this choice was prescribed by the fact that these are the most frequent compositions encountered in the literature. the (w/c) ratio used for the manufacture of control mortars was 1/2. this ratio was validated after the mechanical strength test of two mortars with two different ratios (w/c) equal to 0.5 and 0.55. the results of the mechanical behavior, at 60 days, are summarized in table 5. the values shown are the average of three flexural tensile tests on specimens of dimensions (40x40x160 mm3), and also the average of 6 compression tests performed on fragments recovered from the flexural tensile test. the test samples were immersed in water at (20 ± 3) °c, after unmolding at 24 hours, until the age of 60 days. the mixture of the reference mortar components was done according to standard bs en 196-1 (2005). from the analysis of the results in table 5, a slight difference was noted between the mechanical performances of the two formulations, mainly in the compressive strength. the polymer-modified mortars were prepared with partial substitution of cement at different weight ratios, i.e. 2.5, 5, 10, 15 and 20%. the substitution ratios were calculated using the total solid content in the latex (see table 6). as for the (w/c) ratio, two ways to manufacture a latexmodified mortar were found in the related literature (balayssac, 2011; barluenga and hernandez-olivares, 2004).  the first is to maintain the (w/c) ratio constant in order to have a hydration level close to that of the cement paste (typical laboratory procedure).  the second one, more common (the mortar strength increases), is to adjust the workability of the modified mixture to that of ordinary mortar, usually by adjusting the (w/c) ratio. the second method was used in the present study. the fluidity of the sbr-modified mortars was adjusted so as to have a fluidity between 125 and 165 mm (fluidity of usual mortars, see table 6), whereas the (w/c) ratio was adjusted so as to have the fluidity of the sa-modified mortar similar to that of the reference mortar (125 ± 5) mm. this was done using the flow table test, according to the standard astm c 1437-07 (2007), while using a frustoconical mold, where the spreading is the average of two perpendicular diameters. the components of these polymer-modified mortars were mixed according to the pre-wet method. regarding the literature, the speed, time and procedure of mixing the latex-modified mortars must be carefully chosen in order to prevent the needless air from being trapped. the entrained airs that form when cement and aggregates are mixed with an aqueous polymer solution are not easily removed as they tend to be stabilized by polymers (kim and robertson, 1997). as a result, the properties of the mix in the hardened state will deteriorate (ohama, 1995). to reduce these unnecessary amounts of air, some researchers (kim and robertson, 1997; barluenga and hernandez-olivares, 2004) proposed an alternative approach, which is to pre-wet cement and sand with water, then add the latex last (the pre-wetting method). in order to determine the mechanical parameters and the porosity accessible to water, the molds containing the polymer mortar samples were covered with plastic film, and stored in the laboratory environment. the samples were unmolded after 24 hours, and kept in water for 6 days at (20 ± 3) °c and then in the open air at (20 ± 3) °c with a relative humidity (rh) equal to 55 ± 10%, until the test at 7, 14, 28, 60, 90, 180 and 360 days, because curing in humid conditions, such as immersion into water, or the moist cure, which is applicable to cement mortar and ordinary concrete, is detrimental to latex-modified concrete and mortar. ohama (1995) stated that the optimal properties of modified systems can be achieved by a combination of wet and dry processing. in their work, wang (2005), ramli and tabassi (2012a; 2012b) showed that a 6-day combined processing is more beneficial than wet processing. moreover, folic and radonjanin (1998) indicated that the 6-day combined processing is more benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 115 beneficial than the 2-day combined processing, with a wet processing throughout the entire period. humid period is used to hydrate cement and to avoid cracking due to plastic shrinkage (aci committee 548, 2003), while the dry period is used to evaporate the excess water to allow for the development of the polymer film (ohama, 1995). reference mortars were immersed into water at (20 ± 3) °c until the day of the test, whereas the samples used to determine adherence on two different surfaces, i.e. brick and concrete substrate, were kept in the laboratory environment at (20 ± 3) ° c with a rh = 55 ± 10%, up to the day of the test. this was done to simulate the application in a real environment. table 5. fresh and mechanical performance of mortars prepared with w/c = 0.5 and 0.55 type test w/c=0.5 w/c=0.55 compressive strength (mpa). 50.1 45.8 flexural tensile strength (mpa) 11.47 11.39 fluidity (mm). 125 165 table 6. details of mixing proportions modified mortars designation mixtures sand(g) cement (g) p (g) w/c fluidity (mm) m. ref 1350 450 0 0.5 125 styrene butadiene rubber (sbr) m. 2,5 % sbr 1350 438.75 25 0.498 125 m. 5 % sbr 427.5 50 0.48 130 m. 10 % sbr 405 100 0.425 145 m. 15 % sbr 382 150 0.35 160 m. 20 % sbr 360 200 0.25 165 styrene acrylic (sa) m. 2,5 % sa 1350 438.75 22.5 0.498 125 m. 5 % sa 427.5 45 0.48 125 m. 10 % sa 405 90 0.425 125 m. 15 % sa 382 135 0.35 125 m. 20 % sa 360 180 0.25 125 2.2.2. test procedure the evaluation of the compressive strength and bending tensile strength was performed at 7, 14, 28, 60, 90, 180 and 360 days, according to standard en 196-1 (2005), on specimens of dimensions (40x40x160 mm3). it is known from literature that these properties are the most important, if sustainability indicators are excluded. the measurement of water absorption was done according to the method suggested by ramli (2013). the test is usually measured on dried samples then partially immersed in water and the increase in mass as a percentage of the dry mass is measured. for the representativeness of the samples, a set of three cylindrical samples of size 70 × 70 mm are placed in an oven for 72 h at a temperature of 105 ° c. after drying to constant mass, the samples are removed and left in a sealed container for a period of 24 ± 0.5 h. each sample was then weighed and immediately 116 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 immersed in water for a period of 30 ± 0.5 min (see fig. 4.). the sample is then taken out of the water, the surface wiped and weighed again. water absorption was calculated from the mass increase of the sample and expressed as a percentage of dry specimens multiplied by a correction factor as follows: (1) as for adherence, several researchers have stated that the fundamental purpose of using polymers in the cementitious mixture is to improve the adherence and the durability of adhesion, because the quality of repair and protection of structures depends mainly on the adherence of mortars to the substrate to be repaired or protected (courard, 1998). previous works in this area have shown that the adhesion measurement tests are usually tests of rupture between two materials. they can be achieved either by pulling (traction) or flexural tensile and/or by direct or indirect shear (ngassam, 2013; momayez, 2005; courard and bissonnette, 2004). in this work, the adhesion measurement was carried out using the method shown in fig. 5. according to the literature, this test is easy to perform and can produce good results (ngassam, 2013; momayez, 2005). the peel test by direct pulling, often called "pull-off", was performed on mortars used on hollow clay bricks and concrete substrate. the same formulations of mortars, previously defined, were applied on one of the larger faces of the brick 300 x 200 mm2 and concrete 300 x 300 mm2 (see fig. 6). these faces was wetted before applying mortar, to avoid the absorption of water of mortars in the fresh state, and maintaining a saturation level of the substrate higher than 50% and lower than 90% for a good adherence (mirza, 2014; courard, 2011). the thickness of the applied layer was 20 mm. such a choice was made because generally the thickness of repair or protection mortars exceeds 10 mm, depending on the degree of damage. these mortars were tested after 28 days of curing. the samples were prepared by drilling three circular holes of diameter 50 mm on the mortars applied to the bricks and concrete, 24 hours before the test. then, cylindrical metal disks of the same diameter (50 mm) were stuck on the removed parts with an epoxy adhesive. after 24 hours, a male ball, fixed on the metallic disks, was received in the ball socket which is located at the base of the central axis of the adhesion tester. the peel tests consist of applying a traction force on the male ball, perpendicularly to the surface of the disk, until rupture (see fig. 6.). the value of adhesion (in mpa) of the coating to the brick and concrete is obtained by dividing the maximum force of the fracture (in n) by the surface of the bonded surface (mm2). this value was recorded, and the fracture interface was analyzed in each case. (2) fig 4. water absorption test. benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 117 fig 5. schematic of the method used for measuring adhesion “pull off”. fig 6. adhesion test on clay brick and concrete substrates. 3. results and discussion 3.1. flow according to the results shown in fig 7 and 8, it is easy to see that both types of latex, i.e. sa and sbr, are water reducers. similar observations on the effect of latex on a fresh cementitious matrix were made by barluenga and hernandez-olivares (2004), ohama (1995), wang and wang (2010) and ngassam (2013). 118 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 fig 7. fluidity and w/c as a function of polymer sbr content mortars. fig 8. . fluidity and w/c as a function of polymer sa content mortars. indeed, when the substitution rates went from 0 to 20%, the fluidity of fresh mixture increased significantly, from 125 mm to 165 mm for sbr, but remained constant at 125 mm for sa, while the (w/c) ratio dropped from 0.5 to 0.25. this may be interpreted as an improved coherence, due to the ball-bearing action of the polymer particles, their dispersion, the entrapped air, and the plasticizing effect of latex. therefore, the obtained results show that the two types of latex are water reducers, but sbr is a higher range water reducer than sa latex. this may be due to the large amount of water existing in sbr (≈55%). 3.2. compressive strength the results of the compressive strength of control mortars as well as those modified by sbr and sa as a function of polymer content and age are shown on the semi-logarithmic chart in figures 9 and 10, respectively. these results are the average of six tests on fragments recovered from the flexural tensile strength test. a preliminary analysis of the results allows making the following observations. the evolution curves of the compressive strength versus time (7 to 360 days) show the same trend. overall, the strength of all mortars increases steadily with the conservation period (from7 to 60 days) of specimens. beyond that age, the strength of all mortars remains constant, taking into account the experimental uncertainties. this may be attributed to the time required for cement hydration and its curing. moreover, when examining more closely the values obtained at specific ages, it is found that reference mortars develop greater compressive strengths, at all ages (7 to 360 days). it is obvious that the compressive strength of mortars decreases (loss) while the cement substitution rate increases, for all examined maturities. this loss is 21, 33, 32, 34 and 35%, when the strength of reference mortars is compared to that of mortars modified by sbr at the age of 360 days. it is 23, 28, 32, 33 and 34% when the strength of reference mortars is compared to that of mortars modified by sa at the same age. note that beyond 10% of polymer additions, the values of strength are generally similar. benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 119 fig 9. . influence of age on the compressive strength as a function of polymer sbr content mortars. fig 10. . influence of age on the compressive strength as a function of polymer sa content mortars. several research studies have shown that the presence of polymers has a low impact on the compressive strength, and it may even have a negative impact (aci committee 548, 2003; ngassam, 2013). most of these authors justified these observations by the fact that a polymer has a larger capacity of water retention, a high closed porosity due to air entrainment by the polymer (wang, 2005; wang and wang, 2010; ngassam, 2013) and also to the delay in hydration of cement, caused by the presence of surfactants in the mixture (sikora, 2015). however, other researchers (barluenga and hernandez-olivares, 2004; ramli and tabassi, 2012b) justified these same observations by the low mechanical capacity of the latex and also by the change observed in the microstructure of the mixture. in the co-matrix network of modified mortars, there are two types of bonds, i.e. cement-cement and cement-polymer. the cement-polymer bonds are weaker than the cement-cement bonds. when the polymer content increases, the polymer film covers the hydrated cement and aggregates, thus forming several polymer-cement 120 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 bonds. this results in a decrease in the compressive strength of the modified samples. 3.3. flexural tensile strength the flexural tensile strength of reference and modified mortars as a function of age and polymer content is represented on the semi-logarithmic chart, in figures 11 and 12, respectively. these results represent the average of three tests on prismatic specimens of dimensions (40x40x160 mm3). fig 11. . influence of age on the flexural tensile strength as a function of polymer sbr content mortars. fig 12. . influence of age on the flexural tensile strength as a function of polymer sa content mortars. based on these experimental results, it can be stated that the flexural tensile strength of all polymer-modified and reference mortars increases steadily. similarly, the compressive strength also rises with the conservation period of specimens, from 7 to 60 days. beyond that age, the strength of mortars follows a constant trend, provided that the experimental uncertainties are taken into consideration. this is due, as previously said for the compressive strength, to the benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 121 hydration of cement, its hardening and also to the formation of the polymer film over time. these results corroborate those found in the literature (barluenga and hernandez-olivares, 2004; wang, 2005; wang and wang, 2010). figures 11 and 12 also show that the flexural tensile strength of mortars decreases when the substitution rate of polymer increases, for all maturities (7 to 28 days). the reduction in strength may be attributed to the amount of substituted cement, delayed cement hydration under dry conditions, the fixing of polymer particles on cement particles, and also to the comatrix and the undeveloped polymer film. however, the loss in strength is recovered at 60 days. this strength increases by 5% and 34%, respectively, when mortars modified with 20% of sbr and 20 % sa, are compared to control mortars. this can be explained by the improved cohesion between the aggregates and cement paste. this cohesion is enhanced by the formation of the polymeric film and the co-matrix which is a network structure in which the hydrated cement phase and the polymer phase interpenetrate. comparing the two figures 11 and 12 enables to note that the flexural tensile strength of mortars modified with sa shows better improvement than that of mortars modified with sbr. this is due to the nature and functioning of the polymer as well as to the amount of water that exists in mortar; the quantity of water in mortars modified by sbr is larger than that encountered in those modified by sa, for identical polymer contents. our results confirm the conclusions of gemert (2005) and ngassam (2013). the beneficial effect of polymers is generally more noticeable in the flexural tensile strength than in the compressive strength because polymers enhance the strength of the binder-aggregate interface, which is particularly needed during the flexural tensile tests. 3.4. adhesion to bricks and cementitious substrates the results of the adhesion of control and modified mortars to bricks and concrete substrates as a function of the substitution rates are illustrated in fig 13 and 14. these results are the average of the values obtained from three tests on mortars applied to clay bricks and cementitious substrates. fig 13. . adhesion of mortars to clay bricks. 122 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 fig 14. . adhesion of mortars to concrete substrates the adhesion to bricks was reported to be significantly influenced by the cement substitution rate. this influence is more noticeable beyond 5% cement replacement by the two types of latex. mortars modified by styrene butadiene (sbr) and styrene acrylic (sa) showed an adhesion increase to bricks of 84% and 82%, respectively, for a 20% replacement rate for both latex compared to ordinary control mortars. moreover, the adhesion increase to concrete substrates as those of bricks; however, the influence on this support is greater. the incorporation of 20% of styrene-butadiene (sbr) and acrylic styrene (sa) respectively resulted in a respective increase of 58% and 36%, compared with reference mortars. the improvement in adhesion is mainly attributed to the formation of a polymer film and hydrated cement compounds at the interface between the modified mortar and substrate (mansur, 2009; ngassam, 2013; pierre, 2008). latex films interweave cement hydrates, forming the monolithic polymer– cement co-matrix structure at the interface (modified mortar – substrate), and come bridging the pores and cracks in this interface (mansur, 2009) furthermore, the substrates used in this study are known to be very porous materials; according to mansur (2009), the adhesion of modified mortars to substrates, which have a high water absorption (>6 wt.%) (very porous), exhibits a mechanical anchoring and a general improvement in mortars properties in addition to the formation of a continuous polymer film at the interface. it can be said that the latex and cement hydrates can seep into the porous network of substrates (clay bricks and concrete substrates), and thus adhere strongly to these substrates. our results are in good agreement with the results found by mansur (2009). the model developed by these authors, which explain the mechanisms of adhesion at the interfaces between the mortars and porous substrates, can summarize our results. a closer examination of the results allows noting that better adhesion properties were obtained with sbr-modified mortars, especially for significant substitution rates, compared with mortars modified by sa. an explanation was suggested by ngassam (2013) on the adhesion of mortars modified with the ethylene-vinyl acetate (eva) and the styrene acrylic (sa). the best adhesion performance obtained for mortars modified with sbr is due to their rheological behavior. indeed, these mortars have a higher fluidity than that encountered in mortars containing sa (see table 6). benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 123 several researchers (ngassam, 2013; courard, 1998) defined fluidity in terms of the wettability of the material; they stated that the material should have good wettability and a good flow in order to increase the effective contact surface area between mortar and the substrate. this will certainly improve the adhesion strength of mortars to the different substrates. figs 15 and 16 show the failure mode of the samples, after the peel test. in the case of bricks, it is noted that beyond 10% cement replacement by latex, the failure is purely cohesive within the substrate layer, unlike the case of low replacement levels where the failure is nearly at the interface. at the rate of 10 % substitution by sa, the failure is cohesive both within the substrate and at the interface. by cons, for concrete substrates, the failure is reported at the interface, for all the mortars modified by the sa, which means that the failure is not cohesive, whereas the sbr develops a cohesive failure in the substrates of mortars modified with latex levels greater than 10%. this is probably due to the nature of the surface of the concrete substrates (harder than the surface of the bricks), and also to the high fluidity of the mortars modified by the sbr. fig 15. failure mode of the samples clay bricks – mortars. fig 16. failure mode of the samples concrete substrates – mortars. 124 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 3.5. water absorption the polymeric film fills the pores and voids that generally occur in portland cement mortars. this filling of the cracks increases with the increasing polymer content introduced into the cementitious matrix. as a result, a significant decrease in water absorption is reported as shown in fig. 17. fig 17. water absorption of modified mortars there is a marked reduction in the percentage of water absorption with the increase in the substitution rate. indeed, the increase of this latter from 0 to 20% resulted in a reduction near to 90.5% of the water absorption for the two polymers. at this stage it can be said that the water absorption of the mortars modified by the sbr and the sa is proportional to the substitution dosage and follows a linear trend with satisfactory correlation coefficients of 0.90 and 0.73. 4. conclusions based on the results and discussion presented in this paper, the following conclusions can be drawn: increasing the substitution levels of cement by the latex (sbr and sa), in the cementitious mix, leads to a significant influence on the fluidity and a reduction in the quantity of mixing water. therefore, the latex can be successfully used as water reducers. the flexural tensile strength increases with the increase in latex content in the mix beyond 60 days. however, the compressive strength increases with the increase in cement content and with age. a significant decrease in water absorption is reported in the mortars modified in comparison with the reference mortars. sbrand sa-modified mortars also cause an increase in the bond strength of mortars to clay bricks and to concrete substrates as well. beyond 10% cement replacement, failure in modified mortars is purely cohesive within clay substrates, unlike the case of low substitution levels where the failure occurs at the interface. however, for concrete substrates, the failure is reported at the interface, for all the mortars modified by the sa, whereas the sbr develops a cohesive failure in the substrates of mortars modified with latex levels greater than 10% of substitution. benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 125 5. references aci committee 548. (2003). polymer-modified concrete (pp. 40). farmington hills (mi): american concrete institute. al-zahrani, m. m., maslehuddin, m., al-dulaijan, s. u., & ibrahim, m. (2003). mechanical properties and durability characteristics of polymerand cement-based repair materials. cement & concrete composites, 25, 527–537. amaral, m. d. (2004). assessing the environmental cost of recent progresses in emulsion polymerization. reactive & functional polymers, 58, 197–202. astm c373-88. (2006). standard test method for water absorption, bulk density, apparent porosity, and apparent specific gravity of fired whiteware products (pp. 2). west conshohocken (pa): astm international. astm c1437-07. (2007). standard test method for flow of hydraulic cement mortar (pp. 2): west conshohocken (pa): astm international. balayssac, j. p., nicot, p., ruot, b., devès, o., & détriché, c. h. (2011). influence of admixtures on the cracking sensitivity of mortar layers applied to a mineral substrate. construction and building materials, 25, 2828–2836. barluenga, g., and hernandez-olivares, f. (2004). sbr latex modified mortar rheology and mechanical behaviour. cement and concrete research, 34, 527–535. benali, y., and ghomari, f. (2017). latex influence on the mechanical behavior and durability of cementitious materials. journal of adhesion science and technology, 31(3), 219–241. boukli hacene, s. m. e. a. (2009). contribution a l'étude de la résistance caractéristique des bétons de la région de tlemcen [ contribution to the study of the characteristic strength of the concrete in the region of tlemcen]. [phd thesis], university of abou bekr belkaid, algeria. bs en196-1. (2005). methods of testing cement – part 1: determination of strength (pp. 28). london: br. stand institution. courard, l. (1998). contribution { l’analyse des paramètres influençant la création de l’interface entre un béton et un système de réparation [contribution to the analysis of the parameters influencing the creation of the interface between a concrete and a repair system]. [phd thesis], university of liège, belgium. courard, l., and bissonnette, b. (2004). essai dérivé de l’essai d’adhérence pour la caractérisation de la cohésion superficielle des supports en béton dans les travaux de réparation : analyse des paramètres d’essai [adaptation of the pull-off test for the evaluation of the superficial cohesion of concrete substrates in repair works: analysis of the test parameters]. materials and structures, 37, 342–350. courard, l., lenaers, j.-f., michel, f., & garbacz, a. (2011). saturation level of the superficial zone of concrete and adhesion of repair systems. construction and building materials, 25(5), 2488-2494. diab, a. m., elyamany, h. e., & ali, a. h. (2013). experimental investigation of the effect of latex solid/water ratio on latex modified co-matrix mechanical properties. alexandria engineering journal, 52, 83– 98. diab, a. m., elyamany, h. e., & ali, a. h. (2014). the participation ratios of cement matrix and latex network in latex cement co-matrix strength. alexandria engineering journal, 53, 309–317. erdmenger, t., guerrero-sanchez, c., vitz, j., hoogenbooma, r., & schubert, u. s. (2010). recent developments in the utilization of green solvents in polymer chemistry. chemical society reviews, 39(8), 3317–3333. eren, f., gödek, e., keskinates, m., tosun-felekoglu, k., & felekoglu, b. (2017). effects of latex modification on fresh state consistency, short term strength and long term transport properties of cement mortars. construction and building materials, 133, 226–233. 126 benali and ghomari, j. build. mater. struct. (2018) 5: 110-126 folic, r. j., and radonjanin, v. s. (1998). experimental research on polymer-modified concrete. aci materials journal, 95(4), 463-468. gemert, d. v., czarnecki, l., maultzsch, m., schorn, h., beeldens, a., łukowski, p., & knapen, e. (2005). cement concrete and concrete–polymer composites: two merging worlds. a report from 11th icpic congress in berlin, 2004. cement & concrete composites, 25, 926–933. kim, j.-h., & robertson, r. e. (1997). prevention of air void formation in polymer-modified cement mortar by pre-wetting. cement and concrete research, 27(2), 171-176. mansur, a. a. p., nascimento, o. l. d., & mansur, h. s. (2009). physico-chemical characterization of evamodified mortar and porcelain tiles interfaces. cement and concrete research, 39, 1199–1208. mirza, j., durand, b., bhutta, a. r., & tahir, m. m. (2014). preferred test methods to select suitable surface repair materials in severe climates. construction and building materials, 50, 692–698. momayez, a., ehsani, m. r., ramezanianpour, a. a., & rajaie, h. (2005). comparison of methods for evaluating bond strength between concrete substrate and repair materials. cement and concrete research, 35, 748–757. ngassam, i. l. t. (2013). durabilité des réparations des ouvrages d’art en béton [durability of repairing concrete structures]. [phd thesis]. university of paris-est, france. ohama, y. (1995). handbook of polymer-modified concrete and mortars. properties and process technology: park ridge (nj): noyes publications. parghi, a., & alam, m. s. (2016). effects of curing regimes on the mechanical properties and durability of polymer-modified mortars – an experimental investigation. journal of sustainable cement-based materials, 5(5), 324-347. pierre, n. (2008). interactions mortier-support : éléments déterminants des performances et de [mortarsupport interactions: determinants element of performance and adhesion of mortar]. [phd thesis]. university of toulouse, france. ramli, m., and tabassi, a. a. (2012a). effects of different curing regimes on engineering properties of polymer-modified mortar. journal of materials in civil engineering, 24, 468-478. ramli, m., and tabassi, a. a. (2012b). mechanical behaviour of polymer-modified ferrocement under different exposure conditions: an experimental study. composites: part b, 43, 447–456. ramli, m., tabassi, a. a., & hoe, k. w. (2013). porosity, pore structure and water absorption of polymermodified mortars: an experimental study under different curing conditions. composites: part b, 55, 221–233. said, a. m., quiroz, o. i., hatchett, d. w., & elgawady, m. (2016). latex-modified concrete overlays using waste paint. construction and building materials, 123, 191–197. sikora, p., łukowski, p., cendrowski, k., horszczaruk, e., & mijowskab, e. (2015). the effect of nanosilica on the mechanical properties of polymercement composites (pcc). procedia engineering, 108, 139 – 145. thickett, s. c., & gilbert, r. g. (2007). emulsion polymerization: state of the art in kinetics and mechanisms. polymer, 48, 6965-6991. wang, r., wang, p.-m., & li, x.-g. (2005). physical and mechanical properties of styrene–butadiene rubber emulsion modified cement mortars. cement and concrete research, 35, 900– 906. wang, r., & wang, p. (2010). function of styrene-acrylic ester copolymer latex in cement mortar. materials and structures, 43, 443–451. xu, f., peng, c., zhu, j., & chen, j. (2016). design and evaluation of polyester fiber and sbr latex compoundmodified perlite mortar with rubber powder. construction and building materials, 127, 751–761. j. build. mater. struct. (2021) 8: 19-31 review doi : 10.34118/jbms.v8i1.1054 issn 2353-0057, eissn : 2600-6936 exploration of prefabricated building system in housing construction neha gupta1, mohammad arif kamal 2,*, tejwant singh brar1 1 shushant school of art & architecture, ansal university, gurgaon, india. 2 architecture section, aligarh muslim university, aligarh, india. * cor responding author: architectarif@gmail.com received: 31-12-2020 accepted: 04-02-2021 abstract. the main purpose of this paper is to examine the development and current status of prefabrication techniques and their application in building construction and why its use is still limited in the housing sector in india and why prefabrication is not being used so far to provide affordable housing to all. prefabrication is the practice of assembling components of a structure in factories, and then transporting the complete assemblies or sub-assemblies to the construction site where the structure is to be located. the important aspect is how much of a potential difference it can establish so that appropriate development can be implemented. this paper reviews the current prefabrication system scenario for housing in india. the paper begins with a brief introduction about different types of prefabrication system. subsequent topics address the need of prefabrication and ethical dilemma of technology transfer for prefabricated building system in india. in this paper, a qualitative descriptive evaluation research method has been used. the research methodology comprises of case studies, visual observation and data collection. finally, two case studies around the world have been presented to validate and illustrate the various modern trends and application of design and construction methods of prefabricated building system in housing. key words: prefabrication, building, construction system, housing, india. 1. introduction the prefabrication is defined as the assembly of buildings or their components at a place other than the building site. it is often referred by new term modern methods of construction (mmc) in an order to reflect technical improvements in prefabrication, encompassing a range of on and off-site construction methods. the term ‘modern methods of construction’ covers a wide range of products, including everything from individual building components to entire factory-built structures and modules. the recently available are volumetric elements, such as fully fitted bathrooms or kitchens. the hotel sector has embraced these elements on a large scale. emergence of a lot of factory-made cladding solutions using everything from traditional bricks to modern composites can be seen (arieff and burkhart, 2002). the use of prefabrication can be useful to achieve results for the society’s needs because the fast changing environment, industrialization, residential need and many other factors of transportation like bridges, towers, railways calls for fast settlement and requirement for buildings, offices and industries, hence prefabrication can be the solution for fast construction. the quality of construction will be much higher when components of housing are manufactured in a stable environment such as factory. this is especially true in india where, prefabrication had already become synonymous with modern and western construction methods. materials are used more efficiently, safe from climatic damage, and can be reused. because of these benefits, a general consensus in india is to move towards prefabricated building systems in housing. in this fast growing population country, it is necessary to have more residential with lesser cost and lesser time. cost reduction can be made by several ways and one such way is to use prefabrication. to reduce the overall cost and greatly to reduce the construction time, mailto:architectarif@gmail.com 20 gupta et al., j. build. mater. struct. (2021) 8: 19-31 prefabricated units are adopted. prefabricated structure can also be one, the component member of which is precast, either in factories or in temporary plant, these precast members are transported to the site and then they are set into complete structure. adopting any technology on large scale need to have a guaranteed market to fulfill its function and this cannot be achieved until the product is economical. prefabrication has the capacity to establish a difference within the indian context in economic, social and environmental terms. the ultimate example of off-site manufacture is fully volumetric construction, in which buildings are compiled by attaching together a series of room or apartment modules that have been built, fitted out and finished in factories. prefabrication technique is popularized for schools and hospitals, and has recently being used for the construction of affordable housing (young et al., 2020). 2. types of prefabrication mmc is a broad category that includes a variety of building approaches including off-site manufacturing (osm). whereas all osm can be covered up under mmc, but not all mmc may be regarded as osm. to explain this, there is range of categories (arieff and burkhart, 2002) 2.1. off-site manufacturing (osm)-volumetric volumetric construction (also known as modular construction) includes the production of three dimensional units in factory conditions before transportation to the actual site. units can be manufactured out of materials including steel, concrete and other materials. modules can be brought to the site in a variety ranging from a basic structure to one with all internal and external finishes and services installed, all ready for assembly. 2.2. off-site manufacturing (osm)-panelized flat panel units are produced in a factory and assembled on-site to produce building structure. most common approach is the utilization of open panels which includes a structure only with external cladding, services and internal finishing on-site. more complex panels typically referred as closed panels – includes more factory-based fabrication and can include skin materials. the panels can also include services, internal wall finishes and external claddings. the panelized system is more flexible than volumetric system and can provide variations in unit plan easily. 2.3. off-site manufacturing (osm)-hybrid a method also referred to as semi-volumetric – it combines both panelized and volumetric approaches. typically, volumetric units (sometimes referred to as ‘pods’) are used for the highly services and more repeatable areas such as kitchens and bathrooms, with the remaining building completed by panels. this approach is basically used to provide flexibility on complex sites, because with both volumetric and panelized approaches the degree of factory-based fabrication can vary to a great extent. 2.4. off-site manufacturing (osm)-sub-assemblies and components this category includes factory built sub-assemblies or components in an otherwise traditionally built form. incorporating the use of floor cassettes and precast concrete foundation assemblies, cladding systems, preformed service installations etc. 2.5. nonoff-site manufacturing (osm) based systems these are systems that fall outside the category of ‘off-site manufactured’ such as insulated concrete formwork (icf). only systems which have independent third party approval will meet gupta et al., j. build. mater. struct. (2021) 8: 19-31 21 the requirements of the technical manual. the acceptability of these systems relies heavily on the quality procedures in place for the installation of the system on-site – in accordance with third party approval. 3. aim and objectives of the research the purpose of the study is to focus at the limited use of prefabrication in housing sector in india, mainly focusing on the potential impact it can have on meeting the ever increasing housing demands of increasing population of india. the aim of the study, to determine the factors needed for the successful use of prefabrication in the construction industry specifically housing sector. the objective of the study is to identify, examine and analyze the main problems that limit the use of prefabrication in housing sector in india and o determine why prefabrication has not been more widely adopted to provide higher quality product. the study shall also focus on why the prefabrication not being used so far to remove the ever increasing housing demands and why still manual construction is preferred over multi block prefabrication for multi storey buildings. 4. research methodology this diagram shows the systematic/ stage wise steps which form the theoretical framework to achieve the aim of the research/study. the given below methodology will help in framing the dissertation research in proper structure and help in analyzing the case studies from the factors obtained from a theoretical framework from the literature reviews. fig 1. research methodology for analysing prefabricated building systems. 5. literature review 5.1 criteria for selection of prefabrication in india in india, the technology adopted for housing components should be of the order that, the technology of production and erection can be adjusted to suit the level of skills and handling facilities available under metropolitan, urban and rural conditions. the structural systems and components selected should ensure minimum material utilization with maximum structural merits. but, the component so designed are to be manufactured and erected by manual means 22 gupta et al., j. build. mater. struct. (2021) 8: 19-31 within villages and small towns, semi mechanical techniques in towns and more or less fully mechanical operations in the metropolitan cities. in urban areas, the concentration of construction activity does not justify prefabrication. the answer is hybrid construction. in residential buildings, balcony projections can be provided along the partially precast joists, having an overhang carrying super imposed loads for balcony as specified in code is: 875-1964, with addition to the self-load and the load due to railings. the main reinforcement for the overhang to be given at the top in the in-situ concrete attains sufficient strength. the savings achieved in practical implementations as compared to the conventional rcc slab is about 25%. mass housing targets can be met by replacing the conventional methods of building operation based on special and individual needs and accepting common denominator based on population needs. no single approach or solution is available which can satisfy the community at large. but desirable is to have a system which can provide choice for people and also appropriate techniques to meet the situation. the essence lies in the system approach in building methodology and not necessarily particular construction type or design. adoption of any alternative technology on large scale needs a guaranteed market to function and this cannot be established unless the product is economical. partial prefabrication is an approach towards the above operation under controlled conditions. the methodology for low cost housing has to be of intermediate type. less sophisticated involving less capital investment. (adhalkha and puri, 2013) 5.2 prefabrication in developing countries prefabrication technology has not transferred as easily when compared with other technologies because it is a production technology or knowledge based and not a consumption technology or product based. technology transfer of prefabrication is not as pertinent to architects as it is to manufacturers of building products, but we are caretakers of culture in construction industry. in many cases we are asked to help with many of the transfers that are occurring by way of global practice or working for multi-national firms that are producing prefabricated components and entire buildings for india and elsewhere. although transfers will continue to occur, especially in the area of prefabrication in building, we should be well aware of how the decisions of u.s. and western architects may have an effect on the ethical dilemmas regarding less developed countries’ development and culture (smith and narayanamurthy, 2004). 5.3 prefabrication in india prefabrication in india began with the emergence of the hindustan housing factory. the company was developed by the first prime minister of india, pandit jawaharlal nehru, as a solution to the housing crisis that resulted from the influx of refugees from west pakistan in the 1950s. the hindustan housing factory pioneered the production of pre-stressed concrete railway sleepers to replace dilapidated wooden sleepers on indian railways. the company changed its name shortly thereafter to reflect the diversity of its operations. it is now known as the hindustan prefab limited or hpl. located in delhi, today the governmentrun company prefabricates primarily precast concrete for architectural and civil projects throughout greater india. when hpl began it was intended to produce low-income housing solutions for the deficit in india. precast wall panels and frame members such as beams and columns provided much needed set of tools to erect quick structures for mass housing. the most difficult technology transfer obstacle for the hpl has been the cost of machinery and materials for production. since the government could not recoup the return on investment for the factory through housing production, prefabrication from hpl began to service other markets including higher dollar civil and larger public and hotel buildings. the quality of construction is much higher when components are manufactured in a stable environment such as the factory. this is especially happens in india where nowadays prefabrication has become synonymous with western construction methods. materials are used more effectively, and are safe from climatic damage, gupta et al., j. build. mater. struct. (2021) 8: 19-31 23 and can be easily reused in the material stream. because of these benefits, a general consensus in india is to move prefabricated building systems beyond precast concrete for large-scale construction to additional market sectors including a resurgent interest in applying prefabrication technology to housing (smith and narayanamurthy, 2004). 6. ethical dilemma of technology transfer “technology transfer use to affect the economy, and culture of both the transferring and the receiving nations. it opens too many ethical dilemmas.” prefabrication will continue to grow in india as the demand for fast affordable housing increases. however, technology transfer of prefabrication process, including materials and tools, affects the receiving country negatively. there are risks associated with the transfer of prefabrication technology. the host country may not have the infrastructure, the manufacturing and/or professional prowess to accept unconditionally, on other hand the negative impact can be social, environmental or economical. (smith and narayanamurthy, 2004). 6.1. transportation the shipping modules becomes cost prohibitive when they must travel more than 150 to 200 miles from factory to site. the industry generally recognizes 125 miles as the maximum practical distance modules should need to travel from factory to site. the auroville earth institute in 1999 built a prototype-prefabricated house in new delhi that showed advances in structural capacity during earthquakes. initially envisioned as a disaster resistant and cost effective prototype, it was intended that the house would be precast anywhere and shipped by truck to a disaster location. precast in auroville, and then transported around 2,900 km to the site in new delhi through a single lorry of 22.5 tons, the prototype was assembled in 66 hours by an 18 man team. the transportation cost alone was equal to the cost of manufacturing the model. this was economically unviable for developing country like india. the solution to low cost prefabricated housing must overcome the obstacle of shipping costs. prefabricating regionally might better serve developing countries (mittal, 2018). 6.2. human rights human rights issues are also of concern with regard to prefabrication technology transfer. as technology made way for mass production and assembly line manufacturing methods in the early part of the 20th century in the u.s., developing countries are using the same process to produce goods abroad today. along with industrial manufacturing and economic benefits come labour challenges. prefabrication presents problems: trading traditional handicraft construction jobs for automatic machines. culture of localized building tradition which passed through generations is abruptly affected. countries with a rich cultural background find it hard to accept drastic changes that involve a great deal of compromises in every field. this may directly affect technological advances, and in the construction field, it hinders the progress of prefabrication as a primary mode of construction. prefab necessarily involves fewer labourers on site. it therefore renders helpless many households that depend on traditional methods of construction for their livelihood. with a literacy rate of only 61%, the possibility of the construction industry labourers shifting occupation to an office or even an automated factory is bleak. the current labour market is a lot different from what it was the last decade. with an influx of the software industries (in the dotcom boom) and an opening for over a million jobs outsourced from outside india, the standard of living among the educated class is increasing. 6.3. schedule modular construction allows for compression of the building schedule, because of the ability to overlap the module construction with site work similar to fast-track design-build construction. 24 gupta et al., j. build. mater. struct. (2021) 8: 19-31 some argue that technology has brought human kind many negative effects, including stressrelated diseases caused by people’s inability to cope with the world that is moving too fast due to rapid technological progress. the schedule was measured from the beginning of design to the project completion. the time savings can be achieved by concurrent factory and on-site work, fewer weather delays, and less on-site material stock. for prefab projects, mostly design is more time intensive due to the added degree of coordination necessary to allow for module fabrication. regarding construction schedule in less developed countries, specifically india, the concern is how to take advantage of cost reduction while still being able to employ individuals and maintain a cultural lifestyle that is unique to a society (smith and narayanamurthy, 2004). 6.4. precision one of the benefits of prefabrication technology is an increase in the quality of the products. less developed countries such as india employ vernacular materials and methods in construction. the industry in india does not rely on precision, but the lack thereof in order to build everyday structures. most members of local communities in india are equipped with knowledge of traditional construction. however, in india, a cultural divide between those that do and those who plan is emerging. this social class structural divide limits the ability for the populous to assimilate alternative methods of building quickly and adopt them into their culture of construction (smith and narayanamurthy, 2004). 6.5. climate and vernacular one of the most significant influences on vernacular architecture is the macroclimate of the area in which the building is constructed. buildings invariably perform well when built with regard to the local climate rather than a technological trend. the native environment and the construction materials which market do produce govern many aspects of prefab development. vernacular, by definition, is sustainable, and will not exhaust local resources. for a country that has followed vernacular practices successfully for generations, like india, moving to a concept like prefab may not prove to be climatically as suitable. for example, in many hot regions of india, masonry walls that are heavy and dense conduct heat slowly and gradually. this process is called thermal lag, decreases peak cooling load in summer and peak heating load in winter. it results in a more comfortable home all year long that produces significant savings in energy. however, in india there are 6 distinct climate zones ranging from cold, dry to warm and wet. therefore, india’s architecture is varied in its use of materials with different fashion of construction while having cultural difference that cannot be generalized. prefabrication as a technology transfer mode struggles should pursue in consideration these vernacular differences. 7. need of prefabrication according to the 2011 census, the housing stock in urban india stood at 78.48 million for 78.86 million urban households. urbanization has resulted in people increasingly living in slums and has deteriorated the housing conditions of the economically weaker sections of the society. table 1. housing shortage in india monthly per capita expenditure estimated number of households (2007) housing shortage in million (2007) percentage shortage ews 0-3,300 21.81 21.78 99.9% lig 3,301-7,300 27.89 2.89 10.5% mig 7,301-14,500 16.92 0.04 0.2% hig 14,501and above total shortage 66.30 24.71 37.3% gupta et al., j. build. mater. struct. (2021) 8: 19-31 25 source: report of the technical group (11th five year plan: 2007-12) on estimation of urban housing shortage the housing percentage shortage in ews is 99.9 % which is double than the estimated number of households. where as in hig and mig is so low 0.2% only. it highlights the mismatch between demand and supply of housing units. further, the national sample survey organization, 61st round reports that the number of urban poor had increased by 4.4 million people, between 1993-94 to 2004-05.therefore it is of vital importance that a new national urban housing and habitat policy analyses the ways and means of providing the 'affordable housing to all' with special emphasis on the ews and lig sectors (teotia, 2014). the "national urban housing and habitat policy 2007" paper identifies clearly the need to provide sustainable affordable housing based on some of the following issues: 7.1. lack of housing stock at the advent of the 21st century (2001), the housing stock in india presently is 50.95 million for 55.8 million urban households. major segments of this housing stock was characterized by congestion and obsolescence congestion is particularly acute in inner city slums and peripheral slums. according to the census 2001, 23.1% of the urban population reside in slums. the quality of housing in slums is extremely poor. slums are severely deficient even in the basic services such as potable water, sanitation, sewerage, storm water drainage and solid waste disposal. (d’souza, 2019) 7.2. increase in urban poverty non-affordability of housing by economically weaker sections of society and low income families in urban areas is directly linked with the magnitude of poverty. the number of urban poor has risen by 4.4 million persons during 2004-05. around one fourth of the country's total urban population of 80.7 million persons is below the poverty line. the urban poor constitute 26.7% of the total poor in the country. this fact that the number of urban poor has risen is in stark contrast with rural poverty, where both the total number of rural poor and its incidence with the rural population has fallen. according to the 2001 census, there is a 90%deficiency in drinking water 26% in toilets and 23% in drainage. it is quite understandable that most of this shortage pertains to slums (teotia, 2014). 7.3. need for sustainable habitat development of sustainable habitat is closely related to the adoption of the regional planning, while preparing the master plans of towns/ cities, district plans and regional/sub-regional plans. it includes the maintenance of ecological balance in terms of a symbiotic perspective on rural and urban development while developing urban extensions of existing towns. the new habitat policy realizes the importance of small and medium urban towns. which have potential for future urban growth. the new policy seeks to accelerate the development of such small and medium towns which can serve as generators of economic momentum while at the same time striving to reduce the rate of migration to existing large cities. the need for "sustainable affordable housing" has been realized, efforts have been made to provide low income housing through policy changes and planning regulations applied in cities all over india. but a clear knowledge and understanding of sustainability is amiss in ali previous and present initiatives. the pure need of addressing sustainability in the social integration, economic viability and prosperity, and sensitivity to climatic, social and community comfort has not yet been recognized (d’souza, 2019). 26 gupta et al., j. build. mater. struct. (2021) 8: 19-31 8. advantages and disadvantages of prefabrication 8.1. advantages of prefabrication there are many advantages of prefabrication as compared to the construction building construction systems (adlakha and puri, 2013). they are summarized as below:  self-supporting ready-made components are used, so the need of shuttering, formwork and scaffolding is reduced greatly.  construction time is reduced and buildings are completed sooner, than conventionally built building, thus allowing earlier return of the capital invested.  on-site construction and congestion is minimized.  quality control can be easier in a factory assembly line setting than a construction site.  prefabrication can be located where skilled labour is more readily available and costs of power, materials, space and labour are lower.  time spent in bad weather or hazardous environments at the construction site is minimized.  less waste may be generated and in a factory setting it may be easier to recycle it back into the manufacture process, like it will be less costly to recycle scrap metal generated in a metal fabrication shop than on the construction site.  moulds can be used several times. 8.2. disadvantages of prefabrication there are also few disadvantages of prefabrication as compared to the construction building construction systems (adlakha and puri, 2013). they are summarized as below:  careful handling of prefabricated components such as concrete panels or steel and glass panels is required.  attention has to be paid to the strength and corrosion-resistance of the joining of prefabricated sections to avoid failure of the joint.  similarly, leakages can take place at joints in prefabricated components.  transportation costs may be higher for voluminous prefabricated sections than for the materials of which they are manufactured, which may be packed more effectively.  large prefabricated sections require heavy-duty cranes and precision measurement and handling to place in position.  larger groups of buildings from the same type of prefabricated elements tend to look drab and monotonous.  local jobs are lost. 9. comparison between the prefabricated and conventional housing a comparison of a residential project for karanataka housing board at kengiri, karnataka, which had used the prefabricated system and mahamedha co-operative housing society at hapur, uttar pradesh (a north-indian state), which had used the conventional construction system has been gupta et al., j. build. mater. struct. (2021) 8: 19-31 27 done. the images of the projects have been shown in fig. 2 and comparative analysis has been summarized in the following table no. 2. fig. 2 residential project at hapur and residential project at kengiri table 2. comparative analysis of prefabricated and conventional construction system. prefabrication conventional minimum no. of units required in a for prefabricated construction to be economical is 2500. if the no.of units in an housing is less than 2500 then definitely conventional construction is cheaper. 1. the cost reduces by 20% in super-structure. 1. the cost reduces by 30-35% in super-structure if >2500. 2. time period for concrete to set 1 day in factory. 2. time-period for concrete to set 28 days. 3. waste material used again. 3. waste material cannot be used. 4. labour force reduces and unskilled required is very minimum. 40% labour reduced. site-(s:n-s)-(70-30) (erection) factory-(s:n-s)-(80-20) 4. labour force required in comparison is very high. site(s:n-s)-(1:1.5) (erection) 5. cost-analysis  20% cost reduced from conventional style.  inclusive of labour, material, construction and transportation. cost of superstructure only.  transportation cost is 4.25% if distance between the site and factory is 50 kms.  transportation cost increases is less components have to be transported and decreases if more components.  20% cost to be reduced total saving of 162.5 million only in r.c.c. in superstructure. 5. cost-analysis  no. of units=2500  average area of a unit=150 sqm  total area=3,75,000 sq.m  r. c. c. in super-structure include column+beam+slab  assuming slab thickness to be 150mm.  cost of r.c.c= rs. 5500/cu.m.  volume of r.c.c.=150000 cu .m.  grade of concrete-m20  total cost=rs. 82,50,00,000 6. as 40% labour reduces, it is more economical. 6. high labour charges as large no.of labours used 7. 1ndia being a country which has many festivals and seasons so there is a lot of problem to find labour during festivities. 7. work is severely hampered during these seasons. 8. employment rate reduces and for a country like india where cheap and unskilled labour is available in abundance due to poverty, it is a big set-back. 8. 1t creates more employment opportunities and is some relief to poverty. 28 gupta et al., j. build. mater. struct. (2021) 8: 19-31 10. comparison between different prefabricated residential housing a comparison of prefabricated residential projects for different housing boards in india has been done. a comparative analysis has been summarized in table no. 3. table 3. legend title must be short and concise. examples of residential project images no. of units project cost (in million rs.) average area of unit completion time maharashtra housing board at goregaon, mumbai 1400 4.75 million approx. 150 sqm. 10 months maharashtra housing board at malad, mumbai 486 2.1 million approx. 150 sqm. 8 months maharashtra housing board at dindoshi 3620 7.9 million approx. 150 sqm. 1 year 6 months karanataka housing board at kengiri 2580 6.6 million approx. 150 sqm 1 year 3 months 11. case studies the following two case studies present the techniques and technological advancements in prefabricated building system. 11.1. turbo tower, chandigarh in the town of mohali, a suburb just outside of chandigarh in northwest of india, 10-storey tower was constructed in just 48-hours. the visionary behind this project, harpal singh of the infrastructure company synergy thrislington, told that it was all possible because the components have been manufactured already, water supply components, wiring, doors that can be pre-fitted, sanitation, air conditioning, ducts and everything is prefabricated. the components had been made from around 200 ton steel, and they were all prefabricated in a nearby factory before they were moved to the site on special transport trucks. the structure spread over 25,000 square meters and was completed in all respects including electrical installation in the time schedule. no bricks and sand had been used. the outer walls were double-skinned puf panel. the cost was almost the same as of conventional construction. it saves a lot of time that goes into construction otherwise. singh has gotten his project certified as earthquake and shock-proof by the center for industrial and scientific research. after just 6 hours, 3 floors had been constructed, and in 24 hours, nearly 7 stories had been completed. this ultra-fast construction had more than 80 per cent work pre-made and the rest happened on the site. the gupta et al., j. build. mater. struct. (2021) 8: 19-31 29 material used was manufactured in the previous two months in a nearby factory (korones, 2012). stage 1 stage 2 stage 3 stage 4 fig 3. different stages of prefabricated construction in turbo tower, chandigarh, india. 11.2. the atlantic yards, new york it is the tallest modular building in the world with 32 floors with height reaching 322 feets. its architect shop broke down the monolithic size one expects to encounter street-side by composing the facade in a series of alternating bands of curtain glass and rusted-steel grid work. the modules/units used to construct the complex. all modules are pre-assembled at the navy dockyards, transported here and then completed. modules are picked directly from the truck and placed onto the building by a crane within the construction fence and set by a team of workers. modules are bolted together work is undertaken to complete the connections of preinstalled building system components within each module. each module has a floor level, but no ceiling. when the joining is done, it is kept in mind that the floor of the upper level module will act as a ceiling for the lower level. this further reduces the cost of construction. this tower is part of a $49 billion, 22-acre atlantic yards project in brooklyn. the 3 residential buildings contain a total of approximately 1500 units of residential housing. it is the first of the residential buildings to break ground, and at 32 floors and 363 units, the tallest modular building in the world. the stepwise collection of modules from pod links to the final floor groups which make the construction easier and faster. (stott, 2014) 30 gupta et al., j. build. mater. struct. (2021) 8: 19-31 fig 4. volumetric modular construction in the atlantic yard. fig 5. the module and their placements through cranes. fig 6. stages of module in the atlantic yard gupta et al., j. build. mater. struct. (2021) 8: 19-31 31 12. conclusions from the above study of various aspects of prefabrication, i can conclude that there exists a great potential for modular construction in the delivery of high-rise buildings. production of same modules on a bigger scale can possibly create cost saving, for example in diverse housing developments. the size and weight of the modules to be used in a modular building need to be carefully considered with respect to transportation. according to the study typical module sizes for volumetric construction are 11 feet high, 12 to 16 feet wide, and 55 to 65 feet long. 200-mile distance is the maximum, from the site location is probably the most cost-efficient option with respect to transportation of the modules are the trucks. prefabrication has the capacity to drive down costs and improve the productivity of the construction industry. targets can be met by replacing the conventional techniques of building operation based on some common base on the basis of surveys, no single solution is available which have the capacity to satisfy the community as a whole. but it will be desirable to have a system which can provide option to people and appropriate techniques to tackle different situations. to adopt any alternative technology needs a guaranteed market to function on large scale and this cannot be achieved unless the product is effective. technology transfer of prefabrication is not as pertinent to architects as it is to manufacturers of building products, but we are caretakers industry. sometimes architects are asked to help with many of the transfers that are occurring by way of global practice or working for multi-national firms that are producing prefabricated components and entire buildings for india and elsewhere. there lies interesting opportunities in urban city scale, where architect can provide different designing opportunities by using same building unit. the use of prefabrication merely offers an alternative route to procuring a building, which may offer opportunities for maximizing value for all concerned. hence prefabrication is the solution for fast and time saving construction. 13. references adlakha p. k. & puri h. c. (2013), prefabrication building methodologies for low cost housing, institution of engineers journal, ar, vol. 84, 4-9, 2013. arieff, a. & burkhart, b. (2002). prefab. gibbs smith publisher, utah, usa. d’souza r. (2019), housing poverty in urban india: the failures of past and current strategies and the need for a new blueprint , orf occasional paper no. 187, observer research foundation, india. korones, s. (2012), in india, a 10-story tower built in just 48 hours, retrieved on feb. 24, 2021 from https://www.zdnet.com/article/in-india-a-10-story-tower-built-in-just-48-hours/ smith, r. e. & narayanamurthy (2004), prefabrication in developing countries. from edited book ‘without a hitch: new directions in prefabricated architecture, university of utah, usa. stott, r. (2014). construction halted on shop architects' atlantic yards housing project, retrieved on feb. 24, 2021 from https://www.archdaily.com/545230/construction-halted-on-shop-architects-atlanticyards-housing-project teotia m. k. (2014), housing poverty in urbanizing india: emerging trends and concerns, proceedings of viii isa world congress of sociology, 13-19 july 2014, yokohama, japan. young, b. e., seidu, r. d., thayaparan, m., & appiah, k. j. (2020). modular construction innovation in the uk: the case of residential buildings, proceedings of the international conference on industrial engineering and operations management, march 10-12, 2020, dubai, uae. https://www.archdaily.com/545230/construction-halted-on-shop-architects-atlantic-yards-housing-project https://www.archdaily.com/545230/construction-halted-on-shop-architects-atlantic-yards-housing-project j. build. mater. struct. (2020) 7: 119-129 original article doi : 10.34118/jbms.v7i1.744 issn 2353-0057, eissn : 2600-6936 behavior of selfcompacting concrete incorporating calcined pyrophyllite as supplementary cementitious material mansour sabria malika research unit: materials, process and environment, civil engineering department, university m’hamed bougara of boumerdes, algeria corresponding author: s.mansour@univ-boumerdes.dz received: 03-07-2020 accepted: 24-08-2020 abstract. the current trend of industrial concrete leans more towards the use of selfcompacting concrete. these must have fresh properties well defined as fluidity, filling ability and resistance to segregation. however, to ensure the rheological stability, use mineral fines is required. in this work, powder of calcined pyrophyllite (cp) was used as cement substitution at level of 10% and 20% by weight. the interest is focused on the role played by the calcined pyrophyllite to produce scc with reduced impact environmental.. calcination of pyrophyllite powder was carried out at 750 °c. its effect on the workability and mechanical properties of self-compacting concrete is analyzed. the results show that the properties of workability of scc containing 10% of calcined pyrophyllite tested at fresh state (slump flow, t50, passing ability and segregation resistance) are almost identical to those of the control scc. furthermore, the calcined pyrophyllite increases the compressive strength, tensile and flexural strength of scc approaching without exceeding those of the control scc. it seems that 10 % of calcined pyrophyllite is the optimum replacement rate which improves mechanical strength compared to 20%. replacing cement with the calcined pyrophyllite aims to save cement and reduce the co2 emissions released during the manufacture of cement. key words: calcined pyrophyllite; self-compacting concrete; mechanical strength; workability. 1. introduction self-compacting concrete scc is a very fluid, stable and homogeneous concrete. it differs from ordinary concrete by its fresh properties and moldability. the scc is formulated to obtain the optimal compromise between fluidity and resistance to segregation and to bleeding (aci, 2003). however, to ensure the fresh stability of scc, the use of mineral additives (fine) is required. but researches are still relevant to the understanding of the fresh and physicalmechanical behavior of scc. the addition of finely divided siliceous materials to concrete mixes in order to improve the workability of fresh concrete and subsequently the durability of its hardened state is an established practice in modern concrete technology (uysal & sumer, 2011; busari et al., 2019). siliceous materials of low reactivity are utilized solely to improve the workability of fresh concrete deficient in fines (ouldkhaoua et al., 2020). generally, cementitious or pozzolanic materials are preferred because they eventually also contribute to the strength and durability of the hardened concrete (belaidi et al., 2015; belaidi et al., 2012; boukhelkhal et al., 2016; boukhelkhal et al., 2012; aghabaglou et al., 2014; dembovska et al., 2017; ouldkhaoua et al., 2020). a wide variety of natural materials as well as industrial by-products contain silica that has pozzolanic activity. to maximize its pozzolanic activity, natural pozzolans usually require grinding to cement fineness and may need to be calcined prior to its application (krajèi et al., 2013; mansour et al., 2012; mansour et al., 2013). indeed, the thermal treatment collapses the crystalline structure of the mineral by evaporating the lattice hydroxyl groups, creating a highly reactive amorphous alumina-silicate that has high affinity for reaction with cement hydration mailto:s.mansour@univ-boumerdes.dz 120 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 products (tregger et al., 2010). it has been demonstrated by many researchers (bijeljié et al., 2014; madandoust & mousavi, 2012) that kaolinit in form of metakaolin (calcined kaolinit) can be used as an excellent cement substitute. however, if other clay minerals' pozzolanic reactivity was improved, the use of calcined clays would present a good choice in addressing the cement production reduction problem (rashad, 2015). recently, natural pyrophyllite was discovered in algeria. being calcined and finely ground, becomes a pozzolanic material reacts with calcium hydroxide ca(oh)2 released during the hydration of cement to form the calcium silicate hydrates csh and allow to improve the fresh and mechanical properties of concrete. the pyrophyllite (ai2o3.4sio2.h2o) is a relatively rare mineral because it is not found everywhere in the word; few studies have been done on pyrophyllite used as a cementitious material. therefore, it has generally been neglected in commercial circles, but its high content of silica and alumina and its physical and chemical properties make it useful in many industries, primarily in refractories, ceramics and various uses. pyrophyllite is a soft, white or pale colored silicate mineral. hydrated aluminum silicate al2si4o10(oh)2, comprised as the main constituent of some schistose rocks. pyrophyllite deposits are usually associated with metamorphic rocks, in which the mineral forms packets of pyrophyllite slate or compact agalmatolite aggregates. it sometimes occurs in hydrothermal quartz and ore veins. pyrophyllite is both fireand acid-resistant. it is used commercially as a highly aluminiferous raw material for refractory products and as a chemically stable and insulating material. it has mohs hardness of 1-2 and specific -gravity of 2.6-2.9. pyrophyllite (from the greek words for fire and leaf) gets its name from the fact that it exfoliates when water is driven off upon heating, leaving a flaky mass. in pyrophyllite, two silicate layers are sandwiched with a gibbsite layer between them. thus the overall structure of natural pyrophyllite can be imagined as stacked silicate-gibbsite-silicate sandwiches. after calcination pyrophyllite powder lost its sticky property when combined with water and its color changed from light grey to light orange. in the literature, the raw pyrophyllite is used as an additive or substitute materials at different amounts into a conventional porcelain mixture (mukhopadhyay et al, 2009). extensive and relevant studies on the use of pyrophyllite in building materials such as mortar or concrete are even scarcer (anggraini et al, 2014). demez & karakoç, (2020) assessed the residual mechanical properties of high strength concretes made with pyrophyllite aggregate after high temperature. terzic´ et al, (2020) studied the utilization possibility of activated pyrophyllite in building materials as a pozzolanic mineral additive. researches of lauw and besari (2001) reported that the calcined pyrophyllite decreased strength of lightweight concrete. they showed that it can be effectively used as a partial replacement of cement but to improve its pozzolanic activity, calcination temperature and finesse must be increased. the available studies on the application of pyrophyllite are predominantly limited to its utilization in ceramic materials (whitewater, tiles, porcelain) as a replacement of quartz, clay or feldspar (amritphale et al., 2006; mukhopadhyay et al., 2010). therefore, the general idea behind our investigation was to use algerian calcined pyrophyllite powder as cement substitution at a rate of 10% and 20% to assess its potential in selfcompacting concrete providing additional benefits. this, for economic and environmental reasons by reducing the cost of manufactured cement and co2 gas released. its effect on the workability and mechanical properties of self-compacting concrete was studied. 2. materials and experiment 2.1 materials cement cem ii / a 42.5 was used. natural ground sand with a maximum size of 3 mm was used as natural fine aggregate with a specific gravity of 2.69 g/cm3, fineness modulus of 2.31 and its mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 121 water absorption value is 4.5%. coarse aggregates 3/8 and 8/15 with specific gravity of 2.66 (g/cm3) were also used. superplasticizer medaflow re 25, a high range water reducer polycarboxylate was used to achieve the required workability of the scc mixes. superplasticizer having a ph of 7, a density of 1.06 and chlorine content < 1 g/l and a 25% solids content. used pyrophyllitte comes from the region of bechar located 1150 km south-west of the capital algiers in the form of rock pieces. it was crushed and pulverized using a mill, sieved through a sieve of 80 microns and then calcined at 750 ° c for 3h. physical properties and chemical compositions of the calcined pyrophyllite cp and cement are given in table 1 and table 2. furthermore, xrd analysis of pyrophyllite and calcined pyrophyllite are shown in figure 1 and figure 2. table 1. physical properties of calcined pyrophyllite cp and cement caracteristics cpc cement specific surface area (cm 2 /g) 6200 4400 specific gravity (g/cm 3 ) 2.55 2.99 mineral activity (mg) ca(oh)2/g 118.3 table 2. chemical composition of cp and cement (%, by weight) oxydes sio2 al2o3 fe2o3 cao mgo so3 k2o na2o p 2o4 tio2 pf cpc 53.77 27.33 8.03 1.23 0.70 1.24 2.86 0.64 0.15 1.10 2.94 cement 20.71 5.45 3.63 60.4 2.15 2.37 0.65 0.23 4.28 chemical analysis of the calcined pyrophyllite cp shows that it contains a significant rate of silica and alumina. hence it is categorized as alumino-silicate material. the oxide composition of calcined pyrophyllite used in this investigation was about 53.77 % silica, 27.35% alumina and 2.94% was loss on ignition. in addition, calcined pyrophyllite contains impurities as mgo, so3, k2o, na 2o, p2o4 and tio2. moreover, figure 1 show that the crystalline phases of the pyrophyllite are quartz, kaolinit and gypsum, ilite, pyrophyllite and hematite. but after calcination at 750 ° c for 3 hours, kaolinit and gypsum disappeared and new minerals were formed as the anhydride. fig 1. x-ray diffraction of the pyrophyllite (cu kα filter ni). 122 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 according to figure 2, xrd analysis confirms that applied thermal cycle was not enough to decompose the illite and quartz. temperature of 750 ° c was chosen based on the works of samet et al., (2007), rabehi et al., (2014) and rashad, (2015). at this temperature, there is a departure of the water content (the dehydroxylation) and the formation of material with an amorphous structure which makes it more reactive than the starting clay. the heat treatment causes the transition of the crystalline phase ordered to a disordered phase by a collapse of the crystal lattice. fig 2. x-ray diffraction of the calcined pyrophyllite (cu kα filter ni) 2.2. formulation of self compacting concrete based on the japanese method (okamura & ozawa, 1994), the self-compacting concrete was formulated. the basic data are optimized such as: gravel to sand ratio g/s was fixed to 1, the ratio of water to cement blended w/b = 0.38 with the cement content c = 450 kg/m3, a rate of 10% and 20% of calcined pyrophyllite used as cement substitution was chosen and finally, a dosage of superplasticizer was kept constant at 1.7% by weight. three compositions of scc mixes were prepared, a control self-compacting concrete (scc1) without cp and two concretes scc2 and scc3 containing 10% and 20% of cp. the mix proportion of self compacting concretes is presented in table 3. table 3. mix proportion of self-compacting concretes (kg.m-3) scc/constituent scc1 0% cp scc2 10% cp scc3 20% cp cement 450 405 360 limestone fillers 45 45 45 calcined pyrophyllite cp 45 90 sand 875 875 875 coarse aggregate g3/8 346 346 346 coarse aggregate g8/15 519 519 519 water 182 182 182 superplasticizer 8.42 8.42 8.42 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 123 2.3. mixing, casting, curing and testing specimens for each scc mixture, three prismatic samples (70x70x280mm) and three cylindrical samples (110x220mm) were cast into steel molds according to standard nf en 12390-2 (2012). the molds are kept in a room at ambient temperature, and after 24 hours demolded. to ensure proper curing of scc concrete, the specimens were placed in a tank of water at a temperature of 20° c±2°c, this prevents water loss and to ensure normal operation of hydration process of cement. the concretes were then tested in compression according to nf en 12390-3 (2012) standard, flexural according to nf en 12390-5 (2012) and tensile according to nf en 12390-6 (2012) at maturities 7d, 14d and 28 days. before casting, slump flow and t50 test of mobility of the fresh scc (nf en 12350-8, 2010), lbox test (nf en 12350-10, 2010) and sieve stability test (nf en 12350-11, 2010) were carried on each scc mixture. slump flow test is utilized to weigh flowability of scc in lack of impediments. t50 test is used to weigh horizontal free flow in lack of impediments. a greater flowability is an indication of lower time. l-box test measures filling and passing ability of scc. sieve stability test is performed to assess the stability of scc. 3. results and discussion 3.1. influence of calcined pyrophyllite on fresh properties the results obtained on self-compacting concrete tested at fresh state (flow test, l-box, sieve stability), show that all elaborated scc with and without calcined pyrophyllite have good fresh properties (slump flow diameter, slump flow time t50, passing ability and stability) that comply with the requirements prescribed by efnarc (2005). figure 3-(a) illustrates the slump flow diameter of scc. it is shown that for all sccs, the slump flow was between 55cm and 68 cm, which is an indication of good deformability. when cp is incorporated in scc, the slump flow results come under sf1 classes according to the efnarc (2005) guidelines. the presence of calcined pyrophyllite decreased the slump flow diameter of self-compacting concrete. the reduction is 3% for scc2 and 11% for scc3. these results are confirmed by the values of the time t50. figure 3-(b) shows that all scc have slump flow times which are in the field of scc (greater than 2 sec). t50 is classified into two classes in efnarc (2005) guidelines i.e., vs1 and vs2, for vs1 class outcome is ≤2 and for vs2 class outcome is >2. in this study, outcomes come under vs2 class. (a) (b) fig 3. influence of the rate of calcined pyrophyllite on (a)slump flow, (b)flow time t50 of sccs. results showed that the time of flow to reach the 50 cm diameter increased with increase of cp rate. the presence of cp decreased the flowability and made the scc more viscous compared to scc1. indeed, it was found during tests that when the cp rate increased, the concrete became less fluid and its placement in the test specimens was slow. the reduction in slump flow is probably due to the high fineness of cp compared to that of the cement, which can absorb the 124 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 water and consequently decrease the flowability. similar results have been reported in other researches when the calcined kaolin was used (melo & carneiro, 2010; hassan et al., 2010). moreover, the passing ability determined by l-box is greater than 0.8 for all scc. according to efnarc guidelines (2005), l-box test results ≥ 0.80 comes under pa1 classes with 2 rebars and the test results ≥0.80 comes under pa2 classes with 3 rebars. this is means that the risk of blockage is avoided. the passing ability decreased in the presence of cp when its rate increased from 10% to 20% (figure 4). compared to scc1, the reduction of passing ability is 6% and 9% for scc2 and scc3 respectively. figure 5 illustrates effect of calcined pyrophyllite on the stability to segregation of sccs. according to results, a decrease of segregation resistance of scc was obtained with the increase of cp rate which translated into an increase of the percentage of milt. but, all the studied sccs are stable (milt < 15%) and are classified as sr2. the scc1 without cp is characterized by high stability (milt < 5.14%) and consequently a high resistance to segregation and to bleeding. scc2 and scc3 are homogeneous and less stable than scc1. this is due to increase of the amount of cp fines in scc witch facilitate the passage through the sieve and increases the milt weight. fig 4. influence of the rate of calcined pyrophyllite on the passing ability h2/h1 of sccs. fig 5. influence of the rate of calcined pyrophyllite on the segregation rate/ milt weight of sccs. in general, reduction in workability was attributed to few reasons such as greater fineness of addition than cement (kim et al., 2012; mo et al., 2018), and the rough morphology of particles could interlock and agglomerate together (kim et al., 2012). the three (03) scc concretes all have a slump flow greater than 60 cm, a quantity of milt less than 15% and a passing ability greater than 80%, which confirms their self-compacting behavior. it seems that 10% is the optimum rate for good fresh properties of scc. this concrete is classified as having a normal workability, plastic consistency and stability without risk of segregation. so, behavior of scc2 at fresh state is similar to that of scc1. mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 125 moreover, a correlation between milt of sieve stability test and t50 was suggested. it is clear from the obtained results that the increase in t50 is associated to the increase of the milt and the decrease in resistance to segregation. the curve that describes this relationship is polynomial and the two properties are 100% related. the relation is expressed by the equation (1): milt weight = 0.3658 (t50)2 + 4.91258.6567 (1) fig 6. relation-ship between flow t50 and milt of sieve stability test. 3.2. influence of calcined pyrophyllite cp on hardened properties 3.2.1. compressive strength figure 6 shows that the increase of compressive strength as a function of the age is substantially similar for all samples tested scc (figure 6-(a)). due to its high volume in portland cement (450kg/m3), the control mix has for all ages the highest values of strength. moreover, incorporation of calcined pyrophyllite as cement substitution decreases the compressive strength (figure 6-(b)). (a) (b) fig 6. (a)-compressive strength, (b)-effect of cp rate on compressive strength. the reduction is 4% and 18% at 7 days, 4% and 16% at 14 days, 7% and 19% at 28 days for scc2 and scc3 respectively. the rate of 10% cp generates the lowest reduction at all ages. the strengths of scc2 are almost comparable to those of scc1. this decrease is due to the reduction of c3s and c2s minerals. these are the two main minerals that ensure the development of short and medium-term strength because they lead to the formation of csh increasing the strength (chinje and billong, 2004; baronio and binda, 1997). also, the water destined to cement wetting was mobilized by the cp due to its high fineness, which delayed the hydration process, therefore a decrease in strength has been recorded. another reason is the low reaction rate of calcined 126 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 pyrophyllite due to fact that cement type (cem ii) had a negative influence unlike rapid reaction rate of metakaolin and its ability to accelerate cement hydration. (badogiannis et al., 2015; akcay et al., 2016; lenka and panda, 2017; barkat et al., 2019). 3.2.2. flexural strength figure 7-(a) shows the increase of flexural strength as function of the age for the three compositions of scc. the strengths of scc2 and scc3 at maturities of 7, 14 and 28 days do not reach those of scc1. substituted cement by calcined pyrophyllite cp reduced flexural strength at all maturities (figure 7-(b)). reduction is 17% and 20% at 7 days, 17% and 31% at 14 days, 15% and 33% at 28 days for scc2 and scc3 respectively. the lowest reduction is obtained for concrete containing 10% of cp. (a) (b) fig 7. (a)-flexural strengths, (b)-effect of cp on flexural strength 3.2.3. tensile strength figure 8-(a) clearly shows an increase in tensile strengths according to age for all scc. moreover, incorporation of calcined pyrophyllite decreased the tensile strength of scc2 scc3 at maturities 7, 14 and 28 days (figure 8-(b)). significant reduction was obtained. it is 25% and 33% at 7 days, 31% and 40% at 14 days, 22% and 39% at 28 days for scc2 and scc3 respectively. scc2 mixture is the concrete witch developed tensile strengths approaching those of the control. (a) (b) fig 8. (a)-tensile strength, (b) effect of cp on tensile strength. 4. conclusions this investigation was conducted to assess the fresh and hardened properties of reduced environmental impact scc made with calcined pyrophyllite. from the obtained results following conclusions can be drawn: mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 127 the slump flow of sccs is between 55cm and 68 cm, which is an indication of good deformability. it decreases in presence of calcined pyrophyllite. the lowest reduction of 3% was obtained for scc containing 10% cp. in the other hand, the flow time t50 increased with the increase of the rate of calcined pyrophyllite from 10% to 20% and a slowdown in the flow of scc was observed. the passing ability is greater than 0.8 for all scc. this is means that the risk of blockage is avoided according to efnarc guidelines (2005). the passing ability decreased in the presence of calcined pyrophyllite when its rate increased from 10% to 20%. the 6% lowest reduction is obtained for scc incorporating 10%. the segregation resistance decreased increase of cp rate. but, all the studied sccs are stable (milt < 15%) and are classified as sr2. scc2 and scc3 are homogeneous and less stable than scc1 it seems that 10% is the optimum rate for good workability properties of scc2 compared to 20%. this concrete is classified as having a normal workability, plastic consistency and satisfactory stability is to say no risk of segregation. behaviour of scc2 contained 10% of calcined pyrophyllite at fresh state is similar to that of control scc1 concrete. an excellent relationship between milt of sieve stability test and flow time t50 was suggested. the two properties are correlated at 100%. the use of calcined pyrophyllite as 10% and 20% cement substitution in concrete scc slows down the hardening process of concrete, consequently producing lower strengths of scc concretes. at 28 days, for self-compacting concrete containing 10% cp, reduction is 7%, for compressive strength, 15% for flexural strength and 22% for tensile strength. the rate of 10% cp seems to generate mechanical strengths approaching those of the scc control. workability and mechanical tests show results that support the use of cement with calcined pyrophyllite as part of an economical and environmental self-compacting concrete. 5. references aci (2003). processes, self-compacting concrete’’, advanced concrete technology iii, 3, 203 – 209. aghabaglou, m. a., sezer, g. i̇., & ramyar, k. (2014). comparison of fly ash, silica fume and metakaolin from mechanical properties and durability performance of mortar mixtures view point. construction and building materials, 70, 17-25. akcay, b., sengul, c., & ali tasdemir, m. (2016). fracture behavior and pore structure of concrete with metakaolin. advances in concrete construction, 4(2), 71-88. amritphale, s. s., bhasin, s., & chandra, n. (2006). energy efficient process for making pyrophyllite-based ceramic tiles using phosphoric acid and mineralizers. ceramics international, 32(2), 181-187. anggraini, r., ristinah, r., budio, s. p., soewignyo, s. r., & firmaninda, w. (2014). the effect of pyrophyllite use as admixture in light concrete bricks’s mechanical properties. rekayasa sipil, 7(3), 210-217. badogiannis, e. g., sfikas, i. p., voukia, d. v., trezos, k. g., & tsivilis, s. g. (2015). durability of metakaolin self-compacting concrete. construction and building materials, 82, 133-141. 128 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 barkat, a., kenai, s., menadi, b., kadri, e., & soualhi, h. (2019). effects of local metakaolin addition on rheological and mechanical performance of self-compacting limestone cement concrete. journal of adhesion science and technology, 33(9), 963-985. belaidi, a. s. e., kenai, s., kadri, e. h., soualhi, h., & benchaâ, b. (2016). effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes. journal of adhesion science and technology, 30(3), 247-261. belaidi, a. s. e., azzouz, l., kadri, e., & kenai, s. (2012). effect of natural pozzolana and marble powder on the properties of self-compacting concrete. construction and building materials, 31, 251-257. bijeljié, j., paunovie, s., nesovië, i., & milosevié, b. (2014). inflence of calcined clays on the fresh properties of self-compacting concrete. international conference contemporary achievements in civil engineering, subotica, serbia. 509-515. boukhelkhal, a., azzouz, l., belaïdi, a. s. e., & benabed, b. (2016). effects of marble powder as a partial replacement of cement on some engineering properties of self-compacting concrete. journal of adhesion science and technology, 30(22), 2405-2419. boukhelkhal, a. (2012). rheology, physical and mechanical characterization and durability of selfcompacting concrete made with marble powder. [msc thesis]. university amar telidji of laghouat, algeria. p.170. busari, a., dahunsi, b., akinmusuru, j., loto, t., & ajayi, s. (2019). response surface analysis of the compressive strength of self-compacting concrete incorporating metakaolin. advances in science and technology research journal. 13(2): 7–13. baronio, g., & binda, l. (1997). study of the pozzolanicity of some bricks and clays. construction and building materials, 11(1), 70–78. chinje, m., & billong, n. (2004). activité pouzzolanique des déchets de briques et tuiles cuites. african journal of science and technology (ajst), science and engineering series, 5(1): 92–100. demez, a., & karakoç, m. b. (2020). mechanical properties of high strength concrete made with pyrophyllite aggregates exposed to high temperature. structural concrete, 1–10. https://doi.org/10.1002/suco.201900381. dembovska, l., bajare, d., pundiene, i., & vitola, l. (2017). effect of pozzolanic additives on the strength development of high performance concrete. procedia engineering, 172, 202-210. efnarc (2005). european guidelines for self-compacting concrete: specification, production and use. selfcompacting concrete european project group. hassan, a. a. a., lachemi, m., & hossain, k. m. a. (2010). effect of metakaolin on the rheology of selfconsolidating concrete. in design, production and placement of self-consolidating concrete (pp. 103-112). springer, dordrecht. kim, h. k., hwang, e. a., & lee, h. k. (2012). impacts of metakaolin on lightweight concrete by type of fine aggregate. construction and building materials, 36, 719-726. krajči, ľ., kuliffayová, m., & janotka, i. (2013). ternary cement composites with metakaolin sand and calcined clayey diatomite. procedia engineering, 65, 7-13. lauw, c.g.s., & besari, m.s. (2001). performance of calcined pyrophyllite in lightweight expanded clay concrete. 26th conference on our world in concrete & structures, singapore. 385-392. lenka, s., & panda, k. c. (2017). effect of metakaolin on the properties of conventional and self compacting concrete. advances in concrete construction, 5(1), 01-48. madandoust, r., & mousavi, s. y. (2012). fresh and hardened properties of self-compacting concrete containing metakaolin. construction and building materials, 35, 752-760. mansour, m. s., abadlia, m. t., jauberthie, r., & messaoudene, i. (2012). metakaolin as a pozzolan for highperformance mortar. cement wapno beton, 17(2), 102-108. mansour, m.s., abadlia, m.t., afalfiz, a., & ladaoui, w. (2013). rhéologie du mortier et du béton contenant des ajouts minéraux. journal of cement wapno beton. 5, 264-270. https://doi.org/10.1002/suco.201900381 mansour sabria malika, j. build. mater. struct. (2020) 7: 119-129 129 melo, k. a., & carneiro, a. m. (2010). effect of metakaolin’s finesses and content in self-consolidating concrete. construction and building materials, 24(8), 1529-1535. mo, k. h., mohd anor, f. a., alengaram, u. j., jumaat, m. z., & rao, k. j. (2018). properties of metakaolinblended oil palm shell lightweight concrete. european journal of environmental and civil engineering, 22(7), 852-868. mukhopadhyay, t. k., ghatak, s., & maiti, h. s. (2009). effect of pyrophyllite incorporation in porcelain composition on mechanical properties and microstructure. ceramics international, 35(7), 25552562. mukhopadhyay, t. k., ghatak, s., & maiti, h. s. (2010). pyrophyllite as raw material for ceramic applications in the perspective of its pyro-chemical properties. ceramics international, 36(3), 909-916. nf en 12350-8 (2010). essai pour béton frais – partie 8: béton autoplaçant – essai d’étalement au cône d’abrams. nf en 12350-10 (2010). essai pour béton frais – partie 10: béton autoplaçant – essai à la boite en l. nf en 12350-11 (2010). essai pour béton frais – partie 11: béton autoplaçant – essai de stabilité au tamis. nf en 12390-2 (2012). essais pour béton durci – partie 2: confection et conservation des éprouvettes pour essais de résistance. nf en 12390-3 (2012). essais pour béton durci – partie 3: résistance à la compression des éprouvettes. nf en 12390-5 (2012). essais pour béton durci – partie 5: résistance à la flexion sur éprouvettes. nf en 12390-6 (2012). essais pour béton durci partie 6 : détermination de la résistance en traction par fendage. okamura, h., & ozawa, k. (1994). self compactable high performance concrete. international workshop on high performance concrete, american concrete institute, detroit. 31–44. ouldkhaoua y, benabed b, abousnina r, kadri h, (2020). experimental study on the reuse of cathode ray tubes funnel glass as fine aggregate for developing an ecological self-compacting mortar incorporating metakaolin. journal of building engineering. 27, 100951. ouldkhaoua, y., benabed, b., abousnina, r., kadri, e. h., & khatib, j. (2020). effect of using metakaolin as supplementary cementitious material and recycled crt funnel glass as fine aggregate on the durability of green self-compacting concrete. construction and building materials, 235, 117802. rabehi, b., ghernouti, y., & driss, m. (2014). potential use of calcined silt of dam as a pozzol an in blended portland cement. international journal of concrete structures and materials, 8(3), 259-268. rashad, a. m. (2015). metakaolin: fresh properties and optimum content for mechanical strength in traditional cementitious materials-a comprehensive overview. reviews on advanced materials science, 40(1), 15-44. samet, b., mnif, t., & chaabouni, m. (2007). use of a kaolinitic clay as a pozzolanic material for cements: formulation of blended cement. cement and concrete composites, 29(10), 741-749. terzić, a., radulović, d., pezo, m., stojanović, j., pezo, l., radojević, z., & andrić, l. (2020). prediction model based on artificial neural network for pyrophyllite mechano-chemical activation as an integral step in production of cement binders. construction and building materials, 258, 119721. tregger, a.n., pakula, m. e., shah, s. p. (2010). influence of clays on the rheology of cement pastes, cement and concrete research, 40: 384-391. uysal, m., & sumer, m. (2011). performance of self-compacting concrete containing different mineral admixtures. construction and building materials, 25(11), 4112-4120. j. build. mater. struct. (2020) 7: 67-75 original article doi : 10.34118/jbms.v7i1.765 issn 2353-0057, eissn : 2600-6936 study of the mechanical behavior of a lightweight wood concrete bouabdallah m a department of civil engineering, national polytechnic school of oran, algeria. corresponding author: m-a.bouabdallah@enp-oran.dz received: 01-01-2020 accepted: 17-04-2020 abstract. today, the development of building materials based on toxic or non-toxic industrial waste is a topical issue for the productive structures in industrialized countries. in this article, non-toxic wood waste (wood chips) is used to improve the characteristics of ordinary concrete (lightness, thermal insulation, acoustic absorption, rigidity under stresses, etc.) for the purpose of eventually developing light wood concrete. the present experimental study aims at conducting a comparative behavioral analysis between concretes based on non-toxic wood waste of natural origin on the one hand, and ordinary concrete on the other. in order to achieve this goal, a series of test pieces were made, with five different formulations. four of them are lightweight wood-concretes obtained by the substitution of a volume of aggregates; the fifth formulation is ordinary concrete. a number of tests were carried out at the construction technical control laboratory at different ages, i.e. 7, 14, 21 and 28 days. interesting results were obtained with respect to the evolution of the mechanical characteristics of light wood-concrete at early age. some of these features, such as the long-term compressive strength of concrete, are essential parameters in civil engineering. key words: concrete/wood; mass loss; constraint/deformation; elastic modulus; ultrasound. 1. introduction a number of studies on lightweight wood-concrete have been reported in the literature. the works of bouabdallah et al. (2007, 2008), taazount et al. (2011), benmalek and bederina (2014), medjelekh et al. (2014), and akkaoui (2015) are worth mentioning. in addition, a large number of researchers have attempted to combine different materials with concrete to obtain a composite material with interesting features. among these materials, it is worth mentioning glass (zeghichi et al., 2005), waste concrete powder (wcp) (yi jiang et al., 2020); brick waste (hadjoudja and bederina, 2005), polypropylene fibers (breitenbucher, 1998; oredssen, 1997); polypropylene (mohammadhosseini et al., 2020; bouaziz, 2014); steel waste (kalpana and tayu, 2020) and many others. in the field of construction, the reduction in self-weight, provided by lightweight concrete, may where appropriate prove to be technically and economically attractive, both for the restoration of old structures as well as for the construction of new ones. there is great potential for the development of systems composed of various composite materials. the combination of concrete and wood fibers from wood industry waste makes it possible to obtain lightweight woodconcrete (lwc) with interesting characteristics. the work presented in this article is a good example for the development of a composite material that has the properties of wood and concrete together. for the purpose of studying the characteristics of light wood concrete with respect to durability, it was decided to make a series of lightweight wood concrete (lwc) specimens with four formulations, at different percentages 68 bouabdallah, j. build. mater. struct. (2020) 7: 67-75 2. experimental study 2.1 materials used portland cement type ii cem ii a 42.5 was used, with limestone gravel 0/3, 3/8 and 8/15 and siliceous sea sand 0/1; wood waste and water were subsequently added. table 1. cement identification cement class type of addition in cement clinker % density cp cpj 42,5 pouzzolanique (6 20 %) 80 94 % 3,1 table 2. characteristic of the materials used test gravel 8/15 mm gravel 3/8 mm crushed sand sea sand densities 2,735 2,727 2,714 2,642 absorption coefficients 1,52 1,75 2,65 2,11 los angeles 23,56 sand equivalent test esv 76,86 72 esp 70,53 67,69 0,01 0,1 1 10 100 0 20 40 60 80 100 p a s s in g [ % ] sieve size [mm] sea sand crushed sand gravel 3/8 mm gravel 8/15 mm fig 1. particle size curves. 2.2 method used volume substitution of class 0/3, 3/8 and 8/15 aggregates was achieved by adding wood waste particles, such as wood chips and sawdust generated from wood processing. the density values of wood and calcareous aggregates were determined by the hydrostatic weighing method. due to the dispersion of wood density results, it was decided to use two values for the density. table 3. density of materials mv concrete mv wood 1 mv wood 2 density [kg/m3] 2206 500 685 bouabdallah, j. build. mater. struct. (2020) 7: 67-75 69 the quantity of wood waste used in the formulation of concrete is calculated using the following expression: ∑ eq 01. mixing is an important phase in the manufacture of light wood concrete (lwc). since the water absorption by wood chips is very high, it was decided to use the pre-wetting method of the wood fibers to avoid water absorption during mixing. it should be noted that pre-wetting is a non-toxic and inexpensive method; it is very effective and allows reducing the loss of workability of light concrete. the mixing time of 100 seconds was considered as sufficient to obtain a homogeneous mixture of concrete. 2.3 formulation of concretes the replacement of aggregates (3/8, 8/15 and 15/25) with wood chips was done by volume, at various percentages. table 2 illustrates the composition of the different types of light wood concrete. table 4. composition of concretes under study constituents (kg/m3) ordinary concrete "oc" lightweight wood concrete "lwc" m1 m2 10 % 20 % 10 % 20 % gravel 8/15 mm 777 699.3 621.6 699.3 621.6 gravel 3/8 mm 415 373.5 332 373.5 332 crushed sand 372 334.8 297.6 334.8 297.6 ∑ gravel 8/15, 3/8 and crushed sand 1564 1407,6 1251,2 1407,6 1251,2 90 % 80 % 90 % 80 % 156,4 312,8 156,4 312,8 sea sand 372 372 372 372 372 untreated wood waste uww 35.5 70.9 48.6 97.1 cpj cement 353 353 353 353 353 total amount of water 172 172 172 172 172 slump test s2 s2 s1 s2 s1 figure 2 gives the visual appearance of different types of light wood concrete (lwc). a : lwc m1 10% b : lwc m1 20% c : lwc m2 10% d : lwc m2 20% fig 2. lightweight wood concrete. 70 bouabdallah, j. build. mater. struct. (2020) 7: 67-75 3. results and discussion 3.1 density of concrete during the preparation of concrete with light aggregates, a large amount of mixing water can be needed. it is important to recall that the amount of water absorbed depends on the interconnection of pores within the aggregates, on the level of initial saturation of the aggregates as well as on the water/cement (w/c) ratio of the cementitious matrix. in addition, the water absorbed by aggregates represents a reserve for the subsequent hydration of the cementitious matrix (bentur et al., 2001; bentz and snyder, 1999; kohno et al., 1999). figure 1 illustrates the density results of the concretes under study in the form of histograms. one may easily see that density increases when the amount of substituted granulates goes down. 7 14 21 28 0 500 1000 1500 2000 2500 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) d e n s it y ( k g /m 3 ) age (day) fig 3. density vs. age of concrete 3.2 mass loss of concrete at room temperature figure 4 illustrates the mass loss results of the concretes under study at room temperature. this loss of mass varies proportionally with the different substitution percentages. the results obtained indicate that the compositions produced have the characteristics of a lightweight wood-concrete (lwc) that has a density less than 2100 kg/m3. oc lwc 10% 1 lwc 20% 1 lwc 10% 2 lwc 20% 2 0 500 1000 1500 2000 2500 % (mv initial) % (mv at room temperature) d e n s it y ( k g /m 3 ) concrete fig 4. percentage loss in mass of samples, at 28 days. bouabdallah, j. build. mater. struct. (2020) 7: 67-75 71 3.3 variation of deformation as a function of applied stress the deformations of the specimen were measured as a function of the uniaxial compression. two 1/100 comparators were placed on the press plate to measure the uniaxial displacement, as is clearly shown in figure 5. the displacements were observed on each comparator. the average of the values given by the two comparators represents the uniaxial displacement of the specimen. the deformations of specimens 7x7x7 cm were calculated using the following expression: eq 02. ϵ: relative compressive deformation. l: displacement. l: length of the test piece 7 cm. 1 press plate. 2 concrete specimen 7x7x7 3 comparator 1/100. fig 5. apparatus used to measure the longitudinal deformations of the specimens subjected to uniaxial compression. figures 6, 7, 8 and 9 show the evolution of stress as a function of deformation. specimens of dimensions (7x7x7) cm3 were made for five different types of concrete and were subjected to simple compression, at various ages, i.e. 7 days, 14 days, 21 days and 28 days. it has been found that the resistance of ordinary concrete is much higher than that of light wood concretes (lwcs) for different percentages of substitution (10% and 20%) and different densities (m1 and m2). it also turned out that deformation of ordinary concrete decreased steadily with age; however, different results were found for light wood concrete. the compressive strength of lwc (m210%) turned out to be higher than that of (m1-10%), which in turn is higher than that of lwc (m2-20%). therefore, lwc (m2-20%) proves to be the least resistant. the results obtained show that in general, though lightweight wood concrete (lwc) presents lower resistance than that of ordinary concrete (oc), it has a better compressive strength than that of many other lightweight concretes. 0,000 0,004 0,008 0,012 0,016 0,020 0 5 10 15 20 25 30 35 40 45 50 55 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) c o m p re s s iv e s tr e n g th ( m p a ) deformation 0,000 0,004 0,008 0,012 0,016 0,020 0 5 10 15 20 25 30 35 40 45 50 55 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) c o m p re s s iv e s tr e n g th ( m p a ) deformation fig 6. evolution of the compressive strength as a function of deformation, at 7days. fig 7. evolution of the compressive strength as a function of deformation, at 14 days. 1 2 3 72 bouabdallah, j. build. mater. struct. (2020) 7: 67-75 0,000 0,004 0,008 0,012 0,016 0,020 0 5 10 15 20 25 30 35 40 45 50 55 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) c o m p re s s iv e s tr e n g th ( m p a ) deformation 0,000 0,004 0,008 0,012 0,016 0,020 0 5 10 15 20 25 30 35 40 45 50 55 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) c o m p re s s iv e s tr e n g th ( m p a ) deformation fig 8. evolution of the compressive strength as a function of deformation, at 21 days. fig 9. evolution of the compressive strength as a function of deformation, at 28 days. 3.4 elastic modulus in the present study, the modulus of elasticity was calculated using the classical method, which consists in determining the slope of the stress/strain curve in the elastic domain. eq 03. it was found that the slope of the stress/strain curves increased for ordinary concrete, which implies a progressive increase in the elastic modulus as a function of age. on the other hand, it was noticed that the shape of the curve representing the variation of the elastic modulus of lwc (m1-10%) is similar to that of lwc (m2-10%); the same observation is made when comparing lwc (m1-20%) with lwc (m2-20%). on the other hand, it turned out that the modulus of elasticity decreases as the percentage of substitution of aggregates rose. this was certainly due to the fact that the presence of wood waste particles has a significant impact on the mechanical characteristics of lightweight wood concrete. 7 14 21 28 0 2000 4000 6000 8000 10000 12000 14000 % (oc) % (lwc m1 10%) % (lwc m1 20%) % (lwc m2 10%) % (lwc m2 20%) m o d u lu s o f e la s ti c it y ( m p a ) age (day) fig 10. evolution of the modulus of elasticity as a function of age bouabdallah, j. build. mater. struct. (2020) 7: 67-75 73 3.5 propagation speed figure 11 depicts the speed of waves propagating through different types of concrete. one may clearly note that the speed of propagation of pulses in ordinary concrete is much higher than that observed in light wood concretes, for different percentages of substitution (10% and 20%) and for different densities (m1 and m2). the pulse propagation speed in lwc (m2-10%) is higher than that observed in lwc (m1-10%) in which that rate is higher than that in lwc (m220%). the propagation velocity in lwc (m2-20%) remains the lowest. in general, it may be concluded that wood waste has contributed to reducing the speed of propagation of the pulses emitted by the sonic auscultation device; which confirms the improved properties of concretes. in addition, wood waste helped to improve the insulating properties of concrete. indeed, the cellular structure of wood waste caused trapping of air in small volumes which represent a poor heat conductor; this is another advantage offered by lightweight wood concrete in thermal insulation. oc lwc 10% 1 lwc 20% 1 lwc 10% 2 lwc 20% 2 0 1000 2000 3000 4000 v (m /s ) concrete fig. 11. pulse propagation speed in concrete, at 28 days. 4. conclusion this experimental study made it possible to highlight the influence of wood waste from industry on the mechanical properties of ordinary concrete. volumes of gravel of classes 8/15, 3/8 and 0/3 were replaced by wood waste at two percentages (10% and 20%) to obtain light wood concrete (lwc). the main conclusions of this study are summarized in the following points: light wood concrete (lwc) has a very good compressive strength in comparison with other types of light concrete but is less resistant to compression as compared to other concretes. however, its properties give it a great advantage to be developed and used in the construction field. from an environmental point of view, this would help to get rid of wood waste. in addition, the stress/strain curves made it possible to follow and control the behavior of concretes in the elastic and post-elastic regions, where it was found that the elastic phase ends between 80 and 90% of the resistance to compression, whatever the type of concrete used. furthermore, the modulus of elasticity was calculated using the stress/strain curve in the elastic region. the curve representing the evolution of the elastic modulus of 74 bouabdallah, j. build. mater. struct. (2020) 7: 67-75 light wood concretes shows an irregularity that is mainly due to the heterogeneity of wood waste. wood waste has increased the insulating properties of concrete, which in turn reduced the speed of propagation of pulses. this behavior is attributed to the cellular structure of wood waste that traps air in the form of small volumes. the behavior of light wood concrete (lwc) in the fresh state can be mastered only in precast concrete plant to control its strength and vibration time. our main prospect is to improve the behavior of light weight concrete (lwc) in the fresh state by using appropriate superplasticizers to obtain class s3 or s4 concretes according to the recommended specifications and in order to respect the international standards. a concrete screed may be taken as an example in this case. 5. references akkaoui, a. (2014). bétons de granulats de bois: étude expérimentale et théorique des propriétés thermohydro-mécaniques par des approches multi-échelles. doctoral dissertation, école doctorale science ingénierie et environnement, université paris-est, france. benmalek, l., & bederina, m. (2014). les performances mécaniques et thermiques d’un béton léger à base de déchets industriels solides et de granulats de bois. in matec web of conferences (vol. 11, p. 01040). edp sciences. bentur, a., igarashi, s. i., & kovler, k. (2001). prevention of autogenous shrinkage in high-strength concrete by internal curing using wet lightweight aggregates. cement and concrete research, 31(11), 1587-1591. bentz, d. p., & snyder, k. a. (1999). protected paste volume in concrete: extension to internal curing using saturated lightweight fine aggregate. cement and concrete research, 29(11), 1863-1867. bouabdallah, m.a., (2008). valorisation des déchets de bois. 1er colloque euromaghrébin sur les bois méditerranéens caractérisation et valorisation technologique des bois résineux méditerranéens ; université m’hamed bougara de boumerdès, 30 mars au 2 avril, algeria. bouabdallah, m.a., et al. (2007). comportement du béton léger à base de granulats et des fibres de bois ; séminaire national de « génie civil », université badji mokhtar annaba faculté des sciences de l’ingénieur, département de génie civil & laboratoire de génie civil, 20 & 21 novembre, algeria. bouabdallah, m.a., et al. (2007). etude comparative des bétons légers à base des granulats et des déchets de bois non traites et un béton ordinaire ; séminaire national sur « la gestion intégrée des déchets » organisé par l’ecole normale supérieure d’enseignement technique, e.n.s.e.t. d’oran, 29 & 30 mai, algeria. bouaziz., s., & ait tahar., k. (2014). elaboration et caractérisation d’un béton composite à granulats composites., 82ème congrès de l’acfas., université concordia quebec du 12 au 16 mai. breitenbiicher, r. (1998). developments and applications of high performance concrete. materials and structures, 31, 209-215. hadjoudja, m., & bederina, m. (2005). influence des fillers des déchets de briques sur la durabilité à l’eau du béton de sable de dunes, laboratoire de génie civil, institut de génie civil, université de laghouat, colloque cmedimat 2005, algeria. jiang, y., ling, t. c., & shi, m. (2020). strength enhancement of artificial aggregate prepared with waste concrete powder and its impact on concrete properties. journal of cleaner production, 257, 120515. kalpana, m., & tayu, a. (2020). experimental investigation on lightweight concrete added with industrial waste (steel waste). materials today: proceedings, 22, 887-889. kohno, k., okamoto, t., isikawa, y., sibata, t., & mori, h. (1999). effects of artificial lightweight aggregate on autogenous shrinkage of concrete. cement and concrete research, 29(4), 611-614. bouabdallah, j. build. mater. struct. (2020) 7: 67-75 75 medjelekh, d., ulmet, l., & dubois, f. (2014). mesure et modélisation des transferts hygrothermiques d’une enveloppe en béton de bois'. conférence ibpsa, arras, france. mohammadhosseini, h., alyousef, r., lim, n. h. a. s., tahir, m. m., alabduljabbar, h., & mohamed, a. m. (2020). creep and drying shrinkage performance of concrete composite comprising waste polypropylene carpet fibres and palm oil fuel ash. journal of building engineering, 30, 101250. oredsson, j. (1997). tendency to spalling of high strength concrete. interim report m, 7(4), skanska, np 30. taazount, m., amziane, s., moutou-pitti, r., & molard, d. (2011). elément de planchers composites boisbéton léger ; 20ème congrès français de mécanique. afm, maison de la mécanique, 39/41 rue louis blanc, 92400 courbevoie, france. zeghichi, l., merzougui, a., & chabi, s., (2005). l’influence des déchets de verre sur les propriétés du béton, colloque cmedimat 2005, université de m’sila, algeria. j. build. mater. struct. (2020) 7: 32-41 original article doi : 10.34118/jbms.v7i1.76 issn 2353-0057, eissn : 2600-6936 valorization of calcined kaolinitic clay used in high performance mortar mansour s m*, ghernouti y, chaid r university of m’hamed bougara, dept. civil engineering, ur/mpe lab., avenue de l’indépendance, 35000, boumerdes, algeria * corresponding author: s.mansour@univ-boumerdes.dz received: 18-11-2019 accepted: 04-02-2020 abstract: in this work, an experimental investigation was carried out to evaluate the potential of an industrial pozzolan, the metakaolin, on the behavior of mortar. the aim is to use metakaolin as a 10% partial replacement of cement. its effect on the physico-mechanical properties of the mortar has been analyzed. the results show that the incorporation of metakaolin decreases the density of the dried mortar and increases that of the wet mortar but these remain lower than those of the control mortar. moreover, thermal analysis atd / atg shows that in the heat flow curve appears two endothermic peaks which correspond to the loss of mass of the cement pastes. heat flux of these pastes increases when metakaolin is used into the cement. in addition, metakaolin increases the compressive and flexural strengths of wet and dry mortars by approaching without exceeding those of the control mortar. the use of metakaolin as a cement substitution has shown its potential to be a pozzolanic material that can offer economic, environmental and technical benefits. key words: mortar; metakaolin; valorization; mechanical strengths. 1. introduction the construction sector is particularly emitter of greenhouse gases in particular co2 released during the manufacture of portland cement. to limit these discharges, with equivalent concrete performance, it is possible to replace a portion of the cement by certain additions such as pozzolans. the metakaolin produced from kaolin clays is one of these calcined pozzolans. metakaolin is a product known for several years and manufactured all over the world: france, canada, united states, united kingdom, brazil, china, etc. it results from the calcination of clay, kaolinite, at temperatures between 600 ° c and 850 ° c, according to the degree of order of the initial material (badogiannis et al., 2005). it typically contains 50-55% silica sio2 and 40-45% alumina al2o3 and is highly reactive (kostuch et al., 2000). calcination leads to a dehydroxylation reaction of the material, with a destruction of the initial crystalline structure leading to an amorphous nature of the material, which gives it a high pozzolanic power (poon e al., 2001). as a result, it is used to replace or add portland cement to improve the performance of hardened concrete (sabir et al., 2001; tafraoui et al., 2009). indeed, the incorporation of metakaolin into cements allows better hydration of anhydrous cement. it causes the appearance of a closed porosity favorable to the strength and durability of the cementitious matrices due to the formation of a larger amount of c-s-h and the lack of connection of the pores. as such, the metakaolin used as partial substitution for portland cement improves the mechanical performance of concretes and mortars (mansour et al., 2012; mansour et al., 2013; madandoust and mousavi, 2012). increasingly, a sustained interest is devoted to the use of cementitious materials, especially those which are rich in sio2 and al2o3, in the manufacture of hydraulic cements. metakaolin is mansour et al., j. build. mater. struct. (2020) 7: 32-41 33 therefore a substitute for cement to increase its demand in the coming years, thanks to its high silica and alumina content, its advantageous technical properties, its low environmental impact and the fact that it is not an industrial byproduct. indeed, it is not dependent on the technical and economic hazards of the manufacture of steel (slags) and silicon (silica fume), or the production of electricity (fly ash). the present work invests the effect of an active pozzolan, the metakaolin used as a cement substitution on the physico-mechanical properties of the mortar. a comparative experimental study was established between a control mortar without metakaolin and a mortar incorporating a 10% substitution rate of metakaolin. 2. experimental program 2.1. materials the cem i 52.5r cement of lafarge in accordance with the nf en 197-1 standard is preferably used because it contains a large amount of clinker (at least 95% by weight), has a high reactivity at an early age, and guarantees a 28-day minimum compressive strength of 52.5 mpa on standardized mortars. its specific surface area is 4200 cm2/g and its density is 3.15 g/cm3. siliceous sand according to the standard (en 196-1) of 0/4 mm size with a specific density and water absorption of 2.6 and 1.2% respectively is used. as an addition, the metakaolin having a 137.5 mg ca (oh)2/g mineral activity according to nf p18-513 standard, a density of 2.54 g/cm3 was chosen to replace a part of the cement for an economic and ecological purpose. metakaolin was obtained by calcination at 700 ° c for 5h of crushed and sieved kaolin at 80 μm from the region of algeria-tamazert (milia-jijel). generally, an optimum for kaolin clay calcinations recognized in literature is between 600°c and 900°c (ambroise et al. 1986; sayanam et al. 1989). after removal from the oven, the cooling of obtained product “metakaolin” was accomplished by placing it in a desiccator. the calcined product was then packaged in waterproof plastic bags. metakaolin is characterized by a specific surface area of 7550 cm2/g greater than that of the cement in order to increase the compactness of the mortar and its strength (merabet and belkacemi, 2003). the chemical compositions of metakaolin and cement are given in table 1. table 1. chemical composition of cement and metakaolin. oxides (%) cement metakaolin cao 63.60 1.33 sio2 19.85 58.32 al2o3 4.80 35.36 fe2o3 2.75 1.18 mgo 1.45 0.21 so3 3.45 0 .31 k2o 0.9 1.13 na20 0.15 0.15 loi 2.20 2.01 the x-ray diffraction mineralogical analysis and the scanning electron microscope sem analysis show the mineral phases and the morphology of the metakaolin in figure 1 and figure 2 respectively. the x-ray diffraction mineralogical analysis was carried out with the philips pw 3710 diffractometer. it has a cu anticathode with a ni filter, so the wave length is λ = 1.54å. the step recording is carried out between 5 and 65 ° 2θ. concerning the morphology of metakaolin, tests were carried out with an sem field effect electron microscope (jeol-jsm-6301f) from the insa 34 mansour et al., j. build. mater. struct. (2020) 7: 32-41 of rennes on metakaolin powder previously covered with a thin layer of gold by vacuum metallization to obtain images in secondary electrons. fig. 1. mineral phases of metakaolin by drx. fig. 2. morphology of metakaolin by sem (x10000). 2.2. preparation of samples analyzed by atg / dsc cement pastes (with or without metakaolin) are prepared and maintained in endogenous conditions in heat-sealed bags and then placed in a humid room at a temperature of 20 ° c and 95% humidity, and are kept for 24 hours and 3 days. after a suitable period of hydration, the samples are taken out of their bags and dried in an oven for 12 hours at 80 ° c. until the day of the test, where they are finely ground and tested with the thermogravimetric analysis apparatus. the rate of rise in temperature is 5 ° c / min. thermogravimetric analysis was performed to evaluate the pozzolanic activity of metakaolin through the consumption of lime from prepared cement pastes. lime consumption is evaluated by atg/dsc at 1day and 3 days. analysis thermogravimetric atg/dsc is based on mansour et al., j. build. mater. struct. (2020) 7: 32-41 35 measurement, as a function of time and temperature, of mass variations of a sample subjected to an increase of temperature. the identification of hydrates is deduced by the decomposition temperature ranges being characteristic of solid phases studied (for example portlandite ca(oh)2 and calcium silicate hydrated csh). the rate of lime consumed is deducted from the mass of residual portlandite shown by the mass loss recorded on the atg/dsc diagram. 2.3. preparation of standardized mortars standardized mortars were prepared in accordance with the standard nfp 15-403 (nf p 1996) with a constant water/binder ratio = 0.5 and a sand-cement ratio s/c = 3. the normal mortar described is made to using a hobart mixer, in a five-liter tank meeting the specifications of the nfp 15-411 standard (nf p 1996). a fixed rate of 10% metakaolin mk is chosen as substitution to replace part of cement. after curing and demolding after 24 hours, the 4x4x16 cm3 mortar specimens are stored in a dry room at 20° c and at 50% relative moisture. in addition, other mortar specimens are kept in water at 20°c for measurements of mechanical compressive and flexural strengths nf p15-471-1 (en 196-1) at 1, 3 , 7, 14, 21 and 28 days of age. 3. results and discussion 3.1. xrd and sem analysis scanning electron microscope sem analysis shows that the metakaolin is made up of particles in the form of lamellae and platelets. the observed shape of the particles facilitates the flow and prevents blockage of concrete. from the x-ray diffraction mineralogical analysis of metakaolin, the x-ray analysis of perlite shows a bump which signifies a high content of amorphous silica and peaks which characterizes the crystalline phase such as quartz (sio2) and small amount of illite (k2o, 2h2o, 2(al2(si3al)o10oh). 3.2. chemical analysis the chemical analysis of metakaolin shows that it contains high rate of 58.32% sio2 of silica and 35.36% al2o3 of alumina compared to those of cement which are of the order of 19.85% and 4.80%. this favors the pozzolanic reaction. the contribution of the additions to the development of the strength is mainly due to the filler effect, the dilution effect and the pozzolanic reaction with the portlandite ca(oh)2 released during the hydration of the cement according to the reaction given by equation eq.1: sio2, al2o3 (metakaolin) + ca (oh)2 + water (c-s-h), (c4 ah13), (c2ash8) (1) (c-s-h): hydrated calcium silicates, (c4 ah13): hydrated calcium aluminates, (c2ash8): calcium silicate aluminates hydrated. the products obtained are beneficial because they contribute to the development of mechanical strengths of the elaborated mortars. 3.3. exploitation of tga/dsc thermal analysis results the analysis of thermogravimetric atg curves depends on the relationship between temperature increase and mass variation as a result of dehydration, decomposition and oxidation. these curves can be divided into different important areas. zone (i), between 100 and 300 ° c, is attributed to the dehydration of c-s-h and ettringite. zone (ii), between 290 and 350 ° c, characterizes the decomposition of hydrated calcium silicate, hydrated calcium aluminate and chloroaluminate calcium. the third zone (iii), ranging from 450 to 510 ° c, is attributed to the 36 mansour et al., j. build. mater. struct. (2020) 7: 32-41 dehydration of calcium hydroxide. the same curves show the relationship between the weight of the sample relative to the original weight of the sample and the applied temperature. (a) (b) fig. 3. atd thermogram of cement paste (a) control, (b) containing 10% mk after 24h of hydration. the evolutions of the profiles of the tg and thermal flux curves dsc of the pastes of cement mixtures with or without metakaolin are shown in figure 3 and 4. evolution of each of the curves is related to the initial mass of the studied sample. each heat flux curve (dsc curve) has mansour et al., j. build. mater. struct. (2020) 7: 32-41 37 several endothermic peaks corresponding to mass losses (tg curve) for cement paste 24h or 3 days of hydration. it is clearly shown the existence of two marked endothermic peaks accompanied by mass losses and which spread over time from 1 day to 3 days in presence of metakaolin. this is a sign of reactivity of metakaolin. (a) (b) fig. 4. atd thermogram of cement paste (a) control, (b) containing 10% mk after 3 days of hydration. 38 mansour et al., j. build. mater. struct. (2020) 7: 32-41 the first peak centered on a temperature between 100 ° c and 200 ° c showing a loss of mass which corresponds to the dehydration of hydrated calcium silicates csh indicating the presence of csh hydrates (rojas and cabrera, 2002). the second endothermic peak centered at a temperature between 430 ° c and 500 ° c also showing a loss of mass which corresponds to the dehydration of calcium hydroxide ca (oh)2. between the two peaks, there is a portion between the temperature 250 ° c and 430 ° c showing a loss of mass corresponding to the decomposition of hydrated calcium silicates hcs, hydrated calcium aluminates ach and chloroaluminates. at the time of 1 day and 3 days, we observe the same peaks, but they are more extensive in the presence of metakaolin. this is due to the progress of the pozzolanic reaction. normally, these peaks will spread over time for paste containing metakaolin until they become flat, a sign of ca (oh)2 consumption and increased csh. this clearly shows the reactive effect of metakaolin at a very young age. 3.4. density of dried and wet mortars the evolution of the density of mortar specimens kept in a dry room is illustrated in figure 5a. the density decreases with time for all mortars. that of dried mortars containing metakaolin is smaller than that of control mortars at different ages. the loss of mass obtained due to the departure of water by drying is of the order of 3%. figure 5b shows the evolution of the density of wet mortar specimens kept in water according to their age. the density increases with time for all mortars. it is shown that the mortars kept in the water gain weight compared to the dried mortars, sign that the water tends to occupy the voids of the cement paste: those caused by the air occluded at the setting up and the voids produced by the contraction due to the hydration of the cement. moreover, the density of the mortars containing the metakaolin is reduced compared to that of the control mortars at all the ages. the reduction is around 2%. the loss of mass of dried or wet mortars stored in water is due to the fact that the density of metakaolin substituted to cement is smaller than that of cement. (a) (b) fig. 5. evolution of the density of (a) dried mortars, (b) wet mortars. 3.5. compressive strength of dried and wet mortars the development of mechanical strengths of wet mortars with and without metakaolin tested on specimens after a water cure at 1, 3, 7, 14, 21 and 28 days is shown in figure 6a. the compressive strengths of the mortars increase rapidly to 14 days of age when they reach their maximum values (91.062 mpa for the control mortar mr, 83.625 mpa for the mortar with mansour et al., j. build. mater. struct. (2020) 7: 32-41 39 the metakaolin mmk). at 21 days, a decrease of strength is marked but the latter increase again to 28 days. moreover, the incorporation of the metakaolin mk causes a decrease of the mortars strength compared to those of the control mortars and this, at all ages. the reduction is 3%, 14.5%, 8.4%, 8%, 10% at 1d, 3d, 7d, 14d, 21d, respectively. but at 28 days, compressive strengths of mortars with or without metakaolin are almost aligned, since the reduction is 5%. the rate of development of the strength of the control mortar depends mainly on the rate of hydration of the clinker whereas it depends on the combination of the hydration of the cement and the pozzolanic reaction (pavlíková et al., 2009; ambroise et al., 1994; siddique and klaus, 2009) for a mortar of cement containing the metakaolin. here, the effect of these is well shown. similarly, in figure 6b, it is shown that for the dried mortar specimens, their compressive strengths develop increasing but do not exceed those of the control mortars regardless of the age of the specimens. the reduction is 13%, 25%, 19%, 9%, 14%, and 9% at 1d, 3d, 7d, 14d, 21d, and 28 days respectively. the lowest reduction (9%) is achieved at 28 days. in addition, it should be noted that the compression strengths of mortars tested after a water cure at different ages are higher than those of dried mortars. so the water cure promotes the rapid increase of compressive strengths. the reduction of compressive strengths is due to the fact that the main minerals of the cement which contribute to increase the strengths c3s and c2s decreased since the quantity of cement replaced metakaolin decreased. in addition, the obtained metakaolin may react slowly before 28 days, but its positive effect on mechanical strengths may be shown in the long term. (a) (b) fig. 6. compressive strength of (a) dried mortars, (b) – wet mortars. 3.6 flexural strength of dried and wet mortars the evolution of flexural strengths of dried and wet mortars preserved in water is shown in figures 7a and 7b. the flexural strengths of the mortars containing the metakaolin are very interesting in the sense that they develop increasing without exceeding those of the control mortar but at 28 days, they get closer. the reduction is 17%, 13%, 17%, 10%, 12% and 9% for wet mortars and 20%, 13%, 17%, 6%, 8% and 5% for dried mortars at maturity 1d, 3d, 7d, 14d, 21d and 28 days respectively. the 40 mansour et al., j. build. mater. struct. (2020) 7: 32-41 lowest reduction is obtained at 28 days. in addition, the flexural strengths of dried mortars are lower than those of mortars kept in water. (a) (b) fig. 7. flexural strength of (a) dried mortars, (b) wet mortars 4. conclusions based on the investigation of elaborate mortar mixtures incorporating 10% rate of metakaolin, the following conclusions are drawn:  the high levels of 58.32% silica sio2 and 35.36% alumina al2o3 contained in the metakaolin favored the pozzolanic reaction and contributed to the development of the mechanical strengths of the mortar particularly at 28 days.  the substitution of cement by 10% of metakaolin has a beneficial effect on the cement matrix because it contributes to the densification of the hardened paste by the consumption of portlandite and the formation of the gel of csh silicates and hydrated calcium aluminates cah.  the incorporation of metakaolin as a substitute to cement has led to a slight decrease in compressive and flexural strengths of mortars, especially at 28 days, whatever the state of conservation : in the dry state or after a water cure.  the reduction of compressive strength rc is 5% and 9% for mortars containing metakaolin preserved in water and dried respectively.  the rf flexural strengths of mortars containing metakaolin are very interesting. at 28 days, rf aligns with that of the control mortar.  the smallest relative difference of rf is 9% for wet mortars and 5% for mortars dried at 28 days of age.  the compressive and flexural strengths of mortars tested after a water cure at different ages are higher than those of dried mortars.  the introduction of 10% metakaolin decreases the density of dried mortars and increases the density of wet mortars. this is due to the high water absorption of metakaolin. the density is always lower than that of the control mortar. the reduction is low, around 2%. moreover, the mechanical strengths are sufficient to classify the elaborated mortars incorporating 10% of metakaolin as high performance mortars. mansour et al., j. build. mater. struct. (2020) 7: 32-41 41 from an environmental point of view, the use of metakaolin as a cement substitution is potential because it allows the reduction of the direct release of gases by the greenhouse effect since there is a decrease in the quantity of cement manufactured. from an economic point of view, the metakaolin is beneficial since it can replace a quantity of cement with a high manufacturing cost. finally, this experimental work paves the way for the use of calcined kaolin from the jijel region as a pozzolanic material in the cement industry to improve the physico-mechanical properties and durability of cementitious materials. 5. references ambroise, j., maximilien, s., & pera, j. (1994). properties of metakaolin blended cements. advanced cement based materials, 1(4), 161-168. ambroise, j., murat, m., & pera, j. (1986). investigations on synthetic binders obtained by middletemperature thermal dissication of clay minerals. silicates industries,7(8), 99–107. badogiannis, e., kakali, g., dimopoulou, g., chaniotakis, e., & tsivilis, s. (2005). metakaolin as a main cement constituent. exploitation of poor greek kaolins. cement and concrete composites, 27(2), 197-203. kostuch, j. a., gw, w., & tr, j. (2000). high performance concretes containing metakaolin. a rview concr, 21, 799-811. madandoust, r., & mousavi, s. y. (2012). fresh and hardened properties of self-compacting concrete containing metakaolin. construction and building materials, 35, 752-760. mansour, m. s., abadlia, m. t., afalfiz, a., & ladaoui, w. (2013). reologia zapraw i betonów z dodatkami mineralnymi. cement wapno beton, 18(80, nr 5), 264-270. mansour, m. s., abaldia, m.t., jauberthie, r., & messaoudenne, i. (2012). metakaolin as a pozzolan for high performance mortat.. cement. wapno. beton. 2 : 102-108. merabet, d., & belkacemi, h. (2003, september). caractérisation minéralogique et chimique du kaolin de tamazert (algérie). in annales de chimie science des matériau, 28(5), 61-83. pavlíková, m., brtník, t., keppert, m., & černý, r. (2009). effect of metakaolin as partial portland-cement replacement on properties of high performance mortars. cement wapno beton, 3, 115-122. poon, c. s., lam, l., kou, s. c., wong, y. l., & wong, r. (2001). rate of pozzolanic reaction of metakaolin in high-performance cement pastes. cement and concrete research, 31(9), 1301-1306. rojas, m. f., & cabrera, j. (2002). the effect of temperature on the hydration rate and stability of the hydration phases of metakaolin–lime–water systems. cement and concrete research, 32(1), 133138. sabir, b. b., wild, s., & bai, j. (2001). metakaolin and calcined clays as pozzolans for concrete: a review. cement and concrete composites, 23(6), 441-454. sayanam, r. a., kalsotra, a. k., mehta, s. k., sing, r. s., & mandal, g. (1989). studies on thermal transformations and pozzolanic activities of clay from jammu region (india). journal of thermal analysis,35, 9–106. siddique, r., & klaus, j. (2009). influence of metakaolin on the properties of mortar and concrete: a review. applied clay science, 43(3-4), 392-400. tafraoui, a., escadeillas, g., lebaili, s., & vidal, t. (2009). metakaolin in the formulation of uhpc. construction and building materials, 23(2), 669-674. j. build. mater. struct. (2020) 7: 178-187 original article doi : 10.34118/jbms.v7i2.768 issn 2353-0057, eissn : 2600-6936 influence of segregation on the performance of self-compacting concrete in the fresh and hardened states mohammed krachaï r 1,2, bouabdallah m a 3,4,* 1 l.s.t.e laboratory; department of civil engineering, mustapha stambouli university of mascara, algeria. 2 laboratoire de génie civil et environnement, lgce, sidi bel abbes, algeria. 3,* department of civil engineering, laboratory labmat, national polytechnic school of oran, algeria. 4 lctc, laboratoire de contrôle technique de la construction, oran, algeria. * corresponding author: m-a.bouabdallah@enp-oran.dz & rm.kirachai@univ-mascara.dz received: 12-08-2020 accepted: 18-09-2020 abstract. the granular mixture represents one of most important parameters in the formulation of self-compacting concretes in order to achieve a representative granular distribution. a good resistance to segregation results in a regular distribution of the different sizes of the aggregates in all parts of the element, with the same granule density. the granular mixture must be homogeneous and representative, and has to be able to flow in the absence of dynamic and static segregation. the main objective of the present research is to study the influence of segregation on the performance of self-compacting concrete in the fresh and hardened state, by determining the static segregation index according to the percentage of aggregates of class g 8/15 and that of aggregates of class g 3/8 in order to obtain a homogeneous granular mixture, whatever the volume of self-compacting concrete to be prepared. it is well acknowledged that the threshold of the discontinuation of granular mixing represents a new element with respect to segregation in concrete. the obtained results showed that the percentage of large aggregates has a significant influence on the segregation index and the performance of selfcompacting concrete (scc) at 28 days. key words: self-compacting concrete, segregation index, granular mixture, fresh state test, hardened state test. 1. introduction self-compacting concretes are hyper-fluid concretes that can be placed, without vibration, under the effect of their own weight and because of their flow characteristics. these concretes must have a high fluidity and be able to flow with a sufficient flow rate, without external energy supply, through confined areas even in the presence of obstacles; they can also be placed in tall formworks. concretes must oppose dynamic segregation in the pouring phase, and static segregation, once in place, in order to guarantee the homogeneity of the characteristics and to avoid bleeding or compaction. good resistance to segregation results in a regular distribution of coarse aggregates in all parts of the element and at all levels. therefore, concrete must not undergo any form of horizontal and vertical segregation. the formulation of self-compacting concrete is based on three criteria, i.e. fluidification of concrete paste, limitation of friction between the aggregates in order to promote the flow and stabilization of the mixture, and prevention of segregation in concrete. among the publications and methods presented by some authors on scc segregation, one may cite the procedure of sidky et al. (1981), the japanese cylinder method by umehara et al. (1994), the column test developed by otsuki et al. (1996), the japanese metal pallet method by tangtermsirikul et al. (1991), the column test through the measurement of the electrical resistivity of fresh concrete developed by yim (2020), the sieve method of fujiwara (1992), the method proposed by bui et al. (2002), and the ball penetration test developed by trudel (1995). mailto:m-a.bouabdallah@enp-oran.dz mailto:rm.kirachai@univ-mascara.dz mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 179 similarly, shen et al. (2014) established a new method for measuring the static segregation which is based on the two standards: astm c1712-09 (2009) and c1610 / c1610 m-10 (2010). moreover, bensebti (2015) used a very simple test that allows for the direct assessment of static segregation in self-compacting concretes (sccs). the results obtained by this author indicated that it is possible to obtain a good scc, it would be necessary to have a lower static segregation coefficient that is less than or equal to 5. the objective of the present article is to study the behavior of segregated self-compacting concretes with the objective of obtaining a homogeneous and representative granular mixture in the fresh and hardened state. 2. experimental study 2.1. used materials portland cement type cem ii a 42.5 was used, with limestone gravel 0/3, 3/8 and 8/15 mm and siliceous sea sand 0/1 mm; wood waste and water were subsequently added. table 1. characteristics of the used cement identification cement class type of addition in cement clinker % density cem ii cemii/42.5 a pouzzolanique (6 20 %) 80 94 % 3,1 table 2. characteristic of the materials used test gravel 8/15 mm gravel 3/8 mm crushed sand sea sand densities [g/cm3] 2,735 2,727 2,714 2,642 absorption coefficients 1,52 1,75 2,65 2,11 los angeles 23,56 sand equivalent test [%] esv 76,86 72 esp 70,53 67,69 fig 1. particle size of the used aggregates. 2.2. formulation of concretes table 3 illustrates the composition of the different types of self-compacting concrete (scc). 180 mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 table 3. concrete compositions of different types of self-compacting concrete (scc). constituents (kg/m3) b01 b02 b03 b04 b05 b06 b07 b08 b09 b10 b11 gravel 8/15 mm 0 81,5 163 244,5 326 407,5 489 570,5 652 733,5 815 0 % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% gravel 3/8 mm 815 733,5 652 570,5 489 407,5 326 244,5 163 81,5 0 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% crushed sand 244 244 244 244 244 244 244 244 244 244 244 sea sand 562 562 562 562 562 562 562 562 562 562 562 cement 400 400 400 400 400 400 400 400 400 400 400 sp (% cement) 10 10 10 10 10 10 10 10 10 10 10 water 206 206 206 206 206 206 206 206 206 206 206 2.3. tests methods for measuring scc characteristics and properties a number of tests were conducted in accordance with the recommendations of the french association for civil engineering (afgc, 2008). slump flow concrete test (fig 2), nf en 12350-8 (2019). l-box test (fig 3), nf en 12350-10 (2010). sieve segregation test (fig 4), nf en 12350-11 (2010). column test (fig 5) (astm c1610). (2010) fig 2. slump flow concrete test fig 3. l-box test fig 4. sieve segregation test the column test for the measurement of ssi is illustrated in figure 5. the advantage of this column test lies in the fact that the operation of separation of the different concrete layers takes place after complete stabilization of the granular system. this column test offers a great advantage to the operator in preventing the concrete to flow. in this case, errors due to loss of the material during the separation and weighing procedures are therefore relatively small. mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 181 fig 5. column test (astm c1610). 2.4. description of the column test and methodology used the different stages of this proposed test are presented in the following and are illustrated in figure 6. the mold used is a cylinder with a diameter d = 110 mm and height h = 400 mm. first, the concrete was poured into the mold in a single operation to a height of 20 cm. once the mold was filled, it was leveled off using a metal ruler. the waiting time was close to the concrete setting time. the mold was then separated into three more or less equal parts (upper part, middle part and lower part). after weighing, washing and drying of each part, the ratio of the mass of dry aggregates (> 5mm) to the total mass was determined. the aggregate contents of each part (upper g, middle g and lower g) were then calculated using the ratio of the mass of dry aggregates to the total mass of the part under consideration. fig 6. column test with the different steps to measure (ssi). it is worth knowing that the static segregation index is defined as follows: ( ) (01) 182 mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 3. results and discussion 3.1. analysis of fresh state behavior of self-compacting concrete figure 7 shows the influence of the percentages of gravels 3/8 and 8/15 on the segregation index. it should be noted that increasing the amount of gravel g 8/15 and decreasing that of g 3/8 increases the risk of static segregation. 1 2 3 4 5 6 7 8 0 20 40 60 80 100 g 8/15 g 3/8 iss < 5 % p e rc e n ta g e g 8 /1 5 & g 3 /8 [ % ] indice of segregation iss [%] fig 7. percentages of g 8/15 and g 3/8 as a function of the static segregation index. figure 8 shows the evolution of ssi as a function of concrete spread, for all the formulations from b1 to b11. the behavior of the concretes tested (from b2 to b8) varied with (ssi (%) < 5) which ensures that these concretes have a sufficient spread so they can be classified as selfcompacting concretes, according to the french standard nf 206. on the other hand, the granular mixtures b6, b7 and b8 exhibited a spread greater than 60 cm, with no segregation phenomenon. 1 2 3 4 5 6 7 8 30 40 50 60 70 e ta le m e n t f [ c m ] indice of segregation iss [%] f = f (iss) iss < 5 % f6 > 63 cm f5 > 56 cm f4 > 49 cm f3 > 42 cm f2 > 35 cm fig 8. evolution of the concrete spread as a function of the static segregation index. mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 183 on the other hand, figure 9 displays the results of the l-box test as a function of segregation. the variation of the ration h2/h1 as a function of segregation suggested that there was a high filling rate that was greater than or equal to 0.80 for the granular mixtures b6, b7 and b8. it is also worth noting that concrete passing ability increased as the percentage of g 8/15 became more important than that of g 3/8. it is interesting to mention that the specific surface area of aggregates g 3/8 was greater than that of g 8/15 aggregates, which had an influence on the absorption of mixing water. 2 3 4 5 6 7 8 0,50 0,55 0,60 0,65 0,70 0,75 0,80 0,85 l -b o x ( h 2 /h 1 ) ra ti o indice of segregation iss [%] h2/h1= f (iss) iss < 5 % h2/h1 > 0,80 fig 9. evolution of the ration h2 / h1 as a function of the static segregation index. figure 10 represents the results of the sieve stability test as a function of static segregation. note that the coefficient π represents the percentage of laitance relative to the weight of concrete. it is worth emphasizing that the coefficient π must be less than 15%. 1 2 3 4 5 6 7 8 4 6 8 10 12 14 16 18 s ie v e s ta b il it y π [ % ] indice of segregation iss [%] π = f (iss) iss < 5 % π < 15 cm fig 10. sieve stability π (%) as a function of the static segregation index. 3.2. concrete in the hardened state after placing the concretes to be tested in their molds, the test specimens were kept in a humid room for a period of 24 hours. once the specimens were demolded, they were stored in water at 184 mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 an ambient temperature of 20 °c. all measurements of compressive strength, ultrasonic pulse velocity and modulus of elasticity of concrete were carried out at 28 days. figure 11 groups the results of the compressive strength as a function of ssi for different mixtures of self-compacting concrete. the compressive strength values obtained were quite high; they exceeded 20 mpa. these values are good for structural concretes. however, the obtained results in the fresh state are to be excluded for formulations b9, b10 and b11. 1 2 3 4 5 6 7 8 20 25 30 35 40 rc28 = f (iss) iss < 5 % c o m p re s s iv e s tr e n g th [ m p a ] a t 2 8 d a y s . segregation iss [%] fig 11. evolution of the compressive strength as a function of the static segregation index. figure 12 illustrates the variation of the propagation speed of ultrasonic waves as a function of segregation, for different types of self-compacting concrete mixtures. it should be noted that the results of the ultrasonic pulse velocity test suggest that the reference sccs, i.e. b 09, b10 and b11, had a low compactness in comparison with those of the other formulations. the substitution of 3/8 by 8/15 will increase the compactness by reducing the vacuum is vice versa (figure 13). 1 2 3 4 5 6 7 8 3800 4000 4200 4400 4600 4800 v = f (iss) iss < 5 % u lt ra s o u n d s p e e d v [ m /s ] indice of segregation iss [%] fig 12. propagation speed of ultrasonic waves in concrete as a function of ssi. mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 185 18/15 and sand 2gravel 8/15, 3/8 mm and sand fig 13. granular compactness. furthermore, figure 14 depicts the evolution of the dynamic elasticity modulus as a function of segregation, for different types of self-compacting concrete mixtures. in this study, a non-destructive test method and the density of self-compacting concrete were used to calculate the modulus of elasticity (equation 02). this method proved to be effective for old structures still in use. the dynamic elastic modulus can be determined by the following equation: (02) where ρ is the density of concrete (experimental), ν = 0.2 is poisson's ratio, and v is the speed of sound [km/s]. figure 14 indicates that a very high dynamic elastic modulus was obtained for different sccs, at 28 days. the elastic modulus results are increasing if iss <5% for concretes b1 to b8 and decreasing if iss> 5% for concretes b9 to b11. the decrease in these concrete performances is linked to two phenomena: bleeding and segregation. 1 2 3 4 5 6 7 8 30000 32000 34000 36000 38000 40000 42000 44000 e = f (iss) iss< 5 %m o d u lu s o f e la s ti c it y e [ m p a ] indice of segregation iss [%] fig 14. modulus of elasticity of concrete as a function of the static segregation index. 4. conclusion this experimental study made it possible to highlight the influence of the granular mixture on ssi in the fresh state, and on the mechanical performance in the hardened state. the quantity of 186 mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 gravel of class 8/15 was replaced by gravel of class 3/8, at different percentages, to obtain a selfcompacting concrete with different granular distributions. the main conclusions of this study are summarized in the following points: the results of the tests in the fresh state and in the hardened state indicated that the concretes b6, b7 and b8 proved to satisfy all the requirements, standards and recommendations of class f6. the reference granular mixtures, i.e. b2 to b5, exhibited the characteristics of selfcompacting concrete; these characteristics belong to different classes (from f2 to f5) according to standard nf 206 (afnor, 2014). on the other hand, it was shown that the increase in the specific surface area had a significant effect on the quantity of mixing water absorbed, which had a remarkable impact on the results of the spreading and l-box tests. the formulations b9, b10 and b11 with a high percentage (greater than 80%) of aggregates of class g 8/15 caused a discontinuation in the granular mixture, which engendered a large number of voids inside the self-compacting concrete; this could be confirmed by the ultrasonic pulse velocity test. all the granular mixtures of reference self-compacting concrete, from b1 to b11, possessed a compressive strength (rc > 20 mpa), as required by the seismic regulations. the ultrasonic testing revealed that the granular compactness decreases or increases depending on the quantity of aggregates of class g 8/15 used in concretes b9, b10 and b11. it should be noted that the porosity of self-compacting concrete depends on its granular compactness. this study allowed stating that to prepare self-consolidating concrete with acceptable static segregation index values as recommended by the afgc regulations, the percentage of aggregates of class g 8/15 should be limited to the range between 50% and 70%, while this interval is between 30% and 50% for aggregates of class g 3/8. 5. references afgc (2008), l'association française de génie civil, recommandations pour l’emploi des bétons autoplaçants, document scientifique et technique. astm c1610/c1610m-10 (2010). test method for static segregation of self-consolidating concrete using column technique. astm c1712-09 (2009). test method for rapid assessment of static segregation resistance of selfconsolidating concrete using penetration test. bensebti, s., chabane, a., aggoun, s., & houari, h. (2015) la ségrégation verticale dans les bétons autoplaçants, mise en place d'une procédure expérimentale, rencontres universitaires de génie civil, may, bayonne, france. bui, v. k., montgomery, d., hinczak, i., & turner, k. (2002). rapid testing method for segregation resistance of self-compacting concrete. cement and concrete research, 32(9), 1489-1496. fujiwara, h. (1992). fundamental study on the self-compacting property of high-fluidity concrete. proc japan concr inst, 14(1), 27-32. nf en 12350-10, (2010), essai pour béton frais partie 10 : béton auto-plaçant essai à la boîte en l. afnor, p18-431-10. nf en 12350-11, (2010), essai pour béton frais partie 11 : béton auto-plaçant essai de stabilité au tamis, afnor, p18-431-11. nf en 12350-8, (2019). essais pour béton frais partie 8 : béton auto-plaçant essai d'étalement au cône. afnor, p18-431-8. mohammed krachaï and bouabdallah, j. build. mater. struct. (2020) 7: 178-187 187 otsuki n., hisada m., nagataki s., kamada t., (1996) "an experimental study on fluidity of antiwashout underwater concrete", aci materials journal, 93, 1,20-25. shen, l., jovein, h. b., & li, m. (2014). measuring static stability and robustness of self-consolidating concrete using modified segregation probe. construction and building materials, 70, 210-216.. sidky, m., legrand, c., & barrioulet, m. (1981). influence de la concentration en granulats et du temps de vibration sur la ségrégation interne dans le béton frais. matériaux et construction, 14(5), 367377. tangtermsirikul, s., sakamoto, j., shindoh, t., & matsuoka, y. (1991). evaluation of resistance to segregation of super workable concrete and the role of a new type of viscosity agent. reports of the technical research institution, 24, 369-376. trudel (1995), mise au point d’un essai rapide de mesure de la résistance { la ségrégation du béton frais, rapport de stage, université de sherbrooke, québec, laboratoire central des ponts et chaussées, 122 pages. umehara, h., uehara, t., enomoto, y., & oka, s. (1994). development and usage of lightweight high performance concrete. in proceedings of international conference on high performance concrete (supplementary papers), singapore, american concrete institute, detroit, mi, usa, pp. 339-353. yim, h. j., bae, y. h., & kim, j. h. (2020). method for evaluating segregation in self-consolidating concrete using electrical resistivity measurements. construction and building materials, 232, 117283. j. build. mater. struct. (2020) 7: 159-177 original article doi : 10.34118/jbms.v7i2.708 issn 2353-0057, eissn : 2600-6936 experimental characterisation and numerical modelling of the resilient behaviour of unbound granular materials for roads sandjak k 1,*, ouanani m 2, tiliouine b3 1 faculté de technologie, université m’hamed bougara, 35000, boumerdes, algeria 2 faculté des sciences et de la technologie, université ziane achour, 3117, djelfa, algeria 3 ecole nationale polytechnique, 16200, alger, algeria * corresponding author: k.sandjak@univ-boumerdes.dz received: 15-06-2020 accepted: 16-09-2020 abstract. this research paper deals with experimental characterisation and numerical modelling of the resilient behaviour of unbound granular materials (ugms) usually used in road construction. the first part of this paper describes the main results of an experimental program that was carried out to assess the mechanical properties of two local unbound granular materials (ugms) for construction purposes in road pavement. the second part of this paper is devoted to the numerical modelling of the resilient behaviour of ugms used in flexible pavements. for this purpose, several nonlinear unbound aggregates constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures. in addition, deflection data collected by falling weight deflectometer (fwd) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the constitutive models. finally, conclusions of engineering significance are formulated. key words: unbound granular materials, experimental characterisation, resilient behaviour, finite elements. 1. introduction low to moderate volume roads in algeria cover more than 70% of the total road network of the country (mamma, 2017). these road structures typically consist of thin asphalt layers and structurally significant unbound base and sub-base granular layers over subgrade to carry the traffic load. it follows that accurate modelling of granular layer behaviour is of crucial importance for the analysis and prediction of pavement structural performance (huang, 2004), (cost 337, 2002). in addition, for better understanding of the overall structural performance of flexible pavement structures, experimental tests where real traffic load conditions and in-situ physical and mechanical properties are accurately reproduced are needed. several in-situ testing devices have been so far developed to predict the material behaviour of unbound granular materials (ugms) under static or dynamic loading condition (ekblad ,2008), (ma et al., 2020), (mneina & shalaby, 2020), (tutumluer, 2003). however, due to cost considerations and difficulties to examine the influence of numerous factors affecting material behaviour using in-situ testing, laboratory tests have been developed to determine the mechanical behaviour of ugms for pavement use. repeated loading triaxial (rlt) tests (aashto, 2007), (en 13286-7, 2004) have been extensively used to simulate the loading produced by the rolling wheel on granular materials when used as unbound granular layers in pavement construction under different conditions such as grading, density and moisture contents (uthus et al., 2005). mailto:k.sandjak@univ-boumerdes.dz 160 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 in this experimental study, the variable confining pressure (vcp) type rlt test (en 13286-7, 2004), (rondón et al., 2009) has been used as it offers the capability to apply a wide combination of stress paths by pulsing both the confining pressure and the vertical deviator stress. such stress paths loading tests better simulate actual field conditions since in a pavement structure, the confining and loading stress acting on ugms is cyclic in nature. to analyse experimental tests results, several resilient strain behaviour models have been used by different investigators. these models have been categorized as either resilient modulus models or shear-volumetric strains models (ekblad, 2008), (lekarp et al., 2000). the k–g or shear-volumetric models are based on the decomposition of the principal stress and strain tensors, respectively, into two tensors: a deviatoric (or shear) and a volumetric. in these models, nonlinear behaviour of aggregates is characterized through general equations in terms of stress dependent bulk and shear moduli. basic assumptions are nonlinear elastic and isotropic material behaviour. the k–g or shear-volumetric model with three independent parameters (cost 337, 2002), (jouve & elhannani, 1994) is utilized in the present work to analyse the rlt test results and adequately incorporate the material nonlinearity due to the stress–stiffness dependency of the local aggregates. this model has the advantage to be in good agreement with rlt tests results and offers a reasonable compromise between accurate modelling and simplicity. furthermore, based on extensive investigations of modelling laboratory rlt tests data, it has been found that shear-volumetric strain models give better predictions than resilient modulus models (cost 337, 2002). in the first part of this research work, an extensive experimental study is carried out to examine the physical and mechanical properties of two local ugms for road pavement use in algeria. the study consists of three main stages: 1evaluation of physical properties in accordance with relevant tests standards. 2characterisation of the resilient deformations of the local ugms and assessment of the effect of non-linear stress dependency on their behaviour. 3determination from rlt tests of the constitutive model parameters to be used at a later stage in nonlinear finite element analysis of flexible pavements utilizing the local tested ugms. the main objective of the second part of this research work is to examine the effect of nonlinearity in unbound materials on the response and the performance of a granular pavement. the ugms nonlinear resilient model adopted by the aashto manual design guide is used (nchrp, 2004). this model is then implemented within an axi-symmetric fem code developed herein to evaluate its influence nonlinear analysis and structural performance of road pavements. the finite element simulation results are validated using fwd backcalculated moduli to predict critical pavement response and design life. in addition, the sensitivity of pavement design criteria and estimated pavement design life to the likely variations of unbound granular material mineralogical nature is assessed and conclusions of engineering significance are formulated. 2. experimental study in the following, the materials, their physical properties, the rlt testing equipment and procedure including sample preparation and testing program for the resilient behaviour characterization of the tested ugms, are described. it should be noted that all tests used in the present work, were conducted in conformity with relevant european standards. sandjak et al., j. build. mater. struct. (2020) 7: 159-177 161 2.1. materials aggregates used in this study were provided respectively from cap-djenet and bordj-bouarriridj deposits located in northern algeria (figure 1). these two deposits have great potential for high production levels of granular materials. aggregates issued from cap-djenet (cap) deposit are of basaltic origin. they were produced from volcanic eruptions. basalt is a rough stone, fairly light in weight and gray in color. aggregates issued from bordjbouarreridj (bba) deposit are limestones, produced from crushing sedimentary rocks composed mainly of calcium carbonate (caco3). most limestones are hard and durable. they typically produce strong aggregates with low water absorption and are suitable for roadstones. fig 1. map of aggregate materials deposits in algerian northern region 2.2 physical characterization granular materials consist of a large number of particles of different sizes. previous investigations on their physical characterization show that such materials are dependent on maximum particle size and grain size distribution. accordingly, unbound granular materials have been in the past empirically classified by maximum particle size and grain size distribution. on the other hand, in the french standard and in the european standard en 13285 (2010), (xp p18-545, 2004), the above characteristics are complemented by other tests results especially the los angeles (la) and micro-deval (mde) values. because of their historical use and past acceptance, as well as document relationships to aggregate abrasion resistance and for empirical classification purposes, these two tests are included in the present work. table 1, summarises the main state properties of the studied ugms. table 1. main state properties of the studied ugms deposits vb (%) * fines (%) es (%) mde (%) la (%) cap 2 9.5 55 14 12 bba 1.3 7 55 24 23 *vb methylene bleu value, mde wet micro-deval value, la los angeles value, es sand equivalent ratio the results indicated in table 1 and reported in fig. 2 show that the two local aggregates present acceptable state properties mainly in terms of la and mde values in accordance with the french standard xp p 18–545 (paute et al., 1994), (kolisoja, 1997). in figure 2, areas designated by the letters a to e represent various categories of mechanical resistance of ugms aggregates corresponding to an empirical classification based on the values 162 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 of la and mde. its noted that ugms cap issued from eruptive crushed rocks gives better characteristic values than ugms bba issued from limestone crushed rocks. fig 2. ugms classification using mechanical index tests data 2.3 rlt testing equipment and procedure in order to study the behaviour of ugms when used as unbound granular layers in pavement construction under different traffic and environmental state conditions, rlt tests can be used with advantage. the principal components of the rlt apparatus are illustrated in figure 3 below. fig 3. triaxial cell and lvdts the axial load is capable of applying a vertical stress on samples of 16 cm diameter and 32 cm height. example of triaxial cell and systems for measuring displacements using linear variable displacement transducers (lvdt). sandjak et al., j. build. mater. struct. (2020) 7: 159-177 163 the loading (figure 4) is carried out in exercising cyclically and simultaneously a confining pressure σ3 (applied via pneumatic pressure) and an additional dynamic vertical stress q (deviator stress) (figure 5a). under cyclic loading, ugms present resilient strains which are recovered after each cycle, and permanent strains which accumulate with the number of cycles (figure 5b). fig 4. stress state in triaxial configuration fig 5. applied stresses and measured strains in rlt tests: (a) applied stress history; (b) components of strain under cyclic stresses the testing procedure consists in the following main tests. all tests were conducted in accordance with relevant french and corresponding european standards.  grain size distribution both unbound granular materials bba and cap are sieved in the laboratory in the following four fractions: 164 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 0–3, 3–8, 8–15, 15–25 mm in accordance with french standards nf p 98–125 (2009). it is observed from figure 6 that the associated grading curves of the tested materials are practically similar and follow closely the average standard grain distribution curve. fig 6. particle size distributions  modified proctor test results modified proctor tests are performed on the two local ugms to obtain the densities to which the materials should be compacted in the rlt tests. the results of ugms identification are summarised in table 2. table 2. modified proctor test results ugms mdd (t/m3) omc (%) cap 2.27 7 bba 2.28 5 it is seen from above results that the aggregate samples are characterised by practically the same maximum dry density (mdd) but with slightly different optimum moisture content (omc (%)).  sample preparation the specimens are prepared with a vibro-compression method (en 13286-52, 2004). for the two ugms, all specimens for both ugm are compacted to density equal to 97% of maximum dry density and a moisture content w in such a way that: w = omc -3%. these density and moisture contents values are typical of those encountered in road pavements in algeria.  rlt testing programme tests were conducted following the test procedure for measurement of resilient deformations described by the european standard nf en 13286-7 (en 13268-7, 2004). the number of cycles of loading was set at 20000. the programme included, for each ugms, a series of four tests conducted at constant moisture content and under each of the different stress paths illustrated in figure 7 below. sandjak et al., j. build. mater. struct. (2020) 7: 159-177 165 fig. 7 stress paths schedule 3. analysis of experimental results 3.1 modelling of rlt tests data to analyse the tests results, nonlinear expressions for the volumetric and deviatoric strains derived from a shear-volumetric strain model with three independent parameters were considered (cost 337, 2002), (jouve & elhannani, 1994). this model (often referred to as the k– g model) is used to characterise nonlinear behaviour due to stress–stiffness dependency of the granular materials in terms of bulk and shear moduli. this model has the advantage to be in good agreement with rlt tests results and offers a reasonable compromise between accurate modelling and simplicity. furthermore, based on extensive investigations of modelling laboratory rlt tests data, it has been found that shear-volumetric strain models give better predictions than resilient modulus models (cost 337, 2002). the volumetric and shear components of the stress and strain parameters used in the k-g model can be written as: ; with: ; ; ( ) εv and εq, is the resilient volumetric and deviatoric (or shear) strains, respectively; k, is the bulk modulus and g, is the shear modulus. the stresses σ1, σ3 are major (axial) and the minor (confining) principal stress, respectively. the same notations apply to the principal strains ε1 and ε3. based on the nonlinear elastic properties of the k-g model and assuming material isotropy, the bulk and shear moduli can be determined as follows: ( ) [ ( ) ] (1) 166 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 with: ( ) (3) in the above expressions, the parameters ka , ga , n are material constants and pa is the atmospheric pressure, equal to 100 kpa conventionally. it is also seen from equations 1 and 2 that the parameters ka, ga have the same units as the elastic bulk and shear moduli respectively. it follows that the material constants ka and ga will have pressure units. moreover, the volumetric and deviatoric strain expressions, as a function of the stress invariants, can be written as: [ ( ) ] (4) [ ( )] (5) the values of the model parameters are systematically determined by using a generalisation of the least square regression method applied to both volumetric and deviatoric strains (jouve & elhannani,1994). the accuracy on the two types of measurements can be summarised by the global correlation index: √ √( ) ( ) (6) where ρv and ρq represent the partial correlation indices associated with volumetric and deviatoric strain. the application of the nonlinear regression method to rlt tests data carried out on the local materials has provided the model parameters summarised in table 3. table 3. k-g model parameters ugms ka (mpa) ga (mpa) n cap 86 117 0.454 bba 172 186 0.357 these model parameters are then used in equations. 4 and 5 to calculate both volumetric and deviatoric strains for the cap and bba ugms. it is clearly seen from both figures 8 and 9 (associated, respectively, with ugms bba and cap) that the agreement between measured and calculated strains (volumetric as well as deviatoric) is very good with values of global correlation indices found as follows: ugms cap: ρ = 0.80; ugms bba: ρ = 0.81 ( ) ( ) (2) sandjak et al., j. build. mater. struct. (2020) 7: 159-177 167 fig. 8 comparison between measured and calculated strain for ugms bba. a volumetric; b deviatoric 168 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 fig. 9 comparison between measured and calculated strain for ugms cap. a volumetric; b deviatoric sandjak et al., j. build. mater. struct. (2020) 7: 159-177 169 4. numerical modelling of the nonlinear resilient behaviour of ugms structural analysis of flexible pavements has been and still is currently performed using multilayer elastic theory. however, for thinly surfaced pavements subjected to low to medium volumes of traffics, the importance of nonlinear stress-strain behaviour of ugms requires the use of more sophisticated numerical models for structural design and performance of such pavements. the main objective of this section is to examine the effect of nonlinearity in unbound materials on the response and the performance of a granular pavement. the ugms nonlinear resilient model adopted by the aashto manual design guide is used (nchrp, 2004). this model is then implemented within an axi-symmetric fem code developed herein to evaluate its influence on nonlinear analysis and structural performance of road pavements. the finite element simulation results are validated using fwd backcalculated moduli to predict critical pavement response and design life. in addition, the sensitivity of pavement design criteria and estimated pavement design life to the likely variations of unbound granular material mineralogical nature is assessed and conclusions of engineering significance are formulated. 4.1 analysed pavement structure in order to study the effect of the behaviour nonlinearity in granular layers on pavement response and performance, a typical pavement structure has been selected. details of the analysed pavement structure are summarized in table 4. table 4. layer thicknesses of studied pavement structure asphalt (m) base (m) subbase (m) soil 0.05 0.20 0.20 5 the structure represents, practically, a flexible pavement with structurally significant unbound granular layers commonly used as pavements subjected to low to medium traffic volumes. the pavement structure was analysed by varying the mechanical properties of two unbound granular materials with different mineralogical nature while keeping all other parameters unchanged. the subgrade soil was not considered as a stress dependent material; thus, only the stiffnessstress dependency in the unbound granular material was investigated. 4.2 materials and mechanical properties a frequently used non-destructive in-situ device commonly used to estimate the elastic moduli of the constitutive layers of a pavement structure is the falling weight deflectometer (fwd). the analysis of deflection data collected from fwd in situ tests provides a relatively rapid and reliable procedure to characterize the stiffness properties of constitutive layers of an existing pavement structure. in the present study, based on the fwd measured load and deflections, issued from an experimental pavement section built as part of an intensive project on local unbound granular materials (azzouni, 2010), the elastic moduli of the analysed pavement structure have been backcalculated using the elmod software. various studies have been recently performed (cttp, 2001), (ji et al., 2014) to estimate laboratory measured resilient moduli of subgrade and base materials from fwd backcalculated moduli. the aashto suggests multiplying the backcalculated moduli for ugms and subgrade soils by appropriate adjustment factors to determine the resilient moduli (mr) values used for pavement design, in accordance with the values reported in table 5 (aashto, 2008). 170 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 table 5. ratio of laboratory mr to field backcalculated efwd layer type location mr/efwd aggregates between a stabilized and hma layer 1.43 below a pcc layer 1.32 below an hma layer 0.62 subgrade soil below a stabilized subgrade 0.75 below an hma or pcc layer 0.52 below an unbound aggregate base 0.35 4.2.1 asphalt the experimental results issued from the fwd test show that the backcalculated modulus of the asphalt layer and poisson’s ratio are found to be equal to 5042 mpa and 0.35 respectively. note that this value of asphalt layer elastic modulus is 26% greater than the average value prescribed by the algerian manual for pavement design (cttp, 2001). 4.2.2 unbound granular materials the resilient modulus of pavement granular materials is a key input parameter in the analysis of flexible pavement (nchrp, 2004). it is of paramount importance in ugms characterization and pavement structural performance prediction (almássy, 2002). many techniques including laboratory testing (sandjak & tiliouine, 2014), (rondón et al., 2009), non-destructive in-situ investigations and correlations with empirical parameters (gonzalez et al., 2007), were proposed to measure the resilient modulus of unbound granular materials. however, laboratory determination, in the form of repeated load triaxial tests, has been regarded as the most accurate method of obtaining the resilient modulus property. the resilient modulus (mr) is defined as the ratio of the stress deviator (σd) to the resilient axial strain (εr). with: several models (ekblad, 2008), (lekarp et al., 2000) have been developed over the years that combine applied stresses and material characteristics to describe the nonlinear behavior of granular materials under traffic loading. the k-θ model has been the most famous for characterizing the resilient response of granular bases and sub-base materials (zienkiewicz and taylor, 2005). the resilient modulus (mr) is given as: (7) where is the first invariant of stress tensor given as follows: where, = intermediate principal stress, k1, k2= material constants. uzan observed that the k-θ model did not summarize measured data well when shear stresses were significant, and proposed a three-parameter model. this model is given as: (8) witczak and uzan (1988) proposed a modification to the uzan model by replacing the deviator stress term in (8) by an octahedral shear stress term. this octahedral shear stress model also considers the dilation effect that takes place when a pavement element is subjected to a large principal stress ratio / . this model is called universal model and is given as: (9) sandjak et al., j. build. mater. struct. (2020) 7: 159-177 171 where τoct is the octahedral shear stress given as: √( ) ( ) ( ) the parameters k1, k2, and k3 are multiple regression constants evaluated from resilient modulus test data. the expanded universal model (nchrp, 2004), (aashto, 2008) introduced in the aashto mechanistic empirical pavement design guide (mepdg), estimates the resilient modulus using a generalized constitutive model for level 1 analysis for the nonlinear stressdependent modelling of both the unbound aggregates and fine-grained soils. the resilient modulus used in the 2008 mepdg design procedure, is as: ( ) ( ) (10) where pa is the atmospheric pressure. in this paper, the expanded universal model is used to assess the effect of nonlinearity in granular layers on pavement response and performance. the main results of the regression analysis including the coefficient of determination (r2) are presented in table 6. table 6. model parameters for the studied ugms ugms k1 (mpa) k2 k3 r2 cap 2.58 0.77 -0.58 0.95 bba 3.14 0.70 -0.41 0.98 it is shown that the expanded universal model gives high values of the coefficient of determination for both studied ugm. based on the model regression parameters reported in table 6, the considered constitutive model may be used at a later stage for the nonlinear finite element analysis of flexible pavements utilizing the two local tested aggregates. moreover, this model may be advantageously used to determine more realistic average values of resilient modulus than those issued from empirical classification of unbound granular materials (paute et al., 1994). it is to be noted that the in-situ fwd tests were performed on the pavement test section utilizing ugms bba as base and sub-base granular materials. thus, the value of the field backcalculated modulus efwd must be multiplied by an adjustment factor equal to 0.62 as indicated in table 5. the mechanical properties of the subgrade soil were not considered variable in the present study; the value of 63 mpa for the resilient modulus of the subgrade soil is estimated on the basis of the fwd backcalculated subgrade soil modulus (using elmod software) converted to an equivalent laboratory mr value using an adjustment factor equal to 0.35 (see table 5). poisson's ratio is taken equal to 0.35. note that the above value of the subgrade resilient modulus is rather close to the minimum value of subgrade modulus corresponding to subgrade soil type s2 defined in the algerian guide for pavement design. 4.3 finite element modelling of pavement structure the finite element method is particularly efficient for modelling the nonlinear behaviour of pavement structures as it can easily accommodate variability in material properties, changes in pavement geometry and modifications in applied loading. in pavement engineering, pavement structures are often modelled as axi-symmetric systems. the finite element domain is modelled using 8rectangular ring elements; each node having two degrees of freedom associated with the nodal displacement components in the vertical and the radial directions (tiliouine & sandjak, 2001), (zienkiewicz and taylor, 2005). the elements each contain four 172 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 gaussian points at which stresses and strains are calculated. the mesh is automatically made for a structure by superposed layers of elements, the material parameters being constant for each layer. the mesh is fixed at the bottom allowing no lateral movement and rollers on the sides allow vertical displacement to take place. for illustration purposes, a schematic representation of a f.e model used for pavement analyses is presented in figure10 (not to scale). fig. 10 comparison schematic representation of a f.e model (not to scale) the pavement structure was subjected to a circular static load which has radius of 17.5 cm and uniform pressure of 676 kpa. table 7 summarises constitutive material properties of pavement structure layers including bba granular base and sub-base materials for the three ugms nonlinear models considered in present investigation. table 7. material properties of pavement layers layers adjusted fwd modulus (mpa) linear model modulus (mpa) constitutive models asphalt 5042 5042 -linear elastic base 285 600 -linear elastic nonlinear (10) subbase 285 189 -linear elastic nonlinear (10) subgrade 63 63 -linear elastic 4.4 results of nonlinear analysis and discussion the main results of the numerical analyses were summarised in terms of values of the design criteria generally used in pavement engineering and the number of load repetitions to failure obtained from either the fatigue cracking or the rutting distress models. the three design criteria taken into account are: the deflection at the surface, which is, to some extent, an indication of the structure ability to bear repeated traffic loads. the horizontal tensile strain at the bottom of the bituminous layer usually related to risks of asphalt layer cracking by tensile fatigue failure. the vertical strain at the top of the soil usually related to risks of rutting of pavement. sandjak et al., j. build. mater. struct. (2020) 7: 159-177 173 radial strain at the bottom of asphalt layer and vertical strain at the top of subgrade soil are two critical responses, which are also used to control fatigue and rutting of flexible pavements respectively (cttp, 2001), (huang, 2004). error in computation of these two responses results in erroneous prediction of the pavement performance (bocz, 2009), (sadrnejad et al., 2011), (zhang et al., 2020). several fatigue and rutting models have been developed to relate the asphalt modulus and the measured strains to the number of load repetitions to pavement failure (ekwulo and eme, 2009). most of the fatigue cracking and the rutting failure models usually take the following forms: (11) (12) where, nc: allowable load repetitions to prevent the cracking fatigue of the asphalt layer, nr: allowable load repetitions to prevent the rutting at the top of subgrade soil due to accumulated pavement deformation, εh: maximum horizontal tensile strain at the asphalt layer, εv: compressive vertical strain at the top of subgrade soil, e1 is the elastic modulus of the asphalt layer. fi, i=1,…,5 regression distress model parameters depending on material type, definitions used to identify failure limits and climatic as well as traffic conditions. the design life of a flexible pavement is the minimum number of load repetitions required to cause either fatigue or rutting failure. the performance model considered in this study is the model proposed by asphalt institute (huang, 2004), (murana & olowosulu, 2013), with the following fi values for the regression coefficients: f1= 0.0796, f2= 3.291, f3 = 0.854, f4 = 1.365e-09, f5 = 4.477 the values of the three design criteria and design life (for fatigue cracking and rutting distress models) reported in tables 8 and 9 were computed using the linear and the nonlinear expanded universal model for granular base and sub-base layers of the analysed pavement structure. validation by fwd backcalculations, of finite element simulation results using the ugms bba has been performed and corresponding results are presented in table 8. in addition, for the sake of clarity, variation of design criteria and design life for the linear and nonlinear models based on ugms cap are summarized in table 9. only the mineralogical nature and hence the stiffness of the unbound granular materials was varied. all the other geometrical and mechanical parameters of the pavement layers were kept unchanged. it is seen that design parameter values of the pavement structure are in general affected by the nonlinearity of the resilient behaviour of the unbound aggregates. responses computed assuming linear elastic behaviour for the base layer, present significant differences as compared to those based on nonlinear behaviour of the granular layers. for the case at hand, consideration of nonlinearity resulted in a 36 % higher tensile strain at the bottom of asphalt layer and a 18 % higher vertical strain over the subgrade, than the corresponding values obtained using linear elastic analysis. it is important to note that these differences in the tensile strains and vertical strains will in turn result in exponentially amplified differences when predicting pavement performance (especially for fatigue cracking design life). furthermore, it is noted from tables 8 and 9 that allowable load repetitions computed based on asphalt institute transfer functions for predicting fatigue cracking and rutting design life, are notably different when using linear and nonlinear models of granular layers (especially for the fatigue cracking failure mode). it follows that conventional design methods usually based on multi-layer linear elastic theory significantly overestimate the pavement design life. this clearly illustrates the need of using proper constitutive modelling for characterization of nonlinear aggregate behaviour and prediction of pavement response on the one hand, and the crucial importance of developing well-calibrated distress models especially for predicting fatigue cracking design life on the other hand. 174 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 table 8. validation by fwd back -calculations of f.e. simulation results (ugms bba) design criteria fwd linear model nonlinear model w (mm) 0.870 0.725 (0.83) 0.792 (0.91) εh (10-6) 270 136.20 (0.50) 183 (0.68) εv (10-6) 842 707 (0.84) 824 (0.97) nc 433 332 4 119 670 (9.50) 1 558 521 (3.59) nr 79 526 173 673 (2.18) 87 604 (1.10) values in parentheses represent ratios of f.e simulation results to corresponding fwd backcalculated values. table 9. validation of design criteria based on ugms cap design criteria linear model nonlinear model w (mm) 0.831 0.892 (1.07) εh (10-6) 188 238.6 (1.26) εv (10-6) 821.60 912 (1.11) nc 1 426 217 650 917 (0.46) nr 88 756 55 620 (0.63) values in parentheses represent ratios of f.e nonlinear simulation results to corresponding linear values. the variations within the pavement section (using the two ugms) of the horizontal strain and the vertical strain are plotted in figs. 11, 12 respectively. figs. 11 and 12, clearly show that using aggregate from different mineralogical nature can affect both horizontal and vertical strains specially along to the granular layers. it is observed from the nonlinear simulation results that the three design criteria and pavement design life are very sensitive to changes in ugms mineralogical nature. in particular, the horizontal strain at the bottom of the asphalt layer is the most sensitive design parameter to variations in the mechanical characteristics of the unbound granular materials. in addition, it is clearly seen that the use of stiffer granular materials (ugms bba) can reduce significantly the tensile strain at the bottom of the asphalt layer and hence increase the pavement fatigue life. fig. 11 variation of the horizontal strain with depth using the two ugms sandjak et al., j. build. mater. struct. (2020) 7: 159-177 175 fig. 12 variation of the vertical strain with depth using the two ugms 5. summary and conclusions in the first part of this article, several aggregate specimens from two different deposits within northern algeria have been tested in order to assess their suitability as base and subbase materials in road pavement construction. an experimental investigation including tests on engineering main state characteristics in accordance with empirical classification as well as rlt tests to characterise nonlinear resilient behaviour under cyclic loading, has been carried out. the applicable and relevant standards were employed in all conducted tests. from the experimental results obtained in this investigation, the following main conclusions may be drawn: aggregates issued form both cap and bba local deposits have great potential to be used as base course materials for road pavements subjected to low to moderate volumes of traffic in northern algeria. rlt tests results show that limestone aggregates from bba deposit present significantly better stiffness characteristics than the aggregates of basaltic origin from cap deposit especially in terms of resilient modulus, contrarily to the results obtained from empirical ranking tests. density and moisture content as well as stress dependency have shown significant effects on resilient behaviour of studied aggregates, in conformity with results from previous investigations on other granular materials reported in specialised literature. parameter values of the studied mechanical model to be eventually used at a later stage in non-linear finite element analysis of pavement structures in northern algeria, have been determined from rlt tests results by using a generalisation of the least square regression method applied to both volumetric and shear strains. measured and calculated strains (volumetric as well as shear) are in excellent agreement for both tested aggregate specimens indicating that the mechanical model used in the 176 sandjak et al., j. build. mater. struct. (2020) 7: 159-177 present study reflects with very good approximation their nonlinear resilient behaviour. in the second part of this article, the expanded universal nonlinear resilient model for unbound granular materials has been implemented in a numerical code based on axi-symmetric finite elements to study the nonlinear resilient behaviour of unbound granular materials and the structural performance of road pavements. numerical investigations have been carried out to assess the influence of the nonlinear resilient model on the behaviour of two local unbound aggregates of different mineralogical nature typically used for road construction in algeria. simulation results show that computed critical pavement design criteria and predicted pavement design life using linear and nonlinear analysis are found to be substantially different. this clearly demonstrates the importance of nonlinear characterization of base and sub-base granular aggregates for accurate pavement design and the need to develop well calibrated transfer functions for performance prediction especially for predicting fatigue cracking design life. the simulation results also show that the use of stiffer aggregates can reduce significantly the tensile strain at the bottom of the asphalt layer and hence increase the pavement fatigue life, which could reduce the construction cost of road pavements. this is especially important in flexible road pavements subjected to low to moderate volumes of traffic. 6. references aashto t307-99. (2007). standard method of test for determining the resilient modulus of soils and aggregate materials. american association of state and highway transportation officials, washington. aashto. (2008). mechanistic–empirical pavement design guide: a manual of practice. american association of state and highway transportation officials, washington dc, isbn: 1-56051–423-7 almássy, k. (2002). examination of mechanical properties in unbound road bases. periodica polytechnica civil engineering, 46(1), 53-69. azzouni, a., (2010). simulation numerique des bassins de déflexion issus du système fwd. (in french), thèse de magister enstp, alger, algérie. bocz, p. (2009). the effect of stiffness and duration parameters to the service life of the pavement structure. periodica polytechnica civil engineering, 53(1), 35-41. cost 337. (2002). unbound granular materials for road pavements. final report. ec, directorate general for research and technological development, brussels. cttp (2001). catalogue de dimensionnement des chaussées, direction des routes, ministère des travaux publics, algeria. ekblad, j. (2008). statistical evaluation of resilient models characterizing coarse granular materials. materials and structures, 41(3), 509-525. ekwulo, e. o., & eme, d. b. (2009). fatigue and rutting strain analysis of flexible pavements designed using cbr methods. african journal of environmental science and technology, 3(12), 412-421. en 13286-52 (2004). unbound and hydraulically bound mixtures—part 52: method for the manufacture of test specimens of hydraulically bound mixtures using vibrocompression. european committee for standardization, brussels. en 13286-7. (2004). unbound and hydraulically bound mixtures—part 7: cyclic load triaxial test for unbound mixtures. european committee for standardization, brussels. en13285. (2010). unbound mixtures: specifications. european committee for standardization, brussels. gonzález, a., saleh, m., & ali, a. (2007). evaluating nonlinear elastic models for unbound granular materials in accelerated testing facility. transportation research record, 1990(1), 141-149. huang, y. h. (2004). pavement design and analysis. prentice hall, englewood cliffs, usa. sandjak et al., j. build. mater. struct. (2020) 7: 159-177 177 ji, r., siddiki, n., nantung, t., & kim, d. (2014). evaluation of resilient modulus of subgrade and base materials in indiana and its implementation in mepdg, the scientific world journal, article id 372838, http://dx.doi.org/10.1155/2014/372838 jouve, p., & elhannani, m. (1994). application des modèles nonlinéaires au calcul des chaussées souples, bulletin de liaison des laboratoires des ponts et chaussées, n°. 190, paris, france. kolisoja, p. (1997). resilient deformation characteristics of granular materials. phd thesis, tampere university of technology, no. 223, finland, tampere. lekarp, f., isacsson, u., & dawson, a. (2000). state of the art. i: resilient response of unbound aggregates. journal of transportation engineering, 126(1), 66-75. ma, g., li, h., yang, b., zhang, h., & li, w. (2020). investigation on the deformation behavior of opengraded unbound granular materials for permeable pavement. construction and building materials, 260, 119800. mamma, f. (2017). réseau routier et autoroutier algérien: consistances et perspectives. (in french), conference on road safety, algiers, algeria. mneina, a., & shalaby, a. (2020). relating gradation parameters to mechanical and drainage performance of unbound granular materials. transportation geotechnics, 23, 100315. murana, a., & olowosulu, t. (2013). distress model for nigerian empirical pavement analysis and design system, 4th int. conf. on emerging trends in engineering and technology, 25th -27th october. nchrp, (2004). guide for mechanistic-empirical design of new and rehabilitated pavement structures, part 2. design inputs. nchrp final report. nf p 98-125 (2009). assises de chausséesgraves non-traitées méthodologie d’étude en laboratoire. association française de normalisation. paute, j. l., hornych, p., & benaben, j. p. (1994). comportement mécanique des graves non traitées. bulletin de liaison des laboratoires des ponts et chaussées, (190), 27-38. rondón, h. a., wichtmann, t., triantafyllidis, t., & lizcano, a. (2009). comparison of cyclic triaxial behavior of unbound granular material under constant and variable confining pressure. journal of transportation engineering, 135(7), 467-478. sadrnejad, s. a., ghanizadeh, a. r., & fakhri, m. (2011). evaluation of three constitutive models to characterize granular base for pavement analysis using finite element method. australian journal of basic and applied sciences, 5(1), 778-786. sandjak, k., & tiliouine, b. (2014). experimental evaluation of non-linear resilient deformations of some algerian aggregates under cyclic loading. arabian journal for science and engineering, 39(3), 1507-1516. tiliouine, b., & sandjak, k. (2001). non-linear finite element modelling of unbound granular materials in flexible pavement analysis, euro. conf. compt. mechanics, crakow, poland. tutumluer, e., little, d. n., & kim, s. h. (2003). validated model for predicting field performance of aggregate base courses. transportation research record, 1837(1), 41-49. uthus, l., hoff, i., & horvli, i. (2005). a study on the influence of water and fines on the deformation properties of unbound aggregates. international symposium on bearing capacity of roads, railways and airfields, bcra’05, trondheim, p. 155. witczak, m.w., & uzan, j. (1988). the universal airport pavement design system, report i of iv: granular material characterization. university of maryland, college park, md. xp p 18-545. (2004). granulats—éléments de définition, conformité et codification. association française de normalisation. zhang, l., wang, c., dong, x., & zhang, x. (2020). structural response analysis of nonlinear pavement based on granular material. in iop conference series: materials science and engineering.730 012018. zienkiewicz, o.c., & taylor, r.l. (2005). the finite element method, oxford, 6th edition. http://dx.doi.org/10.1155/2014/372838 j. build. mater. struct. (2020) 7: 210-220 original article doi : 10.34118/jbms.v7i2.770 issn 2353-0057, eissn : 2600-6936 production of green cement from slag enhanced by egyptian metakaolin materials abdeen m. el nagar housing and building national research centre (hbrc), 87 el-tahrir st., dokki, giza, p.o. box 11511 cairo, egypt. * corresponding author: abdeenelnagar@yahoo.com received: 12-08-2020 accepted: 12-10-2020 abstract. new geopolymer-based materials offer excellent perspectives for the future; they should not be regarded as competitive materials for portland cement, which has been the reference construction material for so long, but as alternative materials with a series of important advantages to be considered. metakaolin (mk) produced from firing kaolin material up to 750 ºc for 2 h with a heating rate of 5ºc/min; leads to an enhancement in mechanical and microstructural properties of alkali activated geopolymer of water cooled slag material using (6:6, wt%) of sodium hydroxide and sodium silicate. in the present work the ratios of mk which will be added are less than 20% of the total mass, because of the used mk was very fine with average pore structure less than 30 mµ, which hinders the geopolymerization reaction if used as high ratio. curing was performed under 100% relative humidity at a temperature of 38ºc and ages of 7, 14, 28 & 90 days. the properties of geopolymer specimens have been studied through measurement of xrd, sem imaging, ftir, compressive strength and water absorption. results showed that the mixes of metakaolin up to 15% results in an enhancement in the mechanical properties as compared with slag control mix up to 90 days. key words: geopolymer, kaolin, metakaolin, slag, alkali activation. 1. introduction geopolymers can be thought as a new generation binder that can substitute for the calcium silicate hydrate which are essential components of portland cement, where they have a lower impact on global warming than opc but on the other side they have a higher environmental impact regarding other impact categories (davidovits, 1999). during the last decade, considerable research efforts have been directed towards the development of inorganic geopolymers, due to the wide range of potential applications for these materials. many reports can be found in the previous works on the synthesis, properties and applications of geopolymers (steveson & sagoe-crentsil, 2005). it is found that fly ash, one of the most abundant sources for making geopolymer binders and used it till date is very limited (hardjito et al., 2004). the wide variety of applications of geopolymer includes: fire resistant materials, low energy ceramic tiles, refractory items, cements and concretes (davidovits, 2008). mk is a thermally treated product from kaolin, which is one of the naturally occurring abundant minerals in the earth's crust. kaolin refers to a family of kaolinitic clays that consist of a 1:1-type clay mineral with one tetrahedral sheet and one octahedral sheet depending on the geological and weathering conditions. in geopolymer cement, al plays an important role because of its availability of aluminum controls to a large degree of the geopolymer properties (duxson et al., 2007; fernández-jiménez, 2006). the absolute amount of available aluminum and the rate of its release throughout reaction not only affect final strength, but other properties in the wet and hardened states including setting characteristics, flexural strength, acid resistance, microstructure, and strength development profile. generally, there are about 10% aluminum oxide in slag and 40% in metakaolin. according to the differences in the hydration products and, obviously, the role of al in these two systems is different. alonso and palomo (2001-a,b) found that with the highly alkaline activation of metakaolin in the presence of calcium hydroxide led to the formation of an amorphous sodium aluminosilicate, which has the same properties of geopolymeric gel. this mailto:abdeenelnagar@yahoo.com abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 211 geopolymeric gel formed was found to be similar to that obtained when metakaolin was activated in the absence of calcium hydroxide. csh gel was also formed as a secondary product when metakaolin was activated in the presence of calcium hydroxide. the high water demand of the reacting mixes and the high surface area and particle shape of mk due to calcination (provis et al., 2010), affect the mechanical strength development and stability of these materials, which does not always compare well with the performance of other alkali activated binders based on industrial by-products, such as granulated blast furnace slag (gbfs) or with lower cost and higher potential for large-scale industrial applications than mk. other than the lower aspect ratio of the particles, the main difference between these precursors is the presence of calcium in the gbfs which leads to the development of a microstructure enriched with stable and high density phases such as c-s-h gels, which promotes high compressive strengths (lecomte et al., 2006; lloyd, 2009). the main purpose of this work is to study the preparation of geopolymer materials by alkaline activation of amorphous water cooled slag and different ratios of mk materials. however, mk is not commonly used in most construction cases due to the relatively large specific surface area, which may demand high water/binder ratio to achieve satisfying workability. this means that such a family of abundant resource is not utilized in large volume in geopolymer concrete. so, in the present work the ratios of mk which will be added are less than 20% of the total mass, because of the used metakaolin was very fine with average pore structure less than 30 mµ, which hinders the geopolymerization reaction if used as high ratio. the effect of addition of different ratios of mk on alkali activated slag will be investigated as well as the impacts on mechanical and microstructural characteristics. x-ray florescence, x-ray diffraction, ftir and sem were used to identify the chemical, mineralogical and micro-structure of geopolymer composites. the compressive strength measurement was executed to evaluate the mechanical performance of the geopolymer specimens. 2. experimental procedures 2.1 materials materials used in this work were metakaolin prepared from kaolin collected from sinai, west of gebel gunna, egypt; water cooled slag also called ground granulate blast furnace slag (ggbfs) sourced from iron and steel factoryhelwan, egypt. sodium hydroxide (naoh) with purity 98 % in the form of pellets and sodium silicate (na2sio3) are used as alkali activators. mk was prepared by firing kaolin at 750 ºc for 2 h with heating rate of 5ºc /min. the chemical composition of the starting raw materials is tabulated in table (1). table 1. chemical composition of the starting raw materials (mass, %) materials water cooled slag (ggbfs) metakaolin sio2 35.63 56.00 al2o3 12.69 38.11 fe2o3 0.48 0.48 cao 31.72 0.21 mgo 5.08 0.37 s03 2.35 0.18 na2o 1.23 0.00 k2o 1.52 0.02 tio2 0.55 1.14 p2o5 0.031 0.26 mno 4.72 0.00 cl 0.24 0.00 loss 0.03 3.13 total 99.89 99.89 note bao=3.63 212 abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 the major components of ggbfs are sio2, cao, al2o3 and mgo. while in metakaolin, the two major components are sio2and al2o3. table 2 summarizes the major chemical composition of ggbfs and metakaolin (buchwald et al., 2007; li & ding, 2003; cheng & chiu, 2003). from the chemical composition, we can consider that ggbfs is (si+ca) system and (si+al) is suitable for mk. generally, ggbfs contains massive glass phase, while some crystalline phases may exist in minor level, such as gehlenite and akermanite. on the other hand, mk is ideally synthesized by dehydroxylation of phase pure kaolin while most commercial mk contains levels of impurities, primarily muscovite and titanium dioxide. laser particle size distribution of mk reflected its very fine pore structure. this mean most particle size lower than 30 mµ as indicated in fig. 1. fig. 1. laser particle size distribution of mk. mineralogical characterization of the raw materials was done using x-ray diffraction analysis in powder form as represented in fig. 2. fig. 2. x-ray differaction pattern for the starting raw materials. [qz: quartz an: anataze ak:akermanite] abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 213 the patterns show that ggbfs composed mainly of glassy phases and few crystalline material of akermanite (ca2mgsi2o7), while mk material is composed of quartz and anataze minerals 2.2 geopolymerization and curing geopolymer was made by hand-mixing raw materials of each mixture with the alkaline solution for 5 min and a further 5 min in a mixer. mk was mixed with the ggbfs in ratios as illustrated in table (2). the water binder material ratio (w/c) was different from 0.28 to 0.38% by mass, the other part of water was mixed with the 6% (naoh) + 6% (na2sio3) alkali activators. paste mixture were cast into 25×25×25 mm cubic shaped moulds, vibrated for compaction and sealed with a lid to minimize any loss of evaporable water. all mixes were left to cure at ambient temperature for 24 h, and then subjected to curing temperature of 38 oc and 100% relative humidity. the crushed specimens which obtained from compressive strength test were subjected to stopping of the hydration process by drying at 105ºc for 24 h (bakharev, 2006) and then preserved in a well tight container until the time of testing. table 2. mix design of mk and ggbfs materials. these hardened materials were characterized using xrf, xrd, ftir, and sem. the instrumental conditions used are shown below: chemical analysis was carried out using axios, wd-xrf sequential spectrometer (panalytical, netherland, 2009). xrd analysis was carried out using a philips pw3050/60 diffractometer. the data were identified according to the xrd software. perkin elmer ftir spectrum rx1 spectrometer was used to evaluate the functional groups in the sample. small amount of potassium bromide (kbr) and geopolymer powder were put into a mould with kbr pellets and pressed at 295 mpa for 2 min to produce specimen for examination, the wave number was ranged from 400 to 4000 cm-1 (panias et al., 2007; bakharev, 2006). compressive strength tests were carried out using five tones german brüf pressing machine with a loading rate of 100kg/min determined according to astm-c109-07 (2007). the microstructure of the hardened specimens was studied using sem inspect s (fei company, netherland). the removal free water was accomplished by drying at 105ºc for 24 h (bakharev, 2006). 3. results and discussion 3.1. mineralogical investigation xrd patterns of 90 days of alkali-activated slag specimens incorporating various ratios of mk activated by sodium hydroxide and sodium silicate in the ratios illustrated previously in table (2).the xrd patterns of alkali activated slag pastes with 0%, 5%, 10%, 15 and 20% mk replacement are shown in fig. 3. the main reaction products of all mixes are amorphous phases except small amount of crystalline phases that obtained from the raw materials such as quartz. also, cah was detected mix metakaolin, % slag, % naoh, % na2sio3, % w/c, % a 0 100 6 6 0.34 b 5 95 6 6 0.34 c 10 90 6 6 0.36 d 15 85 6 6 0.38 e 20 80 6 6 0.38 214 abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 as a result phase of slag geopolymerization. the amorphous phases with humps ranging from 25o to 35o 2θcan be regarded as a result of glassy phase of slag geopolymerization progress. on the other hand, the agglomerated mk results in an increased porosity as well as increased carbonation within the matrix as indicated in calcite peak at 29.35o 2θ, more clear in specimens 15% and 20% mk. as the slag content continues to decrease, the intensity peaks at around 30o2θ decrease, which represents the formation of c-s-h type gel from alkali activated slag. the intensity peaks that represent c-s-h gel were more significant in control specimen with higher slag content. fig. 3. the xrd patterns of slag-mk blends cured at 90 days. [qz: quartz, cah: calcium aluminate hydrate csh: calcium silicate hydrate, c: calcite] 3.2. scanning electron microscopy (sem) the scanning electron micrograph of 90 days geopolymer specimens having various mk ratios are shown in fig. 4. its noticed that the microstructure of 10% mk displayed compaction of matrix with the presence of geopolymer gel which filled the pores of the matrix specimens, as compared to the less dense structure 5and 20% of mk percentages of dry mixes. substitution of slag by10% mk leads to the enhancement in the morphological structure of the resulting geopolymer chains. abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 215 the added mk resulted in exceeds of amorphous alumino-silicate structure that enrich the morphological shape and leads to the enhancement in mechanical properties as revealed previously in the compressive strength results. fig. 4. the scanning electron micrograph of geopolymer specimens of slag and mk materials cured at 90 days. the alkaline activation of mk is believed to be a surface reaction, with silicate and aluminate species dissociated from the surface of mk (yunsheng et al., 2010). this phase was found to have no regular shape or morphology and the particles in (fig. 4, b) appear broken than a platy shape. the large surface area of mk and their abundance because of their small size can facilitate the chemical reactions necessary to produce a dense cement matrix with more calcium silicate hydrate (c-s-h) and less calcium hydroxide. on the other hand adding 20% mk lead to the formation of agglomerate which hinders the intact between the reacting materials as shown in (fig. 4, d). 3.3. fourier transform infrared ftir spectroscopy ftir spectra of 90 days cured geopolymer specimens having metakaolin content as a partial replacement of slag are shown in fig. (5). the characteristics bands for the present geopolymer structure are: hydration groups and combined water allocated for stretching vibration of o-h bond at about 3500 cm-1 and bending vibration for ho-h at about 1650 cm-1, stretching vibration of co2located at about1440-1450 cm-1, asymmetric stretching vibration (si–o–si) at about 1050 cm-1 for non-solublized silica, asymmetric stretching vibration (ti–o–si) at about 216 abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 970-1000 cm-1 where t=si or al, symmetric stretching vibration (al –o–si)between740-770 cm-1 and bending vibration (si–o–si and o–si–o) in the region 440-450 cm-1. also the main asymmetric band around 1000 cm-1 turned to be wider with the increase of the added slag up to 90% reflecting the increase of the geopolymerization reaction. cash at 685 cm-1 for the hydration phases resulted from amorphous slag especially in 10% mk specimen and decrease up to 20% mk. also, it is noticed that non-solublized silica decreased in 10% mk specimen but obviously appears when ggbfs replaced by 15% and 20% mk. the weak band observed around 840 cm−1 on 5%, 15% and 20% mk specimens is assigned to the bending vibration of si oh. the presence of si oh in the geopolymer products will lead to decrease the degree of polycondensation reaction, thus a reduction in mechanical strength (yunsheng et al., 2010). the main asymmetric band for t-o-si shifted to higher wave number with increasing mk more than 10% because of adding mk with its fine pore structure hinder propagation of geopolymer chain. fig. 5. ftir spectra of geopolymer specimens of water cooled slag having various mk percentages cured at 90 days. 3.4. compressive strength results of the compressive strength for geopolymer mixes along with cured at 100% relative humidity and at 38o c up to 90 days are shown in (fig. 6).the results show the increase of strength in all mixes along with hydration age up to 90 days. from fig. 5, it can be seen that when the replacement percentage is 10% meta-kaolin, maximum strength is obtained. in other word, as the amount of mk increases up to 20% the compressive strength is accordingly decreases, because of increasing dose of mk with its fine pore structure abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 217 leads to the formation of agglomerate which increased porosity and hinders the intact between the reacting materials. replacing glassy slag by amorphous mk results in the formation of more homogeneous matrix, also there is coexistence of geopolymer chains along with csh binding gel that acts as seeding agent for geopolymer accumulation and so results in a more compact and dense structure, this effect will decrease with increasing mk. the geopolymer manufactured only from 100% slag as a control mix was found to have the highest early strength while that from slag and mk was found to has the highest lately strength and better than 100% of slag control sample especially which has 10% and 15% mk. fig. 6. compressive strength of geopolymer specimens of water cooled slag having various mk percentages cured at 90 days. generally, mechanical strength improvement with the inclusion of calcium has been reported, the main binding phases in the microstructure are alkali alumino-silicate gel and al-substituted calcium silicate hydrate (c-s-h) gel. for mk/ggbfs blends, it has been identified that the mechanism of activation is highly dependent on both the alkalinity of the alkali activator and the ratio between mk and ggbfs, which act together to control the rate of ca2+ dissolution and availability during the reaction (xu & van deventer, 2000). 3.5. water absorption the water absorption of all samples (fig. 7) decreases with increase of curing time, in opposing to compressive strength. also, the water absorption decreases up to 10% mk up to 90 days of curing in all of the mixes. the geopolymer gel formed at 10%mk results in a decrease in the 218 abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 porosity of the matrix and as well as water absorption, while on using 20%, the fine structure and high surface area of added metakaolin, requires higher amount of water and thus cause increase in the porosity of resultant geopolymer fig. 7. water absorption of geopolymer specimens of water cooled slag having various mk percentages cured at 90 days. 4. conclusion addition of different percentages of meta-kaolin improves mechanical and microstructural properties, where: 1. addition of metakaolin provided an enhancement in geopolymer microstructure and results in the formation of well compacted dense structure. 2. ftir spectra confirm the intense amorphous geopolymer structure up on using 10% metakaolin, while the increased crystalline phases are predominant with further metakaolin increase. 3. the compressive strength increase with increasing percentages of metakaolin up to 10%, increasing dose of metakaolin leads to the formation of agglomerate which hinders the intact between the reacting materials 4. the geopolymer manufactured only from 100% slag as a control mix was found to has the highest early strength while that formed from slag and metakaolin was found to has the highest lately strength and better than 100% of slag control sample especially which has 10% and 15% metakaolin. 5. in order to obtain good and low cost alkali activated geopolymer slag-metakaolin binding materials, metakaolin should be added in percent lesser than 20% of the total mass. abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 219 acknowledgements the authors gratefully acknowledge prof. hisham m. khater from housing and building national research centre (hbrc) for supporting and comments. 5. references alonso, s., & palomo, a. (2001-a). alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio. materials letters, 47(1-2), 55-62. alonso, s., & palomo, a. (2001-b). calorimetric study of alkaline activation of calcium hydroxide– metakaolin solid mixtures. cement and concrete research, 31(1), 25-30. astm c109m07. (2007).standard test method for compressive strength of hydraulic cement mortars. bakarev, t. (2006).thermal behavior of geopolymer prepared using class f fly ash and elected temperature curing. cement and concrete research; 36:1134-1147. bakharev, t. (2006). thermal behaviour of geopolymers prepared using class f fly ash and elevated temperature curing. cement and concrete research, 36(6), 1134-1147. buchwald, a., hilbig, h., & kaps, c. (2007). alkali-activated metakaolin-slag blends—performance and structure in dependence of their composition. journal of materials science, 42(9), 3024-3032. cheng, t. w., & chiu, j. p. (2003). fire-resistant geopolymer produced by granulated blast furnace slag. minerals engineering, 16(3), 205-210. davidovits, j. (1999). chemistry of geopolymeric systems [c]. in cordi-geopolymer. terminology, geopolymer 99 proceedings: 2nd international conference, saint quentin (pp. 1-2). davidovits, j. (2008). geopolymer chemistry and applications. 2nd. institute geopolymere, france, 333– 365. duxson, p., fernández-jiménez, a., provis, j. l., lukey, g. c., palomo, a., & van deventer, j. s. (2007). geopolymer technology: the current state of the art. journal of materials science, 42(9), 2917-2933. fernández-jiménez, a., palomo, a., sobrados, i., & sanz, j. (2006). the role played by the reactive alumina content in the alkaline activation of fly ashes. microporous and mesoporous materials, 91(1-3), 111119. hardjito, d., wallah, s. e., sumajouw, d. m. j., & rangan, b. v. (2004). brief review of development of geopolymer concrete. in 8th canmet/aci international conference on fly ash, silica fume, slag and natural pozzolans in concrete. las vegas (usa). lecomte, i., henrist, c., liégeois, m., maseri, f., rulmont, a., & cloots, r. (2006). (micro)-structural comparison between geopolymers, alkali-activated slag cement and portland cement. journal of the european ceramic society, 26(16), 3789-3797. li, z., & ding, z. (2003). property improvement of portland cement by incorporating with metakaolin and slag. cement and concrete research, 33(4), 579-584. lloyd, r.r. (2009). accelerated ageing of geopolymers. in: provis jl, van deventer jsj (eds). geopolymers: structures, processing, properties and industrial applications. woodhead, cambridge, uk, pp. 139166. panias, d., giannopoulou, i. p., & perraki, t. (2007). effect of synthesis parameters on the mechanical properties of fly ash-based geopolymers. colloids and surfaces a: physicochemical and engineering aspects, 301(1-3), 246-254. 220 abdeen m. el nagar, j. build. mater. struct. (2020) 7: 210-220 provis, j. l., duxson, p., & van deventer, j. s. (2010). the role of particle technology in developing sustainable construction materials. advanced powder technology, 21(1), 2-7. steveson, m., & sagoe-crentsil, k. (2005). relationships between composition, structure and strength of inorganic polymers. journal of materials science, 40(8), 2023-2036. xu, h., & van deventer, j. s. j. (2000). the geopolymerisation of alumino-silicate minerals. international journal of mineral processing, 59(3), 247-266. yunsheng, z., wei, s., & zongjin, l. (2010). composition design and microstructural characterization of calcined kaolin-based geopolymer cement. applied clay science, 47(3-4), 271-275. j. build. mater. struct. (2020) 7: 199-209 original article doi : 10.34118/jbms.v7i2.767 issn 2353-0057, eissn : 2600-6936 effect on mechanical properties and stress strain characteristics of normal and high strength concrete at elevated temperature patel v *, singh b, ojha pn, mohapatra bn national council for cement and building materials, 34, km stone, delhi mathura road, nh-2, ballabgarh, haryana. * corresponding author: vikas.patel299@gmail.com received: 27-07-2020 accepted: 10-10-2020 abstract. high strength concrete (hsc) has some disadvantages such as brittleness and poor resistance to fire. fire exposure affects the concrete in way that the disintegration of concrete starts and a severe surface spalling occurs at very high temperatures. therefore, the structural behaviour or response to the load will change after fire exposure and the structural members may not behave as they were designed. further, the basics of flexural design depend on the stressstrain response of the concrete which is also affected upon fire exposure. hence, this study is carried out to provide useful input to aid the provision of a fire resistance for structural behaviour of concrete by investigating the effects on mechanical properties of concrete after exposure to high temperatures up to 600°c and establishing a stress-strain relationship. the concrete cylinders of size 100 mm x 200 mm were exposed to the temperature of 2000c, 4000c and 6000c after which the residual compressive strength, split tensile strength and flexural strength were recorded. for stress strain characteristics, 100 × 200 mm cylinders with polypropylene fiber content of 0.5% by volume of concrete were subjected to temperature exposure of 6000c for durations of 1 hour. curves for reduction factors of strength and stress strain characteristics after fire/elevated temperature exposure has been established. just consideration of reduced strength for assessment after fire exposure will not serve the purpose as the change in load response and increased deformation capacity also needs to be addressed properly. key words: high strength concrete (hsc), stress strain characteristics, spalling of concrete, polypropylene fiber. 1. introduction with the development of concrete technology, hsc has been commonly employed in many concrete structures around the world. hsc offers more strength and durability compared to normal strength concrete (nsc) (arora et al., 2016; 2017). but hsc also comes with the disadvantage of high brittleness and less fire endurance at elevated temperatures as compared to nsc. mechanical properties of the concrete such as compressive strength, modulus of elasticity (moe), stress strain relationship, etc. changes upon exposure to the elevated temperature (phan and carino, 1998). also the structural behaviour of the concrete changes after exposure to elevated temperature which makes it important to study these parameters under fire exposure. in structures heat can come from many sources such as fire and prolonged high temperature on the exposed surface. explosive spalling has been observed by many researchers often resulting in serious deterioration of the concrete. the absence of voids, which could relieve the continuous pressure build-up as a consequence of vaporization of evaporable water, may cause serious damage or even spalling to the concrete. some plastic based fibers influence mechanical properties of concrete positively and may address the disadvantage of brittleness or poor resistance to fire (guendouz et al., 2016). to reduce the risk of deterioration and spalling, previous literatures claimed that the use of fiber such as polypropylene and steel can have sufficient fire protection on the concrete structures. the initial moisture state of the concrete and the rate of heating may be the main parameters determining the effect of polypropylene fibers (nishida and yamazaki, 1995; kalifa e al., 2001; shihada, 2011). the emergence of polypropylene fibers has introduced to the world the possibility of having a highperformance and more cost-effective product in the market place. polypropylene fibers also mailto:vikas.patel299@gmail.com 200 vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 possess better durability as plastic does not rust. it also contributes to the ease in handling as it weighs about one-fifth of an equivalent steel fiber. fire performance of structural members depends on the properties of the constituent materials; knowledge of high-temperature properties of concrete is critical for fire resistance assessment under performance-based codes (kodur et al., 2008). the parameters that control concrete behavior are: compressive strength, tensile strength, peak strain, modulus of elasticity, creep strain, thermal conductivity, thermal strain, etc. that are nonlinear functions of temperature. also, aggregate types of concrete influence the concrete behavior exposed to fire (diederichs et al., 1987). studies conducted in past (tolentino et al., 2002) on the effect of high temperature on the residual performance of portland cement concretes using nsc and hsc and the test specimens were cast using the coarse aggregate, river sand as the fine aggregate and sulfonated melamine super plasticizer as water reducing admixture. specimens were exposed up to 600oc for 2 hours and tested. the study indicated that the increase in temperature, though resulted in significant reduction in compressive strength was mere pronouncing on hsc than nsc. at 600oc, the reduction in compressive strength of nsc was 58% while that in hsc was 69%. the reduction in modulus of elasticity in nsc was 49% while that in hsc was 59% due to the structure of concrete transformed coarser in both cases. studies in past (ravindrarajah et al., 2002) have also indicated that the high-strength concrete, independent of the binder material type used, experiences weight loss and the relationship between the weight loss and maximum temperature is non-linear and the compressive and tensile strengths show noticeable losses (above 15%) even at the temperature of 200oc; and it is observed that the elastic modulus drops marginally by about 5%. four types of hsc specimens were investigated, namely specimens made with siliceous and carbonate aggregate concrete; with and without steel fiber reinforcement. the strain corresponding to peak strength did not significantly change up to about 400°c for all four types of hsc. above this temperature the strains, corresponding respectively to peak strength, increased considerably. the strains attained, corresponding to peak strength at 600°c and 800°c, were twice and seven times the strain at room temperature (cheng et al., 2004). the flexural strength of fly ash concrete under elevated temperatures was investigated (potha raju et al., 2004) using ordinary portland cement (opc), fine sand and coarse aggregate with 0, 10%, 20% and 30% fly ash and mixes with w/c 0.55, 0.50 and 0.45 respectively and cured for 28 days. flexural strength tests were conducted on specimens exposing to three different temperatures of 100oc, 200oc, 250oc in addition to room temperature (28oc), exposing the specimens to1hr, 2hrs and 3hrs. the above investigations reported that the fly ash concrete showed consistently the same behavioral pattern as that of concrete without fly ash under elevated temperatures up to 250oc under flexure. the flexural strength of both concretes decreased with increase in temperature. concretes with 20% fly ash replacement showed better performance than the concrete without fly ash, by retaining more of its strength. the maximum losses recorded in all mixes without fly ash were in the range of 10-39.4%; in all mixes with 10% fly ash, they were 4 31.7%. the change in shape of stress-strain curve and the value of strain at peak stress and ultimate strain changes the stress block parameters used for design of reinforced concrete (rc) members. these parameters are the fundamentals that governs the design philosophies and hence if the stress-strain response is affects by fire exposure than its impact on these parameters needs to be understood and studied (singh et al., 2020). the present study includes investigation of the effects on mechanical properties of concrete upon exposure to high temperatures up to 600°c and establishing a stress-strain relationship. in this study, nsc and hsc were exposed to high temperatures and stress-strain response was studied. the concrete cylinders of size 100 mm x 200 mm were exposed to the temperature of vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 201 2000c, 4000c and 6000c after which the residual compressive strength, split tensile strength and flexural strength were recorded. for stress-strain response 100 × 200 mm cylinders with polypropylene fiber content of 0.5% by volume of concrete were subjected to temperature exposure of 6000c for durations of 1 hour. polypropylene fibers were added to the concrete as hsc undergoes severe spalling sometimes even explosive blast upon exposure to high temperature. addition of appropriate amount of polypropylene fibers will significantly improve the spalling resistance of the concrete which in turn improves the integrity of the concrete specimen so that the stress strain response can be recorded. further, addition of polypropylene fibers has no effect on mechanical properties of concrete at room temperature and even after exposure to elevated temperatures (patel et al., 2019). dosage of the polypropylene fibers as 0.5% by volume of concrete is taken as per the previous work done and other literatures (mydin and soleimanzadeh, 2012; bagherzadeh et al., 2012). 2. concrete ingredients 2.1. materials 2.1.1. cementitious material one brand of ordinary portland cement (opc 53 grade) with fly ash and silica fume are used in this study. the 3 days, 07 days and 28 days’ compressive strength of cement opc 53 grade were 36.00n/mm2, 45.50n/mm2 and 57.50n/mm2 respectively. properties of cement along with fly ash and silica fume are given in table 1. table 1. physical, chemical and strength characteristics of cementitious material characteristics opc -53 grade silica fume fly ash physical tests fineness (m2/kg) 320.00 16701 403 soundness autoclave (%) 00.05 soundness le chatelier (mm) 1.00 setting time initial (min.) & (max.) 170.00 & 220.00 specific gravity 3.16 2.24 2.2 chemical tests loss of ignition (loi) (%) 1.50 1.16 3.64 silica (sio2) (%) 20.38 95.02 62.53 iron oxide (fe2o3) (%) 3.96 0.80 4.66 aluminium oxide (al2o3) 4.95 23.58 calcium oxide (cao) (%) 60.73 1.17 magnesium oxide (mgo) (%) 4.78 0.50 sulphate (so3) (%) 2.07 0.15 alkalies (%) na2o & k2o 0.57 & 0.59 0.73 & 2.96 0.06 & 1.46 chloride (cl) (%) 0.04 0.009 ir (%) 1.20 moisture (%) 0.43 2.1.2 aggregates crushed aggregate with a maximum nominal size of 20 mm was used as coarse aggregate and natural riverbed sand confirming to zone ii as per is: 383 was used as fine aggregate. their physical properties are given in table 2. the petrographic studies conducted on coarse aggregate indicated that the aggregate sample is medium grained with a crystalline texture and partially weathered sample of granite. the major mineral constituents were quartz, biotite, plagioclase-feldspar and orthoclase-feldspar. accessory minerals are calcite, muscovite, tourmaline and iron oxide. the petrographic studies of fine aggregate indicated that the 202 vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 minerals present in order of abundance are quartz, orthoclase-feldspar, hornblende, biotite, muscovite, microcline-feldspar, garnet, plagioclase-feldspar, tourmaline, calcite and iron oxide. for both the coarse aggregate and fine aggregate sample the strained quartz percentage and their undulatory extinction angle (uea) are within permissible limits. feldspar grains are partially fractured and shattered. the quality of both coarse and fine aggregate is fair. the silt content in fine aggregate as per wet sieving method is 0.70 percent. table 2. properties of aggregates property granite fine aggregate 20 mm 10 mm specific gravity 2.83 2.83 2.64 water absorption (%) 0.3 0.3 0.8 sieve analysis cumulative percentage passing (%) 20mm 98 100 100 10 mm 1 68 100 4.75 mm 0 2 95 2.36 mm 0 0 87 1.18 mm 0 0 68 600 µ 0 0 38 300 µ 0 0 10 150 µ 0 0 2 pan 0 0 0 abrasion, impact & crushing value 19, 13, 19 flakiness % & elongation % 29, 25 2.1.3 water water complying with requirements of is: 456-2000 for construction purpose was used. 2.1.4 admixture polycarboxylic group based superplasticizer for w/c ratio 0.20 and 0.36 and naphthalene based for w/c ratio 0.47 complying with requirements of indian standard: 9103 is used throughout the investigation. 2.1.5 polypropylene fiber (pp) polypropylene (pp) is a thermoplastic polymer used in a wide variety of applications. it is produced via chain-growth polymerization from the monomer propylene. properties of the fiber has been given in table 3. table 3. properties of polypropylene fiber properties value cut length (mm) 12 effective diameter (micron) 25-40 specific gravity 0.90-091 melting point (0c) 160-165 elongation (%) 20-60 alkaline stability very good young’s modulus (mpa) ˃4000 2.2. mix design details in this study, the two different mixes of w/c ratio 0.47 (for nsc) & 0.2 (for hsc) using granite aggregate were studied for determining stress strain relationship of nsc and hsc at elevated temperature. the slump of the fresh concrete was kept in the range of 75-100 mm. a pre-study vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 203 was carried out to determine the optimum superplasticizer dosage for achieving the desired workability based on the slump cone test as per indian standard. the mix design details of specimens are given in table 4. adjustment was made in mixing water as a correction for aggregate water absorption. for conducting studies, the concrete mixes were prepared in pan type concrete mixer. before use, the moulds were properly painted with mineral oil, casting was done in three different layers and each layer was compacted on vibration table to minimize air bubbles and voids. after 24 hours, the specimens were demoulded from their respective moulds. the laboratory conditions of temperature and relative humidity were monitored during the different ages at 27±2oc and relative humidity 65% or more. the specimens were taken out from the tank and allowed for surface drying and then tested in saturated surface dried condition. table 4. concrete mix design details for study done w/c total cementitious content [cement c + flyash (fa) + silica fume (sf)] (kg/m3) water content (kg/m3) admixtur e % by weight of cement fine aggregate as % of total aggregate by weight 28-days strength of concrete (n/mm2) 0.47 362 (290+72+0) 170 1.00 35 45.72 0.20 750 (548+112+90) 150 1.75 35 97.76 3. experimental program for mechanical properties study, nsc and hsc cylinders without polypropylene fibers of size 100 mm x 200 mm were exposed to the temperature of 2000c, 4000c and 6000c after which the residual compressive strength, split tensile strength and flexural strength were recorded. for fire exposure, concrete cylinders were placed in an electrical furnace with a rate of heating as 50c/min till the desired temperature is achieved and then exposure temperature was maintained for 1 hour. cooling to room temperature was carried out in closed and disconnected furnace. specimens are tested once they are at room temperature. for stress-strain study, nsc and hsc cylindrical specimens of dimension 100 × 200 mm with polypropylene fiber content of 0.5% by volume of concrete were subjected to temperature exposure of 6000c for durations of 1 hour. polypropylene fibers were used as hsc undergoes severe surface spalling after fire exposure and surface strain using compressometer cannot be recorded on the cracked surface. concrete without fibers undergoes severe spalling and sometimes even blast in the furnace itself as shown in the figure 1-4. therefore, 0.5% of polypropylene fibers by volume of concrete were used to improve the spalling resistance or the integrity of the concrete specimens after fire exposure. grinding of the concrete cylinders is done to have a smooth surface and avoid any errors in stress strain response due to irregularities in surface texture. controlled samples were than tested for stress-strain relationship. fig. 1. cylinder with control hsc mix after blast in furnace fig. 2. cylinder with control hsc mix with severe spalling 204 vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 fig. 3. nsc cylinder with pp fiber after exposure to elevated temperature during testing fig. 4. hsc cylinder with pp fiber after exposure to elevated temperature during testing 4. mechanical properties at elevated temperature mechanical properties of the concrete are affected when exposed to elevated temperature depending on the exposed temperature. as the exposed temperature increases the concrete is deteriorated more severely. reduction in compressive strength, split tensile strength and flexural strength upon fire exposure is expected and was also reported by many researchers in past. the concrete cylinders of size 100 mm x 200 mm were exposed to the temperature of 2000c, 4000c and 6000c after which the residual compressive strength, split tensile strength and flexural strength were recorded. there after a qualitative relationship between ratio of residual strength to the controlled strength (strength at the temperature of 270c) has been plotted with respect to the exposed temperature (figure 5 to figure 7). this will give an idea of the proportional reduction in strength upon elevated temperature exposure. for quantitative relationship between the reduction ratio and exposed temperature needs large sample data with a varied grades of strength so that an accurate and actual relationship can be developed for prediction. however, with these limited data, only qualitative variation can be predicted with an approximates values of reduction ratio. fig. 5. reduction of compressive strength with respect to elevated temperature exposure. vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 205 fig. 6. reduction of split tensile strength with respect to elevated temperature exposure. fig. 7. reduction of flexural strength with respect to elevated temperature exposure. above figures gives the variation of reduction ratios of compressive strength, split tensile strength and flexural strength with respect to temperature exposed. the reduction ratios are more or less same for both nsc and hsc. further, above exposed temperature of 4000c, the reduction ratio decreases at high rate. the experimental values are slightly higher than the values given by eurocode up to the temperature exposure of 6000c. therefore, these curves can be used to have an approximate values of reduction ratios for concrete with indigenous materials. 206 vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 5. stress stain characteristics of normal and high strength concrete at elevated temperature the concrete specimens were tested in a strain controlled compression testing machine of 3000 kn capacity (figure-10-11) at room temperature of 27±20c and relative humidity 65% or more. two extensometers at the middle half of the height were used to get strain and two strains were averaged. to obtain a full stress vs strain curve, a rate of loading 0.4 μm/sec was adopted. the both ends of concrete cylinders were finished parallel by grinding and specimens with minimum surface texture cracks were selected (figure 8-9). the representative stress-strain curve for normal and high strength concrete is shown below in figure-12 to figure 15. experimental results indicate that the nsc strength concrete gradually fails after reaching its peak load, but the hsc suddenly explodes at peak load. fig. 8. surface texture of concrete cylinder without exposure to elevated temperature fig. 9. surface texture of concrete cylinder after exposure to 6000c for 1 hour duration fig. 10. concrete cylinder under testing without elevated temperature exposure fig. 11. concrete cylinder under testing after exposure to 6000c for 1 hour duration there is reduction in compressive strength upon exposure to elevated temperature which can be attributed to the reduction in effective cross-sectional area. reduction in compressive strength is higher in case of hsc as compared to the nsc after same exposure to high temperature. strain at peak stress and ultimate strain increases after exposure to elevated temperatures which can be attributed to the cracks found on the surface due to fire exposure. vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 207 fig. 12. stress strain characteristics of nsc experimentally determined for controlled sample fig.13. stress strain characteristics of nsc experimentally determined after exposure to 6000c for 1 hour duration fig. 14. stress strain characteristics of hsc experimentally determined for controlled sample fig. 15. stress strain characteristics of hsc experimentally determined after exposure to 6000c for 1 hour duration so there are two things going simultaneously, reduction in compressive strength and increase in strain at peak stress, ultimate strain. also we know that strain values are higher for lower strength concrete and lower for hsc. the lower strain in hsc is due to its more compact packing, high density and less voids thus making it less susceptible to deformation. this is the reason hsc undergoes explosive failure as internal stresses generated are not dissipated through deformation and accumulation of large stresses leads to sudden failure. after hsc is exposed to high temperatures, the micro cracks are generated in the concrete matrix some of which extends to the surface of the concrete. these micro cracks allow for the release of internal stresses and allows for deformation as the cracks expands upon load application. therefore, the strain values increase after exposure to elevated temperatures. 6. conclusion from the study done, it can be said that the mechanical properties and structural behaviour of the concrete will be affected by fire exposure and this change observed is more in case of hsc. this is due to the significant reduction in compressive strength and increase in strain values. the compressive strength, split tensile strength and flexural strength decreases with increase in exposed temperature. also the reduction ratios decrease at higher rate above 4000c which can 208 vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 also be seen from experimental results. the experimental values are slightly higher than the values given by eurocode up to the temperature exposure of 6000c. therefore, these curves can be used to have an approximate values of reduction ratios for concrete with indigenous materials. the shape of the stress strain curve also changes and becomes more parabolic after fire exposure as compared to the steeper curve for hsc which may lead to change in the stress block parameters that are fundamentals of flexural design. hence, just consideration of reduced strength for assessment after fire exposure will not serve the purpose as the change in load response and increased deformation capacity also needs to be addressed properly. further, quantification of the change in stress-strain parameters and the impact of these changes in the behaviour of structural member need to be studied so that safety and viability of the structure can be assessed. 7. references arora, v. v., singh, b., & jain, s. (2016). experimental studies on short term mechanical properties of high strength concrete. indian concrete journal, 90(10), 65-75. arora, v. v., singh, b., & jain, s. (2017). effect of indigenous aggregate type on mechanical properties of high strength concrete. indian concr j, 91(1), 34-41. bagherzadeh, r., pakravan, h. r., sadeghi, a. h., latifi, m., & merati, a. a. (2012). an investigation on adding polypropylene fibers to reinforce lightweight cement composites (lwc). journal of engineered fibers and fabrics, 7(4), 155892501200700410. cheng, f. p., kodur, v. k. r., & wang, t. c. (2004). stress-strain curves for high strength concrete at elevated temperatures. journal of materials in civil engineering, 16(1), 84-90. diederichs, u., ehm, c., weber, a., & becker, g. (1987). deformation behaviour of htr-concrete under biaxial stresses and elevated temperatures, proceedings of the 9th international conference on structural mechanics in reactor technology, lausanne (switzerland), vol h, paper h 2/3, aug 17-21. guendouz, m., debieb, f., boukendakdji, o., kadri, e. h., bentchikou, m., & soualhi, h. (2016). use of plastic waste in sand concrete. j. mater. environ. sci, 7(2), 382-389. kalifa, p., chene, g., & galle, c. (2001). high-temperature behaviour of hpc with polypropylene fibres: from spalling to microstructure. cement and concrete research, 31(10), 1487-1499. kodur, v. k., dwaikat, m. m. s., & dwaikat, m. b. (2008). high-temperature properties of concrete for fire resistance modeling of structures. aci materials journal, 105(5), 517. mydin, m. a. o., & soleimanzadeh, s. (2012). effect of polypropylene fiber content on flexural strength of lightweight foamed concrete at ambient and elevated temperatures. advances in applied science research, 3(5), 2837-2846. nishida, a. & yamazaki, n. (1995). study on the properties of high strength concrete with short polypropylene fiber for spalling resistance, proceedings of the international conference on concrete under severe conditions (consec'95). sapporo, japan. august. e&fn spon, london, pp: 1141-1150. patel, v., arora. v. v., singh b., kalra, m. & adhikari s. (2019). study on behavior of polypropylene fiber reinforced high strength concrete exposed to higher temperatures, 16th ncb international seminar phan, l. t., & carino, n. j. (1998). review of mechanical properties of hsc at elevated temperature. journal of materials in civil engineering, 10(1), 58-65. vikas patel et al., j. build. mater. struct. (2020) 7: 199-209 209 potha raju, m., shobha, m., & rambabu, k. (2004). flexural strength of fly ash concrete under elevated temperatures. magazine of concrete research, 56(2), 83-88. ravindrarajah, r. s., lopez, r., & reslan, h. (2002). effect of elevated temperature on the properties of high-strength concrete containing cement supplementary materials. in 9th international conference on durability of building materials and components, brisbane, australia. shihada, s. (2011). effect of polypropylene fibers on concrete fire resistance. journal of civil engineering and management, 17(2), 259-264. singh, b., patel, v., ojha, p. n., & arora, v. v. (2020). analysis of stress block parameters for high strength con-crete. journal of asian concrete federation, 6(1), 1-9. tolentino, e., lameiras, f. s., gomes, a. m., silva, c. a., & vasconcelos, w. l. (2002). effects of high temperature on the residual performance of portland cement concretes. materials research, 5(3), 301-307. j. build. mater. struct. (2023) 10: 1-15 original article doi : 10.34118/jbms.v10i1.2864 issn 2353-0057, eissn : 2600-6936 performance of high volume fly ash concrete in structural applications puneet kaura 1, p.n. ojha 2, brijesh singh 3,* 1 manager, center for construction development and research, national council for cement and building materials, india. 2 joint director and head, center for construction development and research, national council for cement and building materials, india. 3 group manager, center for construction development and research, national council for cement and building materials, india * corresponding author: brijeshsehwagiitr96l@email.com received: 30-01-2023 accepted: 13-02-2023 abstract. application of high volume fly ash concrete is still not advocated by construction fraternity due to lack of standardisation. in india, fly ash as a pozzolanic material can be used in manufacturing of portland pozzolana cement and composite cement with a maximum limit of 35%. present study had been carried out at various percentages of fly ash and a detailed mechanical and durability study was conducted. in this paper, concrete mixes were designed at two water binder ratio with 30%, 35%, 40% and 50% fly ash content. mechanical behaviour of concrete was studied through tests like compressive strength (at age of 1, 3, 7, 28, 56 and 90 days) and flexure strength (at an age of 7, 28 and 90 days). durability aspect of high volume fly ash concrete mixes were determined through various test like rcpt, non-steady state chloride migration, bulk conductivity, accelerated carbonation etc. and comparison is made with control mixes (i.e. concrete made with opc). alkali silica reactivity (asr) study was also carried out at 30%, 35%, 40% and 50% fly ash content using reactive aggregates. it was quite evident from test results that strength characteristics of high volume flyash concrete mix made with 50% flyash content was remarkably lower than that of all other concrete mixtures. high volume flyash concrete mix designed at 40% flyash content had shown exemplarily performance in comparison to other high volume flyash concrete mixes as well as control mixes. flyash content was found to most significant parameter influencing rate of carbonation. key words: high volume fly ash concrete mixes, rcpt, non-steady state chloride migration, bulk conductivity, accelerated carbonation, alkali silica reactivity (asr) 1. introduction in order to achieve sustainability, 21st century has provided momentum to various industry sectors to identify levers to their energy intensive materials and processes (mehta, 2004). in cement and construction industry, use of ordinary portland cement contributes towards high production cost as well as high embodied energy of concrete. production of one tonne of portland cement clinker almost generates one tonne of co2. in recent years, one approach to reduce carbon footprint of the construction industry that has drawn significant attention is the manufacturing of high volume fly ash concrete mixtures. in such concrete mixes, fly ash substitutes the portland cement clinker at a level well above the range of 15 % to 25 % as commonly used in the production of the current fly ash based concrete mixtures (mehta, 2004; obla et al., 2012). as per various international standards and codes, substitution level of portland cement clinker by the fly ash is of the order of 20 % to 35 % (cea, 2022; ojha et al., 2022). as a by-product of coal based thermal power plants, fly ash is the most abundant of all siliceous materials available throughout the world. however, proportion of fly ash as a part replacement of portland cement clinker for reinforced cement concrete (rcc) construction is very small and a major proportion of fly ash is disposed off as a backfilling material or dumped at sites. dumping of fly ash only creates environmental nuisance that requires immediate redressal under the current scenario. in india, use of fly ash has been diversified into various sectors such as cement sector, construction sector, agriculture sector etc (cea, 2022; ojha et al., 2022; jo jacob et al., 2014). their still exist a great opportunity to further enhanced the fly ash level in concrete through a comprehensive study that http://www.oasis-pubs.com/ mailto:brijeshsehwagiitr96l@email.com 2 kaura et al., j. build. mater. struct. (2023) 10: 1-15 can support the revision of the existing standards or codes. fly ash improves workability through “ball bearing action” of spherical shaped fly ash particles and decreases internal temperatures. fly ash leads to improvement in grading of the concrete mix by smoothing out of finer size particle distribution. fly ash decreases the amount of water needed by about 15 to 20% (ojha et al., 2022). mehta (2004) has concluded in his study about mechanisms for reduce in water content in concrete mix with higher than 50% fly ash thereby indicating improvement in workability, reduction in thermal and drying shrinkage and improved durability. increase of fly ash content from 30% to 45% increases the durability perfromance of concrete without decrease in compressive and flexural tensile strength (jo jacob et al., 2014). malhotra and mehta (2002) concluded that hvfac is sustainable, durable and eco-friendly concrete. poon et al. (2000) studied compressive strength at age of 28 days and found that concrete with 45% fly ash achieved compressive strength of 80 mpa and exhibited lower heat of hydration and chloride diffusivity in comparison to ordinary portland concrete. siddique (2004) studied mechanical properties of concrete with fly ash and observed that fly ash concrete has lower mechanical properties compared to opc concrete at early ages but at later ages mechanical properties have been increased continuously. in this research work, a comprehensive study had been carried out on concrete mixes designed at various percentages of fly ash. the study was carried out at two waterbinder ratio (0.40 & 0.60) with 30%, 35%, 40% and 50 % fly ash content. for their application in structural concrete, various mechanical and durability studies were conducted at various ages. alkali silica reactivity (asr) study was also carried out in line with astm c 1567 i.e. accelerated mortar bar test at various replacement percentages of fly ash content using reactive aggregates. 2. experimental program in this present research work, concrete mixes have been designed at 30%, 35%, 40% and 50 % fly ash content. material used in the production of concrete mixes are characterized for basic physical and chemical parameters as mentioned in 2.1. the details of the concrete mix design as well as test conducted are given in 2.2 and 2.3 respectively. 2.1. used materials 2.1.1. cement and fly ash cement used in study is opc-43, conforming to is 269 (2015) whereas fly ash used in study was siliceous in nature with 25 % reactive silica content, conform to requirement of is 3182 part 1 (2017). some of the physical and chemical properties of cement and fly ash is given in table 1 table 1. physical and chemical properties of cement (i.e. opc-43) and fly ash sl no. properties opc-43 fly ash (a) physical analysis: 1 specific gravity 2.22 2 blain's fineness, m2/kg 293 329 3 compressive strength, n/mm2 32.5, 41.50 & 54.00 3 days, 7 days & 28 days 4 lime reactivity (mpa) 5.2 (b) chemical analysis% 1 loss of ignition (loi) 1.86 0.12 2 silica (sio2) 20.22 59.78 3 iron oxide (fe2o3) 3.57 5.13 4 aluminum oxide (al2o3) 5.26 29.81 5 calcium oxide (cao) 61.87 2.04 6 total alkalies as na2o equivalent 1.31 0.76 7 chlorides 0.049 0.004 8 insoluble residue 1.99 kaura et al., j. build. mater. struct. (2023) 10: 1-15 3 2.1.2. aggregate the coarse aggregates (20 mm & 10 mm) and fine aggregate (zone ii), conforming to is 383 (2016) were used in all the concrete mixes. silt content of the fine aggregate was approximately 5%. some of physical properties of aggregates so used are mentioned in table 2. table 2: physical properties of aggregates property fine aggregate (natural) coarse aggregate 20 mm 10 mm specific gravity 2.59 2.73 2.73 water absorption (%) 0.8 0.4 0.3 the gradation curve for fine aggregate is given in figure-1 and it meets requirement of zone-ii category fine aggregate as per is 383 (2016). fig. 1 gradation curve for fine aggregate 2.1.3. admixture naphthalene based super plasticizer normal type confirming to is 9103 was used in concrete mix design. the specific gravity and concentration of solid particles in admixture were 1.24 and 28.14 % respectively. 2.2. concrete mix the water -binder ratio selected for the present research is 0.60 and 0.40. the details of the mix selected for the study are given in table3. in order to achieve the slump value of the concrete mixes in the range of 50-75 mm, dosage of super-plasticizer has been optimized accordingly. in total 10 concrete mixes including two conventional mixes i.e. control concrete (c1/0.60 and c2/0.40) had been studied. the cement was substituted with fly ash by mass for the mixes at sr.no. 2 to 10 studied and presented in table-3 below. 2.3. test conducted mechanical properties of the concrete have been evaluated in terms of compressive strength and flexural strength at various ages as mentioned in table 4. the laboratory conditions of temperature and relative humidity were monitored during the ambient curing i.e. 27±2oc and relative humidity 65±5 as per is: 516. various durability tests or techniques had been selected on the basis of environmental conditions which determines the aggressiveness of deleterious agents. during the working life, a rcc structure is supposed to be exposed to various type of physical as well as chemical attack such as chloride attack, sulphate attack, acid attack etc. therefore, it becomes essential to evaluate the behavior of the concrete as well as concrete making materials against the aggressiveness of exposure conditions. durability test or techniques had been 4 kaura et al., j. build. mater. struct. (2023) 10: 1-15 developed to check the performance of concrete and concrete making ingredients against the penetration of aggressive substances (is-383, 2016; arora and kaura, 2014; 2015; 2016; arora et al., 2017-a; 2017-b; ojha et al. 2021; 2022). for details of the durability tests, refer to table 4. table 3. typical concrete mix proportions sr. no mix identification waterbinder ratio total binder content (kg/m3 ) opc-43 (%) fly ash (%) dose of admixture % by wt. of cement 1. c1/0.60 0.60 300 100 0 0.40 2. m1/0.60/30% 0.60 300 70 30 0.50 3. m2/0.60/35% 0.60 300 65 35 0.65 4. m3/0.60/40% 0.60 300 60 40 0.70 5. m4/0.60/50% 0.60 300 50 50 0.80 6. c2/0.40 0.40 400 100 0 0.50 7. n1/0.40/30% 0.40 400 70 30 0.60 8. n2/0.40/35% 0.40 400 65 35 0.70 9. n3/0.40/40% 0.40 400 60 40 0.85 10. n4/0.40/50% 0.40 400 50 50 0.90 table 4. details of test conducted sr. no test conducted test standards/ guideline type of specimen and size of specimen age of testing (days) 1. compressive strength is 516 (part1/sec1) cube ( 150 mm) 1,3,7,28,56 and 90 2. flexural strength is 516 (part1/sec1) concrete beam (100x100x500 mm) 7, 28and 90 3. rapid chloride penetration test astm c 1202 concrete disc (100 mm diameter x50 mm height ) 28 and 56 4. non steady state chloride migration coefficient nt build 492 concrete disc (100 mm diameter x50 mm height ) 28 and 56 5. bulk conductivity astm c 1760 concrete disc (100 mm diameter x200 mm height ) 28 and 56 6. electrical resistivity using four point wenner probe technique rilem tc 154 concrete slab (300mm x300 mm x100mm) 28 , 56 and 90 7. porosity i.e. volume of permeable voids astm c642 concrete disc (100 mm diameter x50 mm height ) 28 and 56 8. accelerated carbonation depth iso 1920 part 12 concrete beam (100 mm x100mm x500 mm) exposure period = 70days , 140 days and 210 days 9. alkali silica reactivity astm c 1567 mortar bar (25 mmx 25mm x282 mm) 14 days expansion 3. results and discussion mechanical and durability behaviour of high volume fly ash concrete mixes had been studied and comparison was made with the control mixes i.e. concrete made with opc-43 at both water-binder ratios. the results shown in the graph are the averaged results of three test specimens. 3.1. mechanical behaviour of the high volume fly ash concrete mixes compressive strength and flexural strength are the two basic fundamental engineering properties of the concrete. mechanical behaviour of the concrete mixer designed with varying percentages of flyash had been evaluated in terms of compressive strength and flexural strength and comparison had been drawn with the control mixes. compressive strength had been determined kaura et al., j. build. mater. struct. (2023) 10: 1-15 5 using concrete cube specimens (150mm) at an age of 1day, 3 days, 7 days, 28 days, 56 days and 90 days. the result shown in figure 2 and figure 3 are the average of 3 specimens tested as per is 516 (part 1/sec 1). similarly, flexural strength was determined using concrete beam specimens (100mmx100mmx500mm) tested under three point loading as per is 516 (part 1/sec 1). the flexural strength test was conducted at an age of 7 days, 28 days and 90 days, results are the average of 3 specimens and are shown in figure 4 and figure 5. in the present study, two waterbinder ratio i.e. 0.60 and 0.40 had been selected. the selection of the water-binder ratio was to cover different grade of concrete. generally, concrete mix designed at water cement ratio of 0.60 represent m20 or m25 grade of concrete whereas concrete mix designed at water-cement ratio of 0.40 represent m.35 grade of concrete. on the perusal of the test results, it was observed that effect of water-binder ratio along with flyash content had a significant influence over strength value. from the figure 2 to 3, it can be observed that early age compressive strength of the concrete mixer designed with flyash had lower strength in comparison to control mixes. this trend of reduced compressive in high volume fly ash concrete mix continued up to an age of 28days. however, at extended ages i.e. 56 days and 90 days, it can be noticed that high volume fly ash concrete mixtures designed at water-binder ratio of 0.40, compressive strength of the concrete mixes designed with flyash content up to 35% is at par with the control mixes. however, at 0.6 water-binder ratio, compressive of high volume flyash concrete mixtures were not found to be encouraging. concrete mixer designed with 50% fly ash content have significantly lower, compressive strength in comparison to control mixer at all ages. at later ages, gain in the compressive strength in high volume fly ash concrete mixes was observed. this is probably due to the densification of the microstructure resulting from the pozzolanic reaction. pozzalanic reaction in case of fly ash concrete mixes involves reaction between reactive silica and alumina constituent of fly ash with the portlandite. it is essential to have presence of portlandite for the continuation of pozzalanic reaction. pozzolanic reaction in case of fly ash concrete mixes results in the formation of secondary csh and sometimes cash, if alumina is available that contributes towards later age strength (arora et al., 2017; ahmed et al., 2019; du et al., 2021; park and choi, 2021, chen et al., 2019; kumar et al., 2021, sun et al., 2021). the test results of flexural strength indicate that at 7days, high volume flyash concrete mixes had lower flexure strength value in comparison to control mixer. at 28days and 56 days, flexural strength of high volume concrete mixer were found to be higher to equivalent w.r.t control mixes. it was also observed that with an increase in fly ash content (limited to 40%) a proportionate increase in the flexural strength value had been noticed. fig 2. compressive strength for w/b 0.60 fig 3. compressive strength for w/b 0.40 0 10 20 30 40 50 60 1d 3d 7d 28d 56d 90dc o m p re ss iv e s tr e n g th ( i n m p a ) age of testing c1/0.60 m1/0.60/30% m2/0.60/35% m3/0.60/40% m4/0.60/50% 0 10 20 30 40 50 60 1d 3d 7d 28d 56d 90dc o m p re ss iv e s tr e n g th ( i n m p a ) age of testing c2/0.40 n1/0.40/30% n2/0.40/35% n3/0.40/40% n4/0.40/50% 6 kaura et al., j. build. mater. struct. (2023) 10: 1-15 fig 4. flexural strength for w/b 0.60 fig 5. flexural strength for w/b 0.40 3.2. durability aspect of high volume fly ash concrete mixes durability tests had been developed with an aim to quantity the quality of the concrete as well as concrete making constituents w.r.t aggressiveness of the environmental exposure conditions. some test provides a qualitative means of judgement whereas some test provides quantitative means of judgement. durability of concrete is basically defined in terms of permeability characteristics of the material. generally, a porous concrete is termed to be a less durable concrete. for a designing a rcc structure in coastal environmental, it is important to understand the problems that could affects the performance of the structural concrete. one of the major issue that requires immediate action while designing structure under such climatic condition is related with the attack of chloride ions that results in reinforcement corrosion. this problem can be solved, if performance based testing of concrete or concrete making material had been carried out at the design mix stage. various tests like rapid ion penetrability test (also known as rcpt), nonsteady state chloride migration coefficient test (i.e. nt build n94), bulk conductivity test and electrical resistivity had been developed. in the present study, durability of high volume flyash concrete mixes had been studied through various types of performance based tests. the test results of rcpt conducted as per astm c1202 are shown in figure 6 and figure 7. on the perusal of the rpct results it was quite evident that water binder ratio, age of concrete and flyash content had significant influence over charge passed value. according to astm c1202, chloride ion penetrability classes had been described on the basis of the charge passed. if charge passed is less than 100 coulombs such that of concrete will fall under negligible class whereas if charge passed lie in the range of 100-10000 coulombs, concrete will lie in very low category. low category had been defined for a charge passed range of 1000-2000 coulombs, moderate category had been defined for a charge passed range of 2000-40000 coulombs whereas a concrete with charge passed value more than 4000 coulombs, it will fall under high chloride ion penetrability class. during the test, it was observed that penetrability class of the control mixes (i.e. c1/0.60 and c2/0.40) lie in moderate category. whereas penetrability class of the high volume flyash concrete mixtures lie either in very low or low category. high volume flyash concrete mixes designed at 0.40 waterbinder ratio had rcpt value in the range of 240 to 540 coulombs whereas at 0.60 waterbinder ratio, rcpt value of these mixes were found in the range of 730 to 1640 coulombs. a decrease in the rcpt value with age had been observed with all concrete mixes. high 0 1 2 3 4 5 6 7 7d 28d 90d f le x u ra l st re n g th i n m p a age of testing in days c1/0.60 m1/0.60/30% m2/0.60/35% m3/0.60/40% m4/0.60/50% 0 1 2 3 4 5 6 7 7d 28d 90d f le x u ra l st re n g th i n m p a age of testing in days c2/0.40 n1/0.40/30% n2/0.40/35% n3/0.40/40% n4/0.40/50% kaura et al., j. build. mater. struct. (2023) 10: 1-15 7 volume flyash concrete mixes designed with 40% flyash content had the lowest rcpt value in comparison to all other concrete mixtures. the non-steady state chloride migration coefficient of the concrete mixtures was determined as per nordtest method i.e. nt build492 and results are shows in figure 8 and figure 9. as observed from the test results, water-binder ratio, flyash content and age of concrete were the important parameters influençons the test value. for water -binder ratio of 0.60, at 28 days, non-steady state chloride diffusion value of control mix was found to be 9.0x10-12 m2/yr whereas high volume fly ash concrete mixtures had chloride diffusion coefficient in range of 3.0 to 7.7 x 10-12 m2/yr which is approximately 1.2 to 3 times lower than control mix. similarly, at 56 days, for water binder ratio of 0.60, chloride diffusion coefficient of the control mix was found to be 7.3 x 10-12m2/yr, a marginal reduction in comparison to its 28 days’ value whereas in case of high volume fly ash concrete mixtures, chloride diffusion coefficient was found to be in the range of 2.0 to 5.6 x 1012m2/yr which is approximately 1.3 to 3.5 times lower than control mix. for 0.40 water binder ratio, at 28 days, non-steady state chloride diffusion value of control concrete was found to be 7.10x1012m2/yr whereas in case of high volume flyash concrete mixture, chloride diffusion coefficient was found in the range of 1.5 to 2.6 x 10-12m2/yr which is approximately 2.7 to 4.7 times lower than of concrete. similarly, at 56 days, chloride diffusion coefficient of control mix was found to be 5.20x1012m2/yr which is marginally lower than that of its 28 days’ value. in case of high volume flyash concrete mixtures, chloride diffusion rate was found to be in the range of 0.6 to 1.2x10-2m2/yr which is approximately 4.0 to 9.0 times lower than that of control mix. it was quite evident from the test result that addition of flyash had notable influenced over chloride diffusion rate. flyash addition up to 40% shows better resisting property against ingress of chloride ion at both water -binder ratios in comparison to all other concrete mixtures. improvement in permeability characteristics of concrete due to addition of flyash is one of primary reason behind lower chloride diffusivity rate in high volume flyash concrete mixtures (arora and kaura et al., 2019-b; andrade and alonso, 2004; singh et al., 2020-b). bulk conductivity and electrical resistivity test method are generally adopted to measure the electrical resistance of the hardened concrete. both test methods depend upon instrinc property of the material and influenced by several factors like pore solution composition and porosity as well pore size distribution. bulk conductivity test was carried out as per the requirements of astm c1760 at 28 days and 56 days. from the results shown in figure 10 and figure 11, it could be seen that effect of age was insignificant whereas factors like water -binder ratio and flyash content were more prominent. the bulk conductivity value of the control mix at 28 days was found to 13.74 ms/m and 7.9 ms/m at 0.60 and 0.40 water binder ratio respectively. in case of high volume flyash concrete mixes, bulk conductivity was found in the range of 3.14 to 6.12 ms/m and 1.14 to 2.53 ms/m at 0.60 and 0.40 water binder ratio respectively. bulk conductivity value of high volume flyash concrete mixes were found to be 2 to 5 times lower than that of control mixes. it was also observed that as the percentage of flyash increases, there had been exponential decrease in the conductance value provided that flyash content is limited to 40%. beyond 40%, an increase in the bulk conductivity value was noticed that may be due increase in the porosity of the mixtures as reported in the later part of this paper. although, this increase in the conductance value was lower than that of control mix. high volume flyash concrete mix designed at 40% flyash content had the lowest conductivity. 8 kaura et al., j. build. mater. struct. (2023) 10: 1-15 fig.6. rcpt at w/b 0.60 fig. 7. rcpt at w/b 0.40 fig.8. nonsteady state chloride migration coefficient at w/b 0.60 fig.9. nonsteady state chloride migration at w/b 0.40 fig.10. bulk conductivity at w/b 0.60 fig. 11. bulk conductivity at w/b 0.40 0 500 1000 1500 2000 2500 3000 3500 c h a rg e p a ss e d ( ii n c o u lo m b s) sample id 28 d 56d 0 500 1000 1500 2000 2500 3000 3500 c h a rg e p a ss e d ( ii n c o u lo m b s) sample id 28 d 56d 0 1 2 3 4 5 6 7 8 9 10 c h lo ri d e d if fu si o n ( x 1 0 -1 2 m 2 /y r) sample id 28 d 56d 0 1 2 3 4 5 6 7 8 9 10 c h lo ri d e d if fu si o n ( x 1 0 -1 2 m 2 /y r) sample id 28 d 56d 0 2 4 6 8 10 12 14 16 b u lk c o n d u c ti v it y t ( in m s /m ) sample id 28 d 56d 0 2 4 6 8 10 12 14 16 b u lk c o n d u c ti v it y t ( in m s /m ) sample id 28 d 56d kaura et al., j. build. mater. struct. (2023) 10: 1-15 9 fig.12. electrical resistivity at w/b 0.60 fig.13. electrical resistivity at w/b 0.40 electrical resistivity test is an indirect way to measure the probability of occurrence of corrosion (arora et al., 2021; polder, 2001; azarsa and gupta, 2017). according to rilem tc 154 corrosion risk is high when concrete resistivity is less than 10kohm-cm whereas when concrete resistivity lies in the range of 10-50 kohm-cm, risk of corrosion is moderate. however, at concrete resistivity value higher than 100 kohm-cm changes of occurrence of corrosion is either low or negligible (polder, 2001; azarsa and gupta, 2017; arora et al., 2017). in present study, the concrete resistivity of the mixes was evaluated at 28 days, 56 days and 90 days. from the graph shown in figure 12 and figure 13, it was quite evident that waterbinder ratio, flyash content and concrete age had a significant role to play. overall, concrete mixes designed with opc-43 i.e. control mixes fall under the category of high to moderate risk of corrosion. in case of high volume flyash concrete mixes, electrical resistivity values lie in the range of 18 to 90 kohm-cm which means risk of corrosion is moderate to low. with the increase in the flyash level up to 40%, a proportionate increased in resistivity value was noticed in high volume flyash concrete. at higher test age, the variation or increase in electrical resistivity values for 30 %, 35 %, 40 % replacement level is lower when results are compared for 56 and 90 days test age for both water-binder ratio. however, with further addition of flyash, decrease in the electrical resistivity value was observed but still resistivity of the concrete made with 50% flyash is significantly higher than that of control mix. similar type of trend was seen in rcpt, non-steady state chloride migration and bulk conductivity test. at higher test age, the variation or decrease in rcpt, non-steady state chloride migration and bulk conductivity values for 30 %, 35 %, 40 % replacement level is lower when results are compared for 56 days test age for both water-binder ratio. porosity determination was carried out in accordance to astm c642 and results are shown in figure 14 and figure 15 and was defined in terms of percentage of permeable voids. on the analysis of the test results, it was found that high volume flyash concrete mixes designed with flyash content upto 40% had porosity equivalent or at par with the conventional concrete i.e. control concrete. high volume flyash concrete mixes made with 50% flyash had porosity slightly higher than that of control mixes as well as high volume flyash mixture made with flyash content up to 40%. the results show that flyash addition beyond 40% level makes a concrete more porous. carbonation is one of the major challenge associated with the rcc structures located in the noncoastal environmental. carbonation induced corrosion is basically a slow process and take years to occur. in case of carbonation, alkalinity of the concrete reduces to a ph level of less than 9.0 due to the formation of calcium carbonate. calcium carbonate is formed due to the chemical reaction 0 10 20 30 40 50 60 70 80 90 100 e le c tr ic a l r e si st iv it y ( i n k o h m -c m ) sample id 28d 56d 90d 0 10 20 30 40 50 60 70 80 90 100 e le c tr ic a l r e si st iv it y ( i n k o h m -c m ) sample id 28d 56d 90d 10 kaura et al., j. build. mater. struct. (2023) 10: 1-15 between atmospheric co2 and hydration product of cement primarily portlandite, calcium silicate hydrate. as the alkalinity of concrete reduces stability of the passive layer gets jeopardized. under such circumstances when passive layer gets breakdown, process of corrosion gets initiated. since, carbonation induced corrosion affects the serviceability of rcc structure. therefore, it becomes necessary to study the factors that govern the rate of progress of carbonation front and leads to premature determination. as reported in various literature, parameters like grade of concrete, watercement ratio, type of cement as well as supplementary cementitious material (scm) used are the same of the instrinc factors influencing the rate of carbonation whereas environmental parameters like relative humidity, temperature, number of raining and sunshine period govern not only the ingress role of carbonation front in the concrete but also play a decisive role in the process of corrosion (arora and singh, 2017; kaura et al., 2019; 2022; anjos et al., 2020; ojha et al., 2021; 2022-a; 2022-b; saouma, 2020; malvar et al., 2002; is-456, 2000; singh et al., 2021; patel et al., 2020). in the present research work, factors like water binder ratio, role of fly addition had been studied. the study had been carried out at relative humidity level of 65+ 5%, temperature of 27+ 2oc and concrete beam specimens were exposed to carbonation (co2 level kept as 4+ 0.5% by vol.) for an exposure period of 70 days, 140 days and 210 days. the test results of accelerated carbonation are shown in figure 16 and figure 17. the carbonation depth of control mixes were 3 to 5 times lower than the high volume flyash concrete mixtures. in case of high volume flyash concrete mixtures, as the flyash content increases there had been increase in the depth of carbonation. therefore, it can be concluded that high volume flyash concrete mixture had a significant higher rate of carbonation when compared to control mix. this also indicates that resistance offered by the high volume flyash concrete mixtures is low. there are three possibilities due to which high volume flyash concrete mixtures show higher depth of carbonation. firstly, flyash substitutes portland cement clinker (a source of ca(oh)2) that results into lower alkalinity level. secondly, during the pozzolanic reaction, flyash consumes the portlandite formed during the hydration process of portland cement clinker that will further depletes the alkalinity level. it means higher the amount of flyash in concrete lower will the portlandite content which result into reduced alkalinity. thirdly, it is quite evident that for flyash to react, availability of portlandite is must and if all the (ca(oh)2 gets consumed during the pozzolanic reaction, presence of any unreacted flyash will serve only as a filler material. since, flyash is used as a replacement to portland cement clinker, under such condition, the microstructure of flyash mix will be more porous. fig.14. volume of permeable voids at w/b 0.60 fig. 15. volume of permeable voids at w/b 0.40 0 2 4 6 8 10 12 14 28 56 v o lu m e o f p e rm e a b le v o id s ( % ) no of days c1/0.60 m1/0.60/30% m2/0.60/35% m3/0.60/40% m4/0.60/50% 0 2 4 6 8 10 12 14 28 56 v o lu m e o f p e rm e a b le v o id s ( % ) no of days c2/0.40 n1/0.40/30% n2/0.40/35% n3/0.40/40% n4/0.40/50% kaura et al., j. build. mater. struct. (2023) 10: 1-15 11 fig. 16. accelerated carbonation depth at w/b 0.60 fig. 17. accelerated carbonation depth at w/b 0.40 alkali silica reaction involves chemical reaction between alkali (source generally cement) and reactive silica (source, generally aggregate) in the presence of moisture results in to the formation of a gel that swells or shrinks depending upon the availability of moisture. such type of chemical form of attack is quite common in hydraulic structures (ojha et al., 2021-a; 2021-b; 2021-c; malvar et al., 2002; is -456, 2000; singh et al., 2021, patel et al., 2020, singh et al., 2020-a; arora and singh, 2016, arora et al., 2019-a; 2019-b; ojha et al., 2020; ojha et al., 2022, arora et al., 2016). in order to avoid asr, it had been advised to restrict the limit of cement alkalis to 0.60% (by mass). further, certain standards like is: 456 (2020) suggests that to mitigate asr, addition of flyash up to 25% is advantageous when used along with low alkali portland cement (na2o equivalent ≤0.60 %). generally, use of low portland cement is not a cost effective solution to manage the asr problem. the present study had been carried out at 30%, 35%, 40% and 50% flyash content as per astm c1567. the test results are shown in figure 18. from the study, it can be concluded that addition of flyash is beneficial for controlling asr. as the flyash content increases, maximum up to 40%, there had been decreased in the value of % expansion. indeed, with further increase in flyash content i.e. at 50% replacement level, a sudden increase in the % expansion has been observed. this may be attributed to the increase in the porosity which had resulted into a less dense microstructure in comparison to other flyash blends. however, % expansion at 50% flyash content is still significantly lower than that of control mix. fig. 18. asr expansion 0 5 10 15 20 25 30 35 40 45 0 30 60 90 120 150 180 210 c a rb o n a ti o n d e p th i n m m exposure period in days c1/0.60 m1/0.60/30% m2/0.60/35% m3/0.60/40% m4/0.60/50% 0 5 10 15 20 25 30 35 40 45 0 100 200 300 c a rb o n a ti o n d e p th i n m m exposure period in days c2/0.40 n1/0.40/30% n2/0.40/35% n3/0.40/40% n4/0.40/50% 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 control 30 % fly ash 35 % fly ash 40 % fly ash 50 % fly ash a s r e x p a n si o n ( i n % ) sample id 12 kaura et al., j. build. mater. struct. (2023) 10: 1-15 4. conclusions the outcome of the study are as follows: i. parameters like water -binder ratio, flyash content and age of testing/ maturity age had a significant influence over test value. ii. in terms of mechanical behaviour, high volume flyash concrete mixes had shown promising results at later ages. high volume flyash concrete mixes designed at water binder of 0.40 with flyash content up to 40 % had shown strength characteristics comparable to that control mix. however, high volume flyash concrete mixes designed at higher water-binder i.e. 0.60 did not yield encouraging results. it was quite evident from the test results that strength characteristics of high volume flyash concrete mix made with 50% flyash content was remarkably lower than that of all other concrete mixtures. iii. for a chloride rich environment, durability aspect of high volume flyash concrete mixes, when evaluated through tests like rapid chloride penetrability test (rcpt), non-steady state chloride migration test, bulk conductivity test, electrical resistivity test was far superior than that of control mixes. high volume flyash concrete mix designed at 40% flyash content had shown exemplarily performance in comparison to other high volume flyash concrete mixes as well as control mixes. iv. durability aspect of high volume flyash concrete mixes when subjected to carbonation was not found encouraging. from the test results, it was quite apparent that carbonation front in high volume fly ash concrete mixtures were progressing at a very faster pace in comparison to the control mix. flyash content was found to the most significant parameter influencing the rate of carbonation. v. asr study had been carried out using reactive aggregates. the test results show that high volume flyash concretes mixes had better resisting ability to mitigate problem of asr. mortar bar expansion test carried out in accordance to astm c1567 indicates that 40% flyash content is an optimum amount. 5. references aggarwal, v., gupta, s.m., & sachdeva, s.n. (2010). concrete durability through high volume fly ash concrete (hvfc) a literature review’ international journal of engineering science and technology, 2(9), 4473-4477. ahmed, a., john, k., jonida, p., fraser, h., & heni. f. (2019). chemical reactions in pozzolanic concrete. mod. approaches mater. sci, 1, 125-137. andrade, c., & alonso, c. (2004). test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method. materials and structures, 37(9), 623-643. anjos, m. as., aires, c., pedro, c., givanildo, a. a., & ruan, l.s.f. (2020). effect of high volume fly ash and metakaolin with and without hydrated lime on the properties of self-compacting concrete. journal of building engineering, 27, 100985. arora, v. v., & singh, b. (2016). durability studies on prestressed concrete made with portland pozzolana cement, indian concrete journal, 90(8), 41-48. arora, v. v., singh, b., & patel, v. (2019-a). durability and corrosion studies in prestressed concrete made with blended cement, asian concrete federation journal, 5 (1), 15-24. kaura et al., j. build. mater. struct. (2023) 10: 1-15 13 arora, v. v., singh, b., patel, v., daniel, y. n., & mohapatra, b.n. (2019-b). stress–strain behaviour and performance evaluation of high strength steel fibre reinforced concrete” indian concrete journal, 93 (12), 54-61. arora, v.v., & kaura, p. (2014). durability testing of blended cementrelationship between accelerated tests & long term tests. 2nd international congress on durability of concrete, 4-6th december, new delhi, india. arora, v.v., & kaura, p. (2015). durability test methods for service life design of concrete structures – exposed to semi-arid environment”. 14th ncb international seminar, delhi, india. arora, v.v., & kaura, p. (2016). durability design for concrete structure in india (rcc and prestressed). world conference on concrete, 18th may, pragati madan, delhi, india. arora, v.v., & kaura, p. (2017-a). service life design of concrete structures subjected to carbonation”. oneday seminar on durability and service life design of concrete structures, 7th april, ballabagrh, haryana, india. arora, v.v., & kaura, p. (2017-b). suitability of accelerated test methods as a tool for service life prediction for rc structures made of ordinary portland and blended cement.71st rilem annual week & icacms 2017, 3rd – 8th september, chennai, india. arora, v.v., & singh, b. (2017). use of fly ash concrete and recycled concrete aggregates: a cost effective solution and durable option for construction of concrete roads, indian concrete journal, 91 (1) arora, v.v., kaura p., & sharma, s. (2017-b). durability of concrete made with blended cement against reinforcement corrosion. ncb symposium on blended cement for sustainable development, 24 january, ncb-hyderabad, india. arora, v.v., sharma, s., kumar s., & kaura, p. (2017-a). need based advancements in making concrete pavements. international conference on concrete pavements, august, san antonio, texas usa. arora, v.v., singh, b., & yadav, l. (2016). study on flexural and fatigue behaviour of prestressed concrete made with portland pozzolana cement, asian concrete federation journal, 2 (1), 15-23. arora, v.v., singh, b., patel, v., & trivedi, a. (2021). evaluation of modulus of elasticity for normal and high strength concrete with granite and calc‐granulite aggregate,” structural concrete, 22 (s1), doi: 10.1002/suco.202000023 azarsa, p., & gupta, r. (2017). electrical resistivity of concrete for durability evaluation: a review." advances in materials science and engineering. cea (2022). central electricity authority report (2021-2022). chen, how-ji., neng-hao s., chung-hao wu., & shu-ken, lin. (2019). effects of the loss on ignition of fly ash on the properties of high-volume fly ash concrete. sustainability, 11(9), 2704. is 269 (2015). ordinary portland cement–specification, bureau of indian standards, new delhi. is 3812: part-1 (2013). pulverized fuel ash-specification, bureau of indian standards, new delhi. is: 383 (2016). coarse and fine aggregate for concrete-specification, bureau of indian standards, new delhi. is: 456 (2000). plain and reinforced concrete-code of practice, bureau of indian standards, new delhi. jo jacob, r., & jino j. (2014). strength study of high volume fly ash concrete with fibers, intl. journal of advanced structures and geotechnical engineering, 3(1). kaura, p., arora, v.v., & mohapatra, b.n. (2019). service life design of rc structures prone to carbonation using accelerated test methods”. 15th international congress on the chemistry of cement, 16-20th september 2019, prague. kaura, p., ojha p. n., & jain, h. (2022). mechanical and durability performance of portland limestone cement (plc) made with intergrinding having high fineness limestone in concrete. 17th ncb international conference on cement, concrete and building materials, 6-9 december 2022, new delhi, india 14 kaura et al., j. build. mater. struct. (2023) 10: 1-15 kumar, m., kumar, a.s., & kujur, j. (2021). mechanical and durability studies on high‐volume fly‐ash concrete. structural concrete, 22, e1036-e1049. malhotra, v.m., & mehta, p.k. (2002). high-performance, high-volume fly ash concrete, supplementary cementing materials for sustainable development, inc., ottawa, canada, 101. malvar, l.j., cline, g d., burke, d.f, rollings, r., sherman, t.w., & greene, j l. (2002). alkali-silica reaction mitigation: state of the art and recommendations. materials journal. 99 (5), 480-489. mehta, p.k. (2004). high-performance, high-volume fly ash concrete for sustainable development." in proceedings of the international workshop on sustainable development and concrete technology, 3-14. ames, ia, usa. obla, k. h., colin l.l., & haejin k. (2012). the 2012 nrmca supplementary cementitious materials use survey. concrete in focus, 16-18. ojha, p. n., kaura, p., kumar, s., jain, h., singh, b., & mittal, p. (2022). design of low carbon high performance concrete incorporating ultrafine materials." sustainable structures and materials-an international journal, 5(1), 1-12. ojha, p. n., mittal, p., singh, a., singh, b., & arora, v.v. (2020). optimization and evaluation of ultra-highperformance concrete. asian concrete federation journal, 6(1), 26-36. ojha, p. n., singh, b., kaura, p., & satyakam, r. (2022). ash utilization strategy in india—a way forward. in advances in sustainable materials and resilient infrastructure, 145-157. springer, singapore. ojha, p. n., singh, b., prakash, s., singh, p., mandre, m. k., & kumar, s. (2022-b). effect of high ratio fly ash on roller compacted concrete for dam construction. research on engineering structures and materials. https://doi.org/10.17515/resm2022.374ma1216 ojha, p. n., singh, b., singh, p., singh, a., & mandre, m. k. (2022-a). study on effect of flyash and limestone powder on compressive strength of roller compacted concrete for dam construction. journal of asian concrete federation, 8(1), 37-50. ojha, p.n., singh, a., & singh, b. (2021-b). experimental investigations on substitution of natural sand in concrete with copper slag and blast furnace slag, journal of asian concrete federation, 7(1), 1-11. ojha, p.n., singh, b., kaura, p., & singh, a. (2021-c). lightweight geopolymer fly ash sand: an alternative to fine aggregate for concrete production”. res eng struct mater, 7(3), 375-392. ojha, p.n., trivedi a., singh b., n s ak., patel v., & gupta, rk. (2021-a), high performance fiber reinforced concrete – for repair in spillways of concrete dams. res eng struct mater. 7(4), 505-522. https://doi.org/10.17515/resm2021.252ma0128 park, b,, & young cheol, c. (2021). hydration and pore-structure characteristics of high-volume fly ash cement pastes. construction and building materials, 278, 122390. patel, v., singh, b., & arora, v.v. (2020). study on fracture behaviour of high strength concrete including effect of steel fiber. indian concrete journal, 94(4): 1-9. polder, r.b. (2001). test methods for on-site measurement of resistivity of concrete—a rilem tc-154 technical recommendation. construction and building materials 15 (2-3), 125-131. poon, c., lam, l., & wong, y. (2000). a study on high strength concrete prepared with large volumes of low calcium fly ash. cem concr. 30(3), 447–455. https://doi.org/10.1016/s0008-8846 (99)00271-9. saouma, v.e. (2020). diagnosis & prognosis of aar affected structures: state-of-the-art report of the rilem technical committee 259-isr. 31. springer nature. sen, d., zhao, q., & shi, x. (2021). high-volume fly ash-based cementitious composites as sustainable materials: an overview of recent advances." advances in civil engineering. siddique, r. (2004). performance characteristics of high-volume class f fly ash concrete. cem concr res. 34(3), 487–493. https:// doi.org/10.1016/j.cemconres.2003.09.002. singh, b., arora, v. v., & patel, v. (2020-b). experimental study on stress strain behaviour of normal and high strength unconfined concrete. indian concrete journal, 94(4), 10-19. https://doi.org/10.17515/resm2022.374ma1216 https://doi.org/10.1016/s0008-8846 kaura et al., j. build. mater. struct. (2023) 10: 1-15 15 singh, b., ojha, p. n., trivedi, a., patel, v., & arora, v.v. (2021). development of empirical equations for prediction of flexural and split tensile strength for normal and high strength concrete with granite and calc-granulite aggregate, indian concrete journal, 95(11), 36-46 singh, b., patel, v., ojha, p. n., & arora, v. v. (2020-a). analysis of stress block parameters for high strength concrete,” journal of asian concrete federation, 6(1), 1–9. sun, j., xiaodong, s., gang, tan., & jennifer, e.t. (2019). compressive strength and hydration characteristics of high-volume fly ash concrete prepared from fly ash." journal of thermal analysis and calorimetry, 136 (2), 565-580. j. build. mater. struct. (2020) 7: 255-261 original article doi : 10.34118/jbms.v7i2.775 issn 2353-0057, eissn : 2600-6936 experimental investigation of the effect of sisal fiber on the partially replaced cement with groundnut shell ash in concrete sani j e*, afolayan j o, wilson u n, eze oc, nyeri j abstract. an investigation on the effect of sisal fiber on the partially replaced cement with groundnut shell ash in concrete was carried out. sisal fiber of 3.5cm length which forms 1% of the mix by weight with groundnut shell ash as a partial replacement for cement was used in preparing the concrete specimen. compressive strength test was carried out using 0%, 5%, 10%, 15%, 20%, 25% and 30% of groundnut shell ash as replacement of cement at different curing ages of 7, 14, 21 and 28 days. it was observed that at 7 and 14days of curing, it is needless introducing the gsa since the maximum compressive strength obtained were at 0% gsa. at 21 and 28days of curing, a considerable increase in compressive strength was observed for 5% and 10% of gsa. however, 5% of gsa can be regarded as the optimum content since it gives the maximum compressive strength value of 30.1n/mm2 at 28days of curing. this is followed by 10% replacement of gsa yielding 28.10n/mm2 and then 0% gsa replacement yielding 25.01n/mm2. key words: sisal fiber, groundnut shell ash (gsa), compressive strength, curing ages, concrete. 1. introduction the use of cement for construction in developing countries cannot be overemphasized. also, the incessant increase in the price of portland cement is attributable to possible overwhelming rate of demand in the construction industries. this has consequently compelled researchers to search for total or partial alternative building materials among several pozzolanic materials. buari et al., (2013) describes groundnut shell ash (gsa) as a good pozzolanic material which reacts with calcium hydroxide forming calcium silicate hydrate. the specific gravity of the gsa was found to be less than that of the ordinary portland cement (opc) it replaced, this means that a considerable greater volume of cementitious materials will result from mass replacement of the opc with the gsa. the investigation also showed that the compressive strength value of the gsa-opc blended concrete at 10% replacement level performed better and would be acceptable and considered as a good development for construction of masonry walls and mass foundations in low cost housing in nigeria. olutoge et al., (2013) investigated the characteristics strength and durability of gsa blended with cement concrete in sulphate environments. from the result of the tests and analysis carried out, it was deduced that the groundnut shell ash blended with cement concrete has a proven resistance to magnesium sulphate, sodium sulphate and calcium sulphate media and would exhibit a better performance in soils containing these media (mgso4, na2so4, caso4.). it was also observed that there was a decrease in slump value with increase in gsa replacement which is reflective of the fact that gsa can reduce the consistency and ultimately, the workability of concrete. alabadan et al., (2006) having used higher percentage of gsa reported that there is a decrease in the compressive strength of concrete produced as the percentages of gsa increases resulting in maximum strength of 16n/mm2 at 28 day of curing for 70%/30% replacement. likewise, mujedu. and adebara (2016) also carried out the experimental investigation using gsa as partial replacement in concrete varying the percentage from 0% to 75%, at intervals of 15%. the results presented showed that 15% gsa replacement produced concrete of 20.10n/mm2 compressive strength at 28 days of curing. similarly, ikumapayi (2018) worked on gsa as partial replacement of cement department of civil engineering, nigerian defence academy, kaduna, nigeria. * corresponding author: jesani@nda.edu.ng received: 25-08-2020 accepted: 05-12-2020 mailto:jesani@nda.edu.ng 256 sani et al., j. build. mater. struct. (2020) 7: 255-261 in concrete using lower percentage of replacement from 0% to 16%. he reported that 4% replacement produced 16n/mm2 strength of concrete after 28days of curing. it is important to mention that the limitations inherent in concrete as a building material for example, being poor or weak in tension, is also a reason for the litany of researches for how else it can be improved other the use of steel rods to reinforce it or complement its tensile strength. many researches have been carried out in order to investigate the effect of addition of fibers on many strength properties of concrete such as tensile strength, compressive strength and flexural strength. researches into the types of fibers to be used in concrete applications have been intensified since the 1950s alongside researches on the improvement of the composite materials technologies. various types of fiber materials such as steel, carbon, glass, plastic, polypropylene, nylon, and cotton were tested. from the results of these researches, american concrete institute’s (aci) committee 544 (2002) classified fiber reinforced concrete into four groups based on the fiber materials: steel fiber reinforced concrete (sfrc), glass fiber reinforced concrete (gfrc), synthetic fiber reinforced concrete (snfrc), and natural fiber reinforced concrete (nfrc). synthetic fibers such as polyester, acrylic, polyethylene and polypropylene are further subdivided into microsynthetic fibers (for diameter less than 0.30 mm) and macrosynthetic fibers (for diameter greater than 0.30 mm). glass and natural fibers show vulnerability to temperature variation and environmental conditions, respectively, leaving steel and synthetic fibers as the most viable concrete reinforcement options. the focus of this experimental investigation is to establish the effect of sisal fibre on the properties of harden concrete partially replaced with groundnut shell ash. having taking into consideration the experimental results of other researchers using gsa as partial replacement of cement in concrete without addition of sisal fibre. 2. materials and methods 2.1. materials used for the experiment the major materials used for this research work include the following fine aggregate, coarse aggregate, cement, sisal fiber, ground nut shell ash and clean water. 2.1.1. fine aggregate fine aggregate sample was obtained from tipper garage at sabon yelwa chikun lga kaduna, kaduna state. it free from silt and debris that can inhibit the strength development of concrete. the coefficient of absorption of the fine aggregate used was 1% and the fineness value was 2.2 which indicate that it good for concrete since is not up to 3.2 value which is not suitable for concrete material. the maximum size of the fine aggregate is sizes less than 4.75mm. 2.1.2. coarse aggregate crushed granite gravel having the minimum size of 7mm and maximum size of 12mm was chosen as the coarse aggregates, sample is obtained from tipper garage at sabon yelwa chikun lga kaduna, kaduna state. 2.1.3. cement ordinary portland cement of 53grade (astm c150 type i (2020)) with specific gravity of 3.25 was used for preparing the concrete mix. the cement used have the fineness of 3.65% which is below the value of 10% as specified by bs 4550: part 3 (1978) which stated that percentage of cement sample retained on 45, 90 band 300 micro meters sieve should not exceed 10%. sani et al., j. build. mater. struct. (2020) 7: 255-261 257 2.1.4. sisal fibre sisal fiber sample was obtained from tudun wada market, kaduna south lga kaduna, kaduna state. it was cut into 4cm length. the sample of the sisal fibre used in this study is presented in figure 1. the results of the research work carried out by sani et al., (2017) on the properties of sisal fibre was adopted for this investigation as presented in table 1. fig. 1. sample of sisal fibre. table 1. properties of the sisal fibre, (sani et al., (2017)) property quantity natural humidity % 14.48 average diameter, mm 0.13 water absorption, % 340 specific gravity 0.22 tensile strength of 1 strand n/mm2 10.60 tensile strength of 2 strands n/mm2 24.45 tensile strength of 3 strands n/mm2 30.60 elongation at break, mm 5.58 colour shiny white 2.1.5. groundnut shell groundnut shell sample is obtained from television market kaduna south lga kaduna, kaduna state. the groundnut shell was sun dried and put in the open drum and burnt in ashes. this was grinded and sieved with 25mm micro sieve. the sample of groundnut shell burnt to obtain the ash is shown in figure 2 and the chemical composition of the groundnut shell ash (gsa) is as shown in table 2 and it has the fineness of 7.8%. table 2. chemical composition of groundnut shell ash (gsa) oxide percentage composition opc (bs 12 ranges) sio2 24.32 1725 al2o3 5.31 38 fe2o3 1.01 0.56.0 cao 8.93 6067 mgo 5.34 0.14.0 258 sani et al., j. build. mater. struct. (2020) 7: 255-261 fig. 2. sample of groundnut shell 2.2. methods the mix proportion of 1:2:3 was adopted using a mould size of 100x100x100mm. the mix proportion by mass constituted 3.63kg of cement, 7.27kg of fine aggregate (sand) and 11.76kg of coarse aggregate with a water-cement ratio of 0.65. adequate mixing was done in order to produce a cement mortar of homogenous consistency as seen in figure 3. the concrete was first cast with 0% gsa, this is to serve as a control. groundnut shell ash was then introduced as partial replacement of cement using 5%, 10%, 15%, 20%, 25% and 30% with sisal fiber of 3.5cm length subsequently introduced of up to 1% of the concrete cube. a thin film petroleum jelly was used to the clean mould and also the contact surfaces of the bottom of the mould. after placing the concrete in the mould, the concrete was compacted using a rammer or tampering rod for 25 blows in 3 different layers. the cast cube in the mould was covered with an impervious sheet and allowed to set at room temperature for 24 hours. the concrete cube was removed from the mould, marked for identification and immersed in clean water for curing. the concrete cubes were tested at 7days, 14days, 21days and 28days of curing without fiber and 0% of gsa content to serve as control. other concrete specimen were prepared containing 1% sisal fiber as recommended by sani et al., (2019) of average 3.5cm length being added and the cement content being replaced partially with groundnut shell ash at 5%, 10%, 15%, 20%, 25% and 30% . the cubes were then tested at 7days, 14days, 21days and 28days of curing. a slump test was also carried out for all the varied proportions containing gsa replaced with cement. fig. 3. some procedures in the experiment sani et al., j. build. mater. struct. (2020) 7: 255-261 259 2.2.1. statistical analysis statistical analysis was carried out on results obtained using analysis of variance (anova) with the microsoft excel analysis tool pak software package to determine the levels of significance of the effect of sisal fiber on partially replace cement with groundnut shell ash in concrete. 3. results and discussion from the slump test carried out, the following results can be observed as seen in figure 4. from the relationship between the percentage groundnut shell ash and the slump value, it can be deduced that the increase in the groundnut shell ash reduces the consistency and ultimately the workability of the concrete produced. this is traceable to the fact that increase in percentage addition of gsa requires higher water /cement ratio to produce a workable concrete without adding any water reducing agent. fig. 4. relationship between slump value and the gsa percentages it was observed that the inclusion of groundnut shell ash and sisal fiber in a concrete increased the compressive strength of concrete and the highest value of compressive strength was obtained at 5% replacement of gsa in a sisal fiber-reinforced-concrete as seen in figure 5. significant increase in the compressive strength is recorded in 21 and 28 days of curing whose peaks are at 5% replacement in fiber reinforced concrete. this is different from other research findings whose assertion that 10% replacement level performs better and would be acceptable and considered as a good development for construction of masonry walls and mass foundations in low cost housing in nigeria. the 5% optimal replacement arrived at in this research is apparently owing to the sisal fibre introduced. two-way analysis of variance (anova) two way analysis of variance tests was carried out to determine the level of significance of the effect of sisal fiber on partially replace cement with groundnut shell ash in concrete and also the level of significance of the influence of curing age(days) on the compressive strength of the concrete. table 3 shows the result of the two way analysis of variance. the two-way analysis of variance (anova) for compressive strength of gsa replaced cement cured at different curing age (see table 3) shows that the effect of gsa and curing period (days) on the compressive strength of concrete were statistically significant (fcal = 31.06699> fcrit = 2.661305) for gsa 0 10 20 30 40 50 0 5 10 15 20 25 30 s lu m p v a lu e gsa content (%) 260 sani et al., j. build. mater. struct. (2020) 7: 255-261 replaced cement and (fcal = 129.459> fcrit =3.159908) for curing age (days). the effect of curing age (days) was more pronounced than that of gsa replace cement. fig. 5. compressive strengthconcrete age relation table 3. two-way analysis of variance results for compressive strength of gsa replaced cement at different curing age (days). summary count sum average variance 0% gsa 4 83.99 20.9975 14.96602 5% gsa 4 92.02 23.005 45.57903 10% gsa 4 82.78 20.695 47.03663 15% gsa 4 72.18 18.045 36.33097 20% gsa 4 65.28 16.32 41.66947 25% gsa 4 57.61 14.4025 28.61603 30% gsa 4 52.11 13.0275 23.45023 7 days 7 84.8 12.11429 9.504662 14 days 7 101.2 14.45714 17.93752 21 days 7 151.38 21.62571 12.50953 28 days 7 168.59 24.08429 19.8152 anova source of variation ss df ms f p-value f crit gsa 327.0224 6 54.50373 31.06699 1.49e-08 2.661305 curing days 681.366 3 227.122 129.459 2.27e-12 3.159908 error 31.57909 18 1.754394 total 1039.967 27 4. conclusion and recommendation from the results of the study, it can be concluded that groundnut shell ash used as partial replacement for cement with 1% of sisal fiber can significantly increase the compressive strength of a concrete. the compressive strength obtained between 5%, 10% and 15% at 21 and 28 days of curing are satisfactory however, 5% replacement of cement with gsa yields the highest compressive strength value and can hence be regarded as the optimal gsa content required for a sisal-reinforced-concrete. the strength at 10 15% groundnut shell ash replacement at 28 days of curing satisfies bs 4550 part 3 section 3.4 requirements hence, the use of sisal fiber of up to 1 % of the weight of concrete and 10% 15% of replaced cement with sani et al., j. build. mater. struct. (2020) 7: 255-261 261 gsa at 28 days of curing provides compressive strength that is adequate and therefore can be recommended for mass concrete production. 5. references aci committee 544 (2002). design considerations for steel fiber reinforced concrete, aci 544.4r-88. american concrete institute, aci farmington hills alabadan, b. a., njoku, c. f., & yusuf, m. o. (2006). the potentials of groundnut shell ash as concrete admixture. agricultural engineering international: cigr journal. manuscript bc 05 012, vol. viii. astm c150: (2020). standard specification for portland cement, american society for testing and materials. bs 4550 part 3 (1978): method of testing cement, british standard institution, milton keynes, london. buari, t. a., ademola, s. a., & ayegbokiki, s. t. (2013). characteristics strength of groundnut shell ash (gsa) and ordinary portland cement (opc) blended concrete in nigeria. iosr journal of engineering (iosrjen), 3(7), 1-7. ikumapayi, c. m. (2018). properties of groundnut shell (arachis hypogaea) ash blended portland cement. journal of applied sciences and environmental management, 22(10), 1553-1556. mujedu, k. a., & adebara, s. a. (2016). the use of groundnut shell ash as a partial replacement for cement in concrete production''. international journal of sciences, engineering and environmental technology (ijoseet), 1(3), 32-39. olutoge, f. a., buari, t. a., & adeleke, j. s. (2013). characteristics strength and durability of groundnut shell ash (gsa) blended cement concrete in sulphate environment. international journal of scientific and engineering, 4(7), 2122-2134. sani, j. e., afolayan, j. o., chukwujama, i. a., & yohanna, p. (2017). effects of wood saw dust ash admixed with treated sisal fibre on the geotechnical properties of lateritic soil. leonardo electronic journal of practices and technologies, (31), 59-76. sani, j. e., hadiza, a. and rintong, i. b. (2019). effect of inclusion of randomly oriented jute fibre reinforcement on the compressive strength of concrete. nigerian building and road research institute international conference series. theme: construction practices in nigeria: issues, prospects & solutions 2 – 4 july, naf conference centre, kado, abuja, nigeria, book of abstracts, p. 37. j. build. mater. struct. (2020) 7: 1-18 review article doi : 10.34118/jbms.v7i1.73 issn 2353-0057, eissn : 2600-6936 design and construction criteria of twin tunnel: taking an adverse wind condition effects on air pollution short circuit at tunnel portals as a case miloua h department of mechanical engineering, laboratory of structures mechanics and solids lmss, faculty technology, university djillali liabes sidi bel abbes 22000 algeria, phone:+213772397141. orcid.org/00000003-1845-5591 corresponding author: miloua_hadj@yahoo.fr received: 14-10-2019 accepted: 07-01-2020 abstract: this paper aims to study the influence of the tunnel portal designs, wind conditions and ventilation rate on the amount of air pollution short circuit from one tunnel tube to the other. these effects are investigated by computational fluid dynamics (cfd) code used a large eddy simulation (les) method to control air quality inside the tunnel and reduced as far as possible a short circuited (flow recirculation) flow level. a validation of cfd code to experimental data in 1:100 scale model of the road traffic tunnel tested in windtunnel showed that the cfd gave satisfactory prediction of the air pollution short circuit in the vicinity of tunnel portal. the predicted concentration of the gas tracer (co2) used as the safety criterion provide the useful information about a short circuit amount resulted for each structural variant of tunnel portals, such as a central dividing wall built as extensions from the end of road tunnel and offset tunnel portal entrance exit tested under different speed ratio ⁄ of wind and ventilation. a detailed look at results is beyond the scope of analysis to determine optimal air pollution short circuit percentages. finally, the perfect tunnel portals geometry can be suggested. key words: air pollution, tunnel portals, wind, ventilation, cfd. 1. introduction ventilation and fire safety design in road tunnels under external wind effect are one of the most complexes issues that need to be carefully considered and analyzed in the designing stage of any tunnel project. road tunnels create an enclosed space around vehicles where emissions from the vehicles can build up to unacceptable levels without an engineered ventilation system which can be required for dilution emissions by providing fresh air and then removing the exhaust air from the tunnel. most of the road tunnels were designed as a twin tube equipped with longitudinal ventilation system in each traffic direction. the disadvantage of this system of ventilation reported by kashef et al. (2003) is that adverse wind conditions maybe short-circuit the flow from the exhaust tube to the nearby tube, causing the contamination of fresh in supply tube. two portals designs can be used to reduce greatly a flow recirculation: an offset head of one tube relative to another “offset tunnel portal entrance exit”, or more simply, to use a “central dividing wall” at sufficient height built as extensions from the ends of tunnels beyond by staggering the portals longitudinally. futoshi tanaka et al. (2016) investigated the interaction between exhaust jet and wind using a 1:12 scale model tunnel was conducted to evaluate effects of a transverse external wind on the performance of roof openings in fire tunnel. muhič and mazej (2014) clearly indicated the negative effect of external wind in the case of a longitudinally ventilated road tunnel. two different models for the dispersion of tunnel exhausts are developed by oettl et al (2013) to simulate the dispersion of pollutants in the vicinity of road tunnel portals. a testing ventilation system of close tunnel model was established by tan et al. (2015) is intended to provide drivers 2 miloua h., j. build. mater. struct. (2020) 7: 1-18 and passengers with an adequate supply of oxygen and to dilute toxic gases emitted from vehicles to safe concentrations, ventilation systems, such as jet fans and exhaust shafts. a full scale fire tunnel has been presented by yousaf et al. (2014) divided a recirculation to three subphenomenon: the emission, the transmission and the nuisance caused by the smoke. gehrig et al. (2013) study the relation between the smoke source and the tunnel users. the remaining threats to tunnel users are the loss of visibility and of possible intoxication. there are some experimental works (baumann, 1979; chock, 1982) which considers as the earliest on flow recirculation issues involved laboratory scale testing the impact of polluted tunnel exhausts in urban area. the most notable work that done by koopmans (2005) was determinate the amount of air pollution short circuit in a scale-model (1:150) of the tunnel tested with structural variants for the tunnel portals and wind conditions. the technical, architectural and landscape aspects of tunnel portal design are analyzed by peila and pelizza (2002) they provide a systematic comparison of different architectural solutions to force designers to better integrate infrastructure with the environment. brousse et al. (2005) have studied the impact of the background pollution and evaluation of the tunnel exhausts on air quality. yang et al. (2012) study the effect of structural factors on waste gas cross flowing around portal of highway tunnels. there are results obtained by measurements on aeraulic mock-ups (gourdol, 2004). these measurements were made in wind tunnel involved a detailed description of the tests. the measurement were made for a tunnel (or cut-and-cover tunnel) opening into a cutting. an experimental investigation in a wind tunnel described by mirzai et al. (1994) provided some data about the influence of the wind direction of on flow and dispersion of pollutants around small building. also, nadel et al. (2003) use of wind tunnel testing to develop air rights structures over tunnel exit portals. lim and ohba (2015) studies through wind tunnel experiments and a detached eddy simulation a wind flows by variations of direction around rectangular prisms with different sizes. a series of wind-tunnel tests the vertical variation of wind directions were investigates (weerasuriya et al., 2016; li et al., 2016) (i.e., the so-called 'twist effect'). les (large eddy simulation) has been successfully applied to some several airflows related to buildings (davidson and nielsen, 1996; murakami, 1998; dagnew and bitsuamlak, 2013) reviews the up to date state of the art in the numerical evaluation of wind loads on buildings. important aspects of numerical modeling including a turbulence modeling, inflow boundary conditions, ground surface roughness, near wall treatments, and quantification of wind loads using the techniques of computational fluid dynamics (cfd) were summarized. relative advantages of large eddy simulation (les) over reynolds averaged navier-stokes (rans) and hybrid rans-les over les were discussed. overall les based simulations seem suitable for wind load evaluation in tall building by computing large vortices as distinct flow fields and small vortices within the size of the mesh are modeled in terms of the local mean mesh model (dagnew and bitsuamlak, 2014). an admirable paper of lipecki and flaga (2013) presents theoretical background for a semi-empirical, mathematical model of critical vortex excitation of slender structures of compact cross-sections, demonstrate mathematical background of the vortex excitation model for a theoretical case of the structure section and extrapolate a mathematical model for the application to real structures. a tunnel bi-tube, where each of the tubes a particular direction of the traffic circulation, a problem of flow recirculation can occur at the two head of tunnel. indeed, as shows fig.1, if we take place in one of the heads, the forced ventilation imposes for one of the two tubes a polluted debit of air outlet, while in the nearby tube; it imposes a fresh air inlet. so, it is clear that in the absence of particular precautions, such a configuration can impose to short circuit of the polluted air in the tube with fresh air. if these techniques can be considered a contribution in this field, we can nevertheless regret that no (in any case to our knowledge) results of studies allowing quantifying the efficiency of the device according to its geometrical characteristics (size of the central dividing wall, offset length, etc.). the main objective is to provide and answer to miloua h., j. build. mater. struct. (2020) 7: 1-18 3 the diverse questioning related to this problem and their resolution by two methods: central dividing wall used offset tunnel portal entrance exit: what length is it necessary to offsetting head? what should be the dimensions of the central dividing wall to prevent a short circuit effect? are there any critical dimensions or optimal dimensions and wind conditions for different constructional scenarios? series of tests based on a parametric approach is carried out on a reduced scale model. fig. 1. air pollution short circuit in the vicinity of tunnel portal. this paper is divided into three major sections. section 1 is devoted to a detail discussion about cfd code used named fire dynamics simulator (fds) and a numerical sensitivity of a computational mesh is conducted to get the best degree of grid refinement. the second section describes the previous experimental strategy used during a comparison and validation of obtained numerical results. in section 3 a physical analysis followed through the expected code to offer more understanding about obtainable results. finally, some general issues related to the role of modeling to support sustainable tunnel design are discussed. 2. materials ad methods 2.1. calculation tool and computational domain a. domain size the calculation domain is 60*60*60 cm3 in the x y and z directions respectively (figure 2). the regular eulerian grid contains 300*300*300 grid cells, which gives a cell size of 0.2cm in each direction. this cell size has been chosen after testing that results are insensitive to a further refinement of the mesh (1cm; 0.2cm), the actual grid is appropriate which is belonged to the small geometry taken such as central dividing wall thickness of 1 cm (1 m real) at 1:100 reduced scale tunnel(see fig.2). b. boundary and initial conditions the portals of two tubes (see fig.2.a) and their surrounding sited in the computational domain of 60 × 60× 60cm3 to avoid any numerical influence of boundary conditions. the boundary condition for the three sides of the domain(x=x max, y=y max, z=z max) respectively taken passive opening: ambient temperature, ambient pressure and zero velocity gradients. this set 4 miloua h., j. build. mater. struct. (2020) 7: 1-18 up has been chosen in order to stick as much as possible to experimental condition used by vauquelin and lesueur (1998). about a side (x=0) which involved inlet and outlet sections of discharge and nearby tubes, a constant speeds values (m/s) are set in inlet and outlet sections of discharge and nearby tubes respectively(in opposed direction) for simulating the extractor and supply fans. in the right side of exhaust tube y= y min of computational domain, an entrance wind velocity is fixed to simulate a wind effect. (a) (b) (c) fig. 2. representation of the calculation domain used by cfd and experiment in order of 1:100. miloua h., j. build. mater. struct. (2020) 7: 1-18 5 in order to observe the effect of dimensionless ratio ⁄ where is the wind speed and , the flow velocities in the exit tube (discharge) and entry tube (nearby) = = of 10 m.s-1, 5 m.s-1and 2.5 m.s-1 respectively(see fig.2.b&c). the flow boundary condition for the wind speed is 5 m/s and fixed direction for all tests. the tunnel portal and ground materials are assumed to be perfectly insulated, an adiabatic boundary condition is imposed at the surface, as follows,   0,0 ∂ ∂ t x t s k s (1) at the start of calculation, the temperature is ambient, and the flow velocity is zero everywhere. the initial time step is set automatically by dividing the size of a mesh cell by the characteristic velocity of the flow. the default value of time step is   gh zyx 3 1 5  s, where zyx  ,, are the dimensions of the smallest mesh cell, h is the height of the computational domain, and g is the acceleration of gravity 81.9g m.s-1. during the calculation, the time step is adjusted so that the cfl (courant, friedrichs, lewy) condition is satisfied. every time step, the cfl number is computed in each mesh cell, and the time step, ծt, is adjusted if the maximum value of the cfl number is not between cfl_min and cfl_max, whose default values are 0.8 and 1.0, respectively. note that by default the time step is never allowed to increase above its initial value. resetting the stability parameters is not recommended except in very special circumstances, as they can lead to simulations failing due to numerical instabilities. c. cfd model with the advent of more powerful computers, the computational fluid dynamics (cfd) modeling technique is rapidly expanding. fire dynamics simulator (fds) (mcgrattan et al., 2013) is a cfd model of fire-driven fluid flow. the software solves numerically a form of the navier-stokes equations appropriate for low-speed (low mach number), thermally-driven (buoyant) flow with an emphasis on smoke and heat transport from fires. this cfd is open source and freely available provided by the national institute of standards and technology (nist) of the united states department of commerce. the formulation of the equations and the numerical algorithm are presented in the fire dynamics simulator technical reference guide (mcgrattan et al., 2013). fds consists of two computer programs, the first called simply fds, under a fortran 90. the used version of computer program is fds 6.0 (mcgrattan et al., 2013). the second, called smokeview is an opengl graphics program that allows one to visualize the results. all the input parameters required by fds to describe the particular scenario of interest are conveyed via one or two text files created by the user. fds requires a relatively fast cpu and a substantial amount of random-access memory (ram). computer system used characterized by processor intel ® core (tm) i7 4790@3.6 ghz memory ram 16.0 go. d. sub-grid model the basic idea of large eddy simulation (les) demonstrated by rehm and baum (1978) is to resolve the largest turbulent motions and to filter out the small-scale motions. this is achieved by spatial filtering of the governing equations. a full flow field,  tx,   , is decomposed into a resolved component,  tx,   , and a subgrid-scale (sgs)component,  tx,'   , i.e.,      txtxtx ,',,   . the resolvable component,  tx,   , is obtained from the filtering operation by taking a function  ,'xxg  as the filter kernel:       ',,'-, ∫ xdtxxxtx    (1) 6 miloua h., j. build. mater. struct. (2020) 7: 1-18 where δ is the filter width related to the local mesh configuration by  3 1 zyx  with x  , y  and z  the sizes of a grid cell. eddies of a size larger than  are resolved, smaller eddies are filtered out of the governing equations. this means that the resolved values are computed on a numerical grid, while the unresolved field has to be modelled. applying the filtering operation to each term in the conservation equations of mass, momentum, energy and species, and decomposing the dependent variables ( pwvu ,,, ,etc.) into resolved (the large-scale eddies) and subgrid components (the smallest eddies ) results in the filtered governing equations, shown below: 0 ∂ ∂ ∂ ∂  j j x u t  (2)   sgsiji ij jii g x p x uu t u , .∇ ∂ ∂ ∂ ∂ ∂ ∂    (3) where the bar above the various quantities denotes the filtered variable. the unresolved field,  tx,'   , is modeled by the smagorinsky (1963) in which the sgs reynolds stress tensors, sgsij,  ,are related to the local large-scale rate of strain ijtsgsij su2 ,  and          i j j i ij x u x u s ∂ ∂ ∂ ∂ 2 1 . following the analysis of smagorinsky (1963), the eddy viscosity can be modelled as   ijst sc 2   . here, ij s is the magnitude of the large-scale strain rate tensor, ij s , and sc the smagorinsky constant, lying between 0.1 and 0.21, is set as low as possible to reduce numerical diffusion, taken as 0.1 in this paper. the turbulent heat flux is based on an eddy viscosity assumption, resulting in the following energy equation:   rc jt t jj i qq x h xx hu t h .∇ ∂ ∂ pr ∂ ∂ ∂ ∂ ∂ ∂ '''           (4) we solve in such flows case without any heat addition, the flow is assumed incompressible with a low speed flow. this approximation indicates density is not a function of pressure and temperature. the co2 gas was used as a tracer. the tracer, which exhausted co2 at some fixed rates, was installed in the cross section of discharge tube. a perfect gas equation: ( ) ∑ (5) with : la constant of perfect gas, molar mass of species i (co2 and fresh air ) where t pr denotes the turbulent prandtl number varying from 0.2 to 0.9, and is taken as 0.5 in this work, even though there were no significant changes by using different values in the test data near central dividing wall. the energy equation without fire (inert flow): exclude the rate of heat release per unit volume, ''' c q , and the radiant energy flux, rq.∇ : miloua h., j. build. mater. struct. (2020) 7: 1-18 7   0 ∂ ∂ pr ∂ ∂ ∂ ∂ ∂ ∂           jt t jj i x h xx hu t h  (6) e. method of resolution the finite-difference technique is used to discretize the partial differential equations. this procedure entails the subdividing of the calculation domain into a finite number of cells. the velocities (ui) are taken on the boundary of each cell; and all the scalar variables are taken at cell centres. this staggered grid leads to a very efficient differencing scheme for the equations. all spatial derivatives are approximated by second-order central differences and the flow variables are updated using an explicit second-order runge-kutta scheme. the grid size declared above is the most important numerical parameter in the model, as it dictates the spatial and temporal accuracy of the discretized partial differential equations. the calculations were performed using coherent computational mesh based to the best degree of grid refinement can consider that is particularly adequate and done good convergence with experimental data and required during analysis to observe a small vortex and flow movement near wall (see fig.3). a numerical techniques used to solve the governing equations within a model can be a source of error in the predicted results. the error depends upon the length of the time step δt . if this time step is deemed to be too long to introduce severe uncertainties due to the assumptions, the length of forward stepping of the front is decreased resulting in a shorter time step. all the results from the computer output were time-averaged from 20 s to 2 min chose before a several runs tests with different forward length steps have been performed to ensure convergence. musser et al. (2001) investigated the use of fds for course grid modeling of nonfire and fire scenarios. the results of her study indicate that non-fire simulations can be completed more quickly than fire simulations because the time step is not limited by the large flow speeds in a fire plume. (a) (b) fig. 3. meshed model using a coherent numerical grid:(a) mesh grid of central dividing wall and (b) mesh grid of offset tunnel portal entrance exit 8 miloua h., j. build. mater. struct. (2020) 7: 1-18 2.2. outline of the experiment a series of experiments conducted by vauquelin and lesueur (1998) with mock-up of a 1:100 placed in the subsonic wind tunnel with closed vein, as shown in fig.2, which is assumed to be a part of a tunnel underground. built by two tubes of rectangular cross-section arranged parallel at plane where the wind directed perpendicular (this angle is reported to causing maximum recirculation rate) to the axis of both tubes of tunnel in the direction from the exhausted (discharge) tube to supply tube and tunnel portals vicinity area (width=60cm, depth=60cm, height=60cm) were lined with an insulation board. two identical openings are: discharge tube and nearby tube (height=10.0cm, width=6cm) were employed in the experiments. two fans (in an exhaust and supply tubes) are adjusted by adaptation the pressure loss . a cross-wind was supplied from the rectangular duct, whose dimension was 60cm x 60cm, which is connected to the fan via a honeycomb filter. the values of cross-wind mean the average velocities and these were obtained by dividing the total volumetric flow by the effective area. the wall was placed in such a way that its short side faced the cross-winds. its thickness is fixed at 1 cm (1 m real). in all the experiments described in the following, the co2 gas was used as a tracer. the tracer, which exhausted co2 at some fixed rates, was installed in the cross section of discharge tube. gas co2 is adopted, because it is easy to control the exhaust flow rate. in practice, the fan alimented the exhausted tube were used to pump a mixture of air and co2. note that it was not working with a pure carbon dioxide, initially for reasons of economy, but also and especially to minimize the effects of differences density that have no place to exist for these tests. finally, be noted that the mixture of air + co2 (which represents the stale of air in the exhausted tube) is characterized by passive smoke to carry out systematic visualizations. all tests in the experiment and cfd are carried out in the case where = = . the wind speed and wind direction were kept constants m.s-1 blowing at about 90° to the tunnel axis(speed of wind tunnel). the speed in both tubes is adjusted as to cover three values of the parameter of jet: ⁄ =0 .5 (equal to the half of wind velocity), 1.0 (equal to the wind velocity) and 2.0 (equal to the double of wind). two sets of tests, test i, ii, were conducted were carried out for examining the effect of the cross-winds for short circuit flow. the amounts of short circuit flow (recirculation rate) were calculated under variant portal designs such as "central dividing wall", “offset tunnel portal entrance exit” and variant speed ratio ⁄ where is the wind speed and the flow velocity in the neighboring tube ( and ). in the test i of "central dividing wall", each value of speed ratio ⁄ systematically testing three values of the height h (cm) of central dividing wall h =4 cm (4 m real), h = 06 cm (6 m real) and h = 8 cm (8 m real). also, in each value of h testing five values of wall length l (cm): l = 05 cm (5 m real), l = 10 cm, (10 m real), l = 15 cm, (15 m real), l = 20 cm (20 m real) and l = 25 cm (25m real). in the test ii, a range of ∆l (cm) offsetting head “offset tunnel portal entrance exit” (see fig.3) from 5 to 25 cm (5 to 25 m real) were tested. for each configuration, co2 concentrations are measured in both tubes it can be better to measure co2 (carbon dioxide) instead of every toxic component that is always the most predominant product of combustion, and is, therefore, a good standard of the total amount of accumulated exhausts and thereby the necessary ventilation. a diffusion process is governed by the turbulence, thus directly related to the value of the reynolds number. unfortunately, such reduced scale; the conservation of reynolds number can't be realized. consequently, it was proposed to use hydrodynamic similitude called limited, i.e. maintain on model a reynolds numbers sufficiently high to ensure turbulent flow character, with reference to further comprehension about the flow with high reynolds number turbulence and fsi fluid-solid interaction musser et al. (2001). very low speeds were avoided to maintaining a reynolds number upper than the critical value of 5000. the measures to be carried out for this series of tests are: the velocity in the supply and the exhausted tubes, the wind speed (under the wind tunnel) and co2 concentration the discharge tube and nearby tube . air flow velocity in the duct was measured by a pitot velocity probe associated with flow-meters miloua h., j. build. mater. struct. (2020) 7: 1-18 9 of floating ball. pitot tubes are placed centrally within the supply lines, far enough from the entrance so that the flow is established. in order to estimate the co2 concentrations, a gassampling tube for measuring was installed near the head of supply and exhaust tubes. the recirculation rate (yousaf et al., 2014) is a measure for the amount of pollutants that is flowing from the tube’s discharge to a nearby inlet tube. it sums up quantitatively the transmission phenomenon, leaving out all the details of the transmission mechanisms. there are several possible definitions. it may be defined as the ratio of the mass flow of a species entering the inlet tube to the mass flow of the same species leaving the pollutants discharge. another definition (gehrig et al., 2013) reported to recirculation of smoke in fire tunnel, as the visibility in the inlet tube is best related to a smoke concentration. a convenient definition for the purposes of this paper is the ratio of the concentration of a species in the flow entering the inlet tube to the concentration of the same species leaving the pollutant discharge. using co2 as tracer gas for both cfd and experiment their advantage that does not react with the air while transported from one tube to the other. for a given speeds ratio of wind speed and ventilation the efficiency expressed as a percentage level “%” ranging between 0 % (no recirculation) to 100 % (critical recirculation) is defined by: ⁄ . where (kg co2.kg-1 mixture) is the co2 concentration measured in inlet tube and (kg co2.kg-1 mixture) is the co2 concentration measured from exhaust tube. qualitative analysis of flow in the test section exactly near the head is carried out using global visualizations of the mixture (air + co2 + smoke) rejected by the exhausted tube and possibly taken up by the exhausted tube. each test is filmed and stored on videotape. 3. results and discussion 3.1. comparison with experimental results the data given from the experiments are compared with the predicted results of the cfd model based to the values of efficiency in different sizes of central dividing wall and offset tunnel portal entrance exit. the work covers a three range of wind speed ratio and fixed cross wind. a. offset tunnel portal entrance exit in the worst case situations of offset tunnel portal entrance exit with smaller (m) real the rate of air pollution short circuit to the ingoing tunnel portal from the emitted air pollution of the outgoing tunnel portal can reach a 20%, which means that the efficiency up to 80% ( =0.8). with a good tunnel portal design geometry declared by koopmans (2005) the rate of air pollution short circuit effects can be limited to 10% or efficiency =90%. fig. 4. efficiency ε obtained by offset tunnel portal entrance exit method versus the offsetting length δl under different wind/ventilation conditions (m=u_w⁄(v_t )= 0.5, 1and 2). 10 miloua h., j. build. mater. struct. (2020) 7: 1-18 figure.4 indicates that a required offset tunnel portal entrance exit to reach this is between 10 to 15 m real, up to this value for more than 15 cm (15 m real) offset head, the recirculation of air pollution process is almost completely eliminated. b. central dividing wall from the measurements and calculations made for the planned road traffic tunnel see table 1, it appears that the minimum air pollution (aerodynamic) short circuit occurs (high efficiency) registered at a speed ratio of m= 2.0 the short circuit occurring at the other speeds tested 1 and = 0.5 is generally (considerably) lower. as for the influences of wall height see table i, we can observe that the height and length of the wall have depending influence on the value of efficiency ε. with length l ≥15 cm (15m real), the efficiency raises (less recirculation) with the height of the wall, which is reasonable. but, for a short wall lower than l≤ 10 cm (10 m real), we notice that the efficiency decreases as we increase the height. this phenomenon is explained by the fact that the wall creates inevitably air recirculation zone which can be stronger if the height is important. this zone is able to trap the exhausted air. table 1. efficiency ε of the central dividing wall under different wind speed u with fixed ventilation v=5 m.s-1 in both tubes case (a) central dividing wall under speed ratio: ⁄ =0.5 l=5 exp num l=10 exp num l=15 exp num l=20 exp num l=25 exp num h=4 0.56% 0.58% 0.56% 0.59% 0.56% 0.59% 0.61% 0.63% 0.62% 0.63% h=6 0.53% 0.50% 0.53% 0.50% 0.61% 0.68% 0.64% 0.70% 0.68% 0.70% h=8 0.53% 0.50% 0.53% 0.50% 0.64% 0.70% 0.71% 0.75% 0.73% 0.76% case (b) central dividing wall under speed ratio: ⁄ =1.0 l=5 exp num l=10 exp num l=15 exp num l=20 exp num l=25 exp num h=4 0.58% 0.61% 0.60% 0.63% 0.67% 0.69% 0.68% 0.69% 0.7% 0.72% h=6 0.55% 0.52% % 0.58% 0.55% 0.70% 0.7% 0.72% 0.70% h=8 0.55% 0.50% 0.56% 0.55% 0.72% 0.73% 0.77% 0.8% 0.78% 0.82% case (c) central dividing wall under speed ratio ⁄ =2.0 l=5 exp num l=10 exp num l=15 exp num l=20 exp num l=25 exp num h=4 0.62% 0.65% 0.67% 0.68% 0.75% 0.77% 0.75% 0.77% 0.76% 0.80% h=6 0.57% 0.62% 0.61% 0.76% 0.76% 0.79% 0.82% h=8 0.61% 0.62% 0.63% 0.66% 0.80% 0.77% 0.83% 0.86% 0.85% 0.86% as can be seen from the graphs see table 1 the influence of length of the wall, the efficiency increases with the length of the wall. indeed, there is between 0 and 10 cm (short walls), efficiency remains almost constant or increases slightly (between 50 and 65%) and that from 15 cm (or 15 m real) it increases visibly to reach efficiency going to 85%. we can assume from these results that there is wall length (between 10 m and 15m real) be necessary to surpass to get good results in terms of efficiency. qualitatively, it can be seen in the last part of the film recorded from experiment and cfd motion by smoke view that in the case of the influence of parameter without wall extension (l=0 m) a depression zone is visible near the front of exhausted tube. this inevitable area is a trap of smoke and recirculation flow. this phenomenon is very clear up to m= 2. for the essay realized in =3, it seems that most of the plume reaches around this zone. nevertheless, there is still recirculation (short circuit flow). it appears very clearly that the offset tunnel portal entrance exit is more effective than the central dividing wall. an excellent efficiency registered with coherent offsetting head. in other hand, offsetting portal design required more concrete and extending tunnel by supplementary miloua h., j. build. mater. struct. (2020) 7: 1-18 11 confined space. for this reason we focus to the simplest and economical design a central dividing wall. in general, the cfd model agrees reasonably with the experimental data and gives good convergence. a comparison of the short circuit percentages from experiment with the short circuit percentages from the simulation used central dividing wall shows that these can be reproduced in general with sufficient accuracy of +/(1~3%) exception under speed ratio of ⁄ =0.5 see table i case (a) a maximum accuracy occurring between 3~7%. 3.2. physical analysis and optimization in order to better validate the data cited above (table i) which is generally sufficient to provide answers at this stage to control pollutants in vicinity of tunnel portals and prevent air contamination of nearby tube. except certain cases, such as the variation of the efficiency vs. height h of divided wall which may represent particularly significant issue and required more analysis. a sufficiently detailed study using analysis must be carried out in order to provide more detailed answers by cfd code in the same 1:100 scale of experiment to distinguish that there are two different manners in the variation of the efficiency vs. height h of divided wall as of wall length l≈10 cm (10 m real)? fig. 5. efficiency ε versus the height of central dividing wall under fixed speed ratio ⁄ =2. the efficiency increases with elevated wall sizes (see fig.5 l=20 cm) which is quite logical. but, for de smaller length wall less than 10 cm (10 m real) another approach becomes visible warranted by decrease of efficiency with elevate height, in this case it may be helpful to analysis the concentration and flow velocities near the wall. initially we start to illustrate by a confidently co2 concentration for walls of the largest length, which is logical because the great height prevents recirculation (fig. 6). the minimum values for co2 concentration in the supply tube can be seen in the case of a tall wall (see fig.6(a)) to mean more than l≈10 cm (10 m) the recirculation decrease gradually while the wall increase toward the optimal length corresponding to no recirculation. a length of 15 cm (15 m real) is observed as best length of central dividing wall. 12 miloua h., j. build. mater. struct. (2020) 7: 1-18 (a) (b) fig. 6. the evaluation of co2 concentration levels (kg.kg-1) with flow direction for the different sizes of central dividing wall: (a) wall (h=08 cm, l=20 cm) and (b) wall (h=04 cm, l=20cm). in the case of the short wall (h=04 cm, l=05 cm) near the supply tube a turbulent vortex imprison the flow in their area and prevent co2 gas to directed toward the supply tube. however, without a vortex for (h=08 cm, l=05 cm) the ventilated supply tube aspirated quietly a co2 gas. so, the task is to determine which cause that encourage the formation of a vortex for the case of small height (h=04 cm, l=05 cm) (see fig.7). miloua h., j. build. mater. struct. (2020) 7: 1-18 13 (a) (b) (c) fig. 7. co2 concentration (kg. kg-1) in the supply tube (plane y = 7.5):(a) wall (h=08cm,l=05cm) ,(b) wall (h=04cm,l=05cm) and (c)temporal appearance of co2 (kg. kg-1) for a used wall (h=08cm, l=05cm) at time t = 5.6 s. 14 miloua h., j. build. mater. struct. (2020) 7: 1-18 the smaller divided wall playing considerable effect during the vortex creation justified by less blocking effect of the adverse wind as well as favorite more the interaction with longitudinal flow of supply tube. the interaction decrease with elevated height of central dividing wall which can block the short circuit flow in the region near portals and to let mixture near ground of supply tube affected only by longitudinal ventilation imposed by the fan, in addition the cross co2 flow decrease front supply tube with increasing wall length up to a limit of l=15 cm that the supply tube can aspirate only fresh air. furthermore, from animated results of cfd postprocessing, the first appearance of co2 with high concentration in the longitudinal plane of the supply tube is approximately 15 cm in all cases of smaller divided wall we have presented only (h = 08 cm, l= 05 cm) in fig. 7.c. from this distance equal to 15 cm (15 m) the main propagation of co2 from exhaust tube under longitudinal ventilation can be affected by transversal wind easily and the main flow move transversely. after that the co2 collect, diffuse in the fresh air area and obey to speed rate condition of supply tube, they interact gradually in their way to the upward/downward flow of wind crossed the head of a dividing wall. fig. 8. flow velocity in the plane x=5cm toward supply tube formed a vortex observed in upstream side of the wall. a cross analysis near the portal in the coordinate plane x=5 cm chosen to more identify the blocking of turbulence vortex. a vortex observed in upstream side of the wall h= 08 cm which be a sign of the divided cross flow through top of a central dividing wall: one part of the crossflow directed downwardly in upstream the wall and creates a vortex and other flow goes across the wall upwardly (see fig.8). for h= 08 cm subdivisions of the cross flow and creation of the vortex upstream moreover downstream the wall which hinder the upward flow at high-speed, the vortex in this area encourage more recirculation. for h=04 without any vortex produced and upward cross flow with high-speed decreased recirculation and appearance of a stagnation zone in the portal of supply tube h=04 cm, the area downstream of the wall with the lower speed and the maximum concentration, but remains blocked such as the supply tube acquire flow from the descending flow. 4. conclusions from present results of the numerical and experiment studies, the following conclusion can be assumed: large-eddy simulation (les) model can correctly predict pollutant dispersion in the vicinity of road tunnel. a description of the critical pollutants' recirculation rate as a function of the wind speed and wall sizes of central dividing wall has been presented. it uses concentration of contaminant as a safety criterion. computational fluid dynamics (cfd) models validated, for the simulation of the behavior of contaminant originating from short-circuiting flow between miloua h., j. build. mater. struct. (2020) 7: 1-18 15 tube of road tunnel for both structure of tunnel portal designs such as “central dividing wall” and “offset tunnel portal entrance exit” designs. the comparison of this result to the available experimental recirculation data between tunnel portals shows that pollutants recirculation will be sensitive to height of central dividing wall and wind conditions. the recirculation corresponded to offset tunnel portal entrance exit can be expected to be generally less critical due to the less mixing of the pollutants discharge under wind orientation to the ambient air aspirated by offsetting tube. from present results of the numerical and experiment studies, the following conclusion can be assumed: large-eddy simulation (les) model can correctly predict pollutant dispersion in the vicinity of road tunnel. a description of the critical pollutants' recirculation rate as a function of the wind speed and wall sizes of central dividing wall has been presented. it uses concentration of contaminant as a safety criterion. computational fluid dynamics (cfd) models validated, for the simulation of the behavior of contaminant originating from short-circuiting flow between tube of road tunnel for both structures of tunnel portals tested such as a “central dividing wall” and “offset tunnel portal entrance exit” designs. the comparison the cfd data to the available experimental data based to the predicted amount of pollutant air short circuit between tunnel portals shows that this amount is sensitive to height of central dividing wall and wind conditions. this study illustrated the use of cfd to increase insight in building aerodynamics and to support sustainable tunnel design. therefore, information about wind flow patterns around tunnel portals can be important to the designers, should pay more attention in creating more safety tunnel. the results should serve as groundwork for the design of ventilation systems to be as well as for the refurbishment of existing systems. 5. perspective computational fluid dynamics (cfd) models will be used to validate for the simulation of the behavior of smoke originating from fires in the two tunnels. nevertheless, the evaluation of smoke recirculation should more detail in the event of a fire recirculation, it must take into account the models limitations and the transients of a tunnel fire, i.e. the fire growth, the switch from the normal to emergency ventilation. acknowledgments this work was supported by the algerian research organism "dgrsdt directorate general for scientific research and technological development" under the project [no.a11n01un020120150001]. pro acknowledged for pr.olivier vauquelin for his kind help and discussions during the preparation of the present article. the author would also like to thank the institute universitaire des systèmes thermiques industriels, iusti umr cnrs 7343 technopôle de château-gombert. université d’aix-marseille, marseille cedex13, france for their collaboration. 6. references baumann, h.o., (1979). air recirculation between tunnel portals. 3rd int. symposium on the aerodynamics and ventilation of vehicle tunnels, sheffield. brousse, b., vidal, b., ponticq, x., goupil, g., & alary, r. (2005). pollution dispersion at an urban motorway tunnel portal: comparison of the small-scale predictive study with the actual conditions measured on the site. atmospheric environment, 39(13), 2459-2473. chock, d. p. (1982). pollutant dispersion near roadways—experiments and modeling. science of the total environment, 25(2), 111-132. dagnew, a. k., & bitsuamlak, g. t. (2014). computational evaluation of wind loads on a standard tall building using les. wind and structures, 18(5), 567-598. dagnew, a., & bitsuamlak, g. t. (2013). computational evaluation of wind loads on buildings: a review. wind struct, 16(6), 629-660. 16 miloua h., j. build. mater. struct. (2020) 7: 1-18 davidson, l., & nielsen, p, (1996). large eddy simulation of the flow in a three-dimensional ventilation room. 5th international conference on air distribution in rooms, roomvent96, july 17–19. gehrig, s., buchmann, r., & yousaf, r. (2013). how much flow recirculation is acceptable at tunnel portals?. world tunnel congress, geneva underground – the way to the future! g. anagnostou & h. ehrbar. eds taylor & francis group, london. gourdol, f., (2004). study on a mock-up of a dispersion scenario at tunnel portal-test report. cetu guide, environmental studies in road projects "air" and "health" sections the specific case of tunnels. école central de lyon france. http://www.cetu.developpement-durable.gouv.fr kashef, a., lougheed, g. d., & benichou, n. (2003). numerical modelling of movement and behaviour of smoke produced from fires in the ville-marie and lh-la fontaine tunnel: literature review. ottawa: institute for research in construction, national research council canada. koopmans, j. f. w. (2005). air pollution short circuit effects of road traffic tunnel portal. in symposium air quality management vol. 7, istanbul. li, s. w., hu, z. z., tse, k. t., & weerasuriya, a. u. (2016). wind direction field under the influence of topography: part ii: cfd investigations. wind struct, 22(4), 477-501. lim, h. c., & ohba, m. (2015). detached eddy simulation of flow around rectangular bodies with different aspect ratios. wind and structures, 20(1), 37-58. lipecki, t., & flaga, a. (2013). vortex excitation model. part i. mathematical description and numerical implementation. wind and structures, 16(5), 457-476. mcgrattan, k., hostikka, s., mcdermott, r., floyd, j., weinschenk, c., & overholt, k. (2013). fire dynamics simulator user’s guide. nist special publication, 1019(6). mirzai, m. h., harvey, j. k., & jones, c. d. (1994). wind tunnel investigation of dispersion of pollutants due to wind flow around a small building. atmospheric environment, 28(11), 1819-1826. muhic, s., & mazej, m. (2014). computational study of road tunnel exposure to severe wind conditions. wind and structures, 19(2), 185-197. murakami, s. (1998). overview of turbulence models applied in cwe–1997. journal of wind engineering and industrial aerodynamics, 74, 1-24. musser, a., mcgrattan, k. b., & palmer, j. m. (2001). evaluation of a fast, simplified computational fluid dynamics model for solving room airflow problems (no. nist interagency/internal report (nistir)-6760). nadel, c., thompson, k.a., slusarczyk, j.l. & vanderheyden, m.d. (2003). use of wind tunnel testing to develop air rights structures over tunnel exit portals that are compliant with ambient air quality standards. proceedings of the 11th international symposium on aerodynamics and ventilation of vehicle tunnels, luzern, switzerland. oettl, d., sturm, p., almbauer, r., okamoto, s. i., & horiuchi, k. (2003). dispersion from road tunnel portals: comparison of two different modelling approaches. atmospheric environment, 37(37), 51655175. peila, d., & pelizza, s. (2002). criteria for technical and environmental design of tunnel portals. tunnelling and underground space technology, 17(4), 335-340. rehm, r. g., & baum, h. r. (1978). the equations of motion for thermally driven, buoyant flows. journal of research of the nbs, 83(3), 297-308. smagorinsky, j. (1963) general circulation experiments with the primitive equations i, the basic experiment. monthly weather review: 91-99. tan, x., chen, w., dai, y., wu, g., yang, j., jia, s., ... & li, f. (2015). experimental research on the mixture mechanism of polluted and fresh air at the portal of small-space road tunnels. tunnelling and underground space technology, 50, 118-128. tanaka, f., kawabata, n., & ura, f. (2016). effects of a transverse external wind on natural ventilation during fires in shallow urban road tunnels with roof openings. fire safety journal, 79, 20-36. miloua h., j. build. mater. struct. (2020) 7: 1-18 17 vauquelin, o. & lesueur, h., 1998. etude expérimentale sur maquette du recyclage de l'air vicié en tête d'un tunnel bitude. université de valenciennes, report for scetauroute dtts. 'unpublished results' weerasuriya, a. u., hu, z. z., li, s. w., & tse, k. t. (2016). wind direction field under the influence of topography, part i: a descriptive model. wind struct, 22(4), 455-476. yang, y. r., he, c., zeng, y. h., & fang, y. (2012). effect of structural factors on waste gas cross flowing around portal of highway tunnels. zhongguo gonglu xuebao(china journal of highway and transport), 25(4), 107-112. yousaf, r., gehrig, s., & buchmann, r. (2014). evaluating smoke recirculation potential at the portal of a swiss road tunnel in case of a fire. in 7th international conference on tunnel safety and ventilation. pp. 118-125. nomenclature c p specific heat capacity of the gas cs smagorinsky constant cμ, cε empirical constants in turbulence model x  , y  , z  the dimensions of the smallest me g i acceleration of gravity (x,y and z) h enthalpy h height of tunnel exit k turbulent kinetic energy k s thermal conductivity of tunnel portal and ground wall. pressure p0 ambient pressure tpr turbulent prandtl number ''. q r radiative flux to a solid surface. ''. q c convective flux to a solid surface. r universal gas constant sij local large-scale rate of strain sct turbulent schmidt number t time t temperature t 0 ambient temperature  wvuu ,, velocity vector u 0 initial velocity greek symbol  dissipation of the turbulent kinetic energy 18 miloua h., j. build. mater. struct. (2020) 7: 1-18 u dynamic viscosity t u subgrid-scale turbulent viscosity  air density overbar  filtered variable  0 ambient air density  stefan–boltzmann constant τij,sgs subgrid-scale reynolds stress tensor  filter width  tx,   general variable  tx,   large-scale component  tx,'   subgrid-scale component j. build. mater. struct. (2014) 1: 40-46 https://doi.org/10.34118/jbms.v1i2.7 issn 2353-0057 effect of the heat curing on strength development of ultra-high performance fiber reinforced concrete (uhpfrc) containing dune sand and ground brick waste safi b *, aboutair a, saidi m, ghernouti y and oubraham c research unit: materials, processes and environment (ur/mpe), university of boumerdes, algeria. * corresponding author: safi_b73@umbb.dz abstract. this work aims to investigate the strength development of ultra-high performance fiber reinforced concrete (uhpfrc) containing ground dune sand (gds) and ground brick waste (gwb) as a substitutions of cement and dune sand (ds) as an aggregate. the variables are the nature of addition (gds and gwb) in the binder and the heat curing at different temperatures (20°c and 60°c) at 7 days of curing. two temperatures 20°c and 60 °c were applied to samples with intermediate levels for 8 hours in total. in this study, two types of cements (cemi and cemii) were used to prepare uhpfrc. the gwb was replaced by gds at levels of 10, 20 and 30% by weight. the results show that the obtained concretes develop a high mechanical performance with a suitable heat treatment according to the cement type and the used fiber. the compressive strength at 7 days of uhpfrc has increased with heat curing (at 60 °c) compared to that obtained at 28 days and measured at 20 °c. results show also that values of compressive strength of concrete containing ds are close to those obtained by the control concrete. this study has showed that the dune sand can be used in uhprc, and that the substitution of the gwb by gds can provide concretes with acceptable mechanical performance. key words: ultra-high performance fiber reinforced concrete, dune sand, ground dune sand, ground brick waste, compressive strength, heat curing. 1. introduction recent advances in concrete technology have enabled the development of new concretes named ultra high performance concrete (uhpc), which have very high compression strength and a good rigidity (richard, 1994; rossi, 1996; vernet, 1998). in practice, the formulation of such concretes requires adequate components and well controlled composition parameters. fundamental studies on the mechanical properties and behavior analysis of uhpc elements were achieved gradually over the last decade by some researches (richard, 1994; aitcin, 1996; dubey, 1998; vernet, 1998). most of these studies have also studied the use of cementitious materials in uhpc in order to obtain concrete with high mechanical performance. dune sand (ds) can be used as an aggregate and ground dune sand (gds) can be used as a cementitious material in the new generation of concretes. a very detailed study was reported by tafraoui et al. (2006; 2009) and zaitri et al. (2014) on the valuation of ds and gds in the formulation of high performance concrete. the results showed that ds can be considered as an aggregate and gds can be considered as a cementitious material for the formulation of high performance concrete. the present work constitutes an experimental study on the formulation and physic-mechanical characterization of ultra-high performance fiber reinforced concretes (uhpfrc). ds is used both as an aggregate for concrete and as mineral addition (i.e. gds). a ground brick waste (gbw) and a polypropylene fiber were also used in this study. the ds dosage remains constant in all mixtures, while gds was used as a partial substitution of gwb with different gds/gwb ratios (0, 10, 20 and 30%). also, the same variants of uhpfrc, were developed based on two cement types (cem i and cem ii) to see the ds effect on the physic-mechanical properties of uhpfrc, in the presence of these two types of cement. mailto:safi_b73@umbb.dz safi et al., j. build. mater. struct. (2014) 1:40-46 41 2. experimental study 2.1. materials two types of cements (cem i 52.5 and cem ii 42.5) were used in this work. also, gwb and gds were used as cementitious materials. table 1 showed the characteristics of these cementitious materials and cements. ds (0-2mm) was also used as a fine aggregate in all mixtures at fixed dosage. figure 1 shows the particle size distribution of ds. polypropylene fibers (with a 12 mm long and a diameter of 0.18 mm) were used. table 1. characteristics of cementitious binder. compounds cement % (by weight) gds % (by weight) gwb % (by weight) cemi cemii chemical analysis sio2 21.46 17.96 94.40 52.22 al2o3 04.55 4.50 2.23 10.49 fe2o3 04.08 2.98 0.33 02.54 cao 65.01 61.03 0.68 12.83 mgo 3.42 1.98 0.08 13.24 so3 2.08 2.08 0.17 0.52 k2o + na2o 1.21 0.91 1.49 1.24 loss of ignition 0.82 2.52 mineralogical analysis c3s 61.39 59.02 c2s 17.01 19.36 c3a 05.15 06.45 c4af 12.04 12.26 physical properties specific gravity (g/cm3) 3.10 3.02 2.63 2.42 specific surface (m2/kg) 380 390 800 780 fig 1. the particle size distribution of dune sand. 0 10 20 30 40 50 60 70 80 90 100 0 0,08 0,16 0,315 0,63 1,25 2,5 4 particle size (mm) p a s s in g o n s ie v e ( % ) dune sand 42 safi et al., j. build. mater. struct. (2014) 1:40-46 2.2. mix design and proportioning the uhpfrc were established according to the typical formulation of uhpc proposed by cimbéton (2013). most formulations of uhpfrc are currently designed experimentally. to this end, a process was established before the uhpfrc composition, verification of the final composition of the concrete by the mini-cone test. the water/binder ratio used was fixed (w/b = 0.19) and the mixing process was kept constant for all mixtures. table 2 shows the mixes details of control concrete and three uhpfrc. table 2. details of concrete mixtures. cement* (kg) ds (kg) mineral additions (kg) fiber (kg) sp(kg) ext. sec water (l) w/b gds gwb cc 710 1020 203 215 1 12 220 0.19 c10% 710 1020 223,3 194,7 1 12 220 0.19 c20% 710 1020 243.6 174.4 1 12 220 0.19 c30% 710 1020 263.9 154.1 1 12 220 0.19 * two types of cement were used: cemi and cemii. notations: cc: control concrete; c10%, c20% and c30% are respectively uhpfrc with 10%, 20% and 30% of gds by partial substitution of gwb. 2.3. test method to conduct this work, prismatic samples (40x40x160 mm3) were manufactured for each mixture. one day after casting, samples were stored in water under 21±1°c. the other specimens of uhpfrc were subjected to a specific heat curing in water (60°c for 8 hours) at 7 days and then test specimens were stored yet in water for 28 days (kjellsen, 1996; edrogdu, 1998). the various tests and measurements were carried out in order to study the mechanical properties (compressive strength). 3. results and discussions 3.1. fluidity of uhpfrc variation of fluidity, for studied concretes, as function the different content of gds is represented in figure 2. it was observed according these results that all concretes show a spread diameter varying between 18 and 20 cm. however, a slight decrease in the fluidity of c10% was remarked (with cemi see figure 2(a)). although, the decrease of fluidity was observed with c20% in case of cemii (see figure 2(b)). figure 3 shows examples of uhpfrc fluidity test by mini-cone. fig 2. fluidity of studied uhpfrc based on: (a) cem i (b) cemii. safi et al., j. build. mater. struct. (2014) 1:40-46 43 fig 3. fluidity test by mini-cone. 3.2. bulk density figure 4 give the bulk density of uhpfrc as a function the gds content, after 28 days of water maturation of the samples. for all mixtures, the bulk density was slightly increased with the replacement level of gwb by gds; this can be explained by the fact that gds is denser than gwb (see table 1). fig 4. bulk density of studied uhpfrc based on: (a) cem i (b) cemii. 3.4. compressive strength the compressive strength of studied uhpfrc based on cemi and cemii are presented respectively in figure 5(a) and figure 5(b). results show that the compressive strength is remarkably increased with the increase of gdw at all curing times. it can be also seen that the highest compressive strengths were recorded for uhpfrc concrete based on cemi (the highest value was 160 mpa for c30% composition). an attempt was made to improve the compressive strength of uhpfrc prepared by the heat treatment, mentioned above in paragraph (curing specimens at 60°c for 8 hours). the results are shown in figure 5. according to these results, it is remarkable that the compressive strength is significantly enhanced with heat treatment for all concrete. this is explained by the beneficial effect of the temperature, which accelerates the cement hydration reactions (edrogdu, 1998; kjellsen, 1996; tafraoui, 2009). the latter can generate the formation of c-s-h which increases the compressive strength of concrete. 44 safi et al., j. build. mater. struct. (2014) 1:40-46 fig 5. the compressive strength variation of concrete as function on the dune sand content; (a) with cemi (b) with cemii. safi et al., j. build. mater. struct. (2014) 1:40-46 45 3.5. microstructural study a microstructural study by scanning electron microscopy (sem) of the interface fiber-concrete was conducted to analyze the properties of the interfacial zone of these two materials. in figure 6 the fibres – concrete interface in a specimen containing 20% of gds (28 days of hydration) is shown. it can be observed from this figure, that the interfacial zone is more dense with low cracks and with a relatively good adhesion between the polypropylene fiber and cement paste. also, the ds fine aggregates have been observed in the cementitious matrix. according to the images in figure 6, it is clear that ds can be used as an aggregate because the adherence of the latter is very strong to the cementitious matrix. these images show that also gds can be used as a binder because it has given a new product of c-s-h. it should be noted that some studies have shown that gds can have a pozzolanic reactivity. (tafraoui, 2006; bédérina, 2000; azzouz, 2008). fig 6. sem analysis of the polypropylene fiber-binder interface. 4. conclusions this study has presented the use of dune sand (ds) as fine aggregate and ground dune sand (gds) as mineral addition in uhpfrc concrete. the results which could be as follows: the results of the fluidity tests by mini-cone were showed that all concrete studied have a same fluidity that varies between 18 and 20 cm in diameter, which corresponds to a uhpfrc fresh requirements; all uhpfrc studied have the same density regardless of the replacement rate of gwb by gds; 46 safi et al., j. build. mater. struct. (2014) 1:40-46 by using cemi cement type, the largest value of compressive strength of concrete is recorded (around 160 mpa for a gds replacement ratio of 30%); the compressive strength is enhanced in the presence of temperature for all concrete produced. this proves the beneficial effect of the temperature, which accelerates the cement hydration reactions. the effect of temperature is remarkable enough for uhpfrc based on cement cemi compared to concrete based on cemii. 5. references aitcin pc, richard p (1996). the pedestrian/bikeway bridge of sherbrooke. in proceedings 4th international symposium on utilization of high-strength/high-performance concrete, paris (pp. 1399-1406). azzouz l, benabed b, belaidi ase, menadi b (2008). durability of dunes sand mortar in the region of laghouat algeria, the international conference on construction and building technology, kuala lumpur, iccbt 2008 a (32) – pp.355-364. bédérina m (2000). caractérisation mécanique et microstructure des bétons de sables locaux : effet des fillers et de la nature des sables sur le comportement mecanique du materiau. mgister thesis, university of laghouat, algeria (in french). cimbéton (2013). les bétons : formulation, fabrication et mise en œuvre. fiches techniques de cimbéton, centre d'information sur les ciments et ses applications, france (online, in french). dubey a, banthia n (1998). influence of high-reactivity metakaolin and silica fume on the flexural toughness of high-performance steel fiber-reinforced concrete. aci mater. j., (95):284-292. edrogdu s, kurbetci s (1998). optimum heat treatment cycle for cement of different type and composition. cement concrete res., 28(11):1595-1604. kjellsen ko (1996). heat curing and post curing regimes of high performance concrete: influence on microstructure and c-s-h composition. cement concrete res., 26(2): 295-307. richard p, cheyrezy mh (1994). reactive powder concretes with high ductility and 200-800 mpa compressive strength. aci special publication, 144, pp. 507-518. rossi p, renwez s, guerrier f (1996). les bétons fibrés à ultra haute performance-l'expérience actuelle du lcpc. ulletin des laboratoires des ponts et chaussées, (204), pp.87-95. tafraoui a (2009). contribution à la valorisation du sable de dune de l'erg occidental (algérie). application aux nouveaux bétons. doctorate thesis, toulouse university, (in french). tafraoui a, lebaili s, slimani a (2006). study physico-chemical of the sand of the western erg of the area of saoura (western south algeria). j. appl. sci., 6, 2833-2836. vernet c, lukasik j, prat e (1998). nanostructure, porosity, permeability, and diffusivity of ultra high performance concrete (uhpc). symposium international sur les bétons à haute performance et de poudres réactives, sherbrooke, vol. 3, pp. 17-35. zaitri r, bederina m, bouziani t, makhloufi z, hadjoudja m (2014). development of high performances concrete based on the addition of grinded dune sand and limestone rock using the mixture design modelling approach. constr. build. mater., 60:8-16. j. build. mater. struct. (2020) 7: 188-198 original article doi : 10.34118/jbms.v7i2.774 issn 2353-0057, eissn : 2600-6936 ann modelling approach for predicting scc properties research considering algerian experience. part i. development and analysis of models sahraoui m *, bouziani t structures rehabilitation and materials laboratory (sreml), university amar telidji, laghouat, algeria. * corresponding author: med.sahraoui@lagh-univ.dz received: 20-08-2020 accepted: 08-10-2020 abstract. this paper presents research on the use of artificial neural networks (anns) to predict fresh and hardened properties of self compacting concrete (scc) made with algerian materials. a multi-layer perceptron network with 5 nodes, 12 inputs, and 5 outputs is trained and optimized using a database of 167 mixtures collected from literature. the inputs for the ann models are ordinary portland cement (cm), polycarboxylate ether superplasticizer (sp), river sand (rs), crushed sand (cs), dune sand (ds), gravel 3/8 (g1), gravel 8/15 (g2), water (w), limestone filler (lim), marble powder (mp), blast furnace slag (slag) and natural pozzolan (pz). instead, slump flow (slump), v-funnel, l-box, static stability (pi) and 28 days compressive strength (rc28) were the outputs of the study. results indicate that ann models for data sets collected from literature have a strong potential for predicting 28 days compressive strength. slump flow, v-funnel time and l-box ratio could be moderately identified while an acceptable prediction has been obtained for static stability. results have also confirmed by statistical parameters, regression plots and residual analysis. key words: artificial neural networks, self compacting concrete, algerian materials, fresh and hardened properties, prediction. 1. introduction self-compacting concrete (scc) is a high flowable concrete that can flow readily under its selfweight (okamura & ouchi, 2003). the development of a scc formulation is much more complex according to its sensitivity to small variations of mix proportions such as the proportion of water, cement, superplasticizer, aggregates and supplementary cementitious materials. assessing the role of mix constituents considered as a key factor for an adequate formulation. nowadays, several studies have been using various methods such as statistical methods, analytical modelling, and artificial intelligence for predicting fresh and hardened properties of scc based on various components (getahun et al., 2018). anns technique is a statistical method that advance the accuracy using extensive experimental data and neural networks algorithms in order to create an appropriate model which could solve complex problems (ahmadi et al., 2017). in addition, this method could value previous works and making them as mathematical models, which may help to predict properties of concrete mixtures before conducting laboratory experiments. several researchers are recently interested to predict scc properties using anns. sonebi et al. (2016) investigate the feasibility of using anns for prediction the fresh properties of scc, they demonstrate the efficiency of anns to predict the filling ability, flowability and passing ability with good accuracy. abu yaman et al. (2017) reported that mix proportioning of scc mixes could be performed using the trained neural network which in turn assures its effectiveness. douma et al. (2017) indicate that anns have strong potential as a feasible tool for predicting accurately the properties of scc incorporating fly ash. asteris et al. (2016) demonstrate the promising potential of ann for the reliable and robust approximation of the 28 days compressive strength of admixture-based self compacting concrete. mailto:med.sahraoui@lagh-univ.dz sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 189 the main objective of this study is to develop ann models for predicting the fresh and hardened states of scc made with algerian components and based on experimental data gathered from literature. 2. literature review several studies have been done to evaluate the possibility of formulating self compacting concrete based on local materials. boukendakdji et al. (2009) evaluate the effect of algerian slag on the properties of fresh and hardened scc. belaidi et al. (2012) study the influence of formulation parameters on rheological, mechanical and durability of scc, through partial substitution of cement by natural pozzolana of beni-saf and marble powder residue industry shaping and polishing marble. (benabed, 2014) examines the influence of various types of sand with different morphologies and origins on the fresh and hardened properties of self compacting concrete. (bouziani, 2013) provides a statistical approach to evaluate the effect of different kind of sands on the properties of scc. boukhelkhal et al. (2015) study the effect of algerian mineral admixtures (blast furnace slag, natural pozzolana and limestone fillers) on stability and rheology of scc. boukhelkhal et al. (2016) evaluate the effect of incorporating the marble powder as a supplementary cementitious material on rheological and mechanical properties of self compacting concrete. (nécira, 2018) develops a series of high-performance self-compacting concrete using quarry sand, dune sand, limestone filler, natural pozzolana and granulated slag. sahraoui and bouziani. (2019 a,b) study the effects of mixture components and sand contents on rheological and hardened properties of self compacting concrete. benyamina et al. (2019) investigate the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of scc. skender et al. (2019) assess the effects of various amounts of algerian limestone filler, which is expected to modify the physical, mechanical and transport properties of scc. ouldkhaoua et al. (2019) examine how the use of metakaolin powder and catodique ray tube glass will affect the rheological properties of self-compacting concrete. laidani et al. (2020) study the effect of using calcined bentonite as partial replacement of ordinary portland cement on the sustainability of scc. yh aissa et al. (2020) explore the possibility of using calcareous tuff in scc production. details of all mixes collected from literature are resumed in table 1. it should be noted that the above-mentioned works were selected on the basis of the following common components: ordinary portland cement (cemi 42.5); third generation polycarboxylate ether-based (medaflow 30 and 145); three types of sand (rs, cs and ds); limestone-type gravels (3/8) and (8/15); four mineral admixtures (lime stone, marble powder, slag and pozzolan). it is also worth noting that there are about forty other researches have reported the use of local materials to formulate scc, but these studies are not compatible with the selected researches in terms of cement, superplasticizer types and the use of viscosity modifying agent (vma). 190 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 table 1: data sets collected from literature references content cement (kg/m3) rs (kg/m3) cs (kg/m3) ds (kg/m3) gravel 3/8 (g1) gravel 8/15 (g2) w/p sp (%) lim (%) mp (%) slag (%) pz (%) boukendakdji et al. (2009) 352-465 867 0 0 280 560 0.4 1.2-2 0 0 10-25 0 belaidi et al. (2012) 285-475 886 0 0 277 553 0.4 0.9 0 5-30 0 5-25 (bouziani, 2013) 380 848 0 0 880 0 0.4 1.6 0 52.37 0 0 (benabed, 2014) 475 0-886 0-886 0-886 277 553 0.4 0.9-1.5 0 0 0 0 boukhelkhal et al. (2015) 404-467 0 541 360 401 401 0.42 1.6 0-15 0 0-15 0-15 boukhelkhal et al. (2016) 376-470 882.9 0 0 277 553 0.4 0.9 0 0-20 0 0 nécira et al. (2017) 400 0-770.89 0-780 0-776.84 385.45 385.45 0.35 1.5 37.5 0 0 0 (nécira, 2018) 251-501 821.69 0 0 432.9 432.9 0.32 0.6 0-50 0 0-50 0-50 sahraoui and bouziani. (2019 a,b) 420 754-1041 0 0 0-874.5 0-874.5 0.37 0.9 0 0-25 0 0 420 0-877.15 0-877.15 0-877.15 350.86 526.29 0.38 0.95 0 20 0 0 benyamina et al. (2019) 490 0 480-600 323 443 295 0.4 1.4 0-25 0 0 0 skender et al. (2019) 481-490 0 450-600 323 443 295 0.4 1.4 0-25 0 0 0 ouldkhaoua et al. (2019) 469.59 909.78 0 0 329 494 0.4 0.8 0 0 0 0 laidani et al. (2020) 469.59 906.22 0 0 266.1 536.06 0.4 0.8 0 0 0 0 yh aissa et al. (2020) 560 0 960 0 270 545 0.4 0.5 0 0 0 0 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 191 3. methodology a total of 167 scc mixtures collected from literature was used for the training and validation of the anns. these models were built with 5 hidden nodes and validated using a random holdback of 33% of the dataset in order to estimate parameters and assess the predictive ability of models. the equation and structure of the ann models used in this research are expressed in equation 1 and figure 1. ( ( )) ( ( )) (1) where ai, bi, ci,j are the model coefficients (table 2) and tanh is the hyperbolic tangent function which represent the activation function investigated in this work and is defined as: ( ) (2) the training, validation, and test sets are created by subsetting the original data into parts. for this purpose, a holdback method was selected in order to divide the original data into training and validation sets randomly. it could also specify the proportion of the original data to use as the validation set (jmp, 2020). it should be noted that a higher number of nodes results in more effective training, increases model complexity and processing time which required to enhance the computational power. figure 1: architecture of ann models used in this study 192 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 4. results and discussion parameters estimates and model coefficients of the ann models used in this research are shown in tables 2 and 3 respectively. five different statistical parameters have been employed for judging the performance of actual and predicted data including: the squared pearson correlation coefficient (r2), root mean square error (rmse), the mean absolute deviation (mad), the error sums of squares (sse) and the sum of the frequencies (sum freq). it can be seen that all models performed well and provided very good correlation coefficients (r20.8 for training and r20.7 for validation ) except the predicted static stability pi (r2 close to 0.7 for training and 0.64 for validation), this decline may be attributed to the high sensitivity of scc when there have been a small variation of mix proportions (thakre et al. 2017) instead, results obtained in compressive strength at 28 days were correlated a high level (r2 close to 0.97 for training and 0.89 for validation), which lead to conclude that anns were highly successful in learning and predicting the 28 days compressive strength. similar tendency has been observed by (malagavelli & manalel, 2014) (asteris et al., 2016) (saha et al., 2017). rmse was calculated in order to measure the differences between actual and predicted values, a lower value of rmse have been obtained which indicate the good prediction performance of the obtained models. smaller values of mad confirm once more that anns can better fit the data used in this experiment. the high sse values of pi and l-box indicate a large degree of variability within the data set, while the lower sse for rc28 reveals that the data does not vary considerably from the mean value, confirming that the results created by the anns were very close to those of actual values. figures 2 to 6 provide the regression values for all actual and predicted data. it is obvious that rc28 achieves the most reliable prediction while acceptable regressions have been registered for slump and v-funnel. instead, regression values for pi and even for l-box were moderate as report statistics have demonstrated. this confirms that the obtained models were able to reproduce the experimental results with high or acceptable accuracy. residual by predicted plot for all models are presented in figure 7. from this figure, it can be revealed that there aren’t any clear patterns in general. the points in a residual plot of slump and rc28 are randomly dispersed around the horizontal axis and they can be categorized as very good with a random error and this is a further justification of the previous results. residuals of v-funnel, l-box and pi appear clustered on the horizontal axis, confirming once again that the functional part of models does not fit the data perfectly. table 2: details report statistics slump v-funnel l-box pi rc28 training rsquared (r2) 0.880517 0.897185 0.815892 0.696938 0.968663 rmse 2.527693 1.601559 7.183838 4.496816 2.78906 mad 1.983659 1.014633 5.335368 3.437899 2.013808 sse 709.2046 223.1542 5676.828 1900.807 700.097 sum freq 111 87 110 94 90 validation r2 0.701792 0.785027 0.682712 0.641965 0.889876 rmse 4.628809 2.934053 9.577025 5.824216 4.832185 mad 3.659927 1.732885 6.862325 3.73383 3.629195 sse 1199.849 378.7813 5136.287 1594.31 1074.101 sum freq 56 44 56 47 46 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 193 table 3: model coefficients of responses parameter estimate slump v-funnel l-box pi rc28 a0 63.28388 15.14357 69.56581 26.30666 55.77593 a1 9.762795 15.6597 18.5131 2.624009 -3.62263 a2 -10.9652 -9.84658 -18.601 -2.4258 9.297474 a3 10.04468 1.301451 -11.8994 -1.53255 -15.5049 a4 -4.89305 -15.6859 11.33388 -0.35976 4.938328 a5 -12.7381 19.00461 -15.1506 -18.9019 -17.2991 b1 -23.5887 -3.63521 -28.7153 150.8015 -10.2121 b2 16.00778 -0.46792 12.46874 35.01113 -8.83419 b3 -15.9981 -0.34531 16.55757 5.528856 -127.601 b4 -21.0522 -0.16354 -27.9107 -106.68 11.75059 b5 0.006721 1.650363 -11.9844 30.77949 27.11841 c1.1 0.274386 0.051259 -6.44301 -5.33024 2.106865 c1.2 0.015749 -0.00366 0.057676 -0.04392 0.020887 c1.3 0.002319 0.000106 0.002042 0.000492 0.000587 c1.4 0.011904 -0.00028 0.014763 -0.02168 0.002026 c1.5 0.005066 -2.26e-05 -0.01826 0.048427 -0.00046 c1.6 -0.01559 0.00128 -0.00397 -0.009 0.00334 c1.7 0.00682 -0.00101 -0.01635 -0.00989 -0.00107 c1.8 0.059329 0.022315 0.242906 -0.52765 -0.04285 c1.9 -0.00568 0.006374 -0.0087 0.038518 -0.00993 c1.10 0.021006 0.002181 0.034455 -0.10915 -0.01066 c1.11 0.037648 0.001147 -0.08038 0.233543 -0.04839 c1.12 0.028369 0.007646 0.097666 -0.01825 0.028028 c2.1 -0.16161 -0.11075 -0.55608 0.267028 -0.33354 c2.2 0.023716 3.44e-05 -0.03596 -0.01568 0.054679 c2.3 0.000134 0.001165 -0.00084 -0.00347 -0.00446 c2.4 0.003594 -0.0007 0.000406 0.003751 0.000753 c2.5 -0.00305 -0.00363 -0.00323 -0.00531 -0.00482 c2.6 -0.02423 0.000267 0.003523 -0.00161 0.007988 c2.7 -0.0031 0.000168 0.009704 0.005639 0.014136 c2.8 -0.08759 0.004299 0.013601 -0.16777 -0.09512 c2.9 0.020337 -0.00544 -0.0605 -0.00729 0.001271 c2.10 0.004044 0.002177 0.045792 -0.01218 0.005885 c2.11 -0.01047 -0.0107 -0.04933 0.064607 0.027733 c2.12 -0.08962 -0.00113 -0.05144 0.053976 0.008794 c3.1 -0.90575 0.021695 -0.57513 0.047839 2.712765 c3.2 0.012898 0.000114 0.024287 -0.00641 -0.02383 c3.3 0.003106 -0.00004 0.000832 -0.00491 0.003437 c3.4 0.004608 0.000185 0.011968 0.000208 -0.00403 c3.5 -0.00225 -0.00015 -0.00801 0.006895 -0.00104 c3.6 -0.01189 -1.82e-05 -0.0009 0.005767 -0.02916 c3.7 -0.00656 -8.42e-05 0.001794 0.001471 0.014449 c3.8 0.110108 0.001288 -0.14507 -0.02886 0.681383 c3.9 0.074988 0.000322 0.001063 0.01544 0.034961 c3.10 0.001166 -0.00015 -0.05332 -0.01557 -0.03789 c3.11 -0.01852 -0.00042 -0.01343 -0.03729 -0.30774 c3.12 -0.09811 -0.00036 0.068436 0.016709 -0.00431 c4.1 -0.56855 0.060285 -0.04676 0.102512 -0.56029 c4.2 -0.00058 -0.00231 0.037324 0.074527 0.045114 c4.3 -0.00196 0.000563 -0.00744 -0.00271 0.004801 194 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 table3: continued parameter estimate slump v-funnel l-box pi rc28 c4.4 0.00607 -0.0001 0.022628 0.012973 0.008234 c4.5 -0.00017 -0.00148 -0.00307 -0.00569 -0.01172 c4.6 -0.00346 -0.00103 -0.00872 -0.00193 -0.00427 c4.7 -0.00344 0.000349 0.003323 0.003267 -0.00517 c4.8 0.141922 0.007608 0.081171 0.36632 -0.12896 c4.9 -0.01441 0.011606 -0.09656 -0.00705 0.021165 c4.10 0.019381 -0.00544 -0.00735 0.050952 0.005363 c4.11 0.034617 0.005238 0.100924 0.033341 -0.011 c4.12 -0.04773 0.00696 0.038846 -0.0471 0.056323 c5.1 -0.31598 -0.11879 -1.5101 -1.67961 -3.91819 c5.2 -0.0297 0.005039 -0.00144 0.060703 -0.02201 c5.3 -0.00974 0.001052 -0.00261 -0.02415 -0.00348 c5.4 -0.00267 -0.0001 0.011369 -0.03148 0.002148 c5.5 -0.00296 -0.00267 0.007953 -0.02841 0.007107 c5.6 0.000888 -0.0017 -0.00106 0.076022 -0.01745 c5.7 0.00423 0.001507 0.009059 -0.00798 0.035716 c5.8 0.075789 -0.01946 0.026686 -0.20353 -0.02288 c5.9 0.014454 0.004378 0.060278 0.022536 -0.03866 c5.10 -0.01043 -0.00204 0.057819 0.025281 -0.00018 c5.11 -0.01188 0.006042 0.072845 0.026894 0.115404 c5.12 0.015081 0.003512 0.005938 0.076111 0.043143 figure 2: regression for training and validation data results of slump sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 195 figure 3: regression for training and validation data results of v-funnel figure 4: regression for training and validation data results of l-box figure 5: regression for training and validation data results of pi 196 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 figure 6: regression for training and validation data results of rc28 figure 7: residual by predicted plot for all models sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 197 5. conclusion in this work, artificial neural networks accuracy in predicting scc properties was assessed. for this purpose, an ann models consisting of 5 hidden layer nodes, 12 input nodes which represent the components of scc and 5 output nodes representing the fresh and hardened properties of scc containing algerian materials. results conducted and presented in this paper demonstrate that the developed ann models were able to predict 28 days with high accuracy as confirmed with regression plots, residual analysis and statistical parameters. furthermore, this modelling technique performs sufficiently in the estimation of slump, l-box and v-funnel time, while static stability could be predicted with acceptable precision. in general, anns can be considered as good technique in modelling and predicting of scc properties with high reliability. 6. references ahmadi, m., naderpour, h., & kheyroddin, a. (2017). ann model for predicting the compressive strength of circular steel-confined concrete. international journal of civil engineering, 15(2), 213–221. asteris, p. g., kolovos, k. g., douvika, m. g., & roinos, k. (2016). prediction of self-compacting concrete strength using artificial neural networks. european journal of environmental and civil engineering, 20(sup1), s102–s122. belaidi, a. s. e., azzouz, l., kadri, e., & kenai, s. (2012). effect of natural pozzolana and marble powder on the properties of self-compacting concrete. construction and building materials, 31, 251–257. benabed, b. (2014). influence de la qualité et de la nature des sables sur les performances et la durabilité des bétons autoplaçants. université de laghouat-amar telidji. benyamina, s., menadi, b., bernard, s. k., & kenai, s. (2019). performance of self-compacting concrete with manufactured crushed sand. advances in concrete construction, 7(2), 87. boukendakdji, o., kenai, s., kadri, e. h., & rouis, f. (2009). effect of slag on the rheology of fresh selfcompacted concrete. construction and building materials, 23(7), 2593–2598. boukhelkhal, a., azzouz, l., belaïdi, a. s. e., & benabed, b. (2016). effects of marble powder as a partial replacement of cement on some engineering properties of self-compacting concrete. journal of adhesion science and technology, 30(22), 2405–2419. boukhelkhal, d., boukendakdji, o., kenai, s., & bachene, s. (2015). effect of mineral admixture type on stability and rheological properties of self-compacting concrete. bouziani, t. (2013). assessment of fresh properties and compressive strength of self-compacting concrete made with different sand types by mixture design modelling approach. construction and building materials, 49, 308–314. douma, o. b., boukhatem, b., ghrici, m., & tagnit-hamou, a. (2017). prediction of properties of selfcompacting concrete containing fly ash using artificial neural network. neural computing and applications, 28(1), 707–718. getahun, m. a., shitote, s. m., & gariy, z. c. a. (2018). artificial neural network based modelling approach for strength prediction of concrete incorporating agricultural and construction wastes. construction and building materials, 190, 517–525. jmp. (2020). jmp documentation library, 1–5609. sas institute inc. 2020. discovering jmp® 15. cary, nc: sas institute inc. 198 sahraoui and bouziani, j. build. mater. struct. (2020) 7: 188-198 laidani, z. e.-a., benabed, b., abousnina, r., gueddouda, m. k., & kadri, e.-h. (2020). experimental investigation on effects of calcined bentonite on fresh, strength and durability properties of sustainable self-compacting concrete. construction and building materials, 230, 117062. malagavelli, v., & manalel, p. a. (2014). modeling of compressive strength of admixture-based self compacting concrete using fuzzy logic and artificial neural networks. asian journal of applied sciences. https://doi.org/10.3923/ajaps.2014.536.551 nécira, b. (2018). développement des bétons autoplaçants à hautes performances: influence de la composition. université mohamed khider biskra. nécira, b., guettala, a., & guettala, s. (2017). study of the combined effect of different types of sand on the characteristics of high performance self-compacting concrete. journal of adhesion science and technology, 31(17), 1912–1928. okamura, h., & ouchi, m. (2003). self-compacting concrete. journal of advanced concrete technology, 1(1), 5–15. ouldkhaoua, y., benabed, b., abousnina, r., & kadri, e.-h. (2019). rheological properties of blended metakaolin self-compacting concrete containing recycled crt funnel glass aggregate. epitoanyagjournal of silicate based & composite materials, 71(5). saha, p., prasad, m. l. v, & rathishkumar, p. (2017). predicting strength of scc using artificial neural network and multivariable regression analysis. comput. concrete, 20(1), 31–38. sahraoui, m., & bouziani, t. (2019a). effect of coarse aggregates and sand contents on workability and static stability of self-compacting concrete. advances in concrete construction, 7(2), 97. sahraoui, m., & bouziani, t. (2019b). effects of fine aggregates types and contents on rheological and fresh properties of scc. journal of building engineering, 26, 100890. skender, z., bali, a., & kettab, r. (2019). self-compacting concrete (scc) behaviour incorporating limestone fines as cement and sand replacement. european journal of environmental and civil engineering, 1–22. sonebi, m., grünewald, s., cevik, a., & walraven, j. (2016). modelling fresh properties of self-compacting concrete using neural network technique. computers and concrete, 18(4), 903–920. thakre, n., mangrulkar, d., janbandhu, m., & saxena, j. (2017). self-compacting concrete-robustness of scc. international journal of advanced engineering research and science, 4(3), 237086. yaman, m. a., abd elaty, m., & taman, m. (2017). predicting the ingredients of self compacting concrete using artificial neural network. alexandria engineering journal, 56(4), 523–532. yh aissa, y., idriss, g., & benabed, b. (2019). mix-design and properties of self-compacting concrete made with calcareous tuff. journal of building engineering, 27, 100997. https://doi.org/10.1016/j.jobe.2019.100997. j. build. mater. struct. (2020) 7: 140-158 original article doi : 10.34118/jbms.v7i2.766 issn 2353-0057, eissn : 2600-6936 analysis of aqueducts subjected to hydrostatic and dynamic loads using 3d solid modeling jitendra singh yadav1*, suhas s babu2 1,* department of civil engineering, national institute of technology hamirpur, hamirpur, india 2 school of civil and chemical engineering, manipal university jaipur, jaipur, india * corresponding author: jitendershine@gmail.com received: 22-07-2020 accepted: 07-09-2020 abstract. in many areas of developing countries, the access to fresh water is limited even today. aqueducts are the major structures in water supply and diversion schemes when carrying the water over natural and artificial obstacles such as valleys, rivers, roads, railway lines, canals etc. during an earthquake, the effect of water sloshing on the walls of aqueduct and the resulting hydrodynamic forces is often neglected. in this study, the analysis is carried out for a single span elevated aqueduct using finite element analysis, in which the structure is discretized into smaller elements. the structure is modelled using solid elements in staad pro v8i software for different loads. the behavioral response of aqueduct structure subjected to hydrostatic loads and dynamic loads due to seismic ground excitation has been analyzed. it has been observed that the structure is more vulnerable to dynamic loads compared to hydrostatic loads. the effect of dynamic loads due to sloshing of water under seismic forces is predominant. the stresses induced by hydrodynamic loads are observed to be 2.4 times more than hydrostatic loads. key words: aqueducts; tie beams; hydrostatic and hydrodynamic loads; solid modelling. 1. introduction the supply of adequate fresh potable water is one the most important requirements for any community. an aqueduct is a cross drainage structure which is constructed to convey water over an obstacle such as natural streams, valleys etc. aqueduct is derived from latin word, (latin: aqua + ducere, “to lead water”) man-made structure for carrying water. in modern engineering, aqueduct refers to a structure used to convey water from its source to its distribution point. aqueducts have been important particularly for the supply of water to areas with limited direct access to freshwater sources. they form a component of systems that run for very long distances through different terrains from the source to distribution point. they serve as bridge for conveying water and it can also be used for other purposes like foot bridge which help people to cross the valley in remote places (wu et al., 2006). in addition to the above importance, aqueducts also help in regulating flood by draining away the overflow, they can be used for inland navigation and also for major river diversion schemes which is a serious thought taken up by many countries to supply the water from the areas of abundant water resources to areas of water scarcity. thus helps in filling of natural lakes and reservoirs, and regenerate the ground water. thus, the aqueducts which form a major link in irrigation systems are extremely significant structures and needs to be carefully designed. a major earthquake would create serious consequences for the people who are purely dependent on it for water. many studies have been undertaken in the past years regarding the seismic design of aqueducts. aqueducts were designed earlier using bridge design codes. even now there are no stipulated codes for seismic design of aqueducts. but aqueducts are not same as bridges and the conventional bridge design cannot be applied to the design of aqueducts because it consists of mailto:jitendershine@gmail.com yadav and babu, j. build. mater. struct. (2020) 7: 140-158 141 large masses of water in it. an earthquake excitation makes the water mass to cause sloshing on the walls of the aqueduct. this creates the hydrodynamic forces on the walls of the aqueduct which is often not accounted for in much design of aqueducts. but later, some of the linear methods were developed to study the water-structure interaction such as westergard’s additional mass method and housner’s model method. some of the other methods include the non-linear methods to study the water-structure interaction such as boundary element method and ale (arbitrary lagrangian-eulerian) finite element method which considered the effect of water sloshing (bai et al., 2011; gao et al., 2014). haroun and tayel (1985) studied and compared the effect of vertical translation of elastic, cylindrical liquid storage tank under vertical and horizontal seismic excitation for three different support conditions of the wall, namely, fixed, simply supported and partly fixed conditions. from the results, it was found that the maximum wall displacement and the maximum wall stresses in case of variable wall thickness were nearly two thirds of tanks with uniform wall thickness. axial stresses induced in an anchored tank due to the vertical component of earthquake excitation were found to be much smaller than those due to the horizontal components. li et al., (2003) studied the vertical seismic response for a large-scale beam-supported aqueduct. it was observed that the frequencies of aqueduct when it was full were lower than that when it was empty condition due to participating water-mass but the mode shapes in both the cases were identical. for the different seismic inputs, the structural responses of the aqueduct increased with the depth of water in aqueduct. from the results, it was shown that the vertical seismic effects on the aqueduct structure were not small. so, the effects of vertical seismic excitations on the aqueduct should be considered in the structural designs. chen and hao (2004) studied the water-structure interaction and the effects of bearing properties on its responses to seismic ground excitation. it was observed that using isolated bearings in the design can significantly reduce the aqueduct responses compared to the hinge support. when the aqueduct is hinge supported, the stress induced by water vibration is negligible compared to that of aqueduct when a 1:20 scaled aqueduct model with hinge support was tested on shaking table. this study also demonstrated that using rubber bearings to isolate the aqueduct from the piers would greatly reduce aqueduct responses to seismic ground motion as compared to using hinge supports. wu et al., (2006) studied the response of threedimensional high frame supported u-shaped aqueduct under seismic excitation resulting large amplitude sloshing effects of water and effects on the aqueduct structure. it was observed that under strong earthquake actions, the effects of sloshing are significant. the external excitations were found responsible to induce large water sloshing effects that significantly changed the distribution of hydrodynamic pressures and stresses in the aqueduct. the results showed that when the earthquake action reached a peak, the amplitude of the sloshing water may reach a maximum after several periods of water sloshing. mitra and sinhamahapatra, (2007) had discussed, the slosh dynamics of a partially filled rigid container during an earthquake excitation. the characteristics of slosh displacement, slosh frequencies, mode shapes, hydrodynamic pressure over the container wall and around the submerged component had been studied. the analysis was carried out considering only small amplitude waves. it was found that the dimensions of submerged structure had very strong effect on the slosh dynamics. it was also observed that the hydrodynamic pressure on the submerged block increased with height of the submerged block but decreased on the walls of tank. the dynamic pressure on the near wall was found to be increased quite considerably as the submerged block moved towards it, while the pressure on the far wall was decreased. rafiee et al., (2008) had presented the “non-smooth contact dynamics” (nscd) computational method, of rigid or deformable discrete elements for dynamic simulation to analyze the structural behavior and stability of antique structures during an earthquake vibration. the “nîmes arena” and “arles aqueduct” in france using lmgc90 code with 3d rigid element model were studied. the author studied the behavior of masonry structure and the failure modes due to seismic wave 142 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 propagation. the results obtained from the model subjected earthquake vibration showed that the structure was highly vulnerable, especially at the upper level of the outside wall. bai et al., (2011) had discussed the dynamic response of large aqueduct for different water depths in the aqueduct using housner’s method. from the result, it was observed that, the dynamic displacements and dynamic stresses of aqueduct structure increased with the depth of water in aqueduct. as the water increased, the mass of the upper portion of the aqueduct structure was also found to be increased. from the calculation results, the maximum compressive stress was observed in the bottom middle wall of the downstream end, the maximum tensile stress was observed in the bottom middle wall of the upstream end. zhang, et al., (2013) studied the water-structure interaction of the aqueduct structure subjected to windinduced vibration for different depths of water. the stability of the structure for natural vibration characteristics, seismic responses, and wind responses for rigid bearings and isolated bearings is compared. the results showed that the use of isolation bearings was able to improve the performance during an earthquake but it reduced the structural stiffness and increased the vibration period by 1.74 times compared to rigid bearings. the stresses of aqueduct with isolated bearing were lesser than those aqueducts without isolated bearing under seismic conditions. however, under the wind load, the stresses were found to be much larger on the aqueduct with isolated bearing compared to aqueducts without isolated bearing. zhang et al., (2013) studied the dynamic properties of a u-shaped aqueduct induced by the fluctuating winds for rigid bearings isolated rubber bearings. it was observed that the isolated rubber bearings were helpful in improving the earthquake resistance capacity but they reduced the structural stiffness, increased the structural vibration period and reduced the wind resistance performance of aqueduct structures. it was observed that the hydrodynamic pressure and the overturning force on the wall increased with the depth of water in the aqueduct. the values with rubber bearings were found to be greater than the ones with rigid bearings by 4– 7%. the maximum average overturning moment of aqueduct with rubber bearings were approximately 9 times larger than the one with rigid bearings for identical water depth. it was found that the isolated rubber bearings produced maximum stresses and overturning forces which reduced the structural stability for wind resistance of aqueducts. gao et al., (2014) had discussed about the beam-type aqueduct 2.5d fsi (fluid-structure interaction) model to analyze the aqueduct-water coupling system and compared it with typical 3d fsi model in the numerical results. a 3d fsi model and three 2.5d fsi models with different amount of 2d fsi planes were presented in the static and dynamic analyses of the aqueduct. in this model, the beam-type aqueduct body was divided into a number of substructures and meshed by 3d solid elements. in the study, there were three kinds of 2.5d fsi models with 5, 8 and 10 2d fsi planes respectively. the results showed that the 2.5d fsi model with 8 2d fsi planes of 2d fsi planes to had good simulation results for dynamic and static analysis of beam-type aqueduct. it was also shown that the computing time of the 2.5d fsi model is about 4 hours, while the 3d fsi model costs about 7 hours. it was obvious that the 2.5d fsi model greatly reduces the computing time cost on the premise of satisfying requirements of calculation accuracy. from the review of past literature, it is found that the combined effect of aqueduct with and without tie beams subjected to the hydrostatic and hydrodynamic forces has not been studied in detail. the finite element method of modelling of an elevated aqueduct using solid elements in staad pro v8i software has not been carried out. the effects of water sloshing on the walls of the aqueduct induced due to combined effect of horizontal and vertical earthquake forces has not been studied. the aim of this work is to study the structural response of aqueduct subjected to static and dynamic loading. 2. design philosophies the methods available for studying water-structure interaction and for calculation of hydrodynamic pressure are: yadav and babu, j. build. mater. struct. (2020) 7: 140-158 143 1) westergard’s additional mass method 2) housner’s model method 2.1. westergaard’s additional mass method this method was basically developed by prof. h.m wastergaard to study the hydrodynamic pressure on dams. in this method, the water is treated as an additional mass. according to westergaard’s theory, the parabolic hydrodynamic pressure exerted on the vertical face of dam structure on the upstream was determined to be the same as that pressure exerted by water on the wall of dam. this water is treated as “additional mass” which moved with the dam during an earthquake ground motion. prof. westergaard developed equations for these individual masses exerted over the height of dam as a result of horizontal earthquake acceleration (jain and jaiswal, 2007). the equation for the individual masses is given as: zh g w zm * 8 7 )(  where, w= unit weight of water g= acceleration of gravity h= depth of reservoir water z= depth of water from surface in this approach, the structure (dam) is treated as rigid, semi-infinite and have vertical upstream surface. surface waves in fluid are neglected. the distribution of hydrodynamic pressure occurred along upstream surface after earthquake takes into account as mass distribution pulsed with the dam. individual masses calculated with distribution of hydrodynamic pressure are added on the nodes of the finite element mesh along upstream surface of the dam. the water is treated as a compressive non-cohesive fluid body (jain and jaiswal, 2007). 2.2. housner’s method housner’s proposed simple methods to evaluate the influence of dynamic fluid on the rigid rectangular tank subjected to earthquake forces.when the water tank is subjected to earthquake excitation, it causes the sloshing of water. this sloshing of water on the structure will induce the generation of hydrodynamic forces. this is idealized as two components called impulsive and convective masses of water. the impulsive mass of water is assumed as fixed mass which is rigidly connected to the tank and convective mass of water is assumed to be connected with flexible springs to the tank wall to simulate the effects of sloshing motion of water (jain and jaiswal, 2007). the impulsive pressure of water mass on wall of tank is shown in fig. 1(a) and fig. 1(b). in fig. 1(a) hi represents the height where the resultant of impulsive hydrodynamic pressure acts on wall from the bottom of tank. whereas hi* represents the height where the resultant of impulsive hydrodynamic pressure acts on the wall and base is located from the bottom of tank wall (fig. 1(b)). thus, if influence of base pressure is not calculated, impulsive mass of liquid, mi will act at a height of hi and if effect of base pressure is well-thought-out, mi will act at hi*. similarly, fig. 2(a) and fig. 2(b) show the height where the resultant of convective pressure act on the wall represented by hc, while, hc* is the height at which resultant of convective pressure on wall and base is located (jain and jaiswal, 2007). 144 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 fig 1. (a) impulsive pressure on wall (b) impulsive pressure on wall & base fig 2. (a) convective pressure on wall (b) convective pressure on wall & base 2.3. hydrodynamic pressure the main purpose of the aqueduct is conveying water, but because of insufficient researches on the dynamic response of aqueduct structures, the aqueducts are studied and analyzed for their seismic performance only and not hydrodynamic loads. though the aqueducts are considered as bridges for carrying water over obstacles, the dynamic responses of an aqueduct structure are very dissimilar from those of a vehicular bridge. the large mass of water sustained by an aqueduct is far larger than the loads taken by a bridge. these loads on the aqueducts are more pronounced during an earthquake. the liquid motion will cause the sloshing on the base and walls of the structure and significantly induces the hydrodynamic pressure on the aqueduct structure. due to earthquake ground motion, both tank and the liquid are subjected to horizontal acceleration. both the horizontal and vertical earthquake excitation induces the water sloshing and the hydrodynamic loads on the structure. but it is due to the horizontal earthquake acceleration, the effects are more pronounced compared to that due to the vertical ground excitation (li et al., 2003). at the lower region of tank liquid acts like rigid mass and it is called as impulsive liquid mass. this impulsive mass creates hydrodynamic pressure on the side and base of tank. the sloshing motion of water can be seen in the upper region of tank and it is called as convective liquid mass. the convective mass exerts convective hydrodynamic pressure on side and base of tank. during vibrations, the liquid exerts both impulsive and convective hydrodynamic pressure on side and base of tank along with hydrostatic pressure. the water mass present at the bottom of tank acts like a rigid mass. whereas sloshing effect is only produced by water present at the top and it acts like a spring-mass model as shown in fig. 3 (jain and jaiswal, 2007; salamon, 2011). yadav and babu, j. build. mater. struct. (2020) 7: 140-158 145 fig 3. spring-mass model 3. designs 3.1. geometry although in practical situations, the size of aqueduct is decided based upon the actual discharge of water that is required to be pass through the aqueduct. in this study, the structural behavioural response of aqueduct subjected to static and dynamic forces was assessed. an aqueduct of vent size 3.0 m x 3.20 m and elevated 10 m above the ground was modelled using 8noded solid elements in staad pro v8i software. the geometry of aqueduct is shown in fig. 4. the assumed dimensions of the aqueduct to study the behavioural response are as follows: • clear vent size of the aqueduct = 3.0 m wide x 3.20 m deep • length of each span = 20 m • thickness of floor slab = 400 mm • thickness of vertical rc walls = 450 mm • number of tie beams = 6 • size of tie beams at top = 400 mm wide x 400 mm deep • size of beams supporting floor slab and walls = 400 mm wide x 450 mm deep • spacing of tie beams = 4.0 m c/c • grade of concrete = m-25 the proposed aqueduct is considered to be elevated 10 m above the ground, supported on rc piers. fig 4. geometry of aqueduct 146 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 3.2. loading the aqueduct is assumed to be full of water up to the soffit of top beams. firstly, the structure is loaded with self-weight, and the hydrostatic water load on floor slab and side walls. then the earthquake load has been applied by considering the parameters applicable for seismic zone iv as per is 1893-2016, due to which the water present in the aqueduct is subjected to excitation causing the sloshing of water on the walls of the aqueduct which results in the generation of hydrodynamic forces of water on the structure. following loads were considered to be acting on the structure: 1. dead load. 2. hydrostatic water load on floor. 3. hydrostatic water load on side walls. 4. seismic forces (zone iv). 5. hydrodynamic forces. 6. combination of self weight and hydrostatic loads 7. combination of self weight, hydrostatic loads, seismic force and hydrodynamic forces. 3.2.1. static water load calculation the static water loads on different elements of the structure has been calculated for the full span of the structure. it has been considered that the water in the aqueduct is filled up to the soffit of top tie beam and accordingly the load on the floor and side walls have been calculated. preliminary data: total depth of flow = 3.20 m depth of each solid = 0.40 m total number of rows of solids = 8 no's density of water (γ) = 10 kn/m3 distribution of water pressure on vertical side walls varying load (water pressure) from top to bottom = γ*h = 32 kn/m2 where, γ = density of water (kn/m2) h = height of water (m) load distributions for different depths of water are given in table 1. table 1. hydrostatic loads applied on the walls of the aqueduct height (h) in ‘m’ load (kn/m2) 0 0 0.40 4 0.80 8 1.20 12 1.60 16 2.00 20 2.40 24 2.80 28 3.20 32 calculation of water pressure on floor slab height of water flow = 3.20 m yadav and babu, j. build. mater. struct. (2020) 7: 140-158 147 total pressure on floor slab = 32.00 kn/m2. 3.2.2. hydrodynamic pressure calculation the designs for the calculations of the hydrodynamic pressure resulting from the seismic forces considering the impulsive and the convective masses of water on the aqueduct is carried out. the distributions of hydrodynamic pressure applied on the walls of aqueduct are shown in table 2. 3.3. loading under normal serviceability conditions, the structure should be able to safely carry the static load. at times, when an earthquake load is combined along with the normal operating conditions, the resulting effects of water sloshing on the structure will generate hydrodynamic loads. the structure will be subjected to the dynamic loads along with the hydrostatic loads. these different loading is visualized in different load combinations and is applied on the structure to study its behaviour. •load combination 1 (lc1) = dl + hydrostatic water load •load combination 2 (lc2) = dl + hydrostatic water load + seismic ‘z’ + hydrodynamic load table 2. dynamic loads applied on the walls of the aqueduct height (h) in ‘m’ hydrodynamic pressure (p)(kn/m2) 0 0.000 0.40 1.193 0.80 4.774 1.20 10.741 1.60 19.096 2.00 29.837 2.40 42.965 2.80 58.481 3.20 76.383 3.4. seismic design parameters the proposed structure is considered to be in seismic zone iv. therefore, the seismic parameters for calculation of seismic force has been taken according to is 1893-2016.  seismic zone = zone iv  response reduction factor = 5  importance factor = 1.5 3.5. modelling using solid elements the structure has been modelled using 8-noded solid elements in staad pro v8i software and analyzed for the above specified loads and their load combinations in finite element method. a continuous complex problem is divided into separate entities referred as finite elements, connected together at a number of nodes. finite element method (fem) is most preferable 148 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 method for the analysis of simple and complex problems with minimal errors and higher accuracy. the support conditions of the aqueduct structure is considered as fixed at one end and the other end is fixed in ‘y’ and ‘z’ directions but released in ‘x’ direction to make provision for translational movement within the allowable limits and avoid high negative moments at the ends due to the axial forces in the structure. the 3d model of the proposed structure is represented in fig. 5(a) and fig. 5(b).further, to investigate the importance of tie beams at the top, following cases were modelled and compared to observe the deflection behaviour and stress diagram of the structure under hydrostatic load and also the effect on the bottom beams supporting the floor slab, the different cases which were considered for the analysis are as follows: • without tie beam at the top. • with tie beam at the top. fig 5. (a) 3d model of aqueduct (b) 3d model of aqueduct yadav and babu, j. build. mater. struct. (2020) 7: 140-158 149 4. results and discussion 4.1. analysis of aqueduct without tie beams fig. 6(a) shows the 3d view of aqueduct without tie beam. the structure is modelled without tie beams at the top to study the response. the floor slab has not been modelled in this and the loads coming on the floor slab has been calculated and applied on the adjacent beams to study the response of bottom beams. the aqueduct was undergoing excessive deflection beyond permissible limits for static loads itself as shown in fig. 6(b). hence, the effect of dynamic loads has not been considered. fig 6. (a) 3d view of aqueduct without tie beams fig 6. (b) deflection and bending behaviour of aqueduct without tie beams table 3. maximum displacements of aqueduct without and with tie beams displacement (mm) direction x y z resultant without tie beams 2.360 5.010 27.120 27.552 with tie beams 2.436 3.753 0.644 4.029 150 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 from table 3, it was observed from the deflection and bending behaviour of the structure that, in the absence of tie beams at the top of aqueduct, the lateral bending of aqueduct structure was predominant and in fact more than the vertical bending due to hydrostatic loads and self-weight. the displacement of the structure in the absence of tie beams at the top was almost 7 times greater than the structure with tie beams at top. as a result, the bottom tie beams are subjected to negative bending moment and the walls were found to be deflecting apart due to lateral hydrostatic forces. from fig. 7, it was also observed that the bottom tie beams were subjected to maximum tensile stresses at the top face which resulted in failure of beams. the floor slab also will undergo excessive bending ultimately leading to the failure of structure. thus, the tie beams at top prove to be a necessary element for the overall performance of the large aqueduct structure. fig 7. stresses in the components of aqueduct without tie beams 4.2. analysis of aqueduct without tie beams fig. 8 shows the 3d view of aqueduct with tie beam. the structure is modelled with tie beams at the top and analyzed for static loads to compare with the results obtained for the model without tie beams at the top. the behaviour of the structure is shown in fig. 9(a) and fig. 9(b). from table 4, it was observed from the deflection and bending behaviour of the structure that, in the absence of tie beams at the top of aqueduct resulted in lateral bending. the provision tie beams helped in reducing the deflection as shown in fig. 9(b). the values observed for aqueduct with tie beams at the top shows a significant reduction in maximum displacements and maximum stresses on the structure as shown in fig. 10. from the displacement values, it was observed that the displacement was well within the permissible limits (10 mm) when the tie beam at top is provided. fig. 11 shows the comparison of deflection for aqueducts without and with tie beams provided. yadav and babu, j. build. mater. struct. (2020) 7: 140-158 151 fig 8. 3d view of aqueduct with tie beams table 4. maximum stresses of aqueduct with tie beams normal stresses shear stresses direction sxx syy szz sxy syz szx stresses (n/mm2) 2.722 4.453 1.785 2.232 2.522 0.323 fig 9.(a) deflection and bending behavior of aqueduct with tie beams 152 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 fig. 9.(b) top view of deflection and bending behavior of aqueduct with tie beams fig.10. stresses in the components of aqueduct with tie beams fig 11. comparison of deflection of aqueduct with and without tie beams 0 5 10 15 20 25 30 x y z deflection in 'mm' d ir e ct io n s deflection comparison with tie beam without tie beam yadav and babu, j. build. mater. struct. (2020) 7: 140-158 153 permissible values: as per cl. 23.2.1 of (is 456:2000, 2000), permissible value of deflection for simply supported span up to 10m span is 20 mm. but for spans exceeding 10 m, the permissible value of deflection is given: 20 x 10/span in ‘m’. this gives the permissible deflection value as 20*(10/20) = 10 mm. as per is 3370 -2009 (part 2), the permissible value for bending compressive stress & direct stress for concrete grade of m-30 is 10 n/mm2 and 8 n/mm2 respectively. fig. 12(a) and fig. 12(b) show comparison of normal stresses of aqueduct with and without tie beams. it was observed from the results that values of normal stresses for static loads is within permissible limits but the stresses observed for dynamic loads are 2.4 times greater than static loads. for m30 grade of concrete, referring to is 456:2000, maximum permissible shear stress, τc= 3.5 n/mm2. if the values are more than permissible, shear reinforcement shall be provided. fig 12. (a) comparison of aqueduct with and without tie beams under normal stresses fig 12. (b) comparison of aqueduct with and without tie beams under normal stresses shear stress 4.3. analysis of aqueduct with tie beams subjected to both static and dynamic loads the results of different parameters for various load criteria of the elements observed in the aqueduct has been divided into left end, mid span and right end for comparison. 0 10 20 sxx syy szz stress (n/mm^2) d ir e ct io n s normal stresses comparison with tie beam without tie beam 0 5 10 sxy syz szx stress (n/mm^2) d ir e ct io n s shear stresses comparison with tie beam without tie beam 154 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 4.3.1. displacements fig. 13(a) and 13(b) show the bending behaviour of aqueduct for static and dynamic loads. from the results it has been observed that the displacements due to dynamic loads were about 2.4 times compared to that of the static loads. it can be inferred that, the structures which are safe for carrying static loads might be vulnerable to dynamic loads. so, the effect of water sloshing and the dynamic loads has to be considered for design. the maximum displacements of the aqueduct subjected to static loads and dynamic loads are shown in fig. 14. fig 13. (a) bending behaviour for static loads fig. 13 (b) bending behaviour for dynamic loads yadav and babu, j. build. mater. struct. (2020) 7: 140-158 155 fig 14. comparison of deflection of the structure for static & dynamic loads 4.3.2. stresses and its distribution the comparison of normal stresses, shear stresses, and principal stresses on the aqueduct for static and dynamic loading are shown in fig. 15(a) 15(c). it was observed in this case as well, the values of shear stress (without shear reinforcement) were in the safe limits for static loads. but for dynamic loads, shear stresses were very large. it is observed that the stresses are maximum at the supporting ends of the aqueduct. but this can be considerably reduced by taking care of necessary base isolation techniques so that the structure is not heavily damaged. the stress distribution diagrams for hydrostatic loads and hydrodynamic forces under seismic loads have been shown in fig. 16(a) and fig. 16(b). the aqueduct structure was found to undergo vertical bending and the stresses were observed to be maximum at the mid span for static loads. the maximum stresses for the hydrodynamic forces were observed to occur at the outer bottom of the aqueduct structure due to the sloshing water. the stress distribution of tie beams in mid span under static and dynamic loads are shown in fig. 17(a) and fig. 17(b), respectively. 0 1 2 3 4 5 6 7 8 left end mid span right end deflection in 'mm' deflections dynamic load static load 0 10 20 left end mid span right end stress (n/mm^2) (a) normal stresses dynamic load static load 0 5 10 15 left end mid span right end stress (n/mm^2) (b) shear stresses dynamic load static load 156 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 fig 15. comparison of (a) normal stresses (b) shear stresses (c) principal stresses fig 16. stress distribution (a) under static loads (b) dynamic loads 0 20 40 60 left end mid span right end stress (n/mm^2) (c) principal stresses dynamic load static load yadav and babu, j. build. mater. struct. (2020) 7: 140-158 157 fig 17. (a) stress distribution of tie beams in mid span under (a) static loads (b) dynamic loads 5. conclusions based upon the analysis the following conclusions are drawn: • the displacements of the structure in the absence of tie beams at the top is almost 7 times greater than the structure with tie beams under static loads. • provision of tie beams at the top proved to be effective in bracing the walls together by reducing the lateral defection significantly. • the deflections and stresses in the structure due to dynamic forces is predominant compared to the static load. the deflection and stresses developed in the members due to hydrodynamic forces are nearly 2.4 times and 3.8 times more than that due to hydrostatic loads respectively. the deflection is maximum in the mid span and the stresses are maximum at the fixed end of the structure. the maximum stress occurred at the outer bottom of the aqueduct structure caused by the sloshing water and the resulting hydrodynamic forces. 158 yadav and babu, j. build. mater. struct. (2020) 7: 140-158 in this study, elevated aqueduct of single span is modelled and studied. further the structure can be analyzed taking into consideration of the bearings they are resting upon, design of piers subjected to soil pressure or water pressure depending upon the location of the structure in the seismic zone and the effect of it on the aqueduct. the effect of earthquake motions on the piers and eventually on the aqueduct may be considered. it was observed that the stresses are higher at the ends of aqueduct. so, necessary design of bearings may be done to reduce the effect at the bearing ends of the structure. this can be avoided by using a damping equipment such as isolated bearings to reduce the displacement response in a seismic event. the structure can be made to safely withstand the dynamic forces by ductile detailing of the reinforcements. 6. references bai, x. l., fan, y. y., yu, w., & wang, d. f. (2011). dynamic response analysis of large aqueduct structure.in advanced materials research (trans tech publications ltd). 255, 1159-1162. chen, w., & hao, h. (2004). dynamic response analysis of large aqueduct to earthquake ground excitations. in proc., 13th world conf. on earthquake engineering. vancouver, bc: univ. of british columbia. gao, p., wei, d., xu, m., & li, z. (2014). study on the 2.5d fluid-structure interaction model of beam-type aqueduct. journal of information and computational science, 11(13), 4645–4654. haroun, m. a., & tayel, m. a. (1985).response of tanks to vertical seismic excitations.earthquake engineering & structural dynamics, 13(5), 583-595. is 1893 (part 1): 2016 criteria for earthquake resistant design of structures (2016) bureau of indian standards. is 3370-2 (2009): code of practice concrete structures for the storage of liquids, part 2: reinforced concrete structures (2009). is 456:2000 (2000) plain and reinforced concrete code of practice, indian standard. jain, s. k., &jaiswal, o. r. (2007).iitk-gsdma guidelines for seismic design of liquid storage tanks.national information centre of earthquake engineering, kanpur. li, y., lou, m., & pan, d. (2003). evaluation of vertical seismic response for a large‐scale beam‐supported aqueduct.earthquake engineering & structural dynamics, 32(1), 1-14. mitra, s., & sinhamahapatra, k. p. (2007). slosh dynamics of liquid-filled containers with submerged components using pressure-based finite element method. journal of sound and vibration, 304(12), 361-381. rafiee, a., vinches, m., & bohatier, c. (2008).modelling and analysis of the nîmes arena and the arles aqueduct subjected to a seismic loading, using the non-smooth contact dynamics method. engineering structures, 30(12), 3457-3467. salamon, j. w. (2011). seismic induced loads on spillway gates, phase i literature review. tech. rep. dso11-06, u.s. bureau of reclamation, denver, colorado. wu, y., mo, h. h., & yang, c. (2006). study on dynamic performance of a three-dimensional high frame supported u-shaped aqueduct. engineering structures, 28(3), 372-380. zhang, h., liu, l., dong, m., & sun, h. (2013). analysis of wind-induced vibration of fluid–structure interaction system for isolated aqueduct bridge.engineering structures, 46, 28-37. zhang, h., sun, h., liu, l., & dong, m. (2013). resonance mechanism of wind-induced isolated aqueduct– water coupling system. engineering structures, 57, 73-86. j. build. mater. struct. (2021) 8: 63-71 original article doi : 10.34118/jbms.v8i1.778 issn 2353-0057, eissn : 2600-6936 ann modelling approach for predicting scc properties research considering algerian experience. part ii. effects of aggregates types and contents sahraoui m *, bouziani t structures rehabilitation and materials laboratory (sreml), university amar telidji, laghouat, algeria. * corresponding author: med.sahraoui@lagh-univ.dz received: 05-10-2020 accepted: 21-04-2021 abstract. the objective of this investigation is to illustrate the effect of aggregates types and contents on fresh and hardened properties of self-compacting concrete (scc) considering algerian experience. based on experimental data available in the literature, artificial neural network (ann) models are established to illustrate the variation of aggregate types and contents (sand and gravel) in binary and ternary contour plots. modelling results concerning the effect of sand types and proportions in binary and ternary combinations show the beneficial effect of river sand (rs) and crushed sand (cs) on slump flow. the highest l-box ratio was obtained for mixtures composed of 50% of both rs and cs for binary and ternary mixtures. the increase in cs content enhance static stability, while the increase in rs gives higher compressive strength at 28 days. concerning the study of aggregate sizes and contents, it was found that the increase of sand content leads to an increase in flowability and a decrease in static stability. an increase in gravel content leads to a decrease in passing ability, while a significant improvement in viscosity, static stability and mechanical strength with an increase in gravel content were observed. key words: scc, ann, aggregates types and contents, contour plots, fresh and hardened properties. 1. introduction self-compacting concrete (scc) is a highly flowable concrete which can flow and consolidate under its self-weight. due to the complexity of its mix design, scc might be more susceptible to any changes in components compared to conventional concrete (ghoddousi & salehi, 2017). scc is very sensitive to changes in aggregate characteristics (size, grading, shape, texture, and morphology), therefore, the aggregate must be carefully chosen (khaleel, al-mishhadani, & razak, 2011). in order to enhance flowability and passing ability of scc, many researchers suggest the reduction of the total aggregate content within the range of 40-50% of the solid content. the addition of more paste can also contribute to reduce the frequency of collision between coarse particles (ling & kwan, 2015). lin (lin, 2020) show that a higher sand to aggregate ratio (s/a) have a positive effect on flowability, while a decrease in (s/a) ratio improved the mechanical properties of scc. other studies have also evaluated the effects of river, crushed and dune sand in binary and ternary combinations on the fresh and hardened properties of self compacting concretes and mortars (rmili, ouezdou, added, & ghorbel, 2009) (benabed, kadri, azzouz, & kenai, 2012) (bouziani, 2013) (zeghichi, benghazi, & baali, 2014) (sahraoui & bouziani, 2019b). the experimental results indicate an improvement in rheological and mechanical properties with mixtures of cs and ds with rs. artificial neural network (ann) is a predictive tool of machine learning algorithms, which is of great interest to researchers in recent years. this technique allows to modeling the behavior of building materials based on experimental data available in literature (yaman, abd elaty, & taman, 2017) (asteris, kolovos, douvika, & roinos, 2016) . ann is an effective and successful tool to learn and predict scc properties, moreover, this efficient computing system is very useful mailto:med.sahraoui@lagh-univ.dz 64 sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 to treat and combine one or more concrete mix constituents as an independent input variables (gupta, patel, siddique, sharma, & chaudhary, 2019)(jain, jha, & misra, 2008). design of experiments (doe) is also a statistical tool to evaluate the factors and describe the effects of all components proportions as well as all their possible interactions on the variation of each measured responses. response surface methodology is used to investigate the effects of two independent factors, while simplex lattice design is available for mixture models in three factors. in this study, a simplex lattice mixture design approach was used to establish mathematical models in order to illustrate the variation of different types and proportions of three sands in ternary contour plots. on the other hand, mathematical models are also established to illustrate the variation of aggregates size and contents using response surface methodology. 2. methodology the first axis of this research investigates the influence of three types of sands (rs, cs and ds) and their coupled effects on rheological and mechanical properties of scc. a simplex-lattice mixture design was used to describe the effect of sand types (zaitri, bederina, bouziani, makhloufi, & hadjoudja, 2014) (bouziani, 2013)(sahraoui & bouziani, 2019b). this space filling design creates a triangular grid of combinations with three factors and five levels as illustrated in figure 1. the number of experiments or combinations (c) can be calculated by the following equation: (1) where, m and q are the levels and number of factors respectively. with five levels and three factors, the mixture design of this study comprising 21 experiments. each mixture consisted of 450 kg/m3 of cement, 420 kg/m3 of both gravel 3/8 and 8/15 (g1 and g2), total sands content was 860 kg/m3, water to cement ratio (w/c) of 0.4 and the superplasticiser-cement (sp/c) ratios was 1% by weight of cement. a second-degree model was used to describe the effect of sands proportions and their blends. the proposed model is expressed in equation 2: (2) where: y is the output result of ann-based models of predicting scc properties mentioned in the part i of this research (sahraoui & bouziani, 2019c). bi are the model coefficients (table 2) determined by a standard least-square fitting. the second axis devoted to the modelling of aggregate sizes and contents in contours plots using also the ann models of the part i (sahraoui & bouziani, 2019c). the mix proportioning has been designed as follows: sand and gravel contents varying from 750 to 950 kg/m3. three proportions of g1/g2 ratios (0.5, 1 and 2) were chosen. cement content, w/c and sp/c content were kept constant (450 kg/m3, 0.4 and 1% respectively). sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 65 figure 1 simplex-lattice design with 3 factors and 5 levels 3. results and discussion table 1 summarizes test results of predicting fresh and hardened properties of 21 scc mixtures issued from ann models and experimental design of ternary systems. correlation coefficients (r2), root mean square error (rmse), p-values (p) and coefficients of derived models (coeff.) are shown in table 2. this finding shows a strong correlation coefficients (r280%), a lower rmse values and p-value less than 0.05 for all studied responses which is statically significant and indicate the good prediction performance of the obtained models. table 1 sands combinations and output results of ann-based models mix n° sands combinations slump (cm) v-funnel (s) l-box (%) pi (%) rc28 (mpa) rs cs ds 1 1 0 0 77,00 5,68 82,88 13,09 92,93 2 0.8 0 0.2 74,28 5,97 67,11 13,41 80,17 3 0.8 0.2 0 74,84 5,70 85,16 8,22 88,33 4 0.6 0 0.4 72,24 6,58 67,05 12,12 64,34 5 0.6 0.2 0.2 72,37 6,14 88,25 12,18 73,43 6 0.6 0.4 0 71,22 5,81 93,09 5,86 80,74 7 0.4 0 0.6 70,95 7,30 71,62 11,30 55,07 8 0.4 0.2 0.4 70,13 6,75 80,64 11,05 63,67 9 0.4 0.4 0.2 69,10 6,33 96,54 9,80 68,72 10 0.4 0.6 0 69,09 5,98 91,32 3,91 73,32 11 0.2 0 0.8 69,58 8,07 76,11 11,17 53,48 12 0.2 0.2 0.6 68,19 7,37 87,88 10,75 56,07 13 0.2 0.4 0.4 66,81 6,85 84,34 9,54 63,75 14 0.2 0.6 0.2 67,80 6,48 94,05 3,94 66,34 15 0.2 0.8 0 71,77 6,17 89,81 2,33 68,56 16 0 0 1 66,79 8,96 80,68 11,18 53,29 17 0 0.2 0.8 65,23 8,10 93,35 10,82 54,41 18 0 0.4 0.6 64,07 7,41 83,89 9,67 57,15 19 0 0.6 0.4 65,32 6,90 91,90 7,82 64,02 20 0 0.8 0.2 68,91 6,57 90,82 1,33 65,32 21 0 1 0 72,26 6,33 86,18 1,43 66,25 66 sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 table 2 model parameters estimates of measured responses c o e ff ic ie n ts slump (cm) v-funnel (s) l-box (%) pi (%) rc28 (mpa) r2=0.96 r2=0.99 r2=0.80 r2=0.91 r2=0.98 rmse=0.7892 rmse=0.0460 rmse=4.4570 rmse=1.3489 rmse=1.5574 p<0.0001 p<0.0001 p<0.0001 p<0.0001 p<0.0001 coeff. coeff. coeff. coeff. coeff. b1 77.019635 5,5989016 78,531529 12,776154 94,807684 b2 72.370621 6,3419881 84,771469 -0,124884 66,244594 b3 67.115348 8,9467554 82,700394 10,839367 51,931309 b4 -15.10044 -0,170344 52,323887 -3,696535 -13,35029 b5 0.0768441 -1,347922 -41,96906 3,2970021 -51,55611 b6 -18.97238 -1,884983 32,960541 12,166139 6,6548402 ternary contour plots presented in figure 2 and figure 3 illustrate the effects of rs, ds and cs proportions on slump flow and l-box ratio. it can be seen that the increase of rs and cs will improve flowability and the rs has the greatest effect on slump flow measurements. this is apparently caused by the well graded rs particles and the important quantity of fines in cs which resulting in a higher packing (nécira, guettala, & guettala, 2017) (sahraoui & bouziani, 2019b). figure 2 ternary plot of slump flow (cm) as function of rs, cs and ds proportions figure 3 ternary plot of l-box ratio (%) as function of rs, cs and ds proportions sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 67 results also indicate that l-box ratio increases with the increase of cs and ds proportions in rscs and cs-ds binary systems respectively, corresponding to proportions of approximately 0.5 of both cs and ds, and then decreased. this can be explained by the larger amount of excess paste due to the filling effect of cs and ds fine grains (bouziani, 2013). the effect of different sands proportions on the flow time of v-funnel and sieve segregation test are illustrated in figure 4 and figure 5. it is evident that v-funnel time clearly increased with the increase of ds proportion. this can be attributed to the large finesse of ds which requires high water and paste demand (benabed et al., 2012) (rmili et al., 2009). it was also observed that the increase in cs content led to a significant increase in static stability due to the angular shape and the important fines content of cs (zeghichi et al., 2014) (nécira et al., 2017) (bouziani, 2013). figure 4 ternary plot of v-funnel time (s) as function of rs, cs and ds proportions figure 5 ternary plot of sieve stability (%) as function of rs, cs and ds proportions compressive strength plot at 28 days is shown in figure 6. it can be seen that the increase of rs gives higher compressive strengths than those with high ds and cs contents. this enhancement of strength can be attributed to the well graded of rs and the calcareous nature and the angular form of cs, while the decrease in strength is attributed to the high intergranular porosity caused by the rounded shape and the large finesse of ds (zeghichi et al., 2014) (nécira et al., 2017) (bouziani, 2013) (benabed et al., 2012). 68 sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 figure 6 ternary plot of rc28 (mpa) as function of rs, cs and ds proportions the results of slump flow and l-box test are presented figure 7 and figure 8. as clearly shown, the increase of sand content leads to an increase in flowability. on the other hand, slump flow decreases with an increase in gravel content for mixtures made with high contents of g1 (i.e. 2/3g1-1/3g2). an increase in the content of gravel 3/8 leads to a significant increase in the interparticle friction, thus resulting in a reduction in flowability (aïssoun, hwang, & khayat, 2016). in the case of equal proportions of g1 and g2 (i.e. 1/2g1-1/2g2), the increase of gravel content increases slump flow until a maximum value (79 cm) and then decreased. figure 7 contour plots of the slump flow (cm) as function of sand and gravel contents figure 8 contour plots of l-box ratio (%) as function of sand and gravel contents sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 69 this phenomenon can be explained by the fact that sand particles filled spaces between the coarser aggregates g1, thereby increasing the compactness of the mixture and hence larger amount of excess paste for lubrication purpose. once the voids were completely filled, g1 then began to occupy the place of sand particles which results in a large volume of void and consequently the flowability decreases(bouziani, 2013). it should be noted also that the amount of sand content has no appreciable effect on l-box measurements. on the other hand, we note that an increase in gravel content leads to a decrease in passing ability and this is due to the fact that the granular blocking is related to the probability of presence of coarse aggregate (roussel, nguyen, yazoghli, & coussot, 2009). figure 9 and figure 10 present contour plots of v-funnel and sieve segregation test as function of sand ang gravel content. results show that an increase in sand content leads to a decrease in static stability. it was observed also that v-funnel time and static stability increase with an increase in gravel content, which confirm once again that viscosity and static stability enhance with the increase of aggregate size and content (hu & wang, 2011) (sahraoui & bouziani, 2019a). the contour plots of compressive strength presented in figure 11 illustrate the trade-offs between sand and gravel content. in order to better insights the effect of sand and gravel, the preview should be focused on mixtures made with high contents of g1 and g2 where the negative impact of increasing sand content can be clearly shown. on the other hand, an increase of gravel content leads to a significant improvement in mechanical strength. this compressive strength changes can be mainly attributed to the effect of aggregate size on pores characteristics and cement paste thickness (yu, sun, wang, & hu, 2019). figure 9 contour plots of v-funnel time (s) as function of sand and gravel contents figure 10 contour plots of sieve stability (%) as function of sand and gravel contents 70 sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 figure 11 contour plots of rc28 (mpa) as function of sand and gravel contents 4. conclusion based on the results of this modelling investigation, the following conclusions were derived: the design of experiments is a very useful method that aims to analyze, describe and improve the precision of the developed ann models. exploiting the experiment results in binary and ternary contours plots could provide more flexibility for analyzing and interpreting the obtained results. the increase of rs proportion led to a significant increase in flowability the highest passing ability was obtained for sand binary or ternary mixtures composed of 50% of both rs and cs. v-funnel time decreased with the increase of ds proportion, while the enhancement of static stability was attributed to the high amount of fine content of cs. high ds content leads to a decrease in mechanical compressive strength at 28 days. the increase of sand content improves the flowability, while the increase in gravel content leads to a significant decrease in passing ability expressed by l-box test. v-funnel time and static stability increased with the increase of gravel content. a negative impact of increasing sand content in compressive strength can be clearly shown. instead, an increase of gravel content leads to a significant improvement in mechanical strength. 5. references aïssoun, b. m., hwang, s.-d., & khayat, k. h. (2016). influence of aggregate characteristics on workability of superworkable concrete. materials and structures, 49(1–2), 597–609. asteris, p. g., kolovos, k. g., douvika, m. g., & roinos, k. (2016). prediction of self-compacting concrete strength using artificial neural networks. european journal of environmental and civil engineering, 20(sup1), s102–s122. benabed, b., kadri, e.-h., azzouz, l., & kenai, s. (2012). properties of self-compacting mortar made with various types of sand. cement and concrete composites, 34(10), 1167–1173. bouziani, t. (2013). assessment of fresh properties and compressive strength of self-compacting concrete made with different sand types by mixture design modelling approach. construction and building sahraoui and bouziani et al., j. build. mater. struct. (2021) 8: 63-71 71 materials, 49, 308–314. ghoddousi, p., & salehi, a. m. (2017). the evaluation of self compacting concrete robustness based on the rheology parameters. international journal of civil engineering, 15(8), 1097–1106. gupta, t., patel, k. a., siddique, s., sharma, r. k., & chaudhary, s. (2019). prediction of mechanical properties of rubberised concrete exposed to elevated temperature using ann. measurement, 147, 106870. hu, j., & wang, k. (2011). effect of coarse aggregate characteristics on concrete rheology. construction and building materials, 25(3), 1196–1204. jain, a., jha, s. k., & misra, s. (2008). modeling and analysis of concrete slump using artificial neural networks. journal of materials in civil engineering, 20(9), 628–633. khaleel, o. r., al-mishhadani, s. a., & razak, h. a. (2011). the effect of coarse aggregate on fresh and hardened properties of self-compacting concrete (scc). procedia engineering, 14, 805–813. lin, w.-t. (2020). effects of sand/aggregate ratio on strength, durability, and microstructure of selfcompacting concrete. construction and building materials, 242, 118046. ling, s. k., & kwan, a. k. h. (2015). adding ground sand to decrease paste volume, increase cohesiveness and improve passing ability of scc. construction and building materials, 84, 46–53. nécira, b., guettala, a., & guettala, s. (2017). study of the combined effect of different types of sand on the characteristics of high performance self-compacting concrete. journal of adhesion science and technology, 31(17), 1912–1928. rmili, a., ouezdou, m. ben, added, m., & ghorbel, e. (2009). incorporation of crushed sands and tunisian desert sands in the composition of self compacting concretes part ii: scc fresh and hardened states characteristics. international journal of concrete structures and materials, 3(1), 11–14. https://doi.org/10.4334/ijcsm.2009.3.1.011 roussel, n., nguyen, t. l. h., yazoghli, o., & coussot, p. (2009). passing ability of fresh concrete: a probabilistic approach. cement and concrete research, 39(3), 227–232. sahraoui, m., & bouziani, t. (2019a). effect of coarse aggregates and sand contents on workability and static stability of self-compacting concrete. advances in concrete construction, 7(2), 97. sahraoui, m., & bouziani, t. (2019b). effects of fine aggregates types and contents on rheological and fresh properties of scc. journal of building engineering, 26, 100890. yaman, m. a., abd elaty, m., & taman, m. (2017). predicting the ingredients of self compacting concrete using artificial neural network. alexandria engineering journal, 56(4), 523–532. yu, f., sun, d., wang, j., & hu, m. (2019). influence of aggregate size on compressive strength of pervious concrete. construction and building materials, 209, 463–475. zaitri, r., bederina, m., bouziani, t., makhloufi, z., & hadjoudja, m. (2014). development of high performances concrete based on the addition of grinded dune sand and limestone rock using the mixture design modelling approach. construction and building materials, 60, 8–16. zeghichi, l., benghazi, z., & baali, l. (2014). the effect of the kind of sands and additions on the mechanical behaviour of scc. physics procedia, 55, 485–492. j. build. mater. struct. (2021) 8: 1-8 original article doi : 10.34118/jbms.v8i1.783 issn 2353-0057, eissn : 2600-6936 geopolymer cement: an initiative towards the replacement of grey cement by green cement in future mukesh kumar m *, asis kumar k dalmia cement research centre, research unit of dalmia cement bharat ltd. chennai-600116, tamilnadu, india. * corresponding author: mishra.mukesh1@dalmiacement.com received: 23-10-2020 accepted: 06-01-2021 abstract. the emissions of greenhouse gases such as carbon dioxide from the production of ordinary portland cement and blended portland cement have widely affected the environment with increase in infrastructure development worldwide. secondly, due to the continuous mining of limestone for the production of cement there is also simultaneous depletion of natural resources and hardly will it last up to maximum 40 years. hence we need to switch over to some other alternate binders for constructions purpose in future. geopolymer cement is one of the inventions which is produced by a polymeric chain reaction of alkali-activated alumino-silicate materials better known as alkali activator (naoh/na2sio3) binders with the industrial by-product materials such as fly ash, rice husk ash, slag, crusher dust etc. and provides high compressive strength which is comparable to bpc and reduces the carbon foot print. the objective of our study is to prepare the low co2 foot print green geopolymer cement which may substitute the ordinary portland cement and blended portland cement in future and will helpful to reduce the greenhouse effect up to some extent and takes an initiative towards the green revolution movement. key words: geopolymer cement, green cement, carbon foot print, green revolution, alkali activator. 1. introduction the emission of greenhouse gases such as carbon dioxide (co2) from ordinary portland cement (opc) and blended portland cement (bpc) production have widely affected the environment with increase in infrastructure development worldwide due to which the production/ demand of opc as binder in concrete continuously increases (petek et al., 2014). due to the natural resource depletion and co2 emission issues during cement manufacturing, the need of switch over to alternate binders becomes important (deb et al., 2014). however, the alternate binding materials, those replace the opc/bpc should have certain criteria such as they should be ecofriendly, acceptable, readily available and cost effective. the durability and strength of the set mass needs to be as good as that from opc or bpc. geopolymer cement (gpc) is one of the least carbon foot print cement which is mainly produced by a polymeric chain of reaction of alkaliactivated alumino-silicate mineral binder (combination of sodium silicate, and sodium hydroxide) with aluminosilicate rich industrial by-products such as fly ash (fa)/crusher dust (cd)/ blast furnace slag (bfs)/granulated blast furnace slag (gbfs)/ground granulated blast furnace slag (ggbfs)/ ultrafine ground granulated blast furnace slag (uggbfs) (laskar et al., 2017 and part et al., 2015). the term geopolymer was introduced nearly before two to three decades back by davidovits (1989) and according to him geopolymers are consist of a polymeric si–o–al framework, having amorphous structure. they comprise of small aluminosilicate clusters with pores dispersed within a highly porous network having clusters sizes in between 5 and 10 nanometers. basically geo-polymers are classified into three types based on their different monomer units such as polysialate (sioalo) having sio2/al2o3 = 2, polysialatesiloxo (sioalosio) having sio2/al2o3 = 4, and polysialatedisiloxo (sioalo sio sio) having sio2/al2o3 = 6. the alkaline solution dissolves al3+ and si4+ ions from the aluminosilicate rich materials, which subsequently improves compressive strength by forming sodium aluminosilicate hydrate mailto:mishra.mukesh1@dalmiacement.com 2 mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 (nash) and/or potassium alumino silicate (kash) gels (phoo-ngernkham et al., 2015). these are also called as inorganic polymer cement (palomo et al., 2003) and play vital role in the context of sustainability and environmental issues by reducing the co2 emissions originate from the manufacturing of portland cement (bell et al., 2008 and shi et al., 2011) because approximately 5% of global co2 emissions are originated from the manufacturing of portland cement (lawrence et al., 1998 and hardjito et al., 2004). fa is found to be one of the major sources of silica (sio2) and alumina (al2o3) in gp. fa is classified to class c/class f based on its chemical composition, where the main difference is the calcium amount. the class c fa has a higher content of calcium than that of class f fa. a higher content of cao in the fa results in a higher compressive strength of gpc due to the formation of hydrated products, such as calcium silicate hydrate (csh) (diaz et al., 2010). however, at this condition workability of gpc is found to be decreasing significantly (less than 3 min) due to high reactivity of class c fa. hence, class f fa is selected as a good raw material for gpc due to its lower reactivity rate, which leads to a proper workability and reduced water demand (kumar et al., 2010). in order to improve the mechanical properties of gpc made up of class f fa, small amounts of other additives enriched in cao such as bfs can be added (kim et al., 2013). the ggbfs is one of the most common components in geopolymer mortar and concrete, due to improved mechanical and micro structural properties (hubler et al. 2011). gpc may be treated as an alternative to portland cement (pc), with an improved performance compared to traditional concretes (van jaarsveld et al., 2002 and hardjito et al., 2004] while utilizing a suitable proportion of by-product materials. when developing gpc formulations, the type, amount and ratio of the raw materials, curing time and temperature needs to be taken into account (part et al., 2015). bfs based gpc have wide range of potential applications as they may replace the conventional portland cement concrete (pcc) in the construction industry. the use of gpc can reduce the co2 emission which is produced due to the manufacturing of pc. zhang et al. in 2003 had summarized the discussions on geopolymer based on previous research and showed that the geopolymer is nothing but a form of zeolite precursor or intermediate (babajide et al., 2012). moreover, hu et al. (2008) had investigated the compressive strength, bond strength and abrasion resistance of metakaolin (mk) based concrete consisting of geopolymer pastes and found that the early strength and mechanical properties were found to be better than that of portland cement based pastes. increase in fineness of binding material also leads to early strength gain in gpc because early age strength is a desirable property of concrete repairing agent (kim et al., 2017). 2. materials and experimental methods gbfs, fa and alkali activators (naoh/na2sio3) are the major raw materials used in this trial. to get proper fineness, both gbfs and fa are ground in 5 kg capacity lab ball mill at different time interval. r-45 micron sieve residue and fineness (by blaine air permeability apparatus) are the parameters taken into consideration in the ground slag samples. 1:1 ratio of gbfs and fa are taken into consideration for experimental study and 1:1 ratio mixture of 14 m sodium hydroxide and liquid sodium silicate solution are used as alkali activators in this trial. it is because the gpc mixes with 14 m alkali concentration is found to be exhibit higher compressive strength (cst) as compared to other lower molar alkali concentration which is in line with the results obtained in earlier studies (alonso et al., 2001) where the rate of strength gain was explained to be dependent on alkali concentration i.e. lower alkali concentration led to slow rate of formation of polymerization product with lower structural strength (atis et al., 2015) while higher is the alkali concentration higher will be the rate of strength gain at specified days. to prepare geopolymer mortars, gbfs and fa are dry mixed in planetary mixer with 1:1 ratio for 60 seconds and 50% alkali activators solution is added in it and again wet mixed thoroughly for 90 seconds. mortar casting done in 70 mm cubical mould, geopolymer paste is filled in it and vibrated for 2 minutes on vibrating machine @ 12000± 400 rpm for the compaction and mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 3 removal of air voids. after 24 hours, mortars are removed from moulds and they have been kept at room temperature (27 ± 20 c) and cst tests have been done at the intervals of 1, 3, 7 and 28 days. table 1. materials used for geopolymer preparation gbfs 50% fa 50% alkali activator naoh : na2sio3 (1:1) alkali activator : geopowder (fa+gbfs) 1:2 table 2. specific surface area, r-45 and r-90 of geopowder geopowder r-45 (% wt.) 18.23 r-90 (% wt.) specific surface area (m2/kg) 400 3. characterizations the structural analysis of the composite films were characterized by the xrd technique using xray diffraction spectrometer (bruker, d8 endeavor) with cu-kα radiation (λ = 1.54 ǻ) over a wide range of bragg’s angles (80 ≤ 2θ ≤ 700). the elemental analysis was done by x-ray fluorescence spectrometer (panalytical, axiox max). the morphology of the geopolymer cement was studied by philips cm 200 transmission electron microscope. the presences of different functional groups present in the composites were confirmed by using the instrument shimadzu prestige-21 ftir spectrometer over a frequency range of 4000-500 cm-1. the cst was measured on different samples at 1, 3, 7 and 28 days using cstm with a maximum load of 500 kn and a loading force of 2.8 kn/s. 4. results and discussion 4.1. x-ray fluorescence (xrf) study the elemental analysis of the fa, gbfs, gpc and various blended portland cements such as portland pozzolana cement (ppc), portland slag cement (psc) and composite cement (cc) are carried out by x-ray fluorescence spectrometer to know the percentage of elements (in the form of oxides) present in the respective materials and the results are given in table. 3. raw materials oxides % sio2 al2o3 fe2o3 cao mgo so3 k2o na2o fa values 64.14 25.84 3.76 1.81 1.10 0.06 1.56 0.10 gbfs values 33.28 19.03 0.68 36.71 9.10 0.33 0.52 0.38 gpc values 43.23 18.14 2.12 15.76 4.29 0.41 0.89 4.68 ppc values 35.31 14.00 4.00 38.78 1.58 1.77 1.15 0.12 psc values 33 10 2.00 46.00 2.37 2.15 0.32 0.40 cc values 25.4 6.23 3.21 55.12 2.7 2.82 1.12 0.35 4.2. mineralogy study by x-ray diffraction (xrd) the xrd pattern of gpc containing gbfs, fa and alkali activator is shown in figure-1. it is observed from the graph that there are mainly four types of phases such as mullite (m), quartz (q), cristobalite (c) and zeolite phases (z). mullite [al (al0.83si1.08o4.85)] is a rare alumino silicate mineral which is formed by post-clay genesis at elevated temperature and atmospheric pressure by a series of reactions in clay minerals (rashad et al., 2020). the initial endothermic reaction is caused by dehydroxylation of the clay mineral and formation of an amorphous metakaolin phase followed by successive exothermic reactions. the mullite is signified by powder diffraction file 4 mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 (pdf no. 01-79-1453), joint committee on powder diffraction standards (jcpds). quartz is one of the most common minerals in the earth’s crust. it is widely distributed mineral of many varieties which consist of mainly oxygen and silicon having a specific crystalline form (hexagonal) (huang et al., 2020). the quartz is signified by (powder diffraction file (pdf) no. 00-005-0490. cristobalite is a mineral polymorph of silica which is formed at very hightemperature in which the silica tetrahedra are packed in a three-layer structure (qiao et al., 2019). zeolite, any member of a family of hydrated aluminosilicate minerals that contain alkali and alkaline-earth metals. they are known for their lability toward ion-exchange and reversible dehydration (nikolov et al., 2020). the formation of zeolite phase [na8.86 ((al8.38si27.62) o72] indicates that the mullite, cristobalite and quartz phases found in gbfs and fa may be dissolved partly by the binding agent (naoh/na2sio3) and solidified into na-al-silicates which might be a possibility of formation of geopolymer via polymerization reaction. the presence of zeolite phase is responsible for the higher compressive strengths of gpc. fig. 1. xrd image of gpc 4.3. morphology analysis by transmission electron microscope (tem) figure-2 shows the tem images corresponding to the morphological prospective view of gp with fa and gbfs in 1 day and 28 days. it is observed from both the figure that there are some angular to spherical particles present which could be the polymerization product after treating of fa and gbfs with alkali the activator naoh/na2sio3. the morphological changes observed in the gp are due to the suspension of sio2 and al2o3 in alkaline solution leading to the formation of alumino-silicate gel which acts as a precursor during the formation of geopolymer. however, if we observe both figures noticeably it is found that compactness and uniformities of gbfs and fa are low in case of fig. 2 (a) but they are properly compacted and homogenized in fig. 2 (b) due to which the cst is higher in 28 days as described by kumar et al. (2005) due to the formation of a compact microstructure. mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 5 1day 28days fig. 2. gpc with fa and gbfs 4.4. fourier-transform infrared spectroscopy (ftir) analysis in case of fa based gpc a peak is observed nearly at 3500 cm-1 corresponding to ohstr which may be due to the addition of small amount of water to the alumino silicates materials (fa/gbfs) along with the alkali (naoh) and alkali activator (na2sio3). the peaks at 1009 and 1034 cm−1 are attributed to asymmetric stretching of al-o and si-o bonds originated from individual tetrahedral. the peak observed at nearly 1000-1100 cm-1 corresponds to siostr and this may be due to the formation of (sioalo) linkage by the polycondensation reactions between the alumino silicates rich materials and alkaline solution (rajan et al., 2020). fig. 3. ftir spectra of gpc 4.5. compressive strength (cst) of gpc in comparison to other types of bpcs cst is a parameter which is used to describe the mechanical properties of cement and concrete. the results of cst of gpc, portland pozzolana cement (ppc), portland slag cement (psc) and composite cement (cc) are given in figure-4. the cst was found to be increased significantly 6 mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 from day 3 to day 28. similarly the cst of the gpc mixture increases with curing time because the long curing time duration relatively improves the mobility of particles in the mixes leading to their even distribution and thus forming of homogenous mixes and helps to form more compact microstructure of the binder and improving the microstructure of geopolymer matrix (kosmatka et al., 2002). secondly, the na released from the alkali activator (naoh/na2sio3) binders during this period would react with the dissolved silicate from the bfs forming new reaction products proposed as a na-a-s-h type product thereby increasing the later strength (phoo-ngernkham et al., 2015). however, the strength is low at initial period of time which may be attributed to the less reactivity of naoh in the binder and reduced activation of the binder material. this means when the time duration increases the compatibility between the alkali activator and the geopowder (fa+gbfs) also increases which improves their chemical bonding making it more uniform and homogenized and responsible for high compressive strength (kosmatka et al., 2002). fig. 4. cst of gpc in comparison to other types of bpcs at the time interval of 1, 3, 7 and 28 days. 5. conclusion mixes of gbfs and fa in presence of alkali activators were used for conducting the trials. xrd analysis confirmed the presence of zeolite phase which is one of the characteristics peaks indicating the formation of geopolymer after the addition of fa and gbfs to alkali activators. tem indicated the good compactness and uniformities of gbfs & fa in alkali activators in 28 days. the functional feature of gpc was performed by ftir. the elemental analysis was done by xrf spectrometer. the xrd analysis was done to analyze the presence of various phases of gp and gpc. the compressive strength of gpc was found to be higher than that of bpc indicating a good future of gpc which can substitute the bpc for construction purposes and will be responsible for lowering the carbon foot print. acknowledgement the authors would like to thank dalmia cement bharat ltd., india for providing all the facilities to carry out the research work and also for the financial support for smooth work. mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 7 6. references alonso, s., & palomo, a. (2001). alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio. materials letters, 47(1-2), 55-62. atiş, c. d., görür, e. b., karahan, o. k. a. n., bilim, c., i̇lkentapar, s. e. r. h. a. n., & luga, e. (2015). very high strength (120 mpa) class f fly ash geopolymer mortar activated at different naoh amount, heat curing temperature and heat curing duration. construction and building materials, 96, 673-678. babajide, o., musyoka, n., petrik, l., & ameer, f. (2012). novel zeolite na-x synthesized from fly ash as a heterogeneous catalyst in biodiesel production. catalysis today, 190(1), 54-60. bell, j. l., sarin, p., provis, j. l., haggerty, r. p., driemeyer, p. e., chupas, p. j., van deventer, j. s. j., & kriven, w. m. (2008). atomic structure of a cesium aluminosilicate geopolymer: a pair distribution function study. chemistry of materials, 20(14), 4768-4776. davidovits, j. (1989). geopolymers and geopolymeric materials. journal of thermal analysis, 35(2), 429441. deb, p. s., nath, p., & sarker, p. k. (2014). the effects of ground granulated blast-furnace slag blending with fly ash and activator content on the workability and strength properties of geopolymer concrete cured at ambient temperature. materials & design, 62, 32-39. diaz, e. i., allouche, e. n., & eklund, s. (2010). factors affecting the suitability of fly ash as source material for geopolymers. fuel, 89(5), 992-996. hardjito, d., wallah, s. e., sumajouw, d. m., & rangan, b. v. (2004). on the development of fly ash-based geopolymer concrete. materials journal, 101(6), 467-472. hu, s., wang, h., zhang, g., & ding, q. (2008). bonding and abrasion resistance of geopolymeric repair material made with steel slag. cement and concrete composites, 30(3), 239-244. huang, j., xu, w., chen, h., & xu, g. (2020). elucidating how ionic adsorption controls the rheological behavior of quartz and cement-quartz paste. construction and building materials, 272, 121957. hubler, m. h., thomas, j. j., & jennings, h. m. (2011). influence of nucleation seeding on the hydration kinetics and compressive strength of alkali activated slag paste. cement and concrete research, 41(8), 842-846. kim, j. h., & lee, h. s. (2017). improvement of early strength of cement mortar containing granulated blast furnace slag using industrial byproducts. materials, 10(9), 1050. kim, m. s., jun, y., lee, c., & oh, j. e. (2013). use of cao as an activator for producing a price-competitive non-cement structural binder using ground granulated blast furnace slag. cement and concrete research, 54, 208-214. kosmatka, s. h., kerkhoff, b., panarese, w. c., macleod, n. f., & mcgrath, r. j. (2002). design and control of concrete mixtures, seventh canadian edition, cement association of canada, 151. kumar, s., kumar, r., & mehrotra, s. p. (2010). influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer. journal of materials science, 45(3), 607-615. kumar, s., kumar, r., alex, t. c., bandopadhyay, a., & mehrotra, s. p. (2005). effect of mechanically activated fly ash on the properties of geopolymer cement. in proceedings of the 4th world congress on geopolymer (pp. 113-116). 8 mukesh kumar and asis, j. build. mater. struct. (2021) 8: 1-8 laskar, s. m., & talukdar, s. (2017). preparation and tests for workability, compressive and bond strength of ultra-fine slag based geopolymer as concrete repairing agent. construction and building materials, 154, 176-190. lawrence, c.d. (1998). the production of low-energy cements, in: heweit, p, c (eds.), lea's. chemistry of cement and concrete, oxford: butterworth-heinemann, 421. nikolov, a., nugteren, h., & rostovsky, i. (2020). optimization of geopolymers based on natural zeolite clinoptilolite by calcination and use of aluminate activators. construction and building materials, 243, 118257. palomo, a., & dela fuente, j. l. (2003). alkali-activated cementitous materials: alternative matrices for the immobilisation of hazardous wastes: part i. stabilisation of boron. cement and concrete research, 33(2), 281-288. part, w. k., ramli, m., & cheah, c. b. (2015). an overview on the influence of various factors on the properties of geopolymer concrete derived from industrial by-products. construction and building materials, 77, 370-395. petek, a. g., masanet, e., horvath, a., & stadel, a. (2014). life-cycle inventory analysis of concrete production: a critical review. cement and concrete composites, 51, 38-48. phoo-ngernkham, t., maegawa, a., mishima, n., hatanaka, s., & chindaprasirt, p. (2015). effects of sodium hydroxide and sodium silicate solutions on compressive and shear bond strengths of fa–gbfs geopolymer. construction and building materials, 91, 1-8. qiao, z., liu, q., zhang, s., & wu, y. (2019). the mineralogical characteristics between opaline silica in bentonite and α-cristobalite. solid state sciences, 96, 105948. rajan, h. s., & kathirvel, p. (2020). sustainable development of geopolymer binder using sodium silicate synthesized from agricultural waste. journal of cleaner production, 124959. rashad, m., sabu, u., logesh, g., srishilan, c., lodhe, m., joy, a., & balasubramanian, m. (2020). mullite phase evolution in clay with hydrated or anhydrous alf3. journal of the european ceramic society, 40(15), 5974-5983. shi, c., jiménez, a. f., & palomo, a. (2011). new cements for the 21st century: the pursuit of an alternative to portland cement. cement and concrete research, 41(7), 750-763. van jaarsveld, j. g. s., van deventer, j. s. j., & lukey, g. c. (2002). the effect of composition and temperature on the properties of fly ash-and kaolinite-based geopolymers. chemical engineering journal, 89(1-3), 63-73. j. build. mater. struct. (2014) 1: 58-64 https://doi.org/10.34118/jbms.v1i2.12 issn 2353-0057 thermophysical characterization of earth blocks stabilized by cement, sawdust and lime azakine sindanne s 1, ntamack ge 1, lemanle sanga rp 1, *, moubeke ca 1, kelmamo sallaboui es 1, bouabid h 2, mansouri k 3, d’ouazzane sc 4 1 groupe de mécanique et des matériaux, gmm, département de physique, faculté des sciences université de ngaounderé b.p. 454 ngaoundéré, cameroon 2 laboratoire de mécanique et matériaux, faculté des sciences, université mohammed v, agdal, avenue ibn batouta, agdal, rabat, morocco. 3 laboratoire des signaux, systèmes distribués et intelligence artificielle (ssdia) enset, boulevard hassan ii mohammedia, université hassan ii casablanca, morocco. 4 laboratoire de mécanique, thermique et matériaux, lmtm, ecole nationale de l’industrie minérale, enim, b.p. 753 rabat, morocco. * corresponding author: lemanlesanga@yahoo.fr abstract. several buildings throughout the world are built with blocks of compressed and stabilized ground. these blocks do not commonly have the same thermal properties necessary for their use. if the incorporation of stabilizer in these blocks like lime or cement increases the mechanical properties, it is not the case for the thermophysical properties. in this paper, the evolution of the thermal properties of earth blocks according to the rates of stabilizer and their nature was discussed. the experimental method of “hot iron” was applied. results indicate that thermal conductivity increases when percentages of cement and lime increase. however, it decreases when the rates of the sawdust increase. moreover, thermal resistance decreases according to the percentages of lime and cement, and increases according to the percentages of the sawdust. key words: earth blocks, stabilization, thermal conductivity, thermal resistance, cement, lime, sawdust. 1. introduction earth blocks can be done using raw or cooked earth. nowadays, the technique of stabilization is used to improve the mechanical and physical properties of earth blocks (de chazelles, 2011). the stabilization technique can be defined as all physical or chemical processes used to improve the characteristics of earth blocks, in particular its bearing resistance, its sensitivity and its durability (meukam, 2004). several construction techniques using earth as a raw material exist (for example: bauge, adobe, compressed earth brick, mud, earth-straw, etc.) (plat, 1989). in warm regions such as cameroon, morocco and yemen, earth block is used in the form of mud (pignal, 2005). nowadays, earthen construction has experienced a renewed interest thanks to the introduction of new techniques of preparation and scientific analysis. such is the case of compressed earth blocks (ceb) mode. the ceb have a good mechanical resistance and a good thermal inertia. however this resistance is low when compared to that of other building materials. therefore, they are stabilized by cooking either by addition of stabilizers, such as lime, cement or even by adding materials of vegetable such as straw or sawdust. in this paper, the thermophysical properties of compressed and stabilized earth block (cseb) were determined. at first, some heat transfer modes and techniques of thermal insulation in buildings was presented. next, the methods used to estimate the thermophysical properties of the cseb were described. finally an analysis of the experimental results of conductivities and measured thermal resistance was completed. 2. materials and methods there are three types of thermal isolation: interior isolation, exterior and integrated isolation (binici, 2007). the estimation of thermophysical quantities of cseb is an aspect that needs to be mastered by manufacturers. among the many methods developed for the determination of these properties, the following principal methods can be cited: hot iron method (rigacci, 2002); hotmailto:lemanlesanga@yahoo.fr azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 59 wire method (castets, 1982); flash method (parker, 1961) and guarded hot plate method (khedari, 2005). in our work, the technique of hot iron, which has proven its efficiency, has been opted (rigacci, 2002). methods for the experimental identification of sources of heat, heat flux or thermophysical parameters require an instrument for measuring temperature in transient or permanent regime in specific points on the rear surface or prior samples (fourier, 1988). the most commonly used contact measuring instruments are the thermocouple, platinum and thermistor probes. 2.1. description of the hot iron method this method dwells on the use of a cylindrical bar of iron and a thermometer. the matter is to connect the iron to the sector and to introduce it at the center of the test piece. the iron must be isolated from the thermometer to reduce heat loss. iron allows you to heat the tube and cause the rise in temperature in the thermometer. this technique measures the difference of temperature in the cseb between the initial state and the state after heating. the evolution of the temperature depending on the time, that the tube heats up, can be expressed as follows (rigacci, 2002): 2 2 1 1t t t r r d tr        (1) with the following boundary conditions (nagasaka, 1981): 0 , 0, ( , ) ( , ) 0 ( , ) 0, 0, lim( ) 2 , 0, lim( ( , ) 0 r r r t t r t t r t t t r t q t r r r r t t r t                          2 ( , ) ( ) 4 4 q r t r t dt     (2) if: 2 4 r dt  the following equation can be written: 4 ( , ) log( ) ( ) 0( ) 4 q dt t r t e              (3) taking into account the linear asymptote at long time, eq 3 can be simplified to be: 1 ( , ) log( ) log( ) 4 q t r t t te            (4)  : thermal conductivity ; q : flow of heat per unit length e : the thickness of the test piece 60 azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 r : distance from the railway to the thermometer. by standing in the case of a radial transfer in a semi-infinite medium, the formalism of quadruples in the laplace domain allows the time long to approach the temperature t by the relation (oladele, 2003): ( , ) log( )t r t t    (5) with  = 4 q thus, the identification of the slope α of the linear part of the thermogram (log( ))t t in equation (eq 1) leads to estimate the thermal conductivity by the following relation:  = 4 q (6) the thermal resistance can be calculated by the following relation: th e r   (7) 3. results and discussion for the stabilization of our specimens, three types of stabilizers: cement, lime and sawdust were used. a cement type cpj 35 with a mechanical compressive strength of 23 mpa at 2 days and 50 mpa at 28 days was used. a high calcium lime made from a pure caco3 limestone was used. finally, sawdust used was dried, crushed and passed through a sieve of 0.5 mm. 3.1. experimental process the different stabilizers were weighed using a precision scale of 0.1 g. for the preparation of test specimens, the laterites of the city of maroua (cameroon) were used. before any compaction, soil samples were passed to the proctor test that allows checking if the land is suitable for the manufacture of cseb. after these tests, laterites were sprayed two days later and switched to hashing. after this operation, earth blocks were stabilized with the different used stabilizers, taking into account their mass percentage. test specimens were made using a mold of dimension 29x14x9cm. the prepared specimens were dried in two phases for 28 days, either: 14 days under plastic cover and 14 days in the open air. after drying, 10 test specimens were conducted with the following compositions: test tube 1 (e1): 100% of laterites + 0% stabilizer; test tube 2 (e2): 96% of laterites + 4% cement. test tube 3 (e3): 92% of laterites + 8% of cement. test tube 4 (e4): 88% of laterites + 12% of cement. specimen 5 (e5): 96% of laterites + 4% lime. specimen 6 (e6): 92% of laterites + 8% lime. specimen 7 (e7): 88% of laterites + 12% lime. tube 8 (e8): 96% of laterites + 4% wood sawdust. specimen 9 (e9): 92% of laterites + 8% of the sawdust. specimen 10 (e10): 88% of laterites + 12% wood sawdust. azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 61 an iron that delivers a constant flow of 60 w was used. this iron can heat the tube and cause the evolution of the temperature in the thermometer. before any experiment, the ambient temperature of the laboratory must be measured. iron is holding off about 8 cm from the thermometer. using the stopwatch, the evolution of the temperature in the thermometer was noted at regular time interval. for each type of specimen three measurements were conducted. 3.2. determination of thermophysical characteristics to estimate the conductivity and thermal resistance, the linear slope (𝛼) from eq. (1) was determined. this value will allow calculating the thermal conductivity (𝛌) form eq. (2). by applying the formula in eq. (7), the value of the thermal resistance ( th r ) can be deduced. the following curves have been obtained. from the figures 1-3, it can be seen that the curve of the variation of temperature for cseb containing sawdust remains below those of the other two stabilizers types. this implies that sawdust is slowing the evolution of temperatures in cseb comparatively to cement and lime stabilizers. this slowdown can be explained by the gradual decrease of the values of thermal conductivities. fig 1. experimental curves of the temperature variation in the cseb at 4% versus log (t). figure 1 shows that the evolution of the temperature in cement and lime cseb are close for the values between 1.5 and 2.25 of log (t). above 2.25, the evolution of temperature in cseb with lime is above those of the other two types of stabilizers. therefore, it can be deduced that at 4% and for values of log (t) above 2.25, lime transmits more heat compared to cseb with cement and sawdust. in figure 2, it can be seen that, for a dosage value of 8% of stabilizers, cement and lime are neighboring powers of heat transmission for values of log (t) between 1.5 and 2. in the meantime between 2 and 3.3, and unlike the case of stabilization at a dosage of 4%, lime shows more transmission of heat than cseb with cement and sawdust. 62 azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 fig 2. experimental curves of the temperature variation in the cseb at 8% versus log (t). from the value 3.3 of log (t), it can be observed that the variation of temperature in the cseb with cement is lower than that of cseb with the two other types of stabilizers. fig 3. experimental curves of the temperature variation in the cseb at 12% versus log (t). figure 3 reflects the same observation, in which the variation of the temperature in the cseb cement is above those of the other two stabilizers. therefore, even if the addition of cement is suitable in order to increase the compressive strength of cseb (zine-dine, 2000; hakimi, 1999), the transmission of heat becomes important than to that in the presence of lime or sawdust. from figure 4, it can be observed that cseb incorporating about 4 to 9% of cement, the thermal conductivities are low compared to lime and sawdust. it can be also observed that the thermal conductivity increases with the percentage of cement and lime, but decreases with the percentage of sawdust. azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 63 fig 4. curves of thermal conductivity depending on the rate stabilizers. in the range of 0 to 4%, the curves of the thermal conductivity for cseb with cement and lime are nearby. in the meantime, these stabilizers have almost the same power of heat transmission. however, the curve of thermal conductivity of cseb with sawdust decreases with the increase of sawdust percentage. in the range of 4 to 9 % of lime cseb transmits more heat than that with cement. beyond this range, conductivity is reversed to be higher for cseb with cement. for cseb made with sawdust, the thermal conductivity decreases with the increase of the percentage of sawdust. fig 5. curves of thermal resistance depending on the rate of stabilizers the results of thermal resistance obtained, using eq. (7), are presented in figure 5. from this figure, it can be seen that cseb made with sawdust shows higher thermal resistance than the other stabilizers (cement and lime). this can be explained by the alveolar structure of sawdust. it can be also seen that, from 9% of cement, cseb with cement shows lower thermal resistance than sawdust and lime. 64 azakine sindanne et al., j. build. mater. struct. (2014) 1: 58-64 4. conclusions the aim of this work is to determine the thermophysical properties of cseb with different stabilizers (cement, lime and sawdust). the incorporation of stabilizers was conducted in cseb for different percentages: 4%, 8% and 12% for each type of stabilizer. in the light of this experimental investigation, the following conclusions can be drawn: thermal conductivities of cseb increased with the increase of the percentages of cement and lime. the increase in thermal conductivities means that the thermal resistance decreases and consecutively, thermal insulation property of cseb decreases. the use of sawdust as a stabilizer in cseb decreases the thermal conductivity and increases the thermal resistance. as the increase in the thermal resistance is linked to the increase of the thermal insulation, cseb made with sawdust are therefore recommended for construction, especially in the hot regions. 5. references binici h, aksogan o, bodur mn, akca e, kapur s (2007). thermal isolation and mechanical properties of fibre reinforced mud bricks as wall materials. constr. build. mater., 21(4):901-6. castets d, iniesta h (1982) .recherche d’une méthode de mesure des caractéristiques thermophysiques de la terre, matériaux de construction, tef, entpe, vaulx-en-vellin. de chazelles ca, alain k, pousthomis n (2011). les cultures constructives de la brique crue. ecole nationale supérieure d'architecture de montpellier. fourier j (1988). théorie analytique de la chaleur, firmin-didot père et fils, paris, 1822. facsimile, ed. jacques gabay, paris. hakimi a, fassi-fehri o, bouabid h, d'ouazzane sc, el kortbi m (1999). non-linear behaviour of the compressed earthen block by elasticitydamage coupling. mater. struct., 32(7), 539-45. khedari j, watsanasathaporn p, hirunlabh j (2005). development of fibre-based soil–cement block with low thermal conductivity. cement concrete comp., 27(1), 111-6. meukam p (2004). valorisation des briques de terre stabilisées en vue de l’isolation thermique de bâtiments. thèse de doctorat, université de cergy pontoise. nagasaka y, nagashima a (1981). simultaneous measurement of the thermal conductivity and the thermal diffusivity of liquids by the transient hot‐wire method. rev. sci. instrum., 52(2):229-232. oladele i, z (2003). étude comparée des propriétés mécaniques et thermophysiques des briques en terre stabilisée au ciment et en argile cuite. mémoire d’ingéniorat, université d’abomey-calavi, benin. parker wj, jenkins rj, butler cp, abbott gl (1961). flash method of determining thermal diffusivity, heat capacity, and thermal conductivity. j. appl. phys., 32(9):1679-84. pignal b (2005). terre crue, techniques de constructions et de restauration. eyrolles, paris. plat p (1989). influence du matériau sur le métabolisme humain colloque construire en terre, matériau noble à la conquête de l'avenir, toulouse, france. rigacci a, ladevie b, sallee h, chevalier b, achard p, fudym o (2002). measurements of comparative apparent thermal conductivity of large monolithic silica aerogels for transparent superinsulation applications. high temp.-high press., 34(5) : 549-60. zine-dine k, bouabid h, el kortbi m, charif-d'ouazzane s, hakimi a, hammoumi a, fassi-fehri o (2000). rheology of walls in compressed earth blocks in uniaxial compression: study et modelling. mater. struct., 33(8):529-36. j. build. mater. struct. (2021) 8: 9-18 short communication doi : 10.34118/jbms.v8i1.772 issn 2353-0057, eissn : 2600-6936 a case study of foundation failure of a residential building: from diagnosis to reparation ahmed merah university ammartelidji of laghouat , faculty of civil engineering and architecture, research laboratory of civil engineering (lrgc), laghouat, 03000, algeria. * corresponding author: a.merrah@lagh-univ.dz received: 18-08-2020 accepted: 13-11-2020 abstract. the pathology that appears in reinforced concrete structures, old and new, is inevitable and involves all stakeholders at all levels of responsibility, from the technician to the decision maker at the highest level. it also concerns engineers from design offices and experts from offices responsible for diagnosing existing structures, as well as engineers from repair companies. like all countries in the world, the study of the pathology and safety of civil engineering buildings is one of the big problems encountered in the field of construction in algeria. the foundations are among of the structural elements of the buildings most affected by this damage, these constitute the link between the structure and the soil, they allow the transmission of loads from the structure to the soil. if these structural elements are damaged, they affect the general stability of the building. depending on the severity of the damage, it can cause the building collapse. the main objective of this paper is to study a pathological case of foundation failure of a residential building: from diagnosis to reparation. this repair was carried out according to an intervention plan comprising stages spread over time, this allowed the strengthening of the infrastructure and gave the building an acceptable level of security. key words: construction, pathology case, diagnosis, foundation failure, reinforcement. 1. introduction the construction of buildings continues to evolve, in materials, techniques and equipment. however, this evolution can generate structural degradations, giving rise to certain pathological cases. the most important of these cases is the pathology of the foundations. this can be defined as disorders in buildings, their causes, consequences and treatment. this pathology is mainly due to two factors: one is the soil, which is the support of the building foundations and must provide a strength equal to or greater than the load imposed by the superstructure; the other represents the entire structure, which must be sized according to the construction rules specific to each country. furthermore, the loss of bearing capacity of the foundations of a building is one of the most dangerous pathologies which can cause the total ruin of buildings, this problem concerns all actors in the act of building, such as engineers, designers, realization companies. moreover, the cost of repairing damaged foundations is very high compared to its initial cost. in his studies mulyukov (1992) have shown that all damage observed in buildings was linked to foundation pathologies. furthermore, it was also found that the deterioration of the foundations was due to five main causes, insufficient soil studies, errors in the design of the foundations, the poor quality of the foundations, an unfavorable action on the foundations and a change of geological and hydrogeological site conditions. in another way, in order to synthesize the main causes of degradation of reinforced concrete structural elements, (carretero-ayuso et al., 2016) conducted a statistical study based on the analysis of damages, symptoms and their evolutions, the results of this study showed 66% of damages are related to foundations and 90% of these impairments were from walls and isolated footings. mailto:a.merrah@lagh-univ.dz 10 merah a., et al., j. build. mater. struct. (2021) 8: 9-18 in the same context, (thompson and mechling, 2016), through an experimental companion carried out on the soil of the foundations of two buildings in colorado, this led to geotechnical recommendations in order to remedy the damage observed on of the two buildings based on hydro compressive soil. the results obtained show that the characteristics of the foundation soil vary over short distances and the high soil moisture can also be the cause of differential settlement. in addition, (nelson et al., 2017) studied four pathological construction cases implanted on expansive soil and made the following conclusions: choose the soil samples carefully; perform all regulatory tests on these samples and interpret them properly; achieve adequate drainage, contractors need sufficient knowledge about this type of soil. as part of post realization, (vazquez et al., 2016) show through their study that rigor in the design according to the rules of construction and the strict control of the realization of structures in reinforced concrete can avoid many future damages in new constructions. concerning also, the causes of buildings degradations, (nangan et al., 2017) shown that the damages on the foundations is due to various causes, this one being: the poor preparation of the soil, the variation of the soil water content, the presence near the construction of large trees and failures of plumbing systems. these causes generate cracking of walls and partitions. in order to help the authorities to preserve the performance of buildings, (dos santos et al., 2017) analyzed, diagnose, classify and expose the possible causes of the pathologies that have appeared in buildings (public and private) located in sinop mt in brazil and their solutions. the results of this study showed that the cracks were caused first by the construction details, by the action of the temperature, by the poor execution of the works, by the quality of the materials and by the quality of the monitoring of the works. moreover, the direction and nature of cracks is an important factor to facilitate the diagnosis of pathologies. the quality of materials used in the phase of structural reparations is more important in their durability and efficiencies, (mcdonald et al., 1991). in the same way, (mushiri et al., 2017) studied the structural cracks in a hospital in zimbabwe, through the technical documents, the geotechnical tests, the results of these investigations showed that the cracks were due to the poor quality of the brick masonry, the thick mortar of the masonry and the insufficient depth of the foundations and recommend deep foundations for new construction on this site. regarding, the repairing operation of damaged structures is a complex step, since it is faced with constraints such as the existing soil, the type of foundation, nearby buildings, loads applied and access to the place of repair. such constraints lead to the operation becoming costly; hence it is necessary to carry out geotechnical studies to collect the necessary information’s on the soil, (dos santos et al., 2017). in another hand, (guimarães and delgado, 2015) shows in their study that the excessive humidity of soil is the most cause of buildings degradations according to (mulyukov, 1992) for the repair of the pathology of the foundations, there are several types of repair: intervention in the foundation soil: when the cause of the foundation degradation is the soil, in this case a soil treatment is carried out in order to increase its bearing capacity. for this type of reinforcement, grout injections are used to densify the soil such as jet grouting and compaction. increase in the dimensions of the foundations: according to the following equation, merah a., et al., j. build. mater. struct. (2021) 8: 9-18 11 𝜎 = 𝐹 / 𝐴 for a constant force, the stress applied to the ground varies with the surface of the foundation. consequently, when the pressure applied to the soil reaches a value greater than its bearing capacity, increasing the dimensions of the foundation reduces the stress on the soil. micro piles are used to transfer the loads from the structure to another, more resistant layer of soil. in the case of this study, the last cause is the main factor of degradation of the building namely the change of geotechnical characteristics of the soil, by the permanent presence of water in the soil seat. this water comes either from damaged drinking water or sanitation pipes. one of the fundamental components of the rehabilitation of structures involves the reinforcement of their foundations. this kind of intervention leads to the increase of structural safety and load capacity. however, the water is one of the main causes of the damage that can occur on new or old buildings, its presence in initially dry soils causes the soil to lose its mechanical characteristics in this case its bearing capacity. this water usually comes from deteriorated sewer lines, rainwater and sometimes leaky water pipes. in order to sensitize all stakeholders in the act of building, it is certainly good to design a structure from the structural point of view; nevertheless will it be necessary to provide well designed and maintained sanitation pipes in an efficient manner. as a result, the service life of the structures can be extended without prohibitive additional costs. indeed, the cracks that appear in the constructions are warning signs of movement in the loadbearing structure of a structure or these fills that goes from the natural movement remaining in acceptable margins for the exploitation of the structure until alarming movements putting out of use the work even up to its peril. in reinforced concrete structures, cracks will occur due to the low tensile strength of the concrete. however, the opening of the crack should not be important in order to compromise the durability or appearance of the structural member. the cracks warn engineers of the existence of a serious problem in the structure, and thus reduce these performances of service and exert psychological effects on their users. it has been noted that structures that are prone to cracking and not reported in time can present hazards to occupants and enormous expense to homeowners. this study concerns a reinforced concrete building with 3 floors and crawl space situated in laghouat, algeria, for residential use, started exploiting in 1985. the structure is designed as a beam column system with foundations in insulated foundations and floors in solid slabs. it is part of a group of six buildings. (fig. 1). fig. 1. building (r + 3) 12 merah a., et al., j. build. mater. struct. (2021) 8: 9-18 this study attempts to identify the nature, origin, directions of cracks, intensity and incidence of the failure of foundations, besides diagnose and prognosticate, as well as to verify the structural properties of building and propose the solution of confrontment to lead at a building with an acceptable level of security. during this study we will present a real case of pathology of foundation failure and through this case we develop the findings until the solutions and their executions. finally, we present the conclusions obtained as a result of the work performed. 2. degradations 2.1. pre-diagnosis a pre-diagnosis show the appearance of cracks inclined at 45 ° on the exterior walls in double partitions and on the partitions in plaster tiles (fig. 2), these cracks started appear in 1997. fig. 2. cracks in exterior and interior walls the soil of the crawl space of the building was highly humid, showing a failure in the pipes of drinking water or sanitation. more ever, permanent stagnation of wastewater inside the crawl space caused by the saturation of pipes as well as the deterioration of the pipes and manholes. sanitary collectors are heavily degraded in which walls are made walls with masonry blocks. some pipes drain into the crawlspace. the nature of the sitting soil is clay nature. from that preceded, the foundations of the building underwent a differential settlement which caused the damage observed, (burland et al., 1978). 3. methodology of diagnosis the interventions for diagnostic to be performed must be properly planned before starting reparations. identifying the factors that can affect the success of the repair is crucial, including: the nature of the soil, identification of the affected structural elements, the soil moisture content, the interior conditions of the building and its surroundings and their respective locations. with the planning and research conducted, the criterion is established to define the correct technique in each case, thus obtaining a greater success in solving the problem. due to the difficulty and variability of the factors, there is some unpredictability in the results. the selection of the repair must be supported by a complete diagnosis to know the origin of the pathology, by studying the expected efficiency of the repair and by correlating this with the cost of repair. the methodology adopted for the diagnosis of the disorders observed is based on in-situ visual examination, and consists in executing the following steps: collect all technical and graphic information of the building (architectural plans, civil engineering plan, date of construction, building materials, type of supporting structure) merah a., et al., j. build. mater. struct. (2021) 8: 9-18 13 take images inside and outside the building inspecting the immediate environment of the building, this inspection makes it possible to detect if there are for example traces of humidity, deteriorated seams of assault, cracks on the buildings of proximity, stagnations of water near the building, rainwater pipes damaged. realization of the witnesses with plaster on the cracks, in order to follow their evolution drill holes in the soil near cracks in walls, perform a geotechnical study to determine the new properties of the foundation soil under the new hydrogeologic conditions. based on the data collected, draw up a plan of action to begin repairing damaged structural elements. in addition, the pre-diagnosis must make an inventory of the technical and functional situation of the building, as well as its environment. this information facilitates the understanding of pathologies and helps the technician in decision-making to successfully perform the intervention. 4. diagnoses the diagnosis of construction pathology is mainly based on an in situ visual examination. an improper diagnosis can lead to improper decisions which result in loss of money and time. in this sense, for a better understanding of the problem lead to correct technical solution. to follow the steps of diagnosis mentioned above, soundings to diagnose foundations were made, after sounding, fig. 3 shows that the soil was completely saturated with sanitary water. this figure (fig. 3) clearly shows that the sanitary pipes of the building are damaged, and the soil of foundation is completely saturated. fig. 3. the soil of foundations is completely saturated and sanitary collector were damaged. it was recommended that the company remove the spoil under the foundations and repair them alternately to avoid any sudden movement for the building and to ensure the safety of the workers. during the removal of spoil under the first foundations and primers columns, it was found that some of them are heavily damaged (fig.4). 14 merah a., et al., j. build. mater. struct. (2021) 8: 9-18 fig. 4. primary columns rusted and important cracks in foundation. in addition, a complementary soil study was recommended. this study shows that the bearing capacity of the soil is reduced with 50% compared with the initial bearing capacity, caused by the new conditions of change of water content of the ground. other problems of poor workmanship have been found, namely casting of foundations without formwork or the thickness of foundations have some differences from the plans (fig.5). fig. 5. foundation casting without formwork. 5. reparations among the repair objectives is to re-establish the durability of the concrete, elements and to significantly reduce the rate of deterioration. it should be noted that, in most cases where corrosion of embedded metals is the cause of deterioration, completely preventing future deterioration is not practical. the main cause of the disorders is the presence of water in the basement of the building which has softened the clay whose characteristics have fallen sharply. the study of the soil in 1980 show that the soil was described as a good soil with a permissible stress of 3 bars; and advocated the use of a cement type high silica content (hts). other elements of poor workmanship have been identified, namely foundations casting in full excavation or the thickness of foundations have some differences from the plans. following this it was urgent to activate for the comfort of the infrastructure of the building which threatens ruin at any time. the first operation consisted of eliminating the main cause of the incident, namely stopping any water supply to the basement of the building. for this, a total deviation of the wastewater evacuation pipes from the building's right-of-way was carried out (fig. 6) merah a., et al., j. build. mater. struct. (2021) 8: 9-18 15 fig. 6. new sewer lines to evacuate wastewater the adopted pathology repair methodology is the strengthening of foundations and the primers columns, this repair was carried out by concrete jacketing, (thompson and mechling, 2016). the figs. 7 and 8 show the reinforcement principle. fig. 7. foundation reinforcement with thickness increase of the foundation without surface increase in the first case (fig.7), the objectives of these foundation repairs are: reduction of the pressure on the ground under the additional loads as the bending moment (m) and the axial force (n) to the dead weight, increase in bearing capacity (modification of use) reinforcement (degraded) of the foundation, increase rigidity and reinforcement of the foundation. for cracked foundations and damaged primers columns, take back the loads transmitted, we recommended to carry out foundations and the primers columns with fretting (fig. 8) 16 merah a., et al., j. build. mater. struct. (2021) 8: 9-18 fig. 8: reinforcement foundation with increasing the surface and increasing thickness of the foundation in the second case (fig. 8), the objectives of this repair: increase of section and carrying capacity of the column. increase the rigidity of the foundation if the seating area is such that the pressure on the floor is acceptable, (vlad, 2004) . in our study the two reinforcement were used, the adopted extra thickness of damaged foundations is 20 cm with reinforced bars diameter 14 mm spaced 10 cm, the same thickness is adopted to repair the primers columns, the reinforced transverse frames bars were in 10 mm spaced with 10cm in order to increase their cross-sections. the new concrete is dosed at 400 kg / m3 of hts sulphate-resistant cement with the addition of adjuvant; the contact surface between the old and the new concrete must be brushed to remove any rust (fig. 9). fig. 9. reinforcement of the foundations and primers columns for foundations crushed: to ensure the transmission of loads, we recommended to make a counter foundation with spades and to double the primer columns. in the same way, a wall with concrete was made in the circumferential between the floor and the top floor of the crawl space. the fig. 10, shows, the foundation and primer columns after reparation, all foundations are painted with bitumen protection. merah a., et al., j. build. mater. struct. (2021) 8: 9-18 17 fig. 10. foundation and primer columns after reparation the fig. 11, shows the building after reparation fig. 11. building after reparation 6. conclusions in the conclusion of this study, it was show that the reinforcement of building foundations is a subject with a main importance. this pathology of buildings needs a fast intervention in the site in order to ensure the safety of the structure and its users. in this way, the success of a foundation’s reparation needs the knowledge of the characteristics of the foundation and the ground. once the geologic and geotechnical study of the soil was performed, in this case, the choosing the best solution to implement becomes easier and the guarantee of success becomes higher. moreover, the geotechnical study is necessary for all constructions, thereby, all the investment made to study the soil parameters should not be taken as an increased cost, but as an investment. after four months of these repairs, there was stabilization in the evolution of cracks, as well as the occupants tell us that the cracks are no longer perceptible. the repair of interior partitions and the strengthening of some structural poles have not been started, in order to allow time for the structure to stabilize, and that the soil returns to normal humidity. in addition, other piezometric measurements will be made to detect the actual level of the water table which must be probably more than 5 meters. in 2000 and after observing that there is no evolution of cracks (by inspection of plasters made after completing the reinforcement of the infrastructure (1998)) the partitions are reconstructed and as well as cracked walls. in addition, until now the building in question behaves as normally as possible and no visible anomalies were reported. this is why, we reiterate that not only must special attention be paid to the design and construction of structures, but that a special effort must be made to design and maintain the wastewater and drinking water pipes of the construction, because what has been concluded from the study of this pathological case can be repeated on other blocks if the maintenance of 18 merah a., et al., j. build. mater. struct. (2021) 8: 9-18 the wastewater and drinking water pipes is not done efficiently and if any leak is not repaired in due time. besides, a periodical control of the building must be executed after the reparation in order to prevent the pathological processes and failures, and to assure the correct functionality of the building. 7. references burland, j. b., broms, b. b., & de mello, v. f. (1978). behaviour of foundations and structures, geo reports, london, pp. 495-546 carretero-ayuso, m. j., moreno-cansado, a., & cuerda-correa, e. m. (2016). research and analysis on recurring anomalies in foundations and structures. journal of performance of constructed facilities, 30(3), 04015037. dos santos, b. r., pinheiro, r. v., arroyo, f. n., de almeida, d. h., christoforo, a. l., & lahr, f. a. r. (2017). cracks studies case of buildings in sinop city-brazil, international journal of materials engineering, 7(6): 101-110 guimarães, a. s., & delgado, j. m. (2015). building pathology and rehabilitation techniques–a rising damp treatment catalogue. defect and diffusion forum, 365, 291–296. mcdonald, j. e., & mcdonald, w. e. (1991). evaluation and repair of concrete structures : annotated bibliography 1978-1988. volume 2. (repair, evaluation, maintenance and rehabilitation research program). army engineer waterways experiment station vicksburg ms structures lab. mulyukov, é. i. (1992). classification of causes of failure of bases and foundations. soil mechanics and foundation engineering, 29(3), 90-93. mushiri, t., shumba, s., matora, t., mhizha, s., tumbare, m., taaka, d., & musiwa, k. (2017). investigating structural cracks for infrastructure: case study of anonymous hospital, in zimbabwe. eai international conference for research, innovation and development for africa, 432. nangan ii, a. p., ganiron jr, t. u., & martinez, d. t. (2017). concrete foundation systems and footings. world scientific news, 80, 1–17. nelson, e. j., chao, k. c., nelson, j. d., & overton, d. d. (2017). lessons learned from foundation and slab failures on expansive soils. journal of performance of constructed facilities, 31(3), d4016007. thompson, r. w., & mechling, j. (2016). geotechnical engineering for the remediation of structures on collapsing soils. geotechnical and structural engineering congress, pp 735–746. vazquez, e. g., haddad, a. n., qualharini, e. l., alves, l. a., & féo, i. a. (2016). pathologies in reinforced concrete structures. in sustainable construction (p. 213–228). springer. vlad, i. (2004). case study on the foundation and site geotechnical evaluation for the rehabilitation of an emergency hospital building. international conference on case histories in geotechnical engineering. 55. https://scholarsmine.mst.edu/icchge/5icchge/session01/55 https://scholarsmine.mst.edu/icchge/5icchge/session01/55 j. build. mater. struct. (2020) 7: 221-235 original article doi : 10.34118/jbms.v7i2.777 issn 2353-0057, eissn : 2600-6936 pervious concrete, plastic concrete and controlled low strength materiala special applications concrete ojha p n, suresh kumar, brijesh singh*, mohapatra b n national council for cement and building materials, india. * corresponding author: brijeshsehwagiitr96@gmail.com received: 31-08-2020 accepted: 25-11-2020 abstract. the paper presents the study carried out for three special concretes like pervious concrete, plastic concrete and controlled low strength materials (clsm) using locally available materials. pervious concrete is a concrete with high porosity. it is used in a wide range of applications including pervious pavements and helps in improving pavement skid resistance and reducing hydroplaning. this concrete was designed to meet the requirement of 28-day compressive strength of 10 mpa and water permeability of 0.50 cm/sec. plastic concrete has low compressive strength but higher ductility and lower permeability. it is used for creating an impermeable barrier (cut-off wall) for containment of contaminated sites or seepage control in highly permeable dam foundations. this concrete was designed to meet the requirement of 28-day unconfined compressive strength of 1.5 to 2.5 mpa and confined compressive strength of 2.5 to 3.5 mpa at confining pressure of 4 kg/cm2. controlled low strength material (clsm) or flowable fill mixtures are typically specified and used in place of compacted fill especially for backfill, utility bedding, void fill and bridge approaches. clsm is a self-compacting, flowable, low strength cementitious material which suits the requirement of different applications such as excavatable backfill and structural backfill. the properties of clsm that were investigated included bleeding, density of hardened clsm, permeability and unconfined compressive strength at 7 days and 28 days age. key words: plastic concrete, pervious concrete, controlled low strength material. 1. introduction pervious concrete is an open graded, zero slump material consisting of portland cement, coarse aggregate, little or no fine aggregate, admixture and water (aci, 2006). it is also called porous concrete, permeable concrete and no fines concrete. it is a concrete with high porosity resulting from a network of inter-connected pores in the hardened state of concrete. pervious concrete contains pores, ranging in size from 2 to 8 mm that allow water to pass through quickly. the void content in pervious concrete can range from 35% to 18% with typical compressive strengths of 2.8 to 28 mpa and water permeability generally falls in the range of 81 to 730 l/min/m2 (0.135 to 1.22 cm/s) (aci, 2006). pervious concrete has its various environmental benefits such as controlling storm runoff, restoring groundwater supplies, and reducing water and soil pollution (youngs, 2005; kajio et al., 1998). pervious concrete made with single-sized coarse aggregates generally have high permeability but not adequate strength. addition of a small amount of fine sand to the mixes significantly improves the concrete strength and freezethawing resistance while maintaining adequate water permeability (wang et al., 2006). the use of pervious concrete is the solution to overcoming a lot of environmental problems by reducing tire-pavement interaction noise, moderating storm-water runoff, and limiting the pollutants entering the groundwater, mean that an aggregate storage bed will reduce the stormwater runoff volume, rate, and pollutants appropriately. pervious concrete also affects durability by reducing the surface temperature of the paved area. hence, the main function of pervious concrete lies in its ability to transport a large volume of water through its pores to the underlying strata, and it serves as a pavement for vehicles and pedestrians. mailto:brijeshsehwagiitr96@gmail.com 222 ojha et al., j. build. mater. struct. (2020) 7: 221-235 plastic concrete, which is sometimes referred to as low strength concrete or artificial soil, consists of aggregate, cement, water, and bentonite clay mixed at a high water-cement ratio to produce a ductile material (naderi, 2005). plastic concrete has lower compressive strength, higher formability and lower permeability. the addition of bentonite reduces concrete hardness and elasticity coefficient. due to this reason, plastic concrete is used in the construction of cut off walls to reduce seepage through the foundation of earth dams. plastic concrete is also used for control of infiltration of harmful sewage and the penetration of sea water, and more recently for filling the surrounding of water ducts in power plants (naderi, 2005). clsm is a self-compacting flowable, low strength cementitious material consisting of lower cement content, higher fly ash and fine aggregate content, no coarse aggregate, mixed at high water-cement ratio. clsm is used primarily as backfill, void fill and utility bedding as an alternative to compacted fill. several terms are currently used to describe this material, including flowable fill, unshrinkable fill, controlled density fill, flowable mortar, plastic soilcement, soil-cement slurry, k-krete and other various names (katz and kovler, 2004). controlled low strength materials are as materials that result in a compressive strength of 8.3 mpa or less (aci, 1990). however, most current clsm applications require unconfined compressive strength of 2.1 mpa or less. this low strength requirement is necessary to allow for further excavation of clsm in future. because clsm flows and needs no compaction, it is ideal for use in tight or restricted access where placing and compacting soil or granular fill is difficult or even impossible. the cost of clsm is influenced by the cost and local availability of materials, the mixing and transportation method, and the methods of placement. conventional concrete is a material composed of cement, coarse aggregate, fine aggregate, water and admixture, primarily designed taking two properties i.e. compressive strength and workability into consideration. however, for special category modified concrete, apart from these two parameters, other properties like high permeability in case of pervious concrete, low permeability, high strain and low modulus of elasticity in case of plastic concrete and controlled strength and low permeability in case of controlled low strength material are taken into consideration before finalizing the mix proportions. special concrete is a type of concrete which meets the special performance requirements. the aim of this study is to evaluate the performance of three different types of special applications concrete such as pervious concrete, plastic concrete and controlled low strength materials (clsm) using locally available materials in civil engineering construction. 2. special applications concrete 2.1. pervious concrete opc 43 grade conforming to is: 8112-2013, fine aggregate (zone-ii) and coarse aggregate (12 mm downsize) conforming to is: 383 were used in the study carried out for pervious concrete. the mix formulation used in the investigation is shown in table 1. the mix proportioning is done using absolute volume method by varying percentage of sand by volume in total aggregate at 0% and 5%. the water cement ratio is an important consideration for maintaining strength and the void structure of the concrete. experience has shown a range of 0.35 to 0.45 will provide the best aggregate coating and paste stability (aci, 2002). the water cement ratio selected in the present study is 0.35 and 0.40. the proportions for the pervious concrete were designed for cement contents ranging from 200 to 250 kg/m3. the pervious concrete was designed for 28-day characteristic strength of 10 mpa and minimum water permeability of 0.50 cm/sec with no slump workability. due to the permeability requirement, pervious concrete is typically designed with high void content (15-25%). single sized aggregate is commonly used to achieve such void content (tennis et al., 2004). the mix-design trials were carried out by varying the theoretical ojha et al., j. build. mater. struct. (2020) 7: 221-235 223 porosity between 20 to 28%. the theoretical porosity was calculated as per the following procedure: total voids in coarse aggregate system = 100 aggregate coarse ofdensity absolute aggregate) coarse ofdensity bulk roddeddry aggregate coarse ofdensity (absolute  theoretical porosity adopted for mix design = total voids in coarse aggregate system – absolute volume of mortar constituents where, absolute volume of mortar constituents = absolute volume of cement, water and fine aggregate if any sample illustration for trial given in sl no. 1 of table1: dry rodded bulk density of coarse aggregate = 1502 kg/m3 absolute density of coarse aggregate = 2660 kg/m3 total voids in coarse aggregate system = 43% 100 x 2660 1502-2660  absolute volume of cement = 0.0635 1000 1 3.15 200  absolute volume of water = 0.070 1000 1 1 70  absolute volume of mortar constituents = absolute volume of cement + absolute volume of water = 0.0635 + 0.07 = 0.1335 theoretical porosity = total voids in coarse aggregate system – absolute volume of mortar constituents. = 0.43 – 0.1335 = 0.2965 i.e. ≈ 29% theoretical porosity adopted for mix design = 28% similarly, the theoretical porosity for trials given in sl no. 2 to 8 can be found out. however, the actual porosity in hardened concrete might be different from the theoretical porosity adopted at the time of mixing. this is due to the hydration reaction of cement which results in formation of c-s-h gel which has specific gravity in the range of 2.1 to 2.2 which is lesser as compared to the specific gravity of cement. secondly, some water also gets evaporated during the hardening process of concrete. this also results in different porosity in the hardened concrete. actual porosity in pervious concrete in the hardened state can be calculated as: 224 ojha et al., j. build. mater. struct. (2020) 7: 221-235 actual porosity = cumper concrete pervious ofweight cum)per tsconstituen concrete all of weight porosity x al(theoretic actual porosity for sl. no. 1 of table-1 = 1955 )1830 x (28 = 26% similarly the actual porosity for trials given in sl no. 2 to 8 can be found out. the compressive strength test of pervious concrete was carried out on cube specimens of size 150mmx150mmx150mm as per is: 516-1959. the water permeability test was carried out on cylindrical specimens of size 100 mm diameter and 200 mm height as per iso/dis-17785-1. fig. 1 shows the pervious concrete specimens and fig. 2 shows the permeability test set up. table 1. trials conducted for pervious concrete sl. no. water content (kg/m3) cement content (kg/m3) fine aggregate content (kg/m3) coarse aggregate content (kg/m3) theoretical porosity (%) mix 1 70 200 nil 1560 28.0 mix 2 80 200 nil 1560 27.0 mix 3 87 250 nil 1552 25.0 mix 4 100 250 nil 1544 24.0 mix 5 70 200 83 1583 24.0 mix 6 80 200 83 1583 23.0 mix 7 87 250 83 1576 21.0 mix 8 100 250 82 1568 20.0 fig. 1. pervious concrete cube specimens for compressive strength & cylindrical specimens for permeability test fig. 2. permeability test of pervious concrete 2.2. plastic concrete ppc conforming to is: 1489 (part 1), fine aggregate (zone iii) and coarse aggregate (20 mm downsize) conforming to is: 383-1970 and bentonite were used in the study of plastic concrete. the mix formulation used in the investigation is shown in table 2. the proportions for the plastic concrete were designed for cement contents ranging from 150 to 200 kg/m3 and bentonite contents between 20 to 40 kg/m3. the plastic concrete was designed for 28-day unconfined compressive strength of 2.0 mpa and confined compressive strength of 3.0 mpa with ojha et al., j. build. mater. struct. (2020) 7: 221-235 225 the slump requirement of 180-195 mm. for the purpose of preparation of plastic concrete, first of all bentonite is mixed thoroughly with water and is mixed for 24 hours. then slurry is poured in the mixer and mixed for one minute, then cement is added and after another minute, the aggregates are added to the mixture and mixed for another 7 to 10 minutes. slump, air content, density and setting time tests were performed on fresh concrete. to determine the unconfined compressive strength, strain at failure and young modulus of concrete, cylindrical specimens of size 150 mm diameter and 300 mm height were cast. cylindrical specimens of size 100 mm diameter and 200 mm height were cast for confined test. to determine water permeability, cylindrical specimens of size 150 mm diameter and 150 mm height were cast. concrete slab of size 300mmx300mmx100mm were cast to determine the abrasion resistance of plastic concrete. the specimens were de-moulded after 24 hours of casting and stored in water tank at a temperature of 27ºc±2 ºc. fig.3 & 4 show the unconfined and confined test set respectively. table 2. trials conducted for plastic concrete mix id cement content (kg/m3) water content (kg/m3) bentonite content (kg/m3) fine aggregate content (kg/m3) coarse aggregate content (kg/m3) (10-20 mm fraction) (<10 mm fraction) set a 1 150 290 20 877 528 352 2 150 290 25 875 527 351 3 150 290 30 872 525 350 set b 4 165 290 20 870 524 349 5 165 290 40 859 518 345 set c 6 200 290 20 854 514 343 7 200 290 25 851 513 342 8 200 290 40 843 508 338 fig. 3. unconfined test on plastic concrete fig. 4. confined test on plastic concrete at confining pressure of 4 kg/cm2 2.3. controlled low strength material opc 43 grade conforming to is: 8112-2013, fine aggregate (zone i) conforming to per is: 383 and siliceous fly ash conforming to is: 3812 (part 2)-2003 were used in the study of clsm. however, it is not necessary to use the standardized materials as set by many available standard 226 ojha et al., j. build. mater. struct. (2020) 7: 221-235 requirements (aci, 1994). the mix formulation used in the investigation is shown in table 3. the proportions for the clsm mixtures were designed for target cement contents ranging from 30 to 70 kg/m3 and fly ash contents between 460 and 1200 kg/m3.the clsm was designed for 28-day strength of 0.52mpa with the slump requirement of 175-200mm. the target mean strength is calculated by using the equation i.e. fck + 1.65*s, where s is assumed standard deviation as 20% of required characteristics strength at 28-day.the mixing was in a pan mixer for 2 to 3 minutes and workability of clsm mix was checked using slump cone method as per is 1199:1959. the cube specimens of size 100mmx100mmx100mm and cylindrical specimens of size 150 mm diameter and 150 mm height were cast without any vibration. the specimens were stored in a place free from vibration, in moist air of >90% relative humidity and at a temperature of 27˚c±2˚c until the fourth day after preparation. humidity chamber were used to maintain these condition. on the fourth day, specimens were placed in a water curing tank. fig. 5 shows the water permeability test set up and fig. 6 shows the compressive strength test set up of clsm. table 3. trials conducted for clsm sl. no. water content (kg/m3) cement content (kg/m3) fly ash content (kg/m3) fine aggregate content (kg/m3) mix-1 250 30 460 1364 mix-2 250 50 460 1347 mix-3 250 70 460 1330 mix-4 290 30 800 839 mix-5 304 50 800 786 mix-6 355 50 1000 405 mix-7 375 30 1200 122 fig. 5. permeability test of clsm fig. 6. compressive strength test 3. test result and discussions 3.1. pervious concrete the test results of properties studied such as compressive strength, water permeability and density are discussed below and given in table 4: ojha et al., j. build. mater. struct. (2020) 7: 221-235 227 table 4. test results sl. no. dry density (kg/m3) actual porosity (%) 7-day comp. strength of cubes (n/mm2) 28-day comp. strength of cubes (n/mm2) 7-day permeability (cm/sec) 28-day permeability (cm/sec) 1 1955 26.0 9.05 11.72 1.40 1.25 2 1976 25.0 8.27 11.10 0.76 0.63 3 2004 23.5 10.39 12.51 0.55 0.55 4 1957 22.0 7.38 10.07 0.66 0.38 5 1972 23.5 11.30 13.51 1.11 1.02 6 1988 22.5 8.30 13.66 0.71 0.58 7 2013 20.8 12.79 15.82 0.40 0.37 8 2076 19.3 9.20 11.44 0.31 0.23  water permeability increased with increase in theoretical porosity for no fines concrete as well as for concrete with 5% fines as shown in fig 7 & 8. fig. 7. theoretical porosity vs water permeability for no fines pervious concrete 0 0.2 0.4 0.6 0.8 1 1.2 1.4 23 24 25 26 27 28 29 2 8 -d a y w a te r p e r m e a b il it y ( c m /s e c ) theoretical porosity (%) 228 ojha et al., j. build. mater. struct. (2020) 7: 221-235 fig. 8. theoretical porosity vs water permeability for pervious concrete with 5% fines  dry density of pervious concrete decreased with increase in theoretical porosity for no fines concrete as well as for concrete with 5% fines as shown in fig 9 & 10. fig. 9. theoretical porosity vs dry density for no fines pervious concrete 0 0.2 0.4 0.6 0.8 1 1.2 19 20 21 22 23 24 25 2 8 -d a y w a te r p e r m e a b il it y ( c m /s e c ) theoretical porosity (%) 1960 1980 2000 2020 2040 2060 2080 2100 19 20 21 22 23 24 25 d r y d e n si ty ( k g /m 3 ) theoretical porosity (%) ojha et al., j. build. mater. struct. (2020) 7: 221-235 229 fig. 10. theoretical porosity vs dry density for pervious concrete with 5% fines  the range of the compressive strength achieved at 7-day and 28-day was between 7.38 mpa to 12.79 mpa and 10.07 mpa to 15.82 mpa respectively. for best aggregate coating and paste stability, water-cement ratio was kept below 0.40.  the range of water permeability obtained at 7-day and 28-day was between 0.55 to 1.40 cm/sec and 0.38 to 1.25 cm/sec respectively for no fines concrete. the range of water permeability obtained for pervious concrete with 5% fines at 7-day and 28-day was between 0.31 to 1.11 cm/sec and 0.23 to 1.02 cm/sec respectively. the permeability decreased with the introduction of fine aggregate in the mixes. the variation of water permeability with theoretical porosity is shown in fig. 3 and 4.  it can be seen that although the compressive strength of pervious concrete increased with the introduction of fine aggregate in the mixes, however, the strength is not increasing in direct proportion with the decrease in theoretical porosity. this is due to the reason that compressive strength, in addition to porosity, depends on water-cement ratio and pore size distribution in the concrete. pore size refinement may have occurred due to introduction of fine aggregate.  the range of dry density was between 1955 kg/m3 to 2045 kg/m3 for no fines concrete and between 1972 kg/m3 to 2076 kg/m3 for concrete with 5% fines. the dry density increased with the introduction of fines in the concrete. 3.2. plastic concrete from set a, given in table 5 below, it is clear that the various mix proportions like cement, coarse aggregate, fine aggregate and water are same for mix id 1, 2 and 3. the only variable factor is the bentonite content. similarly, the same trend follows for the mix proportions given in set b and set c. 1940 1960 1980 2000 2020 2040 2060 23 24 25 26 27 28 29 d r y d e n si ty ( k g /m 3 ) theoretical porosity (%) 230 ojha et al., j. build. mater. struct. (2020) 7: 221-235 table 5. test results m ix i d w o rk a b il it y o f co n cr e te i n te rm s o f sl u m p ( m m ) u n co n fi n e d s tr e n g th (n / m m 2 ) s tr a in a t f a il u re ( % ) y o u n g m o d u lu s (n / m m 2 ) c o n fi n e d s tr e n g th (n / m m 2 ) (a t co n fi n in g p re ss u re o f 4 k g / cm 2 ) w a te r p e rm e a b il it y (m / se c) a b ra si o n r e si st a n ce (m m ) set a 1 195 2.19 0.620 294 2.80 1.14x10-9 0.343 2 200 1.94 0.654 287 2.62 1.03x10-9 0.352 3 200 1.65 0.669 253 2.35 0.60x10-9 0.394 set b 4 195 2.37 0.609 406 3.62 0.79x10-9 0.293 5 185 2.31 0.655 304 3.48 0.39x10-9 0.304 set c 6 180 3.76 0.502 650 4.11 1.08x10-9 0.246 7 185 3.63 0.521 628 3.86 0.99x10-9 0.260 8 190 3.37 0.540 604 3.71 0.25x10-9 0.278 from the test results given in set a, b and c, it is clear that:  unconfined and confined compressive strength of plastic concrete decreased as bentonite content was increased within the same set as shown in fig 11 & 12 fig. 11. unconfined strength vs bentonite content for results given in set a & c 1 1.5 2 2.5 3 3.5 4 15 20 25 30 35 40 45 u n c o n fi n e d s tr e n g th ( m p a ) bentonite content (kg/cum) set a set c ojha et al., j. build. mater. struct. (2020) 7: 221-235 231 fig. 12. confined strength vs bentonite content for results given in set a & c  strain at failure increased with increase in bentonite content in the same set due to increased deformations in plastic concrete as shown in fig 13.  young modulus of plastic concrete decreased with increase in bentonite content within the same set as shown in fig 14. fig. 13. strain at failure vs bentonite content for results given in set a & c 1.5 2 2.5 3 3.5 4 4.5 15 20 25 30 35 40 45 c o n fi n e d s tr e n g th ( m p a ) bentonite content (kg/cum) set a set c 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 15 20 25 30 35 40 45 s tr a in a t f a il u r e ( % ) bentonite content (kg/cum) set a set c 232 ojha et al., j. build. mater. struct. (2020) 7: 221-235 fig. 14. modulus of elasticity vs bentonite content for results given in set a & c  the water permeability of plastic concrete decreased with the increase in bentonite content within the same set of trials as shown in fig 15. fig. 15. water permeability vs bentonite content for results given in set a & c  the value of abrasion resistance decreased as the bentonite content was increased within the same set of trials as shown in fig 16. 100 350 600 850 15 20 25 30 35 40 45 m o d u lu s o f e la st ic it y ( m p a ) bentonite content (kg/cum) set a set c 0 0.2 0.4 0.6 0.8 1 1.2 1.4 15 20 25 30 35 40 45 w a te r p e r m e a b il it y ( 1 0 -9 ) m /s e c ) bentonite content (kg/cum) set a set c ojha et al., j. build. mater. struct. (2020) 7: 221-235 233  on comparison of test results of set a, b and c, it is clear that with increased cement content and constant bentonite quantity, unconfined and confined strength of plastic concrete increased, strain at failure decreased, young modulus increased, water permeability decreased and abrasion resistance increased. fig. 16. abrasion resistance vs bentonite content for results given in set a & c 3.3. controlled low strength material (clsm) the various tests carried out on clsm like bleeding, density, compressive strength and water permeability are discussed below and given in table -6. table 6. clsm test results sl. no. workability of concrete obtained in terms of slump (mm) 7-day comp. strength of cube (n/mm2) 28-day comp. strength of cube (n/mm2) density of hardened clsm (kg/m3) mix-1 180 0.80 1.45 2122 mix-2 170 1.20 2.99 2126 mix-3 170 1.40 3.62 2132 mix-4 165 0.85 1.77 1976 mix-5 195 1.82 3.68 1954 mix-6 185 1.65 3.09 1832 mix-7 180 0.66 1.47 1736  there was no significant bleeding or segregation observed because only fine aggregates and fillers were used in all the mixtures instead of coarse aggregate. fine particles have smaller void between the particles. with less voids, particles are less likely to be dislocated. unless excessive free water exists or terrible bleeding occurs, segregation of 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 15 20 25 30 35 40 45 a b r a si o n r e si st a n c e ( m m ) bentonite content (kg/cum) set a set c 234 ojha et al., j. build. mater. struct. (2020) 7: 221-235 clsm designed with fine aggregates only is very unlikely to happen (katz and kovler, 2004).  the density of clsm in this experiment obtained varied from 1736 kg/m3 to 2126 kg/m3 which is consistent with the results found by horiguchi et al. (2001), as per which the range of clsm density varies from 1338 kg/m3 to 2056 kg/m3.  it is clear that the higher quantity of cement used produced clsm with higher compressive strength as it has lower water/cement ratio. more cement used can generate more strength as particles are more effectively bonded together (neville, 1996).  the coefficient of permeability of clsm was in the range of 1.00 x 10-8 cm/sec which is lower than clay that has relatively low permeability with a coefficient of permeability in the range of 1.00 x 10-7 cm/sec.  the fly ash used in the study of clsm conforms to is: 3812 (part 2) which is of inferior quality as compared to the fly ash conforming to is: 3812 (part 1). as the fly ash content used in the study is as high as 1200 kg/m3, fly ash being a by-product produced by power plants, has a great potential to be used in clsm as landfill and backfill material. 4. conclusions based on the above study carried out on pervious concrete, plastic concrete and clsm, following conclusion can be drawn: pervious concrete  there is a relationship between theoretical porosity/ actual porosity and water permeability. the graphs between theoretical/actual porosity and water permeability at zero % of fine aggregate and with introduction of fine aggregate with increment of 5% can be generated to develop concrete mix design guidelines for pervious concrete.  the introduction of fine aggregate produces more dense mix as compared to no fines mix, resulting in increased compressive strength.  the compressive strength and water permeability of pervious concrete depends on water-cement ratio, porosity, pore size distribution and fine aggregate content. hence, these parameters should be appropriately adjusted in order to obtain the required compressive strength and water permeability for design of pervious concrete. plastic concrete  bentonite is the main constituent materials of plastic concrete which enhances its impermeability and ductility.  the unconfined and confined compressive strength is significantly lower and water permeability is the same range of the conventional concrete because of the presence of bentonite in the concrete.  in case of plastic concrete, the strain is higher and young modulus is lower than the conventional concrete. these properties of plastic concrete make it more flexible and ductile and help in reducing the cracks that would otherwise be created due to differential settlements between concrete and the soil underneath.  mahmood (2005) has concluded that increasing the quantity of bentonite from 15 kg/m3 to about 28 kg/m3, the compressive strength & modulus of elasticity increase, but when bentonite increases beyond about 30 kg/m3, these parameters are decreased. however, ojha et al., j. build. mater. struct. (2020) 7: 221-235 235 in this study, the value of these parameters decreased throughout with the increase in bentonite content. controlled low strength material (clsm)  for design of clsm, the cement content can be kept in the range of 30 kg/m3 to 70 kg/cm3, siliceous fly ash content in the range of 460 kg/m3 to 1200 kg/m3 and fine aggregate quantity in the range of 120 kg/m3 to 1360 kg/m3 in order to produce a selfcompacting flowable, low strength and less permeable concrete. clsm has a great potential of utilization of even inferior quality of fly ash. this material can be used as landfill and backfill material as an alternative to the conventional granular materials utilizing this industrial waste material i.e. fly ash. 5. references aci, (1990). cement and concrete terminology, aci 116r-90, manual of concrete practice, american concrete institute, detroit, mi. aci, (1994). controlled low-strength materials (clsm), american concrete institute, committee aci 229r-94 report. aci, (2002), guide for selecting proportions for no-slump concrete reported by aci committee 211.3r02. in american concrete institute. aci, (2006). pervious concrete. committee 522r-06, american concrete institute, farmington hills, michigan. horiguchi, t., okumura, h., & saeki, n. (2001). optimization of clsm mix proportion with combination of clinker ash and fly ash. special publication, 199, 307-324. kajio, s., tanaka, s., tomita, r., noda, e., & hashimoto, s. (1998). properties of porous concrete with high strength. in proceedings 8th international symposium on concrete roads, pp. 171-177. katz, a., & kovler, k. (2004). utilization of industrial by-products for the production of controlled low strength materials (clsm). waste management, 24(5), 501-512. naderi, m. (2005). effects of different constituent materials on the properties of plastic concrete. international journal of civil engineering, 3(1), 10-19. neville, a.m. (1996). properties of concrete, 4th edition ed. edinburgh gate, horlow, longman. tennis, p. d., leming, m. l., & akers, d. j. (2004). pervious concrete pavements, special publication by the portland cement association and the national ready mixed concrete association skokie, il. wang, k., schaefer, v. r., kevern, j. t., & suleiman, m. t. (2006). development of mix proportion for functional and durable pervious concrete. in nrmca concrete technology forum: focus on pervious concrete, nashville, pp. 1-12. youngs, a. (2005). pervious concrete it’s for real. in presentation at pervious concrete and parking area design workshop, omaha. j. build. mater. struct. (2021) 8: 160-167 original article doi : 10.34118/jbms.v8i2.1333 issn 2353-0057, eissn : 2600-6936 development of guinea corn husk-cow hair hybrid fibre reinforced cement composite alomaja ja *1, jimoh aa 2, wilson un3, joseph, op1, akinleye, mt1, adeleke ja 1 1 department of civil engineering, adeleke university, ede, nigeria 2 department of civil engineering, university of ilorin, ilorin. nigeria. 3 department of civil engineering, nigerian defence academy kaduna, nigeria. * corresponding author: alomaja.jonathan@adelekeuniversity.edu.ng received: 21-04-2021 accepted: 07-12-2021 abstract. this research work presents the application of guinea corn husk (gch) and cow hair (ch) fibres as reinforcement in cement composite. the influence of the hybrid fibre volume on the flexural performance of the composite has been studied experimentally. the mechanical (flexural strength) and physical (density, water absorptivity, moisture content) characteristics of the gch-ch hybrid fibre reinforced composite were evaluated. the highest flexural strength was 22.37mpa, exhibited by the composite reinforced with 15% (12.5% gch & 2.5% ch) hybrid fibre. the density of the gch-ch hybrid composite ranged from 1019 to 1963 kg/m3. the water absorptivity varied from 22.59 to 38.16% and the moisture content ranged from 3.32 to 11.28%. these limits are within the range in standard therefore, the performance of the composite satisfies the requirements of bs en 12467 standard for ceiling board. key words: guinea corn husk, cow hair, flexural strength, density, water absorptivity. 1. introduction recently, researchers across the world have been working tirelessly to develop innovative and affordable engineering materials from renewable resources with good physical and mechanical properties (ohijeagbon et al., 2021). initially, asbestos fibre was widely used in civil engineering construction for making building products like ceiling tiles, corrugated roofing sheets because it possesses good and desirable mechanical and physical properties (khorami 2011). however, due to the carcinogenic health hazards associated with asbestos fibre, a great demand exists for suitable and better alternative or substitute (lumingkewas 2015). natural organic fibres include those produced by plants and animals. they can be categorized according to their origin. all vegetable fibres are generally based on arrangements of cellulose and hemicellulose, often with lignin (dungani et al., 2016). however, the main structural component of plant fibre is cellulose (lumingkewas 2015). examples include guinea corn husk (gch), cotton, linen, hemp jute, flax, ramie, and sisal etc. previous findings have shown that high strengths and stiffness are obtainable from natural organic fibres and they are characterized by good performance (dungani et al., 2016). also, fibres from animal origin are thread-like in nature for instance, hairs and threads (that is cocoon and spider thread). the hair thread is formed by keratin which is made up of protein containing high concentration of sulfur credited to the presence of amino acid cysteine (valesco et al., 2009). principally, the main component of animal fibre is a protein called keratin (alli et al., 2021). examples are sinews, spider silk, catgut and human or cow hair (ch). the hair fibre has good strength and high modulus of elasticity (poole et al., 2009). the aforementioned characteristics make plant and animal fibres suitable for use in composites with good structural requirements (duggal, 2008; pickering et al., 2016). mailto:alomaja.jonathan@adelekeuniversity.edu.ng alomaja et al., j. build. mater. struct. (2021) 8:160-167 161 also, man-made fibres such as glass, carbon, kevlar, polyethylene, polypropylene and steel have proven to be good replacements or alternatives for asbestos in the construction industry in terms of their mechanical and physical characteristics (oladele et.al, 2009). however, due to the high cost of the aforementioned fibres in the developing countries, researchers are shifting their attentions to more promising, affordable and environmentally friendly alternatives, especially cellulosic and keratin-based natural organic fibres which are available in large quantities in many developing nations of the world (sanjay et al., 2016). the incorporation of two or more fibres to reinforce cement composite is attracting more attention these days. most importantly, fibres from different origin or orientation with distinct characteristics or properties can be utilized to complement the other fibre. according to khorami (2011), the mechanical strengths obtained with cellulosic fibre reinforced composite are not sufficiently high that it could be adopted for various engineering applications and such need to be made stronger by incorporating another reinforcing fibre. this research work was aimed at investigating the influence of guinea corn husk (gch) and cow hair (ch) hybrid fibre as reinforcement in the cement composite. many research works have been carried-out on natural organic fibers as reinforcement in the development of construction materials but limited studies have been made in utilizing the two wastes used in this work as a hybrid fibre in one composite. guinea corn husk (gch) and cow hair (ch) are wastes from agricultural practices. guinea corn husk (gch) is an agro-waste obtained from milling of guinea corn (sorghum vulgare). guinea corn is an essential food crop grown and largely produced in the savannah belt of nigeria. kaduna, niger and benue rivers are some of the places where this crop is largely cultivated in nigeria (ndububa and nurudeen, 2015). it has been reported that about 1.5 million tones of guinea corn is produced within the country on yearly basis which has potential to increase as the economy is diversified to agriculture (akinloye et al., 2014). agro-wastes have been studied and reported to have a greater potential for various application in composites (sanjay et al., 2016). this study presents the physical and mechanical properties of the gch-ch hybrid fibre reinforced cement composite. 2. materials and methods 2.1. materials and equipment the fibre materials used for this research work were obtained from farm and abbatoir in ede, nigeria. the fibre materials used for this research work were guinea corn husk and cow hair. other materials were sodium hydroxide (naoh) for treatment of gch, wooden rectangular moulds, water, cellophane sheets and cement. they were all obtained in ede town, nigeria. the equipment used in this research includes; laboratory oven, digital weighing balance, measuring cylinder, beakers, hydraulic press, head pan, vibrating table, hand trowel and digital display wincom 190811 universal tensile machine with testing power 0-300kn having ±1% precision supplied by wincom company limited, china. 162 alomaja et al., j. build. mater. struct. (2021) 8:160-167 2.2. methods 2.2.1. treatment of fibre the fibre utilized in this research work was treated before use. the cellulosic fibre (guinea corn husk) shown in figure 1 was treated with 0.2m naoh solution. the gch fibre was soaked in the naoh solution for 24 hours to remove the lignin content. the fibre was thoroughly washed with tap water to remove any residual chemical on the fibre surface. meanwhile the keratin fibre (cow hair) shown in figure 2 was washed with water to remove deleterious substances like dung, blood and impurities (oladele et al., 2015). fig. 1. guinea corn husk fig. 2. cow hair 2.2.2. preparation of sample the keratin fibre was cut into size range of 30-40mm in order to ensure even distribution of fibre in the composite and avoid balling problem. the gch-ch fibres and cement were measured using the weighing balance based on the design mix. the mix proportions of the composite are shown in table 1. the materials were manually and thoroughly mixed inside the pan with a water/cement ratio of 0.46 (rahmanzadeh et al., 2018). this was done until homogeneity was obtained. afterwards, the mixture was poured into the wooden rectangular mould having a dimension of 300mm by 150mm with a thickness of 6mm. the sample was vibrated mechanically for few seconds to remove some void. then the sample was compressed for 4 hours. each sample was labelled and cured by wetting for twenty-four hours in the mould before it was removed. all the samples were cured in the laboratory atmosphere for twenty-eight days before carrying the physical and mechanical test on them. the experiment was carried out at room temperature of 22±20c. alomaja et al., j. build. mater. struct. (2021) 8:160-167 163 table 1. mix proportion for the composite in volume sample cement (%) cow hair (%) guinea corn husk (%) va 100 0 0 vb 90 5 5 vc 85 2.5 12.5 vd 85 7.5 7.5 ve 85 10 5 vf 85 12.5 2.5 vg 85 5 10 vh 80 15 5 vi 80 12.5 7.5 vj 80 10 10 vk 80 7.5 12.5 vl 80 5 15 vm 75 10 15 vn 75 15 10 vo 75 5 20 vp 75 12.5 12.5 2.3.3. testing of samples the physical test carried out on the samples includes density, water absorptivity and moisture content respectively. 2.3.3.1. density test the density test was carried out according to bs en 12467. the mass (kg) per unit volume (m3) each sample were measured. the following expression was used to obtain the density of the sample: (1) 2.3.3.2. water absorptivity test water absorptivity test was carried out according to bs en 12467. the percentage water absorptivity for each sample was also calculated using the relation: (2) 2.3.3.3. moisture content test moisture content was carried out according to bs en 12467. the percentage of the moisture content was calculated using the following relation: (3) 2.3.3.4. flexural test flexural test based on the three-point loading principle was carried out on the wincom universal testing machine as shown in figure 3. the sample size used was 300mm x 150mm x 6mm. this test was done in compliance with bs en 12467. 164 alomaja et al., j. build. mater. struct. (2021) 8:160-167 fig. 3. flexural strength test for the composite according to bs en 12467 according to bs en 12467, the flexural strength was determined from the relation in equation 4: (4) where p is the breaking load (n), l is the span of the simple supports (mm), b is the width of the specimen (mm) and h is the thickness of the specimen (mm) 3. results and discussion 3.1. density figure 4 is the graphical representation of the density of the fibre composite. from the results obtained, vm reinforced with 25% (15% gch & 10% ch) hybrid fibre has the lowest density of 1019 kg/m3. the highest density value of 1963 kg/m3 was exhibited by va, the composite with 0% fibres after 28 days of curing. relatively, the increase in the percentage volume of the fibres in the composite resulted in a decrease in density of the samples. the densities are within the range prescribed by bs en 12467 standard for ceiling board. fig. 4. density of gch-ch hybrid fibre reinforced composite 3.2. water absorptivity figure 5 is the graphical representation of the water absorptivity of the composite. from the results obtained, vb reinforced with 10% (5% gch & 5% ch) fibre has the lowest percentage mean water absorptivity with a value of 22.59%. vm reinforced with 25% (15% gch & 10%ch) absorbed the highest quantity of water with a value of 38.16%. it can be deduced from the graph alomaja et al., j. build. mater. struct. (2021) 8:160-167 165 that vm with the highest percentage volume (25%) of fibre has the highest water absorptivity. this could be as a result of plant fibre’s affinity for water. fig. 5. percentage water absorptivity of gch-ch hybrid fibre reinforced composite 3.3. moisture content figure 6 is the graphical representation of the moisture content of the composite after 28 days of curing. from the graph, it was indicated that vm reinforced with 25% (15% gch & 10%ch) hybrid fibre gives the highest moisture content value of 11.28% and the lowest moisture content of 3.32% was exhibited by vf reinforced with 15% (2.5% gch & 12.5% ch) hybrid fibre. the moisture content plays a vital role in the mechanical performance of the composite. fig. 6. percentage moisture content of gch-ch hybrid fibre reinforced composite 3.4. flexural performance the flexural behaviour of the composite is shown in figure 7. this shows that the highest flexural strength belongs to vc reinforced with 15% (12.5% gch & 2.5% ch) hybrid fibre which includes 12.5% of gch and 2.5% of ch. the flexural strength of va with 0% fibre reinforcement (control sample) is 21.44 mpa while that of vc and vg are 22.37 mpa and 22.05mpa respectively. it is obvious from the graph that vc and vg have greater flexural strength than va (sample with no reinforcing fibre). addition of 20% hybrid fibre led to a reduction in flexural strength when compared with the control sample, this could be as a result of decrease in the volume of the cement materials in the composite. according to khorami (2011), decreasing the 166 alomaja et al., j. build. mater. struct. (2021) 8:160-167 cementitious material in the composite would decrease flexural strength. further increase in the fibre content causes a decrease in the matrix-fibre interfacial bond within composite thereby resulting in a decrease in the flexural strength. however, most of the samples meet up with the minimum failure strength for four classes according to the bs en12467. except vf, vl and vo, other samples have flexural strength greater than 20mpa. meanwhile, the minimum failure strength for the fifth or highest class is 22mpa according to the aforementioned code. it means that vc reinforced with 15% (12.5% gch & 2.5% ch) and vg also reinforced with 15% (10% gch & 5% ch) hybrid fibre satisfies and surpasses the minimum failure strength for all the classes. fig. 7. flexural behavior of gch-ch hybrid fibre reinforced composite 4. conclusion the development of composite ceiling board from guinea corn husk (gch), cow hair (ch) and cement has been conducted. this study also shows that the incorporation of the gch-ch hybrid fibre improves the physico-mechanical properties of cement composite. the outcome of the findings shows that plant (guinea corn husk) and animal fibres (cow hair) obtained from waste can be judiciously utilized as reinforcement in fiber cementitious composites. furthermore, the study shows that the optimum composition of hybrid fiber in the board contains: 12.5% of guinea corn husk (gch) fibre, 2.5% of cow hair (ch) fibre and 85% of cement. the corresponding flexural strength at the optimum composition of hybrid is 22.37mpa which surpasses the minimum standard in bs en 12467. the density of the gch-ch hybrid composite ranged from 1019 to 1963 kg/m3. the water absorptivity varied from 22.59 to 38.16% and the moisture content ranged from 3.32 to 11.28%. additionally, the flexural strength decreases with the increasing contents of the hybrid (gchch) in the composite. the overall flexural strengths obtained are acceptable for ceiling applications according to bs en 12467 specifications. the utilization of guinea corn husk and cow hair as hybrid reinforcement in cement composite is not only suitable but will cause a reduction in both air and environmental pollutions. the outcome of this research satisfies the goal of turning agricultural and industrial wastes into useful construction materials. effective utilization of natural fibres in the development of innovative composite board will result in the manufacture of affordable products if embraced in the construction industry. alomaja et al., j. build. mater. struct. (2021) 8:160-167 167 5. references akinloye s. a., bankole g. m. and medubi a. (2014). effect of lime-guinea corn husk ash on the engineering properties of lateritic soil. electronic journal of geotechnical engineering, 19, 1769317699 ali, m. f., hossain, m. s., ahmed, s., and sarwaruddin chowdhury, a. m. (2021). fabrication and characterization of eco-friendly composite materials from natural animal fibers. heliyon, 7(5), e06954. doi:10.1016/j.heliyon.2021.e069. british standard (bs en) 12467, (2012). fibre-cement flat sheets —product specifications and test methods, british standards institution, london, u.k. duggal, s. k. (2008). building materials new age international publishers, 3rd revised edition, 504-505. dungani r., karina m, subyakto, sulaeman a., hermawan d. and hadiyane a. (2016). agricultural waste fibres towards sustainability and advanced utilization: a review. asian j. plant sci., 15, 42-45. khorami, m. (2011) application of natural and synthetic fibres as a replacement for asbestos fibres in cement boards. unpublished phd thesis. coventry: coventry university. lumingkewas, r.h. (2015). development of materials for construction with low environmental impact made with low content of cement and with natural fibers. ph thesis. université bretagne sud. nadzri n. i. m., shamsul j. b. and mazlee m. n. (2012). development and properties of coconut fiber reinforced composite cement with the addition of fly ash. journal of sustainable cement-based materials, 1(4), 186-191. ndububa, e. and nurudeen y., (2015). effect of guinea corn husk ash as partial replacement for cement in concrete, iosr journal of mechanical and civil engineering, 12(2), 40-45. ohijeagbon, i. o., bello-ochende, m. u., adeleke, a. a., ikubanni, p. p., samuel, a. a., lasode, o. a., & atoyebi, o. d. (2021). physico-mechanical properties of cement bonded ceiling board developed from teak and african locust bean tree wood residue. materials today: proceedings, 44, 2865–2873. doi:10.1016/j.matpr.2020.12.117. oladele, i.o., akinwekomi, a.d., aribo, s., and aladenika, a.k., (2009). development of fibre reinforced cementitious composite for ceiling application. journal of minerals &materials characterization & engineering, 8(8), 583-590. oladele, i.o., olajide, j.l., and ogunbadejo, a.s., (2015). effect of chemical treatments on the physicochemical and tensile properties of cow hair fibre for low load bearing composites development. international journal of materials science and applications, 4(3): 189-197. pickering, k.l., aruan-efendy, m.g. and le, t.m. (2016). a review of recent developments in natural fibre composites and their mechanical performance. composites: part a, 83, 98 -112. poole a.j., church j.s and huson m.g. (2009). environmentally sustainable fibers from regenerated protein. biomacromolecules 10, 1-8. rahmanzadeh, b., rahmani, k., piroti, n. (2018). experimental study of the effect of water cement ratio on compressive strength, abrasion resistance, porosity and permeability of nano silica concrete. frattura ed integrità strutturale, 44, 16-24. sanjay, m.r., arpitha, g.r., naik, l.l., gopalakrishna, k. and yogesha, b. (2016). applications of natural fibers and its composites: an overview. natural resources, 7,108-114. velasco m. v. r., dias t. c. s., freitas a. z., vieira júnior n. d., pinto c. a. s. o., kaneko t. m., and baby a. r. (2009). hair fiber characteristics and methods to evaluate hair physical and mechanical properties. brazilian journal of pharmaceutical sciences, 45(1), 154-157. j. build. mater. struct. (2014) 1: 47-57 https://doi.org/10.34118/jbms.v1i2.11 issn 2353-0057 strengthening of concrete beams by cfrp: experimental study and finite element analysis ghernouti y *, 1 , rabehi b1 , benhamna a2 and hadj mostefa a3 1 research unit: materials, processes and environment, university m’hamed bougara of boumerdes. algeria. 2 laboratory lpq3m, university of mascara, algeria. 3 laboratory of civil engineering, university of sidi bel abbes. algeria. * corresponding author: y_ghernouti@yahoo.fr abstract. this work presents an experimental study on the mechanical behavior of structural concrete reinforced by carbon fiber reinforced polymer (cfrp). the main purpose of this study is to test the applicability of this method of reinforcement in the beams to improve the behavior of concrete: strength and ductility. an experimental characterization of mechanical behavior by tensile test by three point bending is achieved, namely, the reinforcement of the lower part of the beam (15x15x75) cm3 with composite material, based on the ansys simulation, a model was developed to validate the different results obtained experimentally. the experimental results show that the reinforced concrete offered a great improvement in strength and ductility; in effect an influence directly on the failure mode is observed and then read by the value of strength and ultimate deformation. the tensile bending of beams reinforced by cfrp is more than 295% in comparison with that of nonreinforced beams. the gain maximum of ductility is 247%. the experimental results have been compared with the theoretical models, a good correlation was obtained. key words: strengthening, cfrp, ductility, finite element analyses fea, simulation. 1. introduction for several years, the rehabilitation and strengthening of reinforced concrete structures are becoming increasingly important in construction. there are several factors that may be necessary to strengthen or repair a structure: corrosion of steel reinforcement, concrete cracking, changes in assignment that imposes new burdens, development standards accidents (chock against an element of the structure), damaged caused by an earthquake, the extending of the life of a structure, etc…. therefore, researchers have attempted to find alternative materials that would solve this problem, and have turned to non-metallic materials, especially fiber reinforced polymer (frp). they have many qualities: a considerably low weight, a high tensile strength, flexibility, enabling them to take many shapes, no corrosion, good durability, and low thickness. composite materials based on frp have been used for confinement of concrete since the early 1980s, although the use of plastic tubes (pvc), filled with concrete, began in the late 1970s. in recent years, significant work is reported on the confinement of concrete columns with frps. these studies are mainly conducted on the compressive strength and stress–strain behavior of concrete reinforced by frp. the use of frp materials in flexural strengthening of reinforced concrete shallow beams has been investigated quite extensively in the past (yoon, 2000; uji, 1992; al-sulaimani, 1994; malvar, 1995; sato, 1996; malek, 1998; chaallal, 1998; triantafillou, 1998). the results of these investigations have demonstrated the effectiveness of different forms of frp systems, namely sheet, strip and wrap to achieve the desired effects. numerous experimental and analytical investigators directed their attention to study the fracture of plain concrete. on the contrary, much less attention, both on experimental and analytical levels, has been given to study the fracture behavior of reinforced concrete. yannopoulos (1989) experimentally tested tensile concrete specimens 76 mm in diameter and mailto:y_ghernouti@yahoo.fr 48 ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 1000 mm long with one 16 mm deformed steel bar in the center of the specimen. azad et al. (1989), azad and baluch (1990) and ashmawi et al. (1993) conducted experimental tests on three-point bend reinforced concrete beams. baluch et al. (1992) tested one beam size with two different reinforcing ratios. yehia (2003) tested 18 specimens with three different beam size and six different reinforcing ratios. sorour (2004) tested 45 specimens with five different reinforcing ratios and same specimen size under displacement controlled testing. sumarac et al. (2003) investigated the fracture of reinforced concrete beams subjected to three-point bending analytically (using fracture mechanics), numerically (using finite elements), and experimentally (using load controlled testing). wahab and yehia (2006) tested 9 flanged and 3 rectangular sections. on the analytical level, few investigations have been directed to apply elastic fracture mechanics approach to reinforced concrete elements. salah and el-adawy (1975) used an energy balance cracking criterion along with finite element analysis in order to predict the cracking moment of reinforced concrete beams. carpinteri et al. (1981) proposed a fracture mechanics model for bending of reinforced concrete beams assuming a linear elastic material model for concrete and a linear elasticplastic model for steel. the effect of reinforcing steel bars was simulated by a closing force whose magnitude was determined by a compatibility condition. ashmawi et al. (1993) and baluch et al. (1992) modified this model to include the nonlinear behavior of concrete under compression. bosco et al. (1990) investigated the minimum reinforcement in concrete beams. a similar analysis based on the fictitious crack model has been proposed by grestel et al. (1992). this article concerns in particular, the study of flexural behavior resulting from the reinforcement effect provided by composite materials made from carbon fiber on concrete beams. the gains in strength and deformation of the concrete are evaluated and analyzed. this up-to-date topic is of major interest in the field of construction and materials, taking into account criteria of sustainability, resilience, and vulnerability in the design of elements of reinforced concrete structures. 2. experimental program 2.1. materials all the cylinders of dimensions 160x320 mm were carried out with only one composition of aggregates, comprising a crushed coarse sand supplied by the tizi quarry (mascara, algeria) and two types of gravel (3/8) and (8/15). cement of the type cem ii 32.5 was supplied by the cement factory of chlef (algeria) with a class of 43 mpa. the concrete composition was determined according to the method of dreux-gorisse (dreux, 1998). 2.2. frp material in this study, the composite material being used is a carbon fiber fabric (sika wrap hex 230c), from the company sika in rolls of 3500 mm length and 300 mm wide with a thickness of 1.2 mm with an unidirectional fabric embedded in a matrix of black epoxy (figure 1(a)). the resin used for bonding composite materials on the concrete surface is a resin called sika dur-330 (figure 1(b)). the mechanical properties of frp material and the resin are represented in the table1. table 1. mechanical properties of frp materials and resin (youcef, 2010; ghernouti, 2012). cfrp resin tensile strength (mpa) 345-690 > 30 at two days and 20°c elastic modulus in tension (gpa) > 165 4.5 at seven days and 23 °c ultimate elongation in tensile (%) 1.7 / compressive stress (mpa) / > 55 at two days and 20°c ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 49 fig 1. materials used for reinforcement: (a) carbon fiber reinforced polymer (cfrp), (b) resin sika dur 330. 2.3. specimens preparation and testing procedure six (6) beams of concrete with (15x15) cm2 of section and 75cm of length were prepared, three of which were reinforced by carbon fiber fabric (crc). three unreinforced reference specimens were studied for comparison (urc). after mixing concrete, the filling of prismatic molds were 15x15 cm2 in section, with 75 cm length was carried out in three phases. for each phase, a vibration of the mold was carried out using a mobile stripe for 20 s. for each series, three specimens were prepared by using the same composition. after demolding, the specimens were deposited in a water vat for 28 days. in this age the specimens underwent an operation using jacketing of carbon fiber or glass fiber. this step consists in reinforced the specimens with carbon fiber fabrics (cfrp). before the reinforced of specimens by composite materials, the concrete surface has been treated to remove any surface grease, laitance and any heterogeneous part. the specimen surface is then cleaned and polished with a wire brush and then dusted with an aspirator. composite material was carefully cut to the desired dimensions. for bonding of the composite on the concrete specimen, we applied a layer of 1mm of the resin on the surface and then we placed manually one (1) layer of composite material on the support. finally, a pressure was exerted on the composite using a roller. an example of preparation of resin and applying the composite on the support beams is shown in figures 2 and 3 respectively. fig 2. preparation of resin (sika dur 330). all the prismatic specimens (15x15x75) cm3 were placed in controlab hydraulic testing machine with the capacity of 600 kn, and subjected to three point flexural load in accordance with standard nfp 18-407 (figures 4 and 5). 50 ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 fig 3. reinforced of specimens by cfrp: a) application of the resin, (b) application of frp. a quasi static rate of loading is applied in the center of specimen, with a speed of 30mm/mn. the force and the displacement are measured and recorded. the objects of this test are, on the one hand, to quantify the contribution in specimen stiffness conferred by the composite materials considered, and on the other hand compare the beam reinforced by cfrp with unreinforced beam. the influence of composite material is observed on the failure mode and the values of resistance and displacement obtained during the crushing specimens. fig 4. three-point bending test. fig 5. loading of specimen in testing machine. ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 51 3. experimental results and discussion the different results obtained from the flexural test, in particular, the load–displacement curves of unreinforced and reinforced concrete, are illustrated by figure 6. fig 6. load–deflection curves of reinforced concrete compared to the unreinforced concrete. 3.1. confinement level the reinforcement by composite materials can significantly increase the ultimate load and the deformation as it is shown in figure 6. all the specimens, the ratios (ftc/fto), (ɛtc/ɛto), are always significant, presenting values superior to one. for concrete beam reinforced by cfrp showed a gain in flexural strength and displacement of about 295% and 247%, respectively. the composite materials offer elastic modulus and rigidity which can modify various behaviors of reinforced concrete, and improving its strength and ductility. this improvement may be due to the characteristics of fiber fabric, which has a good tensile strength and a high modulus of elasticity. the strengthening of the composite beams in the party resisting evil has traction (tense part) aims to amend and prevent the distribution of cracks, so make a less brittle material; more ductile, it takes more energy to advance the crack. the flexural behavior laws obtained from different specimens can show that typically, all curves show an initial slope until a point of inflection, followed by a large zone of plastic deformation. depending on the effectiveness of confinement, the stress level and the plastic zone vary considerably from one variant of confinement to another. table 2. experimental test results. concrete unreinforced concrete reinforced concrete gain of strength gain of ductility ft0 (kn) to  (mm) ftc (kn) tc  (mm) ftc / ft0 /tc to gs (%) gd (%) urc 12 0.90 crc 47.5 3.12 3.95 3.47 295 247 52 ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 3.2. failure mode the analysis of specimens broken during tensile bending test, allows us to better evaluate the contribution of strengthening the tense part of the concrete specimen by composite materials (cfrp) on his ductility and strength as well as his mastery of rupture. by viewing the openings lip cracks, the various findings can be interpreted as follows: the unreinforced concrete (reference concrete) undergoes a classic failure of concrete loaded in bending, the failure mode observed on the concrete specimens, has a high speed of propagation of the crack that goes to loading levels then notices a sudden rupture of the specimen due to the fragility of concrete alone and its low tensile strength developed in the tension zone of the element. this failure mode is shown in figure 7(a). the reinforced concrete by cfrp (crc), a formation of crack in the mid-span can be observed, and then its development parallel to the applied load will be broken by the composite. the failure mode observed on the test specimens of concrete reinforced by cfrp, has a significant improvement on the macro-crack (figure 7(b)). this is explained by the presence of composite in the part that does not resist tensile (stretched part) whose role is to modify and prevent the distribution of cracks, so make a material less brittle; then more ductile so it takes more energy to advance the crack. it can be also noted that both sides of the specimen are assembled. this is due to the presence of fiber fabric, which prevents the propagation of cracks, they can keep the original shape and increase the deformability of the concrete, and thus, the behavior becomes ductile instead of being fragile. this aspect of maintaining the broken pieces of concrete with the composite is very important in construction, since it is a security feature in the ruins of structures. it also allows to building elements bear additional charges even after failure. the failure is obtained by total breaking out of the composite fabric; the reinforced concrete degradation is more advanced than the control concrete. the concrete beam reinforced with cfrp, have all been suffered a failure of carbon fabric (horizontal and vertical), and showed also a detached tissue after bear a very heavy burden that is almost four times higher than for unreinforced concrete. this is due to the characteristics of carbon fiber fabric which has good tensile strength and a high modulus of elasticity. to remedy this separation, we can improve the adhesion between the fabric and the concrete by improving the properties of the resin. fig 7. failure mode of concrete: (a) urc, (b) crc 4. finite element modeling of frp reinforced concrete beams the finite element procedure implemented in this study is developed using the available element types from ansys element library. the concrete is modeled using solid65 element type, whereas the frp reinforcement is modeled with solid 46 element type (chakrabarti, 2008). by adopting and combining these two element types, the reinforced concrete beam model was ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 53 developed. solid65 is used for the three-dimensional modeling of solids with or without reinforcing bars. the solid is capable of cracking in tension, crushing in compression, creep nonlinearity and large deflection geometrical nonlinearity. here, the model without reinforcing bars was used. this element has eight nodes with three degrees of freedom at each node; translations in the nodal x, y, and z directions. solid46 is a layered solid element, the element allows for up to 250 different material layers with different orientations and orthotropic material properties in each layer. the element has three degrees of freedom, namely translations in nodal x, y, and z directions, at each node. concrete is a quasi-brittle material and has different behavior in compression and tension. in compression, the stress–strain curve for concrete is linearly elastic up to about 30% of the maximum compressive strength. above this point, the stress increases gradually up to the maximum compressive strength. once it reaches the maximum compressive strength fco, the curve descends into a softening region, and eventually crushing failure occurs at an ultimate strain fcu. in tension the stress–strain curve for concrete is approximately linearly elastic up to the maximum tensile strength. after this point, the concrete cracks and the strength decreases gradually to zero. the concrete and the frp jacket were defined as anisotropic elastoplastic material and as an orthotropic elastic material respectively. both solid elements were deformable. the maximum strain failure criterion was used to identify the failure of the frp jacket. the element type used to model each material is those from the ansys element library and summarized in table 3. table 3. material types for modeling the beam specimens. materials ansys element type properties concrete solid 65 cfrp solid 46 54 ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 4.1. element meshing after preparing all the input data of material and geometrical properties, the beam models were divided into small elements. the meshing results of all beams specimens used for model validation are shown in figure 8. the solid65 and solid46 elements are fully interconnected each other forming a single solid column model that can simulate the actual behavior of the column specimen. fig 8. element meshing of materials: (a) concrete beam, (b) cfrp. 4.2. loading and boundary condition the beam model was subjected to flexural loading on their top face simulating the actual loading applied in the experimental tests; while the bottom side was reinforced by cfrp. the beam is tested in bending three-point (figure 9). the model is loaded with the same conditions as the experimental test. fig 9. loading beam model. 4.3. numerical results and discussions figure 10, shows a comparison of the stress–displacement response of the specimens reinforced by cfrp obtained by the experiment and by the fea. it is obvious that the fea results are very close to the test results. this means that the fea is validated by the test results. hence, the fea can be used to conduct a parametric analysis; this indicates that the actual behavior of beam specimens under flexural loading can be accurately predicted by the fea approach. the accuracy of the proposed procedure is also confirmed by the close values of peak stress and the displacement at the peak stress obtained from the fea and the experimental test, it can be seen that the differences of specimens reinforced by cfrp are 9.4% for the peak stress and 3.37% for the displacement. ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 55 fig 10. loaddeflection curves comparison of the fea and test data of reinforced concrete by cfrp. 5. conclusions the behavior of concrete beams reinforced with cfrp sheets was studied by the testing and finite element analysis (fea) outlined in this paper. the following conclusions were obtained: the concrete beam reinforced by cfrp showed a gain in flexural strength and displacement of about 295% and 247%, respectively. the composite materials offer elastic modulus and rigidity which can modify various behaviors of reinforced concrete, and improving its strength and ductility; the failure mode observed on the test specimens of concrete reinforced by cfrp, has a significant improvement on prevention of macro-crack. the cfrp prevents the distribution of cracks, it can keep the original shape of beam and increase the deformability of the concrete and thus, the behavior becomes ductile instead of being fragile. the both sides of the specimen remain assembled. the fea results are very close to the test results. this means that the fea is validated by the test results. hence, the fea can be used to conduct a parametric analysis; this indicates that this approach is an effective method for analyzing the behavior of concrete beams strengthened with cfrp. acknowledgement the authors gratefully acknowledge the generous assistance of sika eljazair for the supply of the composite material used in this study. list of symbols fto : fluxural strength of concrete. εto : defletion of concrete at middle of beam. ftc : flexural strength of strengthening concrete. εtc : defletion of strengthening concrete at middle of beam. 56 ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 6. references al-sulaimani gj, sharif a, basunbul ia, baluch mh, ghaleb bn (1994). shear repair of reinforced concrete by fiberglass plate bonding. aci struct. j., 91(4):458–64. ashmawi wm, baluch mh, azad ak (1993). crack control design of reinforced concrete beams in flexure. aci, special publications, 134. azad ak, baluch mh (1990). fracture characterization of reinforced concrete, final report ar7-130, king abdulaziz city for science and technology. azad ak, mirza ms, chan p (1989). fracture energy of weakly reinforced concrete beams. fatigue fract. eng. mater. struct., 12(1):9-18. baluch mh, azad ak, ashmawi w (1992). fracture mechanics application to reinforced concrete members in flexure. applications of fracture mechanics to reinforced concrete, 413-36. bosco c, carpinteri a, debernardi pg (1990). minimum reinforcement in highstrength concrete. j. struct. eng., 116(2):427-37. carpenteri a. a fracture model for reinforced concrete collapse. in: proc. of iabse colloquium on advanced mechanics of reinforced concrete. 1981. p. 17-30. chaallal o, nollet mj, perraton d (1998). shear strengthening of rc beams by externally bonded side cfrp strips. j. compos. constr., 2(2):111–3. chakrabarti a, chandra a, bharagava p (2008). finite element analysis of concrete columns confined with frp sheets. j. reinf. plast. comp., 27(12): 1349-73. dreux g, festa j (1998). nouveau guide du béton et de ses constituants. eyrolles, 8ème edition, paris, (in french). gerstle wh, dey pp, prasad nnv, rahulkumar p, xie m (1992). crack growth in flexural members: a fractural mechanics approach. aci struct. j., 89(6): 617-25. ghernouti y, li a, rabehi b (2012). effectiveness of repair on damaged concrete columns by using fiberreinforced polymer composite and increasing concrete section. j. reinf. plast. comp., 31(23): 1616–29. malek am, saasatmanesh h (1998). ultimate shear capacity of reinforced concrete beams strengthened with web-bonded fiber-reinforced plastic plates. aci struct. j., 95(4):391–9. malvar lj, warren ge, inaba c (1995). rehabilitation of navy pier beams with composite sheets. nonmetallic (frp) reinforcement for concrete structures. in rilem proceedings, chapman & hall. salah as, el-adawy nm (1975). a modified approach of estimation of the cracking moment of reinforced concrete beams. aci(july):356-60. sato y, ueda t, kakuta y, tanaka t (1996). shear reinforcing effect of carbon fiber sheet attached to side of reinforced concrete beams. in proceedings, of the 2nd international conference on advanced composite materials in bridges and structures, acmbs-ii, montreal. sorour mm (2004). fracture behaviour of reinforced concrete beams under four point bending in displacement controlled environment. m.sc. thesis, structural engineering department, cairo university. sumarac d, sekulovic m, krajcinovic d (2003). fracture of reinforced concrete beams subjected to three point bending. int. j. damage mech., 12(1):31-44. triantafillou tc (1998). shear strengthening of reinforced concrete beams using epoxy-bonded frp composites. aci struct. j., 95(2):107–15. uji k. (1992). improving the shear capacity of existing reinforced concrete members by applying carbon fiber sheets. t. jpn. concrete i., 14:253–66. wahab nm, yehia nab (2006). fracture behavior of flanged reinforced concrete beams; experimental investigation. in: the tenth arab structural engineering conference. yannopoulos pj (1989). variation of concrete crack widths through the concrete cover to reinforcement. mag. concrete res., 41(147):63-8. ghernouti et al., j. build. mater. struct. (2014) 1: 47-57 57 yehia nab (2003). size effect on fracture of reinforced concrete beams: experimental investigation. in: the ninth arab structural engineering conference, abu dhabi, united arab emirates, november. yoon kml. (2000) strengthening of concrete beams with fibre reinforced polymer (frp) mesh. undergraduate thesis. department of civil engineering, national university of singapore. youcef sy, amziane s, chemrouk m (2010). geometrical effect on the behavior of cfrp confined and unconfined concrete columns. j. reinf. plast. comp., 29(17): 2621–35. j. build. mater. struct. (2021) 8: 72-81 original article doi : 10.34118/jbms.v8i1.1158 issn 2353-0057, eissn : 2600-6936 a case study on deterioration assessment and rehabilitation of fire damaged reinforced concrete structure ojha p n, brijesh singh*, adarsh kumar n s, abhishek singh, vikas patel national council for cement and building materials, india. * corresponding author: brijeshsehwagiitr96@gmail.com received: 02-02-2021 accepted: 27-05-2021 abstract. fire is one of the most severe hazards that building structures may experience during their lifetime. a fire spread to the whole structure can cause unexpected damages to the structural elements. mainly, the building type is crucially important for the type and the level of damage to the building because of the fire. post fire investigation of damaged structure is required to determine the extent of damage to concrete elements and to work out system of effective repair/rehabilitation measures to maintain the structural integrity of fire effected structural components. the paper covers in brief the strength and durability study on fire damaged building in delhi, india. the study reports the extent of fire damage. optical microscopy (om), x-ray diffraction (xrd) and deferential thermal analysis (dta) studies were carried out on the sample concrete cores extracted from different identified portions of the fire exposed concrete are highlighted in this paper. extent of damage occurred in the reinforced cement concrete (rcc) i.e. rcc columns/beams/slabs are described based on the detailed evaluation by various non-destructive evaluation techniques covering cover study & ultrasonic pulse velocity (upv) testing. repair and remedial measures required for restoration and strengthening of the fire affected rcc columns/beams/slabs using indigenously available repair materials and techniques are also highlighted in this paper. key words: fire damage, field investigation, lab investigation, x-ray diffraction, differential thermal analysis. 1. introduction concrete is being a heterogeneous material, consisting of a composite of cement gel, aggregate and steel (or other) reinforcement. each of these components has a different reaction to thermal exposures in itself, and the behavior of the composite system in fire is not easy to define or model. concrete during high temperature event has a complex behavior due to the differences in coefficient of thermal expansion of each constitution. several factors that affect the fire resistance of concrete are concrete strength, moisture content, concrete density, and aggregate type. steel reinforcement if protected by the minimum cover specified by the code it is expected that the effect of high temperature on the reinforcement bars will be negligible. 60% to 70% per volume of any concrete mixture is coarse aggregate; therefore, change in the concrete proprieties is mainly affected by the type of coarse aggregates used in the mixture. three types of aggregates are commonly used in the construction industry; carbonate, siliceous, and lightweight. the specific heat and thermal conductivity of concrete are greatly affected by aggregate type (pathak et al., 2013). to determine the extent of fire damage occurred in effected rcc columns /beams/slabs of the building field assessment covering quality assessment using upv testing, measurement of concrete cover depth and carbonation depth, followed by laboratory scale assessment of residual strength of concrete, om study, xrd study and dta study is reported in this paper. highlights on suitable materials & techniques to carryout repair and strengthening of the rcc columns/beams/slabs are also briefly described in this paper. extensive studies had been carried out on the behavior of reinforced concrete structures exposed to fire and repair & rehabilitation of such structures in india and abroad. the technical papers covering different aspects of damage assessment, repair and rehabilitation of fire damaged structures are reported by the authors (pathak et al., 2013; yehia & kashwani, 2013; mailto:brijeshsehwagiitr96@gmail.com ojha et al., j. build. mater. struct. (2021) 8: 72-81 73 sangluaia et al., 2013; ingham, 2007; bailey, 2002; fib, 2008; fletcher et al., 2007; capote et al., 2006; usmani et al., 2006; buchanan and abu, 2017; georgali and tsakiridis, 2005; hertz and sørensen, 2005; ali et al., 2004). in the literature, the behavior of ordinary concrete which is not fireproof or containing fine grained component than cement grains with elevated temperature has been sorted in different ways but following the similar stages. the free water inside the concrete starts to evaporate with increasing temperature. above 150°c, the water bound the hydrated calcium silicate has been released and reaches its peak about 270°c. inertial stress development has occurred in this initial stage. dehydration of the matrix and relative thermal expansions of the aggregates in the concrete lead to microcracks in the material after 300°c. this phenomenon leads to decrease in the strength and elasticity modulus of the material. if the concrete is exposed less than 300°c, it can absorb the moisture from the air and recover. however, after the formation of microcracks, the strength loss is not recoverable. therefore, it is recommended to remove the material that exposed above 300°c. between 400-600°c, the calcium hydroxide decomposes into calcium oxide and water, and then water evaporates, and shrinkage occurs in the matrix. the most severe decrease in the strength of the concrete occurs in this range. after the fire, the calcium oxide reacts with the cooling water and the moisture in the air that forms new calcium hydroxide. this reaction causes the expansion of the cracks in the concrete and further decrease (about 20%) in the strength of the material. the hydrated calcium silicate decomposes after 600°c, and the concrete can be crumbled to gravel by the finger after 800°c.then, feldspar melts and remaining minerals of the cement turns into a glass phase above 1150°c (hertz, 2005). the strength of the concrete that is fully hydrated may increase within the first 100-200°c. however, this increase should not be considered in the design stage because of the dependency of the age of the concrete and condition of the material (hertz, 2005). studies done in past indicated that high strength concrete had higher residual strength, although the strength of high strength concrete decreased more sharply than the normal-strength concrete after exposure to high temperature. the porosity and pore size distribution of the concrete were investigated using mercury intrusion porosimetry. study indicated that the changes in pore structure can be used to indicate the degradation of mechanical property of high strength concrete subjected to high temperature (chan et al., 1999). a brief outline of the changes that take place in concrete with increasing temperature is given below (schneider, 1988; stawiski, 2005; aci, 1997): 1. 30–110°c: the evaporable water and a part of the bound water escapes. it is generally considered that the evaporable water is completely eliminated at 120 °c. 2. 110–180°c: the decomposition of gypsum (with a double endo-thermal reaction, the decomposition of ettringite and the loss of water from part of the carbo-aluminate hydrates take place. 3. 180–350°c: the loss of bound water from the decomposition of the c-s-h and carboaluminate hydrates take place. 4. 450–550°c: dehydroxylation of the portlandite (calcium hydroxide). 5. 700–900°c: de-carbonation of calcium carbonate. all the calcium hydroxide is converted to calcium oxide and the c-s-h converts to an anhydrous calcium aluminum silicate. these reactions cause a decrease in volume which leads to cracking in the paste. 6. above 900°c: further decomposition of aggregates. concrete starts burning. the significant loss in strength of reinforcing bar is observed at high temperature resulting into decrease in stiffness of structural members which is responsible for excessive residual deflections. however, recovery of yield strength after cooling is generally complete for temperatures up to 450°c for cold drawn bars and 600°c for hot rolled drawn bars. above these temperatures, there will be a loss in yield strength after cooling. 74 ojha et al., j. build. mater. struct. (2021) 8: 72-81 the deterioration of the compressive strength of the concrete with temperature can be clarified with physical and chemical changes in the concrete with elevated temperature. the physical and chemical changes can be sorted by changes in water content, hydration products, pore structure, microstructure and spalling. the tendency of these changes in the concrete are affected from many parameters: compression strength of the concrete, moisture content, density of the concrete, thermo-physical properties of concrete, external load, pre-stress, temperature gradient, temperature distribution on the structural elements, dimensions of the elements, reinforcement ratio, existing of fibers, aggregate and type of the cement additives, etc. reinforced concrete structures which are damaged due to fire can be rehabilitated and strengthened by using various retrofitting methods. different structural and non-structural members of fire damaged structure are subjected to different repair mechanisms depending upon extent of damages. for example, strengthening of fire damaged reinforced concrete beams and columns with fiber-reinforced polymer (frp) sheets and use of near-surface mounted carbon frp rods for repair of damaged rc slabs are one of the most popular retrofitting methods nowadays. they are sufficiently effective to restore the structural functions of the damaged structural components (aci, 1986; iso, 1975; cen, 2003). 2. investigation in order to take up the research project on fire damaged structures, during the preliminary site investigation it was observed that the fire has occurred at the fifth floor room of the building and its fumes/gases escaped through the duct opening in the roof slab to mezzanine floor at the top. the spalling of plaster from roof slab, beams and columns had occurred at several places (refer fig. 1-2). no documents or drawings other than a basic plan view of the arrangement of rooms on the floors was available. no details regarding the structural design or mix design of concrete were available. accordingly the authors decided to categorize the various investigation studies in two parts i.e. field investigation and laboratory investigation. the field investigation covered (i) determination of quality of concrete using upv testing technique as per is: 13311 (part – i) 1992, (ii) concrete cover study and (iii) extraction of concrete cores samples from identified members for carbonation study at site and to further carry out the laboratory investigation on concrete cores, which covered (a) determination of equivalent cube compressive strength of concrete core as per is 456 (2000) & is:516(1959) (b) chemical analysis of hardened concrete to determine ph value, chloride content and sulphate content. 2.1. field investigation 2.1.1. observations on change in colour of concrete when concrete gets heated to elevated temperatures, a gradual change in colour of the concrete occurs depending on the temperature range it is exposed to fib (2008) gives guidance regarding the probable colour change in concrete depending on the exposure to elevated temperatures. change in colour of concrete to pink was found in some of the beams and columns close to the room where fire was first detected. the depth up to which change in colour of concrete had occurred was also noted on the extracted concrete cores. at locations close to the room where fire was first detected and duration to exposure to fire was more, the maximum depth up to which change in colour of concrete had occurred was found to be about 12-20 mm. at other locations the colour change was visible only up to about 10 mm depth. the color of the cement mortar plaster had changed to light pinkish grey. 2.1.2. quality of concrete using upv testing technique as per is 13311 (1992) quality of concrete was assessed by upv testing (using portable ultrasonic non-destructive digital indicating tester-pundit) on the selected locations of rcc columns/beams. ojha et al., j. build. mater. struct. (2021) 8: 72-81 75 measurements were taken by direct method (cross-probing) as shown in fig.3. based on ultrasonic pulse velocity obtained, the overall quality of concrete was graded as ‘good’. upv measurements were also taken by cross probing technique using 150 khz transducers on some of the extracted concrete cores taken from the fire damaged portion. the results indicated that the upv values near the surface region of concrete, where colour change was visible and the effect of exposure to elevated temperatures was likely to be more, typically had lower upv values as compared to the concrete in the inner regions but all the values were in good quality grading as per is: 13311 (1992). table 1. upv values on extracted concrete cores depth upv values by cross probing on concrete core 20 3.50 40 3.59 60 4.20 80 4.25 100 4.35 120 4.41 2.1.3. concrete cover study the concrete cover study carried out by the ferro-scanning technique (using ferro scanner) to identify the thickness of concrete cover provided on the various identified locations of the fire damaged area of building. the observations were made on total 8 numbers identified rcc members and for each member four measurements were taken. the results indicated that the average concrete cover was varying from 35mm to 45mm in slabs, 35mm in beams and varying from 35mm to 42mm in columns. the thickness of cement mortar plaster on various reinforced cement concrete members was varying from 15mm to 20mm as observed during the field investigation. 2.1.4. carbonation study carbonation study was carried out by spraying a ph indicator (solutions of 1%phenolphthalein in 70%ethyl alcohol) on freshly extracted concrete core samples from identified representative members. the depth of carbonation in different samples was found to be varying from 0mm to 10mm. fig. 1. spalling of plaster in beams & slabs fig. 2. view of lift lobby in fire damaged area fig. 3. upv measurement being recorded 76 ojha et al., j. build. mater. struct. (2021) 8: 72-81 2.2. laboratory investigation 2.2.1. concrete core extraction and testing in order to ascertain the effect of fire damage, if any, on the strength of concrete, cores which were of sufficient length were tested. the equivalent cube compressive strength assessment results of concrete core samples extracted from various reinforced cement concrete members in fire damaged area were found to be satisfying the m25 grade of concrete, which was used in construction of building. strength of the cores extracted from the vicinity of the area where fire was first detected is found to be slightly lower compared to other locations not subjected to fire by about 5 to 10 percent indicating less impact of fire on the rcc components of the structure. 2.2.2. chemical analysis study of concrete powder for carrying out the chemical analysis of hardened concrete, few representative concrete cores samples from identified location were sliced in three layers i.e. (0mm-20mm), (20mm-40mm) & (40mm-60mm) from the exposed surface of the identified rcc member and further grinded to powder. the chloride test results of concrete powder shown that, chloride content in various samples was 0.12 kg/m3 which were within the permissible limit of 0.60 kg/m3 for rcc as prescribed in table 7 of is: 456 – 2000. the sulphate content in various samples was varying from 1.44 % to 2.46 % which was within the permissible limit of 4% (as per clause-8.2.5.3 of is: 456-2000). the ph values of the various representative concrete samples were found to be varying from 12.43 to 12.63. 2.2.3. optical microscopy (om) study the petrographic studies had been carried out on three concrete core samples from identified locations of rcc column c32, slab si & slab s6 (refer fig. 4-7) under stereoscopic microscope (nikon smz-1500). fig. 4. c-32-bottom-1: voids filled with crystalline material fig. 5. -1-middle-2: leached out materials as observed in the sample fig. 6. s-6-middle-3: voids filled with crystalline material fig. 7. s-6-bottom-3: stretching of coarse and fine aggregate due to temperature rise ojha et al., j. build. mater. struct. (2021) 8: 72-81 77 three thin slices (up to 5mm thick) from each of concrete core were drawn, one from top portion of core i.e. from exterior face /top of rcc member (0-30mm), second from middle portion of the core (30-60mm) and third from bottom portion of the core (beyond 60mm). the study was carried out to determine various micro structures, morphological features and pore distribution and development. based on the results obtained on above parameters inferences were drawn to establish the deterioration development caused of the fire. 2.2.4. x-ray diffraction (xrd) x-ray powder diffraction (xrd) is a rapid analytical technique primarily used for phase identification of a crystalline material. crystalline substances act as three-dimensional diffraction gratings for x-ray wavelengths similar to the spacing of planes in a crystal lattice. interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy bragg's law (nλ=2d sin θ), which relates the wavelength (λ) of electromagnetic radiation to the diffraction angle (θ) and the lattice spacing (d) in a crystalline sample. the diffracted x-rays are then detected, processed and counted. conversion of the diffraction peaks to d-spacings allows identification of the mineral because each mineral has a set of unique d-spacings. typically, this is achieved by comparison of d-spacings with standard reference patterns. the x-ray diffraction (xrd) studies had been done on powder samples obtained after grinding of concrete core samples extracted from identified locations of beam b-8 & slab s-1 of the fire damaged area. major mineral phases present were quartz, calcite, albite and portlandite. phlogopite, dolomite, muscovite, kaolinite, larnite etc were present in minor mineral phases. the xrd results indicated quartz, calcite and dolomite were formed most likely due to rise in temperature of the concrete during fire. (refer table-2). whereas, kaolinite, vaterite and cordierite were formed due to rise in temperature. table 2. relative abundance of various minerals as observed in xrd study on concrete samples of fire damaged structure sl. no. phase identified relative abundance beam b8 slab s1 1 quartz [sio2] major major 2 calcite [caco3] major major 3 albite [naalsi3o8] major major 4 portlandite [ca(oh)2] major major 5 dolomite [camg(co3)2] major minor 6 phlogopite [k2 mg6 al2 si6 o24 h4] major minor 7 kaolinite [al2si2o5(oh)4] minor minor 8 larnite [ca2sio4] minor minor 9 muscovite [(k0.77al1.93(al0.5 si3.5) o10(oh)2] minor minor 10 vaterite [caco3] minor minor 11 cordierite [mg2al4si5o18] minor minor 2.2.5. differential thermal analysis (dta) the samples from identified locations covering plaster from beam b8 & beam b32 and sliced concrete cores in layers (0-20mm), (20-40mm) & (40-80mm) from beam b8 and slab s1, were grinded to powder passing 150 micron is sieve. the differential thermal analysis was carried out to assess weight loss corresponding to different temperatures. in sample of beam-b8 plaster, the total weight loss of 11.91 percent for (0-20mm) depth up to a temperature of 1000°c from ambient@ 10°c/minute. graph for beam b8 plaster (0 20mm) shown in fig. 8. in beam-b32 plaster, the total weight loss of 11.069 percent for (0-20mm) depth up to a temperature of 78 ojha et al., j. build. mater. struct. (2021) 8: 72-81 1000°c from ambient@ 10°c/minute was observed. in sample from slab s1, the total weight loss of 15.42 percent for (0-20mm) depth, 15.16 percent for (20-40mm) depth and 13.82 percent for (40-80mm) depth up to a temperature of 1000°c from ambient@ 10°c/minute was observed. graph for slab s1 (0 20mm) is given in fig. 9. fig. 8. graphical representations of study on plaster samples from beam b8 of fire damaged area fig. 9. graphical representations of study on concrete samples from slab s1 of fire damaged area in general, the results of dta analysis done on all samples show that, the first endothermic peak occurred at around 430°c was due to dissociation of calcium hydroxide. inversion of silica ojha et al., j. build. mater. struct. (2021) 8: 72-81 79 occurred at around 575°c and was represented by a small sharp endothermic peak. the third endothermic peak was occurred at around 750 °c due to decarbonation. where effect of fire was negligible, peak due to dissociation of ca(oh)2 was absent in the dta curve at 0-5 mm depth whereas it was present in the dta curves at greater depths. this indicates that at 0-5 mm depth, the peak was absent because of carbonation of concrete (measured depth of carbonation front was found to be maximum 10 mm) and not due to exposure to elevated temperatures due to fire. as carbonation had not progressed beyond this depth, the peaks corresponding to dissociation of ca(oh)2 were present in the dta curves at greater depths. 3. discussion of results in order to determine the effect of the fire on the structural behavior of building the mechanical, chemical and microstructural properties of concrete after the fire needs to be compared with similar concrete not subjected to fire. the results needs to be compared with standard limits for chemical parameters and degradation in strength if any needs to evaluated through concrete core test results. the effect and extent of fire in the rcc member can also be evaluated through supplementary laboratory techniques such as differential thermal analysis, x-ray diffraction, optical microscopy etc. visual observation had indicated cracking & spalling cement mortar plaster from various rcc columns / beams/ slab of fire damaged room of building. in the area outside fire damaged room no spalling of cement mortar plaster was observed. the upv test results indicated that the quality of concrete was “good” in various members, which were exposed to the fire. the equivalent cube compressive strength assessment results of concrete core samples extracted from various members in fire damaged area were found to be satisfying the m25 grade of concrete, which was used in construction of building. the depth of carbonation assessed on various core samples extracted from identified locations indicated that the carbonation depth was 0mm in 8 rcc members and 10mm in one column in the lift lobby. the average cover thickness in various tested members was found to be 35mm to 45mm in slab soffit, 35mm to 42mm in columns and 35mm in beams. these cover thickness values qualifies for fire resistance of 2 hours as per criteria for nominal cover to meet specified period of fire resistance as given in table-16a of is 456:2000. the results of chemical analysis covering chloride content, sulphate content and ph value were found to be within the permissible limits as prescribed in is: 456 – 2000. the microscopic investigation of the fire damaged cores indicated that the distribution pattern of the grains and pores spaces changed drastically. even the morphology of the grains of the fine aggregate component was also changed. large variation was noticed in air void distribution pattern from the bottom to top portion of the roof. bottom portion was directly exposed to fire, which had caused sealed walled air voids bigger in size. size of pores after fire might have increased but have very stable and firm walls, which had presently helped to achieve more strength to the concrete. as the tracking of microscopic analysis gone inside the core, size of air voids reduced drastically. however, partial melting of fine aggregate component was noticed in these areas. all these features have improved the cohesiveness of the concrete. microscopic study also established that there was appreciable increase in the strength of the concrete cores. this had been concluded based on the features of the matrix at the different levels of the cores. this observation was found to be similar in the samples. the fire had damaged least in the top part of the total structure. 4. recommended repair and rehabilitation measures based on the results of various studies as discussed above, the authors suggested indigenously available state of art materials, specifications and technique for effective repair and rehabilitation of fire affected members of building. the suggested repair procedure included. 80 ojha et al., j. build. mater. struct. (2021) 8: 72-81 i) removal of all cracked and loose cement plaster from the reinforced cement concrete members and walls in fire damaged area by chiseling out surface concrete up to 20mm depth in deteriorated structural elements and to remove the existing plaster over the wall also. ii) applying bond coat of sbr (styrene butadiene rubber) latex based polymer modified cement slurry in proportions 1:1 (1 cement: 1 polymer) to be applied on the prepared surfaces of concrete/substrate. iii) to rehabilitate roof slab soffit, columns and beams by building up the profile of structural members up to 40 mm average depth & 20 mm average thickness in walls by polymer modified mortar (pmm) using emulsified sbr latex conforming to astm c1059 (2013) type-i in damaged areas (1 cement-3 part graded cleaned river sand + 15 % latex by weight of cement) with 0.35 w/c ratio, in 10-15 mm thick layers by applying bond coat between successive/each layers including leveling and profiling complete. proper curing to be done for the repair work. gunny bags to be used for effective curing. polypropylene fibres to be added to reduce shrinkage. 5. conclusion field investigation on various representative samples of concrete members indicated ‘good’ quality of concrete, this was also supported by observed ample concrete cover thicknesses and strength of concrete was found to be more than required strength of m25 grade of concrete. comparison of compositional changes in the surface concrete (0-20mm) and subsurface concrete (beyond 20mm) samples as observed in x-ray diffraction and dta studies indicated that the surface concrete in slabs, beams & columns in fire damaged area were subjected to a temperature of about 750oc but sub-surface strata beneath 20mm remained unaffected. based on the various investigation studies, it was suggested that the concrete portion directly exposed to the fire should be removed by chiseling to the depth up to which the damage was observed and building up profile by applying system of sbr bond coat & pmm to compensate for damaged surface concrete in fire exposed concrete elements. 6. references aci (1986). guide for the use of polymer in concrete. committee 548. joumal of the american concrete institute, 83(5), 798-829. aci (1997). standard method for determining fire resistance of concrete and masonry construction assemblies. detroit, american concrete institute committee. ali, f., nadjai, a., silcock, g., & abu-tair, a. (2004). outcomes of a major research on fire resistance of concrete columns. fire safety journal, 39(6), 433-445. astm c1059 (2013) standard specification for latex agents for bonding fresh to hardened concrete. bailey, c. (2002). holistic behaviour of concrete buildings in fire. proceedings of the institution of civil engineers-structures and buildings, 152(3), 199-212. buchanan, a. h., & abu, a. k. (2017). structural design for fire safety. john wiley & sons. capote, j. a., alvear, d., lázaro, m., espina, p., fletcher, i. a., welch, s., & torero, j. l. (2006). analysis of thermal fields generated by natural fires on the structural elements of tall buildings, proceedings, int. cong. fire safety in tall buildings, santander, spain, pp. 93-109. ojha et al., j. build. mater. struct. (2021) 8: 72-81 81 cen (2003). design of concrete structures—part 1-2: general rules—structural fire design. european committee for standardization, en 1992 eurocode 2. chan, y. n., peng, g. f., & anson, m. (1999). residual strength and pore structure of high-strength concrete and normal strength concrete after exposure to high temperatures. cement and concrete composites, 21(1), 23-27. fib(2008). fire design of concrete structures structural behaviour and assessment, the international federation for structural concrete, state-of-art report, bulletin no. 46. fletcher, i. a., welch, s., torero, j. l., carvel, r. o., & usmani, a. (2007). behaviour of concrete structures in fire. thermal science, 11(2), 37-52. georgali, b., & tsakiridis, p. e. (2005). microstructure of fire-damaged concrete. a case study. cement and concrete composites, 27(2), 255-259. hertz, k. d. (2004). reinforcement data for fire safety design. magazine of concrete research, 56(8), 453459. hertz, k. d. (2005). concrete strength for fire safety design. magazine of concrete research, 57(8), 445453. hertz, k. d., & sørensen, l. s. (2005). test method for spalling of fire exposed concrete. fire safety journal, 40(5), 466-476. ingham, j. p. (2007). assessment of fire-damaged concrete and masonry structures: the application of petrography. proceedings of the 11th euroseminar on microscopy applied to building materials, 1-16. is: 13311 (1992). non destructive testing of concrete – methods of test, part – i ultrasonic pulse velocity is: 456 (2000). indian standard for plain and reinforced concrete – code of practice is: 516 (1959). methods of tests for strength of concrete iso (1975). fire resistance tests. elements of building construction, iso 834, international organization for standardization. geneva, pathak, r. p., munzni, b. k., sharma, p., mahure, n. v., vyas, s., & ratnam, m. (2013). estimation of fire damage to concrete structure: a case study. international journal of engineering, 2(4), 130-136. sangluaia, c., haridharan, m. k., natarajan, c., & rajaraman, a. (2013). behaviour of reinforced concrete slab subjected to fire. int. j. comput. eng. res, 3(1), 195-206. schneider, u. (1988). concrete at high temperatures—a general review. fire safety journal, 13(1), 55-68. stawiski, b. (2005). the use of nondestructive methods in postfire diagnostics. kkbn, zakopane, 23-28. usmani, a. s., rotter, j. m., lamont, s., sanad, a. m., & gillie, m. (2001). fundamental principles of structural behaviour under thermal effects. fire safety journal, 36(8), 721-744. yehia, s., & kashwani, g. (2013). performance of structures exposed to extreme high temperature—an overview, open journal of civil engineering, 3(3), 154-161 j. build. mater. struct. (2014) 1: 65-76 https://doi.org/10.34118/jbms.v1i2.10 issn 2353-0057 the effect of hybrid steel fiber on the properties of fresh and hardened self-compacting concrete haddadou n *, 1, chaid r2 , ghernouti y2 and adjou n1 1 national center of studies and integrated research on building engineering (cnerib), cité nouvelle elmokrani, souidania, algiers, algeria. 2 research unit: materials, processes and environment, university m’hamed bougara of boumerdes, algeria. * corresponding author: haddadounai@yahoo.fr abstract. self-compacting concrete (scc) offers several economical and technical benefits, the use of steel fibers extends its possibilities. this study was performed to compare the properties of scc and fiber reinforced self-compacting concrete (frscc) with high volume of mineral addition. six mixtures were elaborated in this study. the content of the cementitious materials and the water/cementitious materials ratio were kept constant, 500 kg/m3 and 0.34 respectively. the self-compacting mixtures have been prepared with a cement replacement of 30% by weight of marble powder. two different types of steel fibers were used in combination with different lengths (50 mm and 30 mm), keeping the total fiber content constant at 60 kg/m3. slump flow time and diameter, sieve stability, and l-box were performed to assess the fresh properties of the scc and frscc. compressive strength, splitting tensile strength, flexural strength and ultrasonic pulse velocity were determined for the hardened properties. a marginal improvement in the ultimate strength was observed. the addition of steel fiber enhanced the ductility significantly and the results indicated that high-volume of marble powder can be used to produce frscc, even though there is some decrease in the compressive strength because of the fiber geometry which affects the properties of scc mixtures not only in the fresh state but also in the hardened state. key words: self-compacting concrete, marble powder, steel fiber, hybrid fiber, workability, strength. 1. introduction in the present time, the constructions in civil engineering have their own structural and durability requirements of the concrete, which can accommodate the intended function of the structure. it is therefore necessary to develop self-compacting concrete (scc) of special properties, so that the structures continue to perform their intended purpose. scc has an excellent applicability for elements with complicated shapes and congested reinforcement. consequently, scc has been recently one of the most important developments in the construction industry (brouwers and radix, 2005). one of the disadvantages of scc is the cost, associated with the usage of chemical admixtures and the high volume of portland cement. as an alternative to reduce the cost of scc is the usage of mineral additives (such as marble powder, natural pozzolan, fly ash and slag) which are finely divided materials added to concrete as separate ingredients either before or during mixing (şahmaran, 2006). the compactness of the scc matrix, due to the higher amount of fine and extra-fine particles, may improve interface zone properties (corinaldesi and moriconi, 2004; moriconi and corinaldesi, 2005), leading to enhanced post-cracking toughness and energy absorption capacity. the addition of steel fibers improves the mechanical properties and the ductility of scc in much the same manner as in vibrated concrete. however, the fibers greatly impair the workability of scc because of their elongated shape and large surface area. the development and the usage of scc have resolved the workability issue. the applicability of steel fibers with scc has been investigated and has proven to be feasible (ding, 2010; ding, 2011). the properties of fibers that are usually of interest are; fiber concentration, fiber geometry, fiber orientation and fiber distribution. fibers which are basically longer need particles to have a significant influence mailto:haddadounai@yahoo.fr 66 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 consistency and a workability of fresh concrete mix. apart from the sheer volume of added fibers. this influence depends on both properties of fibers (aspect ratio of a fiber, characterized by rigidness/flexibility ratio and roughness of a surface) and properties of concrete (paste volume, maximum aggregate size, shape of aggregate particles). hooked steel fibers proved to be a very good solution for enhancing limited mechanical properties of concretes (katzer, 2008; domeski, 2011). the effect of mineral admixtures on the strength and durability of fiber reinforced self-compacting concrete (frscc) has been extensively investigated under different environmental conditions (corinaldesi and moriconi, 2004; sahmaran and yaman, 2007; srinivasa, 2009). the investigation of the frscc by the researchers shows improvement of the mechanical properties in terms of apparent compressive strength, flexural strength, splitting tensile strength, elastic modulus, creep and shrinkage, shear and pullout behavior, as compared to normally vibrated concrete, scc and fiber reinforced normally vibrated concrete under statically applied loads (sahmaran and yaman, 2007; ambroise, 2001; dhonde, 2007; greenough and nehdi, 2008; torrijos, 2008; cunha, 2009). the inherent advantages of frscc enhance the scope of its applications, especially in long span bridges, slabs, highway pavements and offshore platforms for oil production in the deep sea where the predominant mode of loading is flexural fatigue. the objective of this study is to assess the effects of marble powder (mp) replacement on the fresh and hardened properties of scc incorporating different length of steel fibers. even though, the suitability of mp in frscc needs much detailed investigations, this study covers some fresh and hardened properties of such mixtures. in addition to the mp, two different type and sizes of steel fibers were used at different proportions in making the concrete. the total mass of cementitious materials was 500 kg/m3, in which 30% of cement is replaced by mp. for comparison, a control scc mixture without steel fiber was also produced. 2. experimental procedure 2.1. materials a cemii/a 42.5 cement type and a limestone type mp were used as binder materials in the mix proportions. the chemical properties of cement and marble powder are given in table 1 whereas the mineralogical composition of cement is given in table 2. figures 1 and 2 presented the mineralogical composition of cement and marble powder determined by x-ray diffraction. table 1. chemical composition of cement and marble. element cement mp sio2 16,52 0.34 al2o3 4,08 0.04 fe2o3 2,89 0.13 cao 58,49 54.93 mgo 1,47 0.73 k2o 0,47 0.01 na2o 0,24 0.01 so3 1,98 0.06 tio2 0,22 0.01 p2o5 0,14 0.02 insoluble 1,09 / loss of ignition 7,45 43.72 table 2. mineralogical composition of cement. element (%) c3s 56 c2s 20 c3a 05 c4af 13 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 67 fig 1. x-ray diffraction pattern of mp. fig 2. x-ray diffraction pattern of cement. in order to determine the surface characteristics of mp, scanning electron microscopy was performed and the typical secondary electron image is presented in fig. 3. as seen in this figure, mp grains show angular shapes with a rough surface texture. fig 3. scanning electron microscopy (sem) of mp. 68 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 workability improvement of scc mixtures was obtained thanks to the polycarboxylates superplasticizer (medaflow 30) characterized by a chloride content lower than 0.1% and a viscosity modifying admixture (medacol bse). the properties of both admixtures, as provided by their manufactures, are shown in table 3. continuously graded coarse aggregates (3/8 and 8/15) were used with specific gravity and water absorption of 2.56 g/cm3 and 1.03% respectively. natural dune sand and river sand were used. selected sands are subjected to grain size distribution analysis as per xp p 18-540 standard (afnor, 1997). physical properties of used sands are given in table 4. the gradation of coarse and fine aggregates was determined by sieve analysis and presented in figure 4. table 3. properties of chemical admixture. chemical admixture specific gravity ph color dosage(l/m3) main component sp 1,06 5,3 light brown 0,3 to 2 carboxylic ether vma 1,03 6.2 light yelow 0.5 to 2 aqueous dispersion of microscopic silica table 4. properties of used sands (ds and rs). ds rs fineness modulus 1.29 2.85 sand equivalent 48 90 absorption (%) 2.43 0.63 moisture content (%) 1 0.42 fig 4. particle size distribution of coarse and fine aggregates. the first type of fibers used in this research is corrugated steel with low strength (ls) and the second type is hooked-ended steel fibers (hs) with 50 mm in length and 0.55 mm diameter. the reason for using ls steel is that it’s accessible with low cost. these fibers have been used with a rectangular section and length l=30 mm. as long as the influence of this type of corrugated steel fiber is more than simple fiber (okamura and ouchi, 2003). that’s why all the fibers are shaped with machine in sinusoidal wave as shown in fig.5.a. 2.2. mixture proportions six mixtures, one scc and five frscc, were prepared for investigating the effect of type and sizes of steel fibers. water/ (fine materials) ratio was fixed at 0.34 for all concrete mixtures. all of the mixtures had the same amount of marble powder 30% replaced by weight of cement. these were named as scc, rscc1, rscc2, rscc3, rscc4 and rscc5 indicating the two different values haddadou et al., j. build. mater. struct. (2014) 1: 65-76 69 of aspect ratios, and the same percentage of volume fraction of steel fiber incorporated in the mixture(60kg/m3). (a) (b) fig 5. steel fibers used for the production of frscc (a):ls, (b):hs. for all the mixtures, the total amount of binder, water and the amount of steel fiber were all kept constant as seen in table 5. the chemical admixture was added to the mixture until the scc characteristics were obtained. table 5. mix proportions. mix id w/b c (kg/m3) mp (kg/m3) fine aggregate (kg/m3) coarse aggregate (kg/m3) fibers (kg/m3) sp (l/m3) vma (l/m3) 0/1 0/5 ls 30 hs 50 scc 0.34 350 150 173 610 790 0 0 5.9 1.43 rscc1 0.34 350 150 190 720 717 60 0 5.9 1.43 rscc2 0.34 350 150 190 720 717 42 18 5.9 1.43 rscc3 0.34 350 150 190 720 717 30 30 5.9 1.43 rscc4 0.34 350 150 190 720 717 18 42 5.9 1.43 rscc5 0.34 350 150 190 720 717 0 60 5.9 1.43 2.3. preparation and casting of test specimens in the production of scc, mixing sequence and duration are very important, thus the mixing process was kept constant for all concrete mixtures. the following mixing sequence was arrived after several trials for optimizing the workability. all the ingredients were first mixed in dry condition in the concrete mixer for one minute. then 70% of calculated amount of water was added to the dry mix and mixed thoroughly for one minute. the remaining 30% of water was mixed with the sp and vma and was poured into the mixer and mixed for five minutes. at this stage, 20% by weight of the water mixed with sp was poured into mixer and mixed for four minutes. then, 10% by weight of water mixed with vma was poured into the mixer and mixed for one minute. later required quantities of steel fiber were sprinkled over the concrete mix and mixed for one minute to get a uniform mix. thus, the total mixing time was 7 minutes. in this investigation the filling ability was evaluated by slump flow time and diameter. the passing ability was measured by l-box. the resistance to segregation was measured by sieve stability test (efnarc, 2005). for each concrete mixture six cubes of 150mm, six prisms of 70*70*280mm and fifteen cylinders of 150*300mm specimens were cast. 70 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 2.4. tests on fresh concretes slump flow time and diameter tests, l-box and sieve stability test were carried out according to the limitations specified by efnarc as shown in fig.6. the first and second test procedures were discussed by sahmaran and yaman (2007) and are briefly described below. the slump flow is used to evaluate the horizontal free flow (deformability) of scc in the absence of obstructions. the test method is very similar to the test method for determining the slump flow of concrete. the difference is that, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow. the higher the slump flow, the larger is concrete’s ability to fill formwork. during the slump flow test, the time required for the concrete to reach a diameter of 500mm is also measured and recorded as t500. this parameter is an indication of the viscosity of concrete and indicates the stability of the concrete. a lower time points to a greater fluidity or smaller workability loss. according to nagataki and fujiwara (1995), a slump flow diameter ranging from 500 to 700 mm is considered as the slump required for a concrete to be classified as scc. according to specification and guidelines for scc prepared by efnarc (2005) (european federation of national trade associations), a slump flow diameter ranging from 650 to 800 mm can be accepted for scc. in addition to the slump flow test, l-box test and sieve stability test are also performed to assess the flow ability, passing ability and stability of scc. the l-box ratio must be in the range of 0.8 1.0 and the sieve stability values must be in the range of 0-15 %. good flowable and stable concrete would consume short time to flow out. according to khayat and guizani (1997), a good scc has a flow times in the range of 0-5 sec. workability slump flow test l-box test seive stability test conservation of specimens fig 6. workability tests on scc. 2.5. tests on hardened concrete concrete specimens have been batched, moulded and cured according to en 12390-2 (2001). all the moulds were covered by plastic sheets and stored for 24 hours in the laboratory prior to demoulding; afterwards, they were cured in water at 20°c and at relative humidity (rh) in the order of 50–60%. a testing programme has been elaborated and consisted of determining the essential properties of fresh and hardened scc as shown in fig.7. the necessary test specimens have been cast in different moulds and three tests were carried out to assess each required characteristic. for the determination of compressive strength and ultrasonic pulse velocity (upv), concrete cubes of 150*150*150 mm3 (en 12390-3, 2001; en 12504-4, 2005) were used. it was measured at 7, 28 and 56 days old and to determine split tensile strength cylinder, specimens150*300 mm3 (en 12390-6, 2001) were used at 28 and 56 days old, using a testing machine with a maximum load capacity of 3000 kn. the tensile strength was measured on 70*70*280 mm3 prismatic specimens (en 12390-5, 2001) at 28 and 56 days old applying a three-point bending test, using a testing machine with a maximum load capacity of 100 kn. haddadou et al., j. build. mater. struct. (2014) 1: 65-76 71 compressive strength test flexural strength split tensile strength ultrasonic pulse fig 7. hardened tests on scc. 3. results and discussions 3.1. fresh concrete properties to classify a concrete as self-compacting, the requirements for filling and passing ability as well as segregation resistance must be fulfilled. it is specified that the filling ability and stability of scc in the fresh state can be defined by four key characteristics namely flowability, viscosity, passing ability, and segregation resistance (barr, 1996). fresh properties of the concretes were carried out according to the limitations specified by efnarc as shown previously in fig.6. the results obtained are reported in table 6. as seen in this table, the fresh properties are in the range of 612-708 mm for slump flow diameters, 3.32-5.03s for slump flow times, 0.81-0.95 for the l-box ratio and 3.03-5.52% for the sieve stability. all concrete mixtures were considered as self compacting concrete (scc). in all of the scc mixtures, there was no segregation of aggregate near the edges of the spread-out concrete as observed from the slump flow test. table 6. fresh properties of scc. mix id slump flow (mm) t500 (s) l-box ratio sieve stability (%) scc 708 3.32 0.95 5.52 rscc1 705 4.06 0.92 4.9 rscc2 700 4.23 0.93 4.62 rscc3 675 4.51 0.89 4.12 rscc4 648 4.86 0.83 4.22 rscc5 612 5.03 0.81 3.03 the mp can be considered as limestone filler which is one of the materials that have extensively been studied in the literature (elkhadiri, 2002; petit and wirquin, 2010) and have improved the mechanical and durability features of concretes by providing more compact structure through its pore-filling effect. mp helps to evenly disperse fibers during mixing. although the angular shapes with rough surface texture of mp particles provide ball bearing effects and reduce internal friction in fresh concrete and these increase the flowability and compaction of the concrete. the steel fibers have affected slightly the fresh properties of the concrete mixtures. the addition of ls steel fibers did not affect the water requirement of the mixture for the same workability. however, addition of hs fibers which had large sizes reduced the amount of water, as seen in 72 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 table 6, the fresh properties decreased with the increase of hs fiber content. however, this could be explained by the geometry of the fibers. ls fibers have smaller dimensions when compared to hs fibers, thus have less potential to prevent the movement of aggregates. therefore, the shorter size of fibers reduced the energy loss during the movement of concrete ingredients. 3.2. hardened concrete properties the hardened concrete test results are summarized in table 7, which included compressive strength, split tensile strength, flexural strength and upv at different ages. table 7. hardened properties of scc. mix id compressive strenght (mpa) splitting tensile strenght (mpa) flexural strenght (mpa) ultrasonic pulse velocity (upv) (m/s) 7d 28 d 56 d 28 d 56 d 28 d 56 d 7d 28 d 56 d scc 28.63 35.45 38.56 2.32 2.68 4.45 4.79 3926 4038 4158 rscc1 30.63 37.74 40.36 2.51 3.41 4.6 4.89 4098 4252 4398 rscc2 29.45 35.78 38.25 2.72 3.84 5.08 5.28 4162 4292 4303 rscc3 27.22 36.56 36.71 3.12 3.86 5.53 5.31 4208 4312 4377 rscc4 26.57 33.62 37.41 3.52 4.22 5.49 5.97 4158 4271 4359 rscc5 25.44 32.18 34.39 3.83 4.53 5.93 6.29 4247 4324 4358 to evaluate the effect of fibers on the hardened properties, the 56 days properties are normalized with respect to the control mixture (scc) and the results are presented in figs. 8-12. as seen from these figures, the most significant changes were observed on the flexural strength, splitting tensile strength and later on the compressive strength. on the other hand, upv did not seem to be affected by the size of fibers. however, the upv could be used to assess the hardening of the scc mixtures. it was clear from fig. 12 that as hydration continued, the upvs increased for all the scc and frscc mixtures. 20 25 30 35 40 45 0 0,2 0,4 0,6 0,8 1 �7 jour 28 jour 56 jour c o m p r e ss iv e s tr e n g h t (m p a ) vfhs / vfls+vfhs r 2 =0,90 r 2 =0,87 r 2 =0,95 fig 8. effect of hybrid steel fibers on the compressive strength. haddadou et al., j. build. mater. struct. (2014) 1: 65-76 73 fig 9. effect of hybrid steel fibers on the splitting tensile strength. 4 4,5 5 5,5 6 6,5 0 0,2 0,4 0,6 0,8 1 28 jour 56 jour f le x u r a l st r e n g h t (m p a ) vfhs / vfls+vfhs r 2 =0,93 r 2 =0,94 fig 10. effect of steel fibers on the flexural strength. fiber inclusion did not significantly affect the measured mechanical properties. however, as seen in fig. 9 and fig.10, as the volumetric ratio of the ls type fibers increased the compressive strength increased. this was due to the relatively small dimensions of ls type fibers, which gave these fibers the ability to delay the micro-crack formation and to arrest and prevent their propagation afterwards up to a certain extent. another explanation to the increase in the compressive strength could be the decrease of fresh properties which decreased as the amount of hs type fibers increased. however, when the splitting tensile strengths were examined (fig.9), it could be seen that there was a reduction in the splitting tensile and flexural strengths as the 2 2,5 3 3,5 4 4,5 5 0 0,2 0,4 0,6 0,8 1 28 jour 56 jour vfhs / vfls+vfhs r 2 =0,96 r 2 =0,95 74 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 volume of ls type fibers were increased or the fresh properties increased. the reduction in the splitting tensile strength was explained by the loss of the presence of hs fibers. therefore, hs fibers were mainly responsible for the increase in tensile and flexural strengths. otherwise, when the tensile stress is transferred to hs fibers, the transfer can arrest the propagation of macro-cracks and substantially improve the tensile strength of the concrete. as presented in fig. 11, the upv of the scc mixtures seemed to be unaffected by the steel fiber inclusion. nevertheless, the upv could be used to assess the hardening of the scc mixtures. it was clear from fig. 12 that as hydration continued, the upv increased for all the scc mixtures. fig 11. 56 days hardened properties of frscc and scc. 3900 4000 4100 4200 4300 4400 4500 7d 28d 56d scc rscc1 rscc2 rscc3 rscc4 rscc5 u ltr a so n ic p u ls e v e lo ci ty ( m /s ) test age ( days) fig 12. strength gain of scc mixtures. haddadou et al., j. build. mater. struct. (2014) 1: 65-76 75 4. conclusions to assess the fresh and hardened properties of frscc, tests according to efnarc recommendations were performed. two types of steel fibers with different aspect ratio were investigated. the hooked end and corrugated steel fibers were used with a dosage of 60 kg/m3 in the presence of high volume of marble powder. the following general conclusions can be drawn from the study presented in the paper: the results have shown that increasing the smaller fiber content of the concretes slightly reduced the workability of frscc. addition of steel fibers with hooked ends reduces the compressive strength of the scc; it can be attributed to the decrease in the workability. therefore, concrete with the smaller fiber is denser than the one with longer fiber. the presence of steel fibers increased the splitting tensile strength of the scc specimens. steel fibers enhance the splitting tensile strength through bridging the gap between two sides of crack opening. addition of hooked end fiber improved splitting tensile. flexural strength was also improved by utilization of hooked end steel fibers. addition of fibers improves the ultimate load capacity of the scc beams, and it leads to an increase in the flexural strength. incorporating steel fibers is essential in changing the brittle failure mode of sccs into a more ductile one. based on the experimental tests conducted, it can be concluded that smaller fibers in concretes function as a bridge to reduce the micro-cracks; however, they have small effect on the post-peak response of load versus displacement at the mid span of the prism. the longer fibers have no significant effect in preventing the formation of micro-cracks; however, they influence on the post-peak response part of the load versus displacement curve of the prisms, which results in high value of splitting tensile and flexural tensile. the effects of steel fibers on the ultrasonic pulse velocity (upv) seemed to be negligible. mechanical properties are improved by the incorporation of steel fibers in sccs especially splitting tensile strength and flexural strength. the improvement increases as the longer fiber volume fraction investigated in this study increases. 5. references afnor, xp p 18-540 standard (1997). granulats: définitions, conformité, spécifications, association française de normalisation, paris. ambroise j, rols s, pera j (2001). properties of self-leveling concrete reinforced by steel fibers. in proceedings of 43rd brazilian congress of the concrete (ibracon), brazil. barr b, gettu r, al-oraimi s k a, bryars l s (1996). toughness measurement—the need to think again. cement and concrete composites, 18(4), 281-97. brouwers h j h, radix h j (2005). self-compacting concrete: theoretical and experimental study. cement and concrete research, 35(11), 2116-36. corinaldesi v, moriconi g (2004). durable fiber reinforced self-compacting concrete. cement and concrete research, 34(2), 249-54. cunha v m, barros j a, sena-cruz j m (2009). pullout behavior of steel fibers in self-compacting concrete. journal of materials in civil engineering, 22(1), 1-9. dhonde h b, mo y l, hsu t t, vogel j (2007). fresh and hardened properties of self-consolidating fiberreinforced concrete. aci materials journal, 104(5), 491–500. ding y, you z, jalali s (2010). hybrid fiber influence on strength and toughness of rc beams. composite structures, 92(9), 2083-9. 76 haddadou et al., j. build. mater. struct. (2014) 1: 65-76 ding y, you z, jalali s (2011). the composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete. engineering structures, 33(1), 107-17. domeski j (2011). cracking moment in steel fiber reinforced concrete beams based on waste send, ovidius. university annals costantza, series civil engineering, xiii(13):29-34. efnarc (2005). european guidelines for self-compacting concrete: specification, production and use. selfcompacting concrete, european project group. elkhadiri i, diouri a, boukhari a, aride j, puertas f (2002). mechanical behaviour of various mortars made by combined fly ash and limestone in moroccan portland cement. cement and concrete research, 32(10), 1597-603. en 12390-2 (2001). testing hardened concrete – part 2: making and curing specimens for strength tests. en 12390-3 (2001). testing hardened concrete – part 3: compressive strength of test specimens. en 12390-5 (2001). testing hardened concrete – part 5: flexure strength of test specimens. en 12390-6 (2001). testing hardened concrete – part 6: splitting tensile strength of test specimens. en 12504-4 (2005). testing hardened concrete – part 4: ultrasonic pulse velocity of test specimens. greenough t, nehdi m (2008). shear behavior of fiber-reinforced self-consolidating concrete slender beams. aci materials journal, 105(5), 468–77 katzer j (2008). properties of precast sfrcc beams under harmonic load. science and engineering of composite materials, 15(2), 107-20. khayat k h, guizani z (1997). use of viscosity-modifying admixture to enhance stability of fluid concrete. aci materials journal, 94(4), 332-41. moriconi g, corinaldesi v (2005). rheological study of blended cement concrete. in proceeding: cement combinations for durable concrete, edited by dhir rk. harrison ta., newlands md. the 6th int. congress on ‘global construction: ultimate concrete opportunities’. thomas telford, london, uk; p. 211–8. nagataki s, fujiwara h (1995). self-compacting property of highly flowable concrete. aci special publication, 154, 301-14. okamura h, ouchi m (2003). self-compacting concrete. journal of advanced concrete technology, 1(1), 515. petit j y, wirquin e (2010). effect of limestone filler content and superplasticizer dosage on rheological parameters of highly flowable mortar under light pressure conditions. cement and concrete research, 40(2), 235-41. şahmaran m, christianto h a, yaman i̇ ö (2006). the effect of chemical admixtures and mineral additives on the properties of self-compacting mortars. cement and concrete composites, 28(5), 432-40. sahmaran m, yaman i o (2007). hybrid fiber reinforced self-compacting concrete with a high-volume coarse fly ash. construction and building materials, 21(1), 150-6. srinivasa r, sekhar t, sravana p (2009). durability studies on glass fibre scc. the indian concrete journal, 83(10), 44-52. torrijos m c, barragan b e, zerbino r l (2008). physical–mechanical properties, and mesostructure of plain and fibre reinforced self-compacting concrete. construction and building materials, 22(8), 1780-8. j. build. mater. struct. (2021) 8: 128-138 review article doi : 10.34118/jbms.v8i2.1080 issn 2353-0057, eissn : 2600-6936 ann modelling approach for predicting scc properties research considering algerian experience. part iii. effect of mineral admixtures sahraoui m *, bouziani t structures rehabilitation and materials laboratory (sreml), university amar telidji, laghouat, algeria. * corresponding author: med.sahraoui@lagh-univ.dz received: 23-01-2021 accepted: 02-11-2021 abstract. this paper addresses the effect of mineral admixtures on fresh and hardened properties of self compacting concrete (scc). artificial neural networks (ann) and simplex lattice design approach was integrated to predict and evaluate the effect of limestone, marble powder, natural pozzolan and slag on rheological and mechanical properties of scc evaluated by slump flow, l-box, v-funnel, sieve segregation test and 28 days compressive strength. the modelling results show an acceptable prediction accuracy of scc behaviour containing mineral admixtures as substitution of cement especially related to the flow time measured with the v-funnel test and mechanical compressive strength at 28 days. key words: scc, ann, simplex lattice design, mineral admixtures, fresh and hardened properties. 1. introduction self-compacting concrete (scc) is an innovative material characterized by its ability to consolidate without the necessity of mechanical vibration. this advanced concrete should have a low yield stress and moderate viscosity in order to achieve self-compactness and provide high flowability without any segregation between coarse aggregate and mortar (okamura and ouchi, 2003; elemam et al., 2020). it is generally known that workability and segregation resistance can be achieved by reducing coarse aggregate content, minimizing water to binder ratio while increasing the superplasticizer concentration. furthermore, the employment of mineral admixtures was considered as another key factors to offer a high paste volume, forming a lubricating layer and achieve more workability (sahraoui and bouziani, 2019; abendeh and baker, 2021). a number of studies have been performed to investigate the rheological and mechanical properties of scc with different mineral admixtures. daoud and mahgoub (2020) show that limestone powder can be effectively used as partial replacement of cement to enhance the performance of scc in fresh and hardened stages. alyamac et al (2017) confirm the improvement of fresh properties of scc with the addition of marble powder and after an optimum value of substitution, the compressive strength decreases. ghafoori et al (2016) show an improvement in scc fresh properties with incorporation of natural pozzolan while compressive strength is slightly decreased. zhao et al (2015) reported that the use of slag as mineral admixture in the scc had not obvious effect on flowability and stability, while a reduction in mechanical properties was observed. the multilayer perceptron is an artificial neural network technique which can be used to predict scc properties on the basis of input data extracted from literature. this type of network showed an excellent capability to predict fresh and hardened properties of scc with high accuracy(özgür deneme, 2020; nguyen et al., 2020). mailto:med.sahraoui@lagh-univ.dz sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 129 based on scheffe's simplex lattice design technique, many researches were carried out the development of mathematical models in order to predict and provide a better description in the field of concrete materials (ubachukwu and okafor, 2020; okere and sule, 2019; arimanwa et al., 2019). this kind of space-filling design is a symmetrical arrangement of points within the experimental region in a suitable polynomial equation representing the response surface in triangular contour plot (oba and amadi, 2020). 2. methodology the objective of this part is to illustrate the effect of mineral admixtures (limestone, marble powder, pozzolan and slag) as substitution of cement. based on the design of experiments technique, a simplex-lattice mixture design with three factors and five levels was used to evaluate the effect of the above selected mineral admixtures on fresh and hardened properties of scc models developed in the part i (sahraoui and bouziani, 2020). the simplex-lattice modelling approaches can describe the influence of mineral admixtures as well as all their possible combinations with cement in binary and ternary systems. the number of experiments is expressed by the flowing relation: (1) where, m and q are the number of levels and factors respectively. according the equation (1), the number of combinations to be treated is 21 (with m=5 and q=3). as illustrated in figure 1, a1 and a2 present two out of four mineral admixtures (lim, mp, pz and slag) selected in this modelling. while cement remains unchanged in all triangular grid. it should be noted that the developed model is appropriate to predict scc properties with fixed proportions summarized in table 1. the developed model concerning the effect of mineral admixtures is expressed by a secondorder polynomial as follows: (2) where y is the output result of ann-based model developed in the first part (sahraoui and bouziani, 2020). 130 sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 table 1: concrete mixture proportioning sand (kg/m3) gravel 3/8 (kg/m3) gravel 8/15 (kg/m3) cement (kg/m3) lim mp pz slag (kg/m3) w/b sp (%) 860 420 420 225-450 0-225 0.4 1 fig. 1. illustration of the simplex-lattice design with three factors 3. results and discussion mineral admixtures combinations and their output results of ann models are given in table 2 and the estimated modelling parameters of all responses are summarized in table 3. v-funnel derived models have the stronger r-square and the lower root mean square error (r2=0.99 and rmse in the range of 0.2-0.25) which indicate the good prediction performance of v-funnel models in this ann modelling compared to the other test results. l-box derived model developed with mp and slag has the highest rmse value compared to the other models which mean that l-box derived model has a low accuracy in predicting scc passing ability in this case study. it is also noted that slump flow model developed with lim and slag exhibit a low r2 and high rmse compared to that with mp and pz. the p-value lower than 0.05 (p<0.0001) indicates that developed models are accurate and performed satisfactorily to predict scc properties. it is worth bearing in mind that ternary graphs selected in this work are chosen according to high and low values of obtained models in order to better insights the effect of mineral admixtures. sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 131 table 2: mineral admixtures combinations and output results of ann models m ix n ° ma combinations slump (cm) l-box (%) v-funnel (s) pi (%) rc28 (mpa) cm a2 a3 a2 : lim a2 : mp a2 : lim a2 : mp a2 : pz a2 : lim a2 : mp a2 : mp a2 : lim a2 : lim a3 : slag a3 : pz a3 : pz a3 : slag a3 : slag a3 : mp a3 : pz a3 : lim a3 : mp a3 : pz 1 0 0 1 65,54 48,80 95,69 74,23 18,31 5,20 6,91 10,00 44,30 43,30 2 0 0,2 0,8 62,61 51,46 96,53 45,66 17,91 4,28 7,77 11,17 45,93 35,16 3 0 0,4 0,6 76,18 57,05 97,34 28,99 16,99 4,98 8,26 12,32 50,65 24,52 4 0 0,6 0,4 76,31 63,93 85,01 25,10 15,61 7,58 4,77 12,76 50,62 22,55 5 0 0,8 0,2 70,82 67,02 79,46 29,52 13,90 11,50 5,15 8,20 49,31 38,11 6 0 1 0 65,72 64,88 66,87 52,52 12,06 16,02 8,24 8,24 53,41 53,41 7 0,2 0 0,8 64,02 55,43 93,08 86,14 15,56 5,06 7,48 11,02 47,06 44,99 8 0,2 0,2 0,6 68,98 62,42 94,81 58,14 14,79 4,66 8,52 12,25 51,13 40,82 9 0,2 0,4 0,4 84,90 67,93 97,24 43,20 13,69 5,96 7,87 13,01 60,02 31,22 10 0,2 0,6 0,2 81,88 69,85 82,58 45,63 12,37 9,01 5,47 10,08 57,12 34,49 11 0,2 0,8 0 72,63 68,22 81,32 73,62 10,95 13,15 8,34 8,34 54,28 54,28 12 0,4 0 0,6 64,51 66,90 88,94 94,08 12,69 5,12 8,26 12,12 51,67 46,21 13 0,4 0,2 0,4 79,53 70,21 92,66 52,34 11,64 5,13 9,06 13,03 58,09 44,81 14 0,4 0,4 0,2 88,49 71,21 96,85 49,55 10,53 6,86 7,77 13,02 68,63 44,25 15 0,4 0,6 0 83,48 72,06 81,59 80,86 9,45 10,17 8,50 8,50 58,75 58,75 16 0,6 0 0,4 68,16 71,30 83,60 80,59 9,95 5,35 8,99 12,98 56,29 49,50 17 0,6 0,2 0,2 86,81 71,83 93,15 53,00 8,78 5,61 10,38 13,48 66,13 51,80 18 0,6 0,4 0 87,08 75,71 85,58 83,57 7,82 7,59 9,61 9,61 73,38 73,38 19 0,8 0 0,2 74,35 72,13 79,86 70,65 7,64 5,67 10,75 13,52 67,52 59,62 20 0,8 0,2 0 86,46 78,21 94,80 84,33 6,52 6,04 12,94 12,94 79,98 79,98 21 1 0 0 78,79 78,79 83,45 83,45 6,01 6,01 13,78 13,78 79,96 79,96 table 3: model parameters estimates of modelling output results slump (cm) l-box (%) v-funnel (s) pi (%) rc28 (mpa) a2 : lim a2 : mp a2 : lim a2 : mp a2 : pz a2 : lim a2 : mp a2 : mp a2 : lim a2 : lim a3 : slag a3 : pz a3 : pz a3 : slag a3 : slag a3 : mp a3 : pz a3 : lim a3 :mp a3 : pz r2 0.85 0.96 0.83 0.87 0.99 0.99 0.80 0.83 0.93 0.95 rmse 3.93 1.83 3.89 8.68 0.20 0.25 1.15 0.93 3.34 4.31 coeff p<0.0001 b1 78,81 77,68 83,06 78,78 5,71 5,80 13,87 13,88 80,69 81,38 b2 63,02 65,13 7,09 48,81 51,23 b3 65,59 58,12 16,82 6,85 9,58 43,27 b4 60,07 83,72 12,21 b5 46,96 96,12 18,53 5,01 7,90 48,20 b6 68,57 60,41 -1,97 15,75 -7,05 b7 9,73 33,70 -9,88 -3,57 5,07 -27,71 b8 -3,07 -10,79 -1,63 b9 22,89 -9,12 -3,53 -0,71 -8,12 -71,64 b10 15,85 22,60 b11 58,73 b12 48,86 -103,17 b13 -200,87 b14 20,03 -19,03 -3,69 b15 3,75 132 sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 fig. 2. ternary plot of slump flow (cm) as function of cm, lim and slag proportions. fig. 3. ternary plot of slump flow (cm) as function of cm, mp and pz proportions. ternary contour plots presented in figure 2 illustrate the effects of cement, limestone and slag proportions on predicting slump flow. from this figure, it can be seen that slump flow increased with the increase of limestone proportions (corresponding to the rate of 15 to 25% of lim) and then decreased. this is due to the fact that limestone filler scattered between cement particles, the maximum packing density is achieved and hence larger amount of excess water for more lubrication (kounakoff et al., 2017; hanzic and ho, 2017; ren et al., 2020). once the space between cement grains is filled, limestone filler began to occupy the place of cement particles which leads to an increase in specific surface area and hence more effective water for lubrication. therefore, the mixture becomes sticky, denser and hence less self-comparable (benabed et al., 2012; daoud and mahgoub, 2020). figure 2 indicates that the increase in slag results in a reduction of slump flow. results in literature revealed that the addition of slag powder has reasonably enhanced the flowability (pyo and kim, 2017; liu et al., 2018; gopinathan and anand, 2018). in this case study, the decrease in flowability may be attributed to the fact that the mixtures models were designed at fixed water and superplasticizer dosage. slag has a reactive character and requires more water and superplasticizer than almost other inert additions such as limestone filler, moreover, some superplasticizer molecules can be absorbed to the surface of very fine particles slag and leads to a higher request to superplasticizer (brahim, 2018; salehi and mazloom, 2019) . it should be noted that only three studies were intended to study the effect of slag powder behaviour in this study (representing 7 of all 167 mixtures collected from literature) and this could make the model lacks to evaluate the effect of slag compared to the other mineral admixtures. this is also confirmed by high rmse (3.93) and low r2 (0.85) compared to l-box model parameters developed with mp and pz, as shown in table 3. the effect of cm, mp and pz on slump flow is plotted in figure 3. it was observed the same impact of marble powder as limestone on flowability but the optimum substitution is not clearly shown. this might be explained by the increases in paste volume and cohesiveness of scc mixture caused by the lower density of marble powder. the increase in flowability with the sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 133 increase in mp is due also to its pore-filling effect (boukhelkhal et al., 2016; praveenkumar et al., 2017). it can be also seen that the increase of pz proportion leads to a decrease in slump flow diameter and mixtures made with high content of pz exhibit the lowest flowability, this phenomenon is attributed to the higher water demand of pz particles in order to achieve a suitable workability (menadi and kenai, 2018). this is in agreement with the findings of other researchers (belaidi et al., 2012; omrane et al., 2017; ahmad et al., 2019). fig.4. ternary plot of l-box ratio (%) as function of cm, lim and pz proportions. fig. 5. ternary plot of l-box ratio (%) as function of cm, mp and slag proportions. ternary contour graph illustrated in figure 4 presents the effects of lim and pz proportions on the l-box ratio. it is evident that l-box ratio increases to a maximum value with 10-15% of lim. the replacement of cement by limestone filler will broaden the particle size distribution and filling up the interstitial void that increases wet packing density of mixture and therefore the maximum passing ability increases (lai et al., 2019). it can be also seen from figure 4 that while the pz content increases, the l-box ratio increases. this may be explained by the fact that all modelling concrete mixtures were designed at fixed sp dosage, resulting in pz contained mixtures to have better viscosity and consequently the passing ability increased (ghafoori et al., 2016). the variations in l-box ratios, with respect to cm, mp and slag variations are given in figure 5. the acceptable values of passing ability according to efnarc guideline was with 10% of mp in binary systems cm-mp and more 35% of slag in cm-slag binary systems, beyond these combinations, l-box ratios are less than 80% which is out the range prescribed (efnarc, 2002). mp particles provide better filling effect to increase packing density, resulting in a slower horizontal flow in the l-box and therefore a low passing ability (alyousef et al., 2019). beyond this optimum, l-box ratio decreases with the increase in mp contents in binary and ternary systems. the large amount of mp result in a high paste volume, while exhibiting a decrease in the viscosity of scc mixture (alyousef et al., 2018). it is remarkable from figure 5 that the amount of slag proportion does not appear to have a significant effect on predicting l-box ratio in binary system cm-slag, which is confirmed by the highest rmse value (8.68) as mentioned in table 3. 134 sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 fig. 6. ternary plot of v-funnel time (s) as function of cm, pz and slag proportions. fig. 7. ternary plot of v-funnel time (s) as function of cm, lim and mp proportions. the effect of pz and slag proportions on the flow time of v-funnel is illustrated in figure 6 , all vfunnel measurements are in the recommended range (efnarc, 2002). as seen in this figure, the flow time increases with increasing pz and slag content. adjoudj et al (2014) show an increase the viscosity when using high levels of natural pozzolan and blast furnace slag. these results are further confirmed by other researchers (salhi et al., 2020; yahiaoui et al., 2017; belaidi et al., 2012; boukendakdji et al., 2009). figure 7 presents the variation of v-funnel time as a function of limestone and marble powder content. from the obtained results, it can be seen that limestone leads to an increase in flow time of v-funnel while the effect of mp is inconspicuous in this case. this can be explained by the effect of limestone on the enhancement of viscosity, as a result of its contribution in modifying the grading of the solid particles in mixture suspension and modified the water quantity available for the hydration process (ede et al., 2019; youness et al., 2020). similar results were also reported by other researchers (benabed et al., 2012; babikir and ahmed, 2020; daoud and mahgoub, 2020). ternary contour plots showing in figures 8 and 9 illustrate the variations of static stability with respect to mp, pz and lim proportions. results show that pi values decreased with the increase of mp, pz and lim in binary and ternary combinations. tennich et al (2015) and hameed et al (2016) show that the segregation resistance was increased with the increase in mp contents and the viscosity becomes satisfactory. limestone filler provides large specific surface area accessible to unit volume of water due to its small particle size, which helps to reduce segregation and bleeding (li et al., 2018). menadi and kenai (2018) found that scc mixtures containing pz with weight substitution level of 10 or 15% satisfy the fresh-state behaviour requirements related to high segregation resistance. sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 135 fig. 8. ternary plot of sieve stability pi (%) as function of cm, mp and pz proportions. fig. 9. ternary plot of sieve stability pi (%) as function of cm, mp and lim proportions. fig. 10. ternary plot of rc28 (mpa) as function of cm, lim and mp proportions. fig. 11. ternary plot of rc28 (mpa) as function of cm, lim and pz proportions. in figures 10 and 11, compressive strength at 28 days of scc made with all possible binary and ternary combinations of cm, lim, mp and pz were plotted. it is clear that the increase in lim, mp and pz contents decrease the compressive strength at 28 days. a partial replacement of cement by limestone filler causes a decrease in clinker content, and therefore the decrease of 28-day compressive strength (akbar, 2014; ayat et al., 2018). the slower evolution of strength at 28 days shown in figure 11 also caused by the slow pozzolanic reaction of pz compared to c3s hydration of ordinary portland cement (senhadji et al., 2012; belaidi et al., 2012). 4. conclusion in this paper, anns were developed to predict the effect of mineral admixtures on fresh and hardened properties of scc considering algerian experience. following conclusions based on experimental results can be listed as below: 136 sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138  a high flowability was observed for scc mixtures containing 15-25% of limestone filler as partial substitution of cement.  l-box ratio increases to a maximum value with 10-15% of lim and high pz contents.  an acceptable passing ability remains within the limits prescribed by efnarc can be obtained with 10% of mp and up to 35% of slag in cm-mp and cm-slag binary systems respectively.  the time of flow measured with v-funnel test increased with increasing pz and slag contents.  static segregation decreased with the increase of lim, mp and pz and all studied modelling mixtures proves the standard condition prescribed by afgc recommendations (pi index lower than 15%).  a reduction in mechanical compressive strength with increasing lim, mp and pz contents for all possible binary and ternary combinations. 5. references abendeh, r. m., & bani baker, m. (2021). using steel slag aggregate to strengthen self-compacting concrete durability. proceedings of the institution of civil engineers-structures and buildings, 1-15. ahmad, s., mohaisen, k. o., adekunle, s. k., al-dulaijan, s. u., & maslehuddin, m. (2019). influence of admixing natural pozzolan as partial replacement of cement and microsilica in uhpc mixtures. construction and building materials, 198, 437-444. akbar, ramezanianpour ali. (2014). cement replacement materials: properties, durability, sustainability. springer geochemistry/mineralogy alyamac, k. e., ghafari, e., & ince, r. (2017). development of eco-efficient self-compacting concrete with waste marble powder using the response surface method. journal of cleaner production, 144, 192202. alyousef, r., benjeddou, o., khadimallah, m. a., mohamed, a. m., & soussi, c. (2018). study of the effects of marble powder amount on the self-compacting concretes properties by microstructure analysis on cement-marble powder pastes. advances in civil engineering, 2018. alyousef, r., benjeddou, o., soussi, c., khadimallah, m. a., & mustafa mohamed, a. (2019). effects of incorporation of marble powder obtained by recycling waste sludge and limestone powder on rheology, compressive strength, and durability of self-compacting concrete. advances in materials science and engineering. arimanwa, j. i., onwuka, d. o., arimanwa, m. c., & ajoku, c. a. (2019). simplex lattice design models for the determination of modulus of rupture of concretes. nigerian journal of technological development, 16(4), 213-219. ayat, h., kellouche, y., ghrici, m., & boukhatem, b. (2018). compressive strength prediction of limestone filler concrete using artificial neural networks. adv. comput. des, 3(3), 289-302. babikir, k. s. e., & ahmed, y. h. (2020). proportioning self compacting concrete in hot weather utilizing limestone powder. journal of cement based composites, 1, 6-10. belaidi, a. s. e., azzouz, l., kadri, e., & kenai, s. (2012). effect of natural pozzolana and marble powder on the properties of self-compacting concrete. construction and building materials, 31, 251-257. sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 137 benabed, b., kadri, e. h., azzouz, l., & kenai, s. (2012). properties of self-compacting mortar made with various types of sand. cement and concrete composites, 34(10), 1167-1173. boukendakdji, o., kenai, s., kadri, e. h., & rouis, f. (2009). effect of slag on the rheology of fresh selfcompacted concrete. construction and building materials, 23(7), 2593-2598. boukhelkhal, a., azzouz, l., belaïdi, a. s. e., & benabed, b. (2016). effects of marble powder as a partial replacement of cement on some engineering properties of self-compacting concrete. journal of adhesion science and technology, 30(22), 2405-2419. brahim, nécira. (2018). développement des bétons autoplaçants à hautes performances: influence de la composition, doctoral dissertation, university mohamed khider biskra, algeria. daoud, o. m. a., & mahgoub, o. s. (2020). effect of limestone powder on self-compacting concrete. fes journal of engineering sciences, 9(2), 71-78. ede, a. n., oshogbunu, o. b. a. t. a. r. h. i. e., olofinnade, o. m., jolayemi, j., oyebisi, s. o., mark, g., & awoyera, p. o. (2019). effects of bamboo fibers and limestone powder on fresh properties of selfcompacting concrete, mat42, 1-6. efnarc, (2002). specification. guidelines for self-compacting concrete, london, uk: association house 32, p34. elemam, w. e., abdelraheem, a. h., mahdy, m. g., & tahwia, a. m. (2020). optimizing fresh properties and compressive strength of self-consolidating concrete. construction and building materials, 249, 118781.. ghafoori, n., sharbaf, m., najimi, m., & batilov, i. (2016). natural pozzolan contained self-consolidating concrete, fourth international conference on sustainable construction materials and technologies, las vegas, usa. gopinathan, s., & anand, k. b. (2018). properties of cement grout modified with ultra-fine slag. frontiers of structural and civil engineering, 12(1), 58-66. hanzic, l., & ho, j. c. m. (2017). multi-sized fillers to improve strength and flowability of concrete. advances in cement research, 29(3), 112-124. kounakoff, b. a., hanzic, l., & ho, j. c. m. (2017). limestone and silica fume to improve concurrent flowability–segregation limits of concrete. magazine of concrete research, 69(23), 1189-1202. lai, m., hanzic, l., & ho, j. c. (2019). fillers to improve passing ability of concrete. structural concrete, 20(1), 185-197. li, c., jiang, l., xu, n., & jiang, s. (2018). pore structure and permeability of concrete with high volume of limestone powder addition. powder technology, 338, 416-424. liu, z., el-tawil, s., hansen, w., & wang, f. (2018). effect of slag cement on the properties of ultra-high performance concrete. construction and building materials, 190, 830-837. menadi, b., & kenai, s. (2018). influence of natural pozzolana content on self-compacting concrete durability properties. in iop conference series: materials science and engineering,. 431, 10, 102011, iop publishing. nguyen, c. h., tran, l. h., & ho, k. n. (2020). application of neural network to predict the workability parameters of self-compacting concrete. in cigos 2019, innovation for sustainable infrastructure (pp. 1161-1166). springer, singapore. oba, k. m., & amadi, i. g. (2020). a predictive mathematical model for water absorption of sawdust ashsand concrete. international journal of engineering and management research, 10. 138 sahraoui and bouziani, j. build. mater. struct. (2021) 8:128-138 okamura, h., & ouchi, m. (2003). self-compacting concrete. journal of advanced concrete technology, 1(1), 5-15. okere, c. e., and s. sule. (2019). cost optimization of chikoko-cement concrete using scheffe’s polynomial function, international journal of recent engineering science, 6 (3), 1-9. omrane, m., kenai, s., kadri, e. h., & aït-mokhtar, a. (2017). performance and durability of self-compacting concrete using recycled concrete aggregates and natural pozzolan. journal of cleaner production, 165, 415-430. özgür deneme, i̇. (2020). modelling of compressive strength of self-compacting concrete containing fly ash by gene expression programming. revista de la construcción, 19(2), 346-358. praveenkumar, s., k. murugesan, and n. sharan nikhil. (2017). influence of marble powder and fly ash in fresh and hardened properties of self compacting concrete, international journal of chemtech research, 10(8), 314–319. pyo, s., & kim, h. k. (2017). fresh and hardened properties of ultra-high performance concrete incorporating coal bottom ash and slag powder. construction and building materials, 131, 459-466. ren, q., xie, m., zhu, x., zhang, y., & jiang, z. (2020). role of limestone powder in early-age cement paste considering fineness effects. journal of materials in civil engineering, 32(10), 04020289. sahraoui, m., & bouziani, t. (2019). effects of fine aggregates types and contents on rheological and fresh properties of scc. journal of building engineering, 26, 100890. sahraoui, m., & bouziani, t. (2020). ann modelling approach for predicting scc properties-research considering algerian experience. part i. development and analysis of models. journal of building materials and structures, 7(2), 188. salehi, h., & mazloom, m. (2019). opposite effects of ground granulated blast-furnace slag and silica fume on the fracture behavior of self-compacting lightweight concrete. construction and building materials, 222, 622-632. salhi, m., ghrici, m., bilir, t., & uysal, m. (2020). combined effect of temperature and time on the flow properties of self-compacting concrete. construction and building materials, 240, 117914. senhadji, y., escadeillas, g., khelafi, h., mouli, m., & benosman, a. s. (2012). evaluation of natural pozzolan for use as supplementary cementitious material. european journal of environmental and civil engineering, 16(1), 77-96. ubachukwu, o. a., & okafor. f. o. (2020). formulation of predictive model for the compressive strength of oyster shell powder-cement concrete using scheffe’s simplex lattice theory. epitoanyag-journal of silicate based & composite materials, 72(6). yahiaoui, w., kenai, s., menadi, b., & kadri, e. h. (2017). durability of self-compacted concrete containing slag in hot climate. advances in concrete construction, 5(3), 271. youness, d., mechaymech, a., & al wardany, r. (2021). flow assessment and development towards sustainable self-consolidating concrete using blended basalt and limestone-cement systems. journal of cleaner production, 283, 124582. zhao, h., sun, w., wu, x., & gao, b. (2015). the properties of the self-compacting concrete with fly ash and ground granulated blast furnace slag mineral admixtures. journal of cleaner production, 95, 66-74. j. build. mater. struct. (2021) 8: 82-92 original article doi : 10.34118/jbms.v8i1.1208 issn 2353-0057, eissn : 2600-6936 use of bottom ash as part replacement of sand for making concrete blocks satish sharma, vv arora, pn ojha, brijesh singh*, vikas patel, adarsh kumar ns national council for cement and building materials, india. * corresponding author: brijeshsehwagiitr96@gmail.com received: 17-02-2021 accepted: 19-06-2021 abstract. coal-based thermal power plants all over the world facing serious problems of handling and disposal of the ash produced. the productive use of coal bottom ash (ba) is the best way to alleviate the problems associated with its disposal. this paper covers the studies on laboratory scale evaluation of vibro compaction concrete blocks using ba i, ba ii & ba iii collected from three different location of coal fed thermal power station. in the present investigation laboratory investigation have been carried to utilize ba as part replacement of sand in concrete. this study cover manufacture of concrete blocks without flyash & with ba using for making solid block as per specification laid down in is:2185 using vibro compaction machine. three different sources of ba were used in concrete mix each @ 30%, 40% & 50% replacement by weight of sand were adopted in making concrete blocks. comparative study of compressive strength of concrete at different age of curing, wet density, drying shrinkage is reported in this study. wet density is found to be lower in blocks containing ba & dry shrinkage values are found well within the limits of specifications. concrete blocks having ba @ 30% by weight of sand are found suitable for use in the manufacture of concrete blocks. key words: bottom ash, mix proportion, vibro compaction technique, concrete blocks. 1. introduction bottom ash (ba) is the coarser material, which drops into the bottom of the furnace in latest large thermal power plants and constitute about 20% of gross ash content of the coal fed in the boilers. it consists of noncombustible materials, and is the residual part from the incineration of household and similar waste. raw ba is a granular material that consists of a mix of inert materials such as sand, stone, glass, porcelain, metals and ash from burnt materials. aggarwal et al., (2007) have investigated the replacement of ba upto 50% replacement by using the superplasticizer. the study of replacement of ba is done by using high range water reducing admixture because as the replacement of fine aggregate increases the water demand rapidly which also enhances due to high specific surface area ba due to high fine content. hence by the all mechanical properties get affected due to less cementitious material available in per cubic meter content in early age of concrete mix. detailed studies are reported in references. ba is a combination of heavier particulate matter and molten slag, which forms on the walls and the bottom of the combustion chamber of power station boiler fired with pulverized fuel. in appearance it usually ranges from a highly verified, glossy and heavy material to a lightweight, open textured and more friable type. sometimes it is found mixed with fly ash in stockpiles. its precise nature depends on the boiler plant and the coal type but higher fines of fly ash in ba are generally a part of coal ash. this study utilized ba of unchahar super thermal power plant (ntpc) currently there are two boiler systems – wet and dry. each system produces a uniquely different ba – wet ba and dry ba. wet ba has a relatively low melting point and coalesces into large molten masses known as slag. its particles usually are angular to sub angular in shape, have a smooth surface texture and looked much like crushed glass. dry ba has quite angular particles and a highly porous surface texture, usually has the appearance similar to fine sand and lighter in weight per unit volume and colour than bottom slag (bai and barheer, 2001; syahrul et al., 2010). mailto:brijeshsehwagiitr96@gmail.com sharma satish et al., j. build. mater. struct. (2021) 8: 82-9é 83 the compressive strength of concrete mixes made with various percentage of washed bottom ash as sand replacement inclusive of control sample (fully natural sand) was determined at 3, 7, 28, and 60 days of curing (syahrul et al., 2010). study by syahrul et al., (2010) indicated that the compressive strength of concrete mixes of sand replacement is much lower than control sample at all tested day. according to purushothaman and senthamarai (2013), ba added concrete mixes showed enhanced compressive strength than the conventional concrete and shows uniformly higher compressive strengths at almost all ages. the ample gain in strength is thought to be due to very high pozzolanic reactivity of the two mineral admixtures silica fume and ba. tang et al. (2013) found that the compressive and flexural strength of concrete drain with the augmentation of the ba fines at the identical curing age, particularly after 3 and 7 days. study done by remya raju and aboobacker (2014) indicated that compressive strength reduced marginally on the inclusion of ba in concrete and there was decrease in slump values of mixtures with the increase in level of replacement of sand by ba. compressive strength, split tensile strength and flexural strength increased up to 20% replacement of ba. based on the review of existing literature, it can be inferred that there is a potential for use of ba as replacement of fine aggregate in concrete. compared with fly ash, ba usually has no cementitious properties, very little pozzolanic activity, coarse particle size, higher carbon content and higher water demand. therefore, previous studies are mainly focused on using it in blocks, highway sub-base materials, structural filling materials etc. however, due to the leakage of some heavy metal elements from the above mentioned large volume construction work, only part of ba is used in these fields (ghafoori, 1992; ghafoori and cai, 1998; cheriaf et al., 1999). this has led to little recycling and large dumping of ba in landfill sites, which has gradually become a serious environmental problem in both developed and developing countries. furthermore, owing to the construction boom in both developed and developing countries, there is a critical shortage of good quality sand in many areas throughout the world. within the european union, an aggregate tax has been introduced in order to conserve the natural aggregate. therefore, there is a need for reducing the use of natural aggregate by recycling industrial by products. aydin and arel (2017) investigated about the effects of high volume of fly ash in cement mix for low strength applications. supplementary cementitious material in the mix was optimized and physical and mechanical properties were evaluated and predictive model was developed. oruji et al. (2017) had explored the re-usability of coal bottom ash as cement replacement in mortar. the bottom ash was made pulverized and the effect on workability and setting time were studied. kurda et al. (2018) had reviewed all earlier works done by the other researchers on the environmental impact and toxicity characteristics of recycled concrete aggregates (rca), fly ash (fa), cement production as well as their substitution aspect. the analysis with respect to abiotic depletion potential, ozone depletion potential, photochemical ozone creation, acidification potential, eutrophication potential, toxicity, leachability etc. were considered. it was revealed that environmental impact and cost of concrete reduced considerably with such incorporations, and also requirement of landfill space reduced drastically. bottom ash is a by-product from the combustion of coal. recent installation of coal power plant in norachcholai area produces bottom ash and they have no proper usage. this bottom ash has low specific gravity compared with sand. therefore, bottom ash can be used as a raw material to manufacture light-weight masonry blocks (abeykoon, 2012). this paper was carried out by using ba from a thermal power plant, to replace part of sand in concrete. the main purpose was to study the possibility of using ba to make a lightweight, high performance and environmentally friendly concrete. the effect of ba on the workability, compressive strength and durability of concrete are reported in these paper so that the research going on ba found some measuring points as: 84 sharma satish et al., j. build. mater. struct. (2021) 8: 82-92 i) the particle size distribution of the ba from the power station in is close to natural sand which makes it possible to replace the natural sand in concrete with the ba. ii) when ba sand was used in concrete, the workability of fresh concrete improved; when used in medium to high strength concrete even for the same slump value the concrete with ba sand was easier to be cast. iii) the replacement of sand with ba sand causes decrease of compressive strength at all ages and at all w/c. however at later ages, especially after 28 days, the compressive strength of concrete with ba sand was found to increase at a higher rate than that of the control concrete (without ba sand). iv) the durability of concrete was detrimentally affected by increasing the replacement of natural sand with the ba sand. further study on ba to replace the natural sand would be necessary in order to evaluate the beneficial effect of the ba sand on durability of concrete. v) the initial results of this research suggest that ba sand can be used to replace the natural sand. other aspects which require further investigation include the effect of ions & heavy metals present in ba on the long-term performance of concrete. 2. materials used the physical and chemical characteristics of 43 grade ordinary portland cement is given in table-1. the results of cement are satisfying the codal provision laid down in is: 269. coarse aggregates with a maximum nominal size of 10 mm and natural riverbed sand confirming to zone ii as per indian standard is: 383-2016 was used as fine aggregate for concrete (table 2 and table 3). the physical characteristics of ba used in the study is given in table-4. different tests (physical & chemical) were carried out on the bottom ash collected from coal fed thermal power plant of ntpc unchahar. table 1. physical and chemical characteristics of 43 grade ordinary portland cement sl. no. test results obtained 1 blain’s fineness, m2/kg 299.5 2 setting time, minutes: initial & final 126 & 206 3 soundness : lechatlier exp., mm autoclave exp., % 1.00 0.082 4 compressive strength, n/mm2 3 days 7 days 28 days 32 40 48 5 chemical analysis, % : loss on ignition silica (sio2) iron oxide (fe2o3) aluminium (al2o3) calcium oxide (cao) sulphate (so3) magnesium oxide (mgo) 2.05 22.45 5.18 5.44 59.69 1.26 2.80 6 alkalies (%): na2o & k2o 0.57 & 0.36 sharma satish et al., j. build. mater. struct. (2021) 8: 82-9é 85 table 2. physical characteristics of fine aggregate sl. no. parameter/tests test value 1 silt content 2.33% 2 clay lumps nil 3 organic impurities nil 4 soundness 2.27% 5 sp. gravity 2.67 6 water absorption 0.90% 7 sieve analysis sieve size percent passing 10 mm 100.00 4.75 mm 90.60 2.36 mm 78.65 1.18 mm 54.60 600 micron 40.15 300 micron 23.15 150 micron 10.35 pan nil table 3. physical characteristics of coarse aggregate sl no. parameter/tests test results 1 specific gravity 2.69 2 water absorption 0.40% 3 crushing value 24.73% 4 impact value 18.34 5 abrasion value 19.04 6 soundness 0.30% 7 flakiness index (< 10 mm) 29% 8 elongation index (<10 mm) 32.76% 9 sieve analysis sieve size percent passing 10 mm 96.06% 4.75mm 16.40% 2.36mm nil figure-1 shows the gradation curve of ba i, ii & iii and fine aggregate. all three type of ba are found to be very finer than the sand grading. in all three types the 600µ and lower particle size greater than the usually present in coarse sand used in this study. also compare with the grading of plaster sand & masonry sand the grading of ba is not comparable because ba has very fine particle 600µ and down size. ba and boiler slag are made essentially out of silica, alumina, and iron, with smaller percentages of calcium, magnesium, sulfates, and other compounds. the composition of the above particles is controlled principally by the source of the coal and not by the type of furnace. ba or boiler slag derived from lignite or sub-bituminous coals have a higher percentage of calcium than that from anthracite or bituminous coals. due to the salt content and, in some cases, the low ph of ba and boiler slag, these materials could display corrosive properties. when ba or boiler slag is used in an embankment, backfill, sub-base, or even possibly in a base course, the potential for corrosion of metal structures that may come in contact with the material is of high concern and should be investigated prior to use so that it does not pose any problem. water meeting the requirements of indian standard is: 456-2000 has been used. 86 sharma satish et al., j. build. mater. struct. (2021) 8: 82-92 table 4. characteristics of bottom ash (ba) sl no. test ba i ba ii ba iii physical test 1 water absorption (%) 2.90 3.80 4.20 2 sp. gravity 2.11 2.12 2.19 3 lime reactivity (kg/cm 2 ) 19.2 16.0 21.2 4 sieve analysis 4.75 100.00 100.00 100.00 2.36 100.00 98.75 99.00 1.18 95.70 94.62 98.00 600micron 92.40 90.12 95.63 300micron 72.50 66.74 82.00 150micron 41.10 33.61 46.00 pan 0.00 0.00 0.00 chemical test 1 loss on ignition 2.80 1.76 2.63 2 silica (sio2) 62.45 58.75 58.98 3 iron oxide 7.16 14.41 7.81 4 aluminum oxide 22.17 19.69 24.81 5 calcium oxide (cao) 1.34 1.28 1.29 6 magnesium oxide (mgo) 0.48 0.58 0.46 ba i=bottom ash stake i ba ii=bottom ash stake ii ba iii=bottom ash stake iii fig. 1. gradation curve for fine aggregate and bottom ash: ba-i, ii & b-iii 0 10 20 30 40 50 60 70 80 90 100 0.1110 p e rc e n ta g e p a ss in g ( % ) sieve size (mm) ba i ba ii ba iii fa sharma satish et al., j. build. mater. struct. (2021) 8: 82-9é 87 3. selection of mix proportion with different w/c ratio different trial mixes (table-5) were made using: 1. direct replacement of bottom ash (by weight of coarse sand in percentage) 2. replacement in equal volume of coarse sand and bottom ash table 5. matrix for selection of w/c ratio & ratio of concrete mix w/c ratio ratio of cement : sand : aggregate 1:3:6 1:3.125:6.25 1:2.5:5 0.45 seems more water required for casting to block in vibro machine blocks but did not give clear dimensions, so the mix was rejected block successfully but did not give costeffective option 0.50 less sand & less water content observed block caste successfully with economy in view block successfully 0.55 less sand content observed block caste successfully for study of required properties block caste successfully but higher cement content did not allow further work hence, ratio of 1:3.125:6.25 is selected for mix proportion and w/c ratio 0.50 is selected on the basis of strength. method of mix design by replacing the ratio of specific gravity was found suitable than direct replacement of sand, but fines of ba still gave higher specific surface area thus increasing the water demand. water demand also was found higher due to higher water absorption by ba. optimised mix proportion for required strength without using ba (table-6): table 6. optimised mix proportion for required strength without using bottom ash (ba) ingredient in mix cement coarse sand-natural 10 mm aggregatecrushed stone free w/c mix proportion 1 part 3.125 part 6.25 part 0.5 batch mix proportion used in laboratory (w/c = 0.5%) using ba to replace the sand content given in table-7: table 7. mix proportions of concrete blocks ingredient mix proportions without bottom ash mix proportions using bottom ash @30% replacement as fine aggregate @40% replacement as fine aggregate @50% replacement as fine aggregate quantity (kg) quantity (kg) quantity (kg) quantity (kg) cement, kg 188.24 181.17 177.5 170.8 coarse sand, kg/cum 0.37 0.25 0.21 0.17 bottom ash, kg/cum nil 135.16 176.77 212.64 coarse aggregate (<10mm) 0.74 0.57 0.55 0.53 water, ltr 94.11 90.5 90.5 85.4 wet density of concrete, kg/cum 2000 1925 1886 1815 weight of concrete block, kg (390x175x90 mm) 12.28 11.82 11.57 11.14 the study indicated that for various percentages of replacement of sand with bottom ash the workability of concrete decreased with the increase in bottom ash content. the workability of the concrete was correlated to its slump value and it was observed that up to 50% replacement 88 sharma satish et al., j. build. mater. struct. (2021) 8: 82-92 of coal bottom ash, the slump was found to be in the range 60-150 mm. the decrease in workability can be attributed to the fact that the coal bottom ash is irregular in shape, vesicular in texture and porous such that friction between particles is high. thus, with increasing coal bottom ash content, there is an increase in water demand to achieve similar workability as for the control mix. 3.1. procedure using vibro compaction technique for making concrete blocks vibro compaction method is probably the most extensively used technique for compacting concrete. in this method, internal friction between aggregate particles is eliminated for a short time and concrete mixtures behave like liquid and gravitational force will come into effect. following procedure was adopted in making concrete blocks: step i take all the material as per batch given in table-7. step ii make a dummy trial batch (around 10% quantity with same proportion) and remove from concrete mixture so that a thin layer of mix can adhere with surface of mixture for simulating the continuous batch mix. step iii now add all the quantity (excepts aggregate) and mix it for 60 seconds. now add aggregate and mix the total batch for 120 seconds. step iv now remove the batch to a non-water absorbing surface and fill the mould to cast the block in vibro compaction machine. step v when blocks are filled to total mould volume, vibrate for 60 seconds and remove from mould. step vi lift the caste block for drying (in shaded area) for 24 hours. step vii cure the block 3 day with gunny bags/in moist environment and the cure 7 day in submersed condition & there after cure the bock stacks in air by sprinkling water 4. results & discussion 4.1 compressive strength the compressive strength of concrete blocks made with ba i, ii and iii are given in table 8. from this table it can be concluded that 30% replacement of ba i, ii & iii gives results of compressive strength almost similar to control concrete. table 8. compressive strength of concrete blocks obtained. compressive strength (n/mm2) at different age (day) control mix percentage replacement in the ratio of specific of ba/sand 30% 40% 50% using ba–i for ntpc, unchahar (source i) 3 7.01 6.89 2.34 1.92 7 10.02 9.88 2.27 2.11 28 11.24 10.67 3.47 3.50 56 11.74 11.25 4.12 3.85 using ba–ii for ntpc, unchahar (source ii) 3 7.01 6.85 1.57 0.99 7 10.02 9.96 2.89 2.53 28 11.24 10.86 4.02 3.38 56 11.74 11.12 4.44 3.69 using ba–iii for ntpc, unchahar (source iii) 3 7.01 6.95 1.35 0.96 7 10.02 10.12 2.47 2.46 28 11.24 10.50 4.26 3.98 56 11.74 10.76 4.36 4.23 sharma satish et al., j. build. mater. struct. (2021) 8: 82-9é 89 fig. 2. compressive strength of control mix and mix with different replacement percentages of bottom ash at different ages from figure-2 above it can be see that the compressive strength of concrete blocks using ba decreases at early age but slightly increases further at 56 day & 90 day. the results of higher replacement of ba beyond 30% indicates that there is further no substantial increase in compressive strength. 4.2. density & drying shrinkage of concrete block the density of concrete block decreases with increase in percentage of ba (table 9 & figure-3). the density of concrete block also increases when the finer particle from ba is removed. drying shrinkage is found to be slightly higher in ba samples prepared by cutting the concrete blocks samples from concrete blocks with 30%, 40% & 50% of ba as compared to control concrete blocks without ba (tabel-10 and figure-4). the density of concrete block can be increased by using state-of-the-art block making machine or use of superplasticiser (high range water reducer agent) which in turn will improve the compressive strength and density. table 9. density of concrete blocks (in kg/m3) bottom ash replacement percentage 30% 40% 50% control mix ba-i 1925 1886 1815 2000 ba-ii 1915 1868 1794 2000 ba-iii 1754 1854 1787 2000 0 2 4 6 8 10 12 14 c o n tr o l m ix 3 0 % 4 0 % 5 0 % c o n tr o l m ix 3 0 % 4 0 % 5 0 % c o n tr o l m ix 3 0 % 4 0 % 5 0 % c o n tr o l m ix 3 0 % 4 0 % 5 0 % 3 days 7 days 28 days 56 days c o m p re ss iv e s tr e n g th ( n /m m 2 ) percentage replacement at different ages ba–i ba–ii ba–iii 90 sharma satish et al., j. build. mater. struct. (2021) 8: 82-92 fig. 3. density of control mix and mix with different replacement percentages of bottom ash at different ages table 10. drying shrinkage of concrete blocks (%) bottom ash replacement percentage 30% 40% 50% control mix ba-i 0.0692 0.0692 0.0817 0.0413% ba-ii 0.0712 0.0714 0.0720 0.0413 % ba-iii 0.0746 0.0770 0.0890 0.0413 % fig. 4. drying shrinkage of control mix and mix with different replacement percentages of bottom ash at different ages 0 500 1000 1500 2000 2500 control mix 30% replacement 40% replacement 50% replacement d e n s it y o f c o n c r e t e b lo c k s ( in k g /m 3 ) different percentages of replacement of bottom ash ba-i ba-ii ba-iii 0.000% 0.010% 0.020% 0.030% 0.040% 0.050% 0.060% 0.070% 0.080% 0.090% 0.100% control mix 30% replacement 40% replacement 50% replacement d r y in g s h r in k a g e o f c o n c r e t e b lo c k s ( % ) different percentages of replacement of bottom ash ba-i ba-ii ba-iii sharma satish et al., j. build. mater. struct. (2021) 8: 82-9é 91 due to lower density & higher water absorption higher percentage of fines in all the three sources of ba, the coal ba as alternative to sand is not found to be techno-economically viable alternative. it can be said that replacement of sand with ba up to 30% is technically suitable/feasible and meets the requirement of is-2185. although using 40% & 50% of ba from the three sources the compressive strength obtained in concrete blocks is lower than 10 n/mm2 but certainly by use of vibro-compaction technique, all the concrete blocks are found technically suitable as far as the requirement of meeting the compressive strength as laid down in is: 2185 is concerned. higher compacting effort using of modern machinery with use of superplasticiser will definitely improve the strength & density of concrete blocks 5. conclusion and recommendations some of the properties of ba such a higher fine particles and higher water absorption are in general found economically unviable for replacing sand due to the decrease in strength associated with the increased fine content in the concrete. density of concrete blocks is also found lower using 30%, 40% & 50% ba as compared to the concrete blocks without ba irrespective of the source of ba. drying shrinkage is found to be slightly higher in ba samples prepared by cutting the concrete blocks samples from concrete blocks with 30%, 40% & 50% of ba as compared to control concrete blocks without ba. due to lower density & higher drying shrinkage values, concrete blocks, corresponding compressive strength of concrete blocks using 30%, 40% & 50% is also found lower at all ages i.e. 3, 7, 28, 56 & 90 day. this is true for all the three sources of fly ash investigated. 30% replacement of ba i, ii & iii gives results of compressive strength almost similar to control concrete. due to lower density & higher water absorption higher percentage of fines in all the three sources of ba, the coal ba as alternative to sand is not found to be technoeconomically viable alternative. it can be said that replacement of sand with ba upto 30% is technically suitable/feasible and meets the requirement of is-2185. although using 40% & 50% of ba from the three sources the compressive strength obtained in concrete blocks is lower than 10 n/mm2 but certainly by use of vibro compaction technique, all the concrete blocks are found technically suitable as far as the requirement of meeting the compressive strength as laid down in is: 2185 is concerned. to improve the quality of ba to make the same as techno economically viable alternative, sieved ba after removed of after 150µ and 300 down size shall be preferable for usage in concrete blocks. from the grading it is seen that the ba can also be used in mortar making for use in masonry and plastering work as the grading of bottom is found suitable for these works. the grading requirement of fine sand for use in mortar making and after partly removal of 150µ & 300µ sieve. 6. references abeykoon, a. j. m. s. s., anthony, c. s. k. r., & de silva, g. h. m. j. s. (2012). bottom ash as replacement of sand for manufacturing masonry blocks, conference, sri lanka. aggarwal p., aggarwal y., & gupta s.m. (2007). effect of bottom ash as replacement of fine aggregates in concrete. asian journal of civil engineering (building and housing), 8(1), 49-62. 92 sharma satish et al., j. build. mater. struct. (2021) 8: 82-92 aydin, e., & arel, h. ş. (2017). characterization of high-volume fly-ash cement pastes for sustainable construction applications. construction and building materials, 157, 96-107. bai y., & barheer p a m. (2001). influence of furnace ash on workability, compressive strength and durability of concrete. seventh canmet/aci international conference on fly ash, silica fume, slug and natural pozzolana in concrete, chennai (madras), india. cheriaf, m., rocha, j. c., & pera, j. (1999). pozzolanic properties of pulverized coal combustion bottom ash. cement and concrete research, 29(9), 1387-1391. ghafoori, n. (1992). utilisation of type c bottom ash in cement based concrete mixtures. annual report, material technology center, southern illinois university at carbondale, 55-76. ghafoori, n., & cai, y. (1998). laboratory made roller compacted concretes containing dry bottom ash: part i – mechanical properties. aci materials journal, 95 (2), 121-130 kurda, r., silvestre, j. d., & de brito, j. (2018). toxicity and environmental and economic performance of fly ash and recycled concrete aggregates use in concrete: a review. heliyon, 4(4), e00611. oruji, s., brake, n. a., nalluri, l., & guduru, r. k. (2017). strength activity and microstructure of blended ultra-fine coal bottom ash-cement mortar. construction and building materials, 153, 317-326. purushothaman, m., & senthamarai, r. m. (2013). strength properties of high performance concrete using bottom ash as fine aggregate. international journal of civil, 2(3), 35-40. remya raju, m. m. p., & aboobacker, k. a. (2014). strength performance of concrete using bottom ash as fine aggregate. international journal of research in engineering & technology, 2(9), 111-122. syahrul, m. s. h. m., muftah, f., & muda, z. (2010). the properties of special concrete using washed bottom ash (wba) as partial sand replacement. international journal of sustainable construction engineering and technology, 1(2), 65-76. tang, p., yu, q. l., yu, r., & brouwers, h. j. h. (2013, october). the application of mswi bottom ash fines in high performance concrete. in proceedings of the 1st international conference on the chemistry of construction materials, berlin, germany, pp. 435-438. j. build. mater. struct. (2015) 2: 1-9 https://doi.org/10.34118/jbms.v2i1.13 issn 2353-0057 comparative performance of isolated and fixed-base reinforced concrete structures adjou n1,2,* and haddadou n1 1 national center of studies and integrated research on building engineering (cnerib), cité nouvelle elmokrani, souidania, algiers, algeria. 2 university of science and technology houari boumediene (usthb), algeria. * corresponding author: adjounaima@hotmail.fr abstract. the earthquake transmits to the structure a large quantity of energy that causes damage to structures. the seismic isolation technique can absorb a large quantity of the seismic energy. the seismic isolation concept is a new technique in earthquake engineering, its principle is quite simple, and it consists to create a discontinuity between the foundation and the superstructure, so that seismic energy cannot be completely transmitted into the structure. therefore, this article includes a numerical application of the nonlinear static method, the capacity spectrum method (csm), on two types of structures, fixed base structure and isolated base structure. the csm is one of the methods used for the evaluation of seismic performance. its principle consists in superimposing a curve which represents the capacity of the structure originated from a non-linear static analysis (pushover), with a curve representing the solicitation brought by the earthquake. the intersection of these two curves represents the point performance, which evaluates the maximum displacement of the structure in the plastic domain. key words: damping, energy dissipation, lead rubber bearing, nonlinear static method, seismic isolation. 1. introduction the technique of seismic isolation is relatively young when compared to conventional methods of prevention against earthquakes, its appearance dates back to the early 20th century. in algeria, the organization of technical control of construction of chlef (ctc-chlef) was the first to introduce this technique through the construction of the seat of its agency in ain defla, located in an area of high seismicity. the project of the great mosque of algiers, which is under construction, will be built by using this technique. the conventional earthquake resistant designs rely on the strength and ductility of structural elements to resist seismic induced forces and to dissipate the seismic energy, which prevents the collapse of structures in case of earthquake. on the other hand, the approach of base isolation reduces the damages due to the seismic horizontal forces transmitted to the structure (koh and kelly, 1985). the objective of this study was to evaluate the seismic response of two structures, a fixed base structure (conventional structure), and an isolated base structure, the method of analysis used in this study is the method of spectrum capacity (csm). a comparison of the results obtained was made for the two structures, in terms of maximum displacement in the plastic domain (freeman, 2004). 2. the seismic isolation the principle of seismic isolation is quite simple; it consists to create a discontinuity between the foundation and the superstructure, so that seismic energy cannot be entirely transmitted into the structure. there are two categories of isolation systems extensively used. the first category includes the family of elastomeric bearings, in which the high damping rubber bearing system (hdrb), the lead rubber bearing system (lrb) and other systems can be found. the second category includes the family of sliding bearings, in which the friction pendulum system mailto:adjounaima@hotmail.fr 2 adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 (fps), and sliding bearing system without re-centering, known as seismic isolators (si) can be found. all seismic isolation systems must meet the following three requirements (nazé, 2006): sufficient horizontal flexibility to increase the structure period and spectral demand, except for very soft soil sites; sufficient energy dissipation capacity to restrict the displacements of seismic isolators; adequate rigidity for the isolated structure, which must be identical to the fixed base structure under the service loads. 2.1. description of the studied structures two structures are subject to a comparative study, a conventional structure and isolated base structure; these structures are reinforced concrete portal frames. they have a square shape, regular in plan and elevation and composed of five levels. the height of each level is 3m and the plan dimensions are (16m x16m). the mechanical characteristics of the materials are: the compressive strength of concrete at 28 days is 25mpa. the modulus of elasticity of concrete is 3.22 105 kn/m². longitudinal and transverse reinforcement steel: fe e400. the loads g and the overloads q are: terrace: g=6.75 kn/m² and q=1.00 kn/m². floor: g=4.20 kn/m² and q=1.50 kn/m². the structures are considered located in an area of high seismicity (zone iii) on soft ground (s3). the dimensions of structural elements are calculated in accordance with the algerian seismic rules rpa99/version 2003. the lrb isolation system is used in this analysis, with 25 supports (figure 1). fig 1. graphical representation of the studied structures. 2.2. capacity spectrum method the spectrum capacity method (csm) is an analysis approach based on the performance of structure. it was used for the first time by freeman (2004) as a quick way to estimate the adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 3 seismic response of buildings, thereafter it was accepted as a tool for seismic design. its principle consists in superimposing a curve which represents the capacity of the structure outcome from a nonlinear static analysis (pushover), with a graph of the solicitation provided by the earthquake. the intersection of these two curves represents the point of performance which evaluates the maximum displacement of the structure in the plastic range (yang, 2003). the steps of the method are described as follows (saez, 2006): step 1: construction of the capacity curve (curve pushover) of the structure. the pushover analysis is a nonlinear static procedure; it is based on the hypothesis that the response of the structure may be connected to the response of an equivalent system of single degree of freedom. the formulation of the equivalent single degree of freedom system is not unique but the common basic supposition to all approaches is that the shape of the deformation of the system with several degrees of freedom can be represented as an eigenvector {φ} which remains constant during all the analysis independently of the level of deformation. accepting this hypothesis and defining the vector of the relative displacement x of a system with multiple degrees of freedom, x= {φ} x_t ( : roof displacement), the differential equation of the system with several degrees of freedom can be written as (krawinkler, 1996): { } ̈ { } ̇ { } ̈ (1) where : m∶ mass matrix. c∶ damping matrix. f∶ force vector. ̈ : ground acceleration. by defining the equivalent displacement of the system with a single degree of freedom system (sdof ), : { } { } { } { } (2) by multiplying the equation (1) by { } , and substituting the equation (2) into the equation (1), the following differential equation of the equivalent sdof system can be obtained: ̈ ̇ ̈ (3) where: m*,c* and f* are the properties of the equivalent sdof system with a single degree of freedom. { } { } (4) { } (5) { } { } { } { } { } { } (6) assuming that the eigenvector {ϕ} is known, the relation force-deformation f*-x* of the equivalent system with a single degree of freedom can be determined from the results of nonlinear incremental analysis of the system with multiple degrees of freedom (mdof), which results the capacity curve (base shear according to the roof displacement). step 2: conversion of pushover curve in acceleration displacement response spectral format (adrs), capacity diagram (chopra and goel, 1999): 4 adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 fig 2. conversion of the capacity curve in adrs format. with: (7) (8) [ ∑ ϕ ∑ ϕ ] (9) [∑ ϕ ] [∑ ϕ ] (10) m1*: effective modal mass of the first mode γ1: modal participation factor of the first mode mj: mass of jème level ϕj1: amplitude at level j of the fundamental mode n: number of levels ϕr1: amplitude of the first mode at roof level the bilinear representation of the capacity diagram was used to calculate the ratio of ductility (μ) and the equivalent damping which includes viscous damping and hysteretic damping (chopra and goel, 1999). the equivalent bilinear curve is based on the criterion of equivalence of energy. for a value of maximum deformation sdpi, as represented in figure 3, the area under the capacity graph must be equal to that in the bilinear curve (deformation energy), that is, the areas ω1=ω2 in figure 3. on the same figure, say and sapi are the maximum acceleration and the acceleration of the yield strength; sdy and sdpi are the displacements corresponding to accelerations say and sapi respectively. adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 5 fig 3. equivalent bilinear model. the rigidity of the elastic portion ke can be expressed in terms of the elastic period: ( ) (11) the maximum acceleration may be expressed in terms of the ductility ( ) and reducing stiffness α: ( ) ( ) (12) by keeping the elastic period (te) constant, the selection of different values of sdpi gives different values of say and α. generally, the value of say doesn't vary much depending on the choice of a sapi by against, the value of α is very sensitive to the chosen value. when the bilinear equivalence established, the system properties of an equivalent degree of freedom can be calculated. the equivalent elastic period teq: √ (13) the equivalent viscous damping of the system is (atc, 1996): ̂ (14) where: : viscous hysteretic damping. : viscous inherent damping. step 3: conversion of the traditional spectrum to demand spectrum (adrs format). from a pseudo-acceleration spectrum response for a given earthquake can be constructed an equivalent representation by accelerations and displacements, as shown in figure 4 and relation (15). 6 adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 fig 4. conversion of the spectrum. (15) d: spectral displacement. a: spectral acceleration. : natural period. step 4: determination of the performance point of the structure. the applied technology council, atc code 40 specifies three types of methods to estimate the induced deformation. procedures a and b are analytical (atc, 1996). method c is rather graphic. in general method a gives better results. 3. results and discussions 3.1. periods and cumulated modal contribution factors the results obtained for the two types of structures are summarized in table 1. table 1. periods and modal contribution factors cumulated of structures. levels type of structure period frequency mode number 5 conventional 0.578 1.730 5 isolated 1.198 0.835 2 3.2. capacity curve the pushover curves (base shear roof displacement) are the envelopes of forces-displacements of structures and represent the overall response of the structure. the loading model selected in pushover analysis is loading mode. the capacity curves of the two types of structures are shown in figure 5. 3.3. conversion pushover curves in adrs format the capacity curves of the two structures undergo a conversion to capacity diagrams (figure 6). 3.4. evaluation of the performance point in order to determine the performance point, the procedure a (ductility approach) is used, it involves comparing the capacity diagram of the structure (capacity to dissipate the energy and demand for energy to be dissipated) in the form of an inelastic spectrum. the inelastic spectrum is determined by reducing the elastic spectrum by factors related to the ductility and period. the response spectrum used in our work is presented in figure 7. adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 7 fig 5. pushover curves of structures. fig 6. capacity diagram of studied structures. fig 7. inelastic response spectrum. 8 adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 the results obtained for the two types of structures are presented in table 2 and illustrated in figure 8. table 2. result of csm method. conventional structure isolated structure µ dy (cm) ay (g) d (cm) µ calculated µ dy (cm) ay (g) d (cm) µ calculated 1.00 1.75 0.26 3.90 2.23 1.00 1.20 1.70 0.25 3.50 2.06 1.50 0.55 0.13 7.40 13.45 1.30 1.10 0.27 2.25 2.05 2.00 0.55 0.12 6.50 11.82 1.40 1.10 0.23 1.80 1.64 2.50 0.60 0.11 5.80 9.67 1.50 1.10 0.22 1.65 1.50 3.00 0.50 0.11 5.00 10.00 3.50 0.50 0.07 2.10 4.20 3.80 0.50 0.06 2.05 4.10 4.00 0.50 0.06 2.00 4.00 fig 8. performance point of studied structures. the results recapitulated in table 1 show that the effect of the isolation system is to relax the structure by the lengthening of the fundamental period to a greater value compared to the value obtained for the conventional structure. indeed, the shift of the period is the primary reason for the effectiveness of the isolation system. figure 8 shows a comparison between the two spectrum capacity in adrs format, the two structures have a performance point characterized by a spectral displacement, spectral acceleration and ductility (see table 2), it must be noted that the spectral displacement in the isolated structure is greater than that of the conventional structure, and the spectral acceleration in the isolated structure is smaller than the spectral acceleration in the conventional structure. in other words, there is a reduction in the seismic demands which makes the level of the performance of structure most advantageous. the results obtained are summarized as follows (table 2): an increase in the spectral displacement of 21% which represents the displacement of the isolation system. a decrease in the spectral acceleration 73% which represents the reduction of demand in terms of demands brought by the earthquake. adjou and haddadou, j. build. mater. struct. (2015) 2: 1-9 9 4. conclusions the comparative study on the structure with and without isolation system allows highlighting the influence of seismic bearings on reducing the seismic demands, the main results are: the period of the isolated base structure is elongated relative to the period of the fixed base structure; the acceleration of the isolated base structure is smaller compared to the accelerations of the fixed base structure. the seismic isolation system reduces the base shear and the inter-stage displacements which cause significant damage to the structure. the evolution over field of the use of the isolation technique, leads us to suggest the adoption of this new technology in the future algerian earthquake resistant regulations rpa99/version2003. 5. references applied technology council, atc (1996). seismic evaluation and retrofit of concrete buildings. atc-40, volumes 1 and 2, report no. ssc 96-01, seismic safety commission, redwood city, ca. chopra ak, goel rk (1999). capacity-demand-diagram methods for estimating seismic deformation of inelastic structures: sdf systems. pacific earthquake engineering center, university of california, berkeley, report no. peer 1999/02. freeman sa (2004). review of the development of the capacity spectrum method. iset journal of earthquake technology, 41(1), 1-13. koh cg, kelly jm (1985). fractional derivative representation of seismic response of base-isolated models: theory and experiments. ucb/sesm 85/07, university of california at berkeley. krawinkler h (1996). pushover analysis: why, how, when, and when not to use it. in proceedings of the 65th annual convention of the structural engineers association of california. nazé pa (2004). contribution to the prediction of structural damage in reinforced concrete under seismic loading. doctoral dissertation, insa lyon, france. (in french) saez e (2006). design of buildings based on the notion of performance. doctoral dissertation, ecole centrale de paris, france. (in french) yang yb, chang kc, yau jd (2003). base isolation. earthquake engineering handbook, chapter 17, crc press, washington dc. j. build. mater. struct. (2022) 9: 44-56 original article doi : 10.34118/jbms.v9i1.1373 issn 2353-0057, eissn : 2600-6936 basalt powder waste application as affordable concrete admixture mbereyaho l*, niyoyita j b, kimararungu a, ntakiyimana d university of rwanda, college of science and technology. p.o box: 3900 kigali, rwanda. * corresponding author: lmbereyaho2015@gmail.com received: 06-06-2021 accepted: 24-02-2022 abstract. different weather conditions, like temperature and humidity influence on the performance of concrete structures to which they are normally subjected, especially at earlier stage of their service life. one of practical measures has been the regulation of the setting time of fresh concrete. some admixtures are used in concrete to regulate the setting time and therefore increase structures performance under given situation. almost all admixtures used in rwanda are being imported from outside the country and this is one of factors affecting the construction cost. a big quantity of basalt powder at different sites in the country is left without being used and has been negatively impacting the environment. this study aimed at analyzing the potentials of basalt powder waste used in concrete as admixtures in different percentages, e.g. 0%, 5%, 10%, 15% and 20%. different investigations on concrete incorporating basalt powder as admixture, such as the setting time, workability and compression tests were conducted. the results showed that the gradual incorporation of basalt powder waste as admixture up to 20%, accelerated the setting time more than 13 times, but decreased the compressive strength of concrete by around 24.5%, with comparison to normal concrete strength. the application of basalt waste in concrete would contribute not only to the reduction of environmental pollution but also to the provision of more affordable admixtures for mortar and concrete. key words: admixture, basalt powder waste, compressive strength, concrete, setting time, workability. 1. introduction the widespread application of concrete in construction of different structures and under different conditions has increased the requirement not only in its quantity, but also its high quality. concrete used should ensure the adequate performance of implemented structures under any condition to which they are exposed. some special conditions, like high temperature, humidity, etc require that admixtures are added to the concrete mixture immediately before or during mixing in order to regulate its setting time or sustain some desired properties (kosmatka and wilson, 2011). in rwanda, those admixtures have been in use especially when the concreting is performed during sunny period or under humid conditions. these admixtures are usually imported from abroad, and they are still expensive, especially with consideration of transportation services cost. in rwanda basalt waste materials, produced by some construction industries, are disposed in the environment, and consequently they have been causing human health and sanitation concerns. till today, this waste has been under use only as aggregates, especially in road construction projects, while its great part still remained improperly dumped in the environment. the utilization of basaltic waste would become a valuable contribution not only for preservation of the environment, but also in offering affordable product, while using local materials, and this is the main objective of the study. among others, some specific objectives were identification of ordinarily used admixtures for concrete and their properties, survey on the availability of basalt waste in rwanda, and determination of properties of fresh and hard concrete mixed with basaltic powder. mailto:lmbereyaho2015@gmail.com mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 45 basalt rock has been under use in construction projects all over the world, including rwanda. also some previous works on the use of basalt waste in cement or concrete are available. feng (2013), using the experimental study on mechanical properties of basalt fiber reinforced concrete, he found that the mixture with basalt fiber would efficiently enhance the ductility of the concrete and improve the compressive strength and split tensile strength of concrete matrices in different ages. he concluded that the compressive strength of concrete in the age of 3days and the split tensile strength of concrete in the age of 28 days were improved more significantly, by 9% and 19% respectively. dobiszewska and beycioğlu (2017) used four types of common cement which were cem i, cem ii/a-s, cem ii/a-v and cem ii/b-v for investigating the influence of waste basalt powder on selected properties of cement paste and mortar, where they established the positive effect on those properties and concluded that the incorporation of waste basalt powder into cement mortar as a partial substitution of cement was environmentally friendly and economically feasible. in their study about effect of basalt powder on the properties of cement composites, while modifying cement mortar by basalt powder in amount of 10, 20 and 30% by weight of cement, uneik and kmecova (2013) realized that basalt powder had a positive effect on the consistency of fresh cement composites and the strength of hardened composite. the initial and final setting time were prolonged with the increase of the basalt content. during their study on effect of basalt powder addition on properties of mortar, dobiszewska et al. (2019) established that the addition of basalt powder as a replacement of cement leads to deterioration of compressive strength, while the flexural strength of mortar improved in some cases. the study on mortar properties with basalt powder subjected to high temperatures, showed that the ratio of basalt powder does not change the strength reduction rate, and that the flexural strength performance of mortar mainly depended on fibre type and temperature rather than on basalt powder substitution (akyuncu, 2019). in rwanda, a study about engineering characteristics of volcanic rock aggregates found that they had a very high compressive strength and better permeability (mutabaruka et.al, 2016). dobiszewska and barnes (2020) carried out an experimental investigation to evaluate the potential usage of waste basalt powder in concrete production, where the waste basalt powder, replaced 10%, 20%, and 30% sand, and the workability, compressive strength, water transport properties, and microstructural performances were evaluated. among other results, the study showed that the compressive strength of concretes could increase up to 25%. dobiszewska and barnes (2020) investigated on the use of waste basalt powder in mortar when used as a partial replacement of fine aggregate and the experiments were performed on mixtures containing up to 20% replacement of sand by basalt powder to determine the impact on the compressive and flexural strength of mortar as well as on the flow characteristics, density, and porosity. the results indicated that use of basalt powder as a partial replacement of sand leads to improvement of the compressive strength and flexural strength. the mortar porosity in the capillary pore range was reduced. the study on use of basalt powder in a cementitious mortar and concrete as a substitute of sand showed that powder basalt could be used as an effective substitute of fine aggregate in cementitious mortar and concrete and this improved some properties of cementitious mortar and concrete and enabled for the management of industrial waste (dobiszewska, 2016). among other results, the experimental study on basic mechanical properties of basalt fiber reinforced concrete established that basalt fiber significantly improved the toughness and crack resistance performance of concrete and the improvement effect was the highest with the basalt fiber content of 0.3% and 0.4% (zhou et al, 2020). this study is conducted with addition and not replacement of basalt powder in concrete, in order to assess its performance as an admixture. 46 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 2. research materials and methods 2.1. materials 2.1.1. basaltic powder waste the basaltic rocks are available in north-western part of rwanda in the volcanic region (mutabaruka et al., 2016). many of local industries have been using these rocks in different construction activities like road pavement, building construction, where they are crushed and used as road base, asphalt pavement, concrete aggregate, etc. for this study, the samples of basalt waste powder were taken from the basalt rock crushing plant belonging to one of local construction company, npd cotraco ltd located in musanze district. the fig.1 shows the used basaltic powder sample. 2.1.2. cement during this study twiga cement m32.5 grade was used throughout the whole investigation. the fig. 2 presents the packaged and stored twiga cement. fig. 1. basaltic powder fig. 2. twiga cement 2.1.3. coarse and fine aggregates the fine and coarse aggregates with the sizes of 4.75mm and 20mm, as well as specific gravity of 2.61 and 2.655 respectively were extracted from local river. those materials are shown in fig.3 and fig.4 respectively. fig. 3. fine aggregates fig. 4. coarse aggregates 2.1.4. water used clean water was used for mixing and curing of concrete. mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 47 2.2. methods during the mixing process, the design mix proportion 1:2:3 for cement, sand and coarse aggregate respectively was considered, while the used w/c ratio was 45% of cement. 2.2.1. experimental design and laboratory test the purpose of this laboratory experiment was the determination of the compressive strength using concrete specimen, prepared with incorporation of basaltic powder added as admixture. the compressive strength was determined at 28 days of curing on the cubes of 150mm size. other important tests like sieve analysis, setting time and workability of concrete mixed with basaltic powder were also checked. details on these tests are given below, while respective results are presented in section 3. 2.2.2. sieve analysis of sand this test is conducted to determine the distribution of fine aggregate samples using standard sieve meshes, and this is one of aspects used to assess the aggregates quality. 2.2.3. used apparatus standard sieves of different holes’ diameter in mm, shaking machine, laboratory balance, tray, scoop, time stop watch, and calculator. the ordinary normal procedure was used in order to achieve the standard test results. 2.3.4. standard consistency test the consistency of cement is taken when a vicat plunger is allowed to penetrate, with the reading characterized by the standard consistency values in the range between 5-7 mm from the bottom or 33-35 mm from the top of mould. tools used for this test are: vicat with plunger, needle, stop watch, glass plate, tray, balance and measuring cylinder (fig.5). fig. 5. used tools (from left to right: vicat apparatus with plunger and needle, stop watch and balance) 2.3.5. the setting time test for cement as many constructions projects are subjected to different extreme conditions such as humidity or high temperature, the setting time of concrete needs to be checked in order to ensure its quality at earlier stage. the setting time of cement paste is presented into two states that are initial and final setting. the initial setting is regarded as the time elapsed between the moments under which the water is added to cement and the time when the paste starts losing its plasticity, while the final setting is regarded as the time elapsed between the moment at which the water is added into cement to the moment when the paste has completely lost its plasticity. apparatus used: movable rod with cup, needle, standard vicat mould, needle with hallow circular cutting edges of 5mm diameter and weight balance. the standard procedure was used for this test as presented below (see also fig.6). the initial setting time procedure is presented below: 48 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 1. use approximately 300 gram of dry cement with additional of 0.85 p (p=weight of water for standard consistency to make paste). 2. fill the mould with paste, then fix specific needle to moving rod apparatus. 3. release the needle to penetrate cement paste. 4. note the time and depth to which the needle penetrates the cement paste. 5. repeat the procedure until the penetration will be 34.5-35.5 mm from the top of mould, means that it is 5±0.5mm from the bottom of mould. 6. plot a curve between time (minutes) and unpenetrated height in mm. 7. find on graph initial setting time when penetration of needle is within 5±0.5mm. fig. 6. initial setting time test the procedure used for the final setting time test is the following: 1. attach needle with circular cutting edge. 2. release the needle slowly 3. the time when the needle makes impressions on the hardened cement paste is recorded. slump test: the workability is described as ability of fresh concrete to be easily transported, compacted, and placed without any reduction of concrete qualities. the most commonly method used to measure the workability of fresh concrete in laboratory or on site is slump test. apparatus: slump cone (with bottom diameter=200 mm, top diameter=100 mm, and height=300 mm), weighing balance, tray, standard tamping rod, concrete mixing machine. compression test: the compressive strength is the one of the most important properties of hardened concrete which describes its ability to resist forces. this test is mainly conducted on 28 days hardened concrete by using compression testing machine and it plays an important role in controlling and conforming the quality of concrete. apparatus: cube moulds 150mm size, weighing machine, ramming rods, compression testing machine. the fig. 7 shows the mould and used balance mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 49 fig. 7. used cube mould (left) and balance (right) 3. results and discussion as it was stated in section 2, the conducted experiments are: sieve analysis, consistency, setting time, workability and the compressive strength. established results are presented and discussed in this section. 3.1. sieve analysis following the procedure presented earlier, established results are presented in table 1. table 1. sieve analysis sieve size(mm) weight of aggregate retained(g) % of aggregate retained cum % of aggregate retained % of aggregate passing 4.75 8.33 1.40 1.40 98.60 2.36 21.62 3.65 5.05 94.45 1.18 195.38 32.94 37.99 62.01 0.6 123.81 20.88 58.87 41.13 0.3 145.14 24.47 83.34 16.66 0.075 97.56 16.45 99.79 0.21 pan 1.26 0.21 100.00 0.00 total 593.1 100.00 286.44 313.06 fineness modulus=cum % of aggregate retained/100= 286.44/100=2.8644 from the above table the following can be underlined: ● the value of fineness modulus indicates that the used aggregates are “fine aggregates” because its value is within 2-3.2 standard range of fine aggregate as it is recommended by standards ● the maximum sieve size used is 4.75 mm, and minimum is 0 075 mm and the retained aggregates are 1.40% and 16.45% respectively. referring to is 383 (bureau of indian standards, 2016), it can be concluded that this is a fine aggregate of zone ii 3.2. standard consistency test the consistency test results for normal cement and cement mixed with basaltic powder are presented in table 2 and table 3, respectively. table 2. normal consistency of cement s/n % of water initial reading final reading height of penetration 1 20 40 34 6 2 22 40 11 29 3 24 40 6 34 from table 2, it can be seen that the established consistency of cement was 24% of water, and therefore the cement paste was normal (mishra, 2014). 50 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 table 3. normal consistency of cement mixed with 5% basaltic powder s/n % of water initial reading final reading height of penetration 1 20 40 38 2 2 22 40 35 5 3 24 40 31 9 4 26 40 29 11 5 28 40 16 24 6 30 40 7 33 from table 3, it is noted that the consistency of cement mixed with 5% of basaltic powder was 30% of water. the same test with 10%, 15% and 20% of basaltic powder showed the similar percentage of water. 3.3. the setting time test results 3.3.1. initial setting time test following the recommended procedure the following quantities were used: mass of cement =300gr; quantity of water=300*30%*0.85=76.50 gr .test results with 5% of mixed powder are presented in table 4. table 4. setting time data of cement with 5% of basaltic powder s/n time(in minutes) initial reading penetration height remaining height 0 0 40 40 0 1 6.30 40 40 0 2 13.00 40 39 1 3 19.30 40 39 1 4 26.00 40 39 1 5 32.30 40 38 2 6 39.00 40 38 2 7 45.30 40 37 3 8 52.00 40 36 3 9 58.30 40 36 4 10 65.00 40 36 4 11 71.30 40 36 4 12 78.00 40 36 4 13 84.30 40 36 4 14 91.00 40 36 4 15 97.30 40 34.5 5.5 3.3.2. final setting time the fig. 8 demonstrates the variation of penetrated height in function time. mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 51 fig. 8. time versus unpenetrated height hence from chart above  initial setting is 97.30 minutes  final setting is 190 minutes the setting time for concrete mixed with and without basaltic powder is given in table 5, while the respective chart is presented in fig. 9. table 5. initial and final setting time of concrete mixed with and without basaltic powder basaltic in % water in % initial setting time in minutes final setting time in minutes 0 24 30 600 5 30 97.30 190.00 10 30 0-6.30 58.30 15 30 0-6.30 52.30 20 30 0-6.30 45.30 fig. 9. final setting time 52 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 the results in table 5 and respective fig.8 show that the initial setting time at 5% basalt cement is 97.30 minutes and final setting time 190 minutes. then with the increase of basalt content, the initial and final setting time gradually decreased, and it can be noted that the addition of basalt waste up to 20% decreased the sitting time from 600 to 45.30 minutes, giving a setting time reduction of more than 13 times. this may be due to the chemical composition of basalt with regards to the set accelerators admixtures (kosmatka et al., 2008; myrdal, 2007).the initial setting time lay between 0 and 6.30 minutes while final setting time are 48.30, 52.30 and 45.30 respectively. according to krishna (2017), the standard initial and final setting time of cement is 30 and 600 minutes respectively. therefore this result shows that basaltic powder should be the best mineral admixture to be used in humid condition due to its quick setting. 3.4. slump test the used concrete mix is 1:1.6:2.7 (w/c=0.45) ingredients are obtained by weight method. the following standard procedure for this test was used: 1. prepare apparatus. 2. take mix proportion: 1:1.6:2.7 by weight; use water cement ratio=0.45. 3. sampling and measuring the concrete ingredients. 4. prepare mixing machine and pouring the sample. 5. cleaning internal surface of slump cone. 6. fixing slump cone to the base on ground. 7. fill the fresh concrete into slump cone in equal three layer and each layers should be compacted twenty-five blows. 8. level the top of the cone by straight edge. 9. remove the slump cone slowly upward and approach the empty slump cone near by the compacted concrete 10. determine the slump result using gradual rule by measuring the difference between concrete and cone. 11. obtain the height difference in mm as slump of concrete. slump test results are given in table 6, while respective chart is given in fig. 10 table 6. observation of slump cone s.n basaltic powder in percentage (%) height of slump h1(mm) height of subsided concrete h1(mm) slump (h1-h2 =mm) 1 0 300 234 66 2 5 300 236 64 3 10 300 246 54 4 15 300 237.5 62.5 5 20 300 231.5 68.5 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 53 fig. 10. slump test results from the results in fig.10, it can be observed that initially the slump decreased with addition of 10% basalt powder waste from 66 mm up to 54 mm, and then it started increasing and became 68.5 mm at 20% basalt powder in concrete. also, staying on this fig.10, it is noted that the overall slump decrease was only around 3.7%. this situation may be explained by the fact that the structure of basalt allows a slight water absorption until it is saturated. in general, according to standards, the normal slump of concrete should be within 50-100mm for normal reinforced concrete, placed with vibration (bureau of indian standards, 1959). therefore the obtained slump results are normal and the incorporation of the tested basalt powder waste should not damage the workability of concrete. 3.5. compressive strength test the standard procedure was used and the compression test results are presented in table 7, while the respective chart is presented in fig.11 fig. 11. compression test results 54 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 referring to the results presented in fig. 11, it can be observed that the addition of 5% basalt powder waste in concrete, its compressive strength reduced abruptly by 52.80%. then after that the gradual incorporation of basalt powder increased the compressive strength, to finally show a general decrease of around 24.5%. this situation may be attributed not only to the low final water/cement ratio, which made the hydration process difficult and not adequate, but also to the basalt chemical composition which prevented the strength from further sensitive decrease. however, the shown compressive strength at 20% basalt waste incorporation allows confirming that this concrete can still be used where appropriate, depending the designed compressive strength. 3.6. discussion the purpose of the study was to assess the potentials of basalt powder wastes as concrete admixture. though all checked properties are important for assessing concrete performance, the influence on the fresh concrete setting time and on its compressive strength are here discussed. as it was presented earlier, many of previous studies related to basalt waste application in concrete checked its potentials as a replacement of one of concrete components (dobiszewska beycioğlu, 2020; dobiszewska and barnes,2020; akyuncu, 2019; dobiszewska and beycioğlu, 2017; uneik and kmecova, 2013) and quite all reported about the positive influence of basalt material on concrete properties. only dobiszewska et al., (2019) established that the addition of basalt powder as a replacement of cement leads to the deterioration of compressive strength. there was a little about the use of basalt powder as concrete admixture, and therefore only concrete standards values regarding the setting time, slump and compressive strength, as well as basalt chemical composition were used for comparison. setting time test results showed that the addition of basalt waste decreased both the initial and final sitting time for fresh concrete (fig. 9), but remained under the standards limits (krishna, 2017). this is considered as positive result to consider basalt powder waste as set accelerator admixture. the results showed a general decrease of compressive strength of concrete with incorporation of basalt powder waste, comparing with normal concrete, even if there was a gradual increase after 5% basalt powder waste addition (fig.11). these results are in acceptance with previous findings (dobiszewska et al., 2019). for application of this concrete, the % of basalt powder waste incorporation should depend on the designed concrete strength. finally, regarding the new admixture affordability, this is based on the local availability of basalt rock as its raw material, and it has also been confirmed by previous studies (dobiszewska and beycioğlu; 2017). 4. conclusion the general objective of this study was to investigate on the use of basalt powder waste in concrete as admixture, in order to take advantage from its local availability and solve the problem related to its negative impact to the environment. it has shown that the basalt rock is available in rwanda, especially in northern – western province and currently has been used mainly in road pavement and building construction. during this study, the properties of concrete mixed with 0%, 5%, 10%, 15%, 20% basaltic powder like workability, setting time and compression strength were checked. the following key findings were established:  compared to plain concrete, the workability test was achieved up to 80% due to the variation of water quantity.  the amount of water needed during mix was slightly greater than that of plain concrete, and therefore basaltic powder can be used as water reducer. mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 55  the setting time of concrete mixed with basalt waste as admixture decreased with increase of percentages of basalt powder waste, and therefore the waste acted in concrete properly as admixture and would be suitable especially in humid condition.  with increase of the basalt powder in concrete, the compressive strength decreased in the beginning, but after 5% and until fixed 20% basalt powder, the strength started increasing. however, this increase did not attain the compressive strength for normal concrete. from the above, it can be concluded that the use of basalt powder waste in concrete would provide a local and affordable as well as a sustainable solution regarding set accelerator admixture. concerning the concrete compressive strength, due to the initial reduction and then increase of the strength, a due care should be made to ensure the incorporated % of basalt powder does not decrease the designed concrete strength. further study may check the durability of basaltic concrete with varying basalt powder at different ages. this study was more interested in setting time with consideration of other minimum requirements for concrete performances, and it did not establish the % of added basalt waste at which the standard compressive strength would be achieved; therefore this can be the scope for further study. acknowledgement the authors sincerely acknowledge the technical support from the university of rwanda,college of science and technology leaadership, especially regarding the provision of laboratory facilitaties during this study. all individuals or institutions that contributed in one or other ways for the successful completion of this work, but not stated in this section are also acknowledged. 5. references akyuncu v. (2019), basalt powder dependent properties of mortars subjected to high temperatures. građevinar 71 (7) 571-578. doi: https://doi.org/10.14256/jce.2561.2018 bureau of indian standards (2016), indian standard (is 383: 2016).coarse and fine aggregate for concrete – specification (third revision), india. bureau of indian standards (1959), indian standard is code 1199-1959 methods of sampling and analysis of concrete, india dobiszewska, m. (2016), use of basalt powder in a cementitious mortar and concrete as a substitute of sand, construction and architecture, 15(4)75-85. doi: https://doi.org/10.24358/budarch_16_154_08. dobiszewska m., barnes r.w. (2020). properties of mortar made with basalt powder as sand replacement. materials journal, 117(2), 2-9 dobiszewska m, beycioğlu a. (2017). investigating the influence of waste basalt powder on selected properties of cement paste and mortar. iop conf. series: materials science and engineering 245 (2017) 022027. doi: https://doi.org/10.1088/1757-899x/245/2/022027. dobiszewska m,, beycioğlu a. (2020). physical properties and microstructure of concrete with waste basalt powder addition. materials (basel),13(16): 3503. doi: https://doi.org/10.3390/ma13163503. dobiszewska m, pichór w., szołdrap. (2019). effect of basalt powder addition on properties of mortar. matec web of conferences 262, 06002 (2019). krynica 2018. https://doi.org/10.1051/matecconf/201926206002. feng c. (2013). an experimental study on mechanical properties of basalt fiber reinforced concrete. applied mechanics and materials 405(408), 2767-2770 in applied mechanics and materials, trans tech publications ltd. zhou, h., jia, b., huang, h., & mou, y. (2020). experimental study on basic mechanical properties of basalt fiber reinforced concrete. materials, 13(6), 1362. https://doi.org/10.14256/jce.2561.2018 https://doi.org/10.24358/bud-arch_16_154_08 https://doi.org/10.24358/bud-arch_16_154_08 https://doi.org/10.1088/1757-899x/245/2/022027 https://doi.org/10.3390/ma13163503 https://doi.org/10.1051/matecconf/201926206002 56 mbereyaho et al., j. build. mater. struct. (2022) 9: 44-56 kosmatka s.h, kerhoff b., panaresew.c. (2008), design and control of concrete mixtures, portland cement association, usa kosmatka, s. h. ,wilson m. l. (2011). design and control of concrete mixtures, eb001, 15th edition, portland cement association, skokie, illinois, usa, 460 pages krishna, (2017). initial and final setting time of cement. [online]: available at: https://civilread.com/cement-initial-final-setting-time/ mishra, g., (2014). determination of standard consistency of cement. the constructor civil engineering home. [online]: available at: http://theconstructor.org/practical-guide/standard-consistency-ofcement/1549/ moid, e., (2019). what is slump test? its types, procedure, equipments. civil click. [online]: available at: https://www.civilclick.com/slump-test/ mutabaruka j.d., dr pranesh m.r, prof. umaru g.w. (2016). engineering characteristics of volcanic rock aggregates of rwanda. international journal of civil engineering and technology (ijciet), volume 7, issue 3, may–june 2016, pp. 81–90 myrdal r. (2007), accelerating admixtures for concrete, sintef building and infrastructure, norway uneik s., kmecova v. (2013). effect of basalt powder on the properties of cement composites. procedia engineering 65.51-56. doi: https://doi.org/10.1016/j.proeng.2013.09.010 https://civilread.com/cement-initial-final-setting-time https://www.civilclick.com/slump-test/ https://doi.org/10.1016/j.proeng.2013.09.010 j. build. mater. struct. (2023) 10: 40-63 review article doi : 10.34118/jbms.v10i1.2840 issn 2353-0057, eissn : 2600-6936 evaluating the reinforcements efficiency of sawdust and corncob wastes in structural concrete: a comprehensive review abiodun kilani 1, ademilade olubambi 2,*, bolanle ikotun 3, oladipupo seun oladejo 4, babatunde famodimu 5 received: 02-03-2023 accepted: 12-06-2023 abstract. sawdust (sd) and corncob (cc) wastes possess up to 89.4% and 83.03% pozzolanic properties with a high impact on the mechanical properties required for high concrete strength reinforcement respectively. applications of sd and cc wastes in concrete increased the concrete workability by 8.75% and 27.9% respectively. in addition, the use of sd in concrete eased its aggregates’ compatibility rate by 4.4%. the consistency of cement paste with corncob ash (cca) decreased with an increase in the percentage of cca included. in addition, the final and initial setting times of paste with sawdust ash (sda) decreased by 28.2% and 20% with increasing use in the percentage of sda included, while that of cc increased with an increase in the percentage of cc. the densities of sda-concrete and cca – concrete observed were from 300 to 1800kg/m3 and 1998 kg/m3 to 2302kg/m3, and these were classified as lightweight concrete. the review showed that cca had a high potential for increasing the concrete compressive strength by 34.5%. the blending of cc waste with other admixtures was observed to have increased concrete’s tensile properties by 3.9%. cc waste possessed high potential for composite tensile property enhancement up to 68%. the ccaconcrete’s flexural strength observed was low; the blending of cc with other admixtures has increased the concrete’s flexural strength. sdw-concrete suggested to high temperature showed an increase in compressive strength until 6000c is reached, after 6000c, there was a reduction in strength. the cca reduced concrete’s modulus of elasticity by 27%. from the x– ray result, quartz (sio2) shows an essential and main mineralogical content of cca. the concrete’s rate of water absorption increased by 74% with the inclusion of sd. the ann model is efficient and possesses good features for cca and sd – concrete models. in conclusion, sd and cc wastes possess a good potential for the enhancement of structural concrete, which can be processed into types of cement and concrete composites. keywords: sawdust waste, corncob waste, concrete reinforcement, structural properties 1. introduction in recent years, the application of natural fibres in form of admixtures or as an aggregate substitute in concrete will improve the durability properties of the concrete and reduce its rate of co2 and green house gases (ghgs) emissions from concrete. one of the best methods of reducing ghgs emissions from concrete is to replace some percentages of ordinary portland cement (opc) with pozzolanic materials (felman, 2005). sawdust is the waste material obtained from the wood routing, planning, milling and sawing operations. it is made up of small wood chippings. wood dust can be obtained when hand tools, power tools and machinery operate on wood. some animals were feeding on wood such as carpenter ants and woodpeckers. many daily 1 dept. of works and physical planning, eko university of medicine and health science, lagos state, nigeria 2 dept. of civil engineering science, 2006, auckland park kingsway campus, university of johannesburg, south africa 3 dept. of civil engineering, college of engineering, science and technology, florida campus, university of south africa, johannesburg, south africa 4 dept.civil engineering department, ladoke akintola university of technology, ogbomosho, nigeria 5 dept. of civil engineering, federal university oye-ekiti, ekiti state, nigeria * corresponding author: ajoeolubambi@mail.com http://www.oasis-pubs.com/ mailto:ajoeolubambi@mail.com abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 41 used materials were manufactured from wood dust such as wood pulp, particleboard, and icehouses for cooling in the summer. it is also used for models and railroad formation. in the factories, sawdust is used in making pykrete, charcoal briquettes, and cutler’s resin (international agency for research on cancer, iarc, 1995). in the year 2000 to 2003, the estimation made by european union with 25 states members (eu-25) shows that up to 3.6 million individual industrial workers were exposed to wood dust inhalation, especially, in furniture industries and construction sectors. the populations of people inhalable to sawdust were up to 2.0% of eu-25 employee populations (green, 2006; kaupineen et al. 2006). figure 1 shows the picture of common sawdust generated from wood from saw industries. (i) (ii) fig 1. (i) zaagsel saw dust (ii) chainsaw from wood shaving (iarc) (green, 2006; kaupineen et al. 2006) a corncob is a material at the core ear of the corn called maize, and it is obtained after the removal of the corn kernel from the cob. at their mature age, the corn kernels were consumed raw or taken after processing. cobs were used as moisture-absorbing material in animal feeding processing. cobs were used for charcoal production, as bio-fuel, and for the production of abrasive materials. they were used as fibre in making ruminant livestock fodder andused as furfural in chemical industries. the corncobs generated from agricultural farms, and the treatment of corncobs into ashes respectively (aston 2010; murthi et al. 2020). many wastes were generated from wood. these wastes could be from processing and logging activities. the quantity of wood waste generated from sawmills globally is about 3.87 million metre-cubic. the increase in the number of sawmills in nigeria has increased the quantities of waste generated from saw industries. according to the authors, about 20% of these wastes were estimated to be sawdust in the year 1981. also, the growth in saw industries is to about 1200 which is twice the estimated value (over 500) in the year 1975 has increased the quantity of dust production from the mills. authors stated that more than 1.7 million metre cubic of waste from wood were generated from sawmills globally in a year (olafusi et al. 2017). almost 32.45 million metres cubic of wood waste were produced around the globe yearly. its bulk density was estimated to be 160kg/m3. in a year, about 5.2 million tonnes of sawdust were produced in nigeria. in support of this statement, more than 3.89 million metres cubic of dust from sawmills was generated yearly in nigeria (omochie et al. 2018). as estimated by the author, up to 0.66kg of waste municipal was generated in nigeria yearly. out of the municipal wastes generated, about 1.8 metric tonnes of sawdust were produced. in the years 2019 to 2020, the united states was observed to be the largest exporter and producer of corn together with its cob with about 346 million metric tonnes in quantities (world agricultural production (ogwueleka, 2009; oluoti et al. 2014). 42 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 (i) sun dried corncobs (ii) crushed corncobs (iii) burning of crushed corncobs in muffle furnace (iv) crushed corncobs carbonized fig 2 (i-iv). incineration of corncobs (ogwueleka, 2009; oluoti et al. 2014). about ninety million acres of land in america were used for the cultivation of corn. in addition, as estimated, the quantities of corncobs generated from brazil are about 102 million metric tonnes in a year. with this estimation, brazil is referred to as the third largest producer of corn in the globe. in the recent corn production estimate, about 51 million metric tonnes of corncobs were generated from argentina while in ukraine and india, about 35.9 and 25 million metric tonnes of corncobs were generated every year respectively. likewise, in the 27 european union countries, about 66.74 million metric tonnes of corncobs were generated. these countries were known as the fourth–largest corn producers in the globe from the year 2019 to 2020 (kukogho et al. 2011). the global rate of generating sawdust and corncob wastes is high these days. a strategic means of disposing of them to inform of processing to meet the other industrial demand have to be developed. the application of agricultural wastes as construction materials in cement and concrete industries has been gaining appreciation. their effectiveness in concrete needs constant evaluations, to improve their usage in concrete industries. this review focus on evaluating the efficiency of using saw dust (sd) and corncob (cc) wastes in concrete. it covers the evaluation of the level of quality reinforcement developed by applying sd and cc waste to concrete. the effect of sd and cc wastes on some structural properties of concrete such as setting time, consistency, concrete workability, flexural strength, density, durability, tensile strength, and compressive strength. this review aims at evaluating the reinforcement efficiency using sd and cc wastes in concrete, identifying the undeveloped areas, and making suitable suggestions for their enhancement (george & braide, 2014; hussien et al. 2018; ikenyiri et al. 2019). abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 43 2. experimental program this review explains the physical and chemical properties of sawdust and corncob fibres; the fresh and hardened properties, thermal and durability properties, and micro-structural properties of concrete reinforced with both sawdust and corncob fibres. in addition, the responses of the sd and cc fibres to the concrete structural properties were modeled, and appropriate recommendations were made based on the reviewed properties. 2.1 properties and efficiencies of sawdust and corncob fibre in concrete 2.1.1 physical properties of sawdust fibre sawdust possesses some properties needed for the smooth reinforcement of concrete. the physical properties of sawdust suitable for the reinforcement of concrete are presented (table 1). in addition, the moisture content of sawdust is up to 10.8%, which implied that much water is not needed to make use of sawdust fibre in concrete. there will be appropriate compaction of aggregates mixed with sawdust ash (sda) due to its low specific gravity (hussien et al. 2018; oguche et al. 2021). sdf has 50% capacity of retaining water, therefore, its application in concrete should be preceded by proper treatment to prevent the high rate of water retention. with 84% porosity of sda, there is a tendency of absorbing high percentage of water meant for the hydration process in concrete. this high porosity might be because of small variations in sdf’s particle size with distribution sizes ranging from 0.075 (9 mm) to 4.75 (100 mm). table 1. physical properties of sawdust (ash) fibre (hussien et al. 2018) properties value properties value water drainage (m/s) 282.0 particle size distribution (mm) 0.075 9 water retention (%) 50 0.21 30 porosity (%) 84 0.425 48 apparent specific gravity 0.14 0.6 81 moisture content 10.8 2.0 95 4.74 100 specific gravity 2.05 considering the properties of sdf, dust fibre needs proper treatment, especially, on the rate of water absorption and drying, before its application for concrete reinforcement. a highwatercement ratio is required to make use of sdf in concrete. with good physical properties of sdf observed in table 1, sdf possesses high reinforcing physical properties for concrete reinforcement. 2.1.2 chemical properties of sawdust and corncob fibre the chemical properties and composition of the sawdust wastes observed were shown in table 2. as shown in table 2, the percentages of pozzolanic constituents (sio2, al2o3, and fe2o3) of sawdust observed were high. the combination of silicon oxide, aluminate and ferrous oxide, which are the major component of pozzolanic properties,either specified for materials to be used as suitable supplementary material,in form of cement substitute or as partial replacement of aggregates in concrete were up to 76.0% to 89.4% respectively (oguche et al. 2021). sdf possess a higher pozzolanic constituent than the specified standard for supplementary of aggregates in concrete (70%). this proves that sdf possesses good chemical properties for the reinforcement of structural concrete. besides the good chemical constituent of sdf, it was made up of 61.58% of carbon content (nnochiri, 2018). this carbon content is high and it can delay the setting of the concrete when use in concrete. 44 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 table 2. chemical properties and composition of sawdust fibre (george & braide, 2014; hussien et al. 2018; ikenyiri et al. 2019; oguche et al. 2021) chemical composition value chemical properties value oguche et al. (2021) (%) hussein et al. (2018) (%) george and braide (2014) (%) ikenyiri et al. (2019) (%) sio2 68.7 76.3 85 nitrogen (n) 0 al2o3 5.1 5.8 2.7 oxygen (o) (%) 33.04 fe2o3 2.21 2.9 1.7 hydrogen (h) (%) 5.32 cao 5.2 4.7 3.5 carbon (c) (%) 61.58 so3 2.1 1.6 hollo-cellulose (%) 83.8 mgo 1.7 1.2 0.25 lignin 29.3 specific gravity 2.02 extractives 3.3 moisture content 1.53 1.37 fineness 75μm others 2.5 loss of ignition 4.3 pozzolanic properties 76.01 85 89.4 for perfect reinforcement, sdf required standard treatment before use in concrete. furthermore, sdf consists of 83.8% of cellulose content, and with the high percentage of cellulose, the structural properties of the concrete will be highly improved. according to kilani et al. 2022; cellulose is referred to as the firm property well-built of plants. the application of a material with high percentage of cellulose in concrete will highly enhance the concrete properties. also, more improvement is expected on concrete reinforced with sdf as 29.3% of its lignin property will supplement the strength yielding capacity of cellulose of sdf (table 2). all these properties show the chemical fitness and stability of sdf for concrete reinforcement. the chemical composition of concrete with corncob ash (cca) as investigated by different research scholars was presented as shown in table 3. table 3. chemical composition of corncob ash loi k2o na2o mgo cao fe2o3 al2o3 sio2 source 4.23 0.43 2.08 10.24 4.75 10.79 64.90 nnochiri (2018) 12.12 2.91 4.13 3.95 4.01 63.91 suwanmaneechot (2015) 3.89 0.36 1.86 10.57 4.40 6.25 62.30 desai (2018) 4.20 0.39 1.82 10.29 3.74 7.34 67.33 akila et al (2018) 3.01 12.0 5.12 9.42 64.56 komalpreet et al (2017) 5.95 1.05 0.90 1.99 16.23 4.03 6.48 64.50 oyebisi et al (2017) 1.98 1.91 0.98 11.47 9.07 17.57 56.39 oluborode & olofintuyi (2015) 10.8 3.83 0.0003 1.46 8.97 0.64 0.98 79.29 udoeyo & abubakar (2003) 4.92 0.41 2.06 11.57 4.44 7.48 66.38 adesanya and raheem (2009) ≤ 10% ≥ 0.70 ≤ 4% sio2 + al2o3 + fe2o3 > 70% oyebisi et al (2017) the percentage composition of the pozzolanic elements (sio2 + al2o3 + fe2o3) of corncob ash (cca) investigated by research scholars was far more than that of the specified limit (70%) stated for material to function as a supplement of cement in the concrete according to astm c618 specification. this property makes cca a suitable material for concrete reinforcement, either as supplementary material or as a replacement for aggregates (murthi et al. 2020). abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 45 2.2 fresh properties of mortar/concrete with sawdust fibre 2.2.1 workability of concrete with sawdust fibre gibi miriyam et al. (2017) investigation shows that the workability of concrete reinforced with sawdust fibre was gradually decreasing with the increase in the percentage of sdf included. in the investigation, 2.5% to 12.5% of sda was substituted with certain percentages of cement with 2.5% increase interval. the workability of the concrete was measured through a slump test. as observed by the author, the concrete with 0% of sawdust ash (sda) developed a slump loss of 80mm. the rate of slump loss was gradually reduced with the replacement of cement with 2.5% and 5.0% of sda. the reduction range from 80mm to 70mm and from 80mm to 77mm respectively. also, with the application of 7.5% to 12.5% of sda to concrete’s mortar, the concrete workability increased by 8.75% with the reduction in slump fall from 80 to 76mm, and 80 (control) to 73mm (concrete with 12.5% of sda) (table 4). as observed by the authors, sda has great potential for enhancement of concrete workability. it was observed that, sda has high water retaining capacity, so, to obtain good concrete workability with sda, high water cement ratio is suggested for sda-concrete mixing to prevent absorption of large amount of water from the mixed aggregates, and to prevent production of harsh concrete due to poor hydration process in the aggregates. likewise, application of sda in concrete has reduced it compaction factor (cf) from 0.921 (control) to 0.87 (cf) of concrete with 12.5% of sda) which up to 4.4% reduction. the reduction in cf observed might be as a result of good surface property and low specific properties of sda which improve the rate of concrete aggregates’ compatibility. to improve the concrete workability, application of sda in concrete should be up to 12.5% to improve the concrete workability greatly. table 4. workability of concrete with sda (gibi miriyam et al. 2017) percentage of sda (%) 0 2.5 5 7.5 10 12.5 workability slump loss (mm) 80 79 77 76 75 73 compaction factor 0.91 0.90 0.89 0.89 0.88 0.87 in support of gibi et al. 2017), the experimental result of ruhai et al. (2017) likewise indicates that, the concrete reinforced with sda showed a decrease in its slump fall values. according to the authors, the values of slump fall observed were within the range of 30 – 60mm. the increase in the ratio of sda in concrete paste (from 1:1 to 1:3) has caused decrease in slump flow of sdaconcrete mortar from 40 mm (with 1:1 ratio) to 30 mm (with 1:3 mix ratios) (figure 3). therefore, the authors concluded that application of sdf in concrete has a great influence on the reduction of concrete workability. the report of ambika and sabita (2015) proves that; addition of sda to concrete has decreased the concrete workability significantly. this was applicable when the percentages of sda applied in the cast concrete were increasing in the mix (figure 4a). thus, the use of sda in concrete will go in a long way in controlling the segregation in freshly cast concrete. more thick concrete may be produced with the use of sda in concrete mix, and the hydration of the concrete might not be effective. the compaction factor (cf) of the sda-concrete was observed as 0.94 at the inclusion of 15 and 20% of sda in concrete. the value was reduced from 0.94 to 0.93 (figure 4b). having observed this cf, sda was classified as a good aggregates-binder for smooth compatibility. according to observation, the sda have a good surface area and low specific gravity for concrete compassion. according to haveth et al. (2017), sawdust wood wastes (sww) have high moisture absorption capacity. as observed, the pastes samples tested with the inclusion of sawdust, the rate of water absorption of the sww recorded was up to 8.72 ± 0.4% (which is too high). 46 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 fig 3. slump falls of concrete mortar with sda (ruhai et al., 2017) fig 4a. slump values of concrete with sawdust ash (ambika and sabita, 2015) fig 4b. sawdust ash-cement concrete compaction factors (ambika &sabita, 2015) 0 5 10 15 20 25 30 35 40 01:01 01:02 01:03 s lu m p f lo w v a lu e s (m m ) ratio of cement to sawdust in the mix slump fall 0 20 40 60 80 100 120 140 0 5 10 15 20 s lu m p v a lu e s (m m ) percentage of sawdust ash included in the mix (%) slump fall 0,925 0,93 0,935 0,94 0,945 0 5 10 15 20 compaction factors p e rc e n ta g e o f s a w d u st a sh in cl u d e d ( % ) comp. fact. abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 47 2.2.2 consistency of cement paste with sawdust fibre in addition, the findings of hisham et al. (2020) showed that, application of sww in concrete demand for higher volume of water to form consistency with paste. the high viscosity of the aggregates mixed with sdf was noticed to have caused rapid hardening of cement during hydration. this was traced to the absorption of high percentage of an alkaline solution when the fibre was pretreated with the solution before used as a supplement of cement in concrete. with proper pretreatment of sdf before used in concrete, it will go a long way in controlling the high rate of water absorption in concrete which usually dehydrate much water from concrete mix and caused poor concrete-aggregate hydration. it was concluded that application of sdf in concrete required high water cement ratio to attain the standard consistency. furthermore, the report of darweesh and el-suoud (2017) also support that, the use of sawdust wastes in concrete normally increases its consistency. according to the authors, application of sda to concrete paste has brought slight decrease to the consistency of the paste. the reduction was observed to be gradual. as the sda constituent percentage in concrete mix was increasing, the sda-paste consistency was also decreasing (figure 5). fig 5. consistency of cement paste with sawdust ash (darweesh and el-suoud, 2017) the major cause of this was traced to the presence of sod, high content of carbon and fines of sda compared with that ordinary portland cement (opc). in addition, it was observed that a certain percentage of water meant for concrete mixing was absorbed by sda included. 2.2.3 setting time of concrete paste with saw dust fibre as presented in figure 6, the setting time of paste with sda decreased with the increase in the percentage of sda included in the mix. as stated by darweesh and el-suoud (2017), the decrease in the setting time might be a result of the presence of lime in the sda generated from tricalcium and dicalcium silicates hydration process with high pozzolanic compound of sda and cement developed in the reaction (mangi et al. 2017). the findings of hisham et al. (2020) also support the decrease in the sda-cement paste setting time reported by darweesh and el-suoud (2017). as investigated by the authors, both the final and initial setting of concrete paste with sd were decreasing with increase in the percentage of sd in the mix (figure 7). as observed from figure 7, the initial time of the concrete setting range from 39 to 28minutes, while the final one ranges from 60 to 48 minutes with increase in the percentage of sda included (from 0% to 100%). therefore, the increase in the percentage of sdt in concrete will reduce the time specified for its setting, leading to the production of harsh concrete. with this rate of sd-cement paste setting time reduction, the level of water used for paste setting was also increasing. with reduction for water meant for hydration by sd, the elements like: calcium and alumina-silicate might have 23 24 25 26 27 28 29 30 -10 0 10 20 30 c o n si st e n cy o f th e p a st e (% ) percentage of sawdust ash content (%) consistency 48 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 been dissolved during geopolymerization process of the paste. in addition, the report of ozdemir et al. (2022) supports that, application of sdf in concrete always reduced its setting times and also affected the hydration process of the concrete mix, especially, in the area of water absorption. fig 6. initial and final setting time of paste with sawdust ash (darweesh and el-suoud, 2017) fig 7. initial and final setting time of paste with sawdust ash (hisham et al. 2020) more than 98% of concrete compressive strength results obtained were allowed to undertake full hydration process up to 90 days. at 90th day, the sd-concrete increased in its compressive strength. it was observed that, the sd-concrete compressive strength was appreciated when its curing age is increased. likewise, application of sawdust in concrete required higher water/cement ratio for quality concrete production, with good workability and yield high compressive strength. 2.2.4 tensile strength of concrete reinforced with sawdust fibre tensile properties of concrete is the properties possessed by a concrete to resist its tensile splitting and cracks, due to the tensional force (kilani and fapohunda, 2022). as conducted by hisham et al. (2020), the average tensile strength of lightweight concretes (lwcs) was 0 50 100 150 200 250 0 5 10 15 20 25 30 in it ia l n a d f in a l s e tt in g t im e s o f p a st e w it h s d a ( % ) percentage of sawdust ash content (%) init. set. time final. set. time abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 49 decreasing with increase in the percentage of sawdust content included. according to the authors, the test was carried out by replacing certain percentage of coarse and fine aggregates with sawdust, and cured for 28days. from the results of 28days curing, it was observed that, concrete tensile strength decreased from 4.2mpa to 3.9, 3.7, 3.4, and 3.0 mpa with increase in sd content of 0, 25, 50, 75 and 100%. as observed, up to 1.2mpa strength of normal concrete (control) was reduced with the inclusion of sawdust into the concrete mix (figure 8). the reduction in strength was attached to the difference shapes of sawdust particle used, high rate of water absorption of sd and presence of organic substance in sd used. these were developed into formation of weak bonding interaction within the paste of cement, aggregates and sawdust fibre. this has led to the formation of low tensile strength bonding matrices within the concrete composite. so, raw sdf is not suitable for concrete tensile strength increment unless it is treated with chemicals for better improvement. fig 8. tensile strength of concrete with sawdust fibre (hisham et al. 2017) contrary to hisham et al. (2020) report, the findings of joy et al. (2016) proved that, the application of sawdust to concrete mix as contributed to the increase in the tensile strength of the concrete. this increment was observed at 15% of sd inclusion in structural concrete. the maximum tensile strength value observed was 3.58n/mm2 compared with that of the control (3.49n/mm2) was the strength increment of 0.09n/mm2. the next tensile strength increment was observed at the inclusion of 30% of sawdust in concrete, which was 3.53n/mm2 (figure 9). with these, it was observed that, concrete with sawdust get appreciated in tensile strength with the inclusion of 15% and 30% of sawdust. however, the tensile strength increment observed was minimal (0.09n/mm2), but it negates the results, which is based on concrete tensile strength reduction. this strength increment might be because of increase in concrete curing age to 90 days. the concrete with sda shows a little increment in its tensile, especially at its 56th curing day compared with that of the control. the result shows that concrete with 5% of sda yielded 3.2n/mm2 of tensile strength. the maximum strength yielded was more than that of control (2.5n/mm2) by 0.7n/mm2. the result showed that, extension of sda-concrete curing days will increase the hydration process of sda-concrete by forming standard bonding matrices among the concrete composite. ruhal et al. (2017) uses the indirect method of concrete tensile strength testing to determine the tensile strength of sd-concrete. in the investigation, concrete samples were produced using cement to sand ratio of 1:1, 1:2, and 1:3 with water cement ratio of 0.65, 1.00, and 1.40 respectively. the test result shows that, sd-concrete produced developed low tensile strength to that of the tensile strength of normal concrete (control). 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 0 25 50 75 100 t e n si le s tr e n g th o f co n cr e te w it h sa w d u st f ib re ( n /m m 2 ) percentage of sawdust content (%) tensile stre. 50 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 fig 9. tensile strength of concrete with sawdust fibre (joy et al. 2016) still, concrete with 1:3 mixes with 0.65 water-cement ratio had the highest tensile strength (4.1mpa) compared with that of control. the finding shows that concretes with sdf could only gain increment in strength at their long curing ages during which maximum hydration might have been taking place. due to slow in hydration process of sawdust – concrete, longtime of curing is suggested for its sufficient hydration process to really improve its tensile strength yielding capacity. this is achievable with proper treatment of sawdust before applying for concrete operation. likewise, the cement to sawdust ratio in concrete should be limited to that of 1:1 to prevent reduction in its tensile strength. 2.2.5 concrete flexural strength reinforced with sawdust fibre the results of tests on flexural strength of concrete with sawdust fibre (sdf) proofed that, application of sdf to concrete decrease its strength against bending and deflection. as investigated by ruhal et al. (2017), the concrete strength capacity with sawdust fibre were observed using three different mixing ratio of 1:4, 1:3, and 1:1 (cement to sawdust ratio) with different water cement ratios of 1.40, 1.00 and 0.65 respectively. the specimens produced were cured in water for 56, 28, and 7days for proper hydration to take place. from the results obtained, the highest flexural strength of 5.77mpa was observed with the mixing ratio of 1:1, while the least flexural strength (0.77mpa) was obtained at the 56th day of curing in water with 1:3 missing ratio. the result implied that, the percentage of sawdust content in concrete have the great influence on its flexural strength yielding capacity. in other perspective, sawdust fibre was applied for composite reinforcement, which was observed to be a good strength-yielding admixture in composites. according to heckadka et al. (2018), during the experiment, resin composite was produced with different percentages of sawdust fibre as substitute of some percentage of the aggregates. the compositematerial replacements were by 3, 6, and 9% with sawdust, which was referred to as filler. the flexural strength of the composite reinforced with sawdust showed maximum strength increment at the inclusion 3 and 6% of sawdust fibre as presented in figure 10. 3,44 3,46 3,48 3,5 3,52 3,54 3,56 3,58 0 25 50 75 100 t e n si le s tr e n g th o f co n cr e te re in fo rc e d w it h s a w d u st f ib re (n /m m 2 ) percentage of sawdust content (%) tensile stre. abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 51 fig 10. average flexural strength of concrete with sawdust fibre (ruhal et al. 2017) the percentage of strength yielded by including sawdust fibre in composite was by 68% compared with that of control. this was achieved at the inclusion of 3% of sdf in the composite mixing. the least composite flexural strength (44mpa) was observed at the addition of 9% of sdf (filler) in the composite. thus, sawdust waste has the maximum strength yielding capacity for composite reinforcement up to 68% strength increment. so, application of sdf to composite material will make it stronger in resisting the bending, cracking and deformation defects when in usage. in addition, hisham et al. (2020) replaced some percentages of fine and coarse aggregates with sawdust waste (sdw). as investigated by the authors, certain percentages of coarse and fine aggregates were substituted with 25, 50, 75 and 100% of sdw and flexural test was conducted on the sdw-concrete beams produced. the result of the test shows that, sdwconcrete flexural strength decreased from 6.8mpa (control) to 6.2, 5.7, 5.1, and 4.9mpa in order of the increase in the percentages of sdw included in concrete as shown in figure 11. as the percentage of sdw in the concrete mix was increasing from 0% to 100%, the concrete flexural strength was decreased by 27%. with this output, it was observed that concrete flexural strength does not appreciate with the inclusion of sdw. fig 11. concrete’s flexural strength with sawdust fibre (hisham et al. 2020) 0 10 20 30 40 50 60 70 neat resin 0 3 6 9 a v e ra g e f le x u ra l st re n g th o f co n cr e te w it h s a w d u st f ib re (n /m m 2 ) percentage of sawdust (filler) content (%) flexural stre. 0 1 2 3 4 5 6 7 8 -50 0 50 100 150 c o n cr e te f le x u ra l st re n g th ( m p a ) percentage of sawdust included (%) flexural strength 52 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 the experimental result of using sawdust wastes in concrete by joy et al. (2017)proved the findings of hisham et al. (2020) wrong. as reported by the author, there was an increase in the concrete flexural strength from 4.38 n/mm2 (control) to 4.50 n/mm2 at the inclusion of 30% of sawdust fibre as shown in figure 12. however, the flexural strength yielded by substituting some percentages of concrete aggregates with sawdust might be minimal (0.12 n/mm2), yet, concrete strength was developed against deformation. fig 12. flexural strength of concrete with sawdust (joy et al. 2017) furthermore, the report of sasah and kankam (2018) was in agreement with hisham et al. (2020) report. as investigated by the scholars, the brick’s standard mortar flexural strength decreased from 2.54n/mm2 to 0.47 n/mm2 with the increase in percentage of sawdust included from 5 to 50% (figure 13). from the results of the samples prepared from modified brick mortar, it was observed that, the mortar’s flexural strength decreased from 2.56 n/mm2 to 0.85 n/mm2 with the increase in the percentage of sawdust included. therefore, it was observed that, concrete strength against deformation can be increased, if it is reinforced with the treated sawdust fibre, and the little percentage of sawdust should be added to concrete to avoid decrease in strength. fig 13. standard and modified flexural strengths of concrete with sawdust hisham et al. (2020) 4,32 4,34 4,36 4,38 4,4 4,42 4,44 4,46 4,48 4,5 normal 15 20 25 30 c o n cr e te f le x u ra l st re n g th ( n /m m 2 ) percentage of sawdust content (%) flexural (n/mm2) 0 0,5 1 1,5 2 2,5 3 0 5 10 15 20 30 50 f le x u ra l s tr e n g th o f co n cr e te w it h sa w d u st ( n /m m 2 ) percentage of sand replaced with sawdust (%) stand. flexur. modif. flexur. abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 53 2.2.6 modulus of elasticity and temperature transmission of concrete reinforced with sawdust fibre concrete modulus of elasticity (me) as the ratio of stress applied to a concrete structure to its corresponding strain. the structural concrete has to develop good strength against any deformation because of the stress applied on it with substituted 15, 20, 25, and 30% of coarse and fine aggregates with sawdust fibre for the production of concrete. this was carried out to ascertain the capacity of concrete against expansion and contraction conditions, which could lead to deformation and cracking of concrete structures. the result shows that, the elasticity resisting capacity of concrete was decreased from 2.5 x104 n/mm2 (control) to 2.0 x104 n/mm2 with 15% of sawdust content. the inclusion of other percentages of sawdust fibre (20 to 30%) in concrete yielded more strength increment than that of the concrete with 15% of sawdust, 2.22 x104, 2.38 x104 and 2.27 x 104 n/mm2 with 20, 25 and 30% of sdf. but, still less to the strength developed by normal concrete (control) to withstand elasticity defects due to the applied stress on concrete (figure 14). therefore, the application of sd in concrete could lead to increase in its shrinkage, cracks, deformation and creeping. the application of sawdust waste in concrete does not good for the reinforcement of its structural properties against deformation as a result of constant modulus elasticity due to the applied stress. fig 14. sawdust – concrete modulus of elasticity (joy et al., 2017) the result of modulus of elasticity test conducted on sawdust – quarry dust composite followed the same trend with the finding of joy et al. (2017). from the result, it was observed that, the statics modulus of elasticity of sawdust – quarry dust composite decreased from 9.41n/mm2 of the composite produced from 1:1:1 (cement sawdust: quarry dust) to 6.56 n/mm2 with 1:3:3 mix design. the observed reduction in strength was due to the increase in the content of sawdust and quarry dust included in the mix, which is about times three of that of cement mix proportion. with the consideration of average shear modulus of sawdust – quarry dust composite, it was observed that, composite shear strength decreased from 3.90 gpa (of 1:1:1 mix) to 2.43 gpa (from 1:3:3 mix ratio). from authors’ observation, statics and average shear modulus strength of sawdust – quarry dust composite were reduced by 30.3% and 37.7% with application of sawdust in the composite’s mix. (table 5). from the result output, it was concluded that, sawdust waste is not good for the reinforcement of both composite’s and concrete’s modulus of elasticity to prevent unwanted cracks, deflection, shrinkage and shear that might developed from the reinforcement process. 0 0,5 1 1,5 2 2,5 normal 15 20 25 30 s a w d u st c o n cr e te m o d u lu s o f e la st ic it y x 1 0 4 (n /m m 2 ) percentage of sawdust in the mix (%) modul. elastic. 54 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 table 5. statics and average modulus of shear & elasticity of sawdust – quarry dust composite (ibearugbulem et al. 2018) cement : sawdust : quarry mix ratio 1:1:1 1:2:2 1:3:3 static modulus of elasticity (n/mm2) 9.41 8.75 6.56 average shear modulus (gpa) 3.90 3.68 2.43 the concrete transmission temperature is defined as degree of hotness or coldness at which heat is being transferred within the composites of the concrete. it can be measured using thermometer or thermos-guage. the blending of concrete material with 10% substitute of sawdust waste investigated by nimyat and tok (2013) show that, concrete with the blended sawdust waste (sdw) increase in compressive strength with increase in applied temperature. during the investigation, the compressive strength of the concrete with 0% of sdw (control) increased with increase in temperature until 4000c was reached. it was also decreasing until 8000c was reached. while the concrete with 10% of sdw increased in compressive strength until 6000c was reached. its decrease in strength was observed at 8000c temperature (see table 6). table 6. different concrete compressive strengths under different temperatures (nimyat and tok, 2013) percentage of sawdust content (%) concrete compressive strength (n/mm2) water / cement ratio room temp. 2000c 4000c 6000c 8000c 0 20.15 23.31 24.42 18.44 12.22 0.6 10 15.06 15.73 16.09 18.67 14.20 0.6 from table 6, it could be observed that, exposure of sawdust – concrete to thermal expansion increased its compressive strength by 23.97% with 10% inclusion of sawdust fibre up to 6000c. this proof that, sawdust fibre is a good thermal absorption in concrete against splitting, cracking and deformation till 6000c is reached when suggested to thermal transmission. with this result, it was observed that, sawdust –concrete has capacity of withstanding heat transfer within the composites constituent of the concrete up on till 6000c temperature is reached without trace of decrease in temperature. as shown in table 7, normal concrete (with 0% of sd) showed decrease in concrete compressive strength from room temperature of 2000c to 4000c from 1.16 to 1.05 n/mm2. also, the compressive strength of plan concrete was decreased from 1.05n/mm2 (at 4000c) to 1.32 n/mm2 (at 6000c) and 1.51n/mm2 (at 8000c) respectively. while the compressive strength of concrete with 10% of sawdust showed reduction in strength from 1.04n/mm2 of 2000c (room temperature) to 1.02 n/mm2 at 4000c: 2000c and later increased to 1.31n/mm2 at 8000c temperature (table 6). table 7. concrete compressive strength with thermal gain and loss (nimyat and tok, 2013) percentage of aggregate placed sawdust (%) strength gain / loss average percentage loss (%) average percentage gain (%) 8000c: 6000c 6000c: 4000c 4000c: 2000c 2000c: room temperature 0 1.51 1.32 1.05 1.16 29.11 10.22 10 1.31 1.16 1.02 1.04 23.94 7.59 though, the increase in the level of heat transfer within the sd-concrete caused increase in its strength until 8000c, the rate of heat loss /gain shown in the table 7 proofed that, only little increment in concrete strength was observed when suggested to heat. therefore, it was suggested that, concrete with sawdust should not be exposed to high thermal transmission. as presented in table 8, the result of sawdust – concrete thermal sock resistance at 8000c were presented. the concrete with sdw showed good result than that of control. it can be deduced from the investigation that, application of sdw in concrete is good for concrete thermal shock resistance up until 8000c of heat transfer. abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 55 table 8. thermal sock resistance’s result at 8000c (nimyat and tok, 2013) number of resistance in cycle percentage of replacement with sawdust (%) test 1 test 2 test 3 average cycle 3 5 4 4 0 12 14 12 13 10 in addition, hisham et al. (2020) investigated the thermal conductivity properties of concrete with sawdust. in the investigation, the influence of sawdust in concrete was determined by calculating its time of heat transfer after being cured for 28 days in water. according to the author, as the percentage of sawdust included in concrete was increasing, the concrete thermal conductivity properties were decreasing. as observed by the authors, the concrete samples with highest percentage of sawdust had the highest time (188mins) for heat transfer among the lightweight composites produced with sawdust than that of the control (36 minutes). while the time of heat transfer among the concrete samples with 25, 50 and 75% of sawdust in replacement of aggregates were observed to be 61, 108 and 149 minutes respectively (see figure 15). fig 15. thermal conductivity of concrete with sawdust (hisham et al. 2020) in addition, the results of experiment conducted on concrete reinforced with sawdust to enhance its coefficient of thermal conductivity were presented as shown in figure 15. the experimental results showed that, the thermal conductivity coefficient of concrete was decreasing as the percentages of sawdust included were increasing. the decrease in concrete coefficient of thermal conductivity observed were from 0.39 to 0.24, 0.19, 0.13, and 0.09 w/m. k with the increase in the percentage of sawdust content from 0 to 25, 50, 75, and 100% (see figure 16). this result is in agreement with liu et al. (2020) findings stated that, concrete thermal conductivity is lower with increase in the percentage of sawdust content. thus, application of sawdust in concrete is good in controlling the rate of thermal conductivity within the concrete composites, which can improve the durability of concrete. 0 50 100 150 200 1 2 3 4 5 time of heat transfer (mins) / percentage of sawdust content (%) n u m b e r o f sa m p le t e st e d time of heat transfer % of saw dust content 56 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 fig 16. coefficient of thermal conductivity with various percentages of sawdust (hisham et al. 2020) 2.2.7 durability of concrete reinforced with sawdust waste durability is the ability possess by a material or substance to stain long without developing a significant deterioration. while concrete durability is defined as the ability of a concrete to resist abrasion, chemical attack and weathering action in order to maintain its standard engineering properties (kilani et al. 2022). hisham et al. (2020) observed the rate of water absorption in concrete. the result showed that, concrete with sawdust developed high rate of water absorption into the concrete than those of normal concrete. the replacement of 0, 25, 50, 75 and 100% of coarse and fine aggregates with sawdust had caused the increase in the level of water absorption (w.a) in concrete by 9.7, 10.1, 13.4, 15.2 and 16.9% respectively. considering the replacement of concrete aggregates with sawdust fibre, there was increase in the rate of water absorption by 74% while that of 25% of sawdust inclusion was by 4.1% (figure 17). this increment has proofed that, concrete with sawdust waste possess structural porosity and non – reacted silica (hisham et al. 2020). this result is in line with the findings of juarezat (2015) and that of tong et al. (2013). the high rates of water absorption of sd-concrete have to be corrected to improve its durability property. fig. 17 rate of water absorption in concrete with sawdust (hisham et al. 2020) 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0 20 40 60 80 100 120 c o n cr e te t h e rm a l c o n d u ct iv it y (w /m .k ) percentage of sawdust content (%) therm. conductivity 0 20 40 60 80 100 1 2 3 4 5 percentage of sawdust content (%)/ percentage of water absorption of sawdust concrete (%) n u m b e r o f sa m p le s te st e d percent. of water absorpt. abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 57 3. discussions the high rate of global cement production has contributed highly to the emission of co2 and greenhouse gases (ghgs) in the world, causing the destruction of ozone layers. it was observed in the review that application of clinker to the production of cement was found suitable for the reduction of high rate of co2 and ghgs emission up to 52.4%. these emissions were minimized by applying natural admixture to concrete mix. this is a great potential for production of quality concrete, and concrete with very less percentage of co2 and ghgs emissions. the review showed that, there was accurate compaction of concrete aggregates mixed with saw dust ash (sda) due to its low specific gravity and good surface area. also, the percentages of pozzolanic constituents (sio2, al2o3, and fe2o3) of sawdust waste were observed to fall within the range of 76.0% to 89.4% which is greater than that of the limit stated by aci 1999 for supplementary material to be use in concrete. therefore, sd waste was observed to have rich in pozzolanic properties for concrete reinforcement. also, the percentage compositions of the pozzolanic elements (sio2 + al2o3 + fe2o3) in corncob ash (cca) were observed to be within the range of 71.87% to 83.03% which is more than the specified standard stated by aci 1999. likewise, the result of cca x-ray analysis showed that quartz (sio2) is the essential and main mineralogical content of cca, and the next to it is potassium chlorate (kclo3). this showed that, corncob ash possesses both crystalline and amorphous form for standard concrete reinforcement. the results of sem images showed that, application of csa in concrete will really blocks pores, and smoothly mingle with other aggregates for quality concrete production with good durability property. likewise, the application of sawdust in concrete was observed to have reduced the concrete slump fall from 80 to 76mm, and from 80 (control) to 73mm; and thus, increased the concrete workability by 8.75%. while the application of cca in concrete showed increase in concrete workability by 27.9% and 23.5% respectively, and reduced by 1.59%. the review showed that, application of sd in concrete has increased the rate of concrete aggregates’ compatibility 4.4% which is a good quality for strong concreting. the mixing of sda with cca for concrete reinforcement really enhanced the concrete aggregates compatibility. the average slump value of concrete with cca was observed to have decreased to 2mm with 30% of cca from 5mm with 0% of cca. it was also observed that application of sdf in concrete required high water cement ratio to attain the standard consistency. the consistency of cement paste with corncob ash was decreasing with increase in the percentage of cca included. in addition, the rate of water absorption of the pastes with cca was reducing with increase in cca – concrete curing ages. the final and initial setting times of paste with sda were decreasing with the increase in the percentage of sda included by 28.2% and 20%, thus increased the rate of water absorption in concrete and caused poor setting of concrete. concrete paste with cca shows low hydration and setting processes before acquire the desirable hardening state. the densities of sda-concrete were within the limit of 300 to 1800kg/m3 which is classified as light weight concrete. thus, the use of sd fibre in concrete is good for the production light weight concrete. the modified brick mortar’s density observed was increased by 15% with the application of sd waste to its composites. the increase in concrete curing age could lead to the increase in concrete’s compressive strength up to 7.94%. the weight of block with cca was decreasing with the increase in its cca content. the reduction was traced to the reaction of pozzolanic elements with calcium hydroxide (ca(oh)2) which lead to the production of less dense of c-s-h in the mix block composite. the concrete compressive strength with sd was reducing at the initial stages of curing but its strength yielding capacity got increased with increase in curing ages. the more increase in the volume of sd included in concrete, the less is its yielding compressive strengths. the concrete reinforced with cca increased in compressive strength up to 34.5%. concrete with 15% and 30% of sawdust showed increase in concrete tensile strength. the presence of organic substance and difference size particles of sd had caused the formation of weak bonding interaction within the paste of cement, aggregates and sawdust fibre, thus, leading to reduction in concrete’s tensile strength. the application of cca in concrete for cement replacement has shown low tensile 58 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 strength yielding capacity in concrete. sawdust waste has the maximum strength yielding capacity for composite reinforcement up to 68% strength increment but it application in concrete and brick productions lead to the decrease in flexural strength. the use of sawdust waste in concrete does not support reinforcement of its structural properties against deformation from modulus elasticity due to the applied stress. the concrete’s modulus of elasticity reduced from 35809.8 to 26043 (27%) with the inclusion of cca. thus, increased its strength against constant expansion that could result into cracks and deformation. concrete with sd has the capacity to withstand heat / thermal transmission until 6000c after which reduction in strength can take place. concrete with cca showed strength increment until 3000c. the modeling result shows that, at the interaction process, the best neuron number was observed to be 14 in the hidden layers. the result proofed that, ann model used was efficient and had good strength predicting feature, since 0.991 was almost the same with that of experimental result (0.9878). 4. conclusion according to the review on the reinforcement properties and quality of sawdust and corncob wastes for enhancement of concrete properties, the following conclusion was made in according to the earlier stated objectives; from the review, it was observed that more minimized by applying natural admixture to concrete mixing. this leads to the production of concrete with less percentage of co2 and ghgs emissions. in addition, the percentages of pozzolanic constituents (sio2, al2o3, and fe2o3) of sawdust and corncob wastes reviewed were within the range of 76.0% to 89.4% and 71.87% to 83.03%, which were high qualities of supplementary materials for concrete reinforcement. therefore, sd and cc wastes possess high pozzolanic potential for concrete structural strength reinforcement. in addition, the review indicates that the application of sd and cc wastes in concrete has increased the concrete workability by 8.75% and 27.9% respectively. with this increment, the qualities of concrete production were globally appreciated. in addition, the application of sd in concrete has increased the rate of concrete aggregates’ compatibility by 4.4% which is a good for quality concrete production. the consistency of cement paste with corncob ash was decreasing with an increase in the percentage of cca included. in addition, the rate of water absorption of the pastes with cca was reduced with increase in cca – concrete curing ages. the final and initial setting times of paste with sda were decreased with the increase in the percentage of sda included by 28.2% and 20%, thus increasing the rate of water absorption in concrete and caused poor setting of concrete. from the review, it was observed that, densities of interlocking blocks, composite and concrete produced with the inclusion of cca and sd were observed to fall within the limit of light weight concrete, block and composite. therefore, it was concluded that, application of sawdust and corncob wastes in concrete is good for the production of light weight concrete, bricks and composites. like wise from the review, it was observed that, concrete with cca has the potential of increasing its compressive strength by 34.5% while the strength yielding capacity of cc in concrete is very low. the blending of cc with other supplementary material like sawdust in concrete was observed to have increase the concrete compressive strength by 3.9%. concrete with 15% and 30% of sawdust showed increase in concrete tensile strength. the application of cc waste in concrete lead to reduction in concrete tensile strength but increase the composite’s tensile strength by 68%. therefore, it was concluded that, use of cc good for composite’s tensile reinforcement. the ccaconcrete’s flexural strength was low. the blending of cca with other admixture in concrete was observed to have increased the flexural strength of concrete. the review showed that, sd is poor in reinforcing the concrete and composites’ properties against modulus elasticity, statics and average shear modulus. so, cca is appreciated when blended with other material for quality strength yielding in concrete. concrete with cca have capacity of strength increment until 3000c. thus, increase in cca-concrete’s temperature beyond 6000c could result into cracks and deformation. the inclusion of sdw in concrete is good for concrete thermal shock resistance up until 8000c of heat transfer. application of sawdust in concrete is good in controlling the rate of abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 59 thermal conductivity within the concrete composites. application of corn cob ash (cca) to cement – concrete has led to the increase in its workability. it was observed from the review that, ann model used was efficient and had good strength predicting feature, since 0.991 gotten was almost the same with that of experimental result (0.9878). the reinforcing potential of cob corn (cc) in concrete is low, especially on its compressive strength,blending it with other materials like sawdust will make it perform better in concrete. the concrete with sd and cc wastes should be allowed to undergo long hydration process with extension of curing ages to 120, 180 and 210 days. these gaps need quick investigations. application of sawdust in concrete should be preceded with proper treatment to prevent the high rate of water absorption. saw dust fibre needs proper treatment, especially, its rate of water absorption and drying, before its application for concrete reinforcement. the high water cement ratio is required for the use of sdf in concrete. the review shows that sdf were made up of about 61.58% of carbon content, to prevent the delay of sd-concrete setting, proper treatment should be applied to remove carbon effect before use in concrete. high water cement ratio is suggested for sda-concrete mix to prevent the absorption of water meant for hydration process. the addition of sd to concrete should not be more than 12.5% to prevent reduction in concrete workability. it was observed that, low water cement ratio is required to make use of cca in concrete for accurate concrete reinforcement and for quick setting of the paste. applications of other supplementary material together with sd will really minimized the reduction in sd-concrete setting time, then, increase the hydration process of cement – sd – aggregate composites. cca-concrete requires enough time for accurate setting to prevent the production of harsh concrete. it was suggested that, concrete with csa should undergo long hydration process to attain strength yielding of at least 3.75 n/mm2, most especially, from 28 days of curing upward. application of sawdust in concrete required higher water/cement ratio for quality concrete production and high compressive strength yielding. it could be deduced from the experimental results that cca is good for the production of light weight concrete. application of cca in concrete will be well appreciated for the reinforcement of concrete’s tensile strength if it is blended with other admixtures like sawdust. as observed in the review, due to the slow hydration process of sawdust – concrete, long curing age is suggested for sawdust – concrete hydration to really improve its tensile strength yielding capacity. it was recommended that, concrete with sawdust should not be exposed to high thermal transmission. in addition, the exposure of cca – concrete to thermal transmission should not exceed 3000c to avoid weakening and great reduction in concrete strength. the high rates of water absorption of sdconcrete have to be corrected to improve its durability property. engineers and contractors before implementation or before reaching construction stages suggest ann software model for the prediction of sawdust – concrete compressive strength and other strength properties for accurate planning and design. blending of cca with other admixture for concrete reinforcement is recommended for maximum strength yielding against concrete’s deformation and deflection. in addition, its application will improve the concrete properties against chemical attack and serves as water permeability resistance in concrete. 5. references adesanya, d.a., raheem a.a. (2009). a study of the workability and compressive strength characteristics of corncob ash blended cement concrete construction and building materials vol. 23 pp. 311-317. agbi, g.g. (2021). suitability of sawdust as partial replacement for fine aggregate in concrete production. international journal of innovative scientific & engineering@seahi publications 2021, www.seahipaj.org. issn: 2360-896x, 9 (2): 16 – 22. agbi, g.g., akpokodje, o.i., & uguru, h. (2020). compressive strength of commercially produced sandcrete blocks within isoko metropolis of delta state, nigeria. turkish journal of agricultural engineering research (turkager), 1(1), 91-103. http://www.seahipaj.org/ 60 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 akila s, manila a., meera d., nathigamani, g., ramya, s. (2018). a partial replacement of cement with corncob ash in concrete production international journal of advanced research trends in engineering and technology pp.226-233. ali n.; jaffar, a.; anwer, m.; alwi, s.k.k.; anjum, m.n.; ali, n.; raja, m.r.; hussain, a.; ming, x. (2015). the greenhouse gas emissions produced by cement production and its impact on environment: a review of global cement processing. int. journal res. 2015, 2, 488. ambika, n., sabita, d. (2015). a study on strength of concrete with partial replacement of cement with saw dust ash and steel fibre. international journal of engineering research and technology, vol 4, 3, pp 04, http://dx.doi.org/10.17577/ijertv4is030285. astm c618 standard specification for fly ash and raw or calcined natural pozzolan for use as a mineral admixture in portland cement concrete. american society for testing and materials. west conshohocken (pa, usa): astm international (2003). accessed on 26august 2021. aston, a. (2010). bedding for laboratory animals”. aln magazine. archived from the original on september 27, 2015. retrieved october 28, 2015. badejo, s.o. (1995). preliminary study on the utilisation of nigerian sawmill sawdust for the production of water proof cement bonded ceiling boards. frin bulletin. p.58. boob, t.n. (2014) performance of sawdust in low-cost sandcrete blocks. american journal of engineering research, 3, 197-206. chaeyeon l., euntae j., seongho l., changsun j., chaewoon o., kyung n. s. (2020). global trend of cement production and utilization of circular resources. issn 1598-7981,journal of energy engineering, vol. 29, no. 3, pp.57-63, https://doi.org/10.5855/energy.2020.29.3.057. darweesh, h.m., el-suoud, m.r. (2017). sawdust ash substitution for cement pastes – part i. american journal of applied scientific research, 3 (5): 63 – 71. desai p. h. (2018). experimental study on corn cob ash powder as partial replacement of cement in concrete. international research journal of engineering and technology, vol. 5 no.6 pp. 724-728. elzinga, d., j. bennett ,s.j burnard , k.j cazzola, p.j d’ambrosio d., dulac, j.j femandez, pales a., hood c., lafrance m., et al (2015). energy agency perspectives 2015: mobilizing innovation to accelerate climate action. 1st edition international energy agency (iea) publications paris, france, 2015; pp. 1-412. fapohunda, c.a., and kilani, a.j. (2019). structural and application potentials of natural fibers for sustainable production of structural concrete in nigeria: a review. fuw trends in science & technology journal, www.ftstjournal.com. e-issn: 24085162; p-issn: 20485170; december 2019: vol. 4 no. 3, pp. 857 – 863. garcia-gusano d.; hemera i., garrain d., lechon y., cabal h. (2014). life cycle assessment of the spanish cement industries implementation environment –friendly solutions clean technological environmental policy, 17, 59 – 73. gareth, b. (2019). improving the world through better use of concrete. materials, resources and sustainability series, www.riskinsight.com, pp. 1 – 11. george, r.o. & braide, k.h. (2014). stabilization of nigerian deltaic laterites with saw dust ash. international journal of scientific research and management. volume 2, issue, 8, pages 1287-1292. website: www.ijsrm.in issn (e): 2321-3418. gibi m.h., sruthy, b.a., krishnan, g., sruthi, g.r. (2017). an experimental investigation on strength of concrete made with cow dung ash and glass fibre. international journal of engineering research & technology (ijert) http://www.ijert.org issn: 2278-0181 ijertv6is030463 vol. 6 issue 03, march 2017. green, h. (2006). wood: craft, culture, history penguin books, new york, pp. 403, isbn 978 – 11012 – 0185 – 5. hamakareem, m.i. (2018). permeability of concrete and factors influencing it. available online: https://theconstructor.org/concrete/permeability-concrete/1769/ (accessed on 27 april 2022) http://dx.doi.org/10.17577/ijertv4is030285 https://doi.org/10.5855/energy.2020.29.3.057 http://www.riskinsight.com/ abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 61 haseeb, j. (2017). compressive strength of concrete after 7 and 28 days. concrete technology, aboutcivil.com access on 26august 2021. haveth, g., andres, o., jhon, p. (2017). mechanical behaviour of mortar reinforced with sawdust waste. 3rd international conference on natural fibres. advanced materials for a greener world / cnf 2017, 21 – 23, june 2017, braga, portugal. procedia engineering 200 (2017) 325 – 332. heckadka, s.s., nayak, s.y., and gouthaman,p.v., talwar, a., ravishankar v.a., thomas, l.g., mathur, a. (2018). influence of sawdust bio-filler on the tensile, flexural, and impact properties of mangifera indica leaf stalk fibre reinforced polyester composites. matec web of conferences 144, 02024 (2018). heede, v. d. p.; belic, d. (2012). environmental impact and life cycle assessment (lca) of traditional and green concretes: literature review and theoretical calculations. cement concrete composites 34, 431 – 442. hisham, a., ghasan, f.h., abdul-rahman, m.s., rayed, a., hassan, a.a., abdul-aziz, a. (2020). engineering properties of waste sawdust-based lightweight alkali-activated concrete: experimental assessment and numerical prediction. materials 2020, 13, 5490; doi: 10.3390/ma13235490. www.mdpi.com/journal/materials. hussein, k., al-recaby, m., nsaif, m. (2018). stabilization of soft clayey soils with sawdust ashes. matec web of conferences 162, 01006, https://doi.org/10.1051/matecconf/201816201006. bcee32017. ibearugbulem, o. m., christopher. k. a., nwakwasi, n.l., anyaogu, l., arimanwa, j.i., i. c. onyechere, i.c. (2019). structural characteristics of sawdust – quarry dust composite. ssrg international journal of civil engineering volume 6 issue 7, 7-12, july 2019 issn: 2348–8352 /doi:10.14445/23488352/ijce-v6i7p102 © 2019 seventh sense research group®. ikenyiri, p.n., abowei, f.m., ukpaka, c.p., amadi, s.a. (2019). characterization and physicochemical properties of wood sawdust in niger area, nigeria. chemistry international 5(3) 190-197. https://doi.org/10.5281/zenodo.2002187. joy, a.m., jolly, a.k., raju, a.m. and joseph, b.e. (2016). partial replacement of fine aggregates with sawdust for concrete.” international journal for technological research in engineering 3(9):2439– 43. juarez, c., fajardo, g., monroy, s., duran-herrera, a., valdez, p., magniont, c (2015). comparative study between natural and pva fibers to reduce plastic shrinkage cracking in cement-based composite. construction building material; 91:164–170. kaupinnen et al. (2006). occupational exposure to inhalable wood dust in the member state of european union. ann occup. hyg. 50 (6): 549-561. keegan, r. (2020).cement and concrete: the environmental impact. available on: https://www.psci.princeton.edu. khasreen, m.m., banfill, p.f.g, menzies, g.f. (2009). life – cycle assessment and environmental impact building:a review. sustainability 1, 674 -701.available on: https://doi.org/10.3390/su1030674. kilani, a. christopher, f. oluwatobi, a. and charity m. (2022). evaluating the effects of agricultural wastes on concrete and composite mechanical properties: a review. research on engineering structures and materials, 2022; 8(2): 307-336. kilani, a.j., adeleke, o., fapohunda, c.a. (2022). application of machine learning models to investigate the performance of concrete reinforced with oil palm empty fruit brunch (opefb) fibers. asian journal of civil engineering.https://doi.org/10.1007/s42107-022-00424-0. komalpreet, s., jaspal s., sarvesh, k. (2017). a sustainable environmental study on corncob ash subjected to elevated temperature current world environment vol. 13 no. (1) pp.144-150. kukogho, j. aghimien, e.v, ojo, m.o, adams, b.a, akinbosoye, b.s. (2011). assessment of wood waste generated in some selected sawmills in kajola local government area of oyo state. continental journal of agricultural economics, 5(2):8-11. http://www.mdpi.com/journal/materials https://doi.org/10.1051/matecconf/201816201006.%20bcee3-2017 https://doi.org/10.1051/matecconf/201816201006.%20bcee3-2017 file:///c:/users/itec%20cc/desktop/under-review%20publications/jbms%20manuscript/available%20on:%20https:/www.psci.princeton.edu file:///c:/users/itec%20cc/desktop/under-review%20publications/jbms%20manuscript/available%20on:%20https:/www.psci.princeton.edu file:///c:/users/itec%20cc/desktop/under-review%20publications/jbms%20manuscript/available%20on:%20https:/doi.org/10.3390/su1030674 https://doi.org/10.1007/s42107-022-00424-0 62 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 liu, h.y.; wu, h.s.; chou, c.p. (2020). study on engineering and thermal properties of environmentfriendly lightweight concrete made from kinmen oyster shells and sorghum waste. constr. build. mater., 246, 118367. lucy, r. (2018). climate change: the massive co2 emitter you may not know about, 17 december 2018. available on: https://www.bbc.com. makul, n. (2021). a review on methods to improve the quality of recycled concrete. journal of sustainable cement based materials, 10:2, 65-91,https://doi.org/10.1080/21650373.2020.1748742. mangi, s.a., jamaluddin, n., wan, m.h., mohamad, n., sohu, s. (2017). utilization of sawdust ash as cement replacement for the concrete production: a review. engineering science and technology international research journal, vol.1, no.3, sep 2017. issn (e) 2520-7393 issn (p) 2521-5027. mark, o.g., ede, a.n., olofinnade, o., bamigboye, g., okeke, c., oyebisi, s.o. and arum, c. (2019). influence of some selected supplementary cementitious materials on workability and compressive strength of concrete: a review. first international conference on sustainable infrastructural development. iop conf. series: materials science and engineering 640 (2019) 0/2071. doi: 10.1088/ 1757 -899x/ 640/1/0/2071. muhammad b. w., nehal n. a., and khalifa s. a. (2016). use of recycled tire in concrete for partial aggregate replacement. international journal of structural and civil engineering research vol. 5, no. 4, november 2016. murthi, p., poongodi, k., gobinath, r. (2020). effects of corn cob ash as mineral admixture on mechanical and durability properties of concrete-a review. iop conf. series: materials science and engineering 1006 (2020) 012027. iop publishingdoi:10.1088/1757-899x/1006/1/0120271. nimyat, p.s. and tok, y. (2013). effect of saw dust ash (sda) pozzolana on the performance of blended cement paste concrete at high temperatures. international knowledge shearing platform.vol 3, no 11 (2013). https://www.iiste.org/journals/index.php/cer/article/view/8114. nnochiri e. s. (2018). effects of corncob ash on lime stabilized lateritic soil. ssp journal of civil engineering special issue, march 2018. doi: 10.1515/sspjce-2018-0007. obam, s.o. (2012). properties of sawdust, paper and starch composite ceiling board. american journal of scientific and industrial research science huβ. 2012; 3.5; 300:304-300. available:http://www.scihub.org/ajsir.issn: 2153-649x. doi: 10.5251/ajsir. oguche, j. (2021). stabilization of osugu – adupi road’s subbase with sawdust, corncob, and rice husk ashes. a master of engineering thesis submitted to the department of civil engineering, federal university, oye ekiti, nigeria (unpublished), december, 2021. ogwueleka, t.c. (2009). municipal solid waste characteristics and management in nigeria. iran. journal of environmental health science. eng., 6(3):173-180. olafusi, o.s. adewuyi, a.p. sadiq, o.m. adisa, a.f. and abiola, o.s. (2017). rheological and mechanical characteristics of self-compacting concrete containing corncob ash. journal of engineering research (jer), volume 22 no 1 pp. 72-85. oluborode k., olofintuyi, i. (2015). self-compacting concrete: strength evaluation of corncob ash in a blended portland cement. american scientific research journal for engineering, technology, and sciences (asrjets) , issn (print) 2313-4410, issn (online) 2313-4402, volume 13, no 1, pp 123131. oluoti, k., megwai g., pettersson a. and richards t. (2014). nigerian wood waste: a dependable and renewable fuel option for power production. world journal of engineering and technology, 2, p. 234-248. onochie, u.p., e.k. orhorhoro, p.e. oyiboruona (2018).economic potential and benefits of sawdust in nigeria. international journal of research publications, 9(1), 134-141. oyebisi, s.o., olutoge, f.a., ofuyatan, o.m., abioye, a.a. (2017). effect of corncob ash blended cement on the properties of lateritic interlocking blocks.progress in industrial ecology – an international journal, vol. 11, no. 4.pp.373 -387. file:///c:/users/itec%20cc/desktop/under-review%20publications/jbms%20manuscript/available%20on:%20https:/www.bbc.com https://doi.org/10.1080/21650373.2020.1748742 https://www.iiste.org/journals/index.php/cer/article/view/8114 abiodun kilani et al., j. build. mater. struct. (2023) 10: 40-63 63 ozdemir, e., saeidi, n., javadian, a., rossi, a., nolte, n., ren, s., dwan, a., acosta, i., hebel, d., wum j. and eversmann p. (2022). wood-veneer-reinforced mycelium composites for sustainable building components. journal biomimetics, 7(2), 39; https://doi.org/10.3390/biomimetics7020039. pelisser f. barcelos a., santos d., peterson m. and bernardin a.m. (2012). light weight concrete production with low portland cement consumption”. journal of cleaner production no. 23 (1):68 – 4. peter, g.a., masanet, e., horvath, a., stadel, a. (2014). life cycle inventory analysis of concrete production: a critical review. cement concrete composites, 51, 48-48. reinhardt, h. (2013). understanding the tensile properties of concret. cambridge, uk:woodhead publishing; chapter 2, factor affecting the tensile properties of concrete, pp. 19 – 51. rodier, l., villar-cocina, e., ballesteros, j.m., junior, h.s. (2019). potential use of sugarcane bagasse and bamboo leaf ashes for elaboration of green cementitious materials, journal of cleaner production 231, 54 – 63. ruhal, p.m., abdul-rahman, m.s., abdul-awal, s.m, lemar, a. (2017). mechanical and thermal properties of sawdust concrete. article in journal teknologi-august, 2021. sasah, j. and kankam, c.k. (2017). study of brick mortar using sawdust as a partial replacement for sand. journal of civil engineering and construction technology. vol. 8(6), pp. 59-66, july 2017 doi: 10.5897/jcect2017.0450 articles number: 97bc2b264932 issn 2141-2634 copyright ©2017 author(s) retain the copyright of this article http://www.academicjournals.org/jcect. statista research department(2021). production volume of cement in south korea from 2006 to 2017. available on: https://datisinc.com/blog/worldwide-cement-production-from-2015-t02019/#south-korea. accessed on 17november 2022. suwanmaneechot, p., nochaiya, t. and julphunthong, p. (2015). improvement, characterization and use of waste corncob ash in cement-based materials. iop conferenceseries: material science and engineering 103 012023. the european cement association (cembureau), activity report, first edition, cembureau: brussels, belgium, 2017; pp.1-42. available on; https://cembureau/media/1716/activity-report-2017.pdt accessed on 16 october 2022. tiffany, v. (2021). cement tracking progress: the challenge of reaching zero emission in heavy industry. available on: https://www.iea.org. tong, y., zhao, s., ma, j., wang, l., zhang, y., gao, y. (2013). improving cracking and drying shrinkage properties of cement mortar by adding chemically treated luffa fibres. constr. build. mater. ; 71:327–333. udoeyo, f.f., abubakar, s.a. (2003). maize-cob ash as filler in concrete. journal ofmaterials in civil engineering, vol. 15, pp. 205208. https://doi.org/10.3390/biomimetics7020039 http://www.academicjournals.org/jcect https://www.statista.com/aboutus/our-research-commitment https://datisinc.com/blog/worldwide-cement-production-from-2015-t0-2019/#south-korea https://datisinc.com/blog/worldwide-cement-production-from-2015-t0-2019/#south-korea https://cembureau/media/1716/activity-report-2017.pdt https://www.iea.org/ j. build. mater. struct. (2021) 8: 93-102 original article doi : 10.34118/jbms.v8i2.1375 issn 2353-0057, eissn : 2600-6936 pozzolanic properties of white cowpea husk ash wilson u n 1*, gambo z1, mohammed i s 1, eze o c1, odeyemi s o2 1,* department of civil engineering, nigerian defence academy kaduna, nigeria. 2 department of civil and environmental engineering, kwara state university, malete, nigeria. * corresponding author: unwilson@nda.edu.ng received: 07-06-2021 accepted: 07-08-2021 abstract. this research attempts to empirically investigate the pozzolanic properties of white cowpea husk ash (wcha), an agricultural biomass waste, at different percentages of its use as partial replacement of cement in concrete. wcha was obtained after the calcination of white cowpea husk for 3 hours at 5500c. x-ray florescence (xrf) analysis performed revealed that the sample of wcha is a class c pozzolana, which contains 65.4% of the combination of sio2, al2o3, and fe2o3. the wcha shows increase in consistency with increase in the wcha content. this was attributed to the high loss of ignition (loi) of wcha compared to that of the cement. in addition, the results indicated that the initial and final setting time of wcha – cement blended concrete increase with increase in the wcha content. the delay in setting times of wcpa-cement paste could be attributable to the slower pozzolanic reaction. the density of the concrete decreased as the wcha content increases. generally the compressive strength of the wcha concrete increased with increase in curing age and decreases as the wcha content increased from a strength of 28.6 to 20.0 n/mm 2 giving a percentage reduction of 30.1 %. the strength reduction is also attributed to the modification of the bonding properties of the binders’ hydrates. however, the 28 days compressive strength of concrete with up to 10 % wcha content (26.4 n/mm2) satisfied the design characteristic strength of 25 n/mm2. beyond this limit, the compressive strength of the concrete fell below the design strength. hence, 10 % wcha could be regarded as the optimum dose for grade 25 concrete. keywords: concrete, compressive strength, white cowpea husk ash (wcha), x-ray florescence. 1. introduction concrete is reported to be one of the most consumed construction material by man with a worldwide consumption estimated in 2006 of between 21 and 31 billion tonnes (european concrete, 2009; odeyemi et al., 2020). concrete is made from coarse aggregates (gravel or crushed stone), fine aggregates (sand), water, cement and admixtures (european concrete, 2009). cement on the other hand is the most important ingredient in concrete, whose production contributes significantly to the global amount of carbon dioxide (co2) emissions in our environment which is known to be highly inimical and hazardous to human health, making up approximately 2.4 percent of global co2 emissions from industrial and energy sources (marland et al., 1989). however, gas emission during cement production can be reduced by the utilization of mineral additives in concrete (malhotra and mehta, 2002 and awang et al., 2016). there have been extensive studies done on the use of the more common mineral additives in concrete such as; rice husk ash (rha) (habeeb et al, 2009; ogork et al, 2010; atan and awang, 2011; aboshio et al, 2018), fine limestone powder (felekoglu, 2007; ye et al, 2007; esping, 2008), pulverizedfuel ash (sukumar et al., 2008; liu, 2010; siddique, 2011), silica fume (yazici, 2008; gesoglu et al., 2009; turkel, 2009). however, lesser interests are shown on other types of mineral additives due to various factors such as: the availability of certain mineral additives, transportation mailto:unwilson@nda.edu.ng 94 wilson et al., j. build. mater. struct. (2021) 8: 93-102 problems and heterogeneity of the additives chemical components (atan and awang, 2011). a total of 3.3 million tonnes of cowpea dry grain were produced worldwide in 2000 as estimated by food agriculture organization (fao) (iita research, 2001). most cowpeas are grown on the african continent, particularly in nigeria and niger, which account for 66% of world production (singh et al, 1997). brazil is the world's second-leading producer of cowpea seed, accounting for 17% of annual cowpea production (gómez, 2004). large quantity of pods is generated from production of cowpea. utilization of wcha as an additive or partial replacement to cement in concrete production will enhance more cultivation of cowpea. however, limited or no information is available on its previous utilization in concrete 2. materials and methods the materials used for the research include the following: 2.1. white cowpea husk ash wcha was collected from a farmland in gezawa local government area where there is mass production of cowpea. burning of white cowpea (beans) husk was carried out under controlled temperature of between 500 700 ˚c using the incinerator available in school of technology, kano state polytechnic, kano state, nigeria. the ash was ground and sieved to produce a finer ash. 2.1.1. cement the cement used for the investigation is manufactured by dangote cement company (cem ii/al, 42.5n). 2.1.2. aggregate clean river sand (fine aggregate) and crushed rock (coarse aggregate) were used throughout the research. the coarse aggregate size was 20mm and both conformed to bs 882:1992. the wcha before and after calcination are shown in plate 1a and 1b respectively. plate 1a: cowpea pod before calcination plate 1b: calcined cowpea pod ash the fresh concrete was produced manually following the laid down procedure given in bs 1881125 (2013). cement, sand and crushed rock was proportioned by weight as shown in table 1 and mixed homogeneously using water cement ratio obtained from the mix design. fresh concrete with 0, 5, 10, 15, 20 and 25 % wcha replacement of cement by weight respectively were produced following same procedure and treatment. the fresh property of the concrete using slump test was checked and the concrete thereafter was cast in clean and oiled moulds for compressive strength, splitting tensile and flexural strengths. after allowing the concrete to harden for 24 hours, the cubes were demoulded and dipped in a curing tank filled with water until the testing period was reached. plate 2a and 2b shows the batching procedure for the concrete. https://en.wikipedia.org/wiki/nigeria https://en.wikipedia.org/wiki/niger https://en.wikipedia.org/wiki/brazil wilson et al., j. build. mater. struct. (2021) 8: 93-102 95 table 1. material proportioning for concrete % wcpa wcha (kg/m3 ) cement (kg/m3 ) sand (kg/m3 ) granite (kg/m3 ) water (kg/m3 ) 0 0 380 625 1165 190 5 19 361 625 1165 190 10 38 342 625 1165 190 15 57 323 625 1165 190 20 76 304 625 1165 190 25 95 285 625 1165 190 plate 2a and 2b: batching of material 3. results and discussion 3.1. tests on wcha, cement and aggregate the following tests were carried out on various material samples; xrf analysis, specific gravity, consistency, setting time and particle size distribution. the tests were carried out in accordance with the provision by various standard codes discussed in the materials and methods section. the results obtained are presented in tables 2 – 3 and figures 1 6. table 2. oxide composition using xrf analysis oxides wcha (%) cement (%) sio2 41.641 20.171 al2o3 13.682 4.101 fe2o3 10.066 3.899 cao 20.542 63.871 mgo 2.001 2.105 so3 1.401 2.1 na2o 0.234 0.011 k2o 1.135 0.938 p2o5 1.879 0.117 cl 0.086 0.098 tio2 0.287 0.209 cr2o3 0.001 0.003 mn2o3 0.02 0.036 zno 0.237 0.011 sro 0.011 0.232 loi 6.773 2.093 the oxide composition presented in table 2 shows that the cement has cao + sio2: 84.042 (≥ 50 %), cao/sio2: 3.166 (≥ 2 %), so3: 2.1 (≤ 3.5 %), mgo: 2.105 (≤ 5.0 %), cl: 0.098 (≤ 0.1 %). this indicates that the cement satisfied the recommended limit for cem ii 42.5n class given in astm c618 (2005). in addition, the sum sio2 + al2o3 + fe2o3 for wcpa is 65.389 % this is less than the limit (≥ 70 %) provided by astm c618 (2005). however, the material could be regarded as class 96 wilson et al., j. build. mater. struct. (2021) 8: 93-102 c pozzolana since the requirements sio2: 41.641 (≥ 39.90), sio2 + al2o3 + fe2o3: 65.389 (≥ 50 %), so3: 1.401 (≤ 5.0 %), na2o: 0.234 (≤ 1.5) was satisfied. table 3. specific gravities of concrete materials materials values cement 3.15 wcha 2.15 fine aggregate 2.69 coarse aggregate 2.61 from the specific gravities of concrete materials shown in table 3, it was deduced that the specific gravity of the cement is within the recommended value of 3.10 3.16 for ordinary portland cement (opc) (astm c 188, 2005). wcha has a specific gravity of 2.15. this shows that wcha is less dense than opc and hence signifying lesser volume of cement required more volume of equal mass of wcha. the specific gravities of fine and coarse aggregates fall within the specified limit as specified by aci education bulletin, 2007. 3.2. particle size distribution the particle size distribution of the aggregates carried out by dry sieving is presented in figure 1. fig. 1. particle size distribution of fine and coarse aggregates the result of the particle size distribution of fine aggregate as presented in figure 1 shows that the fine aggregate has fineness modulus of 2.57 and it belongs to zone ii class based on bs en 12620:2002+a1:2008 grading limits for fine aggregates. the result of the particle size distribution of the coarse aggregates as presented in the figure shows that the coarse aggregate has dominant particle size of 20 mm with only 71.82 and 21.96 % retained and passing 14 mm sieve respectively. hence, the coarse aggregate could be regarded 20 mm size. in addition, the fineness modulus of the coarse aggregate is 6.97. 3.3. effect of wcha on consistency of cement paste the consistency of cement paste with varied proportion of wcha is presented in figure 2. the consistencies ranged from 30 % at 0 % wcpa to 39 % at 25 % wcpa. this suggests that the consistency of the cement paste increases with increase in wcha content. the increase in consistencies with increase in wcha content could be due to high loi of wcha compared to wilson et al., j. build. mater. struct. (2021) 8: 93-102 97 that of the cement. this finding is similar to the observations of ogork et al (2014) and jaturapitakkul and roongreung (2003). this result is also linked to the lower specific gravity of wcha when compared to that of cement (ogork et al, 2014). fig. 2. consistency of binder with varied proportion of wcpa 3.4. effect of wcha on initial setting and final setting time of cement paste the initial setting and final setting time of wcha-cement paste ranged from 76 to 168 minutes and 172 to 351 minutes respectively for 0 to 25 % wcha replacement as shown in figure 3. the initial and final setting time of wcha-cement is within the allowance specified in bs en 197-1 (2011) (≥ 60 minutes) and (≤ 10 hours) respectively for 42.5 n graded opc. in addition, the results indicate that the initial and final setting times of wcpa – cement paste increase with increase in wcpa content. the delay in setting times of higher percentage content of wchacement paste could be as a result of the slower pozzolanic reaction (jaturapitakkul and roongreung, 2003 and ogork et al, 2014) of wcha. in addition, the delay of setting times of wcha – cement could also be due to lower cement content and dispersion effect provided by the wcha on the cement particles (gesoglu and erdogan, 2007 and ezziane et al., 2010). fig. 3. setting time with varied proportions of wcpa 98 wilson et al., j. build. mater. struct. (2021) 8: 93-102 3.5. effect of wcha on the properties of fresh concrete the workability of the fresh concrete using slump test method carried out in accordance with bs 1881-102(2000) was used to assess the effect of wcha on the properties of fresh concrete. the result as presented in figure 4 shows that the workability of the fresh concrete reduces with increase in wcha content. the reduction in workability could be as a result of the decrease in fluidity of the mix due to high water demand of wcha (obilade, 2014). in addition, the reduction could also be attributed to reduction in density of the mix as wcha content increases (said et al., 2014 and ogork and auwal, 2016) as well as its fineness modulus as compared to that of cement. fig. 4. workability of wcha – concrete 3.6. effect of wcha on the density of concrete the effect of wcha on the density of concrete is shown in figure 5. the density of the concrete decreased as the wcha content increases possibly owing to the lower specific gravity of wcha than that concrete. the peak density is at 5% replacement of wcha. the density range between 2515 kg/m3 – 2286 kg/m3. fig. 5. effect of wcha on density of concrete wilson et al., j. build. mater. struct. (2021) 8: 93-102 99 3.7. effect of wcha on the compressive strength of concrete generally the compressive strength of the wcha concrete increased with increase in curing age and decreases as the wcha content increased. the strength declined from 28.6 to 20.0 n/mm2 giving a percentage reduction of 30.1 % as shown in figure 6. the reduction in strength could be attributed to decrease in densities of the concrete as wcha content increases. the strength reduction could also be as a result of modification of the bonding properties of the binders’ hydrates as reported by phan et al, 2001 and kanema, 2007). however, the 28 days compressive strength of concrete with up to 10 % wcha content (26.4 n/mm2) satisfies the design characteristic strength of 25 n/mm2. beyond this limit, the compressive strength of the concrete was below the design strength. hence, 10 % wcpa could be regarded as the optimum dose for grade 25 concrete. fig. 6. compressive strength of wcha – concrete 4. conclusions from the oxide composition of wcha, it can be concluded that wcha satisfies the requirement for class c pozzolana as provided by astm c618. the consistency, initial and final setting time of cement increased with increase in wcha content. wcha reduces the workability of a concrete. grade 25 concrete can be satisfactorily produced using up to 10 % wcha replacement of cement by weight. disclosure statement no potential conflict of interests of any form regarding the publication of this manuscript is available. acknowledgement all contributors were acknowledged including a late colleague that assisted in the research. funding and sponsors: this research was self-funded. with pain, we wish to acknowledge the tremendous scholarship of late dr. j. o. afolayan who initiated this research concept and therefore dedicate the entire work to his loving memory. 100 wilson et al., j. build. mater. struct. (2021) 8: 93-102 5. references aboshio, a., shuaibu, h. g. and abdulwahab, m. t. (2018). properties of rice husk ash concrete with periwinkle shell as coarse aggregates. nigerian journal of technological development, vol. 15, no. 2, pp. 33–38. aci education bulletin (2007). aggregate for concretematerials for concrete construction. developed by committee e-701, american concrete institute, 38800 country club dr. farmington hills, michigan, united state. astm c618 (2005). standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete. america standard of testing materials international, west conshohocken. atan m. n. and awang h. (2011). the compressive and flexural strengths of self compacting concrete using raw rice husk ash. journal of engineering, science and technology, vol. 6, no. 6, pp. 720-732 awang h., atan m. n., zainul abidin n. and yusof n. (2016). a cost-reduction of self compacting concrete incorporating raw rice husk ash. journal of engineering science and technology. vol. 11, no. 1, pp. 096–108 bs 1881 – 102 (2000),’ method for determination of slump’ british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. bs 1881-125 (2013) testing concrete. method for mixing and sampling of fresh concrete in the laboratory. british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. bs 882. (1992). specification for aggregates from natural sources for concrete. british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. bs 882. (1992). specification for aggregates from natural sources for concrete. british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. bs en 12620:2002+a1:2008. (2008). specification for aggregate from natural sources for concrete. british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. bs en197-1 :(2011). “composition, specification and conformity criteria for common cements”. british standard bsi group headquarters 389 ciswick high road, london, w4 4al, uk, standards policy and strategy committee. esping, o. (2008). effect of limestone filler bet(h2o)-area on the fresh and hardened properties of self compacting concrete. cement and concrete research, 38, 938-944. european concrete (2009). sustainable benefits of concrete structures. european concrete platform asbl, brussels, belgium. ezziane, k., kadri, e.h., hallal, a. and duval, r. (2010). effect of mineral additives on the setting of blended cement by maturity method. materials and structures, 43, 393-401. felekoglu, b. (2007). utilisation of high volumes of limestone quarry wastes in concrete industry (selfcompacting concrete case). resources, conservation and recycling, 51, 770-791. gesoglu, m. and erdogan, o.e. (2007). effect of mineral admixtures on fresh and hardened properties of self-compacting concretes, binary, ternary and quaternary systems, material structures, 40, 923-937. wilson et al., j. build. mater. struct. (2021) 8: 93-102 101 gesoglu, m., guneyisi, e. and ozbay, e. (2009). properties of self compacting concretes made with binary, ternary, and quaternary cementitious blends of fly ash, blast furnace slag, and silica fume. construction and building materials, 23(5), 1847-1854. gómez, c. (2004). "cowpea post-harvest operations". food and agriculture organization of the united nations. retrieved 2017-04-19. habeeb, g.a. and fayyadh, m.m. (2009). rice husk ash concrete: the effect of rha average particle size on mechanical properties and drying shrinkage. australian journal of basic and applied sciences. 3(3): p. 1616-1622. iita (2008). the international institute of tropical agriculture (2008). retrieved from http://intranet/iita4/crop/maize.htm jaturapitakkul, c. and roongreung, b. (2003). cementing material from calcium carbide residue rice husk ash, journal of materials in civil engineering, 15(5), 470-475. kanema m. (2007). doc. thes (french), univ. cergy-pontoise. liu, m. (2010). self-compacting concrete with different levels of pulverized fuel ash. construction and building materials, 24(7), 1245-1252. malhotra, v.m. and mehta, p.k. (2002). high-performance, high-volume fly ash concrete, supplementary cementing materials for sustainable development, inc., ottawa, canada. marland, g., boden, t.a., griffin, r.c., huang, s.f., kanciruk, p. and nelson, t.r. (1989). estimates of co2 emissions from fossil fuel burning and cement manufacturing, based on the united nationals energy statistics and the u.s. bureau of mines cement manufacturing data. report no. #ornl/cdiac-25, carbon dioxide information analysis centre, oak ridge national laboratory, oak ridge, tennessee, usa. odeyemi, s. o., atoyebi, o. d. and ayo, e. k. (2020). effect of guinea corn husk ash on the mechanica l properties of lateritic concrete. iop conf. series: earth and environment science, 445, 012034, pp. 111. ogork, e. n. and uche, o. a. (2014). effects of groundnut husk ash (gha) in cement paste and mortar. international journal of civil engineering and technology (ijciet), volume 5, issue 10, pp. 88-95. ogork, e.n. and auwal, a.m. (2016): mechanical properties of self-compacting concrete (scc) made with corn-cob ash (cca). book of proceedings of the 15th annual international conference/ nigerian materials congress (nimacon 2016), 21st – 25th november, 2016, ahmadu bello university, zaria kaduna state, nigeria, pp. 379-383. phan l.t., lawson j.r. and davis f.l. (2001). material structure 34, 83–91. siddique, r. (2011). properties of self-compacting concrete containing class f fly ash. materials and design, 32, 1502-1507. singh, b. b., chambliss, o. l. and sharma, b. (1997). "recent advances in cowpea breeding" (pdf). in singh, b. b.; mohan, d. r.; dashiell, k. e.; jackai, l. e. n. (eds.). advances in cowpea research. ibadan, nigeria: international institute of tropical agriculture and japan international research center for agricultural sciences. sukumar, b., nagamani, k. and raghavan, r. s. (2008). “evaluation of strength at early ages of selfcompacting concrete with high volume fly ash,” construction and building materials, vol. 22, no. 7, pp. 1394–1401. turkel, s. and altuntas, y. (2009). the effect of limestone powder, fly ash and silica fume on the properties of self-compacting repair mortars. sadhana (india), 34(2), 331-343. http://www.fao.org/documents/card/en/c/6ecefb19-b344-4691-bb92-22888eef05b5/ http://intranet-/iita4/crop/maize.htm http://intranet-/iita4/crop/maize.htm http://pdf.usaid.gov/pdf_docs/pnacb024.pdf https://en.wikipedia.org/wiki/international_institute_of_tropical_agriculture 102 wilson et al., j. build. mater. struct. (2021) 8: 93-102 yazici, h. (2008). the effect of silica fume and high-volume class c fly ash on mechanical properties, chloride penetration and freeze–thaw resistance of self-compacting concrete. construction and building materials, 22(4), 456-462. ye, g., liu, x., de schutter, g., poppe, a.m., and taerwe, l. (2007). influence of limestone powder used as filler in scc on hydration and microstructure of cement pastes. cement and concrete composites, 29, 94-102. j. build. mater. struct. (2020) 7: 42-50 original article doi : 10.34118/jbms.v7i1.137 issn 2353-0057, eissn : 2600-6936 stabilization of compressed earth block clayey materials from adrar (algeria) by lime and crushed sand abbou m 1,2,*, semcha a 1,2, kazi-aoual f 2 1 université ahmed draia,adrar, algeria. 2 laboratoire des matériaux labmat, l’ecole nationale polytechnique d’oran – maurice audin, algeria. * corresponding author: moh.abbou@univ-adrar.dz received: 01-02-2020 accepted: 25-03-2020 abstract: the objective of this article is to determine the physical and mechanical properties of stabilized compressed earth bricks (sceb), made from a mixture of clay with crushed sand, and stabilized by lime. in this study, we first examine the identifying properties of raw materials. then an experimental study was conducted with cylindrical test pieces of a mixture of clay and crushed sand prepared by the addition of lime and statically compaction, to study the physical and mechanical characteristics of the mixture. the experimental study shows that for use as a building material, the clay mixture with 30% crushed sand and stabilized with 4% and 6% lime is the optimum mixture for as a stabilized compressed earth bricks. key words: clay, crushed sand, lime, sceb, physico-mechanical properties. 1. introduction for almost 10,000 years, the earth has been one of the main building materials used on our planet. more than a third of the world's inhabitants today live in earthen habitats. there are very many earth construction methods which reflect the identity of the place; like adobe frames, compressed blocks, rammed earth … (houben and guillaud, 2006). in addition, several studies are devoted to the ceb technique and the various modes of stabilization (rigassi, 1995), for the improvement of mechanical resistance as well as durability (porosity, resistance to erosion etc): (winterkorn, 1975; united nations, 1992; symons et al., 1999; gonzález-lópez et al., 2018). in these studies, it emerges that chemical lime treatment is one of the solutions adopted. the effect of adding lime causes physico-mechanical changes on treated soils (le roux and rivière, 1969; bell, 1996; cabane, 2004; malkanthi et al., 2020). these changes are very slow at room temperature. it takes several months or even years before its effects can be appreciated (arabi and wild, 1989; rao and shivananda, 2005; lasladj, 2009; cabane, 2004). in contrast, the granular composition of the earth is influenced on the mechanical properties and durability of sceb (mkaouar et al., 2019; muhwezi and achanit, 2019). like other localities in the adrar region (southern algeria), earthen constructions made from local materials have proven their existence for millennia. in this context, experimental work is carried out in particular in the design of a stabilized compressed earth block (sceb). the latter expresses the modern evolution of the block of molded earth (the adobe), with the aim of inscribing a new technique of raw clay construction in the adrar region which is known by the adobe technique. this technique of compressed and stabilized earth brick, based on clay offers a new opportunity to the saharan environment and meets the criteria of sustainability. abbou et al., j. build. mater. struct. (2020) 7: 42-50 43 2. materials and technical methods 2.1. identification of the materials used the study targeted two materials that are found in abundance in the adrar region: the first is clay soil and the second is crushed sand from local quarries. 2.1.1. the clay the studied clay is localized in the lower cretaceous commonly called intercalary continental. in the first part of the lower cretaceous sediment area are covered by a thick layer of sand deposits, silt, sandstone debris, quartz pebble and locally anhydrite). the clay deposit of the adrar region (sbâa) in algeria is located at few kilometers north of the town of adrar (east of the national road n ° 06). the material has a red color. however, two complementary methods, wet sieving and sedimentation analysis, respectively according, to xp p94-041(1995) and nf p94-057(1992), determined the particle size distribution. the plastic properties of the fine fraction, particles smaller than 400 μm, were measured as defined in nf p94-051(1993). the density of the solid particles (gs) was measured using a pycnometer nf p 94-054(1992). moreover, analyzes of the chemical compositions are carried out at the center for studies and technological services in the building materials industry laboratory in boumerdès (algeria). the reference used for the choice of earth proposed for the manufacture of sceb is based on the recommendations of craterre (international center for earth construction), houben and guillaud (1995), and the standard xp p 13-901. table 1. geotechnicals properties of the clay used. proprieties values sand ( > 0,02mm) 9% silt (0,02-0,002mm) 54% clay ( <0,002mm) 37% liquid limit wl 81% plastic limit wp 34% plastic index ip 47 vb 8 specific density γs 2.6 g/cm3 table 2. chemical composition of the clay of the adrar. compounds values (%) so4 2 0.41 caco3 3.6 cl 0.14 insoluble (sio2al2o3 fe2o3caomgo) 95.92 2.1.2. crushed sand the quarry is located on the southern part of the center of the city of adrar. the trails leading to the deposit are easy to access. 44 abbou et al., j. build. mater. struct. (2020) 7: 42-50 table 3. physicals properties of the crushed sand. proprieties values equivalent de sable 36.49 % specific density 2.5 g/cm 3 apparent density 1.46 g/cm 3 finesse model 2.79 100 10 1 0,1 0,01 1e-3 1e-4 0 20 40 60 80 100 % p e rc e n t fi n e r b y w e ig h t (% ) grain size (mm) recommendation range nf px p13-901 % crushed sand % clay of adrar(sbaa) fig. 1. particle size distribution of clay and crushed sand. 2.1.3. lime the lime used in this study is the slaked lime ca (oh)2 ,obtained after the hydration of quicklime (cao) produced in the wilaya of ghardaia. 2.2. technical methods 2.2.1. formulation houben and guillaud (1989) highlight some feedback on the formulation of soil-based products and more specifically compressed earth bricks. reference particle size zones are used to determine the ability of a soil to be compressed or not. according to the standard xp13-901, (2001) and the recommendation of the craterre, the approach is to bring on the same granulometric diagram the curves of sandy and clay soils as well as the outline of the desired optimal curve. this method gives the proportion of the finest earth to be mixed with the coarsest earth to obtain a texture that approaches the optimal curve, which can be the midline of the spindle. for the preparation of the mixture (clay and crushed sand), a study on different mixtures is carried out. as a result, the mixture is composed of 30% clay and 70% crushed sand, has shown a composition that approaches it to the middle line of the recommended spindle. the initial amount of lime required to stabilize the blends is 4% by dry weight of the mixture, was determined according to the method developed by eades and grim (1966), astm d 627699a (1996). the ph measurement test assesses the lime content needed to produce a saturated solution of lime in a soil suspension in water and to fully satisfy the ion exchange. the ph threshold is set at 12.4. the amount of lime to obtain this ph is known as the point of attachment of lime. from this ph value, the additional lime is supposed to be available for the development of pozzolanic reactions. so lime dosages of 2%; 4%; 6% are chosen for the mixtures. abbou et al., j. build. mater. struct. (2020) 7: 42-50 45 100 10 1 0,1 0,01 1e-3 1e-4 0 20 40 60 80 100 % p e rc e n t fi n e r b y w e ig h t (% ) grain size (mm) recommendation range of nf px p13-901 mixture 30% clay+ 70% curshed sand crushed sand clay fig. 2. particle-size distribution of the clay and crushed sand mixtures. 2.2.2. optimization, design and manufacture of test specimens according to studies by mesbah et al. (1999) and p'kla (2002), static compaction is better suited to clay soils, and the determination of optimal water content for ceb from the proctor test is inappropriate because compaction is not the same as that of a static compaction used for the manufacture of the ceb. however, this theme is one of the objectives of this study. to optimize the water content of the mixtures, we have also based on the study conducted by olivier and mesbah (1986), which showed that regardless of the materials, the stabilization mode or the compression forces implemented, the optimum water content of manufacturing wocs (ocs: optimum static compaction), correspond to both the maximum dry density and the maximum compressive strength. the raw earth mixtures were compacted under a pressure of 3mpa, using a press with a constant speed is equal to 1.27mm / min. before compacting, the raw material is mixed with a predetermined amount of water in a kneader for 15 minutes. this time is sufficient to ensure a good homogeneity of the mixture (kouakou and morel, 2009). the wet sample is then placed in a sealed environment to prevent loss of water for 24 hours. this step allows the homogeneous redistribution of the water content. finally, the wet material is introduced into a hollow cylindrical mold (fig. 3), in order to obtain cylindrical test pieces (10 × 5) cm of slenderness equal to 2, for each mixture. however, these specimens do not have the same dimensions as those used for concrete since our maximum particle size is less than 5mm (p’kla, 2002) and compacted by applying the pressure level fixed by a press. the material is compacted vertically at the top and at the bottom by means of two cylindrical pistons (fig.3). five test pieces were made for each mixture. fig. 3. optimization of the water content of the crushed sand clay mixture. 46 abbou et al., j. build. mater. struct. (2020) 7: 42-50 2.2.3. condition of cure all test specimens made from the crushed clay-sand mixture are stored in the laboratory at a temperature, t = 20 ° c to a constant mass (fig.4.a). in addition, the covered cylindrical test pieces are stored in an oven at a temperature t = 65 ° c. for different durations of 7 days, 14 days, 28 days and 90 days (fig.4.b). the test specimens concerned by this mode are the sand-cracked clay mixtures plus the different percentages of the slaked lime. to study of the effect of cure time on the mechanical properties of mixtures. fig. 4. the method of conservation of the test pieces. 3. results end discussions 3.1. optimum water content and maximum density fig. 5 shows the optimization obtained for the static compression mixture of the order of 3 mpa. the optimization method is similar to the method used by olivier and mesbah (1986) when static compaction is used, the same method was used to optimize the clay-sand mixture with lime. in this work, the optimal water content and the maximum density of the mixture constituted by local materials are optimized. fig.6 shows that increasing the proportion of lime on the mixture caused an offset of the optimal water content of compaction to higher water contents and a decrease in dry densities. this modification of the optimum is similar with the study conducted by le roux and rivière (1969) on the introduction of lime into a soil of a different clay nature. 4 6 8 10 12 1,68 1,70 1,72 1,74 1,76 1,78 1,80 d ra y d e n s it y water (%) mixture clay +crushed sand fig. 5. optimization of the water content of the crushed sand clay mixture. a b abbou et al., j. build. mater. struct. (2020) 7: 42-50 47 11 12 13 14 15 16 17 18 19 20 21 22 23 1,56 1,57 1,58 1,59 1,60 1,61 1,62 1,63 1,64 1,65 1,66 1,67 1,68 1,69 1,70 1,71 d ry d e n s it y water (%) mixture with 2%lime mixture with 4%lime mixture with 6%lime fig. 6. optimization of the water content of the mixture with slaked lime. 3.2. mechanical properties 3.2.1. dry compressive strength fig.7 shows the effect of lime through the results of variation in dry compressive strength as a function of lime dosage at the age of 7, 14, and 28 days of cure. through the figure below we note that for a stabilization of 2%, 4% and 6% we have resistances to the dry compression at 28 days respectively of 3.2, 4.59 and 5.6 mpa. according to these results, it is noted that there is an increase in the dry compressive strength as a function of the lime content for the crushed clay-sands mixture. indeed, at the age of 28 days, there is formation of portlandite and formation in very small quantities, hydrated calcium silicate and aluminates phases that ensure the bonds between the particles and enhance the mechanical performance of the mixture. these findings were observed by the authors bell (1996), maubec (2010). 0 2 4 6 0 1 2 3 4 5 6 d ry c o m p re s s iv e s tr e n g th ( m p a ) lime (%) 0% lime 7 days 14 days 28 days fig. 7. dry compressive strength of lime-based test specimens based on lime-slurry dosage, and age of preservation. 3.2.2. dry tensile strength the results of the tensile splitting test are presented in fig. 7, which shows an increase in the tensile strength of the test pieces as a function of the increase in the dosage of slaked lime at the age of 90 days cure. 48 abbou et al., j. build. mater. struct. (2020) 7: 42-50 however, for stabilization with slaked lime, the tensile strength of the cylinders (mixtures) gradually increases. the maximum average resistance is reached with a content of 6% of lime that is 1.4 mpa. 0 2 4 6 8 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 d ry t e n s il e s tr e n g th ( m p a ) lime (%) dry tensile strength the 90 days fig. 8. tensile strength of specimens as a function of 90-day slaked lime dosage. 3.3. capillary absorption the results show that there is a difference between specimens at the age of 28 and 90 days of cure, different assays in lime and non-stabilized specimens. for a stabilization at 2, 4 and 6% of slaked lime, the percentage of capillary absorption decreases respectively 18.53, 17.56 and 16.92% at 28 days, at 15.95, 15.3 and 14.8 at 90 days. the difference in these values is approximately 2.3% moreover; the value of the absorption of the mixture without the addition of lime is of the order of 20.14%. so, the slaked lime stabilization resulted in a more compact and less porous mix. 0 2 4 6 13,5 14,0 14,5 15,0 15,5 16,0 16,5 17,0 17,5 18,0 18,5 19,0 19,5 20,0 20,5 a b ( % ) lime (%) 28 days 90 days 0% lime fig. 9. capillary absorption as a function of lime dosage at 28 and 90 days of cure. 4. conclusions the aim of this work was to study the effect of the content of slaked lime on the mechanical properties and the capillary absorption of test pieces made from local materials (clay + crushed sand) statically compacted at 3mpa. based on the results of this experimental study, the following conclusions are drawn: • optimum moisture content increases with increasing rate of slaked lime. • dry density decreases with increasing lime rate. abbou et al., j. build. mater. struct. (2020) 7: 42-50 49 • the dry compressive strength is improved by the addition of lime that depending on the age of preservation, so the maximum value of the dry compressive strength obtained at 28 days of cure with 6% lime off is equal to 5.6mpa. • increasing and improving the splitting tensile strength as the percentage of slaked lime increases. the tensile strength at 90 days of treatment obtained with a stabilization at 6% of slaked lime is equal to 1.41 mpa, while the specimens stabilized at 4% of lime extinguished at 90 days of cure gave about half of the resistance of tensile specimens stabilized at 6%, is 0.77mpa. • for slaked lime stabilization, cylindrical samples have a small percentage for capillary absorption. this depends on the increase in lime content and the cure time. • in view of these results, we can say that the addition of stabilizer (slaked lime) remarkably improves the mechanical characteristics of the mixture as well as the properties (durability) of the absorption. 5. references arabi m., & wild s. (1989). property changes induced in clay soils when using lime stabilization. municipal engineer (london), 6(2), 85 – 99. astm d6276-99a. (1996) standard test method for using ph to estimate the soil-lime proportion requirement for soil stabilization. 427 american testing and materials society, philadelphia. bell, f. g. (1996). lime stabilization of clay minerals and soils. engineering geology, 42(4), 223-237. cabane n (2004). sols traités à la chaux et aux liants hydrauliques: contribution à l'identification et à l'analyse des éléments perturbateurs de la stabilisation, thèse de doctorat, ecole nationale supérieure des mines de st etienne, université jean monet, 182 p. eades, j. l., & grim, r. e. (1966). a quick test to determine lime requirements for lime stabilization. highw res rec 139:61–72. gonzález-lópez, j. r., juárez-alvarado, c. a., ayub-francis, b., & mendoza-rangel, j. m. (2018). compaction effect on the compressive strength and durability of stabilized earth blocks. construction and building materials, 163, 179-188. houben h., & guillaud h. (1989). traité de construction en terre. 3ème ed. parenthèse, editor. france: habitat ressource;. p. 355. houben h., & guillaud h. (1995). traité de construction en terre, craterre. editions paranthèses, marseille. houben h., & guillaud h. (2006). traité de construction en terre. craterre, edition parenthèse, kouakou, c. h., & morel, j. c. (2009). strength and elasto-plastic properties of non-industrial building materials manufactured with clay as a natural binder. applied clay science, 44(1-2), 27-34. lasledj a. (2009). traitement des sols argileux à la chaux : processus physico-chimique et propriétés géotechniques, thèse de doctorat, université d'orléans, 359 p. le roux, a., & rivière, a. (1969). traitement des sols argileux par la chaux. bulletin de liaison des laboratoires des ponts et chaussées, paris (40), 59-95. malkanthi, s. n., balthazaar, n., & perera, a. a. d. a. j. (2020). lime stabilization for compressed stabilized earth blocks with reduced clay and silt. case studies in construction materials, 12, e00326. maubec n. (2010). approche multi-échelle du traitement des sols à la chaux études des interactions avec les argiles. thèse de doctorat, université de nantes, france. p217. mesbah, a., morel, j. c., & olivier, m. (1999). comportement des sols fins argileux pendant un essai de compactage statique: détermination des paramètres pertinents. materials and structures, 32(9), 687-694. 50 abbou et al., j. build. mater. struct. (2020) 7: 42-50 mkaouar, s., maherzi, w., pizette, p., zaitan, h., & benzina, m. (2019). a comparative study of natural tunisian clay types in the formulation of compacted earth blocks. journal of african earth sciences, 160, 103620. muhwezi, l., & achanit, s. e. (2019). effect of sand on the properties of compressed soil-cement stabilized blocks. science, 4(1), 1-6. nf p 94-05. (1993). sols : reconnaissance et essais – détermination des limites d'atterberg – limite de liquidité à la coupelle limite de plasticité au rouleau. afnor. nf p 94-054. (1992) sols : reconnaissance et essais – détermination de la masse volumique des particules solide des sols méthodes du pycnomètre à l'eau. afnor. nf p 94-057. (1992).sols: reconnaissance et essais – analyse granulométrique des sols méthode par sédimentation. afnor. olivier, m., & mesbah, a. (1986). le matériau terre: essai de compactage statique pour la fabrication de briques de terre compressées. bull. liaison lab. ponts et chaussées, 146, 37-43. p'kla, a. (2002). caractérisation en compression simple des blocs de terre comprimée (btc) : application aux maçonneries « btc-mortier de terre. thèse de doctorat, institut national des sciences appliquées de lyon, france. rao, s. m., & shivananda, p. (2005). role of curing temperature in progress of lime-soil reactions. geotechnical & geological engineering, 23(1), 79–85. rigassi v. (1995). blocs de terre comprimée. volume i. manuel de production, craterre-eag, friedrich vieweg & sohn, braunschweig, allemagne, 104 p. symons, m. g., & poli, d. c. (1999). properties of australian soils stabilised with cementitious binders. structural materials and assemblies group, university of south australia, the levels, south australia. united nations, (1992). earth construction technology. united nations centre for human settlements, nairobi, kenya, 200 p. winterkorn, h. f. (1975). soil stabilization. in foundation engineering handbook,winterkorn, h.f. & fang, h.-y., van nostrand reinhold company, 750 pp. xp p 94-041. (1995). sols : reconnaissance et essais –identification granulométrique méthode de tamisage par voie humide. afnor. xp p13-901. (2001).blocs de terre comprimée pour murs et cloisons, définitions –spécifications méthodes d'essaiconditions de réception j. build. mater. struct. (2020) 7: 236-254 review article doi : 10.34118/jbms.v7i2.776 issn 2353-0057, eissn : 2600-6936 an investigation into tensile structure system: construction morphology and architectural interventions mohammad arif kamal architecture section, aligarh muslim university, aligarh, india. corresponding author: architectarif@gmail.com received: 29-08-2020 accepted: 26-11-2020 abstract. tensile structures represent a new chapter in the history of building structures. tensile structure system are capable of spanning large distances while incurring very little weight on supporting structure, developments in the design of fabric structure can dramatically change the ways in which permanent building construction is conceptualized. this paper reviews the current methods and systems for design and construction of fabric structures. the paper begins with a brief historical evolution and explanation of the various types of fabric structure that have previously been built. subsequent topics address the development of computational analysis methods, innovative construction techniques, fabric material types, properties and their characteristics. in this paper, a qualitative descriptive evaluation research method has been used. the research methodology comprises of case studies, visual observation and data collection. finally, five case studies around the world have been presented to validate and illustrate the various modern trends and the direct application of design and construction methods of tensile structure system. key words: tensile structure system, morphology, architectural interventions. 1. introduction a tensile structure is a construction of elements carrying only tension and no compression or bending. tensile structures are the most common type of thin-shell structures. a tensile membrane structure is most often used as a roof, as they can economically and attractively span large distances. most tensile structures are supported by some form of compression or bending elements, such as masts, compression rings or beams. fabric structures are tensile structures in which a membrane is 'stretched' to form a threedimensional surface that can be used to create a roof, shading, or decorative component. tensile structures have long been used in tents, where the guy ropes and tent poles provide pre-tension to the fabric and allow it to withstand loads. steady technological progress has increased the popularity of fabric-roofed structures. the low weight of the materials makes construction easier and cheaper than standard designs, especially when vast open spaces have to be covered (figure 1). however, not only could tension fabric be used as an effective roofing material for large spans, but its lightweight nature, translucent and reflective properties, and environmental adaptability could also be taken advantage in building construction (wikipedia, 2019). fig 1. tensile fabric structure for logistics center at shenzhen, china. (source: https://www.bdir.com/product/tensile-structure-for-logistics-center-tent-fabric-covered-roof) mailto:architectarif@gmail.com kamal arif m., j. build. mater. struct. (2020) 7: 236-254 237 2. research methodology in this paper qualitative analytical research method has been used. the research methodology comprises of case studies, visual observation and data collection. the systematic literature review has been explored through internet and secondary data from relevant published academic literature from journals articles and research papers. the data collection in the qualitative research are the data that comes from a number of case study examples that are described descriptively and are supported by illustrations and photographs to reinforce the arguments put forward. the basic concepts and backgrounds are investigated through literature and on-line media, observations to work for qualitative analysis conducted for tensile structure system to study the fabric architecture buildings, advantages, disadvantages, facades and the fabric future in construction field. finally, five case studies around the world have been presented to validate and illustrate the direct application of design and architectural interventions of tensile structure system. 3. historical evolution of tensile fabric structures the origins of fabric structures can be traced back more than 44,000 years to the ice age and the siberian steppe, where remains have been found of simple shelters constructed from animal skins draped between sticks. from these purely functional origins however, the tent evolved over many centuries to become a symbol of frivolity. in the nineteenth and twentieth centuries, architects became inspired by technological breakthroughs in structural engineering and architectural theorising on an emerging functional aesthetic (fabric, 2020). the russian engineer vladimir shukhov was one of the first to develop practical calculations of stresses and deformations of tensile structures, shells and membranes (figure 2). shukhov designed eight tensile structures and thin-shell structures exhibition pavilions for the nizhny novgorod fair of 1896, covering the area of 27,000 square meters. fig 2. the first tensile steel shell of oval pavilion by vladimir shukhov. (source: https://en.wikipedia.org/wiki/file:tensile_steel_lattice_shell_of_oval_pavilion_by_shukhov) antonio gaudi used the concept in reverse to create a compression-only structure for the colonia guell church. he created a hanging tensile model of the church to calculate the compression forces and to experimentally determine the column and vault geometries. the concept was later championed by german architect and engineer frei otto, whose first use of the idea was in the construction of the west german pavilion at expo 67 in montreal. otto next used the idea for the roof of the olympic stadium for the 1972 summer olympics in munich (wikipedia, 2019). in the 1950s, architects and engineers began to take a renewed interest in using tension as the primary method of transferring loads in structures. two main figures responsible for advancement in this investigation of tensile structures were frei otto and horst 238 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 berger of germany. the concept was later championed by german architect and engineer frei otto, whose first use of the idea was in the construction of the west german pavilion at expo 67 in montreal. otto next used the idea for the roof of the olympic stadium for the 1972 summer olympics in munich (redskyshelters, 2020). some current well known structures utilizing tension fabric include the foldable umbrella form tensile structure system in piazza in medina, saudi arabia (figure 3), the largest cable supported roof in the world of the millennium dome in london, england and the haj terminal in jeddah, saudi arabia, designed in part by berger and currently one of the largest tensile structures in the world (midauser, 2020). fig 3. foldable umbrella form tensile structure system in piazza in medina, saudi arabia. (source : https://en.wikipedia.org/wiki/file:medina_piazza_umbrella.jpg) 4. concept design and criteria for shape finding there are two types of computer models for the concept design that can be used for investigating various fabric forms. they are summarised as below: a) wire frame computer models – these simple computer models are the starting point for investigating various fabric forms and developing the concept design into a practical form to ensure that the design criteria are satisfied. b) fully rendered computer models – models of the final design of the fabric structure can be added to the model of the whole building, and are thus very useful for final presentations to clients. the concept design is the most important stage of the design process – a bad concept will reverberate throughout the design, manufacture and installation process, and will impair the appearance and performance of the final product. a number of factors need to be taken into consideration, including, but not necessarily limited to, the following: a) geometric constraints of the site and adjacent buildings b) sun shading levels required and sun angles c) air flow and ventilation of the space d) light transmission requirements for the space below e) availability and positions of anchorage points f) need for continuously sealed perimeter anchorages g) aesthetic considerations and compatibility with adjacent elements h) achievement of adequate curvature to minimise fabric stresses & movements i) drainage of rainwater and avoidance of ponding j) suitable fabric slopes to ensure adequate self-cleansing k) nature of supporting structure and tensile elements kamal arif m., j. build. mater. struct. (2020) 7: 236-254 239 5. shape and forms of tensile structure system a two dimensional tension fabric membrane can take planar tensile forces, but it cannot take significant forces perpendicular to this plane. therefore, in addition to being pre-stressed, tension fabric must take a certain three dimensional shape in order to remain stable (figure 6). these shapes were discovered by otto and berger during their investigation of natural forms such as soap bubbles. there are two types of general shapes: anticlastic and synclastic shapes (weaver, 2020). they are summarized as below: anticlastic shapes are created by having the radii of the principal curvatures on opposite sides of the tension fabric surface. as a result, when loaded at a particular point, tension will increase on one curve of the membrane and leave the opposite curve, thereby preserving equilibrium and keeping the structure stable. in order to keep anticlastic shapes, some kind of structural frame or support is necessary in the form of cables or steel beams. some examples of anticlastic shapes are saddle, cone, and wave forms (figure 4). fig 4. example of anticlastic shape-saddle structure (source: https://www.masterbuilder.co.in/morphologytensile-structure-systems/) on the other hand, synclastic shapes are characterized by having the radii of the principal curvatures on the same side of the fabric (figure 5). in order to counteract external forces, pressure from within is necessary. this is why synclastic shapes are associated with air inflated structures, as the difference of pressure created by air pumped into the building is able to counteract external forces in the form of wind or snow (kamal, 2016). fig 5. example of synclastic shape-pneumatic structures (source: https://www.masterbuilder.co.in/morphologytensile-structure-systems/) fig 6. different forms of tensile structures (source: https://www.architen.com/articles/basic-theories-oftensile-membrane-architecture/) 240 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 6. types of tensile structure system membrane structures, encompassing both the tensioned fabric and the supporting structure, can span from 3 to 20 meters to spans more than 200 meters. for spans more than 200 meters, the fabric is supported by cables with steel or air so that unsupported span of the fabric is actually less than 30 meters. there are several systems adopted for tensioned fabric systems. while maintaining the concept of tension fabric design, each system is unique. these systems can be combined with each other to create interesting and even more complex designs. there are different types of tensile structure system, but generally there are five prominent types of tensile structure system (armijos, 2020). they are summarized as below: 6.1. mast-supported systems in tensioned fabric structures where the supporting structure consists of masts, fabric is suspended from cables hung off masts or other compression elements. this kind of system is ideal for long span roofs. the masts must support both axial loading and lateral wind and dead loads (for angled masts). to resist buckling, which the masts are highly susceptible as a result of the axial forces increasing the moment stresses, the masts are constructed in lattices (figure 7). fig 7. mast supported tensile structure system (source: https://www.archiexpo.com/prod/fabritecstructures/product-151879-1765809.html) 6.2. point-supported the point support tensile structure system has often hypar shaped (two high, two low connection points). it utilizes an exterior frame or series of peripheral masts. an example of primary point support structures is the simple cone structure that consists of a mast in the center of the membrane and can be repeated in groups to enclose a larger area of space. the existence of a big structural element in the center can also become obstructive (figure 8). fig 8. point supported tensile structure system (source: https://formfindinglab.files.wordpress.com/2016/11/dia.jpg?w=620) kamal arif m., j. build. mater. struct. (2020) 7: 236-254 241 6.3. arch-supported the arch supported introduces a curved compression member. the cross arches often used for the frame. the arch-supported membrane shape is comprised of a saddle with one curving boundary and three straight boundaries. this configuration is conceptually very pleasing since the membrane work in complete tension while the arch is ideally working in complete compression (figure 9). these systems can be designed quite efficiently for spans of about 8m. fig 9. arch supported tensile structure system (source: https://parametrichouse.com/architecture-design-12/) 6.4. frame supported it is space framed. the fabric is attached to a structural frame. the structural components carry all the forces. the fabric is purely used as a cladding (figure 10). fig 10. frame supported tensile structure system (source: https://veldemangroup.com/wpcontent/uploads/2016/05/sfs-binnen-9.jpg.jpg) 6.5. simple saddle/hypar the hypar or saddle tensile structure systems have double curvature. they are generally ‘saddle shape’ and have two high points and two low points. in this type, the opposing directional forces that are introduced by prestressing the fabric in both directions counter balance each other. they also have the minimal surfaces. (figure 11). 242 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 fig. 11. hypar tensile structure system of the serpentine sackler gallery at london, uk. (source: https://www.archdaily.com/433507/the-serpentine-sackler-gallery-zaha-hadid-architects 7. fabric materials: typology and characteristics 7.1 pvc fabric (pvc-coated polyester) the poly vinyl chloride (pvc) fabric is less expensive than polytetrafluoroethylene (ptfe) in material and processing, it has many virtues of soft texture and easy construction. but it is not as good as ptfe fabric in intensity, aging, fire-resistance etc. pvc fabric is made from polyester coated with pvc. the fabric that is commonly used in architecture is produced by the treatment of coating as applying several microns acrylic resin on the surface of pvc, which is in order to improve dirt-resistance. however, after a few years, pvc fabric will generally turn yellow, and is more likely to crack. longevity of pvc fabric is 5-8 years according to different using surroundings. in order to improve weather protection of pvc fabric, fabric, which is coated fluoric resin on top of pvc, to improve its weather protection and dirt-resistance, has been under researches and development in recent years. 7.2. pvdf pvdf is abbreviated of polyvinylidene fluoride. the material coating pvdf resin on pvc fabric surface is called pvdf. the difference between pvdf fabric and common pvc fabric is that the life span of pvdf is lengthened to 5-10 years. 7.3. pvf pvf is abbreviated of polyvinyl fluoride.fabric is laminated with lamellate pvf on top of pvc fabric. compared with pvdf, it is more wear-resistant and dirt-resistant. but it costs more than pvdf. 7.4. ptfe fabric (ptfe coated fiberglass) ptfe fabric is a material coated polyvinylidene fluoride on fiberglass textile. comparing with pvc fabric, ptfe has great virtue of longevity, dirt-resistance and fire-resistance. however, high expense of material and processing, low flexility are the defects. in order to prevent fiberglass breaking, it requires a professional and complete plan in processing, folding, packing, construction techniques. 7.5. fabric options – pvc and ptfe there are three main types of tension fabric used in architectural applications today: pvc coated polyester, silicon coated fiberglass, and teflon coated fiberglass. pvc coated polyester is the cheapest and easiest to manage of the three but also has the shortest life span. teflon and silicon kamal arif m., j. build. mater. struct. (2020) 7: 236-254 243 coated fiberglass are more durable, but are also more expensive (browne, 2019). however, the basic structure of the material is similar for all three. the bottom layer of the tension fabric is a base fabric, usually made out of polyester or fiberglass. this fabric is created with fibers that run perpendicular, or in the warp and welt directions, and are weaved in and out of each other (figure 12). the base fabric is extremely important as it dictates a number of the final fabric properties including stress and strain properties (how much force the fabric can take and how long it can stretch before failure) (seaman, 2000). the topcoats of protective fluorinated polymer lacquers (pvdf) applied to pvc coated polyester enhance its 'cleanability' and provide additional protection. in average climates, this fabric can last 15-20 years, or around 5 years less in sites where there is high exposure to sunlight. in addition to the incredible strength of the base fabrics, they are also relatively translucent and reflective. for example, teflon coated fiberglass has a reflectivity of seventy per cent (gandhi, 2020). fig 12. section of teflon coated fiberglass as tensile fabric material (source: http://en.sztianfa.com/product.html) 7.6. pvc / polyester fabric pvc/polyester fabric consists of a woven polyester base cloth, which is then coated with pvc and another top coating. they can be classified into 2 basic categories, depending on the type of protective top coating, as follows: a) acrylic lacquer b) pvdf/acrylic lacquer alloy coatings in varying proportions these top coatings have a large influence on the performance and appearance of the fabric, because they not only provide the fabric with some of its uv resistance, but they also vastly improve its self-cleaning characteristics. in general, fabrics with acrylic coatings have not performed that well long term in tropical countries, and most examples appear to attract and retain significant amounts of dirt and dust after relatively short times in service. on sites with high uv levels, the acrylic coatings break down fairly quickly, and thus the deterioration in appearance can occur within a few years after installation. the fabrics with pvdf/acrylic alloy coatings are the most commonly used, and have now been in service about 25 years. the pvdf/acrylic coating is heat-fused onto the base fabric as part of the manufacturing process. the top surface of the fabric has a smooth slippery feel, and it is thus very effective in repelling dirt and resisting mould growth. useful lives of 15-25 years are achieved with these fabrics, with the anticipated life being directly proportional to the amount of pvdf in the top coating. 7.7. ptfe / fibreglass fabric the first outdoor ptfe/fibreglass structure was erected in california, usa 40 years ago and is still performing well in service. it is therefore likely that structures which are made with today’s ptfe/fibreglass fabrics will achieve useful lives in excess of 50 years (figure 13). ptfe/fibreglass fabric is very effective in repelling dirt and some structures which have been inspected after years in service have perfectly clean surfaces even though they have never had 244 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 cleaning maintenance. three of the new stadiums built for the soccer world cup in south africa in 2010 had ptfe/fibreglass roofs, but the main disadvantage of ptfe fabric is its high cost – the overall cost of structures using this fabric are almost twice that of pvc structures. fig 13. different layers of fiberglass fabric material for tensile structures (source: https://www.fabricgateway.com/topic/mehler+tensile#&gid=1&pid=27) 8. construction system and fabrication details the constructor of fabric structures has a more important role to play than those of conventional structures, because they are dealing with relatively new materials, methods, and technologies. indeed, fabric roof design is often considered so special that it falls under a separate contract from the main structural system of a building; clients will even sometimes appoint a different structural engineer for the fabric and for the main structure (figure 14). more often than not, the design of fabric structure is limited by manufacturing capabilities. a fabric contractor must therefore be chosen with care. it is the responsibility of the fabricator to help architects and engineers in the material selection process, informing them of special material properties as well as advising them on practical patterning and pre-stressing techniques (walter, 1977). fig 14. connection details of fabric system with the mast (source: http://fabricarchitect.com/componentsand-details.html) 8.1. types of connections the design of connections in fabric structures often requires careful and thorough consideration. unlike connections in conventional buildings, they play a crucial role in the creation of architectural form and concept, as the geometry of a fabric roof is entirely dependent on the proper placement and design of these connections. they are often exposed to view and must therefore be constructed with aesthetics in mind. one of the most important considerations when designing fabric connections is the stress concentration that may occur in the local area surrounding it. being highly sensitive to concentrated applied forces, clamps, cables, and seams should almost always fully develop stresses into the fabric. fabric connections also need to be designed for load path, understanding that loads will tend to follow the stiffest path. in the case of a fabric membrane, applied loads will travel through the flexible membrane into less flexible kamal arif m., j. build. mater. struct. (2020) 7: 236-254 245 interior or edge cables and then into the stiff and rigid supports (figure 15). the following sections present various schemes for the connection of fabric elements (shaeffer, 1996). fig 15. corner plate end-connection of tensile membrane structure (source : http://fabricarchitect.com/uploads/3/4/1/0/34108236/corner-plate-004_orig.jpg) 8.2. fabric to fabric after fabrics are patterned and cut, they can be joined together in a number of ways. these include heat sealing, gluing, and sewing. lap seams are typically laid out in a "shingle" like pattern, with higher pieces of fabric draped over lower ones to facilitate water run-off (figure 16). seam strengths are dependent on coating adhesion and seam widths. fig 16. a standard lap seam joinery detail (source: http://fabricarchitect.com/uploads/3/4/1/0/34108236/clamping-detail.jpg) 8.3. fabric to cable fabrics to cable connections are needed when structural cables help to support a fabric membrane. one-sided connections are made when the fabric terminates at an edge cable and two-sided connections occur when the fabric is sectioned by the cable on both sides (figure 17). sectioning or subdividing fabric is usually done to facilitate the installation process. it also proves beneficial later for building maintenance and repair as fabric can be replaced one section at a time. fabric to cable connections can be done in a few different ways. one method involves a cuff or sleeve, which uniformly transfers stress from the membrane into the cable or vice versa. fig 17. the fabric to cable connection details (source: http://fabricarchitect.com/uploads/3/4/1/0/34108236/slides-030.jpg 246 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 another technique calls for the clamping down of a fabric roped edge. the roped edge will bear against the clamping hardware, which is attached to a base plate or rigid support (figure 18). the clamping mechanism must be designed to distribute stresses evenly between the fabric edge and the fabric itself. they are rounded and padded to protect against unsupported stress concentrations. fig 18. the edge detail of fabric to frame connection (source: http://fabricarchitect.com/uploads/3/4/1/0/34108236/tennect-detail.jpg) 8.4. cable to cable cable clamps and fixings like the ones in figure 19 can be used to connect cables to other cables. these typically join single or double cables running in perpendicular directions, though turnbuckles and adjustable toggles will sometimes be used to splice cables going in the same direction. although most cable end connections will develop the full strength of cable, they must be designed to account for both the breaking strength of cable and the capacity of the fitting. fig 19. the cable to cable support connection details to prevent bending failure (source: https://commons.wikimedia.org/wiki/file:munich_-_frei_otto_tensed_structures_-_5244.jpg) 8.5. anchorages the provision of adequate anchorages and supporting structures must be addressed at the earliest stages of the design process. failure to address these issues early on could result in the tensile structures being impossible to include once the design and construction has progressed beyond a certain stage. even small canopy structures impose significant forces on the substructures, and large structures will require special design features to be able to resist the tensile forces. anchorages or mast-base connections are designed in much the same way as a column-base connection. the only difference here is that vertical masts will sometimes be free to rotate about the base. fixed bases offer more stability during the erection and installation process and create a more rigid fabric roof system overall. however, rotating masts can be useful for fabric pre-stressing and rotating mast-base connections are generally cheaper than fixed bases, which require welding. figure 20 illustrates a standard pinned mast fixing to the ground. kamal arif m., j. build. mater. struct. (2020) 7: 236-254 247 fig 20. the anchorage detail of the base fixing at the ground (source: http://fabricarchitect.com/uploads/3/4/1/0/34108236/red-base_orig.jpg) 9. performance characteristics of tensile fabric system the observation of fabric structures in different situations in various parts of the world show that the particular environment in which the fabric is situated has a very significant effect on its performance (tolani, 2016). the main factors which appear to influence the fabric performance are the following: a) geographic latitude and thus the temperature of the fabric b) uv radiation level reaching the fabric c) humidity level d) pollution level, as well as the type of pollutants e) dust level f) frequency and nature of cleaning operations g) deposition of vegetable matter (leaves, etc.) onto the fabric h) staining resulting from rainwater run-off over other building materials i) exposure to direct rainfall to assist in dirt and dust removal 9.1. light and heat transmission one of the main advantages of fabric is its translucent properties – on average, architectural fabrics transmit about 13% of the light falling on the top surface. this results in a very pleasant light and airy feel to the space below, and can also result in significant cost savings on lighting. fabric is also very effective in reducing the transmission of radiant heat from the sun, and it is a material which has been significantly underutilised in the climatic conditions prevailing in south africa. however, global warming is likely to result in increased usage of tensile fabric structures in future. 9.2. fabric and fire fire safety is a major factor in selection of membranes. these membranes are to be used as a medium to polarize sunlight and use it as an aesthetic formwork. pvc has fire retardant properties, and achieves a class 2 fire rating – meaning that the fabric is self-extinguishing and does not produce drips of molten fabric. this fire rating is generally accepted by most approval authorities for use as a roof enclosure. pvc has an added advantage in a fire situation in that the fabric seams will separate at about 100ºc, thus allowing the very early venting of toxic fumes and smoke. this is a major advantage in saving lives of people who may be trapped in the building. 248 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 9.3. cleaning fabric fabric is easy to clean and can be done using similar methods to those that one would use to clean a car, i.e. soft brushes, light duty, non-acidic detergents and copious rinsing water. personnel can access the fabric by means of ropes and use soft soled shoes to walk on the fabric 9.4. lighting design of fabric lighting is very effective in emphasising the aesthetic appearance of fabric structures and should always be included whenever possible. both back-lighting and front-lighting can be used depending on the effect that is desired. 9.5. cost benefits there is a significant 50-60% cost benefit over conventional systems. the case study shows that the total cost of steel required for covering a specific area with space frame is found to be much greater than the cost of membrane used to cover the same area. the additional cost benefit is that membrane structures provide us with easy and efficient ventilation (both air as well as light) which in turn reduces the electricity bills. 9.6. lightweight nature and earthquake resistance the weight of the membrane in tensile structures is very less and consequently, the quantity of structural steel utilized to support the membrane is also minimal. thus, the weight as well as the overall cost of tensile structures is much less as compared to conventional roofing systems. as less steel is utilized, more useful space free of columns becomes available. as the weight of the structure is so little, it will not experience much acceleration forces under seismic action. as is evident from the above graphs it is found that the total reduction in steel consumption when using tensile structures as opposed to the conventional forms of the structures is about 50%60% in each case. 9.7. low maintenance in case of space frames, the major difference is of steel. the regular maintenance, such as painting, coating, etc. needs to be done, which sums up to be a considerable cost. while in case of membrane structure, membrane itself is resistant to corrosion. as the steel used is very at connections and supports that is the only part need to be taken care of. also the self-cleaning membrane material can be used. 9.8. excellent durability weathering in polymer is a major concern and is definitively caused by the exposure to uv radiation, moisture, temperature, and humidity. the membrane material itself can withstand within the range of -40 oc to +70 oc. companies of warranty for their fabrics and usually the minimum life span of these structures is about 25 years. 9.9. shortened construction schedules the erection of the tensile structures takes less than a week to complete as all the patterning and fabrication works are mostly carried out in warehouses and the structure is erected on site. the construction period is only the time required for its erection, which can be reduced to minimum by using advanced construction equipment. kamal arif m., j. build. mater. struct. (2020) 7: 236-254 249 9.10. flexible design aesthetics membrane structures can be designed, analysed and erected in any of the shape or form we require. it provides extra space for the designer to experiment with different shape. the membrane fabric can even incorporate an artificial lighting, which can add another aesthetic dimension to them. 10. case studies 10.1. the o2 (millennium dome), london, uk the o2 is a large entertainment district in south east london, england. it includes an indoor arena, a music club, a cinema, an exhibition space, piazzas, bars, and restaurants (figure 21). it was built largely within the former millennium dome, a large dome-shaped canopy built to house an exhibition celebrating the turn of the third millennium (wikipedia, 2020). the exhibition opened to the public on 1 january 2000 and ran until 31 december 2000; however, the project and exhibition was the subject of considerable political controversy and it did not attract the number of visitors anticipated, leading to recurring financial problems. in popular usage, the dome canopy is often still called the dome, reflecting the substantial, and often adverse, publicity given to its building in the late 20th century. fig 21. the exterior view of the millenium dome, london, uk (source : static.independent.co.uk_millenium dome) the 12 support towers represent the 12 hours, 12 months and 12 constellations of the sky. the dome is 52 meters at its highest point, representing the 52 weeks of the year. each span is 365 meters apart, symbolic of the numbers of days in a standard year. there are 24 scalloped edges at the base of the canopy, for each hour of the day. the millennium dome features twelve 100m high steel masts that support a tensioned net of seventy kilometers worth of steel cables, arranged radially on the surface of the roof and held in place by hanger and tie down cables (figure 22). fig 22. the interior view of the millennium dome at the time of installation (source: https://www.srm.com/projects/o2-arena/) https://www.srm.com/projects/o2-arena/ 250 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 the canopy itself is a one millimeter white ptfe (polytetraflouroethylene) fabric with an interior lining designed to reduce thermal gain, and improve thermal and acoustic performance – in essence absorb both sound and condensation (burohappold, 2020). 1 0 . 2 . c as e stu dy 2 : denver international airport, usa denver international airport, usa was completed in 1994 and is the world’s third largest airport. the teflon coated fibreglass roof of the airport is designed to resemble the peeks of the rocky mountains in winter, capped with snow (figure 23). the tensile structure has stood the test of time and the structure hasn’t completely failed under the extreme weather conditions that it experiences (landrell, 2019). fig 23. the exterior canopies of the denver international airport, usa (source: https://www.birdair.com/birdair-portfolio/denver-international-airport/) the massive, 1,200by 240-foot facility features a striking ‘mountain range’ canopy that utilizes birdair’s innovative steel cable systems and durable ptfe teflon-coated fabric membrane. punctuating this “ridge and valley” structure is a 900-foot atrium, known as the great hall, which rises to a height of 126 feet and welcomes visitors with an abundance of translucent, natural light. this graceful, lightweight roof incorporates two layers of fabric membrane to ensure proper sound control and sufficient insulation against denver’s demanding climate conditions. to support this load-bearing structure, 34 interior columns and 10 miles of steel cable were used, completely enclosing the building’s exterior envelope. this design, in turn, provides travelers with adequate shade and protection. in addition, two separate exterior canopies extend the full length of the main building, serving vehicle ramps for in-bound and outbound passenger traffic while complementing the terminal’s majestic design. in total, the jeppesen terminal roof required 375,000 square feet of tensile fabric membrane, with the adjacent curbside roofs requiring an additional 75,000 square feet (figure 24). with such a large surface area, birdair’s design and engineering team optimized the sustainable benefits of ptfe fabric, which is chemically inert, highly resistant to dirt and pollution, and provides a long lifecycle with minimal maintenance (birdair, 2019). fig 24. tensile fabric membrane in the interior of denver international airport, usa (source: https://i.pinimg.com/originals/84/8d/a7/848da75c497cfe3b07d69220319f7482.jpg) kamal arif m., j. build. mater. struct. (2020) 7: 236-254 251 10.3. case study 3: haj terminal, jeddah international airport, saudi arabia in 1977 skidmore owens & merril, architects (som) was commissioned by the government of saudi arabia to design a terminal at the international airport in jeddah to serve the pilgrims to mecca during the annual muslim pilgrimage (haj). 80000 people a day had to be accommodated in transition between buses and airplanes. to protect people against the heat of the desert sun, 440000 m² of space had to be covered. ptfe coated glass fiber fabric reflects 70 % of the sun's heat, radiates out during the night, eliminates electric light because of its translucency. som chose a fabric structure concept which divides the building into 10 modules, each consisting of 21 tent units with a plan dimension of 45,75m x 45,75 m. each module covers 320 x 137m (figure 25). two groups of five modules each are arranged along two sides of a central access road. 20 gates for the planes are located at the opposite ends of the modules. to keep the space below open, the structural concept by som's fazlur khan suspends the tent units from high masts which are located at the four corners of each tent. interior supports consist of single columns. along edges and corners two or four columns are combined into frames to resist the lateral forces. this arrangement of the support system gives the architecture of the world's largest roof its powerful image (ishii, 1999). fig 25. tensile structure system of international airport at jeddah, saudi arabia (source: https://www.pinterest.fr/pin/376683956321452042/) 10.4. khan shatyr entertainment center, nur sultan, kazakhstan khan shatyr is a transparent tent located in nur-sultan, the capital city of kazakhstan. built in a neofuturist style, the architectural project was unveiled by the president of kazakhstan nursultan nazarbayev on december 9, 2006 (figure 26). the 150 metres high tent has a 200 metres elliptical base covering 140,000 square metres. under the tent, an area larger than 10 football stadiums, is an urban-scale park, shopping and entertainment venue with squares and cobbled streets, a boating river, shopping centre, minigolf and indoor beach resort. fig 26. tensile structure system of khan shatyr entertainment center, nur sultan, kazakhstan (source: https://en.wikipedia.org/wiki/khan_shatyr_entertainment_center#/media/file:khan_shatyr.jpg) 252 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 the fabric roof is constructed from etfe-cushions provided by vector foiltec, suspended on a network of cables strung from a central spire (figure 27). the transparent material allows sunlight through which, in conjunction with the stack effect, air heating and cooling systems, is designed to maintain an internal temperature between 15–30 °c in the main space and 19–24 °c in the retail units, while outside the temperature varies between −35 and 35 °c across the year (wikipedia, 2019). fig 27. the central mast of khan shatyr entertainment center, nur sultan, kazakhstan (source: https://photos.wikimapia.org/p/00/01/35/30/76_big.jpg) 10.5. yoyogi national gymnasium, tokyo, japan yoyogi national gymnasium is an arena located at yoyogi park in shibuya, tokyo, japan, which is famous for its suspension roof design. it was designed by kenzo tange and built between 1961 and 1964 to house swimming and diving events in the 1964 summer olympics by japan sports council (figure 28). a separate annex was used for the basketball competition at those same games. it will also host handball competitions at the 2020 summer olympics. the design inspired frei otto's arena designs for the olympic stadium in munich (palmer, 2009). fig 28. tensile structure system of yoyogi national gymnasium, tokyo, japan (source: https://commons.wikimedia.org/wiki/file:kokuritsu_yoyogi_ky%c5%8dgij%c5%8d_1.jpg) 11. conclusion fabric structures represent a new chapter in the history of building structures. despite its more extensive use over the past decade or so in architectural applications, tension fabric is still a relatively new building material. discovering necessary forms and amount of pre-stressing can be extremely complex, sometimes only vaguely understood, and therefore much care is taken in designing structures involving this material. the tensile fabric structures are capable of spanning large distances while incurring very little weight on supporting structure, developments in the design of fabric structure can dramatically change the way we conceptualize permanent building construction. however, the advantages of tension fabric cannot be disputed. the design and analysis process is perhaps the most limiting factor in the implementation of fabric structure. exhibiting highly nonlinear behavior, the behavior of fabric kamal arif m., j. build. mater. struct. (2020) 7: 236-254 253 under applied loads is often difficult to understand and to model. beginning with simple fabric models in the days of frei otto at the institute of lightweight structures, analysis theories and methods have adapted into complex computational models capable of quickly and accurately determining the form and behavior of a fabric membrane (fang, 2009). 12. references armijos, s. j. (2020). five steps to a fabric structure experience, [online] available from http://www.fabricarchitect.com, accessed on 10 june 2020. barnes, m. & dickson m. (2000), widespan roof structures, thomas telford publishing, london birdair (2019), denver international airport, [online] available from https://www.birdair.com/birdairportfolio/denver-international-airport/, accessed on 20 august 2020. browne, n. (2019) fabric architecture and signature structures. [online] available from www.fabricarchitecture.co.uk/cpd.htm, accessed on 10 may 2020. burohappold (2020), o2 arena and millennium dome, mill [online] available from https://www.burohappold.com/projects/millennium-dome/#, accessed on 28 july 2020. fang, r. (2009) the design and construction of fabric structures, master of engineering thesis, massachusetts institute of technology, usa. gandhi, u. (2020) design and construction of tension membrane structures. [online] available from http://homepages.cae.wisc.edu/~ukgandhi/documents/tensile%20structures_paper.pdf, accessed on 25 july 2020. ishii k; shin kenchikusha s., enshu bu k. (1999). membrane designs and structures in the world, shin kenchikusha publishers, tokyo. kamal, arif m. (2016 ) the morphology of tensile structure systems, [online] available from https://www.masterbuilder.co.in/morphology-tensile-structure-systems/the-morphology-oftensile-1/, accessed on 10 may 2020. landrell a. (2019), famous examples of tensile structures, [online] available from www.architen.com/2012/05/famous-examples-of-tensile-structures/, accessed on 15 may 2020. mills j. (2010). the khan shatyr entertainment centre by foster + partners, [online] available from https://www.dezeen.com/2010/07/06/the-khan-shatyr-entertainment-centre-by-fosterpartners/, accessed on 10 may 2020. palmer, a. l. (2009), the a to z of architecture. the scarecrow press inc. usa. price k. (2015) practical aspects of design and material specifications [online] available from www.tensionstructures.co.za/tensile-fabric-structures/, accessed on 26 august 2020. redskyshelters (2020). the history of tensile architecture. red sky shelters. [online] available from www.redskyshelters.com/tensilehistory.html, accessed on 25 july 2020. seaman, r., & bradenburg, f. (2000). utilization of vinyl coated polyester fabrics for architectural applications. journal of industrial textiles, 30(1), 63-82. shaeffer, r. e. (1996) tensioned fabric structures: a practical introduction. new york, ny: american society of civil engineers. tolani a. n., patil a. s., patil g. n., vadalkar v. h., barbude p. r. (2016), advantages of tensile structures over other space frame structures, international journal of research in engineering and technology, 5 (5), 568-575. walter, b. (1977) role of the fabricator large fabric structures. asce spring convention and exhibit. dallas, tx: american society of civil engineers. weaver m. (2020), tension fabric: wave of the future [online] available from https://illumin.usc.edu/tension-fabric-waves-of-the-future/, accessed on 15 july 2020. wikipedia.org. (2019) tensile structure, [online] available from www.en.wikipedia.org/wiki/tensile_structure, accessed on 25 august 2020. http://www.fabricarchitect.com/ https://www.burohappold.com/projects/millennium-dome/ https://www.worldcat.org/search?q=au%3aishii%2c+kazuo%2c&qt=hot_author https://www.worldcat.org/search?q=au%3ashin+kenchikusha.+kikaku+henshu%cc%84bu.&qt=hot_author http://www.architen.com/2012/05/famous-examples-of-tensile-structures/ https://www.dezeen.com/2010/07/06/the-khan-shatyr-entertainment-centre-by-foster-partners/ http://www.tensionstructures.co.za/tensile-fabric-structures/ 254 kamal arif m., j. build. mater. struct. (2020) 7: 236-254 wikipedia (2020), the o2 [online] available from https://en.wikipedia.org/wiki/the_o2, accessed on 10 may 2020. https://en.wikipedia.org/wiki/the_o2 j. build. mater. struct. (2015) 2: 18-24 https://doi.org/10.34118/jbms.v2i1.16 issn 2353-0057 performance of coconut shell ash and palm kernel shell ash as partial replacement for cement in concrete oyedepo oj *, olanitori lm and akande sp department of civil and environmental engineering, federal university of technology akure, nigeria. * corresponding author: oyedepoo@yahoo.co.uk abstract. high cost of cement used as binder in the production of concrete has led to a search for alternative. using a mix design ratio of 1:2:4 and water binder ratio of 0.63, concrete cubes were casted using varying ordinary portland cement (opc): palm kernel shell ash (pksa) and ordinary portland cement (opc): coconut shell ash (csa) ratios of 100:0, 90:10, 80:20, 70:30 , 60:40 and 50:50 respectively. this research reveal that partial replacement of cement with 20% pksa and csa in concrete gives an average optimum compressive strength of 15.4 n/mm2 and 17.26 n/mm2 respectively at 28 days. while, the optimum value of compressive strength obtained at 28 days is 20.58 n/mm2 at 10% replacement with csa. the value obtained is suitable for both light weight and heavy weight concrete respectively. thus, the research show that the use of pksa and csa as a partial replacement for cement in concrete, at lower volume of replacement, will enhance the reduction of cement usage in concretes, thereby reducing the production cost and the environmental pollution caused by the dumping of the agricultural waste. key words: cement, concrete, compressive strength, cost, pollution. 1. introduction concrete is the widely used number one structural material in the world today, high cost of cement, used as binder, in the production of mortar, sandcrete blocks, lancrete bricks and concrete has led to a search for alternative. the overall relevance of concrete in virtually all civil engineering practice and building construction works cannot be overemphasized. the growing concern of resource depletion and global pollution has challenged many researchers and engineers to seek and develop new materials relying on renewable resources. these include the use of by-products and waste materials in building construction. many of these by-products are used as aggregate for the production of lightweight concrete (vishwas and sanjay, 2013). with the global economic recession coupled with the market inflationary trends, the constituent materials used for these structures had led to a very high cost of construction. on the other hand, building construction works and civil engineering practice in nigeria depend, to a very large extent, on concrete as major construction material. the versatility, strength and durability of cement are of utmost priority over other construction materials. the basic materials for concrete are: cement, fine aggregate (sand), coarse aggregate (granite chippings or gravel) and water, the overall cost of concrete production depends largely on the availability of these constituents. reduction in construction costs and the ability to produce light-weight concrete structures (lwc) are added advantages. the primary aim is to determining the suitability of partial replacement of cement with coconut shell ash (csa) and palm kernel shell ash (pksa) in concrete. 2. literature review concrete is widely used as construction material for various types of structures due to its durability. for a long time it was considered to be very durable material requiring a little or no maintenance. many environmental phenomena are known significantly the durability of reinforced concrete structures. we build concrete structures in highly polluted urban and industrial areas, aggressive marine environments and many other hostile conditions where mailto:oyedepoo@yahoo.co.uk oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 19 other materials of construction are found to be nondurable. so the use of concrete is unavoidable. at the same time the scarcity of aggregates are also greatly increased nowadays. utilization of industrial soil waste or secondary materials has been encouraged in construction field for the production of cement and concrete because it contributes to reducing the consumption of natural resources. they have been successfully used in the construction industry for partial or full replacement for fine and coarse aggregates. slim and wakefield (1991) investigated the use of water works sludge in the manufacture of clay bricks. osayemwen (1992) studied the use of periwinkle shells as alternative material to granite chips as coarse aggregate in concrete and concluded that the use of periwinkle shells for concrete would result in low cost housing delivery especially in the riverine areas where they are found as waste. nimityongskul and daladar (1995) investigated the use of coconut husk ash, corn cob ash and peanut shell ash as cement replacement in concrete production. falade (1995) also carried out investigation on the use of periwinkle shells partially or wholly in concrete. the results of the investigation showed that the workability of the concrete batches, density, compressive and flexural strengths of specimens tested decreased with increase in the proportion of periwinkle shells to granite in the mixes. ndoke (2006) investigated the suitability of palm kernel shells as partial replacement for coarse aggregates in asphaltic concrete. olanipekun et al. (2006) compared concrete made with coconut shells and palm kernel shells as replacement for coarse aggregates and concluded that coconut shells performed better than palm kernel shells. osarenmwinda et al. (2009) investigated the potential of periwinkle shell as coarse aggregate for concrete. the results showed that concretes produced with ratio 1:1:2, 1:2:3 and 1:2:4 mixes indicated compressive strengths of 25.67 n/mm2, 19.5 n/mm2 and 19.83 n/mm2 at 28 days curing age respectively. these strength values met the astm-77 recommended minimum strength of 17 n/mm2 for structural light weight concrete while the mixes with compressive strengths of 14 n/mm2 and 16.5 n/mm2 respectively did not meet the standard values. in a research carried out by olutoge (2010), he investigated the suitability of sawdust and palm kernel shells as replacement for fine and coarse aggregates in the production of reinforced concrete slabs. he concluded that 25% sawdust and palm kernel substitution reduced the cost of concrete production by 7.45%. he also indicated the possibility of partially replacing sand and granite with sawdust and palm kernel shell in the production of lightweight concrete slabs. also, falade et al (2010) investigate the behaviour of lightweight concrete containing periwinkle shells at elevated temperature; the parameters that were measured are compressive strength, density and bond characteristics of the concrete matrix. the results showed that the compressive strength of concrete decreased with increase in water/cement ratio and temperature but increased with increase in curing age and cement content while the density decreased with increase in temperature. they affirm that lightweight concrete containing periwinkle shells is only suitable for structures that will be subjected to temperature less than 300°c. 3. materials and methods the materials used for this study include: ordinary portland cement (dangote cement) coarse aggregate made of shippings from johnson quarry in akure; fine aggregate (river sand) from ala river in akure; palm kernel shell: palm kernel shell (abiola, 2006) is the hard endocarp of palm kernel fruit that surrounds the palm kernel seed of the oil palm tree (elaeisguineensis). coconut shell: the coconut shell used for the experiment was obtained from badagry town in lagos. 20 oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 the palm kernel tree is native of west africa as well as widely spread throughout the tropics. it grows to about 9 m in height and characterized with a crown of feathery leaves that are up to 5 mm long. flowering is followed by the development of cluster of egg-shaped red, orange or yellowish fruits, each about 3 cm long. palm kernel shells are obtained as crushed pieces after threshing or crushing to remove the palm seed after the production of palm kernel oil. it is estimated that the palm kernel shell constitutes about 34.5% of a single ripe, fresh fruit (aragbaiye, 2007). palm kernel shells are derivable in large quantities and their disposal has continued to constitute major environmental problems. figure 1 shows the palm kernel shell. fig 1. palm kernel shell. coconuts (cocosnucifera) are referred to as "man's most useful trees", "king of the tropical flora" and "tree of life". coconuts are the most important of cultivated palms and the most widely distributed of all palms. coconut is a tall cylindrical-stalked palm tree, reaching 30 m in height and 60-70 cm in diameter. it is a tropical plant for low altitudes and generally suitable for cultivation in sandy seashore. the most important part of the tree is its fruit, which is eggshaped, about 30 cm long and 25 cm in diameter. the more external layer of the fruit is thin and smooth, its fibrous mesocarp is 3-5 cm thick and the endocarp is very hard. the fruit has a large central cavity, which contains a sweet liquid (coconut water). the fruit is ovid in shape and in the husk is about the six of a football. the fruit consists of 4 parts: about 35% husk, 12% shell, 28% meat and 25% water. figure 2 shows different sizes of coconut shell. fig 2. different sizes of coconut shell. the palm kernel shell (pks) and coconut shell (ck) was sun dried for 48 hours to remove moisture from it. it was then subjected to internal combustion using a furnace, burnt for 24 – 48 hours and allowed to cool for about 12 hours. the burnt ash was collected and sieved through a oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 21 bs sieve (75 microns). the resulting palm kernel shell ash (pksa) and coconut shell ash (csa) which has the required fineness was collected for use, figure 3 is the particle size distribution performed on the fine aggregate. using a mix design ratio of 1:2:4 and water binder ratio of 0.63, a total of one hundred and forty four concrete cubes of size 150x150x150 mm were casted using varying opc : pksa and opc : csa ratios of 100:0 , 90:10 , 80:20 , 70:30 , 60:40 and 50:50 respectively i.e. 12 cubes for each percentage of replacement. the cubes were cured and crushed after 7, 14, 21 and 28 days respectively to determine the compressive strength. the various tests carried on the materials used for the experiment are: sieve analysis for fine aggregate, slump test for concrete, compaction factor, compressive strength test, aggregate impact value test and aggregate crushing value test. fig 3. particle size distribution analysis of fine aggregate. from the curve obtained: ; ; ( ) where: is the particle diameter, at which 60 percent by weight of the soil is finer, is particle diameter, at which 30 percent by weight of the soil is finer, is particle diameter, at which 10 percent by weight of the soil is finer, is the coefficient of uniformity and is the coefficient of curvature. note: a well graded soil has a value of 5 or more; thus, the fine soil is well graded since the is 6, i.e. more than 5. 22 oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 calculation of aggregate crushing value (granite) weight retained on 10 mm bs sieve (m1) = 480.0 g weight retained on 2.36 mm bs sieve (m2) = 299.0 g weight passing through 2.36 mm bs sieve (m3) = 152.0 g similarly, the value of aggregate impact value (granite) is calculated in the same manner. aggregate impact value = 22.61. remark: the value obtained is 22.61 which are within the acceptable limit of +3 to -3. 4. results table 1 and table 2 are the summary of results of the test carried out on the concrete mixes; while table 3 is suggested values of workability. figure 4 and figure 5 show the compressive strength variations of partial replacement of cement with pksa and csa respectively. table 1. results of the test carried out on the concrete mix for pksa. replacement (%) slump (mm) fully compacted concrete (fc) partially compacted concrete compacting factor (pc/fc) air entrainment (%) pressure water cement ratio 0 55 17.2 15.2 0.90 1.5 1.5 0.55 10 35 17.2 15.6 0.90 0.5 1.5 0.61 20 50 17.1 16.4 0.95 0.5 1.5 0.63 30 38 17.1 16.0 0.93 1.2 1.5 0.55 40 33 17.2 15.8 0.91 0.8 1.5 0.63 50 35 17.1 16.8 0.98 0.6 1.5 0.55 table 2. results of the test carried out on the concrete mix for csa. replacement (%) slump (mm) fully compacted concrete (fc) partially compacted concrete compacting factor (pc/fc) air entrainment (%) pressure water cement ratio 0 60 17.6 16.5 0.94 1.2 1.5 0.5 10 65 17.58 16.4 0.93 1.0 1.5 0.55 20 65 17.8 16.65 0.94 0.8 1.5 0.6 30 55 17.75 16.8 0.93 0.6 1.5 0.61 40 40 17.63 16.61 0.94 0.61 1.5 0.64 50 55 17.5 16.1 0.92 1.0 1.5 0.64 table 3. suggested values of workability. application slump (mm) compaction factor time in vee-bee (s) 1. concreting of shallow sections with vibrations 0.75-0.80 10-20 2. concreting in light reinforced sections in vibrators 0.80-0.85 5-10 3. concreting of lightly reinforced sections with vibrations 25-75 0.85-0.92 2-5 4. concreting of heavily reinforced sections without vibration 75-125 more than 0.92 as can be seen from table 1 and table 2, slump test results for concrete using pksa and csa with water cement ratio of 0.63 gives a slump value between 33 to 55 mm and 40 to 65 mm oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 23 respectively; when compared with the suggested value for workability in table 3, the average value of the slump is classified as a true slump. fig 4. strength variations with partial replacement of cement with pksa. fig 5. compressive strength variations with partial replacement of cement with csa. the average optimum compressive strength obtained at 28 days is 15.4 n/mm2 at 20% replacement of cement with pksa (figure 4). thus, the value obtained is suitable for light weight aggregate which falls within 15-25 n/mm2 as specify in rigid pavement design manual (2009). however, the optimum value of compressive strength obtained at 28 days is 20.58 n/mm2 at 10% replacement of cement with csa which can be used for heavy weight concrete while 17.26 n/mm2 obtained at 20% replacement is useful for light weight aggregate (figure 5). 24 oyedepo et al. j. build. mater. struct. (2015) 2: 18-24 5. conclusions concrete is used for many structures basically for its compressive strength to support any type of load. this work has shown that partial replacement of cement with 20% palm kernel shell ash (pksa) and coconut shell ash (csa) in concrete gives an average optimum compressive strength of 15.4 n/mm2 and 17.26 n/mm2 respectively at 28 days. the value obtained is suitable for light weight aggregate. however, the optimum value of compressive strength obtained at 28 days is 20.58 n/mm2 at 10% replacement of cement with csa which can be used for heavy weight concrete. thus, partially replaced cement with pksa and csa, using water cement ratio of 0.63 is suitable for the construction of light load structures such as floors lintels and low cost housing project; the use of pksa and csa as a partial replacement of cement produced a cheaper structural lightweight concrete using the optimum compressive strength value specify in the research; the research shows that the use of pksa and csa as a partial replacement for cement in concrete, at lower volume of replacement, will enhance the reduction of cement usage in concretes, thereby reducing the production cost and the environmental pollution caused by the dumping of the agricultural waste. 6. references abiola om. (2006). characteristics of palm kernel shells powder as additive in sandcrete. transaction of the nigeria society of engineers, 2(1), 21-32. aragbaiye ba. (2007). palm kernel shell as composite material in concrete. unpublished b. eng project report. dept of civil engineering, university of ilorin, ilorin, 25-31. falade f (1995). an investigation of periwinkle shells as coarse aggregate in concrete. building and environment, 30(4), 573-577. falade f, ikponmwosa ee and ojediran ni. (2010). behaviour of lightweight concrete containing periwinkle shell at elevated temperature. journal of engineering science and technology, 5(4), 379390. ndoke pn (2006). performance of palm kernel shells as a partial replacement for coarse aggregate in asphalt concrete. leonardo electronic journal of practices and technologies, 5(9), 145-152. nimityongskul p and daladar tu. (1995). use of coconut husk ash, corn cob ash and peanut shell ash as cement replacement. journal of ferrocement, 25(1), 35-44. olanipekun e, olusola k and ata o. (2006). a comparative study of concrete properties using coconut shell and palm kernel shell as coarse aggregates. building and environment, 41(3), 297-301. olutoge f. (2010). investigations on sawdust and palm kernel shells as aggregate replacement. arpn journal of engineering and applied sciences, 5(4), 7-13. osayemwen eo. (1992). an investigation of the characteristics of lightweight concrete made of periwinkle shells, palm kernel shells, sand and sawdust as aggregates. unpublished m.sc. dissertation. department of civil engineering, university of lagos. nigeria. osarenmwinda j and awaro a. (2009). the potential use of periwinkle shell as coarse aggregate for concrete. advanced materials research, 62, 39-43. rigid pavement design manual (2009). published by florida department of transportation. pavement management office, 2(0). slim ja and wakefield rw. (1991). the utilisation of sewage sludge in the manufacture of clay bricks. water s. a., 17(3), 197-202. vishwas pk and sanjay kbg (2013). comparative study on coconut shell aggregate with conventional concrete. international journal of engineering and innovative technology, 2(12), 67-70. j. build. mater. struct. (2021) 8: 168-178 original article doi : 10.34118/jbms.v8i2.1488 issn 2353-0057, eissn : 2600-6936 impact of iso: 17020 for quality assurance system in construction sector vikas patel, brijesh singh*, p n ojha, b. pandu ranga rao, amit sagar 1 national council for cement & building materials, ballabgarh * corresponding author: brijeshsehwagiitr96@gmail.com received: 11-08-2021 accepted: 19-12-2021 abstract. the objective of the paper is to analyze the various factors and loop holes that have a significant impact on effectiveness of quality and quality assurance system and to suggest recommendations to increase the quality performance of the construction projects. the paper also highlights the difference in quality assurance system of projects wherein iso: 17020 is not implemented and the project wherein it is implemented. in the current paper, national council for cement and building materials, india monitored 30 construction projects were selected with a construction cost between five to thirty crores covering 15 project with iso:17020 procedures and 15 project without iso:17020 procedures. the data was collected from these projects on various quality and management related aspects. these projects cover structures such as school buildings, community hall, hostel block, convention centers etc. the study was conducted for construction projects of different government bodies. this analysis has been mainly done covering the factors playing key role in quality of a structure during construction such as client’s commitment towards quality, quality of material, documentation, work practices, personnel etc. based on the data analysis, quality assurance system for these projects were categorized as excellent, good, average and poor in quality grading based on the various factors that directly or indirectly affects the quality and smooth functioning of project during and post construction. the difference in implementation of quality system with and without iso: 17020 is highlighted in the paper. key words: iso: 17020, quality system, quality grading, construction industry. 1. introduction in the era of open economy, quality has emerged as important parameter that determines the success or failure of an organization. quality, though an elusive attribute, has always been an important issue in construction. it is an integral concept that provides a competitive edge to one organization over the other. the construction industry being unique in nature is always expected to create a balance between cost, time and quality. this has become a critical parameter for engineering, procurement, construction and commissioning (epcc) contracts in particular where the agency is responsible for performance of the structure. quality assurance is needed because of the involvement of negligence and lack of knowledge especially in smaller projects which deduces the quality of the construction. how to establish a quality assurance system and implement the quality assurance system for overall upgrading of the construction quality has become a very essential topic. in order to build customer confidence, the quality of its work should be done according to the developed quality assurance program. now a days in order to enhance the quality implementation at construction site; laid down standards such as iso: 17020 accreditation for inspection bodies is the need of hour. the implementation of iso: 17020 is helping inspection bodies to gain confidence of the customers on the technical competence and recognition of good management practice. the construction industry of india is an important indicator of the development as it creates investment opportunities across various sectors. the industry is fragmented, with a handful of major companies involved in the construction activities across all segments and small and medium contractors who work on the subcontractor basis and carry out the work in the field. therefore, quality assurance (qa) becomes important due to involvement of large number of mailto:brijeshsehwagiitr96@gmail.com alomaja et al., j. build. mater. struct. (2021) 8:168-178 169 stakeholders. quality is one of the critical factors in the success of construction projects. quality of construction projects, as well as project success, can be regarded as the fulfillment of expectations (i.e. the satisfaction) of the project participants. the construction industry in india has been struggling with quality issues for many years. the construction costs can be significantly reduced if the construction industry embraces the concept of quality assurance and control. quality control (qc) is concerned with actual measurement, testing or supervision of manufacturers own final product control, either by inspection of each unit or by sample testing. it has become more important nowadays to test buildings to assess whether they are performing as expected well before their anticipated service life attributing the failure in quality system. poor workmanship can lead the construction to an extent that may not meet the requirement of a stable and sustainable infrastructure. the standard of workmanship can be improved by providing adequate training, appropriate instructions and clear checklists as well as ensuring there is on-site supervision and monitoring and an ongoing process of feedback to ensure continuous improvement. unfortunately, quality control is often forgotten in the rush to complete the project, or sometimes just turns into a paper exercise. however, it must be ensured that the quality control is treated seriously, is not only about paperwork, and that people are delegated with specific responsibilities to deliver the correct quality as poor quality results in:  additional costs and delays when work have to be redone.  additional costs when defects have to be repaired later, for increased maintenance costs or for disruptions to their operations while defects are repaired.  can cause injury and death if the structure fails. the objective of construction independent quality assurance is to independently assure that the activities of a specific project are being performed in accordance with all contractual specifications, codes and standards or government regulations. the qa/qc is verified through checks audits, inspections and witnessing. these audit services are carried out completely independently of the individual contractors, materials suppliers, manufacturer or sub-contractor as well as final user. quality assurance (qa) provides the facility owner with adequate confidence that a structure, component, material or system meets pre-stated quality standards and will perform satisfactory during service. independent quality assurance (iqa) examines whether projects and programmes are on track for successful completion or whether action is required to prevent failure. it can improve the probability of successful project delivery and minimize the risk of cost and time blowouts. an iqa often provides very large returns by preventing costly project mistakes and delivering benefits earlier. an iqa is usually conducted on behalf of the project sponsor or executive to provide assurance that the project is appropriately planned, managed and controlled, and that the governance supports the project to best effect. all the quality paperwork in the world, with all their signatures, will not turn a poor quality product into a good quality product. however, the paperwork trail is important in ensuring that proper quality procedures have been implemented and followed. the process of assuring quality by independent quality assurance will further be improved by the implementation of iso: 17020 as the overall system of quality system can be improved with the proper acceptance of the guidelines of the iso: 17020. the requirements of iso 17020 are contained mainly in 14 major sections including: (i) administrative requirements, (ii) requirements for independence, impartiality & integrity, (iii) confidentiality, (iv) organization & management, (v) quality system, (vi) personnel, (vii) facilities & equipment, (viii) inspection methods & procedures, (ix) handling of inspection samples & items, (x) control of records, (xi) inspection reports & inspection certificates, (xii) subcontracting, (xiii) complaints & appeals and (xiv) cooperation with other inspection bodies. iso 17020 requires procedures in several important areas, including procedures for performing inspections, performing non-standard inspections, corrective action, inspection of materials received by the organization, appropriate 170 alomaja et al., j. build. mater. struct. (2021) 8:168-178 storage facilities and protecting the integrity & ensuring the security of data produced by the organization. 2. aim of study the objective of the paper is to analyze the various factors that have a significant impact on effectiveness of quality and quality assurance system. the aim here is to put forward various key aspects and challenges encountered in achieving the quality in construction. the paper highlights the impact of implementation of iso: 17020 in construction system which can contribute to overall up gradation in quality of projects. 3. study analysis to analyze the quality of the different construction projects, national council for cement and building materials, india monitored 30 construction projects (15 before implementation of iso: 17020 and 15 after implementation of iso: 17020) were selected for delhi and ncr with a construction cost between three to five crores and data was collected from these projects on various quality and management related aspects. these 30 projects cover structures such as school buildings, community hall, hostel block, roads, drainage etc. the study was conducted for construction projects of four different government bodies. these projects were assessed for the quality assurance based on the factors playing key role in quality of a structure during construction such as documentation, quality of material, work practices, personnel and client commitment towards quality etc. factors considered to evaluate the quality of project documentation quality of material work practices personnel client commitment towards quality approved structural drawing use of approved /nonconforming material pre-calculation of quantities of material repetition of common issues by workmanship availability of equipments at site mix design storage of material concrete cover at site (durability issue) shortage of staff action taken report on nonconformances source approval material testing alignment & quality of shuttering awareness of latest standards and specifications presence at site qa/qc system available concrete quality reinforcement detailing timely intimation for checking of major work curing at site alomaja et al., j. build. mater. struct. (2021) 8:168-178 171 3.1. factors considered 3.1.1. documentation quality records describe the work involved and contain evidence that work items met the requirements of the plans and specifications; sampling and testing personnel, procedures and equipment were properly certified or accredited; and corrective action was taken for any nonconforming conditions. documents such as structural drawing, source approval and mix design ensure that the construction meets the quality requirement as well as functional requirement post construction. availability of qa/qc system/service ensures the evaluation of overall project performance on a regular basis to provide confidence that the project will satisfy the relevant quality standards. the graph below shows the percentage of the projects that were fulfilling the requirements of the documentation with all the documents duly approved and used during the construction with and without implementation of iso: 17020. fig. 1. graph representing the projects fulfilling documentation requirement the graph here (fig. 1) shows that the documentation after implementation of iso: 17020 has been improved in all respect as while following guidelines of iso: 17020 these documents becomes must to be complied. proper documentation can only be achieved if it is strictly compelled as if kept lenient there surely will be negligence. therefore, iso: 17020 makes sure that the essential documents like drawings, mix design, etc., are reviewed and records are well maintained to assess the quality of work at any time. 3.1.2. quality of material to ensure the quality of materials, all the materials should be procured from the approved sources as per the tender documents and the source should not be changed during course of the project. storage of material (steel, cement, water & bricks etc.) plays an important role and small negligence will result in reduced quality and increased overall cost of the project. material testing is one of the major tools with the construction industry to check the quality of materials used in construction. the major part in any construction project includes concrete and hence quality of concrete has direct influence on the overall performance of structure. taking care of following governing factors can ensure concrete quality: 172 alomaja et al., j. build. mater. struct. (2021) 8:168-178  workability and control / checks on w/c (water cement ratio)  transport and placing time lag, tools used for placement  expansion joints type and execution  finishing of concrete including placement, compaction  provision for maintenance of concrete surface the graph below shows the percentage of the projects that were fulfilling the requirements of the quality of the material used for the construction including the approved source, proper storage and ensuring timely material testing under quality control with and without implementation of iso: 17020. fig. 2. graph representing the projects fulfilling the quality of material used the graph (fig. 2) shows that the storage of materials was not as per the specifications for many projects which is major point of concern. however, with implementation of iso: 17020 the percentage of the projects with proper storage of materials, material testing and concrete quality can be observed as improved when compared to when iso: 17020 was not implemented. improper storage of materials results in degradation of the even good quality materials. iso: 17020 provides with checks that ensures the proper storage, testing, handling and quality of the material used for construction. iso: 17020 not only deals with material but also ensures proper process involved with the use of materials at construction site. 3.1.3. work practices even ensuring the quality of materials will not result in the good quality end product if the construction methods used are not as per the standards. construction procedures and the technology used have a great influence on the quality, which if not met to the specifications will result in structure that is not safe and sustainable. some factors that needs to be taken care of during construction includes pre-calculation of quantities of material, durability related issues such as size, grade, spacing of cover blocks at site, alignment & quality of shuttering and proper reinforcement detailing that can be understood by the site personnels. since the major part of the structure comprises of concrete along with its quality precautions should be taken during the execution of concreting such as proper transportation, placement, compaction and finally curing once concrete is hardened. the graph below shows the percentage of the projects that were fulfilling the requirements of the work practices by ensuring the correct methods and procedures during the execution of the work with and without implementation of iso: 17020. alomaja et al., j. build. mater. struct. (2021) 8:168-178 173 fig. 3. graph representing the projects fulfilling the work practices the above graph (fig. 3) shows that improvement was there after implementation of iso:17020, however this improvement was not significant as the factors involved under this section contains various practical constrains which sometimes becomes difficult to take care at site. their improvement can be achieved in a long run if iso:17020 is followed as the processes involved and the implications of the processes vary with the officials working, time, place, etc. 3.1.4. personnel the construction industry is booming and as a result, increase in construction defects is common nowadays. one of the major areas of concern is poor workmanship. in simple terms, workmanship is the skill and quality used in making the product or completing a project. workmanship is about quality; good or bad. if workers are careless or don’t follow proper protocol, then it leads to a finished product that lacks the quality anticipated. the failures of building structures are due to workmanship negligence and the lack of effort put into quality control processes on the construction site. the construction industry, and the professionals at every level are responsible for meeting standards of quality, care, and expertise. quality work begins with the conscious efforts of contractors to execute the specifications of the contract. unskilled workman, unsuitable equipment and materials, and lack of project management lead to poor workmanship. poor workmanship can result in problems such as corrosion, molding, plumbing issues, injuries and death, loss of water through evaporation, cracks in foundation and walls and leaking roofs. the graph below shows the percentage of the projects that were fulfilling the requirements of the good manpower with technical expertise and awareness of latest specifications and technology used in the construction with and without implementation of iso: 17020. 174 alomaja et al., j. build. mater. struct. (2021) 8:168-178 fig. 4. graph representing the projects fulfilling the requirement of personnel the above graph shows that improvement was there after implementation of iso:17020, however this improvement was not significant as the factors involved under this section attributes to the officials, workers and labors working at site. there major factor that needs to be considered is that the officials, workers, labors needs to be more or less same for particular project during the entire duration of construction. their improvement can be achieved in a long run if iso:17020 is followed as the way and the awareness of the right methods, processes and use of materials vary with the officials working, place, etc. 3.1.5. client commitment towards quality client’s attitude towards the project shapes the progress and quality of the project. presence of client’s representative at site ensures the proper workmanship and work practices used in construction. major problem with the projects is availability of equipments at site that results in improper construction practices. client can play an important role by ensuring that the action is taken on the non-conformances reported and by timely intimating the checking of major work to the independent quality assurance agency. the graph below shows the percentage of the projects where client’s commitment towards the quality was upto the mark. fig. 5. graph representing the projects where quality was ensured by client alomaja et al., j. build. mater. struct. (2021) 8:168-178 175 the above graph shows that improvement was there after implementation of iso: 17020, however the significant improvement was not observed which can be attributed to fact that iso: 17020 provides the guidelines for the improvement of the quantifiable factors and client’s commitment is to be morally developed on itself. however, iso:17020 helps in achieving that as some factors like availability of equipment’s, presence at site, etc., are ensured under its guidelines. 4. quality grading of the quality assurance system for projects studied each factor mentioned above was given weightage (1 to 3) based upon its relative importance towards the quality of the project and was rated on a scale from 2 to 5 based on the inspections and analyzing the data from the projects. based on the ratings obtained by the project, it can be classified under following categories: category/ range of rating conformances to the factors considered excellent (>85%) all major and minor factors conforming. good (70-85%) all the major factors conforming and few nonconformances related to the minor factors such as source approval, pre-calculation of quantities of materials and presence of client at site. average (6070%) few non conformances to major and minor factors considered such as durability, availability of equipments at site, line & levels and alignment & quality of shuttering. poor (<60%) non conformances for the major factors considered such as structural drawings, material testing, concrete quality, durability, training of staff, awareness to latest standard and specifications. category range of rating no. of projects before implementation of iso:17020 after implementation of iso:17020 excellent >85% 0 6 good 70-85% 11 9 average 60-70% 3 0 poor <60% 1 0 fig. 6. pie chart indicating quality grading of quality assurance system for projects studied based on detail study given in table as appendix 1 & 2 176 alomaja et al., j. build. mater. struct. (2021) 8:168-178 5. conclusion the grading distribution obtained for quality assurance system of the projects shows that the most of the projects were categorized under good and average category before implementation of iso: 17020 while after implementation of iso: 17020 all the projects were under excellent and good category. the major negligence found were with storage of materials, work practices used during construction, availability of equipment’s at the site and negligence by the personnel working at site which should be improved in order to attain the desired quality and service life of finished infrastructures. quality is an essential element for sustainability and consumer satisfaction. it is very important to achieve the quality of the finished product in the construction industry. the high cost of the infrastructures makes it necessary to ensure the quality of the finished structure. therefore, a system with proper guidelines to achieve the desired quality should be available and followed at best to have enhanced overall quality of the structure. iso: 17020 specifies the various guidelines to make the quality assurance system more systematic and effective. effective quality assurance system will not only enhanced quality but will rather help in achieving the more sustainable and efficient infrastructure along with optimum usage of resources. based on the study done, it can be inferred that implementation of iso: 17020 has definitely helped in improving the quality system at site and will definitely further improve the quality system which ultimately will lead enhanced service life of structure. 6. references vikas patel, mohd. ali saifi, b. pandu ranga rao, brijesh singh & pritam rawat (2017) “independent quality assurance monitoring system in construction-a case study for delhi” 15th ncb seminar 2017 irc sp 47 – 1998 abdol r. chini. & hector e valdez. (2013) “iso 9000 and the u.s. construction industry” j. manager eng. 19 (2). arditi d. & gunaydin h.m. (1997) “total quality management in the construction process” j. international journal of project management 15(4) state of california department of transportation construction, quality assurance program manual. teena joy (2014), “a study on factors influencing quality of construction projects”, international journal of innovative research and development, 2278-0211. astm, (2007). astm international standards worldwide. ammad hassan khan, salman azhar, arshad mahmood (2008) “quality assurance and control in the construction of infrastructure services in developing countries – a case study of pakistan”, first international conference on construction in developing countries (iccidc–i). griffith, a (1990). “quality assurance in building” macmillan education. appendix – 1 alomaja et al., j. build. mater. struct. (2021) 8:168-178 177 178 alomaja et al., j. build. mater. struct. (2021) 8:168-178 appendix – 2 j. build. mater. struct. (2015) 2: 10-17 https://doi.org/10.34118/jbms.v2i1.14 issn 2353-0057 effect of bentonite on the saturated hydraulic conductivity of landfill liners based on dune sand gueddouda mk 1,*, goual i 1, taibi s 2, aboubekr n3 and lamara m4 1 laboratoire de recherche de génie civil, université amar telidji, laghouat, algeria. 2 laboratoire ondes et milieux complexes, université du havre, le havre, france. 3 laboratoire eau et ouvrages dans leur environnement, université abou bekr belkaid, tlemcen, algeria. 4 laboratoire de recherche de génie civil et environnement, université de jijel, algeria * corresponding author: gueddouda_mk@yahoo.fr abstract. sand-bentonite (sb) mixtures have been used successfully for construction of hydraulic barriers when clayey soils are not available. compacted layers of sb mixtures have been proposed and used in a variety of geotechnical structures as engineered barriers for the enhancement of impervious landfill liners. in the practice we will try to get an economical mixture that satisfies the hydraulic and mechanical requirements. the effects of the bentonite additions are reflected in lower water permeability, and acceptable shear strength. in order to get an adequate dune sand bentonite mixtures, an investigation relative to the hydraulic and mechanical behavior is carried out in this study for different mixtures. according to the results obtained, the adequate percentage of bentonite should be between 12% and 15 %, which result in a hydraulic conductivity less than 10–6 cm/s, and good shear strength. key words: dune sand, bentonite, hydraulic conductivity, shear strength, insulation barriers. 1. introduction rapid technological advances and population needs lead to the generation of increasingly hazardous wastes. the society should face two fundamental issues, the environment protection and the pollution risk control. one of the actual solutions, for handling these contamination problems, is by enclosing the wastes in a specific location, using insulated barriers. the efficiency of these insulated barriers depends largely on their hydraulic and mechanical behavior along with their capacities of attenuation and retention of the contaminant. compacted sandy soils with small additions of bentonite, known also by sand-bentonite (sb) mixtures, have been proposed and used as an adequate material for these insulation layers. in order to be efficient, theses insulation barriers should fulfill some requirements (chapuis, 1990; parker, 1993): the typical thickness for these layers ranges between 15 and 30 cm; permeability at saturated state varies between 10-6and 10-8cm/s (chapuis, 1990; parker, 1993); properties of exchange and adsorption should be capable to hold some preferentially pollutants (ademe, 1999); physical stability of the material in contact with water; a swelling potential that ensure good contact with the host rock and permit the replenishment of existing cracks or that will develop in the future; the sand must also possess some characteristic such grain size distribution, in order to prevent bentonite leaching from the skeleton and hence ensuring the hydraulic stability of the mixture. in algeria, the rapid development of urban areas and the growth of oil industry in the south regions, begin to generate enormous quantities of hazardous wastes. in order to avoid mailto:gueddouda_mk@yahoo.fr gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 11 groundwater pollution and environment degradation, an insulation barrier using dune sand, which is an available and economical local material, enhanced by small addition of bentonite is proposed. in searching for an adequate mixture, an investigation study is carried out on several dune sand calcium bentonite mixtures with different percentages of bentonite additions, which varies between 3% and 15%. 2. materials used for study the bentonite used in this study is extracted from maghnia mine (hammam boughrara, 600 km west of the capital algiers). dune sand is a material which available in large quantities within the algerian south, it is known as desert sand. the dune sand used is a local material from laghouat region. results of chemical analysis showed that maghnia bentonite is composed mostly of silicate with 17 % of aluminates (table 1). for dune sand and according to the chemical analysis (table 1), the major component is silicate sio2 (95%). table 1. chemical composition of maghnia bentonite and dune sand. % sio2 al2o3 na2o cao k2o mgo fe2o3 caco3 so3 bentonite 65.2 17.25 3 5 1.7 3.10 2.10 / 2.65 dune sand 95.87 / / / / / / 2.9 0.91 the grain size distribution of the bentonite is shown in figure 1. it is very fine clay; about 60% of particles have a diameter less than 2 µm (table 2). the value of the plasticity index indicates that the bentonite of maghnia is highly plastic; this is confirmed by large specific surface (sp) of 462 m2/g. according to the classification of skempton (1953), based on the activity, the bentonite of maghnia presents a high percentage of calcite montmorillonite (ca+2). the grain size distribution of dune sand is also plotted in figure 1. values corresponding to uniformity and curvature coefficients are cu = 1,67 and cc=1,1, respectively. thus, the dune sand is classified as poorly graded fine sand according to the unified soil classification system (uscs). the physical characteristics of bentonite and dune sand are summarized in table 2. fig 1. grain size distribution of dune sand-bentonite mixtures (s: dune sand, b: bentonite). dune sand – bentonite (sb) mixtures used in this study are: 3% b + 97% s, 5% b + 95% s, 10% b + 90% s, 12% b + 88% s, 15% b + 85% s. 12 gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 table 2. physical and mechanical properties of sb mixtures  80m c2  2m cu dmax (kn/m) wopt (%) wl wp ip gs sst (m2/g) g (%) pg (kp) 100 % s+0 % b 2% 0% 1,7 19 ,2 10 ------2,65 1,4 ------ 97 % s +3 % b 4% 0% 1,8 19,1 10,5 20 ---2,6395 10 0,85 17 95 % s +5 % b 5% 0% 2,5 18,8 11,5 21 ---2,6325 15 2,2 38 90 % s+10 % b 11% 5% 2,6 18,3 12,8 27 21 6 2,6153 43 5,90 124 88 % s +12 % b 12% 7% 2 ,6 17,8 14,0 28 18 10 2,6085 60 7,30 150 85 % s+15 % b 15 % 9% 3,8 17,0 15,2 34 22 12 2,5983 83 8,70 178 0 % s +100 % b 85% 60% ----12,1 32 141 48 93 2,34 462 47,5 852 atterberg limits obtained for different mixtures are presented in figure 2; mixtures with less than 10% are non-plastic soils, for percentage of bentonite additions between 10% and 12%, the soils become as little plastic clayey soils, while with percentage of 15% the soil appears to be a plastic. evolution of consistence limits according to percentage of bentonite additions follows a parabolic law. the plastic index ranges from 5,9 to 12,5 for bentonite content varies between 10% and 15%. 0 5 10 15 20 0 10 20 30 40 50 l l % , p l % percentage of bentonite % ll pl fig 2. relationship between atterberg limits and bentonite content. swelling tests are carried out using a classical œdomètre. dimensions of samples are 50 mm in diameter and 20 mm in height. the test is realized according to the free swelling method. the dune sand – bentonite mixture samples are prepared by a static compaction (velocity of 1 mm/min) for water contents and dry densities corresponding to the optimum proctor conditions. the total free swelling (g %) is computed using the following relationship: (1) results of free swelling are grouped in table 2. swelling evolution of sb mixtures over time is shown in figure 3. the free swell of the bentonite is approximately 47,5%, while for sb mixtures varying between 0,85% and 8,70% for bentonite content of 3 to 15%. as expected, the free swell is proportional with bentonite additions. for swelling pressure test (pg), we used the constant volume method (serratrice and soyez, 1996). results of swell pressure of sb mixtures are indicated in table 2. the swelling pressures of sb mixtures increases from 17 to 178 kpa for bentonite content 3 to 15% respectively. when bentonite content addition is more than 10%, swelling pressure is over 100kpa. results of physical and mechanical properties of sb mixtures are presented in table 2. gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 13 0,1 1 10 100 1000 10000 0 2 4 6 8 10 12 fr e e s w e ll in g g % time (min) 3% 5% 10% 12% 15% fig 3. swelling evolution of sb mixtures versus time. 3. measure of the hydraulic conductivity 3.1. measure of the hydraulic conductivity using oedometer an indirect method for evaluation of saturated hydraulic conductivity k is based on results of oedometer test (olson and daniel, 1981). in this method the coefficients of volume change mv [m2/kn] and consolidation cv [m2/s] deduced from compressibility and consolidation curves respectively, are used to obtain the conductivity coefficient. a specimen of 50 mm in diameter and 20 mm height is placed in metal ring and saturated during 24 hours. the loading pressure was selected according to a geometric progression σi+1/σi =2. the conductivity coefficient k [cm/s] is obtained using equation (2). in the present study, the cv coefficient is evaluated by taylor’s approach (figure 4). evolution of saturated hydraulic conductivity of sb mixtures as function of loading pressures is shown in figure 5. (2) w: unit weight of water [9.8 kn/m3]. 10 100 1000 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 1e-3 0,01 0,1 1 normal stress log '(kpa) c o e ff ic ie n t o f c o n s o li d a ti o n c v ( m 2 /s ) 0% b +100% s 3% b+97% s 5% b+95% s 10% b+90% s 12% b+88% s 15% b+85% s fig 4. coefficients of consolidation cv evolution of sb mixtures vs normal stress. 14 gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 10 100 1000 1e-13 1e-12 1e-11 1e-10 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 1e-3 0,01 0,1 k =10 -9 m/s h y d ra u li c c o n d u c ti v it y k ( m /s ) normal stress log  v (kpa) 0% b+100% s 3% b+97% s 5% b+95% s 10% b+90% s 12% b+88% s 15% b+85% s% fig 5. saturated hydraulic conductivity of sb mixtures vs normal stress. for all soils, the hydraulic conductivity varies inversely with the loading pressures (figure5); for examples, the saturated hydraulic conductivity for dune sand with 0% addition of bentonite varies between 1,1 10–3 to 1, 9 10–5 cm/s; whereas for mixtures of 15 % addition the values range from to 7,41 10–7 to 4, 58 10–10 cm/s. the effect of applied loading pressures on hydraulic conductivity is less significant, once become more than 400 kpa. other authors found these limiting values around 100 kpa (wu and khera, 1990) and 200 kpa (alston, 1997). olson (1986) has shown that the estimated permeability values are always less than the measured one. hydraulic conductivity of the dune sand bentonite mixtures decreases with increasing bentonite content. the hydraulic conductivity for pressure equal to 25 kpa decreases approximately three orders of magnitude when 12% bentonite content or more is used. for high bentonite content 12%, the saturated hydraulic conductivity is less than 10-6 cm/s. the target values relative to saturated hydraulic conductivity for containment liners, which should be between 10-6 and 10-8 cm/s, can be achieved for percentages of bentonite content greater than 10%, with an applied normal pressure over 200 kpa. for percentage of bentonite addition more than 12%, the hydraulic conductivity is less than 10-6 cm/s under a low vertical pressure (100 kpa). 3.2. measure of the hydraulic conductivity using triaxial cell this section presents the effect of confining stresses and hydraulic gradients on the hydraulic conductivity of compacted mixture (85%s+15%b). the measurement of the saturated hydraulic conductivity is carried on the permanent mode. the saturated hydraulic conductivity is measured using a permeameter with flexible walls. the experimental set up is composed of a triaxial cell (bishop-wesley revolution) equipped with three pressure volume controllers. the set up allows testing specimens of 35 or 50 mm in diameter and variable height to diameter ratio (h/d). the triaxial cell permits to apply an isotropic confining stress (up to 1700 kpa). the flow is directed vertically from the bottom towards the top. specimens are prepared by static compaction with double piston at optimum normal proctor conditions (wopt=15,2%, d max=17 kn/m3). specimen dimensions are d=35 mm and h=70 mm (figure 6). the displacement speed of the press is about 1,14 mm/s. the static compaction was retained because it permits to obtain more homogeneous specimen. gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 15 fig 6. specimen dimensions. once the specimen is placed inside the triaxial cell, a confining stress of 100 kpa is applied in the first time. in order to extrude the existing air bubbles between the membrane and the soil a low back pressure is applied at the base of the specimen (ue: back pressure at the base at the sample, ue =20 kpa, us: the pore pressure at the top at the sample, us=0 kpa). the progressive increase of the confining stress and the back pressure allows to free air bubbles from the connecting tubes (ue=30, ue=40 kpa) meanwhile preserving an average constant effective stress. the final confining stress applied on the sample during the saturation phase must be greater or equal to the swelling pressure of the mixture, which is around 180 kpa. the vertical deformation of the samples was recorded versus time and the samples were considered as saturated when the displacement of the piston became constant (less than 0,01 mm in 24 h) (souli, 2008). 3.3. measurement of the hydraulic conductivity in permanent mode (constant head) the experimental program is carried out using two series-tests. the first one consists to investigate the effect of the average confining effective stress with a constant hydraulic gradient (δu=constant), whereas the second consists to analyze the effect the hydraulic gradient with a constant average confining effective stress (σ3'=constant) (table 3). table 3. experimental program. 3 (kpa) ue (kpa) us (kpa) u (kpa) i 3’ (kpa) constant hydraulic gradient 200 40 0 40 57,14 180 420 240 200 40 57,14 200 620 240 200 40 57,14 400 820 240 200 40 57,14 600 1020 240 200 40 57,14 800 1220 240 200 40 57,14 1000 1520 240 200 40 57,14 1300 constant average confining effective stress 620 240 200 40 57,14 400 640 280 200 80 114,28 400 660 320 200 120 171,42 400 675 350 200 150 214,28 400 16 gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 4. experimental results and discussions 4.1. average confining effective stress effect figure 7 shows the variations of void ratio and the coefficient of hydraulic conductivity as a function of the average confining effective stress, respectively. it can be noted that the effect of the average confining effective stress on the hydraulic conductivity is more significant for values less than 200 kpa, beyond this stress the permeability seems to be almost constant, which in agreement with oedometer results. the measurement of the change in the volume of water throughout the test, allow deducing the final volume of voids. from the same figure, it can be seen that the void ratio decreases when the average confining effective stress increases and consequently result in a reduction of permeability. fig 7. hydraulic conductivity variation versus average confining effective stress. 4.2. average hydraulic gradient effect in the second case of the measurement of the saturated hydraulic conductivity, the average confining effective stress is kipped constant (σ3'= 400 kpa) while varying the hydraulic gradient. figure 8 presents the evolution of the hydraulic conductivity as a function of the hydraulic gradient. the experimental results can be approximated by a linear relation (see figure 8). similar results have been obtained by other authors (kenney, 1992; sayad-gaidi, 2003). fig 8. hydraulic conductivity variation versus average hydraulic gradient. gueddouda et al. j. build. mater. struct. (2015) 2: 10-17 17 5. conclusions in this research study we have shown that it is possible to obtain an adequate mixture intended for insulation barriers, using dune sand and a small amount of bentonite addition. according to the results obtained from this experimental study, we can advance the following conclusions: the common requirement on hydraulic conductivity (should be less than 10−8 to 10−10 m/s) is met for compacted soil with a minimum of 12% of bentonite addition. the results of the hydraulic conductivity obtained by the oedometric tests are lower than those obtained by the triaxial cell, this can be attributed to the lack of saturation of the specimen under oedometric conditions and some air bulbs may remain trapped within the soil. according to the results of permeability obtained by different methods, the adequate mixture proposed for the design of the worked barriers in the arid region (southern of algeria) is 85% s+15% b. in addition such mixture presents a moderate swelling and shrinkage potentials and hence it will be less subjected to cracks under drying conditions. finally, it can be stated that the use of dune sand, which is a local largely available material in the south of algeria, with small quantities of bentonite additions can provide an economical insulation barrier for waste disposal management. the procedure on site for mixing and placing of sand-bentonite mixture along with strict control of compaction procedures play an extremely important role for the final quality of the barrier. 6. references ademe (1999). storage facilities for household and assimilated wastes. techniques et recommandations, ademe editions, paris, 106p. (in french) alston c, daniel de and devroy dj (1997). design and construction of sand bentonite liner for effluent treatment lagoon, marathon, ontario. canadian geotechnical journal, 34(6), 841-852. chapuis rp (1990). sand-bentonite liners: predicting permeability from laboratory tests. canadian geotechnical journal, 27(1), 47-57. kenney tc, veen wv, swallow ma, & sungaila ma (1992). hydraulic conductivity of compacted bentonitesand mixtures. canadian geotechnical journal, 29(3), 364-374. olson re (1986). sate of art: consolidation theory, consolidation of soils: testing and evaluation. yang rn and townsend fc (eds), astm, stp 892, 7-70. olson re, & daniel de (1981). measurement of the hydraulic conductivity of fine-grained soils. permeability and groundwater contaminant transport, astm stp, 746, 18-64. parker rj, bateman s & williams d (1993). design and management of landfills. geotechnical management of waste and contamination, fell, phillips & gerard (eds), balkema, rotterdam, 209-252. sayad-gaidi, c. (2003). flow in saturated and unsaturated low permeability porous media. doctoral dissertation, école centrale de paris, france. (in french) serratrice jf & soyez b (1996). the swelling tests. bulletin des laboratoires des ponts et chaussées, 204, ref .4082, 65-85. (in french) skempton aw (1953). the colloidal activity of clays. proceedings of the third international conferences on soil mechanics and foundations engineering, 1, 57-61. souli h, fleureau jm, trabelsi ayadi m & besnard m (2008). physicochemical analysis of permeability changes in the presence of zinc. geoderma, 145(1), 1-7. wu jy & khera rp (1990). properties of a treated-bentonite/sand mix in contaminant environment. physic-chemical aspects of soil and related materials. astm stp, 1095, 47-59. j. build. mater. struct. (2015) 2: 25-32 https://doi.org/10.34118/jbms.v2i1.17 issn 2353-0057 self-compactibility of flowing sand-concrete containing dune sand and marble powder bouziani t structures rehabilitation and materials laboratory (sreml), university amar telidji-laghouat, algeria. t.bouziani@lagh-univ.dz abstract. this paper evaluates the self-compactibility of flowing sand-concretes (fsc) mixtures, incorporated various dune sand and marble powder contents, by testing flowability (determined by slump flow and v-funnel tests), passing ability (determined by lbox test) and segregation (determined by the visual stability index). the compressive strength at 28 days was also determined. results show that the slump flow of all fsc mixtures lie between 450 and 840 mm, thus satisfying flowability according the recommendations of afgc, except for the mixture made with 150 kg/m3 of marble powder (with a slump flow of 450 mm). v-funnel flow time, t500 time and l-box ratio of all mixtures were about 1.7-3.8 s, 0.6-2.3 s and 0.5-0.93 respectively. these results indicate that fsc have a v-funnel time shorter than the range proposed by efnarc recommendations (8-12 s). despite lower v-funnel times, no visual stability loss has been observed for all studied mixtures (all mixtures have a visual segregation index of 0 and 1). key words: flowing sand-concrete, dune sand, marble powder, self-compatibility. 1. introduction sand-concrete is known with its advantage of using abundant sands in saharan regions (such as dune sand), which has mechanical strength comparable to conventional concretes (bédérina, 2005; bouziani, 2011; bouziani, 2012a). this advantage becomes extremely interesting when sand-concrete can reach certain fluidity in order to flow under its own weight and completely fills the formwork even in the presence of dense reinforcement, without the need of any vibration, whilst maintaining homogeneity. however, to design a proper flowing sand-concrete (fsc) mixture is not a simple task. recent experimental investigations have been carried out in order to assess fresh and hardened properties of fsc (bouziani, 2012b; bouziani, 2013). the evaluation of self-compactibility of such concretes is a key issue in establishing the mix design method, to find out whether it could be appropriate for the site application. at required levels, fresh self-compacting concrete must possess the following key properties (afgc, 2008): flowability passing ability stability to achieve these properties, some of the basic requirements are for fsc mixtures to have high powder content and the incorporation of superplasticizer. the superplasticizer is necessary for producing a flowable mix, while mineral additions, such as marble powder, have a purpose, beside substituting a part of the cement, it propitiate the appropriate stability so that the selfcompactibility is reached. in fsc design, the dosage and fineness of aggregates have an important influence on quality of fresh and hardened properties. bouziani et al. (2012a) have found that dune sand is a useful component in optimizing the particle size distribution of river sand and thereby increasing flowability and mechanical properties of the fsc mixes. in this study, two series of seven fsc mixtures were produced. the self-compactibility of these mixtures was investigated by various tests (mini-slump, slump flow, t500 time, v-funnel flow mailto:t.bouziani@ 26 bouziani, j. build. mater. struct. (2015) 2: 25-32 time, visual stability index and l-box). the mechanical compressive strength at 28 days was also determined. 2. experimental program 2.1. materials an ordinary portland cement (cem i 42.5) and a marble powder (mp) were used. the chemical and physical properties of cement and mp are given in table 1. the sand used was a mixture of natural river sand (rs) and dune sand (ds). selected sands are subjected to grain size distribution analysis as per xp p 18-540 standard (afnor, 1997). the set of sieves are taken from 5 mm to 0.08 mm with aggregate and sieve shaker subjected to vibration for 15 minutes. the particle size gradation obtained thorough sieve analysis method and physical properties of ds and rs are grouped in table 2. the obtained results show that ds is characterized by its fineness and cleanness. a polycarboxylate-type third generation high range water reducing superplasticizer (sp) conforming to the nf en 934-2 standard (afnor, 2002) was used. the solid content, ph and specific gravity are 30 %, 6 and 1.07 respectively. table 1. chemical composition and physical properties of cement and mp. compounds (%) cement mp cao 63.55 53.1 sio2 23.24 0.54 al2o3 4.72 0.29 fe2o3 3.84 0.21 mgo 0.65 0.84 k2o 0.4 0.05 so3 0.28 0.03 na2o 0.1 / cl / 0.1 free cao 0.52 / insoluble residue 0.5 0.4 loss of ignition 2.15 44.4 specific density 3.1 2.7 blaine surface (cm²/g) 3950 3200 table 2. sieve analysis and physical properties of used sands (ds and rs). sieve size (mm) cumulative passing (%) ds rs 5 100 99.5 4 100 97.09 2.5 100 83.56 1.25 99.92 63.27 0.63 98.09 34.85 0.315 82.86 13.65 0.16 19.36 2.44 0.08 1.63 0.84 specific density 2.7 2.56 fineness modulus 1 3.03 sand equivalent 91 87.7 absorption (%) 2.18 0.59 moisture content (%) 1 0.33 2.2. mixtures proportions based on the results of bouziani et al. (2011, 2012a) seven fsc mixtures were designed in order to obtain an adequate fluidity and stability in fresh state and a good mechanical strength in hardened state. in first, four mixtures were prepared in which the sand was composed of a bouziani, j. build. mater. struct. (2015) 2: 25-32 27 binary blend of rs and ds, with different proportions of ds (0, 10, 20 and 30 % by weight of total sand), while keeping a constant marble powder (mp) content of 250 kg/m3. then, three mixtures were prepared in which the ds content was kept constant (10 %), while varying the mp content (150, 200, 250 and 300 kg/m3). the water/powder ratio (w/b) and the dosage of superplasticizer (sp) were kept constant (w/b = 0.43 and sp = 1.6 %). all mixtures were prepared with constant cement content of 350 kg/m3. the compositions of fsc mixtures are presented in table 3. table 3. compositions of prepared fsc mixtures. mix n° ds rs (kg/m3) mp (kg/m3) w/b water (l/m3) sp % kg/m3 (%) (kg/m3) fsc1 0 0 1500 250 0.43 254 1.6 5.6 fsc2 10 150 1350 250 0.43 254 1.6 5.6 fsc3 20 300 1200 250 0.43 254 1.6 5.6 fsc4 30 450 1050 250 0.43 254 1.6 5.6 fsc5 10 150 1350 150 0.43 211 1.6 5.6 fsc6 10 150 1350 200 0.43 232.6 1.6 5.6 fsc7 10 150 1350 300 0.43 275.6 1.6 5.6 2.3. testing procedure the mixing sequence consisted of homogenizing sands, cement and mp in a free fall non-tilting horizontal axis type laboratory mixer for three minutes. next, half of the mixing water was added and the mixture was mixed for three minutes. then, sp and the remaining water were added and mixing was continued for another three minutes. for determining the selfcompactibility of fsc, mini-slump flow, slump flow, t500 time, v-funnel flow time and l-box tests were performed. the tests were performed in accordance with afgc (2008) and efnarc recommendations (efnarc, 2002). due to the finesses of aggregates in fsc, the stability of fresh mixtures was assessed by visual stability index (vsi) (daczko, 2002). this method provides a numerical rating (from 0 to 3) to evaluate the stability of flowing concrete mixtures, based only on a visual observation. 3. results and discussion test results on the effect of ds and mp on mini-slump and slump flow are presented in fig. 1 and fig. 2 respectively. the results of slump flow test to rate the fluidity are of 450–850 mm at all mixtures, which satisfied the range of standard capacity of self-compacting concrete per the three class rating of afgc (2008), except for the mix fsc5 (made with 150 of mp kg/m3). fig 1. mini-slump for fsc: (a) effect of ds, (b) effect of mp. 28 bouziani, j. build. mater. struct. (2015) 2: 25-32 fig 2. slump flow for fsc: (a) effect of ds, (b) effect of mp. the effect of mp content on slump flow seems to be more dominant than the effect of ds replacement ratio. examples of slump flow test for fsc2 and fsc5 mixtures are presented in fig. 3. from the results in fig. 2, it can be seen that the slump flow is higher for the mix fsc2 than the other mixes. this is may be a result of the high compactness of aggregates at 10 % of ds, which results in a smaller volume of void to be filled and hence larger amount of excess paste is gained for lubrication purpose (bouziani, 2012a). results in fig. 2 (b), show also that the slump flow of fsc will increases with the increase of mp amount. fig 3. examples of slump flow test: (a) fsc2, (b) fsc5. many researchers have used the mini-slump as indicator of slump flow of highly flowable concrete mixtures. edmasatu has suggested that values between 250 and 280 mm for minislump will produce successful self-compactibility. however, chai suggested a minimum minislump value of 300 mm (domone, 1999). the relationship between the results of mini-slump and slump flow of fsc is presented in fig. 4. this figure shows that there is a good relationship between mini-slump and slump flow (with r² = 0.91). from these results, it can be concluded that mini-slump values between 250 and 330 mm are sufficient to predict a slump flow ranged between 550 and 850 mm of fsc (interval recommended by afgc (2008)). bouziani, j. build. mater. struct. (2015) 2: 25-32 29 fig 4. correlation between mini-slump and slump test results. with the same test, the time t500 is also measured when the mixture is slumping until it reached 500 mm of slump flow. as shown in fig. 5, the mix fsc2, with 10 % of ds show the minimum value of t500 (0.6 s). this measure of t500 could not be carried out for the mixture fsc5 because it did not reach a slump flow of 500 mm (fig. 3(b)). fig 5. t500 time for fsc: (a) effect of ds, (b) effect of mp. the effect of ds and mp contents, on v-funnel time is presented in fig. 6. these results show that fsc mixtures have a v-funnel time ranged between 1.7 and 3.8 s. it can be observed that v-funnel times of all fsc mixtures are outside the range of 8–12 s, specified by efnarc recommendations. it is considered that a mixture having a v-funnel time below 8 s has a potential of stability loss. conversely, in this experimental study no visual stability loss has been observed at all mixtures (all mixture have a vsi of 0 and 1). such results seemed to be caused by the absence of coarse aggregate in fsc, which allowing rapid deformability without segregation. it should be noted that higher t500 and v-funnel times may reduce the acceptability of mixtures for self-compactibility (felekoğlu, 2007). 30 bouziani, j. build. mater. struct. (2015) 2: 25-32 fig 6. v-funnel time for fsc: (a) effect of ds, (b) effect of mp. the determined l-box ratios h2/h1 of fsc mixtures are presented in fig. 7 (where h1 is the high of fsc, measured inside the vertical part and h2 is the high measured in the extremity of the horizontal part of l-box). it can be observed that studied mixtures have a good filling ability, except for the mixtures fsc4, fsc5 and fsc6 which have l-box ratios lower than 0.8. due to the absence of coarse aggregate in fsc, it can be said that the observed blocking is caused by the high viscosity of fsc mixtures. examples of l-box test for fsc2 and fsc5 mixtures are presented in fig. 8. the decrease in l-box ratio of the mixture fsc4 (made with 30 % of ds) is due to the large finesses of ds and to their need for water (absorption coefficient of ds = 2.18%). for the mixtures fsc5 and fsc6, the decrease in l-box ratios can be reported to the low dosages of mp. fig 7. l-box ratios for fsc: (a) effect of ds, (b) effect of mp. fig 8. examples of slump flow test: (a) fsc2, (b) fsc5. bouziani, j. build. mater. struct. (2015) 2: 25-32 31 fig. 9 represents the results of testing hardened fsc for the compressive strength at 28 days. as shown in this figure, it can be seen that for a constant mp content of 250 kg/m3, the ds has an optimal content (at 10 %) for which the compressive strength at 28 day is better. such result seems to be offered by the high compactness of aggregates at 10 % of ds. it can be also seen that for constant ds content of 10 %, the compressive strength at 28 day decreases (from 41 to 37 mpa) with the increase of mp content (from 150 to 300 kg/m3). for a constant water/binder ratio, the reduction of compressive strength may be caused by the increase of water/cement ratio with the increase of mp content. fig 9. compressive strength at 28 day for fsc: (a) effect of ds, (b) effect of mp. 4. conclusions the following conclusions can be drawn from the present study: the increase of mp content in fsc improves the flowability (by increasing slump flow and decreasing v-funnel flow time). an optimal ds content is obtained (10 %), for which the flowability of fsc is improved (a highest slump flow and a lowest v-funnel times). the relationship between the mini-slump and slump flow of fsc was evaluated by a linear regression. in result, correlation coefficient is 0.91, indicating a close relationship between the two tests. the relationship between the mini-slump and slump flow studied for flowing sand concretes indicates that mini-slump values between 250 and 330 mm are sufficient to predict a slump flow ranged between 550 and 850 mm of fsc (interval recommended by afgc). successful self-compactibility of fsc is obtained, but is not in the limits suggested by afgc and efnarc recommendations, notably with v-funnel time results. even thought, there are much work on self-compactibility of flowing concretes, test methods stipulation are not universally accepted rules. degree of toleration depends on the engineering judgement, material type and variety. further research is necessary to establish proper adequacy between flowability and stability of fsc. 5. references afgc (2008). recommendations for the use of self-compacting concrete, french association of civil engineering, scientific and technical documents, pp. 63. afnor (1997). xp p 18-540 standard, granulats: définitions, conformité, spécifications, association française de normalisation, paris. (in french) afnor (2002). nf en 934-2 standard, béton et constituants des bétons, tome 1: spécification du béton et de ses constituants, 5ème ed., association française de normalisation, paris, 2002. (in french) 32 bouziani, j. build. mater. struct. (2015) 2: 25-32 bédérina m, khenfer m m, dheilly r m, quéneudec, m (2005). reuse of local sand: effect of limestone filler proportion on the rheological and mechanical properties of different sand concretes. cement concrete res., 35(6):1172-1179. bouziani t, bederina m, hadjoudja, m (2012a). effect of dune sand on the properties of flowing sandconcrete (fsc). int. j. concrete struct. mater., 6(1):59-64. bouziani t, benmounah a (2013). correlation between v-funnel and mini-slump test results with viscosity. ksce j. civil eng., 17(1):173-178. bouziani t, benmounah a, bédérina m (2012b). statistical modelling for effet of mix-parameters on properties of high flowing sand concrete. j cent south univ, 19:2966-2975. bouziani t, benmounah a. bédérina m, lamara, m (2011). effect of marble powder on the properties of self-compacting sand concrete. open constr. build. tech. j., 5:25-29 daczko j a (2002). stability of self-consolidating concrete, assumed or ensured? conference proceedings of first north american conference on the design and use of self-consolidating concrete, acmb, pp. 245-251. domone p j, jin j (1999). properties of mortar for self-compacting concrete. in: proceedings of the 1st international rilem symposium on self-compacting concrete, skarendahl a and petersson o editors, pp. 109-120 efnarc (2002). the european guidelines for self-compacting concrete, specification, production and use. the european federation of specialist construction chemicals and concrete systems. felekoğlu b, türkel s, baradan b (2007). effect of water/cement ratio on the fresh and hardened properties of self-compacting concrete. build. environ., 42(4):1795-1802. j. build. mater. struct. (2021) 8: 115-127 review article doi : 10.34118/jbms.v8i2.1288 issn 2353-0057, eissn : 2600-6936 high-speed railway bridges under vehicle moving load and near fault seismic ground motions – review amudhan v 1*, hui qian2 1 research scholar, department of civil engineering, hindustan university, chennai & zhengzhou university, zhengzhou, china. 2 professor, department of civil engineering, zhengzhou university, zhengzhou, china. * corresponding author: amudhanresearch@gmail.com received: 10-03-2021 accepted: 02-11-2021 abstract. all time needs of maintenance of high speed train system and its infrastructure safety is must all over the world. nowadays, for the smooth running of hsr trains, most of the country depend on the hsr bridge structures, but there is still a lack of understanding in the behavior of structures under various factors like seismic and high speed moving load effects. to study the dynamic behavior of hsr bridges, it is important to consider the interaction of moving vehicle – bridge structure – ground surface showing that the different parameters involved in understanding the response of the structure. the main motivation of this study is to initiate the better understanding of the various parameters effects by those seismic and moving vehicles over the dynamic behavior of the hsr bridges. the effects of forward directivity pulses were considered to understand the behavior of hsr bridges against near fault earthquakes, which can make substantial impact over the seismic demand capacity of the moving vehicles and structures. the effects of high speed moving vehicles over the hsr bridges to understand the parameters involved in the dynamic behavior of the coupled system. this literature review can help the beginners and who initiate the study based on the dynamic behavior of high speed railway bridges and its components under seismic and moving load effects. keywords: high speed train, near-fault earthquakes, moving load, dynamics of railway bridges, resonance, vibrations. 1. introduction implementation of high speed rail plays a vital role in the current fastest transportation mode in all over the world due to this necessity of this transport system day by day upgrading with railway design standards occurs for safety and reliability of the system. by the same time due to the high population in china, people were in demand of rapid transport between the commercial cities, fig.1 shows that the high-speed rail developed rapidly in china over the past 15 years with substantial funding from the chinese government, especially the economic stimulus program during the great recession. in that time, the line laying process for successful running of hsr railway system were executed. and bridges were playing a major role in supporting the railway structures and movement of high-speed vehicles. comparison with other countries like germany, italy, united states, japan, spain hsr lines, china having the higher bridge occupation ratios giving the bridge ratio of 1.3–32.2% (fig.2) from various rail lines which helps to protect the agricultural and arable land economically as well as for the speedy constructions without any delay (he et al., 2017). due to smoothness and safety running of the train most of the bridge length were stretching about more than ten to twenty kilometers which makes us to realize that most of the high speed trains will be travelling over the bridges most of the time when the earthquake occurs (xia et al., 2006). so the excessive vibrations induced by the earthquake apart mailto:amudhanresearch@gmail.com 116 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 from the vibrations by moving vehicles which causes the discomfort for the bridge structures also it will affects the safety of the train vehicle which is passing through the structure. fig. 1. china hsr railway line map fig. 2. raising trends of hsr with bridges by the last 10 year plan of china. in the last 20 years, there were more than the count of hundred bridges which were collapsed and damaged due to various reasons worldwide. in those cases, most of the scenarios show that the damage induced to the bridge structure due to seismic vibration and dynamic excitation of the vehicle movements have been raised day by day and it indicates the necessity of implementing various initiatives to study the control measures and dynamic response of the bridge structures due to the excessive vibrations which affects the smooth running of the train as well as long term performance of the structures and its components. recent studies and various personal observations of researchers show that around 95 major earthquakes caused collapse or defects in railway bridges and it’s components that count few are explained by the following information’s. in the 1906 california earthquake, movement along the fault rupture caused separation between the connections of the substructure of southern pacific railroad bridge over the pajaro river. during the 1964 alaska earthquake due to the liquefaction issues the bridge structure experienced the vertical and lateral buckling of timber trestles and the lateral movement of column–trestle connections (william and byers, 2004). in the 1995 kobe earthquake caused a severe damage to the bridges because of collapse in concrete rigid frame viaducts due to inadequate ductile detailing to withstand the seismic loads and also by the bearing and restrainers failure (comartin et al. 1995). one of the common complaints arising frequently is the seating failure of the girder at the interconnection joints which cause the adjacent girders move out of phase. (roberts et al 2005) and the intensive statement says that the major failure due to the unseating problem caused by insufficient support width at the connections. (m. saiid saiidi, et al. 2005) bearing in mind the major earthquakes with high amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 117 intensity (chi-chi, kobe, and northridge earthquakes) shows that the lack of consideration for seismic vibrational control for the acting lateral loads without causing damage to the bridge. high intensity earthquake result in the longitudinal displacement which causes excessive displacement and opening at the intermediate connections in multi-span continuous bridges. wenzhou train collision (fig.3) was the major hsr train collision in china where two trains derailed each other, and four cars fell off the viaduct. 40 people were killed, at least 192 were injured, 12 of which were severe injuries. the collision was the first disastrous smash involving high-speed rail (hsr) in china, and is the third deadliest hsr accident in history. as mentioned above, there was a high intensity niigata earthquake on 2004, one of the high-speed train derailed when running on the elevated bridge at 200 km/hr., which breaks the safety record and creates loads of controversy about japan shinkansen railway system. a brief 12-15 seconds, massive earthquake of 8.9 magnitude hit mainland japan on 2011, which causes displacement of tracks in 2,590 places and the railway supporting structural components damaged . and on the same day, one of the trains running under test without passengers were derailed and halted by the emergency braking. rails where speed or not, but it’s one of the safest transport to go around because as per the national safety council review of 10 years of transportation fatalities between 1990 and 2011the bureau of transportation statistics shows that nearly 900,000 people died in highway crashes, while fewer than 15,000 died in train collisions. based on the statistic, the real fact of safety is really with rails even though the collapse and unexpected damages happened because of the natural calamities. therefore the researchers are keen to take initiatives in all kinds of measures to control the vibrations induced by earthquakes and the excessive vibrations induced by the moving vehicles towards the structure. in this review work, we start by reviewing articles which relate to the dynamic response of bridges under earthquake loads and moving loads of train. fig. 3. wenzhou train collision. china, 2011 2. seismic effects in high speed railway bridges meanwhile we entered 21st century, in and around 800 earthquakes with the magnitude more than 6.0 have happened in china because it is situated between the two largest seismic belts the circum-pacific seismic belt and the circum-indian seismic belt. and the regions cuddled by the pacific plate, the indian plate, and the philippine plate, the seismic fracture zones are well developed in this area. earthquakes have occurred in almost all the provinces, municipalities and autonomous regions except these three regions named guizhou, zhejiang and hong kong which shows the necessity of seismic design consideration for all kind of structures. on october, 2004, an earthquake disaster happened with a magnitude of 6.8, which caused a derailment incident of shinkansen train (fig.4. (a)) carrying about 155 passengers with 200km/hr. from tokyo to nilgata station over japan is a serious case to be recalled. additionally in the following year, another incident occurred in taiwan, where the derailment of high-speed rail carriage during the maximum intensity of 6.4(fig.4. (b)). in that case, the high cost project like high-speed 118 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 railway structural system needs special attention to reduce the damage induced by earthquakes. the railroad industry is vitally interested in maintaining reliability in its infrastructure to assure safety for its employees, passengers, customers’ goods and the public at large (arema, 2018). (a) (b) fig. 4. seismic effects on high speed railway & its structures (a) derailment of high-speed trains on bridges due to niigata chuetsu earthquake (b) ) derailment of high-speed trains on bridges due to taiwan earthquake 2.1 earthquakes in china earthquakes in china happens because of major 23 seismic belts as shown in fig.5 over the five regions whereas taiwan province, south-west areas (tibet, west part of sichuan province and the mid-west of yunnan province), north-western area (gansu province, hexi corridor, qinghai, ningxia and tian mountain areas), northern part (taihang mountain, river beds of fen river and wei river, yin mountain-yan mountain area, mid in shandong and bohai bay) and at last the south-eastern coastal areas, such as guangdong, fujian (xiao, 2015). and these earthquakes were classified base d on the intensity of the waves, highest frequencies, epicenter and the faults wide distribution. according to the above statements, the high speed railway system in china is mostly covers all over the regions where the sites are surrounded by several known major seismic zones. moreover, it becomes a major natural disaster intimidation for the infrastructure and people’s safety in peaceful time (xiao, 2015). fig. 5. schematic distribution of strong earthquakes and seismic belts in china 2.2. earthquake motions based on the faults the high speed rail are mostly pass through all over the major cities in china where the sites are surrounded by different faults, which provides possibilities for trains to experience the effects of different seismic motions. therefore that motions induced by the seismic excitations differ from place to place due to the different propagation path and different earthquake faults. those seismic belts in china amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 119 ground motions replicates with different intensities levels including different peak ground accelerations (pga), durations and characteristic periods and different local site conditions which going to act on the high-speed railway bridges (wei et al., 2018; davoodi et al., 2012). and they were classified based on the distance and magnitude of the shaking such as near fault earthquake which having the large velocity pulse as compared to the far fault earthquake as show in fig.6 (akkar et al., 2005). those pulses will be governed by the distance of the station, location of the rupture fault, direction of the slip on the fault and also the direction of the fault rupture towards the recoding station which termed as “forward directivity effect” and it is generated by the vertical strike slip and dip slip faults (chopra and chintanapakdee, 2001; adanur et al., 2012; beiraghi et al., 2016). fig. 6. velocity time histories of strong ground motion of a) near-fault strong ground motion b) far-fault strong ground motion. 2.3 characteristics of near fault ground motions previous researches conducted numerous comparisons between the near faults and far fault motions to study the structural response of the structures and to understand the characteristics of near fault pulse-like motions. those motions will induce the impulsive velocity effect from the rupture directivity effect and take place normal vertical to the fault plane and it can be witnessed by the velocity time histories of countless strong earthquakes (wu et al., 2016). and the important feature should be observed is formation of step like displacement records which named as fling effect which is induced by the permanent tectonic offset of the rupture fault where the displacement profile and the intensity of the aftershocks were developed asymmetrically with maxima at the opposite end of the fault to the earthquake focus (wu et al., 2016; kim and sanderson, 2008). the investigation carried out through sdof systems with and without fling effect by using matlab model showed that the seismic demand increased also the structural response depends on the ratio of fling pulse to the fundamental period of the structure (jamnani et al., 2013). at last the unique feature of the nf ground motions is the hanging-wall effect which can induce the 46-60% of higher pga values in the range of 5 to 25 kms, it’s mainly due to the proximity of the fault plane to hanging wall sites where the sites on the hanging wall of dipping fault closer to the fault as a whole causes than do sites at the same closest distance on the footwall causes formation of shortest ground motion (tao and wang, 2003). recently response spectrum characteristics of the near fault ground motions also studied and it has been proved that the ratio of the pgv/ pga can be a major parameter to recognize the nf earthquake effect with structural response, when the pgv/pga values are higher indicates ground acceleration response spectrum area width will be further wider which is always interrelated to the structural response (xing and kang, 2013; loh et al., 2002). 3. effect of near-fault earthquake on structures near fault earthquake usually carries one or more pulses in its velocity time histories as shown in fig.6 (chopra and chintanapakdee, 2001; soltangharaei et al., 2016) which grasps the larger elastic spectral acceleration in the short to lengthier time periods striking severe damages to the structures and larger time history response to the bridge structures. due to the larger spectral 120 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 acceleration values, the structures which experiencing near fault motions cause large impact in secondary and global seismic demand capacity parameters also decreasing range in bending strength and ductility of the structures (soltangharaei et al., 2016). the seismic design concept of dph, tph and eph applied with tall buildings was investigated with the velocity pulse like ground motions in fig.7 shows that the models required larger demand in moment envelopes, plastic hinge, curvature ductility, roof drift and displacement as compared with the ff ground motions (beiraghi et al., 2016). (a) (b) (c) fig. 7. (a) velocity & (b) displacement time histories of directivity and fling pulse (c) ground acceleration response spectrum with respect to the ratio of the pga/pgv the investigation of the response of elastic and inelastic sdf systems were carried out with the fault-normal component of the set of 15 selected near fault record imposes much larger amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 121 deformation and strength demands compared to the fault-parallel component (chopra and chintanapakdee, 2001). then the investigation further continued in the upcoming days with the large crossing transmission tower-line system (lctl) results shows that the seismic response higher scatter than the far field ground motions, when the system correlated with the increasing pulse period of near-fault ground motions. where the displacement envelope of lctl are more complex than those of lctl to fling-step ground motions (wu et al., 2014). in multi story steel structures, the study of the effects of forward directivity motions influencing the shape of the maximum story ductility demand and the location of critical story by pulse periods and amplitude of the forward directivity pulse (sehhati et al., 2011). 3.1 effect of near-fault earthquake on bridge structures as we know that the near fault ground motions are very intense to the various structures from the previous research studies (chopra and chintanapakdee, 2001; beiraghi et al., 2016; soltangharaei et al., 2016; wu et al., 2014 ; sehhati et al., 2011) as well as those, earthquakes can produce high intensity ground motions which can produce extensive damages to the bridge structures which are playing a vital role in connecting a highway system with major cities. to retain the bridge, structures remain working and undamaged after the earthquakes take place to maintain the serviceability for smooth running of people’s daily life. many researchers took the initiative to study the structural response of bridge structures after the substantial damages created by the near field ground motions in northridge 1994, kobe 1995, and chi chi earthquakes. those ground motions were created an unusual structural response over the bridge structures than the conventional far field ground motions. in 2011, a geometrically nonlinear analysis of suspension bridges showed that the near fault ground motion is intensely effective on the displacement and internal forces in the bridges but also the maximum displacement and internal forces not occurs at the near fault peak acceleration value (adanur et al., 2012). the three span simply supported bridge which is investigated with the near faultnormal and fault-horizontal components and the magnitude higher than the m=6.0, the results show that the key forces between the bridge piers and bridge decks are reduced, retains the piers stiffened when the time period t1 in between the 0.1 and 0.3s when the magnification factor became larger with the small values of t1 the torsional stiffness of the adjacent deck increased with the results of increased drifts of the piers about 25% to 40% by the wave passage effects. it also showed that the maximum deformations of the deck girder increasing the larger demands on the piers without doubt (jalali et al., 2012). the response of the karnali cable stayed bridges were studied with the near fault earthquakes in the two phases ‘regular’ and ‘inverse’ which is the structure subjected to the horizontal accelerations and the second stage combined horizontal and vertical components, the effect of fdgm shows that the base moment and base shear of the tower amplifies when the pulse period coincides with the natural period of the structure and also the tower base resisting the ‘regular’ ground motion within the elastic range but there is comprehensive damage with complex level of residual displacement when the ‘inverse’ ground motion applied to the structure (shrestha and tuladhar, 2012). in 2014, next generation attenuation (nga) project conducted the study based on the high speed railway system which is subjected to near-fault ground motions and compared the results with far fault ground motions where the response of the girder and pier top tends to increase the displacements demands as shown in fig.8 with the reversed cycles of loading (ling-kun et al., 2014). due to the larger values of the acceleration ratio pga in nearfault ground motions tends to increase the higher upright deflections over the mid-span of the girder, which can alter the axial loads in pier (jalali et al., 2012; ling-kun et al., 2014; chen et al., 2014). the response of the sutong cable stayed bridge with the forward directivity with fling step ground motions and the artificial pulses near-fault pulse-type ground motions were studied by the researchers and the results shows that the fling step ground motions which have low 122 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 pgv/pga, enforce larger deformation and internal forces over the structure than the forward directivity motions (fig.5) (li et al., 2017; hajali et al., 2018). in 2016, there was also an investigation initiated over the curved continuous railway bridges with frequent earthquakes and the assumptions made by earthquake strikes with the first train entering the bridge at different time instants as well as various sets of earthquake records examined. fig. 8. average peak response of the girder: (a) vertical displacement; (b) bending moment (note: f-d pulses denote the forward-directivity records, f-s pulses denote the fling-step records (shuai li, et al 2016)[25] in the first level of investigations shows that the position of running vehicle over the earthquake excitation is unpredictable so the train vehicles examined with different positions on the deck when the earthquake commences and proved that the response of the first vehicles higher when they running over the bridges due to the seismic response of the bridge (fig.9) (zeng and dimitrakopoulos, 2016). fig. 9. the deformation shape of the bridge induced by moving vehicles with simultaneous earthquake excitations (zeng, et al 2016) due to the usage of continuous girder increases over hsr bridges to overcome the undulating terrain and satisfy the safety running of vehicles, the experimental shake table test investigated on the bridge structure to study the seismic response under the peak ground acceleration of 0.38 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 123 g earthquake motions. the shake table results show that the increase in peak ground acceleration (pga from 0.45 g to 1.14 g) which leads to decrease the frequency of piers which also reduces the overall stiffness of the pier subjected to the bidirectional earthquake excitation (jiang et al., 2019). recently, the investigation was carried out to analyze the seismic behavior of the long-span concrete filled tubular arch bridge with fling step motion which can cause more damage to the long-span bridges. the effect of fling-step motion on seismic performance evaluated by some observations, two serious regions of the cfst arch where the arch foot is subjected to the buckling load tube tearing due to the initial compressive state of the arch rib under the gravity action and the strain index investigation has shown that the microscopic strain distribution significantly different than the macroscopic dynamic indices (xin et al., 2019). wei et al. (2018), investigated the damager features of different main components in hsr simply supported hsr bridge under near fault earthquake, the results proved that the background excitations with high frequency motions produced nearly 90% of the pier displacement response, 80% of the sliding layer response, and 85% of the shear alveolar response and concluded that the sliding layer and the shear alveolar are the weakest components which leads to failure of the track system (guo et al., 2020). 4. effects of moving loads in railway bridges 4.1 moving loads the development of high-speed train system started in several countries like japan, germany, korea, and china with different level of speed improvements as per their requirements. when the speed increases more than the 250km/hr, there is a massive rise in research contribution to improve the safety and comfort running of train vehicle and effective track arrangement. moving speed of hsr differed from different countries like china (chr3 – 350km/hr), japan and france (tgv & shinkansen 250km/hr), germany (ice280km/hr) and korea (ktx300km/hr). while evaluating the dynamic behavior of bridge structures which is subjected to high speed train moving load is one of the most important factors to be considered for the structural well-being concerns. therefore many researchers took the initiative to study the dynamic behavior of vehicle – track interaction when the operating speeds of the vehicle are increasing to 350km/hr with 2d & 3d models for predicting the exact outcomes. various studies point out that the moving load causing the vibrations to the bridges which can affect the running stability and also the safety of the moving vehicles, it is mandatory to consider the moving load as a major factor to perform the dynamic analysis of the railway bridges (mittal et al., 2016). when the high speed train above 160km/hr passing through the small or medium span railway bridges which induce resonance from the parameters of the bridge(natural frequencies of bridge) and train (axles distances of the train, train speed) replicates increase in dynamic response with increase in deflection amplitude of the superstructure (goicolea et al., 2010). 4.2 effect of moving loads the dynamic effect study conducted with the simplified 2d model as shown in fig.10 of acceptable finite element track and a vehicle model, which shows that the vehicle interaction force which is initiated by the primary suspension in the bogie between the wheel and the rail were very sensitive to the irregularity of the track and vehicle passing speeds.[30] and to overcome the complexity of 3d models, where the 2d planar models (orthotropic plate fe model) were used to study the dynamic behavior and the serviceability limit of the infrastructure experienced by the train vehicle traffic shows that the structure undergoing most alarming vertical acceleration when the train hits above 200km/hr to 270 km/hr operational speed which leads to experience the excessive vibration with growing fatigue problems and facing inadmissible vertical acceleration initiated by the resonance of first longitudinal bending 124 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 mode of plane beam model. some of the researchers used mathematical simulation to simulate the dynamic performance of vehicle-bridge interaction with moving vehicle loads. for example, the mathematical model superposition analysis approach presented with small and medium span simply supported railway bridges subjected to a series of moving vehicles with identical loads (ic coaches-160km/hr) which shows that the higher number of moving loads creates free vibration results in the resonance vibration having adverse effects on the degradation of the super structure. and the observed that the resonance amplitude enhances the dynamic deflection in short to medium spans influenced by the ratio of length to velocity, the driving frequency of the vehicle in structure and the natural frequency of the bridges and the resonance amplitude can be decreased with the increasing damping stiffness value.[milan moravčík1, 2017 #66] fig. 10. simple 2d models of multi body vehicle models with many degrees of freedom a) single degree of freedom b) two degree of freedom c) two degree of freedom some researchers also compared the results with experimental and analytical to study the impact effects like impact factor (im) of the moving train on the bridge to ensure the reliability of the bridge and safety run of train, the study came up with the results where the im strongly depends on the track irregularities but also its increase with the speed of the train and decreases with the increase of train weight. and the observation cleared that the track irregularities are also increase the im which can lead to track surface degradation, and the train-bridge interaction will be more intense for long-term operation of the bridge structure for safety running of train vehicle. [gou, 2018 #68] and the same author studied the dynamic behavior of tied arch railway bridge under the moving train load, observed that the increase in train speed increases the vertical and transverse accelerations and also increases the derailment coefficient under double line loading is less than that of single line loading.[hongye gou0, 2019 #69] recently the study carried out with the double simply supported beam system subjected to the moving loads using the combination of finite sin-fourier transform and numerical laplace transform based on durbin transform, an analytical calculation method was developed for the spatial displacement time-domain response of a multiple simply supported beam system and also compared with the finite element analysis using ansys software results and it shows that the double beam system has multiple points of resonance and cancellation which may cause unexpected situations in future and also the variation in mass and flexural stiffness parameters of first simply supported beam initiates problems for the dynamic responses for second simply supported beam in the double simply supported rail-bridge system. 5. conclusions by studying the literatures based on the near fault ground motions and moving load and their effects on the dynamic behavior of high-speed railway bridges are a complex behavior to be considered in the upcoming research studies and working on updating the design codal provisions regarding the response reduction factor parameters which can reduce the dynamic response of the bridges. and the significant conclusions can be drawn as follows as amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 125  many of the researchers talked about the effects of far fault earthquake motions, but not much paper dealing with the near-fault motion creates impulsive velocity effect and the hanging wall effect which can induce 46-60% of higher pga values indicates the ground acceleration response spectrum area width will be further wider which is always interrelated to the structural response of the hsr bridges and as well as the safety run of trains.  the effect of near-fault motions over the bridges, where increasing displacement and internal forces, increased drifts of the piers about 25% to 40% by the wave -passage effects, concluded that the sliding layer and the shear alveolar are the weakest components which leads to failure of the track system.  to overcome the complexity of 3d models of the train bridge interaction, 2d models were sufficient than the 3d models to get the exact outcomes of the dynamic behavior of vehicle – track interaction when the vehicle running speed is over 200 – 350 km/hr.  the effect of moving loads over the bridges where the resonance caused by the various parameters of train (axles distances of the train, train speed and weight of the train) and the irregularity of the track causes increase in deflection amplitude, growing fatigue problems, inadmissible vertical and horizontal acceleration, derailment coefficient  its observed that china has the hsr bridge ratio of 1.3–32.2%, which clearly shows that the high speed train operates over the bridges is most of the time when the earthquake occurs, which may cause to experience excessive vibrations with the resonance induced by the moving vehicles loads when the operating speed hits up to 200 – 350 km/hr. but there is not at all sufficient research found that considering effects of both moving load (from vehicle to the structure leads to the ground) and earthquake loads (from ground to structure to the vehicle) to study the dynamic behavior of the high speed train bridge structures declarations abbreviations hsr: high speed train; pga: peak ground acceleration; nf: near-fault; f.f: far fault; pgv: peak ground velocity; sdof – single degree of freedom; dphdual plastic hinge; tph tripleplastic hinge; eph: elasto plastic hinge; lctl: large crossing transmission tower-line system; fdgm-forward directivity ground motions; cfst: cold formed steel tubular; im: impact measure. acknowledgements the authors would like to acknowledge all the mentioned reference for sharing their database on high speed train bridges, near-fault earthquakes. authors’ contributions both author contributed equally to the formulation and drafting of this paper. the authors read and approved the final manuscript. funding no funding was received during this research. availability of data and materials the data can be requested from the authors. competing interests the authors declare that they have no competing interests. 126 amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 6. references adanur, s., altunişik, a. c., bayraktar, a., & akköse, m. (2012). comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. natural hazards, 64(1), 593-614. akkar, s., yazgan, u., & gülkan, p. (2005). drift estimates in frame buildings subjected to near-fault ground motions. journal of structural engineering, 131(7), 1014-1024. arema (2018). american railway engineering and maintanence of way associaction. arema manual for railway engineering. beiraghi, h., kheyroddin, a., & kafi, m. a. (2016). forward directivity near‐fault and far‐fault ground motion effects on the behavior of reinforced concrete wall tall buildings with one and more plastic hinges. the structural design of tall and special buildings, 25(11), 519-539. chen, l. k., zhang, n., jiang, l. z., zeng, z. p., chen, g. w., & guo, w. (2014). near-fault directivity pulse-like ground motion effect on high-speed railway bridge. journal of central south university, 21(6), 24252436. chopra, a. k., & chintanapakdee, c. (2001). comparing response of sdf systems to near‐fault and far‐fault earthquake motions in the context of spectral regions. earthquake engineering & structural dynamics, 30(12), 1769-1789. davoodi, m., sadjadi, m., goljahani, p., & kamalian, m. (2012). effects of near-field and far-field earthquakes on seismic response of sdof system considering soil structure interaction. in 15th world conference on earthquake engineering. lisbon, portugal. goicolea, j. m., nguyen, k., galbadón, f., bermejo, m., topping, b. h. v., adam, j. m., ... & romero, m. l. (2010). dynamic analysis of high speed railway traffic loads on ballast and slab tracks. in proceedings of the tenth international conference on engineering computational technology. civilcomp press. guo, w., gao, x., hu, p., hu, y., zhai, z., bu, d., & jiang, l. (2020). seismic damage features of high-speed railway simply supported bridge–track system under near-fault earthquake. advances in structural engineering, 23(8), 1573-1586. hajali, m., jalali, a., & maleki, a. (2018). effects of near fault and far fault ground motions on nonlinear dynamic response and seismic improvement of bridges. civil engineering journal, 4(6), 1456-1466. he, x., wu, t., zou, y., chen, y. f., guo, h., & yu, z. (2017). recent developments of high-speed railway bridges in china. structure and infrastructure engineering, 13(12), 1584-1595. jalali, r. s., jokandan, m. b., & trifunac, m. d. (2012). earthquake response of a three-span, simply supported bridge to near-field pulse and permanent-displacement step. soil dynamics and earthquake engineering, 43, 380-397. jamnani, h. h., karbassi, a., & lestuzzi, p. (2013). fling-step effect on the seismic behaviour of high-rise rc buildings during the christchurch earthquake. in 2013 nzsee conference. jiang, l., kang, x., li, c., & shao, g. (2019). earthquake response of continuous girder bridge for high-speed railway: a shaking table test study. engineering structures, 180, 249-263. kim, y. s., & sanderson, d. j. (2008). earthquake and fault propagation, displacement and damage zones. structural geology: new research, 1, 99-117. li, s., zhang, f., wang, j. q., alam, m. s., & zhang, j. (2017). effects of near-fault motions and artificial pulsetype ground motions on super-span cable-stayed bridge systems. journal of bridge engineering, 22(3), 04016128. ling-kun, c., li-zhong, j., wei, g., wen-shuo, l., zhi-ping, z., & ge-wei, c. (2014). the seismic response of high-speed railway bridges subjected to near-fault forward directivity ground motions using a vehicle-track-bridge element. shock and vibration, 2014. volume12, article id 985602. amudhan and hui qian, j. build. mater. struct. (2021) 8: 115-127 127 loh, c. h., wan, s., & liao, w. i. (2002). effects of hysteretic model on seismic demands: consideration of near‐fault ground motions. the structural design of tall buildings, 11(3), 155-169. mittal, r. k., sai, v. k., & maiti, p. r. (2016). effect of mass of moving load on dynamic response of a simply supported railway bridge. i-manager's journal on structural engineering, 5(4), 23. sehhati, r., rodriguez-marek, a., elgawady, m., & cofer, w. f. (2011). effects of near-fault ground motions and equivalent pulses on multi-story structures. engineering structures, 33(3), 767-779. shrestha, b., & tuladhar, r. (2012). the response of karnali bridge, nepal to near-fault earthquakes. in proceedings of the institution of civil engineers-bridge engineering, thomas telford ltd., 165 (4), 223-232. soltangharaei, v., razi, m., & gerami, m. (2016). comparative evaluation of behavior factor of smrf structures for near and far fault ground motions. periodica polytechnica civil engineering, 60(1), 7582. tao, x. x., & wang, g. x. (2003). rupture directivity and hanging wall effect in near field strong ground motion simulation. acta seismologica sinica, 16(2), 205-212. wei, b., yang, t., jiang, l., & he, x. (2018). effects of uncertain characteristic periods of ground motions on seismic vulnerabilities of a continuous track–bridge system of high-speed railway. bulletin of earthquake engineering, 16(9), 3739-3769. william, g., & byers, p. e. (2004). railroad lifeline damage in earthquakes. in 13 world of conference on earthquake engineering. wu, g., zhai, c., li, s., & xie, l. (2014). effects of near-fault ground motions and equivalent pulses on large crossing transmission tower-line system. engineering structures, 77, 161-169. wu, s. l., charatpangoon, b., kiyono, j., maeda, y., nakatani, t., & li, s. y. (2016). synthesis of near-fault ground motion using a hybrid method of stochastic and theoretical green’s functions. frontiers in built environment, 2, 24. xia, h., han, y., zhang, n., & guo, w. (2006). dynamic analysis of train–bridge system subjected to non‐ uniform seismic excitations. earthquake engineering & structural dynamics, 35(12), 1563-1579. xiao, d.y., (2015). china a country of many earthquakes. computer network information center of chinese academy of sciences. xin, l., li, x., zhang, z., & zhao, l. (2019). seismic behavior of long-span concrete-filled steel tubular arch bridge subjected to near-fault fling-step motions. engineering structures, 180, 148-159. xing, f., & kang, r. (2013). response spectrum characteristics of near-fault ground motions and influence to cfst arch bridge. in advanced materials research. trans tech publications ltd., 671, 1367-1371. zeng, q., & dimitrakopoulos, e. g. (2016). seismic response analysis of an interacting curved bridge–train system under frequent earthquakes. earthquake engineering & structural dynamics, 45(7), 11291148. j. build. mater. struct. (2022) 9: 1-11 original article doi : 10.34118/jbms.v9i1.1374 issn 2353-0057, eissn : 2600-6936 seismic analysis of souk tlata dam behaviour using finite element simulation louadj s *, smail l laboratoire géomatériaux, environnement et aménagement, université mouloud mammeri de tizi-ouzou, bp. 17, rp 15000, algérie * corresponding author: samia.louadj@ummto.dz received: 07-06-2021 accepted: 13-01-2022 abstract. in this study, earthquake resistance of souk tlata earth dam was examined. it corresponds to a preliminary investigation of the behaviour of the dam under earthquake loading with a dominant frequency close to the fundamental frequency of the dam. the dam was modeled with plane-strain finite elements using plaxis-2d program. the behaviour of both the fill and core of the dam is described using the simple non associated mohr-coulomb criterion. the development of the safety factors as a function of the displacement of the dam crest dam reveals that the static stability of the dam under conditions of drawdown is not assured. dynamic analyses are conducted under a real earthquake motion, which corresponds to the main shock of may 21, 2003 in algeria. the results show that the seismic loading, with peak acceleration exceeding 0.10g, induces significant settlement at the crest of the dam and substantial displacement in the upper part of the rip-rap in the upstream side. key words: earth dam, finite element analysis, safety factor, earthquake loading, settlement at crest. 1. introduction earth or rockfill dams that predominate for some 65 % of dams are the archetype of embankment dams (icold, 2019). their resistance is provided by natural soil-type materials available nearby. the design and construction of these structures have evolved significantly over the past century, and has gone from a relatively simple construction of homogeneous dikes or embankment dams composed of two zones at the beginning of the 20th century, to extremely complex earth or rockfill dams. the height of theses dams is continually increasing also, with many dams being more than 200 m high and even reaching 300 m like nurek dam (300 m) and rogun dam (335 m) in tajikistan(icold, 2019). many of them are located in areas with a number of large-scale, high-intensity active faults and have been damaged during strong earthquakes and even broken in some serious cases. ambraseys (1960) reviewed 58 dams damaged in 24 earthquakes and suggested that inertial forces and pore-pressure had the greatest effect on the structure. wood (1973) showed that when the frequency at which the seismic power of the input motions approaches the fundamental frequency of the unrestrained backfill, dynamic amplification becomes an important factor, which is not considered in engineering approaches that assess the embankment dam stability. seed et al. (1978) and seed (1979) reported that the seismic performance of embankment dams has been good in general. they noted that well-built compacted embankment dam can withstand moderate earthquake shaking, with peak acceleration of 0.2 g and more with no detrimental effects. harder et al. (1998) summarized more than 20 case histories of earth and rockfill dams experienced earthquakes and presented the relationship of peak crest accelerations against peak ground accelerations. youd and idriss, (2001), wang (2007), chen et al. (2009), holzer et al. (2010), huang and jiang (2010), cao et al. (2011), hou et al. (2011) and liu et al. (2016) have shown that medium–strong earthquakes (mw 5.5–6.5) will not cause fissures in earth dams, but do cause sand liquefaction over large areas. dakoulas (2012) reported that the seismic response of an earth or rockfill dam depends on a large number of factors, such as the quality of rockfill compaction, the dam geometry, the mailto:samia.louadj@ummto.dz 2 louadj and smail, j. build. mater. struct. (2022) 9: 1-11 narrowness of the canyon, the irregularity of the abutments, the flexibility of the canyon rock, the ground motion intensity and its frequency characteristics, spatial variability of the seismic motion. internal erosion and seepage problems increased leakage through cracks resulting from differential settlements and different dynamic responses of various parts of the dam following the earthquake. shear failure of the dam caused by the movement of a fault crossing the foundation is also indicated. only settlements of the crest and landslides may be computed. for internal erosion, a modeling of the phenomena is not easy because of the random mechanisms of particle flow and transport. yu et al. (2012) summarized 43 case histories and 18 numerical analyses of earth and rockfill dam behaviour during earthquake, focusing on the characteristics of seismic response and found that the narrowness of canyon, seismic motion input, angle of incidence, shear modulus of rockfill, and dam height have moderate effects on the value of the peak crest acceleration. in addition, they concluded that both case histories and numerical analyses show that seismic measures for high embankment dams should focus on the mid-top area of the dam. chen et al. (2014) analyzed a total of 670 earth dams damaged by the wenchuan earthquake and found that fissures in the dams were one of the most important causes of damage. kong et al. (2018) considered relative settlement ratios of 0.4%, 0.7%, and 1% of the dam crest as the assessment limitation and analyzed the fragility when this dam exhibited minor, moderate and severe failure. the paper presents a numerical study of the seismic behaviour of souk tlata earth dam using a 2-d finite element modeling. it will mainly focus on the seismic response of the dam under the main shock of may 21, 2003 in algeria with dominant frequency close to the fundamental frequency of the dam and with a peak acceleration exceeding the peak accelerations estimated for the dam project. to conduct the analyses within the framework of plasticity, the behaviour of both the fill and core of the dam is described using the simple non associated mohr-coulomb criterion. the static analysis is conducted, prior to cyclic loading in the dam body, for various stages including end of construction, impounding and rapid drawdown. the induced displacement under seismic loading is computed for the evaluation of the stability of the dam since it is dependent on the geometric and mechanical properties of the dam as well as the frequency and amplitude of the input loading. this paper considers the dam with water impoundment but does not consider the fluid-skeleton interaction which could have a significant influence on the seismic response of the dam. 2. experimental site description and geotechnical characterisation the souk tlata dam on the bougdoura stream is located at the western end of the great kabylia 8.5 km from tizi-ouzou, about 80 km from algiers in the eastern direction. the reservoir will consist essentially of two branches formed by the valleys of acif tlata and tala imedrane respectively, which meet all upstream of the dam. souk tlata dam of approximately 95 m high above the foundation is under construction and is the second largest hydraulic dam in the province of tizi-ouzou. the crest of the dams is 151 m long, 10 m wide and about 376 m width at the base. the dam will serve primarily to satisfy water supply of tizi-ouzou, boumerdes and algiers provinces, and will also cover certain local irrigation needs. a total of 1,132,000 m3 of earth and fill materials will be used for the construction of the souk tlata dam. the dam is composed of several different types of materials. in the central part of the dam, a core made up of clayey colluviums is implemented. the dam body is commonly composed of disaggregated sandstone, sandy and gravelly alluvium. also, filter and transition materials exist in the dam. a rockfill cover protects upstream slope from erosion possibly produced by changes in the water level. it is made of a layer of limestone boulders from the hassi youcef quarry resting on a gravel bed from the same quarry. on the other hand, the burdigalian sandstone sediments are widely present in the dam area and in fact constitute the foundation louadj and smail, j. build. mater. struct. (2022) 9: 1-11 3 rock for the supports of the structure. the principal dike is founded on twenty meters of gravelly alluviums that are excavated under the core of the dam. figure 1 shows the maximum cross section of the souk tlata dam. it is mentioned in the dam monography that an extensive field exploration program was undertaken by geosonda from yugoslavia for the purpose of identifying the embankment materials, foundation soils and bedrock, and establishing the phreatic surface in the embankment. a total of 63 holes have been performed. samples, which were carried out by the public center laboratory (ltcp), were recovered for laboratory tests which included classification tests (water content, humid and saturated density, atterberg limits), compaction tests and triaxial tests. some properties of the used materials in construction of souk tlata dam, and that were deducted from this extensive investigation, are summarized in table 1 and table 2 (dam monography). no seismic fault has been recorded at the dam site for the past 200 years within a radius of 40 km but the dam is not very far from the transverse tectonic accidents with direction n140° and n75° which played an important role in the uplift of the atlas mountains. therefore, it is possible that the dam area could feel the earthquakes from the surrounding active seismotectonic regions. indeed, it is far from the large sedimentary basins, still subsidizing today from the lower miocene (cheliff, mitidja, soummam, hodna) which are the center of the most dangerous seismic faults in algeria. according to algeria's historical seismicity catalog, many earthquakes were felt in the dam area with intensities of vi at least. the peak accelerations estimated for the dam project are between 0.06 g and 0.10 g with a return period of 100 years and 0.15 g with a return period of 500 years (dam monography). fig 1. cross section of souk tlata dam and foundation layers (adapted from dam monography). 3. numerical model and static analysis the analysis is performed with the finite element program plaxis-2d. a simplified embankment cross section, shown in figure 2, is considered. the numerical model, shown in figure 3, consists of a dam overlying a foundation. the model consists of 2387 plane strain finite elements. to consider the stage construction of the dam in the analysis, the dam body is built in diverse phases. the dam materials are added in horizontal layers after the calculation for the initial equilibrium state of the foundation with a depth of 100 m. the boundary conditions are specified, such as the bottom of the model is fixed from movement in both the –horizontaland – vertical directions. in order to assess the stresses, prior to cyclic loading in the dam body, static analyses were carried out for various stages including end of construction, impounding and rapid drawdown. the behaviour of dam materials is described using the simple non associated mohr coulomb criterion. the use of this constitutive model is justified by the difficulty to obtain constitutive parameters for more advanced constitutive relations including both isotropic and kinematic 4 louadj and smail, j. build. mater. struct. (2022) 9: 1-11 hardening. the used material properties for numerical analyses are presented in table 1 and table 2. fig 2. simplified cross section showing different material zones. fig 3. finite element mesh employed in the analysis. table 1. index and physical properties. material γh (kn/m3) γsat (kn/m3) k (cm/s) wo (%) wl (%) ip (%) schist 24.5 24.5 gravelly materials 21 22 10-3-10-4 7.3 sand-gravel 20 20.5 clayey colluviums 18 19 10-5-10-6 14.7 35.3 16.6 sandstone 19.5 20 4×10-7 3.6 27.4 12.2 backfill 18 20 2.4×10-6 17.5 44 22.5 table 2. shear strength characteristics. material c’ (kpa) φ' (°) schist 70 30 gravelly materials 0 35 sand-gravel 0 32 clayey colluviums 35-55 18-19 sandstone 0 34 backfill 0.5 10 3. 1. end of construction stage to consider the stage construction of the dam in the analysis, the dam body is built in diverse phases. after the calculation for the initial equilibrium state of the foundation with a depth of 100 m, the dam materials are added in horizontal layers in order to take into account the stress history resulting from gravitational loading. as shown in figure 4(a), a total of 30.63 cm of vertical displacement is predicted from this analysis. from figure 4(b), a maximum horizontal displacement about 14.5 cm is induced in the upper part of the downstream side of the dam. zone 1: schist zone 2: gravelly materials zone 3: sand-gravel zone 4: limestone zone 5: clayey colluviums zone 6: sandstone zone 7: backfill louadj and smail, j. build. mater. struct. (2022) 9: 1-11 5 fig 4. vertical and horizontal displacements under gravity loads at the end of construction stage. 3.2. impounding and drawdown conditions water level increases to a height of 86 m above the foundation which is considered impermeable. during impounding, the hydrostatic force acts on the upstream surface. initial stresses and initial pore water pressures of the dam under normal working conditions are calculated using gravity loading. the water pressure distribution contours, shown in figure 5(a), are obtained after filling to full supply level using steady state ground water flow analysis. the induced horizontal displacement is not significant like shown in figure 6(a). the stability of the dam under conditions of drawdown is also analyzed. the situation is considered where the water level drops 46 m rapidly. the water inside the dam does not have time to dissipate and it is important to know the behaviour of the dam in this case. to analyze this situation, a fully coupled flow-deformation is used. as shown in figure 6(b), fast reduction of the reservoir level leads to instability of the upstream side of the dam with a peak horizontal displacement of about 1.076 m due to high pore water pressures that remain inside the dam as indicated in figure 5(b). the development of the safety factors as a function of the displacement of the dam crest is shown in figure 7 for the three situations considered for the static analysis. by comparing with the minimum admissible regulatory values for each case of stability, one can note that the stability of the dam is ensured at the end of construction (fs = 2.08), and even after the impoundment (fs = 1.57), but in the case of a rapid drawdown, the stability of the structure is not ensured (fs = 1.08). fig 5. pore pressure contours(a) after impounding, (b) after rapid drawdown. (a) (b) (a) (b) 6 louadj and smail, j. build. mater. struct. (2022) 9: 1-11 fig 6. horizontal displacement(a) after impounding, (b) after rapid drawdown. 0 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 u (m) 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 s m s f at the end of construction full reservoir rapid drawdown fig 7. safety factors as a function of the displacement of the dam crest. 4. dynamic analysis 4.1. input loading the earth dam is subjected to earthquake loading representative of the 2003 boumerdes main shock in algeria (mw=6.8), recorded at bedrock by the stations of the national accelerograph network in the n-s direction. the estimated peak acceleration is approximately -0.228 g, and the duration is approximately 28 s. the record for base acceleration and velocity waves are shown in figure 8(a) and figure 9(a) (records at keddara site). the computed acceleration fourier spectra indicates that the seismic power mainly concentrated in a range of frequencies lower than 15 hz. it should be noted that two wavelets are present in the spectral representation of the motions like shown in figure 8(b). the first one corresponds to content lower than 5 hz and the second one greater than 5 hz. fourier analysis of the recorded velocity results in a power spectrum depicted in figure 9(b). the velocity spectrum reveals a dominant frequency of about 0.52 hz. from the other hand, the natural frequencies of the dam-foundation system were determined by a fourier analysis of the free vibration response of the dam (figure 10). it shows a fundamental frequency f1=0.38 hz which is close to dominant frequency of seismic loading (f=0.51 hz). (b) (a) louadj and smail, j. build. mater. struct. (2022) 9: 1-11 7 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 frequency (hz) 0 100 200 300 400 500 s p e c tr a l v e lo c it y (b) 0 5 10 15 20 25 30 time (s) -30 -20 -10 0 10 20 30 v e lo c it y ( c m /s ) (a) fig 8. acceleration time history of rock station in the n-s direction recorded during 2003 main shock in algeria and respective fourier spectrum. fig 9. velocity time history of rock station in the n-s direction recorded during 2003 main shock in algeria and respective fourier spectrum. fig 10. response spectra of the free horizontal motion at the dam crest. 4.2. analysis of the seismically induced response in the souk tlata dam dynamic loading is applied at the base of the foundation layer as an acceleration excitation. the procedure of free-field boundaries used in plaxis-2d aims absorbing outward waves originating from the structure. the lateral boundaries of the main grid are coupled to the free field grid by viscous dashpots to simulate a quiet boundary. amount of 2% of rayleigh damping is considered to compensate the energy dissipation through the medium (paolucci, 2002; lokmer et al. 2002). 0 5 10 15 20 25 30 time (s) -3 -2 -1 0 1 2 3 a c c e le ra ti o n ( m /s ²) (a) 0 5 10 15 20 25 30 frequency (hz) 0 40 80 120 160 200 a m p li tu d e f o u ri e r s p e c tr u m (b) 8 louadj and smail, j. build. mater. struct. (2022) 9: 1-11 figure 11 shows the acceleration time history computed at crest in the upstream-downstream direction, and respective fourier transform. at the base of the foundation, the aforementioned peak acceleration was -0.228g. the dam responded to the applied motion with amplification, and a peak acceleration of approximately -0.31 g is reached. the computed fourier spectra indicates that the response of the dam at crest is observed during the first wavelet corresponding to a frequency content less than 5 hz while the response of the dam to the second wavelet with the frequency content below 15 hz is not significant. 0 5 10 15 20 time(s) -4 -3 -2 -1 0 1 2 3 4 a c c e le ra ti o n ( m /s ²) 0 5 10 15 20 25 30 frequencies(hz) 0 50 100 150 f o u ri e r a m p li tu d e s p e c tr u m fig 11. acceleration time history of dam crest response in the upstream-downstream direction and respective fourier spectrum. the general pattern of horizontal and vertical displacement, respectively, as a result of seismic loading is shown in figure 12. it is evident that the predicted deformation involves settlement at the crest. at 10 s of shaking, a peak of vertical displacement of 22 cm is reached and slumping of upper part of the rip rap on the upstream side of the dam is observed. fig 12. vertical and horizontal displacement under seismic excitation at 10 s. figure 13 summarizes the change of horizontal and vertical displacement at crest of the dam for 20 s of shaking. as this figure illustrates, the maximum horizontal and vertical displacement occurs at approximately 10 s of dynamic excitation. the displacement is increasing almost linearly until 10 s and then remains relatively constant. the maximum magnitude of the horizontal movement is about 14 cm like shown in figure 13(a) and as depicted in figure 13(b) a maximum settlement of 22.18 cm is reached. louadj and smail, j. build. mater. struct. (2022) 9: 1-11 9 0 5 10 15 20 time(s) -0.16 -0.12 -0.08 -0.04 0 0.04 x d is p la c e m e n t (m ) 0 5 10 15 20 time(s) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 y d is p la c e m e n t (m ) fig 13. horizontal and vertical displacement under seismic excitation at crest of the dam. figure 14 shows the displacement pattern in the axis of the dam and in the transversal direction at the middle height of the dam at the maximum of seismic excitation. it can be observed that the displacement increases with the distance from the foundation to the crest of the dam. it displays significant increase in the upper one-third of the dam, like shown in figure 14(a). okamoto (1973) points out that all observations indicate that the top part of the dam vibrates more severely as compared to the bottom part, and moreover the ration is fairly high, it reasonable to consider the design seismic coefficient at a high value for the top of the dam in the case of a high dam. on the other hand, the variation of the lateral displacement in the transversal direction at the middle height of the dam, shown in figure 14(b), indicates a uniform distribution of the displacement in the downstream side but we observe a significant increase of the displacement when approaching the lateral extremity near the upstream side of the dam. 0 0.04 0.08 0.12 0.16 0.2 xdisplacement (m) 0 0.2 0.4 0.6 0.8 1 h /h 0 0.2 0.4 0.6 0.8 1 l/l 0 0.04 0.08 0.12 0.16 xd is p la ce m e n t (m ) fig 14. displacement pattern at maximum of acceleration(a) in the axis of the dam, (b) the transversal direction at the middle height of the dam. figure 15 shows the location of the zones concerned by plastic deformation at the peak of the seismic excitation. it can be observed that plasticity is induced on the rip-rap on the upstream face of the dam and in the backfill layer in the downstream side of the dam. the whole others parts of the dam remain in the elastic domain. (a) (b) (a) (b) 10 louadj and smail, j. build. mater. struct. (2022) 9: 1-11 fig. 15. distribution of plasticity points in the dam under the dynamic excitationat 10 s. 5. conclusions this study presents a preliminary investigation of the behaviour of souk tlata earth dam under earthquake loading with a dominant frequency close to the fundamental frequency of the dam. the induced response was evaluated using the two-dimensional finite element program plaxis and the mohr coulomb constitutive model. the main shock of may 21, 2003, boumerdes earthquake in algeria was selected for this study. the seismic behaviour corresponds to the response of the dam after water impoundment. the conducted static analysis to assess the stresses, prior to cyclic loading in the dam body, reveals significant instability of the upstream side of the dam under drawdown conditions with a safety factor lower than 1.2. under the given excitation, nonlinear dynamic analyses show that the predicted deformation involves settlement of 22 cm at the crest and slumping of rip rap and alluviums on the upstream side of the dam. the mechanical role of the central core is not significant compared to the shell in the induced response of the dam. the variation of the displacement in the middle height shows a sharp increase at the upstream extremity, which could indicate the imminence of instability in this area. a design should take into account dominant frequency of the seismic excitation and the dam where the amplification is significant and particular consideration should be given to the crest and the upstream side. advanced analyses must also be undertaken to predict alluviums liquefaction above the foundation of the dam as well as the extent and timing leading to significant permanent deformation. 6. references ambraseys, n. n. (1960). on the seismic behaviour of earth dams. proc. 2nd world conf. earthquake eng. 2, 331–358. cao, z. z., youd, t. l., & yuan, x. m. (2011). gravelly soils that liquefied during 2008 wenchuan, china earthquake, ms _ 8.0. soil dyn. earthq. eng. 31,1132–1143. doi:10.1016/j.soildyn.2011.04.001. chen, g., jin, d., mao, j., gao, h., wang, z., jing, l., et al. (2014). seismic damage and behavior analysis of earth dams during the 2008 wenchuan earthquake, china. eng. geology. 180, 99–129. doi:10.1016/j.enggeo.2014.06.001. chen, l. w., yuan, x. m., cao, z. z., hou, l. q., sun, r., dong, l., et al. (2009). liquefaction macrophenomena in the great wenchuan earthquake. earthq. eng. eng. vib. 8, 219–229. doi:10.1007/s11803-0099033-4. dakoulas, p. (2012). nonlinear seismic response of tall concrete-faced rockfill dams in narrow canyons. soil dynamics and earthquake engineering. 34:1,11-24. harder, l.h., bray, j.d., volpe, r.l., & rodda, k.v. (1998). performance of earth dams during loma prieta earthquake. the loma prieta, california, earthquake of october 17, 1989earth structures and engineering characterization of ground motion. 3-26. louadj and smail, j. build. mater. struct. (2022) 9: 1-11 11 holzer, t, l., jayko, a. s., hauksson, e., fletcher, j. p. b., noce, t. e., bennett, m. j., et al. (2010). liquefaction caused by the 2009 olancha, california (usa),m5.2 earthquake. eng. geology. 116 (1–2), 184– 188. doi:10.1016/ j.enggeo.2010.07.009. hou, l. q., li, a. f., & qiu, z. m. (2011). characteristics of gravelly soil liquefaction in wenchuan earthquake. appl. mech. mater. 90–93, 1498–1502. doi:10.4028/www.scientific.net/amm.9093.1498. huang, y., & jiang, x. m. (2010). field-observed phenomena of seismic liquefaction and subsidence during the 2008 wenchuan earthquake in china. nat. hazards. 54, 839–850. doi:10.1007/s11069010-9509-6. icold (2019). general synthesis of world register of dams, in: https://www.icoldcigb. org/gb/world register/general_synthesis.asp. kong, x. j., pang, r., zou, d. g. xu, b., zhou, y. (2018). seismic performance evaluation of high cfrds based on incremental dynamic analysis, yantu gongcheng xuebao/chinese j. geotech. eng., vol. 40, n.o 6, pp. 978-984. liu, z, j., wang, p., zhang, z. h., li, z. g., cao, z. z. zhang, j. y., et al. (2016). liquefaction in western sichuan basin during the 2008 mw 7.9 wenchuan earthquake. china: tectono-physics, 1–25. lokmer, i. , herak, m., panza, g.f., & vaccari, f. (2002). amplification of strong ground motion in the city of zagreb, croatia, estimated by computation of synthetic seismograms. soil dynamics and earthquake engineering, 22, 105-113. monographie du barrage souk tlata (2002). avant projet détaillé du barrage de souk tlata : mémoire de synthèse. agence nationale des barrages, pp 1-66. okamoto, a. (1973). introduction to earthquake engineering, university of tokyo press. paolucci, r. (2002). amplification of earthquake ground motion by steep topographic irregularitie. earthquake engineering and structural dynamics, 31, 1831-1853. seed, h.b. (1979). considerations in the earthquake resistant design of earth and rockfill dams. 19th rankine lecture of the british geotechnical society, geotech., 29(3), 215-263. seed, h.b., makdisi, f.i., & de alba, p. (1978). performance of earth dams during earthquakes. j. geotech. eng., american society of civil engineering, 104(gt7), 967-994. wang, c. y. (2007). liquefaction beyond the near field. seismological res. lett. 78 (5), 512–517. doi:10.1785/gssrl.78.5.512 wood, j. (1973). earthquake-induced soil pressures on structures. report eerl 73-05, california institute of technology, pasadena p. 311. youd, t. l., & idriss, i. m. (2001). liquefaction resistance of soils: summary report from the 1996 nceer and 1998 mceer/ nsf workshops on evaluation of liquefaction resistance of soils. j. geotechnical geo-environmental eng. 2001(10), 297–313. doi:10.1061/(asce)10900241(2001)127:4(297) yu, l., kong, x., & xu, b. (2012). seismic response characteristics of earth and rockfill dams. 15th world conference on earthquake engineering, lisboa, portugal. https://www.icoldcigb/ j. build. mater. struct. (2022) 9: 22-32 original article doi : 10.34118/jbms.v9i1.1895 issn 2353-0057, eissn : 2600-6936 free vibrational analysis of composite beams reinforced with randomly aligned and oriented carbon nanotubes, resting on an elastic foundation chatbi m 1,*, harrat z r 1, ghazoul t 1, bachir bouiadjra m 1,2 1 djillali liabés university, lsmagctp laboratory, sidi bel abbés, algeria. 2 thematic agency for scientific and technological research, algeria. * corresponding author: moh-ing17@outlook.com received: 17-06-2021 accepted: 21-01-2022 abstract. the main interest of this paperwork is to examinate the dynamic behavior (free vibrational response) of carbon nanotubes (cnt) composite beams standing on an elastic foundation of winkler-pasternak’s. the affected beam consists of a polymer matrix reinforced with single-wall carbon nanotubes (swcnt’s), in which, a large number of cnt’s reinforcement of infinite length are distributed in a linear elastic polymer matrix. in this study the cnt’s are considered either aligned or randomly oriented on the matrix. a refined high-order beam theory (rbt) is adopted in the present analysis using a new shape function. the refined beam theory which is summarized by differentiating the displacement along the beam transverse section into shear and bending components, initially the material properties of the composite beam (cntrc) are estimated using the mori-tanaka’s method. the beam is considered simply supported on the edge-lines. navier’s solutions are proposed to solve the boundary conditions problems. since there are no results to compare with in the literature; the results in this study are compared with a free vibrational analysis of an isotropic beam. several aspects such as the length/thickness ratio, volume fraction of nanotubes, and vibrational modes are carried out in the parametric study. key words: free vibration analyses, mori-tanaka’s method, carbon nanotube reinforced beams, elastic foundation, refined beam theory. 1. introduction in the last few decades, carbon nanotubes (cnt’s) were presented as a huge revelation in all construction fields because of their significant mechanical and electrical properties. cnt’s were classified among the toughest materials in the world. in addition cnt’s are easily employed as a result of their high flexibility. as researches continued to investigate, cnt’s were becoming more usable especially in providing high performance materials for construction domains. therefore, cnt’s can be potentially integrated in the aerospace industry. (thostenson et al., 2001; esawi and farag, 2007). in civil engineering the preferable application of polymers/carbon nanotube is found in reinforcing structural elements such as beams and plates to improve several mechanical, thermal and electrical material characteristics. furthermore, cnt’s have been recently accepted as an excellent candidate for strengthening polymer composites because of their high elastic modulus, tensile strength and their low density which makes the resultant composites more efficient and remarkably light weighted. the material properties of composites reinforced with carbon nanotubes (cntrc) have been examined by many investigators, such as fidelus et al. (2005) and hu et al. (2005). in the same way, shi et al. (2004) studied the stiffening effect of carbon nanotubes by employing the moritanaka effective-field method to calculate the effective elastic moduli of composites while considering the effects of waviness and agglomeration of cnt’s on the effective stiffness. mailto:moh-ing17@outlook.com chatbi et al., j. build. mater. struct. (2022) 9: 22-32 23 on the other hand, there is still a lack of studies on the mechanical behavior of cntrcs in the open literature. for example, ke et al. (2010) analysed the non-linear free vibration of cntrc using timoshenko’s theory of beams. yas and heshmati (2012) presented the dynamic response of nano composite beams with carbon nanotubes oriented randomly under a dynamic load. wattanasakulpong and ungbhakorn (2013) studied the bending, buckling and vibration behaviors of carbon nanotube-reinforced composite beams resting on elastic foundation. furthermore, tegrara et al. (2015) analyzed the mechanical behavior of nanotube-reinforced composite beams using the refined beam theory (rbt). yas and samadi (2012) evaluated the free vibrations and buckling responses of carbon nanotube-reinforced composite timoshenko beams resting on elastic foundation. in the current analysis, and in order to estimate the engineering constants (young’s modulus and poisson’s ratio) of composites with aligned or randomly oriented straight single-walled nanotubes in polymer matrix, mori-tanaka effective-field method is employed (suresh, 1998). thereafter, we aim to analyze the free vibrational response of cnt reinforced beams placed on elastic foundation. 2. mathematical formulation 2.1. material properties of composites reinforced with aligned cnt’s we consider first a polymer isotropic matrix with young’s modulus , and poisson’s ratio . the polymer matrix is strengthened with straight transversely isotropic cnt’s aligned in the xaxis direction (figure 1). the stress-strain relation of the composite can be expressed as follow. { } [ ] { } (1) where k, m, l, n, and p are hill’s elastic moduli (hill , 1965). fig 1. geometry of cntrc beam resting on elastic foundation. the effective material properties of cntrcs can be estimated using the mori-tanaka’s method, such that: (2) 24 chatbi et al., j. build. mater. struct. (2022) 9: 22-32 ( ( )( ( ))) ( )( ( ) ( )) ( ( ( )) ( )) ( )( ( ) ( )) (( ) ( )( ) ( )) ( )( ( ) ( )) ( ( ) ( ) ) ( ) ( ) ( ( ) ( )) ( )( ( ) ( )) ( ( )( )) ( )( ( ( )) ( )) where , , , , , , and , are the elastic constants of swcnt’s. therefore, the expressions of the effective parallel and normal young's modulus of cntrcs are as follows. ( ) (3) 2.2. material properties of composites reinforced with randomly oriented cnt’s when cnts are completely randomly oriented in the isotropic matrix with young’s modulus , and poisson’s ratio , the composite is then considered isotropic, and its bulk modulus k and shear modulus g are defined as: ( ) ( ) (4) where ( ( )( ) ) (5) ( ) ( ( ( )) ( ) ( ) ) (5) chatbi et al., j. build. mater. struct. (2022) 9: 22-32 25 ( ( ( ) ( )) ( ) ( ) ) in which , and are the bulk and shear modulus of the polymer matrix respectively. (6) the effective young’s modulus e and poisson’s ratio n of the composite are given by: (7) 2.3. displacement field based on the refined plate theory assumptions (shimpi et al., 2006), the displacement field in the refined theory can be written as: { ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (8) where u0 is the mid-plane displacement of the beam along the x-direction, ‘wb’ and ‘ws’ are the bending and shear components of transverse displacement in z-direction, respectively. while the function f(z) represents shape functions determining the distribution of the transverse shear strains and stresses across the plate thickness; if the function is neglected, the displacements are reduced to the classical plate theory (cpt), else if the function is linear, the displacements are reduced to the first order deformation theory (fsdt). in this analysis a new shape functions are proposed. ( ) ( ) (9) it should be noted that unlike the first-order shear deformation theory, these theories do not require shear correction factors. the linear strain expressions associated with the displacements in the equation 8, are: ( ) ( ( ) ) ( ) (10) the strain components derived from the displacement field are well founded for thin and thick plates, where: (11) in which, the prime indicates differentiation of the function with respect to z, such that: 26 chatbi et al., j. build. mater. struct. (2022) 9: 22-32 ( ) ( ) '( ) , ( ) 1 . df z df z f z g z dz dz    (12) the expression of the constitutive relations can be expressed as: (13) where qij are the elastic constants, namely. (14) 2.4. governing equations the virtual work’s principle is applied to develop the equations of motion: ∫ ( ) (15) where and are the virtual variation of the internal strain energy, the virtual work done by external forces. firstly, the expression of the virtual strain energy is.  1 1 n n n h x xx y yy xy xy yz yz xz xz h n a u dadx                   (16) by substituting equation 10 into equation 16, we find: ∫{ ( ) ( )} (17) by substituting equation 14 into equation 17, we obtain the stress resultants in form of material stiffness and displacement components: (18a) (18b) (18c) 44 55 0 0 s yz xz s w q as y asq w x                           (18d) where , are the plate stiffness, defined by: chatbi et al., j. build. mater. struct. (2022) 9: 22-32 27 [ ] ∑∫ [ ] [ ] ∫ [ ( ) ( ) ( ) ] [ ] ∑∫ ( ) (19) the expression of the virtual work done by external loads while considering the effect of the elastic foundation can be expressed as follow. ∫ ∫ ( ( )( ) ( ) ( ) ) (20) where kw, and ks are the winkler and shearing layer spring constants. for the dynamic analysis, the virtual kinetic energy ( ) is required for the equations of motion, which takes the form ∫ ( )( ̇ ̇ ̇ ̇) (21) following the navier closed-form solutions, we assume the following solution form for the displacement functions expanded in double trigonometric fourier’s series that satisfies the boundary conditions. at edges 0x  and x a either 0 x n  or 0 u is prescribed either 0 b x m  or / b dw dx is prescribed either 0 s x m  or is prescribed where stress resultants can be expressed as follows: ( ) ∑∫ ( ( ) ( ) ( ) ) (22a) and i0, i2 are mass inertias defined as: ( ) ∑∫ ( )( ) (22b) by substituting equation 8 into equation 13, we obtain the stress resultants in form of material stiffness and displacement components: ̈ 28 chatbi et al., j. build. mater. struct. (2022) 9: 22-32 ( ) ( ) ( ̈ ̈ ) ̈ ( ) ( ) ( ̈ ̈) ̈ 2.5. navier solutions to formulate the closed-form solutions for bending and buckling problems of simply supported laminated plates, the navier method is employed: ( ) ∑ ( ) ( ) ∑ ( ) ( ) ∑ ( ) (23) where , and are the arbitrary parameters to be determined. , and n are vibrational mode shape. substituting equation 23 into the equilibrium equations, we obtain the closed-form solutions which are presented in the following matrix form. ([ ] [ ]) (24) where 3. results and discussions the navier solution was employed to determine the natural frequencies of cnt composite beams by solving the eigenvalue (equation 24). before analyzing the free vibrations of carbon nanotubes reinforced composite (cntrc) beams resting on winkler-pasternak elastic foundation, the material properties were calculated and presented in (figure 2) for the aligned cnt’s and (figure 3) oriented cnt’s, these properties (young’s modulus) were defined using the mori-tanaka’s approach, such that the young’s modulus and poisson’s ratio of polystyrene are and , respectively. for the reinforcement, we use the following representative values of the elastic constants of swcnt’s: , , , and , which are taken from the analytical results of popov et al. (2000). in which and are the hill’s elastic moduli for the reinforcing phase (cnt’s). chatbi et al., j. build. mater. struct. (2022) 9: 22-32 29 fig 2. young’s modulus in terms of the fraction volume of aligned cnt’s fig 3. young’s modulus in terms of the fraction volume of oriented cnt’s figures 2 and 3 show the variation of young’s modulus of cntc’s in terms of the volume fraction of cnt’s, knowing that the young modulus of cnt’s in the fibers direction is two orders of magnitude higher than the normal young modulus, the cnt’s are considered highly anisotropic. it is observed from (figure 2) that, because of cnts’ anisotropic property, the elastic modulus of the composite in the reinforcement direction increases much more rapidly with the volume fraction “cr” than the normal to the cnt direction. when the cnt’s volume fraction cr=0, the composite is pure isotropic polystyrene. in a similar way, (figure 3) presents the effective young’s modulus versus the volume fraction of randomly oriented, straight cnts in the same polystyrene matrix, it shows that the young modulus of the oriented carbon nanotubes reinforcement increases in parallel with the increase of the volume fraction of cnt’s. from figures 2 and 3 it can be seen that the aligned cnt’s in the polystyrene matrix is much more effective than the oriented cnt’s in terms of the young modulus magnitude. 30 chatbi et al., j. build. mater. struct. (2022) 9: 22-32 fig 4. dimensionless natural frequency of cntrc beam (l=10h, n=1). for the vibrational analysis of cntrc beams resting of elastic foundation, and in order to verify the accuracy of the present mathematical models and the proposed shape shear function in predicting vibrational analysis of beams. we used the following properties: , and for the polymer matrix. , , , , and , for the swcnt’s reinforcements. all analytical results are presented in the dimensionless forms which can be written as follows: √ where and are and of beam made of pure matrix material, respectively. for the elastic foundation spring constants, the following expressions are used: figures 4 and 5, present the dimensionless frequencies of cntrc beam with, the reinforcement which are considered oriented in the polystyrene matrix, the influence of cnt volume fraction is obvious in compare to an isotropic polymer beam (cr=0), the more “cr” presence gets raised in the matrix, more the dimensionless natural frequency increased. fig 5. dimensionless natural frequency of cntrc beam (l=10h, n=1, ). chatbi et al., j. build. mater. struct. (2022) 9: 22-32 31 4. conclusions in the present study, the material properties of carbon nanotubes reinforced composite beams are defined using the mori-tanaka’s method, while considering aligned and randomly oriented cnt’s, it is concluded that the aligned reinforcement in the polymer matrix is much more effective than the randomly oriented cnt’s, because cnt’s laid in an aligned way have high properties due to the high elastic properties of the cnt’s in disposition direction. as well a dynamic study of cntrc beams was presented in this work with and without the elastic foundation, the spring and shear layer constants of the elastic foundation have a very minor effect on the vibration frequencies regardless of cnt’s volume fraction in the polymer matrix. 5. references esawi, a. m., & farag, m. m. (2007). carbon nanotube reinforced composites: potential and current challenges. materials & design, 28(9), 2394-2401. fidelus, j. d., wiesel, e., gojny, f. h., schulte, k., & wagner, h. d. (2005). thermo-mechanical properties of randomly oriented carbon/epoxy nanocomposites. composites part a: applied science and manufacturing, 36(11), 1555-1561. hill, r. (1965). a self-consistent mechanics of composite materials. journal of the mechanics and physics of solids, 13(4), 213-222. hu, n., fukunaga, h., lu, c., kameyama, m., & yan, b. (2005). prediction of elastic properties of carbon nanotube reinforced composites. proceedings of the royal society a: mathematical, physical and engineering sciences, 461(2058), 1685-1710. kargarnovin, m. h., & arghavani, j. (2007). limit analysis of fgm circular plates subjected to arbitrary rotational symmetric loads. international journal of mechanical and mechatronics engineering, 1(12), 719-724.s.h. shen, compos. struct. 91 (2009) 9–19. ke, l. l., yang, j., & kitipornchai, s. (2010). nonlinear free vibration of functionally graded carbon nanotube-reinforced composite beams. composite structures, 92(3), 676-683. popov, v. n., van doren, v. e., & balkanski, m. j. s. s. c. (2000). elastic properties of crystals of singlewalled carbon nanotubes. solid state communications, 114(7), 395-399. shi, d. l., feng, x. q., huang, y. y., hwang, k. c., & gao, h. (2004). the effect of nanotube waviness and agglomeration on the elastic property of carbon nanotube-reinforced composites. j. eng. mater. technol., 126(3), 250-257. shimpi, r. p., & patel, h. g. (2006). free vibrations of plate using two variable refined plate theory. journal of sound and vibration, 296(4-5), 979-999. suresh, s. (1998). fatigue of materials. cambridge university press. tagrara, s. h., benachour, a., bouiadjra, m. b., & tounsi, a. (2015). on bending, buckling and vibration responses of functionally graded carbon nanotube-reinforced composite beams. steel and composite structures, 19(5), 1259-1277. thostenson, e. t., ren, z., & chou, t. w. (2001). advances in the science and technology of carbon nanotubes and their composites: a review. composites science and technology, 61(13), 18991912. 32 chatbi et al., j. build. mater. struct. (2022) 9: 22-32 wattanasakulpong, n., & ungbhakorn, v. (2013). analytical solutions for bending, buckling and vibration responses of carbon nanotube-reinforced composite beams resting on elastic foundation. computational materials science, 71, 201-208. yas, m. h., & heshmati, m. (2012). dynamic analysis of functionally graded nanocomposite beams reinforced by randomly oriented carbon nanotube under the action of moving load. applied mathematical modelling, 36(4), 1371-1394. yas, m. h., & samadi, n. (2012). free vibrations and buckling analysis of carbon nanotube-reinforced composite timoshenko beams on elastic foundation. international journal of pressure vessels and piping, 98, 119-128. j. build. mater. struct. (2021) 8:103-114 original article doi : 10.34118/jbms.v8i2.1487 issn 2353-0057, eissn : 2600-6936 empirical equation for concrete made with ppc or opc with fly ash by accelerated mix design method ojha p n, suresh kumar, manish mandre, piyush mittal, brijesh singh*, arora v v national council for cement and building materials, india * corresponding author: brijeshsehwagiitr96@gmail.com received: 11-08-2021 accepted: 02-11-2021 abstract. assessment of 28 days strength from accelerated strength (1 day) can be extremely helpful. early prediction of 28 days compressive strength is required basically for two purposes. first, to finalize the concrete mix proportions in the laboratory and secondly, for quality control purpose during construction. through this concept designers can easily identify the uncalculated errors during mix design or variations in materials and exposure conditions etc. and take necessary correction and modification measures to attain the desired strengths at 28 days. as per is: 9013 methodology to predict the 28 days strength of concrete from accelerated cured strength are indicated only for normal/control concrete. in the past few year focus has shifted from ordinary portland cement (opc) to portland pozzolana cement (ppc). fly ash is also being used widely at sites as replacement of opc. however, there is no such guideline available by which the assessment of 28 days strength of indian fly ash concrete can be made from accelerated strength tests. in the present study an attempt has been made to predict the expected 28 days compressive strength of concrete having ppc or opc with fly ash using accelerated temperature regime methods. the experimental study includes the use of 2 brands of ppc, 5 brands of opc and 2 sources of fly ash for replacement of opc ranging from 20% to 45 %. two temperature regimes 900c and 820c were used for accelerated curing. the samples were cured for 7.5 hours and 20hours respectively in each regime for expected 28 day compressive strength. the mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900c for 7.5 hours for mixes having ppc, opc mixed with fly ash 20% to 35% is fexp28 = 1.223 facs +2.024. the mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900c for 7.5 hours for mixes having ppc, opc mixed with fly ash more than 35% and up to 45% is fexp28 = 0.993 facs + 6.044. keywords: mix design, accelerated method, ppc, compressive strength, mathematical equation. 1. introduction according to indian standard acceptance and rejection of any type of concrete should be done by determining 28 days compressive strength (is456, 2000). it was observed that normal concrete achieve its potential strength within this time period. but for fly ash concrete, 28 days strength does not yield its potential strength as its rate of strength development is significantly slower compared to normal concrete. potential strength of fly ash concrete may develop at 90 days or even after 180 days (tokyay, 1999). it is also known that the strength of normally cured concrete at 28 days is considered for structural design. this time difference may lead to loss of valuable time and money. accelerated curing of normal concrete by warm water method and boiling water method provided by is:9013 (1978) are helpful to predict 28 days strength of control concrete with respect to accelerated cured strength by means of correlation between accelerated strength and normal curing strength. for the prediction of 28 days strength of fly ash concretes no such correlation is available. in this current paper provides some strength prediction models have been proposed (jayanta and jaydeep, 2016). mailto:brijeshsehwagiitr96@gmail.com 104 ojha et al., j. build. mater. struct. (2021) 8: 103-114 construction projects go through time overrun and cost overrun, due to delay in decision making in appropriate time frame. many activities are involved in execution of a project. finalization of concrete mix proportions is the most important activity. usually 28 days moist cured compressive strength test results are required to finalize concrete mix proportions (udoeyo et al., 2010). the guidelines and procedures given in is 9013: 1978 which is based on elevated temperature curing method helps in early decision making about mix proportions within 48 to 72 hours when mix has opc as cementing material. in past few years, focus has shifted from opc to a wider application of blended cement such as ppc, psc etc. many industrial by products are being used as supplementary cementitious materials and fly ash is one of them. fly ash is used in two ways, one in cement industry as part of cement itself i.e. as ppc and another as part replacement of opc during concrete mix design. however no empirical formula or guidelines are available for predicting 28 days moist cured compressive strength concrete having ppc or opc with fly ash as binder (nikitha and kameswara, 2019). it is well established that an increase in curing temperature increases the rate of hydration of cement. the increase in rate of hydration reaction and strength development of opc, at elevated curing temperature is also well documented in existing literatures (shelke and gadve, 2013). the use of fly ash and other supplementary cementitious material is increasing not only due to an economic and sustainability point of view but also these materials improve the rheology of concrete and other engineering properties of hardened concrete. however the rate of strength gain in opc with fly ash concrete is slower than in concrete with opc only (bhanja and pan, 2013; jayadevan et al., 2014). fly ash is used in concrete mix generally to reduce the heat of hydration but because of this there is reduction in early strength development of concrete. many parameters affect the strength of concrete such as quantum of fly ash, quality and quantity of binder material, aggregate size, curing regime, chemical effect, concrete grade used and mix proportions. hydration itself is affected by the temperature (khan et al., 2019; krishna et al., 2010). to accelerate the strength gain at early age and to relate it to the 28-days compressive strength, proper trend lines and calibration curves are needed. for the accelerated curing of concrete, different methods and techniques have been classified earlier also such as maturity methods, curing in oven, curing in heated water and expanded polystyrene molds method (amritkar and more, 2015, shah and bhavnashah, 2011). in such scenario, there is need to develop the mathematical equations to determine strength of concrete which will generate confidence to the construction fraternity for use of concrete made with blended cement by using accelerated curing method. a number of methods of accelerated and early age testing of cubes have been developed that allow early prediction to be made of strength development at later ages. indian standard is: 9013 covers two methods. in warm water method the concrete specimens are cured at elevated temperature of 55±20c for 19 hours 50minutes and in boiling water method the concrete specimens are cured at elevated temperature of 1000c for 3.5h±5minutes. expected 28 days compressive strength is calculated by empirical formula given in the code. it is found that the above two methods are useful for prediction of expected 28 days compressive strength when concrete is made using opc. bs 1881(1983) covers three methods of accelerated curing, under which the concrete specimens are cured at elevated temperature of 350c, 550c and 820c for 24hours ±15minutes, 20hours ±10minutes, and 14hours ±15minutes respectively. similarly astm c-684 (aci 214.1r, 1987; astm c 684, 1999) covers 4 procedures for estimation of 28 days compressive strength. in warm water method concrete specimens are cured at elevated temperature of 350c for 23.5hours ±30minutes, in boiling water method at 1000c for ojha et al., j. build. mater. struct. (2021) 8: 103-114 105 3.5hours ±5minutes, in autogenous method at 21±60c for 48hours ±15minutes and in high temperature and pressure method, the concrete specimens are cured at 1500c & 10.3±0.2 mpa pressure for 5 hours ±5 minutes. canadian standard csa a23.1 (1970) has an establish procedure, which is independent of cement type, mix proportion and admixture type. in this method, the concrete specimens are cured at elevated temperature of 1000c for 16 hours once the concrete is finally set after casting. the methods given in bs: 1881 & astm c 684 recommend, to develop appropriate correlation using accelerated compressive strength and actual 28 days compressive strength for the materials and mix used. they do not provide any general empirical relationship to predict the expected 28 days compressive strength. ncb has conducted this experimental study to develop a simple empirical relationship between accelerated compressive strength and 28 days moist cured compressive strength of concrete cubes. the objective of this research is to develop guidelines to determine the expected 28 days compressive strength of concrete having ppc or opc with fly ash as cementitious material using accelerated curing. the developed method can also be used at site for quality control purposes. 2. materials 2.1. cement five brands of opc-43 grade cements designated as opc-i, opc-ii, opc-iii, opc-iv and opc-v conforming to is: 269 (2015) and two brands of ppc designated as ppc-i & ppc-ii conforming to is: 1489 (2015) were used for the experimental work. all the cements were tested as per is: 4031 and is: 4032. the test results of physical and chemical analysis are given in table-1. 2.2. flyash two flyash samples from different sources designated as fly ash 1 and fly ash 2 were used in the experimental work. the fly ash samples were tested as per is: 1727: 1967 and the results were conforming to is 3812 (2013). the tests results are given in table-2. table 1. test results of cement sample ordinary portland cement (opc) and portland pozzolana cement (ppc) s.no. properties opc1 opc2 opc3 opc4 opc5 ppc1 ppc2 1 blain’s fineness, (m2/kg) 282 355 292 336 306 379 358 2 setting time, (in minutes) initial final 230 280 115 180 160 215 120 195 160 210 135 205 140 210 3 compressive strength (n/mm2) 3 days 7 days 28 days 34.5 45.0 55.5 36.5 44.5 55.0 31.5 41.0 47.5 35.5 45.0 53.5 39.5 49.0 60.0 30.0 41.5 55.5 27.5 39.0 53.5 4 soundness by autoclave, % le chatelier exp (mm) 0.01 1.50 0.05 0.50 0.09 1.0 0.04 1.0 0.01 1.0 0.07 2.00 0.08 2.00 5 specific gravity 3.15 3.15 3.15 3.15 3.15 2.85 2.87 table 2. test results of fly ash sample sl no. properties fly ash source 1 fly ash source 2 1 blain’s fineness, m2/kg 403 329 2 specific gravity 2.20 2.20 3 lime reactivity, n/mm2 8.0 4.92 106 ojha et al., j. build. mater. struct. (2021) 8: 103-114 2.3. coarse aggregate: crushed angular coarse aggregate with 20mm maximum size were used in the experimental work. the coarse aggregates were tested as per is: 2386 and were found to conform to is: 383 (2016). the test results are given in table 3 2.4. fine aggregate the fine aggregate from natural source i.e. river sand conforming to zone-i was used in the experimental work. the fine aggregate was tested as per is: 2386 and were found to conform to is: 383 (2016). the test results are given in table-4 table 3. test results of coarse aggregate sample sl no. test carried out results obtained for 20 mm results obtained for 10 mm 1 specific gravity 2.79 2.81 2 water absorption % 0.60 0.40 3 abrasion value % 25.00 30.00 4 crushing value % 25.00 25.00 5 impact value % 16.00 20.00 6 flakiness index % 17.00 21.00 7 elongation index % 14.00 13.00 8 soundness (na2so4) % 0.30 1.20 9 grading percentage passing sieve size 20mm 10mm 40 mm 100.00 20 mm 98.00 12.5 mm 100.00 10 mm 1.00 68.00 4.75 mm 0 2.00 2.36 mm 0.00 table 4. test results of fine aggregate sample (natural) sl no. test carried out results obtained 1 specific gravity 2.63 2 water absorption, % 1.0 3 silt wet sieving % 2.0 4 grading sieve size percentage passing 10 mm 100 4.75 mm 74 2.36 mm 54 1.18 mm 38 600 micron 22 300 micron 8 150 micron 4 2.5. chemical admixture superplasticizer (normal type) conforming to is: 9103 (1999) was used in the experimental work. ojha et al., j. build. mater. struct. (2021) 8: 103-114 107 3. experimental programme 3.1. initial trials to get the early age compressive strength through accelerated curing, some initial trials were conducted. the mix proportions used for initial trials are given in table-5a & table-5b. the following parameters were fixed for initial trials:  three temperature regimes for accelerated curing were selected for initial trials i. boiling water with time duration of 3.5h, 5.5 h and 7.5 hours. ii. hot water at 900c temperature with time duration of 3.5h, 5.5h and 7.5hours. iii. hot water at 820c temperature with time duration of 16h, 18h, 20h, 22h and 24hours.  one brand of opc and fly ash from one source were used.  two brands of ppc were used.  25% opc cement was replaced with fly ash (by weight of total cementitious materials). water-cement/cementitious ratio was kept 0.50, 0.45 and 0.40. table 5.a. mix proportion used for initial trials using ppc mix constituents ( kg) for one cubic meter w/c ratio 0.50 0.45 0.40 water 165 165 165 cement 330 367 412 chemical admixture(kg/cum) 3.30 3.70 4.10 fine aggregate(kg/cum) 829 804 723 coarse aggregate (kg/cum) 20mm 672 665 690 10mm 451 446 463 table 5.b. mix proportion used for initial trials using opc mixed with 25% flyash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.50 0.45 0.40 water 165 165 165 cement 248 275 309 fly ash (25% as replacement) 82 92 103 chemical admixture(kg/cum) 3.30 3.70 4.10 fine aggregate(kg/cum) 829 796 750 coarse aggregate (kg/cum) 20mm 672 671 673 10mm 451 451 452 based on initial trials, the results of the two methods were found encouraging:  accelerated curing in hot water at 900c and time duration of 7.5 hrs.  accelerated curing in hot water at 820c for longer duration of 20 hrs. 3.2. detailed trials the detailed trials were carried out by fixing following parameters for accelerated curing.  accelerated curing in hot water at 900c and time duration of 7.5 hrs.  accelerated curing in hot water at 820c for longer duration of 20 hrs. 108 ojha et al., j. build. mater. struct. (2021) 8: 103-114  five brands of opc and flyash from two sources were used.  two brands of ppc were used.  fly ash, ranging from 20% to 45% was added (as replacement of opc) by weight of cementitious materials.  water cement/cementitious ratio were kept ranging from 0.35 to 0.55. the mix proportions used for detailed trials are given in table-6a to table-6g. detail trials the detail trials were carried out with two brands of ppc and five brands of opc. two sources of fly ash were used with 20% to 45% replacement in increment of 5%. five water-cementitious ratios were selected from 0.35 to 0.55 for detail trials. normal type chemical admixture @1 % by weight of cementitious material was used for all the trials. with 5 opc, 2 sources of fly ash and 6 replacement levels of opc by fly ash (20% to 45%) a total 300 nos. of samples (one sample comprising 3 cube specimens of 150 mm size) were cast at various water cementitious ratios ranging from 0.55 to 0.35. similarly with 2 ppc, 10 samples were cast at same water cement ratios for accelerated curing under each temperature regime i.e. 310 nos. of samples were cast for regime i & 310 nos. of samples were cast for regime ii. corresponding to accelerated cured samples, 310 nos. of samples were also cast and tested for determination of 28 days compressive strength of moist cured samples. when accelerated curing was done the following procedures were followed:  all specimens were cured at 27c and more than 90% humidity for first 24 hours.  all accelerated curing specimens were kept in open case after de-molding in accelerated curing tank. when accelerated curing was completed as given regime i and regime ii above, they were cured at 27c for two hours. then compressive strength was determined as per procedure given in is: 516. corresponding to each temperature regime, the specimens were also kept for moist curing at 27+2c for 28 days and after 28 days compressive strength was determined as per procedure given in is :516. table 6a. mix proportions used for detailed trials using ppc cement mix constituents ( kg) for one cubic meter w/c ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 300 330 367 412 471 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregates (kg/cum) 861 829 804 723 674 coarse aggregates (kg/cum) 20mm 669 672 665 690 685 10mm 449 451 446 463 460 table 6a. mix proportions used for detailed trials using opc mixed with 20 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 240 264 293 330 377 fly ash (20% as replacement) 60 66 73 83 94 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregates (kg/cum) 863 831 798 753 704 coarse aggregates (kg/cum) 20mm 671 674 673 675 672 10mm 451 452 452 453 451 ojha et al., j. build. mater. struct. (2021) 8: 103-114 109 table 6c. mix proportions used for detailed trials using opc mixed with 25 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 225 247 275 310 353 fly ash (25% as replacement) 75 83 92 103 118 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregates (kg/cum) 861 829 795 750 700 coarse aggregates (kg/cum) 20mm 669 671 671 672 668 10mm 449 451 450 451 449 table 6d. mix proportions used for detailed trials using opc mixed with 30 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 210 231 257 289 330 fly ash (30% as replacement) 90 99 110 124 141 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregates (kg/cum) 858 826 792 746 697 coarse aggregate (kg/cum) 20mm 667 669 668 669 665 10mm 448 449 449 450 447 table 6e. mix proportions used for detailed trials using opc mixed with 35 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 195 214 239 269 306 fly ash (35% as replacement) 105 116 128 144 165 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregate(kg/cum) 856 824 789 743 693 coarse aggregate (kg/cum) 20mm 666 667 666 667 662 10mm 447 448 447 448 444 table 6f. mix proportions used for detailed trials using opc mixed with 40 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 180 198 220 248 282 fly ash (40% as replacement) 120 132 147 165 189 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregate(kg/cum) 853 821 786 740 690 coarse aggregate (kg/cum) 20mm 664 665 664 664 659 10mm 446 447 446 446 442 table 6g. mix proportions used for detailed trials using opc mixed with 45 % fly ash mix constituents ( kg) for one cubic meter water/cementitious ratio 0.55 0.50 0.45 0.40 0.35 water 165 165 165 165 165 cement 165 181 202 227 259 fly ash (45% as replacement) 135 149 165 186 212 chemical admixture(kg/cum) 3.00 3.30 3.70 4.10 4.70 fine aggregate(kg/cum) 851 818 784 737 687 coarse aggregate (kg/cum) 20mm 662 663 661 661 656 10mm 444 445 444 444 440 110 ojha et al., j. build. mater. struct. (2021) 8: 103-114 3.3. specimen cast and curing 150mm cube specimens were cast for compressive strength. the specimens were kept at 27 + 20c and relative humidity more than 90% for 24 hours initially. for accelerated curing the specimens were submerged in hot water immediately after demoulding in open cage, at different temperature regimes and for different time duration. after the completion of accelerated curing specimens were taken out from hot water and were kept in water at 27 + 20c for 1½ hour. the specimens were tested for accelerated compressive strength after 1 ½ hour as per is 516. for 28 days’ compressive strength, the specimens were kept in water at 27 + 20c for curing up to 28 days. 4. methodology adopted to develop empirical relationship following steps were followed for the development of empirical relationship between accelerated compressive strength and 28 days moist cured compressive strength: i. all the trial results of accelerated compressive strength and 28 day compressive strengths are tabulated and standard deviation is calculated. ii. two categories of data sets corresponding to each temperature regime are taken for analysis of the trial results as given below. category 1: hot water at 900c for 7.5 hours a) 20-35% fly ash replacement at 900c and 7.5hours b) 40-45% fly ash replacement at 900c and 7.5hours category 2: hot water at 820c for 20 hours a) 20-35% fly ash replacement at 820 c and 20hours b) 40-45% fly ash replacement at 820c and 20hours iii. best fit line is plotted and expected 28 days strength is calculated by this best fit line equation. iv. upper and lower control limits were fixed as per criteria given below and the points above/below upper/lower limits were treated as outliers criteria for fixing outliers: a. mean ± se (standard error) x 2.5 (considering 98 % confidence level) b. mean ± 15% (both the criteria were nearly matching) it was seen that total outliers were less than 10% of total data. v. data beyond the upper limit and lower limit was eliminated. vi. the best fit line was plotted again by adopting the same procedure as given in step no. (iii) & (iv). vii. in the case of hot water procedure using temperature regime of 900c for 7.5 hours, the best fit line was lowered by 8% to bring more than 90% data above this line as shown in fig.1 and fig. 2. viii. in the case of hot water procedure using temperature regime of 820c for 20 hours, the best fit line was lowered by 10% to bring more than 90% data above this line as shown in fig.3 and fig. 4. ojha et al., j. build. mater. struct. (2021) 8: 103-114 111 ix. the line (after lower down) where less than 10 % data remain below is adopted for calculating the expected 28 days compressive strength. the validation of equation was done for temperature regime 900c for 7.5 hours only as the best fit line was lower down 8 % only in comparison to 10% in the case of temperature regime of 820c for 20 hours, to bring more than 90% results above best fit line plotted. fig. 1. proposed 90˚c 7.5 hours graph for ppc and opc + flyash (15% to <35%) fig. 2. proposed 90˚c 7.5 hours graph for ppc and opc + flyash (>35% to 45%) 112 ojha et al., j. build. mater. struct. (2021) 8: 103-114 fig. 3. 82˚c 20h graph for ppc cement and opc + flyash (20% to <35%) fig. 4. 820c 20h graph for ppc and opc + flyash (>35%-45%) 5. conclusions early prediction of 28 days compressive strength results through existing codal provision is not possible for concrete mixes having pozzolana like fly ash, due to the effect of their physical and chemical properties on the rate of strength gain. based on validation of developed relationships, it is concluded that for ppc and at different replacement level of opc by flyash (20% to 45%), the elevated temperature curing regime i.e. 900c for 7.5 hours can be adopted for prediction of expected 28 days compressive strength. ojha et al., j. build. mater. struct. (2021) 8: 103-114 113 however, since the rate of strength development differs with the level of flyash replacement and therefore, for the following two cases, two separate empirical relationships can be adopted: a. for the mixes made with ppc and opc with flyash up to 35% b. for the mixes made with opc and flyash more than 35% up to 45%. mathematical equations for early prediction of 28 days compressive strength of concrete are proposed separately for the mixes having ppc cement, opc mixed with fly ash (20% to 35%) and the mixes having opc mixed with fly ash more than 35% and up to 45%. these mathematical equations give the confident level around 90%. the mathematical equations to estimate the 28 days compressive strength of concrete, cured at 900c for 7.5 hours for mixes having ppc, opc mixed with fly ash 20% to 35% is fexp28 = 1.223 facs +2.024 and mixes having opc mixed with fly ash more than 35% and up to 45% is fexp28 = 0.993 facs + 6.044 where: fexp28 = expected 28 days’ compressive strength of concrete in n/mm2 facs = accelerated compressive strength in n/mm2 6. references aci 214.1r (1987). use of accelerated strength testing, aci manual of concrete practice. amritkar, s., & more, n. (2015). statistical modeling to forecast the strength of concrete using accelerated curing, international journal of research in engineering and technology, 4, 11. astm c 684 (1999). standard test method for making, accelerated curing and testing concrete compression test specimens bhanja, s., & pan, s. (2013). modified water cement ratio law for fly ash concrete‖ the indian concrete journal, 87, 21-28. bs 1881(1983). part 112 , methods of accelerated curing of test cubes, british standards. csa a23.1 (1970). accelerating the curing of cylinders and determining their compressive strength canadian standards agency. is456 (2000). indian standard code of practice for plain and reinforced concrete, fourth revision, is: 456-2000, bureau of indian standards, new delhi. is9013 (1978). method of making curing and determining compressive strength of accelerated cured concrete test specimens. is: 1489 (2015). part 1, specification for portland pozzolana cement (fly ash based), bureau of indian standards, new delhi. is: 269 (2015). ordinary portland cement specification, bureau of indian standards, new delhi. is: 3812 (2013). part 1, specification for pulverized fuel ash, bureau of indian standards, new delhi. is: 383 (2016). specification for coarse and fine aggregates from natural sources for concrete, bureau of indian standards, new delhi. is: 9103 (1999). specification for concrete admixture, bureau of indian standards, new delhi. jayadevan, v., valsalakumary, v. r., & sufeera, o. b. (2014). reliability of accelerated curing techniques for speedy design of concrete mixes—an appraisal of is 9013: 1978 code. indian concrete journal, 5760. 114 ojha et al., j. build. mater. struct. (2021) 8: 103-114 jayanta, n. c., & jaydeep c. (2016). development of strength prediction models of 28 days fly ash concrete strength by accelerated curing method, international journal of scientific & engineering research, 7(4), 83-86. khan, m. a., chowdhry, m. a., javed, a., ahmed, m. l., & kanwal, h. (2019). strength prediction model for accelerated cured fly-ash based concrete. mehran university research journal of engineering & technology, 38(4), 1057-1066. krishna, r., kumar, r. p., & khan, a. m. (2010). a study on the influence of curing on the strength of a standard grade concrete mix. facta universitatis-series: architecture and civil engineering, 8(1), 2334. nikitha, p. & kameswara r. b. (2019). accelerated method of concrete mix proportioning by incorporating fly ash and silica fume, international journal of recent technology and engineering, 7(6c2). shah, p., & bhavnashah, s. (2011). development of mathematical model to predict early age strength for blended cement through accelerated curing. in published: national conference on recent trends in engineering & technology on may. shelke, n. l., & gadve, s., (2013). prediction of compressive strength using accelerated curing”, international journal of pure & applied research in engineering & technology, 8(1), 90-99. tokyay, m. (1999). strength prediction of fly ash concretes by accelerated testing. cement and concrete research, 29(11), 1737-1741. udoeyo, f. f., brooks, r., udo-inyang, p., & nsan, r. o. (2010). early prediction of laterized concrete strength by accelerated testing. ijrras, 5(1), 10. 1345-1353. j. build. mater. struct. (2022) 9: 87-97 original article doi : 10.34118/jbms.v9i1.1598 issn 2353-0057, eissn : 2600-6936 influence of the thermomechanical loading on the behavior of high performance concrete and ordinary concrete bouabdallah moulaï abdellah 1, 2 1 department of civil engineering, national polytechnic school maurice audin of oran, algeria. 2 lctc, laboratory for construction technical control in oran algeria. corresponding author: m-a.bouabdallah@enp-oran.dz received: 22-11-2021 accepted: 29-04-2022 abstract. the present article aims to present an experimental study to investigate the behavior of high performance concrete and ordinary concrete that were subjected to thermomechanical loading. the mechanical properties of both types of concrete, which underwent heat treatment, were studied at room temperature. in addition, the compressive strength was tested and calculated at different ages, namely 7, 14, 28 and 60 days. for each test, the samples were heated at a rate of 5 °c/min, until the following temperatures were reached, i.e. 250 °c, 350 °c, 450 °c, 600 °c and 900 °c. the target temperature was kept constant for one hour in order to ensure that it was uniform throughout the sample, before cooling. moreover, the sample weight was measured before and after heating in order to determine the weight loss of the samples tested. the findings allowed concluding that the mechanical characteristics of concrete were enhanced after exposure to temperatures within the range from 250 °c to 450 °c. key words: high performance concrete; ordinary concrete, thermomechanical loading; constraint/deformation; elastic modulus; ultrasound. 1. introduction it is worth indicating that a quite large number of studies on high performance concrete subjected to thermomechanical loadings are currently available in the literature. for example, that has previously been carried out by bouabdallah (2006, 2008), horszczaruk et al. (2015), torelli et al. (2020), noumowé (1995), drzymała et al. (2017), and tsimbrovska (1998). in particular, simonin (2000) investigated the effect of thermomechanical loading on the behavior of refractory concretes. on the other hand, several research works were performed in order to examine the influence of temperature on recycled concrete aggregates (liu et al., 2018). similarly, a number of researchers in the field attempted to investigate the behavior of prestressed concrete subjected to high temperature gradients (dubois et al., 1967). furthermore, nguyen et al. (2019) performed a study on the thermomechanical behavior of reinforced concrete samples at high temperatures. moreover, alarcon-ruiz (2003) analyzed the effect of temperature on concrete microstructures. with regard to the recycling of building materials, it is worth mentioning the work of prajapati et al. (2021) and liu et al. (2018) who sought to examine the effect of temperature on recycled concrete aggregates. further, several numerical simulations were performed on various types of concrete. in this context, courivaud et al. (1997) carried out a study on cellular concrete that was subjected to a vapor pressure gradient at high temperatures. in the same context, douk et al. (2021) carried out a numerical investigation of the thermomechanical behaviour of concrete beams with and without textile-reinforced concrete (trc) strengthening. on the other hand, another research was carried out by yermak (2015) on the behavior of concrete incorporating fibers and exposed to high temperatures. in the same 88 bouabdallah., j. build. mater. struct. (2022) 9: 87-97 context, nastica (2019) investigated the shrinkage and creep strains of concrete subjected to low relative humidity and high temperature environments. further, other similar studies were also carried out in the same field. the present work aims primarily to conduct an experimental study on the behavior of ordinary concrete (oc) and high performance concrete (hpc) that were subjected to thermomechanical loadings. in order to carry out this study, it was decided to prepare a series of test specimens from ordinary concrete and high performance concrete. these test pieces were then exposed to different temperatures, i.e. 20, 250, 350, 450, 600, and 900 °c. this experimental study was carried out at different ages, i.e. 7 days, 14 days, 28 days and 60 days. it should be noted that the thermomechanical loading tests were carried out after cooling the specimens to reach ambient temperature. the results obtained concern the evolution of the compressive stress of ordinary concrete and high performance concrete as a function of temperature at different ages, the evolution of mass loss of ordinary concrete and high performance concrete as a function of temperature and age. afterwards, these results were compared with those obtained at room temperature (20 °c). 2. experimental study 2.1. materials used portland cement type ii cem ii a 42.5 was used, with limestone gravel 3/8 and 8/15, crushed sand 0/5 and siliceous sea sand 0/1. table 1. characteristic of the cement used identification cement class type of addition in cement clinker % density cp cpj 42,5 pozzolanic (6 20 %) 80 94 % 3,1 table 2. characteristic of the materials used test gravel 8/15 mm gravel 3/8 mm crushed sand sea sand densities 2,735 2,727 2,714 2,642 absorption coefficients 1,52 1,75 2,65 2,11 los angeles 23,56 sand equivalent test esv 76,86 72 esp 70,53 67,69 fig 1. particle size curve. 0,01 0,1 1 10 100 0 20 40 60 80 100 p a s s in g [ % ] sieve size [mm] sea sand crushed sand gravel 3/8 mm gravel 8/15 mm bouabdallah., j. build. mater. struct. (2022) 9: 87-97 89 2.2. formulation of concretes table 3 illustrates the composition of the different types of concrete. table 3. composition of concretes under study constituents (kg/m3) ordinary concrete "oc" hpc gravel 8/15 mm 777 gravel 3/8 mm 415 1011 crushed sand 372 sea sand 372 722 cpj cement 353 400 pozzolana 40 plasticizer, [2,5 % by weight of cement] 10 fine limestone 72.2 total amount of water 172 140 water/cement ratio 0.49 0.29 slump test [cm] 8 15 2.3. equipment it is worth noting that the thermal loading of both types of concrete specimens, of dimensions (7x7x7) cm3, was carried out using an electric furnace scm 011, of internal dimensions (130x120x270) mm3, and whose temperature can reach a maximum value of 1200 °c, as shown in figure 2. fig 2. furnace 1200°c (scm 011). 2.4. thermal loading we have taken into account the damage caused by the thermal gradients that developed between the core and the surface of the specimen during the different heating phases, with a rate of 5°c/min and a plateau of 1h 30min, in order to get as close as possible to the situation of real fires. during the cooling phase, the cooling rates should be sufficiently slow, similar to cooling in the open air. the bearing temperatures were 250°c, 350°c, 450°c, 600°c and 900°c. the choice of temperatures was made according to the following description. the temperature range from 250 °c to 350 °c corresponds to small endothermic peaks, indicating the effects of decomposition and oxidation of metallic elements (ferric). at the temperature 400°c, there is portlandite decomposes and gives free lime. at 600°c, the c-s-h phases decompose and cause the formation of β-c2s. in the second step, there is dehydration of the hydrated calcium silicates 90 bouabdallah., j. build. mater. struct. (2022) 9: 87-97 and therefore engender a new form of calcium silicates. finally, at 900°c, there is decomposition of calcium carbonate. limestone decomposes at around 800 °c. a strongly endothermic reaction takes place and releases carbon dioxide (noumowé, 1995). for each material, a test was carried out on unheated specimens in order to have a reference value (20°c ± 2). the heating-cooling cycles therefore have the following form: fig 3. pattern of heating-cooling cycles. 3. results and discussion 3.1. density of concrete figures 4 (a), (b), (c), and (d) were utilized to make a direct comparison between the weight changes of both types of concrete. these weight variations were measured on the prepared specimens, at different ages, during the same heating cycle, with the heating rate of 5 °c/min. these changes were recorded for different temperatures. it is important to mention that the ambient temperature was taken as the reference temperature (temperature before placing the sample inside the oven) in order to accurately assess the reduction in weight after heating. furthermore, it is worth noting that the weight of each concrete specimen went through three distinct phases that are described below: in the first phase, for temperatures between 20 °c and 250 °c, a rapid decrease in the test piece weight was observed as the temperature went up. in the second phase, corresponding to temperatures between 250 °c and 600 °c, a slight decrease in the weight of the test piece was noted. in the third phase, between 600 °c and 900 °c, a weight change, similar to that observed in the first phase but more important, was noticed. the weight loss results mainly from the evaporation of the water existing inside the concrete through cracks caused by the expansion of concrete. t°c slopes of 5°c/min  level 1h 30min time bouabdallah., j. build. mater. struct. (2022) 9: 87-97 91 a b c d fig 4. evolution of weight of ordinary concrete and high performance concrete as a function of temperature. 3.2. mass loss of concrete likewise, figures 5 (a), (b), (c) and (d) present a direct comparison of the evolution of mass loss values for both types of concrete (oc and hpc), at different ages (7 days, 14 days, 28 days and 60 days), during the same heating cycle. the heating rate was equal to 5 ° c/min. the mass loss rates were recorded as a function of temperature. it was observed that the loss of mass of each concrete specimen went through three distinct phases: in the first phase, the mass loss of the test piece increased rapidly as the temperature went up to reach 250 °c. in the second phase, which corresponds to temperatures between 250 °c to 600 °c, the mass loss of the test piece continued to increase slowly. the third phase corresponds to temperatures above 600 °c; here the mass loss increased significantly again, in a similar manner as in the first phase. 0 200 400 600 800 1000 0,60 0,65 0,70 0,75 0,80 0,85 0,90 w e ig h t (k g ) temperature (°c) oc (t=20°c at 7 days) oc (t°c variable at 7 days) hpc (t=20°c at 7days) hpc (t°c variable at 7days) 0 200 400 600 800 1000 0,60 0,65 0,70 0,75 0,80 0,85 0,90 oc (t=20°c at 14 days) oc (t°c variable at 14 days) hpc (t=20°c at 14 days) hpc (t°c variable at 14 days) w e ig h t (k g ) temperature (°c) 0 200 400 600 800 1000 0,60 0,65 0,70 0,75 0,80 0,85 0,90 oc (t=20°c at 28 days) oc (t°c variable at 28 days) hpc (t=20°c at 28 days) hpc (t°c variable at 28 days) w e ig h t (k g ) temperature (°c) 0 200 400 600 800 1000 0,60 0,65 0,70 0,75 0,80 0,85 0,90 oc (t=20°c at 60 days) oc (t°c variable at 60 days) hpc (t=20°c at 60 days) hpc (t°c variable at 60 days) w e ig h t (k g ) temperature (°c) 92 bouabdallah., j. build. mater. struct. (2022) 9: 87-97 a b c d figure 5. variation of mass loss as a function of temperature. 3.3. compressive strength as a function of temperature and age figures 6 (a), (b), (c) and (d) display the evolution of compressive stress as a function of temperature, for different ages (7, 14, 28, and 60 days). simple comparison of the results obtained indicates that the compressive strength of high performance concrete is significantly higher than that of ordinary concrete. it was also observed that for the two types of concrete under study, as the temperature increased, the compressive strength went up until reaching the maximum threshold value. beyond this maximum value, the compressive strength started to decrease, though the temperature was still increasing. figure 6 (a) clearly shows an increase in compressive strength for the temperature range between 20 °c and 250 °c for ordinary concrete, and between 20 °c and 350 °c for high performance concrete. figure 6 (b) indicates that the compressive strength went up while the temperature dropped between 20 °c and 450 °c for ordinary concrete, and between 20 °c and 350 °c for high performance concrete. with regard to figure 6 (c), it shows that the compressive strength was rising proportionally with temperature between 20 °c and 250 °c for ordinary concrete, and between 20 °c and 350 °c for concrete high performance. finally, in figure 6 (d), one may easily see compressive strength increase for temperatures between 20 °c and 250 °c for ordinary concrete, and between 20 °c and 250 °c for high performance concrete. beyond these temperatures, the compressive strength started to drop though the temperature was still increasing. 0 200 400 600 800 1000 0,00 0,05 0,10 0,15 0,20 m a s s l o s s ( k g ) temperature (°c) oc at 7 days hpc at 7 days 0 200 400 600 800 1000 0,00 0,05 0,10 0,15 0,20 m a s s l o s s ( k g ) temperature (°c) oc at 14 days hpc at 14 days 0 200 400 600 800 1000 0,00 0,05 0,10 0,15 0,20 m a s s l o s s ( k g ) temperature (°c) oc at 28 days hpc at 28 days 0 200 400 600 800 1000 0,00 0,05 0,10 0,15 0,20 oc at 60 days) hpc at 60 days m a s s l o s s ( k g ) temperature (°c) bouabdallah., j. build. mater. struct. (2022) 9: 87-97 93 a b c d fig 6. evolution of the compressive strength as a function of temperature. 3.4. variation of deformation as a function of applied stress the deformations of the specimen were measured as a function of the uniaxial compression. two 1/100 comparators were placed on the press plate to measure the uniaxial displacement, as is clearly shown in figure 7. fig 7. apparatus used to measure the longitudinal deformations of the specimens subjected to uniaxial compression. the displacements were observed on each comparator. the average of the values given by the two comparators represents the uniaxial displacement of the specimen. the deformations of specimens 7x7x7 cm were calculated using the following expression: eq 01. : relative compressive deformation. 0 200 400 600 800 1000 0 10 20 30 40 50 60 70 80 90 c o m p re s s iv e s tr e n g th ( m p a ) temperature (°c) oc at 7 days hpc at 7 days 0 200 400 600 800 1000 0 10 20 30 40 50 60 70 80 90 c o m p re s s iv e s tr e n g th ( m p a ) temperature (°c) oc at 14 days hpc at 14 days 0 200 400 600 800 1000 0 10 20 30 40 50 60 70 80 90 oc at 28 days hpc at 28 days c o m p re s s iv e s tr e n g th ( m p a ) temperature (°c) 0 200 400 600 800 1000 0 10 20 30 40 50 60 70 80 90 oc at 60 days hpc at 60 days c o m p re s s iv e s tr e n g th ( m p a ) temperature (°c) 1 2 3  1 press plate.  2 concrete specimen 7x7x7  3 comparator 1/100. 94 bouabdallah., j. build. mater. struct. (2022) 9: 87-97 l: displacement. l: length of the test piece 7 cm. furthermore, figures 8 (a), (b), (c) and (d) show the evolution of deformations of ordinary concrete as a function of stress, for different temperatures. it was observed that the concrete deformations observed at 7 days were greater than those recorded at 14, 28 and 60 days. in addition, it was noticed that at 7 days, the compressive strength was very low compared to those obtained at 14, 28 and 60 days. this can be explained by the fact that the compressive strength increased and the deformation decreased with age, which allows saying that age has a positive effect on the evolution of the compressive strength. on the other hand, it was noted that beyond 14 days, the compressive strength of the test pieces, subjected to temperatures 250 °c, 350 °c and 450 °c, increased while deformations decreased in comparison with those observed at the reference temperature (room temperature 20 °c). it should be mentioned that at the temperature of 600 °c, concrete became very deformable, although the compressive strength was increasing. beyond this temperature, i.e. at 900 °c, the compressive strength began decreasing and the deformations increased considerably. a b c d fig 8. evolution contrainte/déformation du béton ordinaire, at 7, 14, 28 and 60 days. figures 9 (a), (b), (c) and (d) present the evolution of deformations of high performance concrete as a function of stress, at different temperatures. it was observed that the compressive strength values of high performance concrete increased remarkably at temperatures 250 °c, 350 °c and 450 °c, for all ages, in comparison with those obtained at room temperature (20 ± 2) °c. note also that at the temperature of 600 °c, the compressive strength increased and caused 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 c o m p re s s iv e s tr e n g th ( m p a ) deformation () oc at 7 days 20 °c oc at 7 days 250 °c oc at 7 days 350 °c oc at 7 days 450 °c oc at 7 days 600 °c oc at 7 days 900 °c 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 c o m p re s s iv e s tr e n g th ( m p a ) deformation () oc at 14 days 20°c oc at 14 days 250°c oc at 14 days 350°c oc at 14 days 450°c oc at 14 days 600°c oc at 14 days 900°c 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 oc at 28 days 20°c oc at 28 days 250°c oc at 28 days 350°c oc at 28 days 450°c oc at 28 days 600°c oc at 28 days 900°c c o m p re s s iv e s tr e n g th ( m p a ) deformation () 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 oc at 60 days 20°c oc at 60 days 250°c oc at 60 days 350°c oc at 60 days 450°c oc at 60 days 600°c oc at 60 days 900°c c o m p re s s iv e s tr e n g th ( m p a ) deformation () bouabdallah., j. build. mater. struct. (2022) 9: 87-97 95 much larger deformations than those observed at ambient temperature. above this temperature, i.e. 900 °c, a very large deformation, and a very low compressive strength, were recorded. the curves of figure 10, obtained at 7, 14 and 28 days, at the temperature of 250 °c, allow concluding that the heat treatment of high performance concrete (hpc) increased the compressive strength but decreased deformations. the same phenomenon, i.e. high compressive strength and low deformation, occurred at a temperature of 350 °c, at 7 and 14 days. furthermore, the stress/strain curves indicate that at 7 days the elastic phase of high performance concrete and ordinary concrete ends at 80% of the breaking load. then, after, the material enters the plastic phase. for the other ages, namely at 14, 28, and 60 days, the elastic phase ends at 90% of the breaking load. the plastic phase begins immediately after. phenomenon of bursting at 60 days for hpc; the bursting and explosive behavior of high performance concrete was observed at 60 days for hpc (figure 9 (d)). this behavior may be attributed to temperatures within the range between 250 °c and 450 °c. a b c d fig 9. evolution of the compressive strength as a function of deformation, at 7, 14, 28 and 60 days. 4. conclusion this experimental study made it possible to highlight the influence of thermomechanical loading on the behavior of ordinary concrete and high performance concrete. in addition, the thermal loading was carried out at different temperatures (250, 350, 450, 600 and 900 °c). this thermal loading was done at the rate of 5 °c/min, while keeping the temperature constant for a period of 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 70 80 90 c o m p re s s iv e s tr e n g th ( m p a ) deformation () hpc at 7 days 20 °c hpc at 7 days 250 °c hpc at 7 days 350 °c hpc at 7 days 450 °c hpc at 7 days 600 °c hpc at 7 days 900 °c 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 70 80 90 hpc at 14 days 20°c hpc at 14 days 250°c hpc at 14 days 350°c hpc at 14 days 450°c hpc at 14 days 600°c hpc at 14 days 900°c c o m p re s s iv e s tr e n g th ( m p a ) deformation () 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 70 80 90 hpc at 28 days 20°c hpc at 28 days 250°c hpc at 28 days 350°c hpc at 28 days 450°c hpc at 28 days 600°c hpc at 28 days 900°c c o m p re s s iv e s tr e n g th ( m p a ) deformation () 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0 10 20 30 40 50 60 70 80 90 hpc at 60 days 20°c hpc at 60 days 250°c hpc at 60 days 350°c hpc at 60 days 450°c hpc at 60 days 600°c hpc at 60 days 900°c c o m p re s s iv e s tr e n g th ( m p a ) deformation () 96 bouabdallah., j. build. mater. struct. (2022) 9: 87-97 1h30min. the findings of the present study allowed drawing the following fundamental conclusions: the mass loss of high performance concrete at the temperature of 600 °c was significantly greater than the initial quantity of water. this suggests that in addition to water, there were other constituents that escaped from concrete. the two temperatures 250 °c and 350 °c had a positive effect on high performance concrete. indeed, a compressive strength increase was observed in the samples that underwent heat treatment. the bursting and explosive behavior of high performance concrete was observed at 60 days. this behavior may be attributed to temperatures within the range between 250 °c and 450 °c. the bursting of concrete can be manifested by the detachment of pieces of concrete, one after the other, or by explosive spalling of a structural element. 5. references alarcon-ruiz, l. (2003). analyse de l'évolution des propriétés microstructurales des bétons lors d'une élévation de la température (doctoral dissertation, marne-la-vallée, enpc). bouabdallah, m. a. (2006). comportement du béton sous l’effet d’une élévation de la température, thèse de magister, département de génie civil, université des sciences et de la technologie d’oran mohamed boudiaf. bouabdallah, m. a. (2008). etude comparative du béton haute performance et un béton ordinaire soumises à un chargement thermomécanique , actes des 6ème journées de mécanique de l’ecole militaire polytechnique, 15-16 avril, bordj el bahri, alger. courivaud, j. m., bacon, g., & crausse, p. (1997). simulation numérique du comportement d'un béton cellulaire dans sa phase d'élaboration sous gradient de pression de vapeur à haute température. revue générale de thermique, 36(4), 264-275. douk, n., vu, x. h., larbi, a. s., audebert, m., & chatelin, r. (2021). numerical study of thermomechanical behaviour of reinforced concrete beams with and without textile reinforced concrete (trc) strengthening: effects of trc thickness and thermal loading rate. engineering structures, 231, 111737. drzymała, t., jackiewicz-rek, w., tomaszewski, m., kuś, a., gałaj, j., & šukys, r. (2017). effects of high temperature on the properties of high performance concrete (hpc). procedia engineering, 172, 256-263. dubois, f., bonvalet, c., dawance, g., & marechal, j. c. (1967). comportement d'un caisson en béton précontraint soumis à un gradient de température élevé. nuclear engineering and design, 6(3), 273-300. horszczaruk, e., sikora, p., & zaporowski, p. (2015). mechanical properties of shielding concrete with magnetite aggregate subjected to high temperature. procedia engineering, 108, 39-46. liu, f., feng, w., xiong, z., tu, g., & li, l. (2018). static and impact behaviour of recycled aggregate concrete under daily temperature variations. journal of cleaner production, 191, 283-296. nastic, m., bentz, e. c., kwon, o. s., papanikolaou, v., & tcherner, j. (2019). shrinkage and creep strains of concrete exposed to low relative humidity and high temperature environments. nuclear engineering and design, 352, 110154. nguyen, p. l., vu, x. h., & ferrier, e. (2019). elevated temperature thermomechanical behaviour of near surface mounted cfrp reinforced concrete specimens: effect of adhesive at concrete/cfrp interface. engineering structures, 197, 109361. noumowé, n. a. (1995). effet de hautes températures (20 c-600 c) sur le béton. casparticulier du bhp (doctoral dissertation, thèse de doctorat de l'insa de lyon). bouabdallah., j. build. mater. struct. (2022) 9: 87-97 97 prajapati, r., gettu, r., & singh, s. (2021). thermomechanical beneficiation of recycled concrete aggregates (rca). construction and building materials, 310, 125200. simonin, f. (2000). comportement thermomécanique de bétons réfractaires alumineux contenant du spinelle du magnésium, thèse de doctorat de l'insa de lyon. 165 p (2000). torelli, g., gillie, m., mandal, p., draup, j., & tran, v. x. (2020). a moisture-dependent thermomechanical constitutive model for concrete subjected to transient high temperatures. engineering structures, 210, 110170.. tsimbrovska, m., (1998. dégradation des bétons à hautes performances soumis à des températures élevées, évolution de la perméabilité en liaison avec la microstructure, thèse de doctorat de l’université joseph fourier grenoble 1. yermak, n. (2015). comportement à hautes températures des bétons additionnés de fibres, thèse de doctorat, l’université de cergy-pontoise. j. build. mater. struct. (2015)2: 33-40 https://doi.org/10.34118/jbms.v2i2.18 issn 2353-0057 experimental investigation of the performance of palm kernel shell and periwinkle shell as partial replacement for coarse aggregate in asphaltic concrete oyedepo oj * and olukanni eo department of civil and environmental engineering, federal university of technology akure, nigeria. * corresponding author: oyedepoo@yahoo.co.uk abstract. performance of non-conventional materials namely palm kernel shell (pks) and periwinkle shell (pws) were investigated. sieve analysis, aggregate impact value (aiv), aggregate crushing value (acv), bitumen penetration, marshall stability, flash and fire point were carried out in accordance with american standard for materials and testing (astm) and british standard (bs) specifications. a total of thirty-six samples were prepared by partially replacing coarse aggregate with pks and pws at 0%, 10%, 20%, 30%, 40% and 50%. the aiv and acv values of 35.85% and 11.49% were obtained for pws, while 6.42% and 9.22% respectively were obtained for pks; this is usable for wearing course. the 10% partial replacement with pws has marshall stability value of 2.33kn; 10% and 20% partial replacement with pks has marshall stability values of 3.0kn and 2.2kn respectively, while 10%, 20% and 30% partial replacement with combination of pws and pks has marshall stability values of 3.22kn, 2.41kn and 2.21kn respectively; thus satisfying the requirement for light traffic road. also, 10% and 20% partial replacement with the combination of pws and pks gives a flow value of 8.9 mm and 8.5 mm which can be used for light traffic. hence, 10% to 20% partial replacement of coarse aggregate with pws and pks can be used as alternative material in asphaltic concrete to reduce the cost of construction. key words: palm kernel, periwinkle, asphalt, aggregate, traffic. 1. introduction significant increases in axle loads have increase stress induced on road surface and thus increase in maintenance which has been a challenge on road pavement operation. factors such as durability, strength and economic needs have to be considered in the design and construction of road pavement. therefore, road paving industry is interested in utilizing alternative and sustainable materials that will satisfy aforementioned needs and aid in the production, placement, and performance of road pavement. asphaltic concrete is a combination of binder, filler, coarse aggregate and fine aggregate which are blended in a specific ratio to get the required quality and provide a smooth driving surface to vehicles and bikes while driving and braking on the highway. the demand for more roads, increasing expense of production of asphaltic blend and shortage of naturally occurring materials being utilized has required the quest for alternative and manageable materials that will fulfill the previously stated needs and help in the production and use of asphalts. additionally, growth in population, expanding urbanization and rising ways of life due to technological advancements have added to increment in the amount of solid waste generated by modern, mining, local and farming exercises. nwaobakata and agunwamba (2014) researched the utilization of biomaterials and agro-waste specifically is a subject of extraordinary intrigue these days not just from the innovative and logical perspectives, additionally socially, and financially, as far as work, expense and natural issues. therefore, this research examines the execution of palm kernel shell (pks) and periwinkle shell (pws) as incomplete substitution for coarse aggregate in asphaltic cement. mailto:oyedepoo@yahoo.co.uk 34 oyedepo et al. j. build. mater. struct. (2015)2:33-40 1.1. overview of properties palm kernel shell palm kernel shell (pks) is the hard endocarp of palm kernel natural product that encompasses the palm kernel seed of the oil palm tree (elaeisguineensis) (abiola, 2006). the palm kernel tree is local of west africa and broadly spread all through the tropics. it develops to around 9 meter in height and characterized with a crown of fluffy leaves that are over 5 mm long. pks comprises of little size particles, medium size particles and substantial size particles in the extent 0-5 mm, 5-10 mm and 10-15 mm (alengaram, 2010). it is evaluated that the pks constitutes around 34.5% of a single ripe, fresh fruit, (aragbaiye, 2007). pks’s are derivable in expansive amounts; the shells have no commercial value, yet constitute major natural issues. 1.2. overview of properties periwinkle shell periwinkle has been described by badmus et al. (2007) as small marine snails with spiral cone, shaped shells having a round opening and dull interior. the major species reported by beredugo (1984), to be available in the lagoon and mudflats of nigeria’s niger delta, between calabar in the east and badagry in the west, are tympanostomus spp and pachmellania spp. a survey by umoh and olusola (2012) discovered that large quantities of periwinkle shells are available in many riverine communities of the south-south geopolitical region of nigeria. most periwinkles are edible, the fleshy (edible) parts are usually removed after boiling in water, and the shells are usually discarded. continuous dumping of the discarded part has become a serious source of land pollution in areas where they are found. accordingly, dahunsi and bamisaye (2002) reported that large quantities of periwinkle shells have accumulated in many parts of the country such as warri, western ijaw, burutu, ogoni, ogalaga and lotughene of the niger delta of nigeria. 2. materials and methodology utilized for evaluation 2.1. materials the materials utilized for this research work were chosen carefully to meet with standard requirement of materials utilized as a part of asphaltic cement; these are as filler, bitumen, coarse aggregates, fine aggregates, periwinkle shell (pws) and palm kernel shell (pks). fine and coarse aggregates: the fine aggregates in figure 1 is a finely chosen river sand free from deleterious material got from irese town in ondo state. the coarse aggregates passing through 19-12mm sieve in figure 2 and filler were acquired from simbo quarry, aye in ondo state. the coarse aggregates were painstakingly chosen to conform with the required specification and free from deleterious materials. additionally, 70/80 penetration grade bitumen was acquired from sapelle in delta state nigeria. fig 1. fine aggregate fig 2. coarse aggregates periwinkle and palm kernel shell: the precisely chose pws shown in figure 3 was gotten from rumuji town, emohua local government area in port-harcout, river state. the carefully oyedepo et al. j. build. mater. struct. (2015)2:33-40 35 selected pks in figure 4 was acquired from engr. akinjo's farm situated at oke-ijebu in akure, ondo state nigeria. fig 3. periwinkle shell fig 4. palm kernel shell 2.2. methods specified proportions of each material such as 4% filler of size 0.075mm, 6% quarry dust of maximum size 5mm, 66% river sand of maximum size 5mm and 28% coarse aggregate of size 516mm with 6% bitumen of penetration grade 70/80 was mixed together at 150˚c. the mixture was compacted with 50 blows both at the top and bottom to obtain cylindrical samples for the marshall stability test. pks were partially replaced at 0%, 10%, 20%, 30%, 40% and 50% by weight of total coarse aggregate in the mixture. three samples each shown in figures 5 and 6 were prepared for each percentage replacement of coarse aggregate with pks and pws. same procedure was repeated for pws to replace coarse aggregate, however, a total of thirty-six samples were prepared for both pks and pws for the study. fig 5. marshall stability test specimen (pks) fig 6. marshall stability test specimen (pws) several tests were performed in accordance to the standard specifications as follows: sieve analysis (astm c136-06, 2006). aggregate impact value (aiv) test (bs 812-112, 1990). aggregate crushing value (acv) test (bs 812-110, 1990). specific gravity test (astm c127-12, 2012) and (astm c128-12, 2012) for coarse and fine aggregates respectively. bitumen penetration test (bs 2000-487, 2009). marshall stability test (astm d6927-06, 2006). moisture content test (dean and stark method). 36 oyedepo et al. j. build. mater. struct. (2015)2:33-40 flash and fire point test. 3. results and discussion figure 7 shows the particle size distribution curve of pks and pws, fa and ca aggregates respectively, which are carried out in accordance with astm c136/c136m. fig 7. particle grading curves of palm kernel shell (pks), periwinkle shell (pws), fine aggregate (fa) and coarse aggregate (ca). from the curves: cu and for pks d10= 1.964 mm, d30= 5.245 mm, d60= 8.186 mm ; ( ) where: d60 is the particle diameter, at which 60 percent by weight of the soil is finer, d30 is particle diameter, at which 30 percent by weight of the soil is finer, d10 is particle diameter, at which 10 percent by weight of the soil is finer, cu is the coefficient of uniformity and cc is the coefficient of curvature. note: for a gravel to be classified as well graded, cu> 4 & 1 < cc< 3; thus, the pks used is well graded since the cu is 4.17, i.e. more than 4. similarly, the cu and for pws, fa and ca were calculated in the same manner. cu and for pws d10= 1.956 mm, d30= 5.755 mm, d60= 12.562 mm, cu = 6.42 and cc= 1.35 for a gravel to be classified as well graded, cu> 4 & 1 < cc< 3; thus, the cu value obtained for pws shows that it is well graded. cu and for, fa d10= 0.425 mm, d30= 1.18 mm, d60= 2.1 mm, cu = 4.94 and cc= 1.56; for a sand to be classified as well graded the cu > 4 and 1< cc< 3; thus, the value obtained indicate that the fine aggregate is well graded. oyedepo et al. j. build. mater. struct. (2015)2:33-40 37 cu and for ca d10= 0.574 mm, d30= 1.706mm, d60= 6.978mm, cu = 12.16 and cc= 0.73. the cu value of coarse aggregate showed that it is well graded. tables 1 presents the summary of results of various tests carried out on the materials, while table 2 is the summary of marshall stability test. however, figures 8 and 9 show plot of stability versus composition and flow versus percentage composition respectively. table 1. summary of test results. s/n properties results obtained recommended standard remarks 1 los angeles abrasion test ca = 27.5% pws = 2 pks = 27.5% max. limit for bituminous concrete surface coarse (30%) satisfactory for road surfacing/wearing course 2 moisture content on fine aggregate 2.10% satisfactory 3 aggregate impact value test specified limit (%) toughness properties ca=22.4% pws=35.85% pks=6.42% < 10 10-20 20-30 >35 exceptionally tough / strong very tough / strong good for pavement surface course weak for pavement surface course satisfactory for road surfacing/wearing course 4 aggregate crushing value test specified limit (%) ca=27.92% pws=11.49% pks=9.22% not more than 30% for surface or wearing course satisfactory 5 water in bitumen test 3.9% max. permissible is 5% satisfactory 6 penetration test 75.44 7 flash point test fire point test 288 326 280 3000c 300 – 320oc satisfactory satisfactory table 2. summary of marshall stability test results. the aiv and acv values of 35.85% and 11.49% were obtained for pws, while 6.42% and 9.22% respectively were obtained for pks as shown in table 1; this indicate that it could be used for surface or wearing course. also, the moisture content of 3.9% in bitumen showed that the value is absolutely small and can be easily burnt off during the production of hot mix asphalt; an average penetration of bitumen used is 75.44. the flash point of the bitumen of 288°c indicates that the bitumen could be used in the production of hot mix asphalt. % composition pws pks pws+pks stability (kn) flow (mm) stability (kn) flow (mm) stability (kn) flow (mm) 0 3.151 9.2 3.63 9.3 3.39 9.4 10 2.33 8.1 3.08 8.4 3.22 8.9 20 2.1 7.7 2.28 8.0 2.41 8.5 30 1.63 4.5 1.92 4.85 2.21 7.9 40 1.18 3.87 1.04 3.60 1.04 3.64 50 1.105 4.50 1.01 4.8 0.70 4.6 38 oyedepo et al. j. build. mater. struct. (2015)2:33-40 fig 8. graph of stability versus percentage composition. the marshall design criteria for stability provided by the asphalt institute requires minimum values for different traffic classifications as: 2.223 kn for light traffic. 3.336 kn for medium traffic. 6.672 kn for heavy traffic. the 10% partial replacement with pws has 2.33 kn which is more than the value stated for light traffic. also, 10% and 20% partial replacement with pks has stability values of 3.08% and 2.28% respectively, which is higher than the value designated for light traffic. however, 10%, 20% and 30% partial replacement with combination of pws and pks has marshall stability values of 3.22kn, 2.41 kn and 2.21kn respectively, which satisfy the requirement for light traffic. fig 9. graph of flow versus percentage composition the marshall design criteria for flow at 0.25 mm provided by the asphalt institute for different traffic classifications are: 8 – 20 mm for light traffic. 8 – 18 mm for medium traffic. oyedepo et al. j. build. mater. struct. (2015)2:33-40 39 8 16 mm for heavy traffic. the results show that 10% partial replacement with pws gives a flow value of 8.1mm while, 10% and 20% partial replacement with pks gives a flow value of 8.4mm and 8.0mm does satisfying light traffic requirement. however, 10% and 20% partial replacement with the combination of pws and pks gives a flow value of 8.9mm and 8.5mm which can be used for light traffic. 4. conclusion the aiv and acv values of 35.85% and 11.49% were obtained for pws, while 6.42% and 9.22% respectively were obtained for pks indicating that it could be used for surface or wearing course. the moisture content of 3.9% and flash point of the bitumen of 288°c showed that the bitumen can be used in the production of hot mix asphalt. in addition, the 10% partial replacement with pws has 2.33 kn which is more than the value stated for light traffic. also, 10% and 20% partial replacement with pks have stability values of 3.08kn and 2.28kn respectively, which is higher than the value designated for light traffic. however, 10%, 20% and 30% partial replacement with combination of pws and pks have marshall stability values of 3.22kn, 2.41kn and 2.21kn respectively; thus, it satisfies the requirement for light traffic. the results also show that 10% partial replacement with pws gives a flow value of 8.1mm while, 10% and 20% partial replacement with pks give a flow value of 8.4mm and 8.0mm does satisfying light traffic requirement. however, 10% and 20% partial replacement with the combination of pws and pks give flow values of 8.9mm and 8.5mm which can be used for light traffic. hence, 10% to 20% partial replacement of coarse aggregate with pws and pks can be used as alternative material for light traffic roads. it is therefore recommended that this agrobased product can be used as partial alternate material in asphaltic concrete to reduce the cost of construction 5. references abiola om. (2006). characteristics of palm kernel shells powder as additive in sandcrete. transaction of the nigeria society of engineers, 2(1), 21-32. adewuyi ap, adegoke t. (2008). exploratory study of periwinkle shells as coarse aggregates in concrete works. arpn journal of engineering and applied sciences, 3(6), 1-5. agbede oi, manasseh j. (2009). suitability of periwinkle shell as partial replacement for river gravel in concrete. leonardo electronic journal of practices and technologies, 8(15), 59-66. alengaram uj, mahmud h, jumaat mz, & shirazi sm. (2010). effect of aggregate size and proportion on strength properties of palm kernel shell concrete. international journal of the physical sciences, 5(12), 1848-1856. aragbaiye ba. (2007). palm kernel shell as composite material in concrete. unpublished b. eng project report. dept of civil engineering, university of ilorin, ilorin, 25-31. astm c127-12 (2012). standard test method for density, relative density (specific gravity), and absorption of coarse aggregate. astm international, west conshohocken, pa. astm c128-12 (2012). standard test method for density, relative density (specific gravity), and absorption of fine aggregate, astm international, west conshohocken, pa astm c136-06. (2006). standard test method for sieve analysis of fine and coarse aggregates. astm international, west conshohocken, pa. astm d6927-06 (2006). standard test method for marshall stability and flow of bituminous mixtures, astm international, west conshohocken, pa. badmus mao, audu tok, anyata bu. (2007). removal of lead ion from industrial wastewaters by activated carbon prepared from periwinkle shells (typanotonus fuscatus). turkish journal of engineering and environmental science, 31(4), 251-263. 40 oyedepo et al. j. build. mater. struct. (2015)2:33-40 beredugo yo. (1984). periwinkle shells as concrete aggregates. nigerian building and road research institute, federal ministry of education, science and technology. bs 2000-487 (2009). bitumen and bituminous binder: determination of penetration power of bituminous emulsion. british standard. bs 812-110 (1990). testing aggregates method for determination of aggregate crushing value (acv). british standard. bs 812-112 (1990). testing aggregates method for determination of aggregate impact value (aiv). british standard. dahunsi bio, bamisaye ja. (2002). use of periwinkle shell ash (psa) as partial replacement for cement in concrete. in proceedings of nigerian materials congress and meeting of nigerian materials research society, pp. 184-186. dahunsi bio, olufemi sa, akinpelu m, olafusi o s. (2013). investigation of the properties of “pure water” sachet modified bitumen. civil and environmental research, 3(2):47-61. edeh je, manasseh j, ibanga u. (2012). palm kernel shell ash stabilization of reclaimed asphalt pavements as highway pavement materials. journal of sustainable development and environmental protection, 2(1):89-110. nwaobakata c, agunwamba jc. (2014). effect of palm kernel shells ash as filler on the mechanical properties of hot mix asphalt. archives of applied science research, 6(5):42-49. oyedepo oj, olanitori lm, olukanni eo. (2015). investigation of palm kernel shell as partial replacement for aggregate in asphaltic concrete. malaysian journal of civil engineering, 27(2):223-234. oyedepo oj, oluwajana sd. (2014). evaluation of properties of bitumen modified with waste tyre. nigerian journal of technology, 33(1), 119-124. umoh aa, & olusola ko. (2012). effect of different sulphate types and concentrations on compressive strength of periwinkle shell ash blended cement concrete. international journal of engineering & technology, 12(5), 10-17. j. build. mater. struct. (2021) 8:139-159 original article doi : 10.34118/jbms.v8i2.1441 issn 2353-0057, eissn : 2600-6936 mechanical characteristics of compressed earth blocks, compressed stabilized earth blocks and stabilized adobe bricks with cement in the town of ngaoundere cameroon goutsaya j 1*, ntamack ge 1*, kenmeugne b 2, charif d’ouazzane s 3 1 groupe de mécanique, matériaux et acoustique (gmma), département de physique, faculté des sciences, université de ngaoundéré, b.p.: 454 ngaoundéré, cameroun. 2 département des génies industriel et mécanique, ecole nationale supérieure polytechnique de yaoundé, université de yaoundé 1, b.p.: 8390 yaoundé, cameroun 3 lmtm: laboratoire de mécanique, thermique et matériaux, ecole nationale supérieure des mines, rabat, ensm, b.p. 753 rabat, maroc. * corresponding author: janviergoutsaya@gmail.com ; guyedgar@yahoo.fr received: 16-07-2021 accepted: 25-11-2021 abstract. the aim of this study is to examine the effects of cement stabilization on the mechanical stress of compressed stabilized earth blocks (csebs) and adobe stabilized earth bricks (asebs). hence, this work is based on an experimental study carried out in order to determine the geotechnical properties of the samples soil, namely, the dry particle size analysis after washing, the particle size distribution by sedimentometry, atterberg limits, and the preparation of specimens with different levels of cement proportions. moreover, single compression and three-point bending compression out on specimens measuring 4x4x4cm3 and 4x4x16cm3 respectively. the findings indicate that dosing with 8% cement results in a clear increase in compression stress of approximately 25.55% for csebs compared to the reference set at 0% and 22.85% for asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by simple compression of around 3.26% for csebs and 3.14% for asebs. for three-point bending compression for a cement dosage of 8%, there is also an increase in stress of about 25% for the csebs compared to the reference taken at 0% and 23.02% for the asebs. key words: adobe earth bricks; adobe stabilized earth bricks, plasticity; stabilization; compressed earth blocks; compressed stabilized earth blocks. 1. introduction the earth has been one of the main construction materials used on our planet for almost 10.000 years. today, more than one third of our planet's inhabitants live in earth-based habitats. the population of the town of ngaoundere mostly build in adobe earth bricks, owing to the quality and availability of its red clay soil. studies on compressed stabilized earth blocks (cebs) have been carried out by several researchers (walker, 2004; kariyawasam and jayasinghe, 2016; zhang et al., 2017; toure et al., 2017; sekhar and nayak, 2018; ruiz, 2018; inim et al., 2018). the research shows that, the bonding materials have an effect on the overall stability of masonry structure (ronglin, 2020). the axial compression failure initial cracks appeared on the contact surfaces of the two blocks, followed by cracking at the corner of the specimen (guanqi et al., 2021). this material shows its current form with numerous assets necessary for the construction of sustainable, comfortable and economic accommodations (houben et al., 1996; césaire et al., 2020). the use of local materials to build houses is an important strategy to counter our worsening global environmental problems (ghorab et al., 2007). however, the use of raw earth as a building material for adobe earth bricks presents significant limitations, such as the high absorption rate due to the relatively high porosity, the formation of drawback during drying and a low resistance to humidity. at the same time, it offers good thermal insulation properties when stabilized at ideal conditions (meukam et al., 2004; elisabete et al., 2020). in mailto:janviergoutsaya@gmail.com mailto:guyedgar@yahoo.fr 140 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 our study, we will determine the geotechnical properties of soil samples obtained from three experimental sites. these properties will be determined by dry particle size distribution after washing (grain sizes above 80μm), particle size analysis by sedimentometry (grain sizes below 80μm), atterberg limits and the preparation of specimens with different cement dosages (0%, 04%, 08%). subsequently, the mechanical properties will be assessed on compressed earth blocks, compressed stabilized earth blocks (csebs), adobe earth bricks (aebs) and adobe stabilized earth bricks (asebs) through simple compression tests, three-point bending compression and absorption tests. 2. material and methods 2.1. location of the study and sampling areas the soil samples were collected in the adamawa region (ngaoundere town), located in the northern part of cameroon, in the vina division, more precisely in ngaoundere i (bamyanga: bam), ngaoundere ii (gadamabanga: gad) and ngaoundere iii (maiborno: mai) sub-divisions. soil samples were collected at 50cm depth in these three neighbourhoods. this choice is based on the high number of constructions with adobe earth bricks, representing about 80% according to field surveys. fig. 1. soil samples gad, mai and bam 2.2. climate the adamawa region has a tropical savana climate, and very wet given its high altitude, average 1100m. the ngaoundere weather station receives up to 1575 mm of rain in seven months, from march to november (amougou et al., 2015). the climate in this region is irregular, with a dry season lasting about 5 months, november to march, and a rainy season covering about 7 months, april to october. average rainfall is between 900mm and 1500mm. minimum temperatures of 10-19oc are recorded from december to january and maximum temperatures are 27-34oc in mai bam gad goutsaya et al., j. build. mater. struct. (2021) 8:139-159 141 march. average temperatures are relatively low: 22°c in ngaoundere, with an equally low annual temperature range of 3.1°c (amougou et al., 2015). 2.3. geotechnical identification tests the geotechnical properties of the soil will help to understand and predict the behaviour of the material. the tests below were carried out on three soil samples collected at the local materials promotion authority (mipromalo) laboratory in yaounde. these included: dry particle size analysis after washing: grains greater than 80μm; particle size distribution by sedimentometry analysis: grains lower than 80μm; atterberg limits (liquidity limits: ll, plastic limits: pl and plasticity index: pi) and methylene blue test. 2.4. specimens fabrication 2.4.1. test specimens fabrication of cebs, csebs, aebs and asebs the cebs, csebs, aebs and asebs specimens were made with the dimensions 4x4x16cm3 for three-point bending tests, 4x4x4cm3 for simple compression tests, 8x4x2cm3 and 4x4x16cm3 for absorption tests with different percentages of cement stabilization cpj 35. the cement cpj 35 is mainly composed of: sio2; al2o3; fe2o3; cao; mgo; so3; k2o; na2o; free lime, insoluble residue with a compressive strength of 28mpa after 28 days (nf en p15-101-1, 1995b). procedures for the manufacturing of cebs and csebs the manufacturing of cebs and csebs is performed in several stages:  dig the soil to a depth of 50cm at three different locations on each sampling site;  weigh with a scale the masses of soil sufficient for making the different specimens (figure 1);  weigh the quantities of cement cpj 35 at 4% and 8% of the soil mass, then proceed with dry mixing;  hydrate the whole (earth + cement) with about 12% water (houben et al., 1996);  proceed to the compression of test piece with pression of 3mpa;  mold and remove the 4x4x16cm3, 4x4x4cm3 and 8x4x2cm3 specimens from the mold ;  wrap and leave the specimens to dry for 28 days. procedures for the manufacturing of aebs and asebs in order to manufacture aebs and asebs, we need several stages:  dig the soil to a depth of 50cm at three different locations on each site;  weigh the quantity of cement at 4% and 8% of the soil mass, then proceed with dry mixing;  hydrate the whole (earth + cement) with about 25% water (experiments in situ);  mold and remove the 4x4x16cm3 specimens from the mold; 142 goutsaya et al., j. build. mater. struct. (2021) 8:139-159  dry the specimens during 28 days. 2.4.2. three-point bending compression three-point bending tests were carried out on cebs, csebs, aebs and asebs specimens of 4x4x16cm3 size, stabilized with 4% and 8% cement after 28 days using the electric press of brand impact. it weighs 5 tons, with a charge rate of 0.025mm/s. the tests findings are collected from the electric press which indicates the maximum charge stress in mpa by each test. 2.4.3. simple compression tests simple compression tests were carried out on cebs, csebs aeb and asebs 4x4x4cm3 specimens, stabilized with 4% and 8% cement after 28 days using the electric press of brand impact. it weighs 5 tons and have a charge rate of 0.03 mm/s. 2.5. absorption of cebs, csebs, aebs and asebs this test consists of immersing cebs, csebs, aebs and asebs of 4x4x16cm3 in a container of water for 5 hours for the aebs and asebs. however 5 days for the cebs and csebs, then measuring the increase in the wet weight of the mass mh compared to the dry weight ms initially measured before immersion. a rapid depigmentation is observed after two hours of immersion on aebs compared to cebs. 3. results and discussion 3.1. geotechnical properties the results of the geotechnical identification tests are presented in the following, including the complete particle size distribution, atterberg limits and methylene blue test. complete particle size distribution the three soil samples analysed are recommended for the manufacturing of cebs according to the nf p94-056 and nf p94-057 standards, which define the range of the recommended spindle (figure 2). this spindle has been blacked out as a guide, only a small overflow of the gad curve out of the low spindle is observed, but this does not have a significant influence. the proportions of gravel, sand, silt and clay grains in our samples are shown in the table 1. table 1. proportions of gravel, sand, silt and clay (mai, bam and gad). % gravel φ > 2000µm % sand 20<φ<2000µm % silt 2<φ<20 µm % clay φ≤ 2 µm mai 1,5 53,3 28,2 17 bam 14 48,2 14,3 23,5 gad 10,5 55,5 26 8 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 143 fig. 2. complete particle size distribution curve of mai, bam and gad soil samples. the triangular classification of soil, presents the ideal zone of the soils (figure 3). fig. 3. triangular classification of soil. in addition, the gad soil with the lowest clay content is the least resistant though the results are quite comparable. the most resistant is the bam soil with higher clay content. the clay acts as a binder in the production of cebs. the analysis of findings shows that, the highest proportions of 144 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 grains in gad samples are sand and silt, so we have sandy-silt type soils in out of the ideal zone. whereas sand and clay are the highest proportions of grains in mai and bam, so we have sandysilt-clay in the ideal zone. atterberg limits the liquidity and plastic limits and the plasticity index are summarised in table 2: table 2. atterberg limits. atterberg limits n0 sample ll (%) pl (%) pi (%) 1 mai 44.3 26.1 18.6 2 bam 43.59 24.18 19.4 3 gad 44.66 24.33 20.32 for the plasticity index (pi) of these samples ranged from 15 40, we have plastic soils according to the french standard nf 94-051. fig. 4. plasticity chart for soils specified in the xp p 13-901 standard. standard nf p 94-051 recommends for the manufacture of cebs, soils whose properties belong to the spindle of the plasticity chart in figure 4. this is the case for bam and gad samples, the mai sample is at the limit of the recommended range. methylene blue test the results of the methylene blue test are presented in table 3. table 3. methylene blue value, specific surface area (sp) and blue activity index (acb) n0 sample vbs (g/100g) sp(m2/g) acb 1 mai 4.33 90.93 11.04 2 bam 2.5 52.5 07.09 3 gad 3.16 66.48 10.25 the sample with the lowest clay content is that of bam with 52.5m2 per 1g. with regard to the blue activity index, all three samples are between 5 and 13, so we have soils with medium active clay levels according to the standard nf p 94 068 (chrétien and fabre, 2007). goutsaya et al., j. build. mater. struct. (2021) 8:139-159 145 3.2. three-point bending compression strength of the cebs and csebs the results of the maximum stresses of the three-point bending compression tests of the cebs and csebs specimens are shown in the diagram in figure 5. fig. 5. bending compression stress of the cebs and csebs. fig. 6. bending compression stress based on the strain of mai. fig. 7. bending compression stress based on the strain of bam. 146 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 fig. 8. bending compression stress based on the strain of mal. table 4. medium bending compression stresses of the cebs and csebs. sample rmoy (0%) rmoy (4%) rmoy (8%) mai 3,37 3,44 4,42 bam 3,56 3,64 4,29 gad 3,34 3,42 4,11 fig. 9. evolution of medium bending compression stresses of the cebs and csebs. we observe that dosages with 8% cement show a clear increase in the average bending stress of about 25% compared to the reference taken at 0% (figure 5). this is due to the stabilization rate (clay + cement) which becomes greater than 30% (figures 6 to 8). dosages of 4% produce a slight average increase of about 4.5%. this is due to the stabilization rate (clay + cement) which becomes less than 30% (figures 6 to 8). our experimental results show that the three-point bending compression strain values for 4% and 8% csebs are higher than those of morel (morel et al., 2002). akpokodje examined the effect on the strength of soil with different cement contents. he found that, adding cement to a soil significantly increases its compressive strength (akpokodje, 1985). 3.3. simple compression stress of the cebs and csebs the results of the maximum stresses of the simple compression tests of the cebs and csebs specimens are shown in figure 10. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 147 fig. 10. simple compression stress of the csebs and cebs specimens. fig. 11. simple compression stress based on the strain of mai. fig. 12. simple compression stress based on the strain of bam. 148 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 fig. 13. simple compression stress based on the strain of mal. table 5. medium simple compression stresses of the csebs and cebs. sample rcmoy (0%) rcmoy (4%) rcmoy (8%) mai 4,1 4,24 5,18 bam 4,3 4,43 5,2 gad 4,02 4,15 5,04 fig. 14. evolution of medium simple compression stresses of the cebs and csebs. the results of the maximum stresses of the simple compression tests of the cebs and csebs specimens are shown in the diagram in figure 10. here, dosages with 8% cement show an increase in the average compression stress of about 25.55% compared to the reference taken at 0% (figure 10). these results are in agreement with those of bahar (bahar et al., 2004) who showed that the compression and tensile stress by splitting increases with increasing cement content. our results are also in agreement with those obtained by ntamack (ntamack et al., 2012) on cement stabilization. they also show 4% higher stabilized simple compression stress values obtained by bahar and tran. whereas our values are 8% lower as compared to tran own and higher than that of bahar (bahar et al., 2004; tran et al., 2018). 3.4. three-point bending compression strength of the aebs and asebs the results of the maximum stresses of the three-point bending compression tests aebs and asebs specimens are shown in the diagram in figure 15. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 149 fig. 15. three-point bending compression stress of the aebs and asebs. fig. 16. variation of the bending compression stress with the strain of mai (0%, 4% and 8%). fig. 17. variation of the bending compression stress with the strain of bam (0%, 4% and 8%). 150 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 fig. 18. variation of the bending compression stress with the strain of gad (0%, 4% and 8%). table 6. medium bending compression stresses of the aebs and asebs. sample rmoy (0%) rmoy (4%) rmoy(8%) mai 2,42 2,52 2,95 bam 2,58 2,66 3,09 gad 2,39 2,5 2,84 fig. 19. evolution of medium bending compression stresses of the aebs and asebs. here, dosages with 8% cement show an increase in the average bending stress of about 23.02% compared to the reference taken at 0% (figure 15). this is due to the stabilization rate (clay + cement) which becomes greater than 30% (figures 16 to 18). dosages of 4%, produces a slight average increase of about 5.49%. this is due to the stabilization rate (clay + cement) which becomes is less than 30% (figures 16 to 18). 3.5. simple compression strength on aebs and asebs the results of the maximum stresses of the simple compression tests aeb and asebs at 4% and 8% on 4x4x4cm3 specimens are shown in the diagram in figure 20. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 151 fig. 20. simple compression stress of aebs and asebs. fig. 21. variation of simple compression stress of the strain of mai. fig. 22. variation of simple compression stress of the strain of bam. 152 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 fig. 23. variation of simple compression stress of the strain of gad. table 7. medium simple compression stresses of aebs and asebs. sample rcmoy (0%) rcmoy (4%) rcmoy (8%) mai 2,67 2,74 3,24 bam 2,77 2,86 3,37 gad 2,47 2,55 3,07 fig. 24. evolution of medium simple compression stresses of the aebs and asebs. the results of the maximum stresses of the simple compression tests aebs, asebs at 4% and 8% on 4x4x4cm3 specimens are shown in the diagram in figure 20. here, dosages with 8% cement show an increase in the average bending stress of about 22.85% compared to the reference taken at 0% (figure 20). this is due to the stabilization rate (clay + cement) which becomes greater than 30% (figures 21 to 23). the dosages of 4% produce a slight average increase of about 3.14%. this is due to the stabilization rate (clay + cement) which becomes is less than 30% (figures 21 to 23). our results show higher values of simple compression stress stabilized at 0% and 8% cement compared to the studies of dao (dao et al., 2018). nevertheless, our values are 4% lower than the results of the latter. 3.6. absorption rates of cebs and csebs results obtained by immersing our cebs and csebs specimens for 5 days. these specimens cebs and csebs at 4% and 8% respectively and are shown in figures 25 to 27. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 153 fig. 25. absorption rate of cebs at 0%. fig. 26. absorption rate of csebs at 4%. fig. 27. absorption rate of csebs at 8%. we can observe how immersion time and cement dosage levels influence the rate of absorption of the cebs. a clear decrease in the rate of absorption is obtained when the dosage of stabilizer is increased (figures 25 to 27), thus cement stabilization considerably reduces the porosity of csebs. these findings corroborate meukam (meukam al. 2004) studies, which show that the 154 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 addition of cement has a beneficial effect on the water absorption of stabilized earth blocks. indeed, he found that the rate of water absorption decreases as the cement content increases. this results in the interaction between clay and cement. the increasing of the cohesive strength of the particles reduces the porosity. 3.7. absorption rates of aebs and asebs the results were obtained by immersing our aebs and asebs specimens in water for 5 hours. this happens because of their high sensitivity to water, which causes them to depigment rapidly after a few hours of immersion, because of their high porosity. these specimens aebs at 0% and asebs at 4% and 8% respectively are shown in figures 28 to 30. fig. 28. absorption rate of aebs at 0%c. fig. 29. absorption rate of asebs at 4%c. in addition, the cement dosage levels also influence the absorption rate of aebs, with a decrease in absorption rate being observed when the cement dosage increases, in figures 28 to 30. the same reaction is observed as in asebs, with a water absorption rate that decreases with increasing cement, but with a better result at 8% compared to 4% cement. we can observe how immersion time and cement dosage levels influence the rate of absorption of the cebs. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 155 fig. 30. absorption rate of asebs at 8%c. 3.8. medium stresses comparison between cebs, csebs, aebs and asebs the results of the means stress comparison of the simple compression and the three-point bending compression between cebs, csebs, aebs and aseb are present in the tables 8 to 15. 3.8.1. means stress comparison of the bending compression strength between cses, csebs, aebs and asebs the results of the medium stresses comparison of the three-point bending compression between cebs, csebs, aebs and asebs are present in the tables 8 to 11. table 8. medium bending compression stresses of cses, csebs and aebs, asebs proportions aebs cebs asebs csebs asebs csebs n0 soil gravel +sand silt clay rcm (0%) rcm (4%) rcm (8%) 1 mai 54,8 28,2 17 2,42 3,37 2,52 3,44 2,95 4,42 2 bam 62,2 14,3 23,5 2,58 3,56 2,66 3,64 3,09 4,29 3 gad 66 26 8 2,39 3,34 2,50 3,42 2,84 4,11 table 9. the gain of the medium bending compression stresses of cebs and aebs at 0%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (0%) rcm (0%) gain 1 mai 54,8 28,2 17 2,42 3,37 39% 2 bam 62,2 14,3 23,5 2,58 3,56 38% 3 gad 66 26 8 2,39 3,34 40% table 10. the gain of the medium bending compression stresses of csebs and asebs at 4%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (4%) rcm (4%) gain 1 mai 54,8 28,2 17 2,52 3,44 37% 2 bam 62,2 14,3 23,5 2,66 3,64 37% 3 gad 66 26 8 2,50 3,42 37% table 11. the gain of the medium bending compression stresses of csebs and asebs at 8%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (8%) rcm (8%) gain 1 mai 54,8 28,2 17 2,95 4,42 50% 2 bam 62,2 14,3 23,5 3,09 4,29 39% 3 gad 66 26 8 2,84 4,11 45% 156 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 the results were obtained for three-point bending compression for a cement dosage of 8%, there is also an increase in stress of about 45% for the csebs compared to the asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by three-point bending compression of around 37% for csebs compared to the asebs. for a dosage of 0%, we observe a slight increase in stress by the three-point bending compression of around 39% for cebs compared to the aebs. 3.8.2. means stress comparison of the simple compression stress between cebs, csebs, aebs and asebs the results of the medium stresses comparison of the simple compression between cebs, csebs, aebs and asebs are present in tables 12 to 15. table 12. medium simple compression stresses of cebs, csebs, aebs and asebs. proportions aebs cebs asebs csebs asebs csebs n0 soil gravel +sand silt clay rcm (0%) rcm (4%) rcm (8%) 1 mai 54,8 28,2 17 2,67 4,10 2,74 4,24 3,24 5,18 2 bam 62,2 14,3 23,5 2,77 4,30 2,86 4,43 3,37 5,20 3 gad 66 26 8 2,47 4,02 2,55 4,15 3,07 5,04 table 13. the gain of the medium simple compression stresses of cebs and aebs at 0%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (0%) rcm (0%) gain 1 mai 54,8 28,2 17 2,67 4,10 54% 2 bam 62,2 14,3 23,5 2,77 4,30 55% 3 gad 66 26 8 2,47 4,02 63% table 14. the gain of the medium simple compression stresses of csebs and asebs at 4%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (4%) rcm (4%) gain 1 mai 54,8 28,2 17 2,74 4,24 55% 2 bam 62,2 14,3 23,5 2,86 4,43 55% 3 gad 66 26 8 2,55 4,15 63% table 15. the gain of the medium simple compression stresses of csebs and asebs at 8%. proportions aebs cebs cebs/aebs n0 soil gravel + sand silt clay rcm (8%) rcm (8%) gain 1 mai 54,8 28,2 17 3,24 5,18 60% 2 bam 62,2 14,3 23,5 3,37 5,20 54% 3 gad 66 26 8 3,07 5,04 64% the findings indicate that dosing with 8% cement results in a clear increase in compression stress of approximately 59% for csebs compared to the asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by simple compression of around 58% for csebs compared to the asebs. for a dosage of 0%, we observe a slight increase in stress by simple compression of around 57% for cebs compared to the aebs. compressed and stabilized earth brings double the benefits of compression and stabilization. stabilisation with cement a blend of limestone and clay can increase the resistance of the earth block by at least 20%. the cement content in the aebs can be increased to the desired value for a given strength. however, when a certain proportion is added, the resistance of the earth block hardly varies. hence, compressed earth is less expensive and requires a manual press which can be easily done. the resistance is enhanced by about 40% in bending and 58% in simple compression that is two to three times greater than with the addition of cement. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 157 4. conclusions this study aimed at evaluating the effects of cement stabilization on the mechanical performance of compressed stabilized earth blocks (csebs) and adobe stabilized earth bricks (asebs). to this end, the geotechnical properties of the sampled soils were analysed, namely dry particle size distribution after washing, particle size distribution by sedimentometry, atterberg limits (ll, pl and pi), methylene blue test and the preparation of specimens (4x4x16cm3, 4x4x4cm3 and 2x4x8cm3) with different levels of cement (stabilizer) proportions (0%, 04%, 08%). the findings indicate that dosing with 8% cement results in a clear increase in compression stress of approximately 25.55% for csebs compared to the reference set at 0% and 22.85% for asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by simple compression of around 3.26% for csebs and 3.14% for asebs. for three-point bending compression for a cement dosage of 8%, there is also an increase in stress of about 25% for the csebs compared to the reference taken at 0% and 23.02% for the asebs. however, we observe a slight increase in stress at 4% by simple compression of around 4.5% for csebs and 5.49% for asebs. the results were obtained for three-point bending compression for a cement dosage of 8%, there is also an increase in stress of about 45% for the csebs compared to the asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by three-point bending compression of around 37% for csebs compared to the asebs. for a dosage of 0%, we observe a slight increase in stress by simple compression of around 39% for cebs compared to the aebs. the findings indicate that dosing with 8% cement results in a clear increase in compression stress of approximately 59% for csebs compared to the asebs. on the other hand, for a dosage of 4%, we observe a slight increase in stress by simple compression of around 58% for csebs compared to the asebs. for a dosage of 0%, we observe a slight increase in stress by simple compression of around 57% for cebs compared to the aebs. in terms of absorption rate, csebs resist up to one day before depigmentation is observed, whereas asebs, from the second hour of immersion, depigmentation is already visible. thus, we can conclude that csebs have a low rate of swelling (porosity), hence a better resistance to humidity, which makes it on one hand more resistant to mechanical appeals (three-point bending compression, simple compression) than cebs and less absorbing on the other than aebs. these findings firstly show that csebs are more resistant than asebs considering the maximum stress obtained by each specimen, in the same proportion of stabilized (0%, 4% and 8%) as well as simple compression and three point-bending compressions. with the intent to obtain the best characteristics of csebs and asebs from the three types of soil, we recommend a dosage of about 8% of cement. acknowledgments we are also grateful to the general manager of mipromalo yaounde where the experiments have been performed. one of us is grateful to mr j. deutou and mr loweh for their help during experiments. 5. references afnor (1993a), nf p 94-051. sols: reconnaissance et essai détermination des limites d’atterberg limite de liquidité à la coupelle-limite de plasticité au rouleau. afnor (1995a), nf p 94-056. reconnaissance et essais identification granulométrique méthode de tamisage par voie humide. afnor (1992), nf p94-057. analyse granulométrique des sols, méthode par sédimentation. afnor (1993b), nf p 94-068. mesure de la quantité et de l’activité de la fraction argileuse essai { la tâche. 158 goutsaya et al., j. build. mater. struct. (2021) 8:139-159 afnor (1995b), nf en 197-1 (p15-101-1): ciment-partie 1 : composition, spécifications et critères de conformité de ciment courants. akpokodje eg. (1985). the stabilization of some arid zone soils with cement and lime. quarterly journal of engineering geology london, 18, 173–180. amougou, j. a., abossolo, s. a., hindjang, m., (2015). variabilité des précipitations à koundja et à ngaoundere en rapport avec les anomalies de la température de l’océan atlantique et el nino. rev. ivoire sciences technologie, 25 : 111 112. bahar, r., benazzoug, m., kenai, s., (2004). performance of compacted cement stabilised soil. cem. concr. compos., 26 : 811820. césaire, h., adamah, m., abdou, l., georey, m., v., (2020). impact of the design of walls made of compressed earth blocks on the thermal comfort of housing in hot climate. buildings, 10: 157. chrétien, m., fabre, r., (2007). recherche des paramètres d’identification géotechnique optimaux pour une classification des sols sensibles au retrait-gonflement. géotechnique,: 91-106. dao, k., ouedraogo, m., millogo, y., aubert, j. e., gomina, m., (2018). thermal, hydric and mechanical behaviours of adobes stabilized with cement. constr. build. mater., 158: 84 96. elisabete, r. t., gilberto, m., adilson, p. j., christiane, g., (2020). mechanical and thermal performance characterisation of compressed earth blocks. energies, 13: 2978. ghorab h. y., anter a., el miniawy h., (2007). building with local materials: stabilized soil and industrial wastes. materials and manufacturing processes., 22 : 157-162. guanqi l., sisi c., yihong w., and ying c., (2021). methods to test the compressive strength of earth blocks. hindawi advances in materials science and engineering, id 1767238: 11 https://doi.org/10.1155/2021/1767238. houben, h., rigassi, v., garnier, p., (1996). blocs de terre comprimée: équipements de production. craterre bruxelles belgique, isbn: 2-906901-12-1. inim, i. j., affiah, u. e., eminue, o. o., (2018). assessment of bamboo leaf ash/lime-stabilized lateritic soils as construction materials. innovation infrastructure solution, 3: 32. kariyawasam, kkgkd., jayasinghe, k., (2016). cement stabilized rammed earth as a sustainable construction material. constr. build. mater., 105: 519 527. ronglin, c., (2020). mechanical and thermal behaviors of cement stabilized compressed earth bricks. earth environ. sci. 474 072090. doi:10.1088/1755-1315/474/7/072090. ruiz, g., zhang, x., edris, w. f., cañas, i., garijo, l., (2018). a comprehensive study of mechanical properties of compressed earth blocks. constr. build. mater., 176: 566-572. meukam, p., jannot, y., noumowe, a., kofane, t.c., (2004). thermo-physical characteristics of economical building materials. constr. build. mater., 18: 438 442. morel j. c., abalé p., di benedetto (2003). essai in situ sur blocs de terre comprimée. revue française de génie civil, 7:2, 221-237, doi 10.1080/12795119.2003.9692490. ntamack, g., degho, t., beda, t., charif d’ouazzane, s., (2012). determination of mechanical characteristics of compressed and stabilized earth blocks by cement, by the mixture cement and sawdust, and by the lime through the elasticity-damaging coupling model. international journal of science and technology, issn 2224-3577: 669 670. sekhar, d. c., nayak, s., (2018). utilization of granulated blast furnace slag and cement in the manufacture of compressed stabilized earth blocks. constr. build. mater., 166: 531-536. goutsaya et al., j. build. mater. struct. (2021) 8:139-159 159 toure, p. m., sambou, v., faye, m., thiam, a., adj, m., azilinon, m., (2017). mechanical and hygrothermal properties of compressed stabilized earth bricks (cseb). j build eng., 13: 266 271. tran, k., satomi, t., takahashi, h., (2018). improvement of mechanical behavior of cemented soil reinforced with waste cornsilk fibers. constr. build. mater., 178: 204 210. walker, p. j., (2004). strength and erosion characteristics of earth blocks and earth block masonry. j mater civ eng., 16(5): 497 506. zhang, l., gustavsen, a., jelle, b.p., yang, l., gao, t., wang, y., (2017). thermal conductivity of cement stabilized earth blocks. constr. build. mater. 151: 504 511. j. build. mater. struct. (2022) 9: 33-43 original article doi : 10.34118/jbms.v9i1.1897 issn 2353-0057, eissn : 2600-6936 valorization of dune sand of djelfa (algeria) treated by hydraulic binders in pavement foundations smaida a 1 * , cheriet r 1, haddadi s 2, nechnech a 2 1 civil engineering department, university of djelfa, 17000 djelfa, algeria 2 laboratory environment, water, geomechanics and structures, (leego), usthb, algeria * corresponding author: smaidaali@yahoo.fr received: 23-06-2021 accepted: 21-01-2022 abstract. the purpose of this work is the study and the valorization of sand dune which is found in abundance in the region of djelfa (algeria); for use in pavement foundations. for this investigation a method of formulation has been proposed, which based on the stabilization of this local material using a mixture of two hydraulic binders. various mixtures were subjected to classification tests, tests grain size distributions, tests of compaction with modified proctor, shear strength, tests of bearing pressure (cbr unsoaked and soaked), compressive strength and tensile strength. the results obtained have shown that some mixtures are of high mechanical characteristics and could be then used in road foundations. key words: dune sand; hydraulic binders; valorization; pavements. 1. introduction dune sand constitutes a huge deposit almost 60% of the territory of algeria. the current trend of nowadays research is the exploitation of local materials. this has prompted us to perform the present contribution aiming to the valorization of local materials, in particular the dune sand, in the foundations of pavements. the role of pavement foundations is essential to take up the vertical forces and to distribute the resulting normal stresses on the support ground. previous studies done on this subject have shown that the materials used must have certain specifications in terms of their bearing capacity and their fine material content. many studies have been carried out with the aim of improving the mechanical characteristics of the different materials used in road construction by adding binders (cement, clay, lime, pozzolan, fly ash ...) (grzegorz, 2006; setra, 2008; tran, 2009; damiot, 2011; ghrieb et mitichekettab, 2013; azadegan et al., 2013; rios et al., 2016 and tataranni et al, 2018). in the present work, we report on the improvement of the physical and mechanical characteristics of dune sand used for road construction. it is shown that by adding a mixed hydraulic binder all the investigated features are found to be improved. 2. identification of used materials 2.1 dune sand the studied sand comes from the region of djelfa located about 300 km from algiers to the center (algeria). besides, both center and south of algeria are known by their huge sand dunes that constitute an important fraction of the surface of the country. using this dune sand in the road domain is of great interest from the economic, technical and environment friendliness points of view. according to the gtr 2000 soil classification (lcpc-setra, 2000), dune sand belongs to the d1 class. it is characterized as permeable, incoherent, and poorly graded soil. this suggests that dune sand alone will not be sufficiently compact, and subsequently its immediate bearing index is not adequate. therefore, a treatment of this sand with hydraulic binders as correctors will be essential. 34 smaida et al., j. build. mater. struct. (2022) 9:33-43 it’s clear from the chemical analysis summarized in table 1, that our sand is siliceous, formed of a large quantity of sio2 (silica), with the presence of some traces of calcium and magnesium species. x-ray analyzes reveal the presence of quartz with a high percentage, and traces of illite and calcite. table 1. chemical composition of dune sand material sio2 co2 fe2o3,al2o3 caso4,h2o nacl caco3 p.f1 h2o bilan dune sand 93.56% 1.49% 1% traces 0.29% 3.39% 1.73% 0.24 98.48% the physical properties of dune sand are summarized in table 2. table 2. physical properties of the dune sand. coefficient of uniformity cu 1.87 coefficient of curvature cc 1.09 apparent density (g/cm3) 1.48 absolute density (g/cm3) 2.54 visual sand equivalent (%) 82 sand equivalent with the piston (%) 68 blue value for 100g 0.07 fineness modulus 0.9 2.2 lime the lime used in the present study comes from the west of algeria. it is a slaked lime which has a low concentration of oxides such as sio2 (silicate) < 2.2% and mgo (aluminate) <0.4% and a high concentration of basic elements such as cao (free lime) < 67.4% and 73.25%, with more than 90% passing through 80μm sieve. its absolute density is 2.559 g / cm3, and its specific surface area is 11053 cm2 / g. table 3 summarizes the chemical composition of the lime. table 3. chemical composition of the lime. 2.3 natural pozzolan the natural pozzolan used is of volcanic origin extracted from the bouhamidi deposit (western algeria). this pozzolan consists mainly of well-stratified slate and pumice stones, ranging in color from red to black. the natural pozzolan used in all tests is in the form of a powder resulting from the crushing of pozzolanic slags; steamed for 24 hours at a temperature of 50 ° c to remove their moisture, and then crushed until the resulting powder can pass through a sieve mesh of 80 µm fig 1. slags of natural pozzolan before grinding. fig 2. powder of natural after grinding < 80 µm. cao mgo fe2o3 al2o3 sio2 so3 co2 caco3 >67.4% <0.4% <2% <1% <2.2% <1% <5% <10% smaida et al., j. build. mater. struct. (2022) 9:33-43 35 x-ray diffraction of this pozzolan shows that it consists of crystalline minerals rich in silica, alumina, iron and magnesium. the chemical composition of natural pozzolan after grinding is shown in table 4. table 4. chemical composition of natural pozzolan. it is noted that the blaine specific surface of natural pozzolan is 4330 cm2/g with an absolute density of 2.45 g/cm3. 3. test methods to stabilize the studied dune sand is carried out by adding the mass substitutes on the physical and mechanical behavior: physical stabilization: correction of the grading by adding 10 %, 15%, 20% and 25% of fine elements (pozzolan+lime), where those percentages are chosen according to the recommendations of the standards of road networks (setra-lcpc, 1998). mechanical stabilization: densification by compaction operation. the mixtures are denoted by ds-pz-li; where ds is the dune sand of djelfa, pz the percentage of pozzolan, li the percentage of lime respectively. details of the mixtures proportions are given in table 5. table 5. mixtures proportions. mixture % of dune sand % of natural pozzolan % of lime % of (pozzolan+lime) ds 100-0-0 100 0 0 0 ds 90-8-2 90 8 2 10 ds 85-12-3 85 12 3 15 ds 80-16-4 80 16 4 20 ds 75-20-5 75 20 5 25 4. evolution of the physical and mechanical characteristics 4.1. grain size distributions figure 3 shows the grain size distributions of the mixtures. there is a slight upward shift of the curve. this shift becomes more accentuated as the percentage of additive (pozzolan+lime)) is increased. this can indicate an increase in the fraction of fine elements in favor of a decrease of larger elements (ismael, 2006; tataranni et al., 2018) especially those less than 0.2mm. dubois has reported that the fraction of fines (% of particles whose diameter is less than 63 μm) in the mixture is more critical for providing adequate bearing capacity. the fine fraction was limited to 20% in its mixtures. schlosser has set two criteria as for respecting uniformity of curvature. these two criteria are expressed as, cu = d60/d10 > 6; cc = d30²/ (d60×d10); (cu and cc are in between 1 and 3). accordingly, two among our mixtures (ds 80-16-4 and ds 75-20-5) do fulfill these criteria; with a small advantage for the last mixture cao sio2 al2o3 fe2o3 so3 k2o na2o mgo cl caco3 12,36% 42,95% 16,32% 9,49% 0,01% 1,39% 3,00% 4,20% 0,00% 10,75% 36 smaida et al., j. build. mater. struct. (2022) 9:33-43 fig 3. grain size distribution 4.2 evolution of the proctor characteristics these mixtures studied have been first compacted at different water contents in order to determine the optimal water content along with the maximal dry density via the modified proctor test according to the nf p94-093 normalization. by inspecting figure 4, we can see that the dry density of the mixtures is increased with a notable shift of the proctor curve to the right, and hence towards higher water contents. this is because of the binders absorb a part of the available water to their hydration resulting thus in the diminution of the water proportion acting as lubricant. furthermore, hydraulic binders are fine particles that can help to obtain an improved granulometric distribution by reducing voids. fig 4. modified proctor cure according to the percentage of pozzolan+lime. smaida et al., j. build. mater. struct. (2022) 9:33-43 37 the sand incorporation has permitted to densify the material by increasing its density from 1.72 g/cm3 à 1.87 g/cm3 and its optimal water content (figure 5) from 5% to 11%. our results show that the incorporation of pozolan+lime tends to improve the compaction optimal characteristics of the mixtures as compared to those of the dune sand with no adding. fig 5. optimum water content and maximum dry density according to the percentage of pozzolan + lime. 4.3 evolution of direct shear strength the mixtures studied are statically compacted at the proctor optimum prior to placement in the straight shear box. the test mode is conditioned by a fast speed of 1 mm / min corresponding to an unconsolidated undrained test (uu) according to the standard nf p 94-071-1. figure 6 shows the variation of the shear strength as a function of the normal stress. fig 6. intrinsic curves for the mixtures. from figure 6, we note that the shear strength improves with the increase of the dosage of the hydraulic binder. this evolution is usually accompanied by an increase of the cohesion and a decrease of the angle of friction (figure 7). 38 smaida et al., j. build. mater. struct. (2022) 9:33-43 fig 7. evolution of cohesion and angle of friction for the mixtures the mixtures showed that the cohesion steadily increases from 0.02 bars for dune sand untreated (incoherent material) to a maximum value of 0.79 and 0.97 bars, respectively for the mixture ds 80-16-4 and ds 75-20-5. therefore, the friction angle decreases from 36.65° to 19.6° for the ds 80-16-4 and from 36.65° to 22.88° for the mixture ds 75-20-5 . 4.4 evolution of bearing capacity cbr (%) the cbr test was carried out according to the standard nf p 94-078, where cbr (unsoaked) is determined immediately, just after compaction, or after four days of immersion (cbr soaked). the test consists of punching test specimens made at different compaction energies (10 blows per layer, 25 b / l and 55 b / l) in the cbr mold and at water contents corresponding to the optimum of the modified proctor test. figure 8.a illustrates the piston pressure as a function of penetration. the cbr is determined for each compaction energy, which is used to represent the variation of the dry density as a function of the cbr, and then the cbr is determined. it corresponds to 95% of the maximum of dry density obtained in the modified proctor test (figure 8.b exp: ds 75-20-5). fig 8. a) evolution of pression according to its penetration. b) evolution of maximum dry density according to the cbr (%). smaida et al., j. build. mater. struct. (2022) 9:33-43 39 figure 9 shows the added binder (pozzolan + lime) dependent evolution of the immediate load bearing has a steep slope in the range 0-25% of added binder. the unsoaked cbr increases from 8.28% up to 41.8% whereas the soaked cbr increases from 6.45% for untreated dune sand to 12.51% for ds 75-20-5 showing a slower slope. fig 9. evolution of cbr (%) at 95% of opm according to the mixtures. 4.5 evolution of compression and tensile strength a series of cylindrical specimens with dimensions (φ = 100mm, h = 100mm) was prepared according to the standard en 13286-53, for the different mixtures. the mixture is put in a single layer in a double piston mold and then statically compacted, at the dry density and the water content of the proctor modified according to en 13286-41. after that the specimens were preserved in bags at a temperature of 20 ± 2 ° c until the date of the test. these tests were performed at age of 7, 14, 28, 60 and 90 days for the compressive tests; while the tests tensile were measured by the indirect tensile strength according to the standard en 13286-42 after preparing the specimens by the same way they were preserved in bags at the same temperature until the test date of 90 days. figure 10 illustrates the evolution of the compressive strength as a function of the percentages of the binder for different curing times and figure 10.b represent the evolution of the tensile strength as a function of the added binders. figure 10 shows that the compressive strength increases very significantly and follows a linear function with the increase of the quantity of (pozzolan+lime). the effect of the added binder becomes more significant beyond 15% of (pozzolan+lime). note that compressive strength corresponding to a cure time of 90 days is greater than that corresponding to the others cure times. 40 smaida et al., j. build. mater. struct. (2022) 9:33-43 fig 10. evolution of the compressive strength according to the percentage of pozzolan+lime. fig 11. evolution of the tensile strength according to the percentage of pozzolan+lime. in a similar way to compressive strength, figure 11 confirms an increase of the tensile strength with the proportion of added pozzolan + lime. this quantity ranges from almost zero in the case of untreated dune sand to 0.28 mpa for 10% of binder (ds 90-8-2) giving thus a very clear idea of the effectiveness of our added binder. this is the case for all mixtures up to a maximum value of 0.71 mpa for the mixture (ds 75-20-5). 5. classification of optimal mixtures the standard nf 14227-1 states that there are 6 resistance classes from t0 to t5 and that t2, t3 and t4 are recommended for use in road layers base. table 6 summarized the mechanical characteristics of the mixtures. smaida et al., j. build. mater. struct. (2022) 9:33-43 41 table 6 the mechanical characteristics of the mixtures. mechanical characteristics ds 90-8-2 ds 85-12-3 ds 80-16-4 ds 75-20-5 optimum water content (%) 8 9.8 9.9 11.7 maximum dry density (g/cm3) 1.79 1.81 1.86 1.87 cbr unsoaked at 95% of opm (%) 23.4 26.5 37 41.8 cbr soaked at 95% of opm (%) 7.57 10.35 11.1 12.55 cohesion c (bars) 0.42 0.44 0.79 0.97 friction angle (degree) 33.94 35.77 19.6 22.88 compressive strength at 60 days (mpa) 2.671 3.439 5.255 6.790 tensile strength at 60 days (mpa) 0.28 0.48 0.58 0.71 elastic modulus (mpa) 3123 4021 4533 7066 the classification is based on the tensile strength-modulus of elasticity (rt, e). the modulus of elasticity e was measured according to the standard nf 13286-43. for this classification, the curing times were considered is 60 days. the values rt360, e360 corresponding to a duration of one year are estimated from the ratio rt60 / rt360 and e60 / e360 which are respectively equal to 0.78 and 0.82 according to standard nf en 14227-5. the standard en 14227-1 recommends that materials whose torque (rt, e) is under the zone of class t2 are not used in foundation road. fortunately, our materials are located at least in the zone t2 as shown in figure 12 and therefore usable as a layer of seats. it is noted in particular that the mixture ds 75 – 20 – 5 is visibly much better than the other two because it is located in the t3 zone. fig 12. classification of mixtures according to en 14227-1. 6. conclusion the objective of this work is to valorize dune sand in the layers of pavement foundations; this abundant material is known for its poor geotechnical properties: poorly graded, incoherent, porous, without fine elements and low bearing capacity. the improvement of these physical and 42 smaida et al., j. build. mater. struct. (2022) 9:33-43 mechanical properties was made by the addition of percentages of hydraulic binders (pozzolan + lime). the experimental results were very encouraging, and show that all the mixtures have resulted in sufficient mechanical characteristics to valorize this material in layers of pavement foundations, which according to these results draws the following conclusions: the incorporation of the pozzolan + lime percentages allowed to have mixtures with a spread and graduated curves. the maximum dry density and optimum water content increase proportionally to the percentages added, and therefore have a denser (compact) material. the mixed hydraulic binder (pozzolan + lime) improve mechanical characteristics: bearing capacity (cbr (%), unsoaked and soaked), shear strength, compressive strength and tensile strength. the modulus of elasticity increases in proportion to the percentage of binder added; which always confirms the effectiveness of binder (pozzolan + lime) used. the classification of our treated material shows that all the mixtures can be used in pavement foundations with an advantage for the both mixtures ds 80 16 4 and ds 75 20 – 5. 7. références afnor 1994, nf p94-071-1. sols ; reconnaissance et essais – essais de cisaillement rectiligne à la boîte partie 1 : cisaillement direct. afnor 1994, nf p94-093.sols : reconnaissance et essais détermination des références de compactage d'un matériau, essai proctor normal — essai proctor modifié. afnor 1997, nf p94-078. sols : reconnaissance et essais indice cbr après immersion-indice cbr immédiatindice portant immédiat. afnor 2003, nf en 13286-41. mélanges traités et mélanges non traités aux liants hydrauliques partie 41: méthode d’essai pour la détermination de la résistance à la compression des mélanges traités aux liants hydrauliques. afnor 2003, nf en 13286-42. mélanges traités et mélanges non traités aux liants hydrauliques partie 42: méthode d’essai pour la détermination de la résistance à la traction indirect des mélanges traités aux liants hydrauliques. afnor 2003, nf en 13286-43. mélanges traités et mélanges non traités aux liants hydrauliques partie 43: méthode d’essai pour la détermination du module d’élasticité des mélanges traités aux liants hydrauliques. afnor 2005, nf en 13286-53. mélanges traités et mélanges non traités aux liants hydrauliques partie 53 : méthode de confection par compression axiale des éprouvettes de matériaux traités aux liants hydrauliques. afnor 2005, nf en 14227-1. mélanges traités aux liants hydrauliques partie 1: mélanges granulaires traités au ciment. afnor 2005, nf en 14227-5. mélanges traités aux liants hydrauliquesspécifications partie 5: mélanges granulaires traités au liant hydraulique routier. azadegan, o., yaghoubi, e., & li, j. (2013). evaluation of the performance of lime and cement treated base layers in unpaved roads. the electronic journal of geotechnical engineering, 18, 1593-1602. damiot d. (2011). elaboration de liants hydrauliques routiers à base de pouzzolane naturelle ou de cendre volante de papeterie. doctorat de l’université de toulouse. smaida et al., j. build. mater. struct. (2022) 9:33-43 43 dubois v. (2006). etude du comportement physico-mécanique et caractérisation environnementale des sédiments marins – valorisation en technique routière thèse de doctorat,université d’artois, france. ghrieb, a., mitiche-kettab, r., & bali, a. (2014). stabilization and utilization of dune sand in road engineering. arabian journal for science and engineering, 39(3), 1517-1529. grzegorz k. (2006). etude de comportement mécanique des mélanges sable/argiles thèse de doctorat de l’institut national des sciences appliquées de lyon, france. haach, v. g., vasconcelos, g., & lourenço, p. b. (2011). influence of aggregates grading and water/cement ratio in workability and hardened properties of mortars. construction and building materials, 25(6), 2980-2987. ismael, n. f. (2006). influence of fines on the properties of arid climate sand deposits. in unsaturated soils 2006 (pp. 1617-1626). lcpc-setra, g. t. r. (2000). guide technique pour la réalisation des remblais et des couches de forme, fascicule i, principes généraux, p 166. lcpc-setra. (1998) assises de chaussées – guide d’application des normes pour le réseau routier national en graves non traitées et matériaux traités aux liants hydrauliques. reddy, b. v., & gupta, a. (2008). influence of sand grading on the characteristics of mortars and soil– cement block masonry. construction and building materials, 22(8), 1614-1623. rios, s., da fonseca, a. v., & bangaru, s. s. (2016). silty sand stabilized with different binders. procedia engineering, 143, 187-195. schlosser f (1988). eléments de mécanique des sols, presses de l’ecole nationale des ponts et chaussées, isbn 2-85978-104-8, 276p. setra. (2008). technical guide. treatement of soils with lime and / or hydraulic binders – application to the construction of pavement base layers. tataranni, p., sangiorgi, c., simone, a., vignali, v., lantieri, c., & dondi, g. (2018). a laboratory and field study on 100% recycled cement bound mixture for base layers. international journal of pavement research and technology, 11(5), 427-434. tran n.t. (2009). valorisation de sédiments marins et fluviaux en technique routière. thèse de doctorat, université d’artois, france. j. build. mater. struct. (2022) 9: 12-21 original article doi : 10.34118/jbms.v9i1.1882 issn 2353-0057, eissn : 2600-6936 static and dynamic behaviors of laminated composite plates resting on elastic foundation ghazoul t *, benatta m a , bachir bouiadjra m 1 laboratoire des structures et matériaux avancés dans le génie civil et travaux publics, université de sidi bel abbes, bp 89 cité ben mhidi, sidi bel abbés, algérie. * corresponding author : taherghazoul@gmail.com received: 16-06-2021 accepted: 20-01-2022 abstract. this present study consists to analyze the mechanical buckling and the free vibration stabilities of antisymmetric cross-ply and angle-ply laminated composite plates using a refined high order shear deformation theory of four variables against five in other high order theories. among the advantages of this new theory it takes into consideration the shearing effect in the calculation of deformation without the need for shear correction factors and giving rise to a variation of the shear stresses along the thickness and satisfying the zero shear stresses condition in faces of the plate. the laminate resting on the pasternak elastic foundation, including a shear layer and winkler spring, are considered. the equations of the motion are derived from hamilton’s principal. the closed form solution of simply supported rectangular plates has been obtained by using the navier method. in addition, the effects of various parameters of the laminated composite plate on static buckling and dynamic are presented. key words: laminate composite plates, buckling, free vibration, elastic foundation, refined theory. 1. introduction the ability to control the selection of the proper composite materials, the number of plies, and the fiber orientation give the laminated composite plates much attention in industry applications and fields of technology. this promising feature allows designers to acquire desired structural responses under a given set of operating conditions. many shear deformation theories accounting for transverse shear effects have been developed to overcome the deficiencies of the classical plate theory (cpt). the first-order shear deformation theories (fsdt) based on reissner (1945) and mindlin (1951) account for the transverse shear effects by the way of linear variation through the thickness. in references (srinivas and rao, 1970; bert, 1974) a shear correction factors are required to rectify the equilibrium conditions and satisfying the zero shear stresses condition at the top and bottom faces of the plate. in order to overcome the limitations of the first-order shear deformation theories (fsdt), higher-order shear deformation theories (hsdt) were developed, among them the reddy’s theory is the most widely used due to its high efficiency and simplicity (reddy and phan, 1985; mallikarjuna and kant, 1993). shimpi (2002) for isotropic plates developed a refined plate theory using only two unknown, then it was extended by shimpi and patel (2006a-b) for orthotropic plates. in the present study, an attempt is made to check the efficiency of four variable refined shear deformation theories for the buckling and free vibration analysis of cross-ply laminated composite plates resting on elastic foundation. the theory satisfies zero shear stress conditions at top and bottom surfaces of the plates and does not need shear correction factor. the elastic foundation is modeled as two parameter pasternak foundation. governing equations and boundary conditions are obtained using the hamilton principle. a closed form solution is obtained by using a double trigonometric series technique developed by navier. mailto:taherghazoul@gmail.com ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 13 2. theoretical formulation 2.1. main assumptions consider a rectangular plate of total thickness h composed of n orthotropic layers with the coordinate system as shown in figure 1. the principal assumption of the refined plates theory is that the transverse displacement w includes two components of bending wb and shear ws. these components are functions of coordinates (x, y) and time t only. fig 1. geometry and coordinate system of laminated plate on elastic foundation. 2.2. kinematics the displacement field can be obtained as                                           0 0 , , , , , , , , , , , , , , , , , , , , , , , , , b s b s b s w x y t w x y t u x y z t u x y t z f z x x w x y t w x y t v x y z t v x y t z f z y y w x y z t w x y t w x y t where 0 u and 0 v denote the in-plane displacements in the directions of x and y , respectively; b w and s w are the bending and shear components of the transverse displacement, respectively; ( )f z represents shape function determining the distribution of the transverse shear strains and stresses along the thickness and is used as 1 1 2 ( )         p p f z z p h ,  3,5,...p 2.3. constitutive relations since the laminate is made of several orthotropic layers with their material axes oriented arbitrarily with respect to the laminate coordinates, the constitutive equations of each layer must be transformed to the laminate coordinates (x, y, z). the stress-strain relations in the laminate coordinates of the kth layer are given as (1) (2) 14 ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 11 12 16 12 22 26 16 26 66 44 45 45 55 0 0 0 0 0 0 0 0 0 0 0 0                                             kk x x y y xy xy yz yz xz xz q q q q q q q q q q q q q           where  k ;   and    k ij q are the stress vector, strain vector and transformed stiffness matrix, respectively. with the non-zero strains components associated with the displacement field in equation (1) can be defined as follows 0 0 0 ( )                                                       b s x x xx b s y y y y b s xy xy xy xy k k z k f z k k k      , ( )                  s yz yz s xy xz g z     , ( ) 1 ( ) g z f z where 0 0 0 0 0 0 0                                       x y xy u x v y u v y x , 2 2 2 2 2 2                                   b b x b b y b xy b w x k w k y k w x y , 2 2 2 2 2 2                                   s s x s s y s xy s w x k w k y k w x y ,                         s s yz s sxz w y w x 2.4. governing equation the application of hamilton principle leads to                /2 0 0 /2 2 2 2 2 0 0 22 2 2 2 2 0 0 /2 ha b x x y y xy xy yz yz xz xz h a b b s b s w b s b s s b s ha b b s b s b s h dzdydx w w w w k w w w w k w w dydx x y w wu v q w w dydx u v w w t t t                                                                              /2 0 0 2 2 2 0 0 0 2 2 0 0 2 a b a b b s b s b s xx yy xy b s dzdydx w w w w w w n n n w w dydx x y x y                        where 0 x n ; 0 y n ; 0 xy n are in-plane applied loads.  is the composite density. w k and s k are the winkler and shear layer spring constants, in this study, the laminated rectangular plate is taken to be simply supported at the edges. the solution of equations (6) can be obtained analytically by using the following boundary conditions: 0 0 0 0             b s b s x x x b s b s y y y v w w n m m u w w n m m 0 0 0 0             b s b s x x x b s b s y y y u w w n m m v w w n m m the following approximate solution that satisfies the boundary conditions is applied as cross-ply laminated plate: at y=0,b angle -ply laminated plate: at x=0,a (3) (4) (6) (7) (5) ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 15                 0 1 1 0 1 1 1 1 1 1 ( , , ) cos sin ( , , ) sin cos ( , , ) sin sin ( , , ) sin sin                             i t mn m n i t mn m n i t b bmn m n i t s smn m n u x y t u e x y v x y t v e x y w x y t w e x y w x y t w e x y                             0 1 1 0 1 1 1 1 1 1 ( , , ) sin cos ( , , ) cos sin ( , , ) sin sin ( , , ) sin sin                             i t mn m n i t mn m n i t b bmn m n i t s smn m n u x y t u e x y v x y t v e x y w x y t w e x y w x y t w e x y             in which mn u , mn v , b mn w and s mn w are arbitrary parameters to be determined.  is the eigen frequency associated with ( m , n ) the eigen mode, and /  m a and /  n b . the analytical solutions can be obtained from the following equations for buckling and free vibration problem 11 12 13 14 11 12 22 23 24 222 13 23 33 34 33 34 14 24 34 44 34 44 0 0 0 0 0 0 0 0 0 0 0 0 0 0                                                             mn mn bmn smn s s s s m u s s s s m v s s s k s k m m w s s s k s k m m w  where         2 2 11 11 66 12 12 66 2 2 22 66 22 4 2 2 2 33 11 12 66 22 4 2 2 4 34 11 12 66 22 4 2 2 4 2 2 44 11 12 66 22 55 44 , 2 2 2 2 2 2                                        s s s s s s s s s s s a a s a a s a a s d d d d s d d d d s h h h h a a 3 13 11 3 14 11 3 23 11 3 24 11                 s s s b s b s b s b         2 3 13 16 26 2 3 14 16 26 3 3 23 16 26 3 3 24 16 26 3 3 3 3                              s s s s s b b s b b s b b s b b       2 2 11 22 1 33 1 3 2 2 2 2 34 1 5 44 1 6 0 2 0 2 0 , , 2                        x y xy m m i m i i m i i m i i k n n n with 2 2 1 1 ( , , , , , ) (1, , , ( ), ( ), ( ))      n hs s s kk ij ij ij ij ij ij ijhk k a b d b d h q z z f z z f z f z dz ( , ) (1, 2, 6)i j 2 1 1 ( )      n hs kk ij ijhk k a q g z dz ( , ) (4,5)i j    2 21 2 3 4 5 6 1 1 , , , , , 1, , , ( ), ( ), ( )      n h kk hk k i i i i i i z z f z zf z f z dz cross-ply laminated plate: angle -ply laminated plate: (8) (9) for antisymmetric cross-ply for antisymmetric angle-ply (10) (11) 16 ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 3. results and discussion the lamina properties used in this study are given in table 1. the following nondimensionalizations are used in presenting the numerical results in tabular and graphical form: 4 3 2 w w k a k e h  , 2 3 2 s s k a k e h  2 2 a h e    , 2 3 2 cr a n n e h         table 1. lamina properties. 1 e 12 13 g g 23 g 12 13   from 3 to 40 2 e 0.6 2 e 0.5 2 e 0.25 3.1. free vibration analysis in order to verify the accuracy of the present analysis, some numerical examples were solved. as a first example, the fundamental natural frequencies of a simply supported anti-symmetric cross-ply (0/90)n plates were calculated by varying the number of plies n and the orthotropic ratio e1/e2. figure 2 shows the comparison between the present results and the solutions given by reddy (1989) for different values of orthotropic ratio. the results clearly indicate that the fundamental natural frequencies predicted by the present model and reddy (1989) are almost identical. 0 5 10 15 20 25 30 35 40 6 7 8 9 10 11 12 ref. [13] (0°/90°) 1 present (0°/90°) 1 ref. [13] (0°/90°) 2 present (0°/90°) 2 ref. [13] (0°/90°) 3 present (0°/90°) 3 ref. [13] (0°/90°) 5 present (0°/90°) 5 e 1 /e 2  fig 2. comparison of the fundamental frequency  of simply supported anti-symmetric cross-ply square laminates (a/h=10, kw=ks=0). in order to validate the present model in the case of elastic foundation, the results for the fundamental natural frequency parameter of isotropic plate with different values of thicknessto-length ratios and different values of elastic coefficients are compared in table 2 with those obtained by baferani et al. (2011) and thai and choi (2011). excellent agreement of the three methods can be seen. (10) ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 17 table 2. comparison of the fundamental frequency 2 /h e   of isotropic square plates. kw ks sources h/a 0.05 0.1 0.15 0.2 0 0 ref. [10] 0.0291 0.1134 0.2454 0.4154 ref. [11] 0.0291 0.1135 0.2454 0.4154 present 0.0291 0.1134 0.2452 0.4150 0 100 ref. [10] 0.0406 0.1599 0.3515 0.6080 ref. [11] 0.0406 0.1599 0.3515 0.6080 present 0.0406 0.1597 0.3512 0.6075 100 0 ref. [10] 0.0298 0.1162 0.2519 0.4273 ref. [11] 0.0298 0.1163 0.2519 0.4273 present 0.0298 0.1162 0.2515 0.4269 100 100 ref. [10] 0.0411 0.1619 0.3560 0.6162 ref. [11] 0.0411 0.1619 0.3560 0.6162 present 0.0411 0.1617 0.3557 0.6156 figure 3 shows the effect of the thickness ratio a/h on the dimensionless natural frequencies of both cross-ply and angle-ply simply supported laminates with and without the elastic foundation. as shown in this figure, the dimensionless natural frequencies increase with increasing thickness ratio and number of plies. besides, the frequencies of laminates increase when foundation parameters increase, this increase is more significant in cases of cross-ply laminates. 0 20 40 60 80 100 5 10 15 20 25 a/h  kw=0,ks=0 (0/90)1 (0/90)2 (0/90)3 (0/90)5 kw=50,ks=10 (0°/90°)1 (0°/90°)2 (0°/90°)3 (0°/90°)5 0 20 40 60 80 100 5 10 15 20 25 30  kw=0,ks=0 (45/-45)1 (45/-45)2 (45/-45)3 (45/-45)4 kw=50,ks=10 (45/-45)1 (45/-45)2 (45/-45)3 (45/-45)4 a/h fig 3. the effect of side-to-thickness ratio on fundamental frequency  of simply supported anti-symmetric (0/90)n cross-ply and (45/-45)n angle-ply square laminates on the elastic foundation (e1/e2=40). figure 4 illustrates the variations of dimensionless fundamental frequencies of anti-symmetric cross-ply (0/90/0/90) laminate on elastic foundation against orthotropic ratio e1/e2. it is seen that an increase in the degree of orthotropy produces an increase in the fundamental frequency. additionally, it is observed that the frequencies of laminates increase when foundation parameters increase. 18 ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 0 5 10 15 20 25 30 35 40 12 14 16 18 20 22 24 26 (a) kw=0 kw=20 kw=40 kw=60 kw=80 kw=100  e 1 /e 2 0 5 10 15 20 25 30 35 40 10 12 14 16 18 20 22 24 26 (b) ks=0 ks=2 ks=4 ks=6 ks=8 ks=10  e 1 /e 2 fig 4. variation of fundamental frequency  versus orthotropy ratio for simply supported anti-symmetric laminated (0/90/0/90) square plate on the elastic foundation (a/h=10, (a): ks=10, (b): kw=100). the effects of angle  on the dimensionless fundamental frequencies of angle-ply ( /- ) laminate with different values of foundation parameters are shown in figure 5. it is found that the curves are symmetric to the line of 45   and it presents the highest values of fundamental frequencies for all cases. 0 10 20 30 40 50 60 70 80 90 18 19 20 21 22 23 (a) kw=0 kw=50 kw=100   0 10 20 30 40 50 60 70 80 90 15 16 17 18 19 20 21 22 23 24 (b) ks=0 ks=5 ks=10   fig 5. effect of the lamination angle  on fundamental frequency  of simply supported anti-symmetric laminated ( /- )1 angle-ply square plate on the elastic foundation (a/h=10, (a): ks=10, (b): kw=100). 3.2. buckling analysis for buckling analysis, it is also begun with numerical validation to verify the accuracy of the present mathematical models in predicting buckling analysis of laminated composite plates with elastic foundation. a simply supported anti-symmetric cross-ply (0/90)n square laminates subjected to uniaxial compressive load is considered. figure 6 shows a comparison between the present solutions and the solutions obtained by reddy and khdeirt (1989). from this figure, it can be seen, the present solutions are almost identical with solutions obtained by reddy and khdeirt (reddy, 1989) for all different values of orthotropic ratio. ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 19 0 5 10 15 20 25 30 35 40 5 10 15 20 25 e1/e2 ref. [12] (0°/90°) 1 ref. [12] (0°/90°) 2 ref. [12] (0°/90°) 3 ref. [12] (0°/90°) 5 present (0°/90°) 1 present (0°/90°) 2 present(0°/90°) 4 present (0°/90°) 5n fig 6. comparison of the uniaxial buckling load n of simply supported anti-symmetric cross-ply square laminates (a/h=10, kw=ks=0). figure 7 contains plots of dimensionless uniaxial critical buckling load versus thickness ratio a/h of a simply supported anti-symmetric cross-ply and angle-ply with and without the elastic foundation. the results show that the dimensionless buckling loads increase with increasing thickness ratio and number of plies. also, it can be observed that the dimensionless buckling loads of laminates increase when foundation parameters increase, this increase is more significant in cases of cross-ply laminates. 0 20 40 60 80 100 0 20 40 60 80 100 n kw=50,ks=10 (45/-45)1 (45/-45)2 (45/-45)3 (45/-45)4 kw=0,ks=0 (45/-45)1 (45/-45)2 (45/-45)3 (45/-45)4 a/h 0 20 40 60 80 100 0 10 20 30 40 50 60 n kw=50,ks=10 (0°/90°)1 (0°/90°)2 (0°/90°)3 (0°/90°)5 kw=0,ks=0 (0/90)1 (0/90)2 (0/90)3 (0/90)5 a/h fig 7. the effect of side-to-thickness ratio on uniaxial buckling load n of simply supported anti-symmetric (0/90)n cross-ply and (45/-45)n angle-ply square laminates on the elastic foundation (e1/e2=40). 20 ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 the effect of orthotropy ratio e1/e2 on dimensionless uniaxial critical buckling loads of antisymmetric cross-ply (0/90/0/90/0/90) laminate on elastic foundation is shown in figure 8. it is seen that an increase in the degree of orthotropy leads to an increase in the dimensionless buckling loads. additionally, it is observed that the dimensionless buckling loads increase when foundation parameters increase. 0 5 10 15 20 25 30 35 40 15 20 25 30 35 40 45 50 55 60 (a) kw=0 kw=20 kw=40 kw=60 kw=80 kw=100 e 1 /e 2 n 0 5 10 15 20 25 30 35 40 10 15 20 25 30 35 40 45 50 55 60 (b) ks=0 ks=2 ks=4 ks=6 ks=8 ks=10 e 1 /e 2 n fig 8. variation of uniaxial buckling load n versus orthotropy ratio for simply supported anti-symmetric laminated (0/90/0/90/0/90) square plate on the elastic foundation (a/h=10, (a): ks=10, (b): kw=100). figure 9 contains plots of dimensionless uniaxial critical buckling loads versus lamination angle  of angle-ply ( /- )1 laminate with different values of foundation parameters. it is found that the curves are symmetric to the line of 45   where the latter presents the largest values of dimensionless buckling loads for all cases. 0 10 20 30 40 50 60 70 80 90 36 38 40 42 44 46 48 50 52 kw=0 kw=50 kw=100  n 0 10 20 30 40 50 60 70 80 90 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 ks=0 ks=5 ks=10  n fig 9. effect of the lamination angle  on uniaxial buckling load n of simply supported anti-symmetric laminated ( /- )1 angle-ply square plate on the elastic foundation (a/h=10, (a): ks=10, (b): kw=100). 4. conclusions in this paper, a refined higher order shear deformation theory has been used to determine natural frequencies and buckling loads of simply supported antisymmetric cross-ply and angleply laminated rectangular plates on two parameters elastic foundation. from the results and discussion it can be concluded that the theory proposed is accurate and efficient in predicting the vibration and the buckling responses of laminated plates. ghazoul, t et al., j. build. mater. struct. (2022) 9: 12-21 21 the influence of the side to thickness ratio, number of layers, lamination angle, orthotropic ratio and elastic foundation parameters on both nondimensional fundamental frequencies and critical buckling loads is studied. the results showed that these parameters have significant influence on the buckling and free vibration characteristics of antisymmetric laminated composite plates. it is also concluded that the presence of elastic foundation increases buckling load and frequencies of antisymmetric laminates plates. while, the winkler stiffness does not have as much of effect on natural frequency and buckling loads as shear layer stiffness. 5. references baferani, a.h., saidi, a.r., ehteshami, h. (2011). accurate solution for free vibration analysis of functionally graded thick rectangular plates resting on elastic foundation. compos struct., 93(7):1842–53. bert, c.w. (1974). structure design and analysis: part i, in: c. c. chamis (ed.), analysis of plates. academic press, new york (chap. 4). mallikarjuna, m., kant, t. (1993). a critical review and some results of recently developed refined theories of fiber-reinforced laminated composites and sandwiches, compos. struct. 23, 293–312. mindlin, r.d. (1951). influence of rotary inertia and shear on flexural motions of isotropic, elastic plates, j. appl.mech. trans. asme 18, 31–8. reddy, j.n., khdeirt, a.a. (1989). buckling and vibration of laminated composite plates using various plate theories. aiaa j. vol. 98, no. 2, pp. 157-170. reddy, j.n., phan, n. d. (1985). "stability and vibration of isotropic, orthotropic, and laminated plates according to a higherorder deformation theory," journal of sound and vibration, vol. 98, no. 2, pp. 157-170. reissner, e. (1945). the effect of transverse shear deformation on the bending of elastic plates, j. appl. mech. trans. asme 12, 69–77. shimpi, r.p. (2002). refined plate theory and its variants, aiaa j., vol. 40, pp. 137–146. shimpi, r.p., patel, h.g. (2006a). a two variable refined plate theory for orthotropic plate analysis, int. j. solids struct. 43, 6783–6799. shimpi, r.p., patel, h.g. (2006b). free vibrations of plate using two variable refined plate theory, j. sound vib. 296, 979–999. srinivas, s., rao, a.k. (1970). bending, vibration and buckling of simply supported thick orthotropic rectangular plates and laminates, int. j. solids struct. 6, 1463–1481. thai, h.t., choi, d.h. (2011). a refined plate theory for functionally graded plates resting on elastic foundation. composites science and technology. 71, 1850–1858. . j. build. mater. struct. (2022) 9: 122-132 original article doi : 10.34118/jbms.v9i2.1772 issn 2353-0057, eissn : 2600-6936 fatigue behavior of damaged concrete beams repaired with composite material k. hadjazi 1,*, a. hamiani1, z. sereir1, s. amziane2 1 laboratoire de structures de composites et matériaux innovants, faculté de génie mécanique, université des sciences et de la technologie d’oran, bp 1505 el m’naouer, usto, oran, algérie. 2 université clermont auvergne, cnrs, inp clermont, institut pascal, f-63000 clermont-ferrand, france. * corresponding author: khamishadj@yahoo.fr received: 31-01-2022 accepted: 21-08-2022 abstract. by the present paper, an analytical model was developed to study the cracked frp-strengthened reinforced concrete beams subjected to fatigue loading. in order to follow the distribution of interfacial shear stresses causing the debonding phenomenon, a new analytical model based on the cohesive zone (cz) approach was developed. the present model has the possibility to describe the evolution of the shear stress in the three zones (elastic, microcrack and debonding) and the bearing capacity of the repaired structure. interface damage scenarios were evaluated for a fatigue load estimated to 90% of the elastic load and another at 60% of the ultimate load pu. results obtained are in good agreement with those given by the literature. the results showed that the shear strength developed by the repaired beam is sensitive to the variation of the mechanical properties (concrete, frp and adhesive layer), the fatigue load ratio and the number of cycles. these parameters can be considered as indicators of damage affecting the health status of the structure repaired during fatigue. the debonding at the frp-concrete interface noticeably reduced the strength and lifespan of the repaired structure. key words: frp/concrete, crack, repair, fatigue, cz model, shear stresses, debonding. 1. introduction in order to preserve the existing structures and not to resort to the manufacture of new buildings, the recourse to the repair of constructions degraded by their aging, proves to be an effective solution. for this reason, new and innovative methods must therefore be developed, including the technique of rehabilitation of structures by adding bonded composite reinforcements. this technique constitutes a rapid and economical solution for consulting engineers to a growing need for repairing aging or damaged structures. however, and despite the many advantages offered by composite materials (a good resistance in terms of service life of rc structures reinforced under cyclic loading), their adaptations to reinforcement applications reveal many problems, (wu et al., 2003; diab et al., 2009). the major problem in this technique is the debonding of the material edge by fatigue or creep loads caused by the sliding between the frp plate and the concrete beam. this phenomenon creates the great interface shear stresses developed during this loading. in this context, several authors have proposed an analytical method to solve static and dynamic separation problems in frp reinforced concrete beams (tounsi, 2006; wang, 2006; bennegadi et al., 2016; houachine et al., 2022). among the tools most used in the literature to study the fatigue behavior of adhesively bonded joints in structural applications is the cohesive zone model (czm) approach (rezazadeh and carvelli, 2018; ghovanlou et al., 2014). this model relates the stresses to the displacement through an interface where the crack can be created. in order to identify the problem of the cracks propagation at the interface, (hadjazi et al., 2012 and 2016) have developed an analytical model to describe the behavior of the frp-to-concrete bonded interfaces during the short and long term. (wahab et al., 2012; wahab et al., 2015) proposed an analytical model to predict the interfacial stress distribution and the fatigue life of rc beams mailto:khamishadj@yahoo.fr hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 123 strengthened with frp plate under fatigue loads. in recent years, the application of the czm has been extended to fatigue damage evolution analysis in the repair applications especially at frp-toconcrete bonded interface. in this purpose, damage parameters are introduced into the czm to quantify the degradation of the interfacial stiffness and strength under cyclic loading (xinyan et al., 2019; johar et al., 2014). (roe and siegmund, 2003) used the damage mechanics concept into the czm and developed a damage evolution model. (xuan and vormwald, 2013) proposed a czm to describe the fatigue damage process. for fatigue models applied to structures reinforced with prestressed frps, (oudah and el-hacha, 2013) presented a model taking into account the degradation of material properties (concrete and epoxy-concrete) under cyclic loading. (chen and cheng, 2016) developed an analytical model to evaluate the shear stresses distribution of the frpconcrete interface under fatigue load. based on the above papers, the present study aims to estimate the behavior of cracked frp-strengthened reinforced concrete beams under cyclic loads. the purpose of this work is to highlight an analytical model that addresses the interface problems between the cracked concrete beam repaired by a composite plate under fatigue load using czm. the proposed model gives the shear stresses distribution in three zones (elastic, microcrack, debonding zone) near the crack and the bearing capacity of the repaired structure. a fatigue life prediction was also presented to capture the fatigue life of reinforced concrete (rc) structures. finally, a parametric study was carried out to test the sensitivity of our model to the variation in the number of cycles and load level on the fatigue behavior of frp-to-concrete interface. 2. czm for fatigue life prediction of rc beam strengthened with frp 2.1 performance degradation of concrete under fatigue loading under cyclic loading, the elastic modulus of concrete beam decrease versus the loading cycle number. due to the internal damage accumulation of concrete, several research (xinyan et al., 2019; sherif et al., 2001) showed that the elastic modulus of concrete (e1,n) varied continuously under the effect of the fatigue load. this variation is given by: 1, 1 1 0.33 n f n e e n          (1) where, e1 is the initial young's modulus of the concrete beam, n is the number of cycles and nf is the number of accumulated load cycles to concrete failure. in addition, the maximum compressive stress of concrete (σci) can be given by (wu, 2003): 0.9885 0.0618 lg ci c c f f f n   (2) where, fc is the uniaxial compressive strength. 2.2. performance degradation of frp plate under fatigue loading in order to evaluate the fatigue degradation of the frp plate mechanical properties, (bigaud and ali, 2014) proposed a simplified expression to predict the effective elasticity modulus of the frp plate versus the number of cycles n, as follows: 2 2 10 ( ) (1 0.071 log ( ))e n e n  (3) with, e2 is the initial young's modulus of the frp plate. 2.3. performance degradation of the interface under fatigue loading the cumulative damage of frp-to-concrete interface during the fatigue process is quantified in terms of a damage parameter. the fatigue damage accumulation of the interface was defined by, (johar et al., 2014): 1 b d n cyc   (4) 124 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 from (johar et al., 2014), the degradation of initial elastic stiffness at the interface, kn, can be estimated by:  0 1n n cyck k d    (5) where, kn=0 is the interface stiffness during the loading process at n=0. b is a constant determined experimentally. 3. analytical czm for fatigue behavior to evaluate the accuracy of the proposed model, a simply supported concrete beam, cracked at mid-span and strengthened by a composite material, was analyzed. the retrofitted beam is made by: concrete, adhesive layer and frp reinforcement. the concrete beam strengthened by frp plate is subjected to fatigue three point loads with a flexural pre-crack at mid-span (figure 1, a). the geometry of the plated beam is similar to that proposed by (wang, 2006; and wang and zhang, 2008; hadjazi et al., 2016). the subscripts 1 and 2 denote the concrete beam and the frp plate, respectively. fig 1. composite-plate rc beam with a mid-span crack. figure 1, c, shows a section of the forces in infinitesimal element of a frp-plated reinforced concrete (rc) beam. in this figure q, n and m are the shear force, the horizontal axial force and couple moment, respectively. using elasticity laws, the axial forces ni and bending moments mi for these two beams (i = 1, 2) read: , 2 , 2 i i i n i i i i n i du n e a dx d w m e i dx    (6) where ui and wi are the axial and vertical displacements of beam i (i = 1, 2), respectively. ai=bihi, ei,n, bi, hi and ii are cross section of beam i, young’s modulus of beam i , width and height of beam i and the moment of inertia of the beam i (i = 1, 2) , respectively considering a typical infinitesimal isolated body as shown in figure 1,c, the equilibrium equations on axial direction and bending moment are given by: 1 1 dn b dx  (7) 2 2 dn b dx   (8) 1 2 2 1 2 ( ) a m m m n y y h     (9) ha p l1 l2 b1 h1 h2 b2 a1 (b) (a) (c) τ σ m2+δm2 n2+δn2 q2+δq2 q2 n2 m2 y2 m τ σ m1+δm1 n1+δn 1 q1+δq1 τ τ q1 n1 m1 y1 a1 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 125 τ is the interface shear stress. y1 and y2 are the distances from the bottom of adherent 1 and the top of adherent 2 to their centroids respectively. if the depth of the crack is known, the rotational stiffness of the spring kr is given as (paipetis and dimarogonas, 1986):   1 1 1, 1,r nk c a h e i (10) where a1 is the depth of the crack, for a1 < 0.6h1, c(a1, h1) is given by (paipetis and dimarogonas, 1986). base on the concept of czm in static loading, a new concept of the czm is presented for a fatigue cyclic loading. the analytical model is based on the progressive degradation of czm parameters of concrete and frp plate as the number of cycles increased until the debonding initiates and grows along the interface frp-concrete. for that, a bilinear traction-separation law is supposed for simplicity to adequately describe the cohesive behavior of the adhesive joint interface and the fatigue behavior of rc beam strengthened by frp. from figure 2, all czm parameters are expected to degrade under cyclic loading. fig 2. cyclic degradation of frp-concrete interface, (johar et al., 2014). the use of the czm (figure 2) aims to analyze the separation of the interface and to determine the bearing capacity of the beam repaired by a nonlinear method. therefore, during the loading phase, the nonlinear relationship (dai et al., 2005; attari et al., 2010) adopted can be described by the following equations set:   1 1 1 1 0 0 n f n f f f f f elastic zone softening zone debonding zone                                (11) where, n f  and δf are the interfacial bond strength and the separation slip for the fatigue loading. the separation of the interface δ in the shear directions under cyclic loading is given by (wang, 2006; hadjazi et al., 2012): 1 2 1 1 2 2 w w u y u y x x          (12) as the number of cycles increased, the slip along the interface δ, become: 126 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 1n n       (13) where δn and δn+1 are the slip along the interface under fatigue loading at n and n+1 cycle, respectively. the area under the traction-relative displacement curve is the fracture energy n c g written as: 1 2 n n c f f g   (14) using the czm, the fatigue behavior of concrete beams reinforced by frp plate for these three stages is given as follows. 3.1. elastic zone in this zone, the distribution of interfacial shear stresses is given by substituting eq. (12) into the first equation of eq. (11). 2 2 1 1 2 2 1 22 2 1 n f u w u w y y x x x x x                   (15) substituting eq. (6) into eq. (15), we have: 2 2 1 2 1 2 1 22 2 1 1, 1 2, 2 n f n n n n d w d wd y y dx e a e a dx dx             (16) according to the literature (hadjazi et al., 2012; rasheed and pervaiz, 2002), the frp plate and the concrete beam have the same curvature, i.e. 2 2 1 2 2 2 w w x x      (17) substituting eq. (17) and eq. (6) into eq. (9), eq. (16) becomes:   1 2 1 2 1 2 2 1 1, 1 2, 2 1, 1 2, 2 n f a n n n n n n y yd m y y h n dx e a e a e i e i               (18) differentiating both sides of eq. (18) and considering equilibrium eqs. (7)–(8) we obtain:  2 1 2 1 2 1 2 22 1, 1 2, 2 1, 1 2, 2 1, 1 2, 2 ( )1 1 an n n n n n n n y y y y h y yd k b k m dx e a e a e i e i e i e i                        (19) with: 1 2 n n  and 1 / n n f k   the differential equation of the second order (19) takes the solution: 1 1x x c ae be         (20) τc: is the particular solution, where: 1 n c k    c c m    1 2 1 2 2 1, 1 2, 2 1, 1 2, 2 ( )( )1 1 a n n n n y y h y y c b e a e a e i e i            (21) hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 127   1 2 2 1, 1 2, 2n n y y c e i e i c      when x is sufficient large, shear stress is limited and converges to its particular solution τc so b=0, (wang and qiao, 2004). to determine the value of a, displacement boundary condition at x = 0 is used. the corresponding slip δ along the interface in elastic stage can be easily obtained by substituting eq. (20) into the first equation of eq. (11).  11 xn cn f ae        (22) 3.2. elastic-microcrack zone for loading and unloading conditions, the substrates deform. a part of the interface begins to soften and two regions along the interface are formed: a) in the linearly elastic region (n1), the solution of shear stress has the same form as in eq. (20) with the same condition of b1 = 0.  1 1 1 x a c a e        (23) the coefficient a1 is obtained by the following boundary condition at x = a1. from the eq. 11 and eq. (23), the slip δ along the interface for this region is given by:   1 11 1 x a cn f a e         (24) where a1 is the length of the microcrack zone. the coefficient a1 is obtained by the following boundary condition at x = a1 : 1 n fx a     (25) b) in the microcrack zone (1nf), the second bond-slip relation expression of eq. (11) and eqs. (6), (12) and (17) becomes:     2 1 2 1 2 2 1 2 2 22 1, 1 2, 2 1, 1 2, 2 1, 1 2, 2 1 1n n a n n n n n n y y y yd k y y h b k m dx e a e a e i e i e i e i                         (26) with: 2 1 n fn f k      the differential equation of the second order (26) takes the solution: 2 1 2 1 cos( ( )) sin( ( )) c c x a d x a        (27) from eqs. (11) and (27), the corresponding slip δ along the interface for this region is given by :   1 2 1 2 1cos( ( )) sin( ( )) f f c f c x a d x a                (28) where: 2 2 n c k    (29) the coefficients c and d are determined by continuous conditions at x = a1. as the number of cycles increased, the material is damaged gradually until the debonding at the frp-concrete interface. 128 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 3.3. elastic, microcrack and debonding zone in this section the three stages, elastic, microcrack and debonding zone are considered. the shear stress for each stage is given by:  elastic zone: 1 ( ) 1 ux d a c a e         (30)  microcrack zone: 2 2 cos( ( )) sin( ( )) u u c c x d a d x d a          (31)  debonding zone: 0  (32) 4. results and discussion in the present section, results are presented and discussed in terms of stress distribution in the interface, progressive interface damage accumulation and bearing capacity of repaired structure. for all applications, mechanical and geometrical characteristics given in tables 1 and 2 are the same as those used by (hadjazi et al., 2016; wu, 2003). table1: mechanical properties of frp plate-concrete for n=0. e1 [gpa] e2 [gpa] f n=0 [mpa] kn=0 [mpa/mm] gfn=0 [n/mm] fc [mpa] 25 230 1.8 160 0.5 20-80 table2: geometrical properties of frp plate-concrete. l [mm] l1 [mm] h1 [mm] h2 [mm] ha [mm] b1 [mm] b2 [mm] ba [mm] c(a1, h1) 750 700 150 0.11 0.1 100 100 100 0.0001167 the frp-strengthened reinforced concrete beams was subjected to repeated fatigue loading, with constant amplitude. figure 3 shows the cyclic loading with a positive stress ratio. fig 3. loading and unloading condition to provide the fatigue resistance of the repaired concrete beam, the evolution of shear stress at the adhesive interface throughout the applied fatigue cycles is illustrated in figure 4. under fatigue loading, the evolution of shear stress is caused by both degradation of concrete beam and the frp plate. near the flexural crack tip, the increase of fatigue cycles has a significant effect on shear stress evolution, particularly at the microcrack zone until full debonding initiates (at n≈106 cycles). we deduced that, the increase in the fatigue cycles affect significantly the distribution of shear stress along the interface between frp and concrete and debonding growth. hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 129 0 25 50 75 100 125 150 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 in te rf a c ia l s h e a r s tr e ss [ m p a ] x [mm] static model of hadjazi, 2012 n=10 3 cycles n=10 4 cycles n=10 5 cycles n=5*10 5 cycles n=10 6 cycles fig 4. fatigue load-interfacial shear stress. figure 5, examines the effect of cycles number (at failure) on the externally applied load evolution against the bond slip. it is clearly visible that an increase in the number of cycles generates a reduction in the fatigue capacity of the frp-concrete bond. this reduction is caused by the degradation of the mechanical performance of the concrete/frp plate. for fatigue loads close 24% of the ultimate static capacity, frp reinforced concrete beams often yield to 106 cycles. so, it is possible to predict the fatigue life of our repaired structure depending on the load level. both figures 6 and 7 represent the bond slip curves of frp-plate concrete beam for two load ratios (r = pmin/pmax). the r lower limit was set to 60% of pe and 30% of pu, (r=0.5). but, the r upper limit was set to 90% of pe and 60% of pu of the static bond capacity (r=0.66). where pe is the maximum value of static load applied to the beam without causing softening in the frp-concrete interface and pu is the ultimate static load (hadjazi et al., 2012), respectively. from both figures, we noticed that the variation of r changes remarkably the fatigue behavior of frp-concrete interface. 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0 2 4 6 8 10 12 14 f a ti g u e l o a d p [ k n ] bond slip at the interface [mm] static model of hadjazi, 2012 n=103cycles n=104cycles n=105cycles n=5*105cycles n=106cycles fig 5. fatigue response of interfacial bond slip. after a series of n cycles (figure 6), the bond slip at the interface is not reached because the interface still remains in the elastic zone. from figure 7, interface damage progression can be 130 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 separated into three stages; cracks initiation, damage accumulation and debonding stage. this damage development results from the degradation of the strength and the rigidity of the interface cfrp-concrete (3,5 104 cycles). in this regard, cyclic loading and r have the significant effects on the bond between frp materials and concrete. this causes a reduction in bond strength and an acceleration of bond deterioration as the cycle number increases. 0,00 0,02 0,04 0,06 0,08 0,10 0,0 0,2 0,4 0,6 0,8 1,0 . 60%pe f a ti g u e l o a d p [ k n ] bond slip at the interface [mm] 90%pe. 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0 2 4 6 8 10 12 . . pu 30% pu f a ti g u e l o a d p [ k n ] bond slip at the interface [mm] cyclic loading static loading hadjazi, 2012 60% pu. fig 6. fatigue response of interfacial bond slip for a loading ratio r = 0.66 fig 7. fatigue response of interfacial bond slip for a loading ratio r = 0.5 0 2 4 6 8 10 12 0,0 0,1 0,2 0,3 0,4 0,5 0,6 unstably increasing stably increasing rapid increasing d is p la c e m e n t [m m ] n [10 3 cycles] p max = 5 kn p max = 6 kn p max = 7 kn fig 8. curves of displacement-cycles under different loading level the relationships between the displacement (slip) and the number of loading cycles for cracked frp-strengthened reinforced concrete beams with different loading levels are presented in figure 8. from this figure, it's clearly visible that the fatigue behavior of the interface can be divided into three stages: the fast propagation, the stable propagation and the unstable propagation stage. in all three stages, the initiation and rupture time is very short. the stable propagation stage accounts for approximately 95% of the total fatigue life. it can also be seen that a higher load level causes greater damage. moreover, the service life of the retrofitted beam decreases with increasing loading level. hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 131 5. conclusion an analytical model based on the cohesive zone approach has been developed to predict the fatigue life of frp strengthened rc beam. the model considers the degradation of the concrete, interface and frp plate. this study predicted the fatigue life, interfacial shear stresses distribution, and load-bearing capacity of frp-repaired reinforced concrete beams. based on the results, the following conclusions were drawn:  the model is able to capture the evolution of interfacial shear stresses with increasing load cycles, and the number of load cycles to failure.  the cumulative damage of the interface increases with the number of loading cycles.  the cumulative damage growth rate of the interface became important with the increase of load level.  the service life and the bearing capacity of cracked frp-strengthened reinforced concrete beams decreases as the cyclic loading and load frequency increases. this decrease takes place due to the losses in the resistance and rigidity of the component materials. acknowledgments the author would like to acknowledge prof. sereir zouaoui, director of the laboratory for structures of composites and innovative materials and all members of the laboratory for their contribution. 6. references attari, n., amziane, s., & chemrouk, m. (2010). efficiency of beam–column joint strengthened by frp laminates. advanced composite materials, 19(2), 171-183. bennegadi, m. l., hadjazi, k., sereir, z., amziane, s., & el mahi, b. (2016). general cohesive zone model for prediction of interfacial stresses induced by intermediate flexural crack of frp-plated rc beams. engineering structures, 126, 147-157. bigaud, d., & ali, o. (2014). time-variant flexural reliability of rc beams with externally bonded cfrp under combined fatigue-corrosion actions. reliability engineering & system safety, 131, 257-270. chen, c., & cheng, l. (2016). theoretical solution to fatigue bond stress distribution of nsm frp reinforcement in concrete. composites part b: engineering, 99, 453-464. dai, j., ueda, t., & sato, y. (2005). development of the nonlinear bond stress-slip model of fiber reinforced plastics sheet-concrete interfaces with a simple method. journal of composites for construction, 9(1), 52-62. diab, h. m., wu, z., & iwashita, k. (2009). theoretical solution for fatigue debonding growth and fatigue life prediction of frp-concrete interfaces. advances in structural engineering, 12(6), 781-792. ghovanlou, m k., jahed, h., & khajepour, a. (2014). cohesive zone modeling of fatigue crack growth in brazed joints. engineering fracture mechanics, 120, 43-59. hadjazi, k., sereir, z., & amziane, s. (2012). cohesive zone model for the prediction of interfacial shear stresses in a composite-plate rc beam with an intermediate flexural crack. composite structures, 94(12), 3574-3582. hadjazi, k., sereir, z., & amziane, s. (2016). creep response of intermediate flexural cracking behavior of reinforced concrete beam strengthened with an externally bonded frp plate. international journal of solids and structures, 94, 196-205. houachine, h. r., sereir, z., & amziane, s. (2022). creep model for the long-term behaviour of combined cohesive-bridging model of frp–concrete interface debonding under axial loading. european journal of environmental and civil engineering, 26(12), 5594-5616. 132 hadjazi et al., j. build. mater. struct. (2022) 9: 122-132 johar, m., kosnan, m. s. e., & tamin, m. n. (2014). cyclic cohesive zone model for simulation of fatigue failure process in adhesive joints. in applied mechanics and materials (vol. 606, pp. 217-221). trans tech publications ltd. oudah, f., & el-hacha, r. (2013). analytical fatigue prediction model of rc beams strengthened in flexure using prestressed frp reinforcement. engineering structures, 46, 173-183. paipetis, a. s., dimarogonas, a. d. (1986). analytical methods in rotor dynamics. elsevier applied science, london. rasheed, h. a., & pervaiz, s. (2002). bond slip analysis of fiber-reinforced polymer-strengthened beams. journal of engineering mechanics, 128(1), 78-86. rezazadeh, m., & carvelli, v. (2018). a damage model for high-cycle fatigue behavior of bond between frp bar and concrete. international journal of fatigue, 111, 101-111. roe, k. l., & siegmund, t. (2003). an irreversible cohesive zone model for interface fatigue crack growth simulation. engineering fracture mechanics, 70(2), 209-232. sherif el-tawil, ogunc, c., okeil, a., & shahawy, m. (2001). static and fatigue analyses of rc beams strengthened with cfrp laminates. journal of composites for construction, 5(4), 258-267. tounsi, a. (2006). improved theoretical solution for interfacial stresses in concrete beams strengthened with frp plate. international journal of solids and structures, 43(14-15), 4154-4174. wahab, n., soudki, k. a., & topper, t. (2012). experimental investigation of bond fatigue behavior of concrete beams strengthened with nsm prestressed cfrp rods. journal of composites for construction, 16(6), 684-692. wahab, n., topper, t., & soudki, k. a. (2015). modelling experimental bond fatigue failures of concrete beams strengthened with nsm cfrp rods. composites part b: engineering, 70, 113-121. wang, j. (2006). cohesive zone model of intermediate crack-induced debonding of frp-plated concrete beam. international journal of solids and structures, 43(21), 6630-6648. wang, j., & qiao, p. (2004). interface crack between two shear deformable elastic layers. journal of the mechanics and physics of solids, 52(4), 891-905. wang, j., & zhang, c. (2008). nonlinear fracture mechanics of flexural–shear crack induced debonding of frp strengthened concrete beams. international journal of solids and structures, 45(10), 2916-2936. wu, z., & yin, j. (2003). fracturing behaviors of frp-strengthened concrete structures. engineering fracture mechanics, 70(10), 1339-1355. wu, z., iwashita, k., ishikawa, t., hayashi, k., hanamori, n., higuchi, t., ... & ichiryu, t. (2003). fatigue performance of rc beams strengthened with externally prestressed pbo fiber sheets. in fibrereinforced polymer reinforcement for concrete structures: (in 2 volumes) (pp. 885-894). xinyan, g., wang, y., huang, p., & chen, z. (2019). finite element modeling for fatigue life prediction of rc beam strengthened with prestressed cfrp based on failure modes. composite structures, 226, 111289. xuan, c., & vormwald, m. (2013). application of a new cohesive zone model in low cycle fatigue. solids and structures, 2(3), 31-40.. j. build. mater. struct. (2015)2: 41-50 https://doi.org/10.34118/jbms.v2i2.19 issn 2353-0057 fresh and hardened properties of self-compacting concrete with different mineral additions and fibers haddadou n 1, chaid r2, ghernouti y2,*, adjou n1 and bouzoualegh m1 1 national center of studies and integrated research on building engineering (cnerib), cité nouvelle elmokrani, souidania, algiers, algeria. 2 research unit: materials, processes and environment (ur/mpe), university of boumerdes, cité frantz fanon, boumerdes, algeria. * corresponding author: y_ghernouti@yahoo.fr abstract. in this work, several reinforced self-compacting concretes were prepared by using three types of fibers made of steel, polypropylene and glass, and three different types of mineral additions (marble powder, metakaolin and limestone powder). the water to cement ratio was kept constant at 0.34 and fibers were used in combination, keeping the total fiber content constant at 60 kg/m3. slump flow diameter, l-box, stability and air content were performed to assess the fresh properties of the concrete. compressive strength, flexural strength, splitting tensile strength and ultrasonic pulse velocity of the concrete were determined for the hardened properties. noteworthy performances were generally obtained, particularly in hardened properties for the self-compacting concretes prepared with steel fibers in association with polypropylene fiber and marble powder as mineral addition. key words: self-compacting concrete, mineral additions, workability, fibers, hardened properties. 1. introduction self-compacting concrete (scc) was developed in japan in the late 1980’s. it is a new concrete which is fully compacted without external energy. scc has economic, social and environmental benefits over conventionally vibrated concrete. scc is made from the same basic constituents as conventional concrete but with the addition of high levels of superplasticizer admixtures and occasionally a viscosity modifying admixture to impart high workability. the cement (powder) content of scc is relatively high and the ratio of fine to coarse aggregates is more important than traditional concretes. fine fillers such as fly ash, silica fume, slag, metakaolin and marble powder may be used in addition to cement to increase the paste content. but, one of the disadvantages of scc is the cost, associated with the usage of chemical admixtures and the high volume of portland cement. one alternative to reduce the cost of scc is the usage of mineral additions which are finely divided materials added to concrete as separate ingredients either before or during mixing (moriconi and corinaldesi, 2005). the compactness of the scc matrix, due to the higher amount of fine and extra-fine particles, may improve interface zone properties (ding, 2010; 2011). nowadays, the ecological trend aims at limiting the use of natural raw materials in the field of building materials and hence there is an increased interest in the use of alternative materials (waste) from various industrial activities, which presents significant advantages in economic, energetic and environmental terms. the objective of this study is to assess the effects of mineral additions replacement on the fresh and hardened properties of sccs incorporating different fibers in combination. marble powder (mp) has been used as an important building material for centuries, especially for decorative purposes. during sawing, shaping, and polishing process, 25% of the processed marble turned into dust or powder form (alyamaç and ince, 2009).the use of mp in the concrete had not found adequate attention. corinaldesi et al. (2010) stated that since its high degree of fineness, mp was proved to be very effective in providing very good cohesiveness of mortar and concrete. even mailto:%20y_ghernouti@yahoo.fr 42 haddadou et al. j. build. mater. struct. (2015)2:41-50 though, the suitability of using such sub-standard mp in fiber-reinforced self-compacting concrete needs much detailed investigation. metakaolin (mk) is a pozzolanic material, obtained by dehydroxylation of kaolin (lamberov, 2012). in recent years mk was applied as mineral addition for preparation of scc. mk leads to improved mechanical properties and durability of the concrete. the particle size of mk is much fine than cement and prevent, the aggregation. furthermore, scc with participation of mp showed enhanced viscosity and workability (cassagnabère, 2013; rashad, 2013). limestone powder (lp) is widely applied for preparation of scc. when high volumes of lp are added to scc mixture, the required self-compacting properties are achieved at a lower water/binder ratio. the strength after 28 days is also increased, due to filler effect resulting in improved fine-particle packing with lp particles. partial substitution of cement with lp, leads to increasing slump flow, viscosity, and compressive strength at early ages. also lp reduces, the amount of used cement, which respectively influence at the price of prepared concrete (uysal and yilmaz, 2011; topcu, 2009). this paper covers some fresh and hardened properties of such mixtures. in addition to the mp, mk and lp are used; three different fibers were used in different proportions in making the concrete. the total mass of cementitious materials is 500 kg/m3, where 30% of cement is replaced by mineral addition. for comparison, a control scc mixture without fibers was also produced. the commercially available chemical admixtures used in this study included a viscosity modifying admixture (vma) and polycarboxylic based superplasticizer (sp). 2. experimental procedure 2.1. materials a 42.5 cem ii/a cement from m’sila factory is the type of binder used for making concretes for the purpose of the work undertaken and metakaolin (mk), limestone powder (lp) and marble powder (mp) were used as cementitious materials in the mix proportions. the chemical properties of cement, mk, lp and mp are given in table 1 whereas the mineralogical composition of cement is given in table 2. workability improvement of sccs was obtained thanks to the polycarboxylate superplasticizer (sp) medaflow 145 and the viscosity modifying admixture (vma) medacol bse. the properties of both admixtures, as provided by their manufactures, are shown in table 3. continuously graded coarse aggregates (3/8 and 8/15) were used with specific gravity and water absorption of 2.56 g/cm3 and 1.03% respectively. natural dune sand (ds) and river sand (rs) were used. selected sands are subjected to grain size distribution analysis as per xp p 18-540 standard (1997). the set of sieves are taken from 5mm to 0.063mm with aggregate and sieve shaker subjected to vibration for 15minutes. physical properties of used sands are given in table 4. the gradation of coarse and fine aggregates was determined by sieve analysis and presented in figure 1. different types of fibers were used, polypropylene fibers (p), steel fibers (s) and glass fibers (g) (figure 2). tap water was used to produce all mixtures. table 1. chemical properties of binders. element (%) cement mp mk lp sio2 16.80 0.48 73.60 0.7 al2o3 4.46 0.10 16.36 0.15 fe2o3 2.94 0.12 1.07 0.09 cao 58.83 54.54 0.39 54.42 mgo 1.68 0.72 0.16 1.22 so3 2.35 0.46 0.01 0.01 k2o2 0.60 0.01 4.56 0.01 na2o 0.03 0.01 3.22 0.13 p2o5 0.15 0.02 0.13 0.01 tio2 0.22 0.01 0.08 0.01 loss of ignition 11.74 43.53 0.43 43.24 haddadou et al. j. build. mater. struct. (2015)2:41-50 43 table 2. mineralogical composition of cement. element (%) c3s 56 c2s 20 c3a 5 c4af 13 table 3. properties of chemical admixture. table 4. properties of sands. fig 1. particle size distribution of coarse and fine aggregates. a) b) c) fig 2. fibers used for the production of rscc: a) polypropylene (p), b) steel (s) and c) glass (g). 2.2. mixture proportions numbers of attempts were made in laboratory to get optimum mix proportion to produce scc without segregation and bleeding with satisfying the properties both in fresh and hardened states. for this study totally twelve scc mixes were prepared with a constant water to binder ratio of 0.34 and with 1.7% of superplasticiser. four types of mixes were prepared with different binder contents, without fibers (scc) and with different type of fiber reinforcement (rscc). the chemical admixture specific gravity ph color recommended dosage (l/m3) main component sp 1.06 5.5 light brown 0.3 to 2 carboxylic ether aqueous dispersion of microscopic silica vma 1.03 6.2 light yellow 0.5 to 2 properties ds rs fineness modulus 1.29 2.85 sand equivalent (%) 48 90 absorption (%) 2.43 0.63 moisture content (%) 1 0.42 44 haddadou et al. j. build. mater. struct. (2015)2:41-50 prepared mixes were designated as, scc (scc30%mp, scc30%mk, scc30%lp), rscci (30%mp+ 60kg of steel fiber, 30%mp+ 60kg of steel fiber+ polypropylene, 30%mp+ 60kg of steel fiber+ glass fiber ), rsccii (30%mk+ 60kg of steel fiber, 30%mk+ 60kg of steel fiber+ polypropylene, 30%mk+ 60kg of steel fiber+ glass fiber ) and rscciii (30%lp+ 60kg of steel fiber, 30%lp+ 60kg of steel fiber+ polypropylene, 30%lp+ 60kg of steel fiber+ glass fiber ).the mix proportions are presented in table 5. the scc was mixed for 5 minutes in laboratory drum mixer. for all mixes, nine cube specimens of 150mm size were cast from each mix for compressive strength testing. six cylindrical specimens of 150mm diameter and 300mm height were also cast from each mix for determining the splitting tensile strength. before compression test, all specimens were tried and used for ultrasonic pulse velocity test. six prisms of 70*70*280mm were cast from each mix for flexural strength. after casting, all the specimens were left covered in the casting room for 24 hours. the specimens were demoulded and transferred to moist curing room until the time of testing. table 5. mix proportions. sccs quantities (kg/m3) cement mineral addition water fine aggregates coarse aggregates vma sp fibers rs ds s p g m1 scc-30%mp 350 150 170 173 610 790 1.45 7.9 0 0 0 m2 scc-30%mk 191 645 790 1.45 7.9 0 0 0 m3 scc-30%lp 202 706 790 1.45 8.5 0 0 0 m4 rscci-30%mp+s 586 245 717 1.45 8.5 60 0 0 m5 rscci-30%mp+s+p 586 245 717 1.45 8.5 59.4 0.6 0 m6 rscci-30%mp+s+g 586 245 717 1.45 8.5 54.4 0 5.6 m7 rsccii-30%mk+s 586 245 717 1.45 8.5 60 0 0 m8 rsccii-30%mk+s+p 586 245 717 1.45 8.5 59.4 0.6 0 m9 rsccii-30%mk+s+g 586 245 717 1.45 8.5 54.4 0 5.6 m10 rscciii-30%lp+s 586 245 717 1.45 8.5 60 0 0 m11 rscciii-30%lp+s+p 586 245 717 1.45 8.5 59.4 0.6 0 m12 rscciii-30%lp+s+g 586 245 717 1.45 8.5 54.4 0 5.6 2.2.1. preparation and casting of test specimens the mixing procedure and time are very important, thus the mixing process was kept constant for all concrete mixtures. the following mixing sequence was obtained after several trials for optimizing the workability. all the ingredients were first mixed under dry condition in the concrete mixer for one minute. then 70% of calculating amount of water was added to the dry mix and mixed thoroughly for one minute. the remaining 30% of water was mixed with the sp and vma and was poured into the mixer and mixed for five minutes (four minutes for 20% of the remaining water with sp and one minute for 10% of remaining water with the vma). later, required quantities of fibers were sprinkled over the concrete mix and mixed for one minute to get a uniform mix. thus, the total mixing time was 7 minutes. in this investigation, fresh properties were evaluated by the flowability (slump flow diameter), passing ability (l-box), air content and stability (sieve stability test) (efnarc, 2005), as represented in figure 3. workability tests slump flow test l-box test sieve stability test fig 3. fresh properties tests. haddadou et al. j. build. mater. struct. (2015)2:41-50 45 2.2.2. test on hardened concrete concrete specimens have been batched, moulded and cured according to afnor standard (en 12390-2, 2001). all the moulds were covered by plastic sheets and stored for 24 hours in the laboratory prior to demoulding; afterwards, they were cured in water at 20°c and at relative humidity (rh) in the order of 50–60%. a testing programme has been elaborated and consisted of determining the essential properties of hardened self-compacting concretes. the necessary test specimens have been cast in different moulds and three tests were carried out to assess each required characteristic. for the determination of compressive strength and ultrasonic pulse velocity concrete cubes of 150* 150* 150 mm3 were used (en 12390-3, 2001; en 12504-4, 2005). compressive strength was measured at 7, 28 and 56 days old using a testing machine with a maximum load capacity of 3000 kn. the splitting tensile strength and flexural strength was measured on 150*300 mm3 cylindrical and 70*70*280 mm3 specimens at 28 and 56 days, using a testing machine with a maximum load capacity of 100 kn. the average of three specimen properties at a particular age was considered as its property. 3. results and discussion 3.1. fresh concrete properties to classify a concrete as self-compacting, the requirements for filling and passing abilities as well as segregation resistance must be fulfilled in order to provide ease of flow in the presence of formwork or reinforcement and an ability to remain homogeneous in fresh state. it is specified that the filling ability and stability of scc in the fresh state can be defined by four key characteristics namely flowability, viscosity, passing ability, and segregation resistance (barr, 1996). fresh properties of the concretes were carried out according to the limitations specified by efnarc (2005). the results obtained of fresh properties are reported in table 6. as seen from this table, the fresh properties are in the range of 65.577 cm for the slump flow, 0.80-0.89 for the l-box ratio, 1.90-2.85% for air content of and 3.72-6.85% for the sieve stability. all concrete mixtures were considered as scc. in all scc mixtures, there was no segregation of aggregate near the edges of the spread-out concrete as observed from the slump flow test. table 6. fresh properties of self-compacting concretes. mix n° mix id slump flow (cm) air content (%) l-box ratio (%) sieve stability (%) m1 scc-30%mp 75 02.00 0.89 05.59 m2 scc-30%mk 68 01.90 0.84 06.65 m3 scc-30%lp 77 02.15 0.88 06.32 m4 rscci-30%mp+s 70.5 02.70 0.80 04.13 m5 rscci-30%mp+s+p 73 02.60 0.83 04.96 m6 rscci-30%mp+s+g 70 02.60 0.81 04.47 m7 rsccii-30%mk+s 65.5 02.14 0.79 03.85 m8 rsccii-30%mk+s+p 68.5 02.54 0.80 03.72 m9 rsccii-30%mk+s+g 69 02.85 0.80 03.87 m10 rscciii-30%lp+s 72 02.80 0.84 06.76 m11 rscciii-30%lp+s+p 69 02.23 0.81 06.01 m12 rscciii-30%lp+s+g 67 02.60 0.83 06.85 the comparison between scc, rscci, rsccii and rscciii a replacement of cement by mp have shown good slump values, therefore mp can be considered as limestone filler which is one of the materials that have extensively been studied in the literature (elkhadiri, 2002; petit and wirquin, 2010) and have improved the performances of concretes by providing more compact structure through its pore-filling effect. mp helps to evenly disperse aggregates during mixing 46 haddadou et al. j. build. mater. struct. (2015)2:41-50 but it needs more superplasticizer to improve a good flowability. although the angular shapes with rough surface texture of mp particle, it provide ball bearing effects and reduce internal friction in fresh concrete and these increase the flowability and compaction of the concrete. in other hand, using of mk has slightly affect workability measures in comparison with mp and lp. the fiber-matrix adhesion as well as geometry of the fiber affects pullout behavior of the fibers. mp, mk and lp help to evenly disperse fibers during mixing. mp and lp particles provide ball bearing effects and reduce internal friction in fresh concrete and these increase the flowability and compaction of the concrete. the fibers have also affected the fresh properties of the concrete mixtures. for the same workability, the addition of polypropylene and glass fibers did not affect the water requirement of rscc mixture with steel fibers. 3.1. hardened concrete properties to evaluate the effect of mineral additions and fibers on the hardened properties of studied scc mixtures, different tests are conducted (figure 4). the hardened concrete test results are presented in figures 5, 6, 7 and 8 which included the 7, 28 and 56 days for compressive strength, 28 and 56 days for flexural and splitting strength and ultrasonic pulse velocity at 56 days. compressive strength flexural strength split tensile strength ultrasonic pulse velocity (upv) fig 4. hardened properties tests. as seen from the obtained results, the most significant changes were observed respectively on the flexural strength, splitting tensile strength, compressive strength and lastly on the ultrasonic pulse velocities. compressive strengths of various concrete mixtures are given figure 5. the compressive strengths of sccs and rsccs were in the range of 22.68– 39.78 mpa from 7 days to 56 days. the binary use of cement with mineral addition increases the compressive strength of rsccs. however, replacement of cement with 30% of mp caused a reduction about 5 % in the compressive strength comparing to mk. conversely, this adverse effect of mp seemed to be remedied by the combined use of the mineral additions. interestingly, the concrete containing 30% mk achieved the highest compressive strength of all mixtures. therefore, the test results suggested that it was the mp, among the mineral additions used that governed the reduction in the compressive strength of the sccs mixtures. haddadou et al. j. build. mater. struct. (2015)2:41-50 47 0 5 10 15 20 25 30 35 40 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 7d 28d 56d c o m p re ss iv e st re ng ht (m p a) fig 5. compressive strength of sccs. results obtained for flexural strength (figure 6) showed the effectiveness of mineral additions in improving the flexural behavior of concrete (enhanced also by the presence of fibers). 0 1 2 3 4 5 6 7 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 28d 56d f le xu ra l s tr en gh t ( m p a) fig 6. flexural strength (mpa). splitting tensile strength (figure 7), seemed to be affected by the fibers and the effect of fiber hybridization can be observed on the obtained test results. highest splitting tensile strength obtained in m8 (polypropylene fiber in combination with steel fiber reinforced concrete) and in m7 (steel fibers reinforced concrete). it can be observed that all mixes containing fibers have splitting tensile strength greater than the control mix. the increasing of tensile strength in mixes containing steel fibers can be attributing to the properties of these fibers which make the concrete less brittle and more ductile. ultrasonic pulse velocity (upv) test results are presented in figure 8. it can be seen from this figure that the upv test values did not seem to be affected by the size of fibers in this research. 48 haddadou et al. j. build. mater. struct. (2015)2:41-50 however, the upv test could be used to assess the hardening of the scc mixtures. it is clear that as hydration continued, the upvs increased for all the sccs mixtures. the values of upv in this research were ranged from 4235 m/s to 4415 m/s. similar to the compressive strength, the concrete with 30% mk had the highest upv value. whitehurst (1951) classified the concrete quality according to upv values as excellent (4500 m/s and above), good (3500–4500 m/s), doubtful (3000–3500 m/s), poor (2000–3000 m/s) and very poor (2000 m/s). the concretes produced in this study have upv values greater than 3500 m/s and lower than 4500, so that the rating of the concretes was found to be good. 0 1 2 3 4 5 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 28 days 56 days s pl itt in g te n si le s tr e ng ht ( m p a) fig 7. splitting tensile strength (mpa). 0 1000 2000 3000 4000 5000 m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 u lt ra s o n ic p u ls v il o s it y ( m /s ) fig 8. ultrasonic pulse velocity (m/s). haddadou et al. j. build. mater. struct. (2015)2:41-50 49 4. conclusions an experimental programme has been undertaken to investigate the performance of selfcompacting concrete containing marble powder, limestone powder and metakaolin as a partial replacement of cement. steel, polypropylene and glass fibers are used to produce reinforced selfcompacting concrete. the following conclusions can be drawn from this study:  it was observed that for all fiber and mineral addition types and mixture proportions tested, there were no problems in mixing and the fiber distribution was uniform.  all mixtures tested in this study were able to attain 60 kg/m3 of steel, polypropylene and glass fibers without loss of flow and workability. it is important to note that all of volume fiber fractions used in reinforced mixtures exceeded the upper limits suggested by efnarc. although, all mixtures have good flowability and possessed self-compacting characteristics.  it was found that the flow behavior of hybrid fiber reinforced concrete differs from that of plain self-compacting concrete with 30% of mineral addition.  it was found that a considerable amount of hybrid fibers can allowed a good self compactability. in order to retain high level workability with fiber reinforcement, the amount of paste in the mix should be increased to provide better dispersion of fibers.  it is possible to produce hybrid fiber concretes using polypropylene fibers and glass fibers in combination with steel fibers, with an enhanced strengths compared to controlled concrete without fibers.  scc with steel and polypropylene hybrid fiber with metakaolin as mineral addition showed the high mechanical properties over reference concrete (m1, m2, m3) or single fibers and hybrid with glass fiber. 5. references alyamaç, k. e., & ince, r. (2009). a preliminary concrete mix design for scc with marble powders. construction and building materials, 23(3), 1201-1210. barr, b., gettu, r., al-oraimi, s. k. a., & bryars, l. s. (1996). toughness measurement—the need to think again. cement and concrete composites, 18(4), 281-297. cassagnabère, f., diederich, p., mouret, m., escadeillas, g., & lachemi, m. (2013). impact of metakaolin characteristics on the rheological properties of mortar in the fresh state. cement and concrete composites, 37, 95-107. corinaldesi, v., moriconi, g., & naik, t. r. (2010). characterization of marble powder for its use in mortar and concrete. construction and building materials, 24(1), 113-117. ding, y., you, z., & jalali, s. (2010). hybrid fiber influence on strength and toughness of rc beams. composite structures, 92(9), 2083-2089. ding, y., you, z., & jalali, s. (2011). the composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete. engineering structures, 33(1), 107-117. efnarc (2005). european guidelines for self-compacting concrete: specification, production and use. selfcompacting concrete, european project group. elkhadiri, i., diouri, a., boukhari, a., aride, j., & puertas, f. (2002). mechanical behaviour of various mortars made by combined fly ash and limestone in moroccan portland cement. cement and concrete research, 32(10), 1597-1603. en 12390-2 (2001). testing hardened concrete – part 2: making and curing specimens for strength tests. en 12390-3 (2001). testing hardened concrete – part 3: compressive strength of test specimens. en 12504-4 (2005). testing hardened concrete – part 4: ultrasonic pulse velocity of test specimens. 50 haddadou et al. j. build. mater. struct. (2015)2:41-50 lamberov, a. a., sitnikova, e. y., & abdulganeeva, a. s. (2012). kinetic features of phase transformation of kaolinite into metakaolinite for kaolin clays from different deposits. russian journal of applied chemistry, 85(6), 892-897. moriconi, g., & corinaldesi, v. (2005). rheological study of blended cement concrete. in proceeding: cement combinations for durable concrete, edited by dhir rk. harrison ta., newlands md. in the 6th int. congress on “global construction: ultimate concrete opportunities”. thomas telford, london, uk, pp. 211-218. petit, j. y., & wirquin, e. (2010). effect of limestone filler content and superplasticizer dosage on rheological parameters of highly flowable mortar under light pressure conditions. cement and concrete research, 40(2), 235-241. rashad, a. m. (2013). metakaolin as cementitious material: history, scours, production and composition–a comprehensive overview. construction and building materials, 41, 303-318. topcu, i. b., bilir, t., & uygunoğlu, t. (2009). effect of waste marble dust content as filler on properties of self-compacting concrete. construction and building materials, 23(5), 1947-1953. uysal, m., & yilmaz, k. (2011). effect of mineral admixtures on properties of self-compacting concrete. cement and concrete composites, 33(7), 771-776. whitehurst, e. a. (1951). soniscope tests concrete structures. in journal proceedings of american concrete institute, 47(2), 433-444. xp p 18-540 standard (1997). granulats: définitions, conformité, spécifications, association française de normalisation, paris, (in french). j. build. mater. struct. (2020) 7: 51-59 original article doi : 10.34118/jbms.v7i1.208 issn 2353-0057, eissn : 2600-6936 optimal seismic response using a passive tuned mass damper inerter (tmdi) djerouni s 1,*, ounis a 1 , athamnia b 2, charrouf me 1, abdeddaim m 1, djedoui n 1 1 department of civil engineering and hydraulics, mohamed khider university, biskra, algeria. 2 department of civil engineering ,, larbi tébessi university, tebessa, algeria. * corresponding author: djerouni100@gmail.com received: 29-01-2020 accepted: 10-04-2020 abstract. the latest earthquakes history shows that resistant conception, safe and economical structures are a daily challenge for structural engineers. among the newest vibration control devices figures the inerter which is a device which can develop a large fictive mass (it consists of a mass amplification effect) using rotational inertia. in this research work, the effectiveness of a traditional passive tuned mass damper (tmd) is compared with a tuned mass damper inerter (tmdi) which consists generally of tuned mass damper coupled with an inerter. both devices are used to control a base-isolated structure vibration submitted to several seismic records. in this study, a base-isolated structure of six stories (6 dof) was equipped with (tmd) and (tmdi) and a time history analysis were performed under different earthquake records (el centro, kobe, kocaeli). the mathematical model of the building is established in matlab simulink. the simulation results illustrated he robustness, performance and effectiveness of the structure equipped with a (tmdi). the dynamical parameters of interest were base and top displacement as well as the base shear force and peak inerter force produced. keywords: vibration control, hybrid system, passive system, tuned mass damper inerter, inertance, inerter. 1. introduction the research of an effective vibration suppression systems such as (passive, active, semi-active and hybrid ) has been a daily challenge in the civil engineering area, mainly for mitigating the dynamic vibration and decreasing the effects of the damage due to natural phenomena, such as earthquakes and winds or several excitations (brzeski et al., 2015). the base-isolated passive control can be used to reduce the buildings response. hence, achieve buildings protection from any natural damages (earthquakes, winds). therefore, the base-isolation is one of the oldest aseismic design strategies, based on decoupling the super-structure from the ground movement to decrease the effects of different excitations and to mitigate the forces being transmitted to the building from the ground for a natural frequency that is much longer than the fundamental frequency of the ground movement. on the other hand, a long natural frequency mostly produced in small ground acceleration, it will results in large displacement at the base-isolated ground (building’s move such as a rigid block). hence, lowering or reducing these large displacements is an essential problem or case to consider when base-isolated is adjacent to other buildings. further, to control base-isolated structure acceleration without producing a significant rise in displacement, supplemental seismic control strategies can be used (shi et al., 2018; djerouni et al., 2019). mailto:email@email.com 52 djerouni et al., j. build. mater. struct. (2020) 7: 51-59 the hybrid control is usually a result of two different control systems combinations, such as combining the structural base isolator with other devices such as mr damper, tmd, tld, tmdi, and tid. in recent years, the most common devices using in the hybrid control system are a tuned mass damper connection (tmd) at lowest or at roof with a base-isolated structure (tsai, 1995; hadi et al., 1998; palazzo and petti, 1999; djedoui and ounis, 2014; de domenico and ricciardi, 2018; elias and matsagar, 2018). the classic passive tuned mass damper (tmd) is one of the most effective, performance devices characterized by a linear damper, a mass, and a spring installed or attached in high-rise buildings at the roof usually (den hartog, 1929). furthermore, passive system tmds are centered on the rule of energy reduction in the nature of oscillation of the mass damper and the induction of mass inertial force in the opposite phase of the applied counter force to the building. in addition, the natural vibration mode of the classic tmd is tuned to the first natural vibration mode of the structure. however, as for example the skyscraper (taipei 101 in taiwan 508 meters) (fig 1) is equipped with 730 ton tmd acting like a large pendulum to counteract (counterforce opposing) the building's movement decreasing sway due to wind by 30 to 40%) (djerouni et al., 2019). fig 1. tmd giant pendulum installed at the top in taipei 101 (taiwan 508 meters) (bekdaş and nigdeli, 2011). the last recent research shows that an adequate hybrid control system can decrease the displacement generated using the base-isolated from (15 % to 25 %), a (tmd) mounted having a mass ratio offer of 5% less or more of the building total mass. a limitation about passive tmds is related to the (tmd) mass, which may be unbelievable large or big, thus needing a large space/clearance in the building to confirm the displacement request of this additional or supplemental mass, occasionally same overriding the maximum acceptable displacement of the base-isolated (de domenico and ricciardi, 2018; charrouf et al., 2019). in a try to overcome the weakness of both the base isolator and tmd, this paper uses a new small device namely “ inerter “ established with mass augmentation effect connected in passive (tmd) for enhancing the performance of this (tmd) with less mass. hence, this paper presents a combination of three (03) hybrid structures with different devices mounted on:  base isolated structure without any device (l1)  base isolated structure with tmd connected at the bottom (l2)  base isolated structure with tmdi connected at the bottom (l3) (using the same apparent mass or physical /weight of the tmd). djerouni et al., j. build. mater. struct. (2020) 7: 51-59 53 1.1. review of the tuned mass damper inerter (tmdi) the first suggestion to use an inerter was in the domain of racing car (formula 1 car’s) under name j-damper (fig 2) by pr. malcolm smith and his research team from cambridge university in 2002 (de domenico and ricciardi, 2018; charrouf et al., 2019). the perfect inerter is based on a mechanism system employing in a collective organization a rack, some gears, and pinions, connected to turning flywheels. this small device creates a large force resisting between its terminals, its force is proportional to the relative acceleration. after the successful use of an inerter in the domain of car racing, several numbers of studies on other possible applications of inerter in the structural system, buildings, vibration suppression were performed (hu and chen, 2015) . fig 2. ideal inerter with two poles (barredo et al., 2019). tuned mass damper inerter (tmdi) creates a conventional generalization passive tuned mass damper (tmd) mass, spring, damper, and inerter.tmdi getting the attention of the researcher (giaralis and taflanidis, 2015). in this last study, the tmd inerter enables beneficial in reducing vibration motion from earthquakes and winds that advantage dubbed inertance (the mass effect of tmdi) which can reach of size to 200 times higher than its apparent mass established (brzeski et al., 2015; giaralis and taflanidis, 2015; hu and chen, 2015; de domenico and ricciardi, 2018; charrouf et al., 2019; jia et al., 2019). 2. equation of motion using d’alembert’s law, the principal equations of combined motion n dof system are shown in equation (1), while,  x t ,  x t and  x t are the system displacement, velocity, and acceleration vectors, can be easily written in matrix form as follows (brzeski et al., 2015; giaralis and taflanidis, hu and chen, 2015; abdeddaim et al., 2018; de domenico and ricciardi, 2018; charrouf et al., 2019; jia et al., 2019):                 gm x t c x t k x t m x t     (1) where  m is the masse matrix,  k the stiffness matrix and  c the damping matrix of the structure. while the ground acceleration force distribution vector is expressed as    1 1 1 t   (2) 3. numerical study to demonstrate the performance, robustness, and adequacy of the novel passive tuned mass damper inerter, the three (03) structures (l1), (l2), (l3) (benchmark model) taken from paper deastra et al. (2018), presented above for combining the response of its (03) devices (baseisolated, base-isolated & tmd, base-isolated & tmdi) installed in mdof primary structure. the following (table1) shows the properties of the structure and base isolator used in his paper. otherwise, the tuning of the frequency of tmd & tmdi is tuned to the first frequency (first mode) of a base-isolated structure (l1). 54 djerouni et al., j. build. mater. struct. (2020) 7: 51-59 table 1. properties of the considered base isolator system and main structure (deastra et al., 2018). floor mass ( ton ) stiffness 103 (kn/m) damping (kn.s/m) 1 3.5 35 35 . 3.5 35 35 5 3.5 35 35 base-isolated 3.5 0.21 2.66 tmd and tmdi device tuning formulas for calculating and parameters shown in the following table (table 2). table 2. expressions for optimal tuning with tmd and tmdi for n dof structure (marian and giaralis, 2017). frequency ratio ( ) damping ratio(  ) force excited tmd  0 1 1   3( ) 8(1 )       force excited tmdi  0 fig 3. the (03) structures with several passive devices studies 4. results and discussion the system described in the previous section was considered. the structures are subjected to (el centro, kobe, kocaeli) normalized earthquakes records, with a pga of 0.3g. for the three structures (l1), (l2), (l3) proposed configurations, the tmd is tuned using the den hartog approach and the tmdi is tuned using marian and giaralis (2017) manner demonstrated in (table 2). different strategies were used and results were compared: the tmdi connected between the ground and the base-isolated in structure (l3) and tmd placed in the same position of tmdi in structure (l2) showed in previous (fig 3). the responses amount investigated are the maximum displacement of the last story and the first story, the maximum base shear and the peak force inerter between two poles. djerouni et al., j. build. mater. struct. (2020) 7: 51-59 55 in order to estimate the effectiveness of the hybrid system, a base-isolated structure with a tuned mass damper called (l2) and a base-isolated structure with tuned mass damper inerter called (l3) are compared with a conventional base-isolated structure called (l1) (benchmark model). the results in fig (4-7) show the top displacement, base displacement, maximum base shear, inerter force under (el centro, kobe, kocaeli) earthquakes near-field (nf) and far-field (ff). fig 4. maximum displacement of the last storey under el centro, kobe, kocaeli earthquakes fig 4, shows that top floor displacement in structure (l3) is smaller than in structure (l2). otherwise, in structure (l3) the tmdi gives maximal inertance values. the fact that the herein considered tmdis are better suited to suppress floor displacement rather than floor displacements, compared to the tmd. as can be seen from fig 4, the response mitigation in peak top floor displacement represents the reduction of (03) structures mentioned earlier (l1, l2, l3) in terms of inertance factor, noted with (l1) is 22,831 cm and (l2) is 19,087 cm and (l3) from 18,655 to 9,811 cm under el centro earthquake, also (l1) is 13,747 cm and (l2) is 11,853 cm and (l3) from 9,681 to 6,376 cm under kobe earthquake, while (l1) is 37,893 cm and (l2) is 29,767 cm and (l3) from 24,294 to 15,829 cm under kocaeli earthquake. fig 4, shows that the top floor displacement in structure (l3) is smaller than in structure (l2). accordingly, in structure (l3), the tmdi gives maximal and smaller inertance values respectively under el centro and kobe earthquake equal to 18,655 cm and 6,376 cm. 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 el centro d is p la c e m e n t a t to p i n [ c m ] inertance [%] l 1 l 2 l 3 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 l 1 l 2 l 3 kobe d is p la c e m e n t a t to p i n [ c m ] inertance [%] 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 l 1 l 2 l 3kocaeli d is p la c e m e n t a t to p i n [ c m ] inertance [%] 56 djerouni et al., j. build. mater. struct. (2020) 7: 51-59 from fig 5, the novel passive tmd inerter used in (l3) does much better than the passive conventional tmd used in (l2) in moderating the peak base floor displacement, improved peak base floor displacement mitigation is accomplished for relatively high inertance values. fig5. maximum displacement of the first storey under el centro, kobe, kocaeli earthquakes the fact that the herein considered tmdis is better suited to suppress floor displacement, compared to the tmd. as it can be seen from fig 5, the response reduction in peak base or bottom floor displacement, represents the reduction for the structures mentioned earlier (l1, l2, l3) in terms of inertance factor: noted (l1) is 22,492 cm and (l2) is 18,820 cm and (l3) from 18,417 to 9,686 cm under el centro earthquake, also (l1) is 13,543 cm and (l2) is 11,683 cm and (l3) from 9,544 to 6,292 cm under kobe earthquake, while (l1) is 37,332 cm and (l2) is 29,341 cm and (l3) from 23,940 to 15,621 cm under kocaeli earthquake. according to fig 5, the maximum base floor displacement in structure (l3) is reduced compared with other structures (l1) and (l2). consequently, the maximal and smaller inertance factor value are respectively obtained under kocaeli and kobe earthquake by a value equal to 37,233 cm and 6,292 cm. from fig 6, the response reduction in maximum base shear of the (03) buildings is about 52,020 [kn] by (l1), 43,151 [kn] by (l2), and increasing from 46,903 to 76,119 [kn] by (l3) for el centro earthquake. also, a reduction of about 29,607 [kn] by (l1), 25,628 [kn] by (l2), a reduction from 23,174 to 20,553 [kn] by (l3) for kobe earthquake. a reduction of about 78,368 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 el centro d is p la c e m e n t a t b a s e i n [ c m ] inertance [%] l1 l2 l3 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 l1 l2 l3 kobe d is p la c e m e n t a t b a s e i n [ c m ] inertance [%] 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 l1 l2 l3kocaeli d is p la c e m e n t a t b a s e i n [ c m ] inertance [%] djerouni et al., j. build. mater. struct. (2020) 7: 51-59 57 [kn] by (l1), 61,683 [kn] by (l2), a decrease from 50,998 to 35,187 [kn] by (l3) for kocaeli earthquake. according to fig 6, the results show an increase of the maximum base shear force in structure (l3) compared to the structure (l1) and structure (l2) by the maximum value equal to 78,368 [kn] under kobe earthquake. fig 6. maximum base shear under el centro, kobe, kocaeli earthquakes fig 7. peak force inerter under el centro, kobe, kocaeli earthquakes 0 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 l1 l2 l3el centro b a s e s h e a r [ k n ] inertance [%] 0 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 l1 l2 l3 kobe b a s e s h e a r [ k n ] inertance [%] 0 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 l1 l2 l3 kocaeli b a s e s h e a r [ k n ] inertance [%] 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 i n e r te r f o r c e [ k n ] inertance [%] el centro kobe kocaeli 58 djerouni et al., j. build. mater. struct. (2020) 7: 51-59 based on force equilibrium considerations, the above-discussed stroke reduction is readily attributed to the inerter force, applied to the attached mass. with this in the background, the peak inerter force is plotted as a function of the values of inertance ratio. it is seen that the inerter force rises quickly with the inertance factor against several earthquakes. where reach the force generated with inerter about 75 [kn] under the kocaeli earthquake. fig 7, presents the inerter force relative to the percentage of inertance (%). the inertance force takes the maximum value of inertance equal to 75 [kn] under the kocaeli earthquake (far-field) and smaller value equal to 67 [kn] under kobe (near-field) earthquake. 5. conclusions this paper deals with some novel configurations of a so-called tuned–mass-damper-inerter (tmdi) presented by authors to suppress the ground motion such as (base or force excited) placed in a structure combining an inerter device with a conventional tuned mass damper (tmd). • it is observed that the tmdi composed a simplification of the passive conventional tmd combining a mass amplification inerter device in a supplement to the spring and linear damper elements of the tmd to connect an attached mass to the main building structure. • the tmdi is more efficient using the same mass/weight of a traditional passive tmd to suppress vibrations near to the natural frequency of the base isolator structure. • the tmdi gives the possibility of being placed or connected in any floor or story in buildings compared to classical tmd, the last requirement always installed at the top or sometimes at the bottom of the building. • the novel passive tmdi outperforms the passive conventional tmd, for large values of inertance. • a new passive tmdi can attain the same field of performance as the conventional passive tmd for significantly less attached mass/weight; this performance is researched for all studied dynamical parameters. 6. references abdeddaim, m., kasar, a. a., & djedoui, n. (2018). seismic vibration control using a novel inerto-elastic damper. in matec web of conferences (vol. 211, p. 14003). edp sciences. barredo, e., larios, j. m., mayén, j., flores-hernández, a. a., colín, j., & montiel, m. a. (2019). optimal design for high-performance passive dynamic vibration absorbers under random vibration. engineering structures, 195, 469-489. bekdaş, g., & nigdeli, s. m. (2011). estimating optimum parameters of tuned mass dampers using harmony search. engineering structures, 33(9), 2716-2723. brzeski, p., kapitaniak, t., & perlikowski, p. (2015). novel type of tuned mass damper with inerter which enables changes of inertance. journal of sound and vibration, 349, 56-66. charrouf, m. e., djerouni, s., abdeddaim, m., djedoui, n., & ounis, a. (2019). combined control strategy for earthquake induced vibrations in structures. 4th eurasian conference on civil and environmental engineering (ecocee) lstanbul: 13. de domenico, d., & ricciardi, g. (2018). an enhanced base isolation system equipped with optimal tuned mass damper inerter (tmdi). earthquake engineering & structural dynamics, 47(5), 1169-1192. de domenico, d., & ricciardi, g. (2018). improving the dynamic performance of base‐isolated structures via tuned mass damper and inerter devices: a comparative study. structural control and health monitoring, 25(10), e2234. djerouni et al., j. build. mater. struct. (2020) 7: 51-59 59 deastra, p., wagg, d. j., & sims, n. d. (2018). the effect of a tuned-inerter-damper on the seismic response of base-isolated structures. in 16th european conference on earthquake engineering (pp. 18-21). sheffield. den hartog, j. p. (1929). mechanical vibrations in penstocks of hydraulic turbine installations. transactions of asme, 101-110. djedoui, n., & ounis, a. (2014). tuned mass damper for base isolated structures. sciences & technologie. b, sciences de l'ingénieur, (40), 29-34. djerouni, s., charrouf, m. e., abdeddaim, m., djedoui, n., & ounis, a. (2019). optimization of the seismic response of buildings with hybrid control using tuned mass damper (tmd) and base isolation. the first international conference on materials, environment, mechanical and industrial systems, icmemis’19, djelfa, algeria. elias, s., & matsagar, v. (2018). wind response control of tall buildings with a tuned mass damper. journal of building engineering, 15, 51-60. giaralis, a., & taflanidis, a. a. (2015). reliability-based design of tuned mass-damper-inerter (tmdi) equipped multi-storey frame buildings under seismic excitation. in 12th international conference on applications of statistics and probability in civil engineering, icasp 2015. university of british columbia library. hadi, m. n., & arfiadi, y. (1998). optimum design of absorber for mdof structures. journal of structural engineering, 124(11), 1272-1280. hu, y., & chen, m. z. (2015). performance evaluation for inerter-based dynamic vibration absorbers. international journal of mechanical sciences, 99, 297-307. jia, y., li, l., wang, c., lu, z., & zhang, r. (2019). a novel shape memory alloy damping inerter for vibration mitigation. smart materials and structures, 28(11), 115002. marian, l., & giaralis, a. (2017). the tuned mass-damper-inerter for harmonic vibrations suppression, attached mass reduction, and energy harvesting. smart structures and systems, 19(6), 665-678. palazzo, b., & petti, l. (1999). combined control strategy: base isolation and tuned mass damping. iset journal of earthquake technology, 36(2-4), 121-137. shi, y., saburi, k., & nakashima, m. (2018). second‐mode tuned mass dampers in base‐isolated structures for reduction of floor acceleration. earthquake engineering & structural dynamics, 47(12), 25192538. tsai, h. c. (1995). the effect of tuned-mass dampers on the seismic response of base-isolated structures. international journal of solids and structures, 32(8-9), 1195-1210. j. build. mater. struct. (2022) 9: 150-157 original article doi : 10.34118/jbms.v9i2.2797 issn 2353-0057, eissn : 2600-6936 properties of construction material based-diss fibers: physicomechanical characterisation i. zaid 1, 2, m. merzoud 1, a. benazzouk 2,* 1 laboratory of innovative technologies (ur-upjv 3899), university of picardie jules verne, amiens, france. 2 laboratory of civil engineering, university badji mokhtar, annaba, algeria. * corresponding author: amar.benazzouk@u-picardie.fr received: 21-09-2022 accepted: 23-12-2022 abstract. in the building sector, issues related to sustainable development have become a major concern. the choice of materials has fundamental importance since it has a considerable influence on the energy consumption of the building and also on the overall environmental impact of the construction. materials reinforced with vegetable fibres and/or particles are currently considered amongst the most promising materials in sustainable engineering technologies due to their several potential applications. in addition to its sustainable credentials, the application of these elements is interesting as they exhibit a set of important advantages, such as wide availability at relatively low cost, bio-renewability, ability to be recycled, biodegradability, non-hazardous nature, zero carbon footprint, and interesting hygro-thermal and mechanical properties. the viability of using vegetable diss fibers for developing a sustainable lightweight construction material was investigated in this paper. the produced specimen contained 4/1 volume ratio of diss fibers to binder. in order to mitigate the inhibitory effect exerted by vegetable materials on binder hydration, diss fibers were treated with hot water, while air lime-based tradical pf70 binder has been selected to replace traditionally used cementitious binder. the study conducted on hardened material properties has indicated that despite a significant reduction in mechanical strength, the material exhibits higher residual stress that highlighted a ductile behaviour, compared to the reference specimen containing neat binder without diss fibers. key words: diss fibers, composite, physico-mechanical properties, ductility, brittleness index. 1. introduction in recent years, the building sector has been marked by a general awareness of the need to limit the impact of the materials used on the environment. to achieve this objective, both economic and environmental restrictions should be taken in consideration, which encourage the integration of the "sustainable development" concept in the choice of materials. in this context, the building sector must therefore work to convert its constructive practices and to offer innovative materials that meet the new requirements of users and legislation in terms of environmental and health impact, and comfort. in this context, innovative building solutions for conserving non-renewable resources have motivated extensive research to develop sustainable building materials based on easily renewable natural raw material resources. there is a growing interest in the utilisation of vegetable materials as aggregates and/or fibers reinforcement into lightweight composites called "green" composites/concretes for sustainable constructions. however, various types of vegetable wastes (flax, hemp, coir, jute, bamboo, palm, kenaf, diss…), after being processed, have been used in particles form as replacement of sand and aggregates in concrete and mortars (elfordy et al., (2008), gavrilescu et al., (2009), pereira et al., (2019), sassoni et al., (2014). due to their many advantageous properties as their eco-friendly and economical characteristics, vegetable materials http://www.oasis-pubs.com/ mailto:amar.benazzouk@u-picardie.fr i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 151 can adequately replace mineral aggregates in construction field. these materials exhibit a high insulation capacity associated to a low density, and provide healthy living solutions, thanks to the vegetable materials ability to regulate humidity inside buildings by absorbing and/or releasing water, depending on the air conditions (ardanuy et al., (2015), barra et al., (2012). although all the mentioned advantages, the production of specimen materials reinforced with vegetable particles is limited by their long-term durability. the degradation problem is associated with an increase in vegetable materials fracture due to a combination of their weakening by alkali attack, related to their both mineralization and high-water absorption (ruth & ranyl, (2010), de bruijn et al., (2009). this causes the material to have a reduction in post-cracking strength and toughness. the role of vegetable materials as reinforcement lies in the proper interfacial bond between the particles and the matrix as well as to ensure the durability of the specimen. to enhance the performances of vegetable particles, several approaches have been studied including particles impregnation with blocking agent and water-repellent agent, sealing of the matrix pores system, reduction of the matrix alkalinity, and combination of particles impregnation and matrix modification (karade, (2010), mohr et al., (2005), daher et al., (2018). the main objective of this work was to investigate the potential use of diss fibres as reinforcement additives in tradical pf70 hydraulic binder, within the scope of providing an alternative solution to an environmental approach. the diss fibres are added at a volume ratio of 4:1 to preformulated tradical pf70based-binder. in order to mitigate the inhibitory effect exerted by vegetable particles on hydration reaction of binder, due alkali-dissolved components, the diss fibers were treated with hot water. the effect of diss fibers has been assessed by means of mechanical properties, such as compressive and flexural strengths, cracking behavior, and brittleness index. 2. materials and experimental testing 2.1. materials and specimen production the binder used in this study consists of a preformulated mixture of 75% air lime, 10% hydraulic lime, and 15% of pozzolan, and called "tradical pf70". the binder material is produced by lhoist industry (bcb, (2015), which is located in the northern region of france. the diss (ampélodesmos mauritanicus, from poaceae family) is a very widespread grass in north africa and the dry regions of greece to spain. because of its fibrous nature, diss fibers contain a high amount of silica in the amorphous state, which highlight a high tensile strength. in order to overcome the inhibitory effect excreted on hydraulic binder, the diss fibers were boiled with hot water to ensure the dissolved components partial extraction that affect the hydration reaction of binder. after treatment, the diss fibers were dried in an oven drying, converted into fibers and then sieved with a maximum length of 1 cm. figure 1 shows the shapes of natural plant of diss and derived fibers after drying and crushing. the properties of treated diss fibers are listed in table 1. table 1. properties of treated diss fibers bulk density (kg/m3) absolute density (kg/m3) porosity (%) water absorption (%) 47 1380.5 97 290 152 i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 fig. 1. shape of plant (a) and derived treated diss fibers (b) the control specimen consists of a neat binder without diss fibers, with total mixing water to binder ratio of 0.6. tradical binder and mixing water were initially mixed for 2 minutes in a planetary mixer. the vegetable diss fibers were then uniformly dispersed with slow increment throughout the binder and the fresh materials were allowed to mix for three additional minutes. at the end of this stage, the fresh material was cast into cylindrical (110 x 220 mm) and prismatic (40 x 40 x 160 mm) samples. all specimens were well compacted on a vibrating table and moistcured for 28-days at 20 ± 2 °c and 98 % relative humidity, before testing. the specimen mixes and their designations are shown in table 2. table 2. composition-mixes and i.d of specimens material specimen-id ts 1 tds 2 tradical binder (m3) 1 0 diss fibers (m3) 1 4 water/binder ratio (in mass) 0.6 0.7 1 control specimen (neat tradical binder) ; 2 tradical diss specimen (with 4 volumes of diss fibers) 2.2. experimental testing the 28-days properties tested on the hardened specimens included dry unit weight, as determined by means geometrical measurement and weighting. the compressive and flexural strength-tests were conducted according to the european standard en 196-1 (afnor, (1995)). the compressive strength-tests were carried out on (110 x 220 mm) cylindrical samples, using an electromechanical testing machine shimadzu ag-ic model with a maximum load capacity of 250 kn and a constant rate of 4 mm/min (fig. 2a). the compressive stress-strain diagrams were recorded to evaluate the variation of ultimate strain, elastic modulus, and ductile and/or brittle nature of the specimens. the three-point bending flexural-tests are performed on (40 x 40 x 160 mm) prismatic samples. the electromechanical testing machine tinius olsen h50ks type was used with a load cell capacity of 50 kn and 0.4 mm/min of loading rate (fig. 2b). the load-deflection diagrams were recorded to evaluate several parameters such us flexural strength, ultimate deflection at peak load, elastic modulus of rupture, and ductile and/or brittle nature of the specimens through the brittleness index (ib), as evaluated by eq. 1. the correspondent schematic diagram of load-deflection is shown in fig. 3 (consoli et al., (2002). if (ib) tends to 1, the specimen is brittle, while (ib) tends to 0, the specimen exhibited a ductile behavior. a b i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 153 fig. 2. mechanical-test machines. (a): compressive-test ; (b): flexural-test ib = 1fres fmax (1) fig. 3. brittleness index-value determination 3. results and discussion 3.1. compressive strength of reinforced specimens the 28-days stress-strain curves of specimens are shown in fig. 4. the results indicated that the addition of diss fibers serves to decrease compressive strength from 6.7 mpa, for control specimen, to 2.8 mpa for specimen containing diss fibers. it corresponds to reduction of approximately 58 %. the decrease in strength is related to the mechanical properties of diss materials since they are less stiff than the surrounding hydraulic binder. the roughness surface of fibers may be the important limiting factor that leads to interfacial bond defects between particles and matrix. it is assumed that mechanical strength of specimen is opposite to its unit weight. in addition, the decrease in compressive strength is related to porous structure of specimen. the 28-days parameter-values derived from compressive-test are shown in table 3. the corresponding elastic modulus-value varied from 962 to 57.2 mpa when diss fibers were added. however, the results also highlighted the ductile failure of the specimen-based diss materials that exhibits high plastic phase and underwent significant displacement before fracture. the correspondent ultimate strain-value varied from 7.22 mm/m, for control specimen, to 145.21 mm/m for tds sample. fig. 5 shows the failure shape of diss fibers-reinforced specimen a b cylindrical specimen load sensor prismatic specimen 154 i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 after ultimate fracture. it indicates a large difference in ductility between the control specimen (ts) which exhibited a brittle failure and shattered into small pieces, when it reached the peak load. the addition of diss fibers changes the brittle behavior while the specimen experienced a more ductile failure. however, the specimen was able to sustain loads after reaching its ultimate capacity. in addition, a high packing in the area subjected to loading has been observed. fig. 4. stress-strain diagram of specimens under compressive test table 3. 28-days parameter-values of specimens under compressive test specimen-id compressive strength (mpa) ultimate strain (mm/m) elastic modulus (mpa) ts 6.7 ± 0.2 7.22 ± 1.0 962.0 ± 10 tds 2.8 ± 0.4 145.21 ± 10 57.2 ± 15 ts sample tds sample fig. 5. specimen shapes after failure under compressive-test 3.2. flexural strength of reinforced specimens the 28-days load-deflection response of specimens submitted to flexural-test is shown in fig. 6. a reduction in flexural strength was observed when diss fibers were added. value decreased from 1 mpa, for reference specimen (ts), to 1.05 mpa for tds sample with 4 volumes of vegetable fibers. the value corresponds to reduction of up to approximately 50 %. this finding suggests that both mechanical properties of vegetable materials and sample’s porous structure lead to decrease the mechanical strengths of specimen. results also indicated that the decrease in flexural strength 0 1 2 3 4 5 6 7 8 0 25 50 75 100 125 150 175 200 s tr e ss ( m p a ) strain (mm/m) ts tds i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 155 is lower than that observed in compressive strength, probably due to the dilution effect of diss fibers.it is considered that the tension effect of the fibers occurs during the diffuse micro-cracking phase of "bending" the active micro-cracks and then in delaying the onset of their appearance, which serves to improve material flexibility. this could also explained by the capability of fibers to bridge the cracks and lead to limit their progression in the matrix. this bridging effect makes the diss reinforcement specimen ductile behavior which exhibited brittleness index ib-value of 0.4, while control specimen showed a value of 1. the corresponding parameters, reported in table 4, show an increase in deflection with diss fibers addition. the variation of elastic modulus confirmed this tendency with decreasing the corresponding value. fig. 7 shows the shape of specimens after failure under flexion-test. the bridging action of diss fibers during the flexural loading for tds sample was observed. unlike the control specimen, the reinforced sample retains its structure and the crack lips remain linked by the fibers. the presence of fibers allows the better control of cracks propagation which thus results in delaying of the rupture phase. fig. 6. load-deflection diagram of specimens under flexural test table 4. 28-days parameter-values of specimens under flexural test specimen-id specimen-id ts tds max. load (n) 346 ± 15 184 ± 20 residual load (n) 0.0 ± 0.2 107.5 ± 20 max. stress (mpa) 1.05 ± 0.1 0.52 ± 0.2 ultimate deflection (mm) 0.13 ± 0.06 1.23 ± 0.12 elastic modulus (mpa) 485 ± 10 30 ± 12 brittleness index ib 1.00 ± 0.1 0.41 ± 0.12 fig. 7. shapes of specimens after flexural failure 0 50 100 150 200 250 300 350 400 0 0,5 1 1,5 2 2,5 3 3,5 4 lo a d ( n ) displacement (mm) bridging effect tds sample ts sample sudden fracture 156 i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 4. conclusions in this study, experiments have been performed to investigate the feasibility and mechanical properties of diss fibers reinforced specimen, using tradical pf70 binder, as other traditionally binders replacement to such as cement, lime, clay.... the procedure has been conducted throughout compressive/flexural strengths, and the examination of elasticity behavior. these properties are also compared with those obtained with specimen without diss fibers addition. tests performed on hardened specimen have shown that the use of diss fibers reinforcement induced significant reduction in mechanical strengths. although the loss in the compressivestrength which attained 58%, the reinforced specimen satisfies the basic requirement for loadbearing wall, according to the rilem classification (rilem lc2., (1978). however, the decrease in flexural strength is less important than to the compressive strength. this may be due to the dilution effect that leads to limit the progression of the cracks in the matrix, derived from the bridging phenomena. results also highlight the ductile failure of diss fibers reinforced specimen which exhibits high plastic phase and underwent significant displacement before fracture. 5. references afnor, (1995). méthodes d’essais des ciments, partie 1: détermination des résistances mécaniques. ardanuy, m., claramunt, j., toledo filho, r.d. (2015). cellulosic fiber reinforced cement-based composites: a review of recent research. construction and building materials, 79, 115–128. barra, b., bergo, p., alves, c. jr., savastano, h. jr., ghavami, k. (2012). effects of methane cold plasma in sisal fibers, key engineering materials, 517, 458–468. bcb. (2015). http://www.bcb-tradical.fr. consoli, n.c., montardo, j.p., prietto, p.d.m., pasa. g.s. (2002). engineering behavior of sand reinforced with plastic waste, journal of geotechnical and engineering, asce, 128(6), 462-472. daher, s., benazzouk, a., zerrouki, r., chargui, s., langlet, t., beji, h. (2018). durability of construction materials based-vegetable particles (rapeseed straw) subjected to wetting and drying cycles". international conference on materials & energy "icome 2018", april 30-may 04 2018, san sebastian, spain. de bruijn, p.b., jeppsson, k.h., sandin, k., nilsson, c.h. (2009). mechanical properties of lime hemp concrete containing shives and fibres, biosystems engineering, 103(4), 474–479. elfordy, s., lucas, f., tancret, f., scudeller, y., goudet, l. (2008). mechanical and thermal properties of lime and hemp concrete (hempcrete) manufactured by a projection process. construction and building materials, 22, 2116–2123. gavrilescu, d., tofanicä, b.m., puitel, a.c., pétrea, p. (2009), sustainable use of vegetal fibres in composites. sources of vegetal fibres. environmental engineering management journal, 8(3), 429–438. karade, s.r. (2010). cement-bonded composites from lignocellulosic wastes, construction and building materials, 24, 1323–1330. rilem lc2. (1978). functional classification of lightweight concrete. materials and structures, 11, 281–286. mohr, b.j., nanko, h., kurtis, k.e. (2005). durability of kraft pulp fiber–cement composites to wet/dry cycling, cement and concrete composite, 25, 435-448. pereira, j.f., ferreira, d.p., bessa, j., matos, j., cunha, f., araújo, i., silva, l.f., pinho, e., fangueiro, r. (2019). mechanical performance of thermoplastic olefin composites reinforced with coir and sisal natural fibers: influence of surface pretreatment. polymer composites, 40(9), 3472-3481. ruth, b., ranyl, r. (2010). an investigation of the thermal properties of hemp and clay monolithic walls, in: advances in computing and technology the school of computing, information technology and engineering, 5th annual conference 2010, 63–170. i. zaid et al., j. build. mater. struct. (2022) 9: 150-157 157 sassoni, e., manzi, s., motori, a., montecchi, m., canti. m. (2014). novel sustainable hemp-based composites for application in the building industry: physical, thermal and mechanical characterization. energy building. 77, 219–226. j. build. mater. struct. (2022) 9:98-109 original article doi : 10.34118/jbms.v9i1.2082 formulation and characterisation of micro and macro polypropylene fibre reinforced mortar bendjilali f 1, bendjillali k 2,*, krobba b 2 1 department of civil engineering, faculty of civil engineering and architecture, university hassiba benbouali, chlef, algeria. 2 laboratory of structures rehabilitation and materials, faculty of civil engineering and architecture, university amar telidji, laghouat, algeria. * corresponding author: k.bendjillali@lagh-univ.dz, received: 12-09-2021 accepted: 28-05-2022 abstract. the objective of this work is to study the physical and mechanical characteristics of mortars reinforced by synthetic fibres. the work is carried out on mortars, using limestone crushing sand, composite cement and synthetic fibres. the fibres used as reinforcement of these mortars are synthetic fibres of polypropylene coming from industrial wastes; micro fibres having a diameter of 0.25 mm and macro fibres with a diameter of 0.45 mm. the used fibres have the same length of 30 mm. the results revealed that the addition of polypropylene fibres has a negative effect on the workability of the mixture, especially micro fibres. however, the mechanical properties of mortars have been enhanced. the weight loss is close in all mortars. key words: mortar, polypropylene fibres, micro fibre, macro fibre, workability, mechanical strength, weight loss. 1. introduction based on statistic studies, the concrete is considered as the most used material in the world after water. concrete is a durable material, with a high compressive strength and stiffness and it can be moldable into complicated shapes. however, concrete has a low tensile strength and a low ductility (manaswini, 2015). to improve this weakness, many technical solutions are proposed; such as the introduction of fibres in its mass. during the mixing process, fibres are distributed throughout the concrete in all directions. consequently, the concrete tensile strength as well as modulus of elasticity is thus increased. the problem of the addition of fibres to concrete is the decrease of its workability, thus for improving this property, mixing water volume should be increased or water reducing super plasticizers will be added to the mixture. in construction, there are several types of fibres used for the reinforcement of concrete, such as metallic (hadjoudja et al., 2019; 2021; ammari et al., 2020), synthetic (bendjillali and chemrouk, 2018), mineral and vegetable fibres (krobba et al., 2018). it has been established that the addition of metallic or polypropylene fibres to cement based materials can increase their fracture toughness, ductility and their mechanical resistance. synthetic fibres are nonbiodegradable and their presence in the nature cause environmental pollution. in order to reduce the air, water and ground pollution, synthetic fibres are used in concrete and their use represents an economic gain in the field of civil engineering. synthetic fibres of polypropylene or polypropylene-based are often preferred over steel fibres due to their lower production cost, lower weight and their high deformation and also because they do not absorb water or react chemically with cement. the presence of synthetic fibres in concrete reduces the workability and improves efficiently the mechanical strength, and can significantly affect the lifespan of the structure by reducing the permeability, the amount of shrinkage and the expansion of concrete. according to the same authors, polypropylene fibres increase the fire resistance of the structure mailto:k.bendjillali@lagh-univ.dz 99 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 due to the low melting point of the polymers and inferential formation of water vapour capillaries in the structure of concrete (antoš et al, 2017). polypropylene fibres have a good resistance to degradation and sufficient mechanical properties, such as tensile strength and toughness and they have the ability to disperse easily in the concrete and to control plastic shrinkage cracks (banthia and gupta, 2006). sand is the essential aggregate used in the composition of the mortar. the river sand is the most commonly used for construction in algeria. the excessive extractions of this sand have contributed significantly to the depletion of resources and have caused adverse effects on the environment. many parts of the world are experiencing this situation and must now look for alternative materials to meet the growing demand for concrete and mortar aggregates. crushing sands are very often the only alternative. however, they must meet their own quality criteria and be available in sufficient quantities at reasonable prices. in this experimental work, crushing limestone sand produced by ouazzane station (situated in the north of laghouat city) is used for preparing the test’s mortars. the fibres used as reinforcement of these mortars are synthetic fibres of polypropylene coming from industrial wastes; macro fibres with a diameter of 0.45 mm produced by plast bros factory of bordj bou arreridj (algeria) and micro fibres with a diameter of 0.25 mm obtained from the market. the used fibres have the same length of 30 mm. the valorization of these materials as reinforcement seems to be a good solution for the economic, environmental and technical problems of concrete constructions. the present investigation is carried out to study the physical and mechanical characteristics of mortars reinforced by synthetic fibres of polypropylene. 2. experimental programme 2.1. material and formulation for the realisation of this work, we have used limestone crushed sand as fine aggregate in the mortar composition. it is a crushing residue obtained from the fabrication of limestone gravel in ouazzane station in the north of laghouat. the sand has a particle size ranging between 0 and 3.15 mm. the size graduation and the characterization of the used sand are presented in figure 1 and table 1. fig 1. size graduation of sand. a portland cement cem ii/b-l 42.5 n was used; it is produced by m'sila cement factory (algerian company). table 2 gives the different properties of the used cement. a superplasticizer type sika viscocrete tempo12 and a potable water were used for the mixing. the employed 0,1 1 20 40 60 80 100 p a s s in g ( % ) seive size (mm) bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 100 fibres are of polypropylene (pp) with two different diameters, micro (figure 2.a) and macro fibres (figure 2.b). micro fibres are obtained from the market and macro fibres are produced by plast bros factory of bordj bou arreridj (algeria), table 3 illustrates their properties. table 1. sand characterisation results. properties results interpretations specific gravity 2.60 g/cm3 current aggregates (neville, 2002) bulk density 1.49 g/cm3 fineness modulus 2.45 medium sand (dreux and festa, 2006) esv / esp 64 % / 59 % crushed sand contains many fines (dreux and festa, 2006) vb 0.14 ml/g (vb ˂ 1) satisfactory sand and fines are not harmful for material (dreux and festa, 2006) table 2. cement characterisation results. properties results specific gravity 3.1 g/m3 bulk density 1.13 g/m3 fineness 3700 cm²/g consistency 26.5 ± 2.0 % cement setting 150 ± 30 min 7th compressive strength 37.89 ± 1.88 mpa 7th flexural strength 6.45 ± 0.44 mpa a. micro fibre b. macro fibre. fig 2. polypropylene fibres. table 3. fibres characteristics. characteristics micro fibres macro fibres diameter(mm) 0.25 0.45 length (mm) 30 30 specific gravity 0.99 0.99 absorption to water none none tensile strength (mpa) 235 204 elongation (cm) 14 4 in this work mortar mixes are prepared with a sand to cement ratio (s/c) equal to 1/3 (c = 450 g), a fibre dosage of 1 % by weight, which is previously fixed (bendjillali, 2015). mixtures are prepared as follows: 101 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 vary the water to cement ratio (w/c) to achieve a desirable workability, without the use of admixture. find out the percentage of superplasticizer sp, which gives the desirable workability of mortars for a given w/c ratio. find out the percentage of superplasticizer which gives the desirable workability of fibre mortar, for a given w/c and a percentage of fibres of 1 %. mixing process is carried out with a mortar mixer as below:  cement and sand are mixed for 60 sec,  70% of water is added; the wet mixing is kept for 30sec,  the rest of water (30 %) is added with the superplasticizer; mixing is kept for another 30sec,  fibres are added to the wet mortar and mixed for 90 sec. during the first 210 sec, the mixing is realised with a slow speed and then with a fast speed during another 30sec to ensure that the fibres can evenly disperse throughout the mortar. after, the mixture is relaxed for 90sec and then remixed for 60 sec with a fast speed. 2.3. preparing and curing of specimens starting with the measure of workability of the fresh mortar then, filling in prismatic moulds (40×40×160) mm (figure 3.a), which are covered with a plastic film (figure 3.b). samples are demoulded after 24 h and conserved in controlled chamber (t = 22°c, rh = 92 %) for mechanical tests or in uncontrolled chamber (t = 20 ± 5°c, rh = 20 ± 5 %), for weight loss test a. molding mortar b. curing of samples under a plastic cover fig 3. molding and curing of samples 2.4. tests the measure of the workability was yielded according to nfp18-452 by a maniabilimeter b, which is consists of a parallelepiped mould with a mobile wall and a vibrator. the principle of the test consists after removing the mobile wall, to measure the time taken by the mortar under vibration to reach a mark engraved on the inner face of the mould. numerous mixes were prepared and tested until obtaining a good workability, which corresponding to a flow time of 16 ± 4 seconds. according to en 196-1, compressive and flexural strength were measured after 28 days of age. the flexural strength was tested on prismatic specimens (40×40×160) mm (figure 4.a) and the half-prisms(figure 4.b) were utilized for the compressive test using “controls” testing machine(figure 4.c), with a maximum charge load of 100 kn. for the bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 102 evaluation of the weight loss, prismatic specimens (40×40×160) mm were prepared and exposed to the atmospheric air (t = 20 ± 5°c, rh = 20 ± 5 %) during 28 days then a daily measure of weight is made using a0.01g balance precision. the weight loss is the ratio of the mass difference, between the initial mass and the daily mass to the initial mass. a. three point flexural test. b. compressive test. c. testing machine. fig 4. mechanical test 3. results and discussions 3.1. formulation of control mortar without superplasticizer the experimental results of this test are shown in table 4. the figure 5 confirms the practical reality that the flow time decreases with the addition of water. to reach a good workability, mixtures need a high w/c ratio which is between 0.60 and 0.69. the high w/c ratio is due to the important absorption of the used sand (= 6.23 %). table 4. composition and flow time of control mortar without superplasticizer mortar c (g) s (g) w (g) w/c (%) flow time (s) visual observations m’0 450 1350 270.0 0.60 45 very dry mix m’1 450 1350 292.5 0.65 30 dry mix m’2 450 1350 301.5 0.67 10 wet mix m’3 450 1350 310.5 0.69 6 self-levelling mix 103 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 3.2. formulation of control mortarwith superplasticizer for respecting the practical recommendations, the w/c ratio is reduced to 0.55 and then to 0.50. for each w/c ratio, the percentage of superplasticizer is measured. according to the table 5, the mixes m2 and m7 give the good workability. figure 6 illustrates the variation of the flow time with the percentage of superplasticizer. the figure confirmed the roleof the used superplasticizer, which is a water-reducer, to reduce the water dosage. this conclusion is in accord with the study of kheribet et al. (2011) established on the effect of the superplasticizer on the rheological properties of concrete. the viscosity of the mixture decreases that means that the utilisation of superplasticizer reduces water requirement to have a workable mixture, this can be explained by the dispersing effect of the superplasticizer, which, causes a steric repulsion between the cement particles, reducing their agglomeration (kheribet et al., 2011). fig 5. variation of flow time of mortars in function of w/c ratio. the mixture m7 is chosen as control mortar mc, because it requires an acceptable water dosage and a superplasticizer percentage (= 0.93 %) lower than that required by m2 (= 1.2). since the superplasticizer is a commercial material, it is very important to use lowest dosages for not increasing the mortar cost. we note that control mortar gives a good strength at the 28th day. the table 6 gives the final formulation of control mortar. table 5. composition and flow time of control mortar with superplasticizer. mortars c (g) s (g) w (g) w/c (%) sp (%) flow time (s) visual observations m1 450 1350 225 0.50 1.0 28 very dry mix m2 450 1350 225 0.50 1.2 16 plastic mix m3 450 1350 225 0.50 1.3 9 wet mix m4 450 1350 247.5 0.55 0.6 35 very dry mix m5 450 1350 247.5 0.55 0.8 30 very dry mix m6 450 1350 247.5 0.55 0.9 25 dry mix m7 450 1350 247.5 0.55 0.93 15 plastic mix m8 450 1350 247.5 0.55 0.95 10 wet mix m9 450 1350 247.5 0.55 1.0 7 wet mix m10 450 1350 247.5 0.55 2.0 1 self-levelling mix 0,60 0,62 0,64 0,66 0,68 0,70 0 10 20 30 40 50 f lo w t im e ( s ) w/c (%) bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 104 fig 6. variation of the flow time in function of the superplasticizer percentage. table 6. final composition of control mortar mortar c (g) s (g) w (g) w/c (%) sp (%) rc28d (mpa) rf28d (mpa) mc 450 1350 247.5 0.55 0.93 43.83 ± 2.10 9.36 ± 0.62 3.3. formulation of fibres mortars with the same composition of control mortar (c = 450 g, s = 1350 g and w/c = 0.55), fibre mortars are prepared with a new optimisation of superplasticizer. for each mixture, numerous tests are conducted to look for the superplasticizer dosages sp, which give the desirable workability. table 7 illustrates the composition of the workable mixtures. table 7. composition of fibres mortars. mortar c (g) s (g) w (g) w/c (%) micro fibre (g) macro fibre (g) sp (%) flow time (s) mc 450 1350 247.5 0.55 00 00 0.93 15 micf 450 1350 247.5 0.55 20.5 00 1.60 19 macf 450 1350 247.5 0.55 00 20.5 1.28 14 3.4. workability of fibres mortars figure 7 presents the variation of superplasticizer dosage of fibres mortars. it is remarked that fibres mortars need higher dosage of superplasticizer compared to control mortar, while micro fibres mortars require the most important dosage compared to macro fibres mixes this could be due to their high specific surface. the majority of the literature studies confirmed that the addition of fibres to concretes and mortars negatively affect their workability and increase their viscosity (sebaibi et al., 2014; söylev and özturan, 2014; manaswini and deva, 2015; bendjillali and chemrouk, 2017; abdullah et al., 2020). 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 0 5 10 15 20 25 30 35 40 w/c=0,55 w/c=0,50 f lo w t im e ( s ) superplasticizer (%) 105 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 fig 7. variation of superplasticizer dosage of fibres mortars. 3.5. flexural strength of fibres mortars the flexural strength of all mortars is measured at 28 days and schematized in the figure 8. for a good discussion, the strength gains of the flexural strength offibres mortars (figure 9) is calculated compared to control mortar as following: (1) with: rf: strength gain of the flexural strength (%) rf: flexion strength of fibre mortar (mpa) rf0: flexion strength of control mortar (mpa) fig 8. flexural strength of mortars. fig 9. strength gain of the flexural strength. it is very important to note that fibres mortars produce higher flexural strengths (figure 8), compared to the control mortar that means that the addition of polypropylene fibres to mortar enhances its flexural behaviour. this result is found in the most of the literature studies 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 macfmicfmc s u p e rp la s ti z e r( % ) mixes 0 2 4 6 8 10 12 14 16 18 20 macfmicfmc f le x u ra l s tr e n g th ( m p a ) mixes 0 20 40 60 80 100 micf macf v a ri a ti o n r a te o f th e f le x u ra l s tr e n g th ( % ) mixes bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 106 (mamlouk and zaniewski, 2011; pereira de oliveira et al., 2011). this increase in flexural strength is due to the fibre bridging properties, as reported by some authors (hasan et al., 2011). according to the same authors, under flexural test, the load is transferred to the fibres when the matrix began to crack. fibres with high tensile strength transfer higher tensile stresses from a cracked matrix to the fibres (song et al., 2005). it is remarked through the figure 9, that the effect of macro polypropylene fibres is slightly more important than micro fibres, with a strength gain of 104 %. macro fibres disperse better in the matrix than micro fibres, which explain their positive effect. the good dispersion of fibres in the matrix can affect positively the mechanical performance of the materials as reported by other studies (akkaya et al., 2001; ozyurt et al., 2007). 3.6. compressive strength of fibres mortars the variation of the compressive strength of mortars at 28 days is given in figure 10. in figure 11, the strength gain of the compressive strength of fibres mortars is presented. this strength gain is calculated by comparison to control mortar with the following relation: (2) with: rc: strength gain of the compressive strength (%) rc: compressive strength of fibre mortar (mpa) rc0: compressive strength of control mortar (mpa) fig 10. compressive strength of mortars. fig 11. strength gain of the compressive strength. the figure 10 shows that all mortars give a good mechanical behaviour. the maximum values of the compressive strength are recorded in micro fibres mortar. by comparison with control mortar, the fibre mortar shows amelioration about 5 % (figure 11). the highest compressive strengths are produced in polypropylene fibres mortars, as in flexural strength, which shows the positive effect of the addition of polypropylene fibres to mortar. some researchers (hasan et al., 2011; alengaram et al., 2013; bendjillali and chemrouk, 2016; sohaib et al., 2018) have reported a compared conclusion. 3.7. weight loss of fibres mortars figure 12 presents the variation of weight loss with time. it can be remarked that the weight loss develops rapidly with age, especially during the first two weeks from around 2 % to 7 %; then it continuous to evolve slowly until the stabilisation nearly to 7.5 %. in general, the weight loss measurements are close during all tests. that means that scattered fibres in the matrix did not 0 10 20 30 40 macfmicfmc c o m p re s s iv e s tr e n g th ( m p a ) mixes 0 1 2 3 4 5 micf macf v a ri a ti o n r a te o f c o m p re s s iv e s tr e n g th ( % ) mixes 107 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 affect negatively the size of pores (increase) in the material as well as their volume, by increasing the capillary intensity, and obstructing the evaporation of water contrary to what other authors found (mesbah and buyle-bodin, 1999). fig 12. variation of weight loss of different mortars. 4. conclusions this paper has been concerned with the investigation of workability, mechanical behaviour and weight loss of mortar reinforced with macro and micro synthetic fibres. hence, the conclusions summarized as: the used viscocrete tempo 12 efficiently improves the workability of fibres mortars. the workability of mortars is reduced by the addition of polypropylene fibres. the addition of polypropylene fibres enhanced significantly the flexural strength of mortar. the enhancement is mainly attributed to the fibre bridging process that allowed additional stress to develop for the cracks to propagate. macro fibres mortar presents the highest flexural strength with an amelioration of 104 %. micro fibres mortar gives the highest compressive strength and the most important variation rate is about 5 %. the weight loss is very close in all mortars until the age of 28 days. by the addition of polypropylene fibres to mortar, we can improve its mechanical properties and certainly increase the chance to use it as composite material for more strong and durable structures in the future, which can open a new area in the field of construction materials. 5. references abdullah, m. z., afzal, h. k. & bassam, a. t. (2020). durability and strength characteristics of high-strength concrete incorporated with volcanic pumice powder and polypropylene fibers. journal of materials research and technology, 9(1), 806-818. akkaya. y., shah. s. p. & ankenman. b. (2001). effect of fiber dispersion on multiple cracking of cement composites. journal of engineering mechanics, 127(4), 311-316. 0 7 14 21 28 2 3 4 5 6 7 8 w e ig h t lo s s ( % ) age (days) mc micf macf bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 108 alengaram, u. j., soon, p.y. & jumaat, m. z. (2013). enhancement of mechanical properties in polypropylene and nylon fibre reinforced oil palm shell concrete. material and design journal, 49, 1034-1041. ammari, m. s., bederina, m. belhadj. b. & merrah.a. (2020). effect of steel fibers on the durability properties of sand concrete with barley straws. construction and building materials, 264, 120689. antoš, j., dejdar, l., trejbal, j.& prošek, z. (2017). performance of cement composites reinforced with surface-modified polypropylene micro-and macro-fibers. acta. polytechnica ctu proceedings, 13, 11-15. banthia, n. & gupta, r. (2006). influence of polypropylene fiber geometry on plastic shrinkage cracking in concrete. cement and concrete research journal, 36, 1263-1267. bendjillali, k. & chemrouk, m. (2016). efficiency of plastic fibres waste on the physico-mechanical properties of mortars in hot-dry conditions. international journal of natural sciences research, 4(4), 75-82. bendjillali, k. & chemrouk, m. (2017). use of recycled pp fibres in concrete. 3rd international symposium on materials and sustainable development, 07-08 nov, boumerdes, algeria, p 462. bendjillali, k. & chemrouk, m. (2018). study of the reinforcement of structure members by polypropylene fibres waste. matec web of conferences, p 149. bendjillali, k. (2015). etude de l’influence de renforcement fibreux en polypropylène sur les performances physico-mécaniques et sur la durabilité des mortiers de ciment à base de sable calcaire. doctoral thesis, houari boumediene university usthb, algiers, algeria. dreux. g, & festa. j. 2006. nouveau guide de béton et de ses constituants. eyrolles. huitième edition. hadjoudja, m., benzaid, r., mesbah, h. a., makhloufi, z. & bederina, m. (2021). effect of mineral additions and metal fibers on the resistance of cracking of the dune sand concretes. iranian journal of science and technology. hadjoudja, m., mesbah, h. a., bederina, m. & makhloufi, z. (2019). modeling of dimensional variations of a dune sand concrete reinforced by addition of steel fibers. journal of adhesion science and technology. hasan, m. j., afroz, m. & mahmud, h. m. i. (2011). an experimental investigation on mechanical behavior of macro synthetic fiber reinforced concrete. international journal of civil and environmental engineering ijcee-ijens, 11(03), p 6. kheribet, r., benmounah, a., samar, m. & saidi, m. (2011). action de superplastfiants poly carboxylate et poly naphtalène sulfonâtes sur les propriétés rhéologiques et physico mécaniques des ciments cemi et crs. séminaire international, innovation et valorisation en génie civil et matériaux de construction, 1, 314-321. krobba, b., bouhicha, m., kenai, s. & courard, l. (2018). formulation of low cost eco-repair mortar based on dune sand and stipa tenacissima microfibers plant. construction and building materials, 10, 950–959. mamlouk, m. s. & zaniewski, j. p. (2011). materials for civil and construction engineers, 3rd edition. upper saddle river: prentice hall. manaswini, c. & vasu, deva. (2015), fibre reinforced concrete from industrial waste-a review, international journal of innovative research in science, engineering and technology, 4(12), 11751-11758. mesbah, h. a. & buyle-bodin, f. (1999). efficiency of polypropylene and metallic fibres on control of shrinkage and cracking of recycled aggregate mortars. construction and building materials, 13(8), 439-447. ozyurt, n., mason, t. o. & shah, s. p. (2007). correlation of fiber dispersion, rheology and mechanical performance of frcs. cement and concrete composites, 29(2), 70-79. 109 bendjillali et al., j. build. mater. struct. (2022) 9: 98-109 pereira de oliveira, l. a. & castro-gomes, j. p. (2011). physical and mechanical behaviour of recycled pet fibre reinforced mortar. construction and building materials journal, 25, 1712-1717. sebaibi, n., benzerzour, m. & abriak, n. e. (2014). influence of the distribution and orientation of fibres in a reinforced concrete with waste fibres and powders. construction and building materials journal, 65, 254-263. sohaib, n., mamoon, r., seemab, f., & sana. g. (2018). using polypropylene fibres in concrete to achieve maximum strength. conference: eighth international conference on advances in civil and structural engineering cse 2018, malaysia, 37-42. song, p. s., hwang, s.&sheu, b. c. (2005). strength properties of nylon-and polypropylene-fiber-reinforced concretes. cement and concrete research, 35, 1546-1550. söylev, t. a. & özturan, t.(2014). durability, physical and mechanical properties of fiber reinforced concretes at low volume fraction. construction and building materials journal, 73, 67-75. j. build. mater. struct. (2022) 9: 74-86 original article doi : 10.34118/jbms .v9i1.1896 issn 2353-0057, eissn : 2600-6936 experimental investigation on effect of corrosion on curvatureductility relationship of rcc member in flexure p.n. ojha 1, sumit kumar 2, puneet kaura 3, brijesh singh 4,*, pranay singh 5 1 joint director and head, center for construction development and research, national council for cement and building materials, india. 2 project scientist, center for construction development and research, national council for cement and building materials, india. 3 manager, center for construction development and research, national council for cement and building materials, india. 4 group manager, center for construction development and research, national council for cement and building materials, india. 5 project engineer, center for construction development and research, national council for cement and building materials, india. * corresponding author: brijeshsehwagiitr96l@email.com received: 22-02-2022 accepted: 24-04-2022 abstract. corrosion of reinforcement in concrete is the biggest concern when it comes to durability of concrete structure. it is not only detrimental to the health of the structure but also has economic implications with regard to the money and energy required for repair of concrete elements deteriorated by corrosion of steel. this study is dedicated to understand the effect of corrosion in concrete induced by chloride ingress using an accelerated technique involving the application of external voltage to laboratory cast rc beam specimens. all the specimens used in this study were cast in laboratory using m20 grade concrete using opc (ordinary portland cement). the diffusion coefficient of chloride ions into concrete was estimated using nt build 492 test. finally, the effect of corrosion on ductility, moment-curvature relationship and reduction in flexural strength of beams was measured using a two-point load flexural test. reduction in strength and ductility was observed as the corrosion level increased. key words: reinforced concrete flexural member, accelerated chloride induced corrosion, corrosion level, moment-curvature relationship 1. introduction cement is second most used material on earth only next to water. large portion of cement is used in rc which is used in infrastructure development of any nation. a good quality and durable construction is important not only for health of the structure and safety of people, but also in a greater sense for economic development of any nation. achieving the desired durability in concrete is as important as achieving the desired strength. for many decades, the main focus of concrete design for any structure has been strength and workability; therefore, there is ample evidence of impulsive deterioration of recently built structures (ahmad, 2003; arora and singh, 2016, arora at al., 2016, 2019). as per american concrete report (aci 201.2r-08, 2008) concrete durability can be defined as capability of concrete to resist, chemical attack, abrasion, weathering action or any other process of deterioration. concrete is said to be durable if it can sustain its original form, quality as well as serviceability upon exposure to environment. rc chiefly consists of cement, aggregates and reinforcement mostly in form of steel bars (. deterioration of concrete begins immediately after casting and is affected by a variety of internal and external factors which cause damage to either constituent, viz. hydrated cement paste, aggregates or reinforcement bars, by physical and/or chemical mechanisms. however, the biggest hurdle in achieving desired durability is due to mailto:brijeshsehwagiitr96l@email.com ojha et al., j. build. mater. struct. (2022) 9: 74-86 75 deterioration of steel by means of corrosion. the reinforcement corrosion is a problem of serious concern. significant proportion of a developed nation’s gdp (gross domestic product) is used for repair of corrosion related deterioration (bhaskaran et al., 2014). concrete act as the environment for steel in reinforced concrete (rc) structure. concrete provide alkaline medium to reinforcement owing to the presence of calcium hydroxide, a product of hydration of cement. in the range of ph of 12-13, a protective layer forms on the surface of rebar and prevents iron atoms from dissolving. presence of oxygen, water, stray electric currents, foreign substances like chloride ion, acidic gas such as co2 etc. decreases the alkaline nature of concrete and break the passive layer of corrosion (emmons, 1993). corrosion causes deterioration in two ways. the products of corrosion occupy larger volume than the existing volume of steel. this reduces the operative area of reinforcement and causes tensile stresses in the concrete and reduction in structural capacity, cracking and cover spalling and delamination (bossio et al., 2019). corrosion has potential to collapse the structure. (webster and clark, 2016; ahmad, 2003; bossio et al., 2019) studied the effect of corrosion on different diameter of rebar. the residual strength of flexure member was estimated at different level of corrosion and concluded that at 30% level of corrosion, flexure member lost its complete strength. (cabrera and ghoddoussi, 1992) studied the impact of corrosion on flexure behavior rcc member and reported that bond strength reduced at 9% corrosion level and also showed that deflection also increase due to increase in corrosion level. campione et al., (2016) studied the effect of corrosion on the flexure and shear strength and failure mode. in the seismic design of rc beams of structures, the potential plastic hinge regions need to be carefully detailed for ductility in order to ensure that the shaking from large earthquakes will not cause collapse. adequate ductility of members of rc frames is also necessary to ensure that moment redistribution can occur. although adequate flexural ductility is essential for structures in high seismicity regions, many serious problems relating to the behavior of rc structures under severe seismic action can be traced due to the poor detailing of rc (olivia 2005). olivia et.al. (2005) concluded that the ductility of flexural element also has been reduced with increasing the corrosion level. the ductility of rc flexural members depends upon a number of factors, including percentage of tensile reinforcement, percentage of compressive reinforcement, percentage of lateral reinforcement and strength of concrete. investigation regarding ductility of flexural members utilizing these factors has been explored in number of studies. to investigate the influence of the corrosion level on the beam ductility, an experimental program is conducted. the corrosion was induced using accelerated chloride induced corrosion technique and applied 30v dc (direct current) voltage. in this study the effect of corrosion on moment-curvature relationship and curvature ductility of flexure member was investigated to understand the failure mechanisms under seismic conditions where, higher ductility demands are placed on rc members. kashani et al., (2019) provided a comprehensive review of the experimental studies on the corrosion-damaged rc components and the residual flexural strength prediction capacity of the existing numerical model. cross-sectional moment-curvature evaluations utilising cutting-edge corrosion damage models revealed a strong correlation between anticipated residual flexural capacity and experimental data. moment-curvature relationship characterizes the nonlinear behavior of critical section of rc beam. moment-curvature relationship also represents the rotation or ductility capacity of flexure member. moment-curvature diagram of flexure rcc member has been divided into three states as shown in 1 moment-curvature relationship of rc as shown in figure 1 (baji and ronagh, 2011). 76 ojha et al., j. build. mater. struct. (2022) 9: 74-86 fig. 1. moment-curvature relationship of rc beam (baji and ronagh, 2011) moment of beam at critical section (at mid span of beam) is calculated from load using equation (1) at each time step during flexure test. at the same time the strain profile is also noted with the help of strain gauge using data logger. curvature is calculated from equation (2) m=(p*l)/6 (1) φ=ɛc/x (2) in the given equations, m is the moment at mid span, p represents the applied load, l is the effective span of the beam, ɛc is the compressive strain, φ represents the curvature and x is the neutral axis depth. fig. 2. cross section of beam and strain profile of critical section from moment-curvature relationship of the beams the yield curvature (φy) and ultimate curvature (φu) were found with respect to yield moment and ultimate moment respectively. the ratio of ultimate curvature (φu) to yield curvature (φy) is called ductility coefficient (μ) which characterizes the plastic region length and rotation capacity of the beam. μ=φu/φy (3) in equation (3) μ is the ductility coefficient, φu is the ultimate curvature and φy is yield curvature. ojha et al., j. build. mater. struct. (2022) 9: 74-86 77 2. experimental program a total of 19 specimens of varying dimensions has been used for performing various tests in the study. the specimen sets consisted of three 150 mm cubes for compressive strength estimation. three cylinders of 150 mm diameter and 300 mm height were used for capturing the stress strain behavior of the hardened concrete. one cylinder of 100 mm dia. and 200 mm height was used for evaluating the diffusion coefficient of chloride. and 12 rc beams of size 150x150x700 mm were cast for flexure testing at different level of corrosion. as tension reinforcement, two 8 mm bars were used. the rc beams were designed as per is :456 (2000) as shown in figure 3. minimum reinforcement in compression zone was also provided to support the stirrups, and its contribution is resisting bending moment was neglected. the beam is designed with m20 grade concrete and as shown in the figure 3 the cross-sectional height and width of the beam was 150 mm. the section view of the beam shows the reinforcement used in the beam. all the reinforcement shown are 8 mm in diameter. all the specimens were cast in single go to avoid influence of factors such as casting conditions, batch and age of cement, workmanship, quality control. also, the specimens were cured for 28 days by keeping in water. the rc beams, cubes and cylinders were casted in laboratory and placed in moist curing room at 20ᵒc and 95±5% relative humidity for 24 hours. the specimens demolded after 24 hour and placed in water curing tank for next 27 days. the cubes, cylinder and control beams (three) were tested at 28 days after removing from curing tank. the remaining beams (nine) are tested after inducing corrosion, these beams combination three of were placed into chloride solution for 24, 48 and 72 hours exposure period to induce different level of corrosion. the corrosion rate was measured for each exposure period and the level of induced corrosion was measured by equation (5). the duration of exposure period for beams is given in table 2. fig. 3. beam specimen details (all dimension in mm) 2.1. concrete mix design the m20 grade of concrete were used to cast the beams. the mix proportion of concrete was given in table 1. table 1. concrete mix proportion sr no w/c ratio mix constituents cement (opc) (kg/m3) fine aggregate (kg/m3) coarse aggregate (kg/m3) 1 0.60 300 721.24 1235.29 78 ojha et al., j. build. mater. struct. (2022) 9: 74-86 for the design of beam as per is: 456 (2000) the characteristic strength of concrete was taken as 20 mpa, which represents the grade of concrete as m20. 2.2. nt build 492 diffusion coefficient or diffusivity, can be described as, the quantity of molecule of one substance that can diffuse into another substance through their unit contact surface area in unit time. in this case chloride ions are diffused into concrete by means of dc voltage. the rate of diffusion, which in turn depends on numerous factors like type of cement, w/c ratio, grade of concrete etc. is characterized by diffusion coefficient. for this study, the diffusion coefficient was found as per procedure given in nt build 492 (1999) and it can be used to characterize the behavior of concrete against the chloride ion penetration. the 100 mm diameter and 200 mm height cylinder was cut into three equal heighted 50 mm diameter specimen of height 50 mm each, and test was performed on each of these specimens. the non-steady diffusion coefficient is reported to be the average value of three specimens 2.3. accelerated chloride induced corrosion test in practice, the corrosion of steel rebar in concrete is very slow process and takes years and can be due to different agents such as chloride in case of chloride induced corrosion and carbon dioxide in case of carbonation corrosion (belda et.al. 2018). in both the cases, the alkalinity of the concrete is reduced thus leading to corrosion (ahmad, 2009). for the purpose of study, accelerated corrosion chloride induced corrosion techniques was used as shown in figure 4. an external voltage is applied to penetrate chloride ion from electrolyte solution in which the cast specimens are kept immersed. since corrosion is an electrolytic process, the steel reinforcement acts as anode electrode and stainless-steel plate, placed beneath the beam, as cathode electrode. fig. 4. accelerated chloride induced corrosion setup the beam and stainless-steel plate were placed into 16.5% nacl solution and dc voltage of 30v was applied on the electrodes. nacl solution acts as electrolyte which accelerates the corrosion process by breaking the passive layer of reinforcement. the beams were placed for certain duration period to induce different level of corrosion as shown in table 2. the beams were designated based on exposure duration. figure 5 shows the corroded beams after the test. ojha et al., j. build. mater. struct. (2022) 9: 74-86 79 table 2. exposure duration of beams no of beams sample id duration (hour) 3 co 3 e1 24 3 e2 48 3 e3 72 fig. 5. corroded beam 2.4. corrosion rate and corrosion level measurements the rate of induced corrosion can be used to estimate the level of corrosion. the linear polarization resistance (lpr) technique was used to determine the rate of corrosion, which measures the corrosion current density (icorr) as per astm g59 (2009) (figure 6). the following equations were used to calculate the level of corrosion. (andrade et al. 2004). ( ) (4) ( ) (5) ( ) (6) here, rpis polarization resistance(ohm), icorr is corrosion current density(μa/cm2), βa & βc represents tafel’s constants, cr denotes rate of corrosion(mm/year), t is the exposure period of beam(year), and d is the diameter of rebar(mm). fig. 6. current density measurement 80 ojha et al., j. build. mater. struct. (2022) 9: 74-86 2.5. flexure testing of beams two-point load test was performed to estimate the flexural capacity of the rc beams (is :516, 2021). the testing plan given in table 3 flexure testing plan. three control beams were tested(c0) at 28 days after water curing. the remaining nine beams e1, e2 and e3 were tested in combination of three at three exposure regimes i.e. 24,48 and 72 hours in nacl solutions. the specimens were tested after inducing corrosion to find out the effect of corrosion level on flexure performance of beams. two strain gauges were installed at mid span of beam to record the strain at different time step of loading. the locations of strain gauges along the depth were, parallel to tensile reinforcement, along neutral axis depth and along compression reinforcement. the linear variable differential transferor (lvdt) device was also installed at mid-section of beam to measure the central deflection of beam (arora et.al. 2018). the flexure test was performed as displacement control mode at minimum rate of loading 0.01 mm/sec to examine the behavior of beam. the minimum rate of loading was applied to avoid the early damage of strain gauges and slow rate of loading gives more data points which helps better examination of the flexure behavior. 3. results and discussion 3.1. stress-strain behaviour of concrete the stress-strain curve of concrete was made to characterize the behavior of concrete in compression zone, throughout flexure testing (singh et.al 2018). three number of concrete cubes of size, 150 mm side, were used to determine the stress strain curve of concrete. the maximum compressive strain of concrete was found 0.003711 and corresponding stress in concrete was found to be 22.7 mpa. 3.2. diffusion coefficient of chloride ion in general range chloride diffusivity found in the range of 6.4*10-12 m2/s – 12.4*10-12 m2/s for concrete exposed to seawater (erdogdu et al., 2004). in this study, the diffusion coefficient (d) was found to be 8.87 *10-12 m2/s. this value is relatively higher diffusivity of chloride ion into concrete. 3.3. corrosion level measurement this may be attributed to relatively higher w/c ratio i.e. 0.6 and opc as binder. the higher value of diffusion coefficient helped accelerate chloride induction for testing purpose but is not suitable for real concrete. the corrosion rate was measured using linear polarization resistance technique. the corrosion current density was calculated using stern geary equation by measuring the polarization resistance and tafel’s constant. in order to acquire uniformity in the test, influencing parameter in test like applied voltage, electrolyte solution (16.5 % nacl solution), cover depth, diameter of rebar (i.e. grade of the rebar and diameter of rebar) and grade of concrete remains the same for each beam. the average corrosion current density of three beams for each exposure condition was estimated using equation (5). the average level of corrosion of three beams was estimated using equation (6) for each exposure condition. the average results of corrosion current density and level of corrosion was given in table 3. the average level of corrosion in the terms of % reduction in diameter was induced 2.27%, 4.93% and 9.24% for exposure regimes i.e. 24, 48and 72-hours exposure period respectively. the corrosion level characterizes the loss in the diameter with respect to 8 mm diameter of rebars. the corrosion rates represent the penetration of depth in per unit time. the total penetration represents the loss in diameter of rebar which is determined using equation (5). ojha et al., j. build. mater. struct. (2022) 9: 74-86 81 table 3. duration, current intensity and corrosion level for different beams no of beams sample id average corrosion current density (icorr in ma/cm2) corrosion rate (m/year) duration (hour) corrosion level (based on reduction in diameter of rebar) 3 c0 0% 3 e1 2.87 0.033 24 2.27% 3 e2 3.12 0.036 48 4.93% 3 e3 3.89 0.045 72 9.24% 3.4. flexural strength of beams the flexure strength is maximum load that can be sustained by beam before failure in bending. two-point load test was used, in which two equal points loads were applied gradually at one third length of the beam so that the middle third portion of beam is subjected to pure bending (arora et.al. 2016, arora et.al. 2018) as shown in figure (7). the adopted testing plan is given in table 4. the ultimate flexure load and corresponding maximum deflection at mid span are shown in table 5 flexure test results. it can be observed that average ultimate failure load and corresponding deflection of control beams and 2.27% corroded beams (e1) is comparable. however, significant reduction is failure load and maximum deflection is seen when corrosion level is increased beyond 2.27%. it is also observed that, the relation between corrosion level and ultimate failure load was found non linear. increase of the degree of corrosion leads to beam moment capacity reduction. this reduction can be more attributed to the reduction of area of reinforcements than the decline in the bond due to the change in the surface characteristics of bars. fig. 7. flexure testing of beam table 4. flexure testing plan no. of beams sample id exposure period (hours) level of corrosion (%) remarks 3 c0 0 three beams are tested at zero corrosion level as control specimen after 28 days curing 3 e1 24 2.27 these beams were placed for 28-day water curing, then placed for accelerated induced corrosion and after measurement of corrosion level, flexure tests were performed. 3 e2 48 4.93 3 e3 72 9.24 82 ojha et al., j. build. mater. struct. (2022) 9: 74-86 table 5. flexure test results s. no. sample id corrosion level (%) ultimate flexure strength (kn) average value of flexure load (kn) maximum deflection (mm) average of maximum deflection (mm) 1 c0 0 88.48 85.30 15.13 14.98 83.26 14.63 84.18 15.19 2 e1 2.27 84.06 81.01 14.28 13.68 78.26 13.35 80.72 13.42 3 e2 4.93 76.42 73.94 12.91 12.14 71.56 11.14 73.84 12.37 4 e3 9.24 63.45 61.44 10.82 10.48 59.23 10.24 61.65 10.36 3.5. moment-curvature of beams the maximum bending moment at middle third span at each load increment was calculated using equation (1) and the curvature at mid-span was calculated using equation (2). the moment-curvature relationship was found by mapping the strain profile of mid-section beam and shown in figure 8 moment-curvature relationship at different level of corrosion. corrosion reduced the cross section of rebar which lead to reduction in cross section area of the rebars, which in turn reduced the flexural performance of the rc beam. it was observed that as the level of corrosion increased the ultimate moment taking capacity of beams decreased. the yield moment when there is no corrosion and 2.27% is comparable. however, notable reduction in yield moment of beam corroded by 4.93% and 9.24% was observed with respect to control beam. curvature also significantly reduced as the level of corrosion increased with respect to the control beam. the reduction in curvature will be caused in reduction of the rotation capacity and ductility of the beam. fig. 8. moment-curvature relationship at different level of corrosion corrosion reduced the cross section of rebar which lead to reduction in cross section area of the rebars, which in turn reduced the flexural performance of the rc beam. it was observed that as ojha et al., j. build. mater. struct. (2022) 9: 74-86 83 the level of corrosion increased the ultimate moment taking capacity of beams decreased. the yield moment when there is no corrosion and 2.27% is comparable. however, notable reduction in yield moment of beam corroded by 4.93% and 9.24% was observed with respect to control beam. curvature also significantly reduced as the level of corrosion increased with respect to the control beam. the reduction in curvature will be caused in reduction of the rotation capacity and ductility of the beam. fig. 9. experimental and idealized curves obtained for different levels of corrosion of reinforcement figure 9 shows individual moment curvature curves for the tested beams. for each of the experimentally obtained curves an idealized curve is drawn. based on sudden change in the slope. idealized curve is divided into three points, marked by the points named as, crack, yield and ultimate. table 6 shows the values of moment and curvature at three demarcated points on the idealized curve. reduction in ultimate deflection signifies loss in ductility of the corroded beams and the failure of the corroded beams indicates transfer from ductile failure mode with a large mid-span deflection to a brittle failure mode with only a few limited deflections gradually (peng et al.,, 2019; yuksel and sakcalı, 2022). thus, it can be said that, corrosion of rebars is likely to make the real structures brittle and may cause sudden failure, which can be even more detrimental. 84 ojha et al., j. build. mater. struct. (2022) 9: 74-86 table 6 moment (kn-m)-curvature (10^-3 * rad/m) relationship at different level of corrosion points 0% corrosion 2.27% corrosion 4.93% corrosion 9.24% corrosion moment curvature moment curvature moment curvature moment curvature crack 4.3 1.45 2.67 1.2 2.11 0.48 0.84 2.07 yield 7.50 9.3 7.40 4.0 5.78 2.75 5.13 6.57 ultimate 8.6 44.48 8.11 43.0 7.48 33.19 5.57 27.99 3.6. ductility coefficient from moment-curvature relationship of the beams the yield curvature(φy) and ultimate curvature(φu) calculated corresponds to yield moment and ultimate moment respectively. the ratio of ultimate curvature(φu) to yield curvature (φy) is called ductility coefficient(μ) which characterizes the plastic region length and rotation capacity of the beam. fig. 10. ductility coefficient vs corrosion level (%) relationship curve the relationship between ductility coefficient of rc flexural member and corrosion level (%), using curve fitting method is found to be y = 5.5202e-0.129x (6) this result of the ductility coefficient of the control beam obtained in our study was found to be in line with the (rao et al., 2017; kwan et al., 2002). the section ductility of rc beams exponential reduced with increased in corrosion level in the tensile reinforcement. for severe corrosion cases, reductions in moment and curvature capacities lead to shifting in the structural behaviour of the load-bearing members from ductile to brittle as suggested by past researchers (yuksel and sakcalı, 2022). 4. conclusions impact of corrosion on curvature ductility rc beams which was designed as per is: 456 (2000) code was subject of this study and significant effect of corrosion on the flexure behavior of rc beam was observed. corrosion to a certain level (2.27%) does not cause any significant reduction in load carrying capacity of rc members. however, with further increase in the corrosion level, the load carrying capacity reduced upto 28 % at the 9.24 % corrosion level. the curvature ductility exponentially decreased with increased in the corrosion level. the lower curvature ductility leads to brittle failure of the flexure member, which is not desirable for seismic performance of any structural element. curvature ductility coefficient of beam corroded at 9.24% corrosion level obtained 5 times lower as compare to control rc beam. reduction in ojha et al., j. build. mater. struct. (2022) 9: 74-86 85 ultimate deflection signifies loss in ductility of the corroded beams and the failure of the corroded beams indicates transfer from ductile failure mode with a large mid-span deflection to a brittle failure mode with only a few limited deflections gradually. thus, it can be said that, corrosion of rebars is likely to make the real structures brittle and may cause sudden failure, which can be even more detrimental. 5. references aci committee 201.2r-08 (2008). guide to durable concrete, american concrete institute, 53p. ahmad, s. (2003). reinforcement corrosion in concrete structures, its monitoring and service life prediction––a review. cement and concrete composites, 25(4-5), 459-471. https://doi.org/10.1016/s0958-9465(02)00086-0 ahmad, s. (2009). techniques for inducing accelerated corrosion of steel in concrete. arabian journal for science and engineering, 34(2), 95. andrade, c., alonso, c., gulikers, j., polder, r., cigna, r., vennesland, … elsener, b. (2004). test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method. materials and structures, 37(273), 623–643. arora, v. v, singh, b., & jain, s. (2016). experimental studies on short term mechanical properties of high strength concrete. indian concrete journal, 90(10), 65–75. arora, v. v., & singh, b. (2016). durability studies on prestressed concrete made with portland pozzolana cement. indian concrete joural 90(8). arora, v. v., singh, b., & patel, v. (2018), “study on flexural behaviour of reinforced high strength concrete beams,” indian concrete journal, vol. 92, no. 7 arora, v. v., singh, b., & patel, v. (2019). durability and corrosion studies in prestressed concrete made with blended cement. journal of asian concrete federation, 5(1), 15-24. arora, v. v., singh, b., & yadav, l. (2016). flexural and fatigue behavior of prestressed concrete beams made with portland pozzolana cement. journal of asian concrete federation, 2(1), 15-23. astm, g59. (2009). standard test method for conducting potentiodynamic polarization resistance measurements. annual book of astm standards, 3, 237-239. baji, h., & ronagh, h. (2011). investigation of ductility of rc beams designed based on as3600. in international postgraduate conference on engineering, designing and developing the built environment for sustainable wellbeing. belda revert, a., de weerdt, k., hornbostel, k., & geiker, m. r. (2018). carbonation-induced corrosion: investigation of the corrosion onset. construction and building materials, 162, 847–856. https://doi.org/10.1016/j.conbuildmat.2017.12.066 bhaskaran, r., bhalla, l., rahman, a., juneja, s., sonik u., kaur s., kaur s. & rengaswamy, n. s. (2014). an analysis of the updated cost of corrosion in india. materials performance, 53(8), 56-65. bossio, a., imperatore, s., & kioumarsi, m. (2019). ultimate flexural capacity of reinforced concrete elements damaged by corrosion. buildings, 9(7), 160. cabrera, j. g., & ghoddoussi, p. (1992). the effect of reinforcement corrosion on the strength of the steel/concrete bond. in international conference on bond in concrete (pp. 11-24p). ceb riga, latvia. campione, g., cannella, f., cavaleri, l., di trapani, f., & minafo, g. (2016). shear and flexural strength of corroded rc beams. in italian concrete days 2016-giornate aicap e congresso cte (pp. 1-9). gwmax srl. emmons, p. h. (1993). concrete repair and maintenance illustrated: problem analysis, repair strategy, and techniques. rsmeans, p. 320. https://doi.org/10.1016/s0958-9465(02)00086-0 https://doi.org/10.1016/j.conbuildmat.2017.12.066 86 ojha et al., j. build. mater. struct. (2022) 9: 74-86 erdoǧdu, ş., kondratova, i. l., & bremner, t. w. (2004). determination of chloride diffusion coefficient of concrete using open-circuit potential measurements. cement and concrete research, 34(4), 603– 609. https://doi.org/10.1016/j.cemconres.2003.09.024 is :456 (2000). plain and rccode of practice. bureau of indian standards, new delhi, 1–114. is :516 (2021). hardened concrete method of test-part :i testing of strength of hardened concrete, parti, section-i : compressive, flexural and split tensile strength, bureau of indian standards, new delhi, india (pp. 1–9). kashani, m. m., maddocks, j., & dizaj, e. a. (2019). residual capacity of corroded reinforced concrete bridge components: state-of-the-art review. journal of bridge engineering, 24(7), 03119001. https://doi.org/10.1061/(asce)be.1943-5592.0001429 kwan, a. k. h., ho, j. c. m., & pam, h. j. (2002). flexural strength and ductility of reinforced concrete beams. proceedings of the institution of civil engineers-structures and buildings, 152(4), 361-369. https://doi.org/10.1680/stbu.2002.152.4.361 nt build 492. (1999). concrete, mortar and cement-based repair materials: chloride migration coefficient from non-steady-state migration experiments. measurement, 1–8. ojha, p.n., kaura, p., & singh b., (2022). durability design of reinforced concrete structures-national & international scenario, ce&cr magazine, pages 42-49, april-2019 olivia, m., & mandal, p. (2005). curvature ductility of reinforced concrete beam. journal of civil engineering, 6(1) peng, j., xiao, l., zhang, j., cai, c. s., & wang, l. (2019). flexural behavior of corroded hps beams. engineering structures, 195, 274-287. rao, g. a., vijayanand, i., & eligehausen, r. (2017). studies on ductility of rc beams in flexure and size effect. proceedings of the 6th international conference on fracture mechanics of concrete and concrete structures, 2, 671–675. singh, b., arora, v. v, & patel, v. (2018). study on stress strain characteristics of high strength concrete. indian concrete journal, 92(6), 37–43. webster, m. p., & clark, l. a. (2000). the structural effect of corrosion–an overview of the mechanism. proceedings of the concrete communication, birmingham, uk, 409-421. yuksel, i., & sakcalı, g. b. (2022). effects of reinforcement corrosion on reinforced concrete buildings. proceedings of the institution of civil engineers-structures and buildings, 175(3), 244258. https://doi.org/10.1680/jstbu.19.0011 https://doi.org/10.1016/j.cemconres.2003.09.024 https://doi.org/10.1061/(asce)be.1943-5592.0001429 https://doi.org/10.1680/stbu.2002.152.4.361 https://doi.org/10.1680/jstbu.19.0011 j. build. mater. struct. (2022) 9: 133-140 original article doi : 10.34118/jbms.v9i2.2782 issn 2353-0057, eissn : 2600-6936 viability of flax particles to develop cellular construction materials: physico-mechanical characterisation m. hamadou-ali 1, a. benazzouk 1,*, h. ben hamed 1 1 laboratory of innovative technologies (ur-upjv 3899), university of picardie jules verne, amiens, france. * corresponding author: amar.benazzouk@u-picardie.fr received: 21-09-2022 accepted: 23-12-2022 abstract. the problems related to environmental issues have motivated extensive research on environmentally friendly materials. the built environment is responsible for high primary energy use and more of energy related co2 emissions. however, it is important to develop lowembodied energy, carbon-negative, sustainable construction materials to replace conventional products. in this context, agricultural wastes are the excellent alternative materials to substitute mineral aggregates because they are widespread and easily accessible. the application of these elements is interesting as regards the recycling of the vegetable particles, since these are easily available and renewable low-cost raw materials, and has advantage for economy and environment. however, the reduction of energy consumption in construction, production of thermal insulation materials, and the solution of environmental problems by recycling waste are becoming greater problems. various types of agriculture waste, after being processed, have been used as particles in concrete or mortars. these materials display lower density and have several potential applications such as acoustic and thermal insulation, fire resistance cladding…etc. the study reported in this paper was undertaken to investigate the physico-mechanical properties of cellular materials based on flax particles, in order to produce usable materials in cellular concrete applications. the material produced containing different volumes of fla x particles (0v (control mortar), 1v, and 2v) was lightened by creating a porous structure in the matrix through a chemical reaction between aluminium powder and free lime. a study conducted on hardened material properties has indicated a significant reduction in sample unit weight, thereby resulting in a level of compressive strength compatible with a loadbearing wall. the reduction in flexural strength was lower than that in compressive strength. these results shown that the cellular material based on flax particles can be used as suitable insulated load-bearing walls. key words: flax particles, cellular concrete, feasibility, porous structure, physico-mechanical properties. 1. introduction wastes from different sources are causing environmental problems associated with their storage and their rising quantities (europäische kommission, 2014). in the construction field, the recycling of agricultural wastes is increasingly considered. the needs to conserve traditional building materials that are facing depletion have obliged engineers to consider alternative materials. however, the use of renewable raw material derived from agricultural products has been the subject of extensive research, while different types of agricultural wastes including hemp, flax, rapeseed, jute, palm… have been used as particles and/or fibres replacement of sand and aggregates in concrete and mortars (islam and ahmed, 2019; benmahiddine et al., 2020; alkutti et al., 2018). the application of these elements is interesting as regards the recycling of the wastes, since these are easily available and renewable low-cost raw materials, and has advantage for economy and environment. http://www.oasis-pubs.com/ mailto:amar.benazzouk@u-picardie.fr 134 m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 the versatility of using vegetable materials in concrete to replace mineral aggregates has given rise to several applications in lightweight construction field. according to the literature, extensive studies have shown the benefits of hemp particles reinforced materials, as non-load bearing construction materials, while the influence of different parameters including particle sizes, hydraulic and/or organic binder type, and casting process have been reported. the results have promoted several interesting properties of specimen such as a low density, acoustic and thermal insulation, fire resistance, and higher hygro-thermal performances (ingrao et al., 2015; arnaud and gourlay, 2012; evrard and de herde, 2009; le et al., 2015). in addition, the hemp particles reinforced concrete offers a high-quality living environment due capability to regulate indoor humidity of buildings by absorbing and/or releasing water (mazhoud et al., 2021, benmahiddine et al., 2020; de bruijn and johansson, 2013; asli et al., 2021). the panels based on hemp hurds with novel hybrid organic-inorganic binders characterized by their physical, microstructural, thermal, and mechanical properties have shown parameters comparable to those of commercially available products (santos et al., 2015; manzi et al., 2013). although the demand for vegetable materials is growing worldwide, the specimen-based these plants need further research with respect to the opportunities for their use, and to provide novel products with improved properties. another more innovative way consists to develop new cellular construction materials based on flax particles, in order to produce usable specimen in cellular concrete applications. through appropriate production methods, cellular concrete featuring a wide range of densities (300–1800 kg/m3) may be obtained, in comparison with 2300 kg/m3 in density for traditional concrete (panesar, 2013). a further innovative strategy is the lightened of the materials by creating a porous structure in the matrix through a chemical reaction between aluminum powder and free lime contained in hydraulic binder. according to the researches down, these materials remain relatively unexplored. the scope of this study is to investigate the potential use of flax particles in preformulated tradical pf70 hydraulic based-binder, within the scope of providing usable specimen in cellular concrete applications. the influence of flax particles volume (0v (cellular control specimen), 1v, and 2v) on the physic-mechanical and thermal properties has been evaluated. 2. materials and experimental testing 2.1. materials and specimen production the vegetable particles used in this study are waste by-products materials derived from linen industry. resulting from flax fibres stripping process, these materials contain a mixture of flax particles, steam fragments, lint, and wood shaves. the shape and properties of flax particles used in this study are shown in fig. 1 and table 1, respectively. fig. 1. shape (a) and particle size distribution (b) of flax particles a b m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 135 table 1. properties of flax particles bulk density (kg/m3) absolute density (kg/m3) porosity (%) water absorption (%) 100 1054 90.5 280 the preformulated lime binder used in this study, called “tradical pf70” is supplied by “lhoist” industry, of the northern region of france (bcb, 2015). it contains 75% air lime, 10% hydraulic lime, and15% of pozzolan mixture, where the binder is already used to produce hemp concrete. the use of this binder has several advantages that are related to its hydrophobic nature which acts as protective barrier for included vegetable particles when specimen exposed to hygroscopic environment. constituent materials mixes included aluminum powder with 325 mesh in size and 99% purity, used for the lightening process, and flax particles added at different volume of 0 (control specimen), 1, and 2. the used amount of aluminum powder in mixes is 0.3% by weight of binder. both tradical pf70 binder and aluminum powder were initially mixed in a planetary mixer. after water adding, flax particles were uniformly dispersed with slow increment throughout the binder. the fresh materials were allowed to mix for three additional minutes. all the specimens were then cast on a vibrating table and moist-cured for 28 days at 20 ± 2 °c and 98 % relative humidity. for hardened properties measurement, prismatic (40 x 40 x 160 mm) and cylindrical (110 x 220 mm) samples were prepared for flexural and compressive-tests, respectively. the expanded volume of fresh specimen after casting due to the chemical reaction between aluminum powder and free lime contained in binder is shown in fig. 2, while the chemical reaction occurred produces hydrogen gas in the binder, and thus creates microscopic air bubbles in the matrix, according the chemical reaction mechanism illustrated bellow. after 24h and before demoulding, the expanded parts of the hardened samples were cut. the corresponding composition-mixes and designations of samples are summarized in table 2. fig. 2. shape of fresh specimens 2𝐴𝑙 + 3𝐶𝑎(𝑂𝐻)2 + 6𝐻2𝑂 → 3𝐶𝑎𝑂. 𝐴𝑙2𝑂3. 6𝐻2𝑂 + 3𝐻2 aluminum powder + calcium hydroxide tricalcium hydrate + hydrogen expanded part of specimen due to aluminum reaction 136 m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 table 2. composition-mix and i.d of specimens specimen-id tradical binder (kg/m3) flax particles (kg/m3) alum./binder ratio by mass (%) water/binder ratio (by mass) csa 528 0 0.8 0.50 mf1b 287 39.85 0.8 0.65 mf2c 199 55.34 0.8 0.80 a control specimen ; b specimen with 1 volume flax ; c specimen with 2 volumes flax 2.2. experimental testing after 28 days of curing time, the dry bulk density was measured, after oven-drying the samples at 70 ± 2 °c, by means geometrical measurement and weighting. the apparent open porosity measurement was performed using the vacuum saturation method (astm c20–00, 2019). a dry sample of 40 x 40 x 40 mm in dimensions was placed in a desiccator and air was evacuated during several hours, using a vacuum pump and then water was injected until total immersion of the sample. as the material reached constant weight, the open porosity can be deduced from three mass measurements: dry mass and saturated mass obtained by weighing in air and saturated mass obtained by hydrostatic weighing. the mechanical properties were evaluated by performing compressive and flexural tests, in accordance with european standard nf en 196-1 (afnor, 1995), using an electromechanical testing machine tinus olsen h50ks model, equipped with a load cell of 50 kn (fig. 3). the rates of compressive and flexural loading were 4 mm/min and 0.4 mm/min, respectively. three replications were used for each property tested. the compressive stress-strain and the flexural load-deflection diagrams were recorded to evaluate several mechanical parameters of specimens. fig. 3. mechanical-test machines. (a): compressive-test ; (b): flexural-test 3. results and discussion 3.1. specimen lightening the effect of change in flax particles volume on dry unit weight of the specimen is shown in fig. 4, while the value decreased from 1080 kg/m3, for control specimen (0 volume of flax), to 590 kg/m3 for specimen with 2 volumes of flax particles. these values correspond to reduction of up to 44%. the decrease in unit weight is due to the physical properties of flax, since it has low density. in addition, the reaction between aluminum powder and free lime creates porous structure that lightened the samples. fig. 5 shows the air void structures of control specimen compared to the a b cylindrical specimen lvdt transducers load sensor prismatic specimen m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 137 specimen-mix with 2 volumes of flax particles, while uniform air voids distribution and continuous cells were observed in all specimen mixes. as reported in table 3, the total porosityvalues, measured by vacuum saturation, indicated that the increase of flax particles increases porosity of specimen. the corresponding value varied from 28 % to 69 %. this contributes to lightening the material which make in the same magnitude of traditional cellular concrete in term of density ranged from 300 to 1800 kg/m3. fig. 4. variation of dry unit weight vs. flax volume fig. 5. sem micrographs of specimen microstructure table 3. physical properties of specimens specimen-id bulk density (kg/m3) open porosity (%) cs 1080 ± 20 28 ± 5 mf1 713 ± 25 63 ± 10 mf2 590 ± 35 69 ± 12 3.2. compressive strength of specimens the 28-days stress-strain diagram of specimens with respect to the flax particle content is presented in fig. 6. the results indicated that the increase of flax particles volume serves to reduce compressive strength. value decreases from 1.52 mpa, for control specimen, to 0.74 mpa for specimen containing 2 volumes of flax (mf2). it corresponds to reduction of approximately 53 %. the decrease in compressive strength is related to the mechanical properties of flax materials since they are less stiff than the surrounding hydraulic binder paste. the low strength of flax may be the important limiting factor affecting the specimen mechanical properties that leads to interfacial bond defects between particles and matrix. the decrease in compressive strength is also related to porous structure of sample. the more the air-bubble ratio, the lighter the specimen and the lower its mechanical strengths. the 28-days parameter-values of specimens, subjected to compressive test, are shown in table 4. the corresponding elastic modulus-value varied from 353 0 200 400 600 800 1000 1200 0 1 2 u n it w e ig th ( k g /m 3 ) volume of flax particles cs specimen a b mf2 specimen 138 m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 to 212.5 mpa for mf2 specimen. the results highlight the ductile failure of the specimen-based flax particles that exhibits high plastic phase and underwent significant displacement before fracture. the variation of ultimate strain-value from 6.95 mm/m to 12.55 mm/m, showed that the addition of flax particles allows to make the specimen more ductile, as regards the elastic behaviour. fig. 6. stress-strain diagram of specimens under compressive test table 4. 28-days parameter-values of specimens under compressive test specimen-id compressive strength (mpa) ultimate strain (mm/m) elastic modulus (mpa) cs 1.52 ± 0.10 6.95 ± 0.52 353.0 ± 25 mf1 1.38 ± 0.15 8.18 ± 0.95 242.4 ± 44 mf2 0.74 ± 0.18 12.55 ± 1.14 212.5 ± 53 3.3. flexural strength of specimens the 28-days load-deflection curves in flexural behaviour with different flax volume is shown in fig. 7. a low reduction in the flexural strength of the specimen is observed with particles adding. value decreases from 1.18 mpa, for reference specimen, to 1.05 mpa for mf2 sample with 2 volumes of flax. the value corresponds to reduction of up to approximately 11 %. this finding suggests that both mechanical properties of particles and sample’s porous structure decrease the mechanical strengths of specimen. results also indicated that for a given flax ratio, the decrease in flexural strength is lower than that in compressive strength, probably due to the dilution effect of flax particles. it is considered that the tension effect of the flax particles occurs during the diffuse micro-cracking phase of "bending" the active micro-cracks and then in delaying the onset of their appearance, which serves to improve material flexibility. this could be also explained by the capability of flax particles to bridge the cracks and lead to limit their progression in the matrix. this bridge effect makes ductile material. the corresponding parameters, indicated in table 5, show an increase in deflection with flax particles addition from 0.20 to 1.29 mm with 2 volume of flax addition. the variation of elastic modulus confirms this tendency with decreasing the corresponding value from 331.70 to 78.56 mpa, thus showing a ductile behavior of specimen containing flax particle, as compared to that without flax which in contrast exhibited a brittle failure. m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 139 fig. 8, which compares the shapes of specimens after failure, highlighted the bridging effect of flax particles thus allowing to control the rate of cracks propagation. in contrast to the control specimen which exhibited a sudden fracture followed by fast crack propagation, the addition of flax particles allowed the sample to fail progressively and to maintain its structure due to the bridging effect of flax particles. fig. 7. load-deflection diagram of specimens under flexural test table 5. 28-days parameter-values of specimens under flexural test specimen-id flexural strength (mpa) ultimate deflection (mm) elastic modulus (mpa) cs 1.18 ± 0.03 0.20 ± 0.05 331.70 ± 25 mf1 1.07 ± 0.05 0.43 ± 0.08 222.89 ± 35 mf2 1.05 ± 0.07 1.29 ± 0.10 78.56 ± 18 . fig. 8. shapes of specimens after flexural failure 4. conclusions a test program was conducted in this study to develop information about properties of cellular specimen based on flax particles. the test results indicated that there is great potential for the use of flax by-product in binder mixes to produce usable lightweight construction materials in cellular concrete applications, such as load-bearing wall materials. tests-result, performed on hardened specimen, have shown that the sample reached a dry unit weight of about 590 kg/m3 with a compressive strength of 0.74 mpa. the reduction is related to both low stiffness of particles and porous structure of the specimen. the decrease in flexural strength is lower than that in compressive strength due to the bridging effect of flax particle. this research highlighted the effect bridging effect mf2 sample cs sample sudden fracture 140 m. hamadou-ali et al., j. build. mater. struct. (2022) 9: 133-140 of adding flax particles to attain substantial properties of innovative cellular materials and allows considering a broad range of applications in the field of cellular concrete. in spite of the positive implications of the test-results, supplementary research is required to examine the effect of varying porous structure level on physico-mechanical and thermal properties of the materials. 5. references al-kutti, w., et al. (2018). an overview and experimental study on hybrid binders containing date palm ash, fly ash, opc and activator composites. construction and building materials, 159, 567-577. arnaud, l., gourlay, e. (2012). experimental study of parameters influencing mechanical properties of hemp concretes. construction and building materials, 28(1), 50-56. asli, m., et al. (2021). thermal and hygroscopic study of hemp concrete in real ambient conditions. journal of building engineering, 44,102612. astm c20–00, 2019. standard test methods for apparent porosity, water absorption, apparent specific gravity, and bulk density of burned refractory brick and shapes by boiling water 1. bcb. (2015). http://www.bcb-tradical.fr. benmahiddine, f., et al. (2020). effect of flax shives content and size on the hygrothermal and mechanical properties of flax concrete. construction and building materials. 262, 120077. benmahiddine, f., et al. (2020). experimental investigation on the influence of immersion/drying cycles on the hygrothermal and mechanical properties of hemp concrete. journal of building engineering, 32, 101758. de bruijn, p., and johansson, p. (2013). moisture fixation and thermal properties of lime–hemp concrete. construction and building materials, 47, 1235-1242. europäische kommission generaldirektion (2014). eu energy, transport and ghg emissions trends to 2050 reference scenario, ed. e. publ. off. of the europ. union. evrard, a., and de herde, a. (2009). hygrothermal performance of lime-hemp wall assemblies. journal of building physics, 34(1), 5-25. ingrao, c., et al. (2015). energy and environmental assessment of industrial hemp for building applications: a review. renewable and sustainable energy reviews, 51, 29-42. islam, m.s. and ahmed s.j.u. (2018). influence of jute fiber on concrete properties. construction and building materials, 189, 768-776. le, a.t., et al. (2015). influence of various starch/hemp mixtures on mechanical and acoustical behavior of starch-hemp composite materials. composites part b: engineering, 75, 201-211. manzi, s., sassoni, e., motori, a., montecchi, m., canti, m. (2013). new composite with hemp hurds for sustainable buildings. environ. engineering management journal, 12, 31–34. mazhoud, b., et al. (2021). effect of hemp content and clay stabilization on hygric and thermal properties of hemp-clay composites. construction and building materials, 300, 123878. norme afnor. (1995). méthodes d’essais des ciments, partie 1: détermination des résistances mécaniques. panesar, d.k. (2013). cellular concrete properties and the effect of synthetic and protein foaming agents. construction and building materials, 44, 575-584. santos s.f., tonoli, g.h.d., melja, j.e.b., florelli, j., savastano, h. jr. (2015). non-conventional cement-based composites reinforced with vegetable fibers: a review of strategies to improve durability. materiales de construcción, 65, 317, 1-19. http://www.sciencedirect.com/science/article/pii/s0950061813002298 j. build. mater. struct. (2022) 9: 141-149 original article doi : 10.34118/jbms.v9i2.2780 issn 2353-0057, eissn : 2600-6936 characterization of a bio-based concrete using virgin cork aggregate hariz s. *, ghomari f. , touil b. eole laboratory, faculty of technology, university of tlemcen, algeria * corresponding author: samah.hrz@gmail.com received: 21-09-2022 accepted: 23-12-2022 abstract. the field of construction, like other field besides, faces new challenges, particularly that relating to reduction of the environmental impact and the improvement of the thermal and energy performances. to this end, the work presented in this article concerns bio-based concrete which complies with the new regulatory provisions inherent in cementitious materials. this is a concrete where 25% of the mineral volume is replaced by the same plant volume (male cork) in the dry state and immersed for 2 hours in water while adding 10% of filler. a first experimental campaign was carried out in the laboratory in order to identify the rheological behavior of the composite in the fresh state and the mechanical behavior in the hardened state. the results showed that this material can be used in many civil engineering applications. key words: lightweight concrete, virgin cork, filler, porosity, rheology, strength. 1. introduction sustainability, energy and environment requirements have become a major concern in european directives (2012/27/ue and 2010/30/ue, gomes et al., 2019). to promote energy efficiency in buildings and to solve the problem of depletion of natural resources in many countries, taking into account the importance of environmental issues (salem et al., 2020). many researchers have been conducted in recent years and the development of more thermal insulation systems in buildings in order to reach the required economic and environmental requirements and to provide mechanical properties to ensure an adequate durability for constructions. gomes et al., (2019). these researches have worked to develop eco-concretes that include light insulating materials with density of less than 150 kg/m3 and a thermal conductivity of less than 0.05 w/mk (rodrigues et al., 2009). likewise, inorganic materials (such as porous sedimentary rocks, expanded glass, and expanded clay). also, organic materials (such as expanded polystyrene or cork) (eurolightconr1, 1988; stefanidou, 2014). moreover, some studies have developed incorporation of high thermal insulation aggregates but the latter is still not available in the market (de fátima júlio et al., 2016; gomes et al., 2017). expanded polystyrene (eps) and cork are most commonly used as lightweight aggregates in industrial heat treatment formulations (gomes et al., 2019). cork is the outer bark of the cork oak tree (suber quercus l) which is abundant in southern europe and north africa (silva et al., 2017; pereira, 2007; knapic et al., 2016; gil, 2009). it is a natural and renewable plant that is harvested every (gomes et al., 2017; silva et al., 2017; pereira, 2007; knapic et al., 2016) years when the bark becomes peelable and the material is denser. in its lifetime, the cork oak produces three types of cork, male cork from the first stripping, reproduction cork from the second stripping and reproduction cork from subsequent strips (silva et al., 2017). cork is a cellular material, light, flexible and permeable to gases and liquids, as well as having high insulating abilities (silva et al., 2017; pereira, 2007 knapic et al., 2016). the applications of cork vary according to its quality and different properties (density, microstructure and chemical composition) shown in the table 1 and 2. (tedjditi et al., 2020). reproduction cork is characterized by high quality, uniform cell structure and smooth surface http://www.oasis-pubs.com/ mailto:samah.hrz@gmail.com 142 hariz et al., j. build. mater. struct. (2022) 9: 141-149 used in the production of cork stoppers. while male cork does not achieve the required quality, as it is characterized by a rough surface and an irregular cellular structure, so it is used in the production of shoes and cork boards (pereira, 2007). algeria is considered the third in the world among the countries that contain the cork oak tree with an area of 410,000 hectares, but it occupies the last ranks in terms of exploitation (garavaglia and besacier, 2012). table 1. properties of virgin and reproduction cork. (tedjditi et al., 2020) authors surface nature (silva et al., 2005) density (kg/m3) (fortes and rosa, 1988) microstructure (pereira, 2007) virgin cork rough 160-240 irregular structure. distortion in radial alignment of cell rows. corrugation of cells reproduction cork smooth and unblemished 120-180 structure more regular than virgin cork. enhancement of celle corrugation table 2. chemical composition of virgin and reproduction cork. (tedjditi et al., 2020) author cork type suberin lignin polysaccharides (cellulose and hemicellulose) extractables ash others pereira (2007) virgin cork 45 21 13 19 1.2 0.8 reproduction cork 33.5 26 25 13 2.5 caldas (1986) virgin cork 45 27 12 10 5 reproduction cork 48 29 12 8.5 2.1 in order to avoid throwing and wasting cork as well as to expand its use, natural and expanded cork granules were incorporated into cement compounds. bras et al., (2013) evaluated the rheological, mechanical and thermal properties of synthetic cork mortar intended for the correction of thermal bridges, they tested different doses (0-80%) of 0.5-2 mm cork granules. merabti et al., (2021) studied the mechanical, thermal and physical properties of the composite of granular waste cork with slag cement. the size distribution of waste cork is from 2.5 to 8 mm. the slag used is granular glass furnace slag (ggbfs). cement was partially replaced by 15%, 30% and 50% ggbfs by weight cement. they concluded that the increase in cork volume decreases density and thermal conductivity. there is a significant decrease in strength with the presence of cork. in long-term, they also note the increase of compressive strength with the addition of slag. sudagar et al., (2018) studied the effect of waste cork residues on geopolymers based on metakaolin and zeolite. cork residue (20%) was added. besides the reference geopolymer based on metakaolin also, 25, 50 and 75% metakaolin was replaced by zeolite. they concluded that the addition of zeolite improved the compressive strength of the geopolymers (the highest strength of the geopolymers was 50:50 metakaolin: zeolite and 20% by weight of cork residue). the further increase in zeolite affected the strength of the geopolymer negatively. the adsorption increased with the increase of metakaolin in the structure. they also found that the cork residue enhanced the compressive strength as well as the adsorption properties of geopolymers. in the last two decades, most of the research focused on the use of reproductive cork, as well as the cork resulting from waste stoppers and cork boards, but what we want to discover is the possibility of using and exploiting male cork in lightweight concrete. tedjditi et al., (2020) previously researched in this regard, where they studied the possibility of producing lightweight concrete using male cork, as they replaced the aggregates with cork (0, 25, 50, 75, 100%) by volume and concluded that the introduction of male cork in concrete leads to a decrease in the workability and viscosity. they noticed that the increase in porosity and capillary absorption reduced the mechanical strength compared to the reference concrete. they also found that concrete containing more than 50% male cork provided good thermal conductivity with a value of (0.041 to 0.56) w/m.k. to complement the research conducted by tedjditi and in order to improve the mechanical properties as well as ensure the sustainability and durability of male cork concrete, our study aims to explore the possibility of using natural and expanded cork granules (0-4, 4-8 and 8-16 mm) with 10% of filler in the hariz et al., j. build. mater. struct. (2022) 9: 141-149 143 production of lightweight concrete suitable for construction use. aggregates were replaced in term of volume by (0 and 25%) of cork aggregates. our research includes: workability, plastic viscosity, mechanical strength. 2. research significance for the first time, tedjditi et al., (2020). carried out an experimental work to develop lightweight concrete using virgin cork granules and reached good results, especially in the field of thermal insulation, but it remained unsuitable for construction. for this reason and to go deeper in this field, we completed this research, as we studied concrete with 25% of cork immersed in water for 2 hours (concrete that provided the best results) with increasing the amount of cement also adding 10% of filler in order to improve the mechanical properties. 3. experimental program the experimental program was carried out at eole (water and structures in their environment) laboratory which is situated in abou bekr belkaid tlemcen university, algeria. 3.1. materials male cork concrete mixtures were made by using: composite portland cement (cpj-cemii/a 42.5 n) which presents an apparent density of 1011 kg/m3, particle density of 3024 kg/m3 and blaine specific surface area of 3142 cm2/g, produced by beni-saf cement company situated in western algeria. sand with grain size 0–4mmand gravel with grain size 4–8mm and 8–16 mm, purchased from national company of aggregates situated in sidi abdelli, tlemcen algeria. superplasticizer water reducer modified polycarboxylate which have density of 1060 kg/m3, purchased from orachem concrete company located in boutlelis, oran, algeria. table 3. physical properties of mineral aggregates (tedjditi et al., 2020) table 4. physical properties of virgin cork aggregates (tedjditi et al., 2020) virgin cork granules with grain size 0–4 mm, 4–8 mm and 8–16 mm grinded and sieved in the laboratory. fig. 1. different sizes of the used virgin cork granules, (tedjditi & al, 2020). mineral aggregate bulk density (kg/m3) particle density (kg/m3) water absorption (%) inter particle porosity (%) sand 1636.4 2701.1 1.71 39.4 gravel 4-8 1310.9 2592.2 1.59 49.4 gravel 8-16 1179.6 2580.0 1.22 54.3 cork aggregate apparent density (kg/m3) particle density (kg/m3) water absorption (%) inter particle porosity (%) cork 0-4 88.9 218 168.67 59.2 cork4-8 83.8 184 116.78 54.5 cork8-16 86.0 223 68.89 61.4 144 hariz et al., j. build. mater. struct. (2022) 9: 141-149 3.2. mixture design and mixing procedure based on tedjditi (2021) search, the absorption results showed that this cork can absorb twice of its weight. also, the cork absorption varies from one category to another, so that the smaller size of aggregate is the most absorbent (the highest absorption of cork aggregate was (0-4) mm). table 5. water absorption ratios of dry cork classes. dry cork classes (mm) 0 – 4 4 – 8 8 – 16 water absorption ratios (%) 92 60 39 according to tedjditi (2021) research, two hours were chosen exactly because this time corresponds to the beginning of the phase, which is characterized by relatively slow absorption kinetics. as well as concrete with 25% of cork immersed in water for 2 hours showed good fresh homogeneity resulting a significant improvement in the consistency of cork concrete (tedjditi et al., 2022). six concrete mixtures were prepared. two control mixes, the first was regular concrete and the second was concrete with 10 % filler as well as two mixtures in which the proportions of sand and gravel 4-8 mm and gravel 8-16 mm, in size, were replaced by their equivalent of virgin cork 0-4 mm, 4-8 mm and 816 mm, respectively. ratio: 25%. in the first mixture, we used dry cork. in the second mixture, we soaked the cork for two hours in water before using. a superplasticizer of 0.7% by weight of cement was used. table 6. mixture proportions for studied virgin cork concretes in kg. concrete code reference ordinary concrete oc reference oc+10%fille r oc-f10 oc+25% dry cork oc-25dc oc+25% cork 2h in water oc-25hc oc+10%fille r+25% dry cork oc-10f25dc oc+10%fi ller+25%c ork (2hwater) oc-10f25hc water/binder cement mix water cork abs water total water super-plasticizer sand gravel 4–8 gravel 8–16 filler cork 0–4 cork 4–8 cork 8–16 0.45 450 202.5 / 202.5 3.6 700.2 161.6 788.2 / / / / 0.45 450 223 / 223 3.5 658.46 152 741.23 45 / / / 0.45 450 202.5 19.02 221.52 3.6 525.15 121.21 591.13 / 11.92 3.08 15.9 0.45 450 202.5 21.3 223.8 3.6 525.15 121.21 591.13 / 11.92 3.08 15.9 0.45 450 223 17.86 240.86 3.5 493.84 113.98 555.91 45 11.2 2.89 14.95 0.45 450 223 21.3 244.3 3.5 493.84 113.98 555.91 45 11.2 2.89 14.95 in the vertical axis mixer, virgin cork granules with their own absorbent water were introduced (table 5) and mixed for 90 seconds. then cement, sand and 50% superplasticizer were added and mixed for 4 minutes (water was added gradually for 90 seconds), after the gravel and the remaining superplasticizer water were added and mixed for 1 minute. finally, the mixture was stirred for 90 s. after removal from the molds, the test samples were treated with water until the day of the test. cross-sections were obtained from cylindrical samples with a diameter of 110 mm and a height of 220 mm in fig. 2. the images of the samples show the absence of separation marks, indicating good homogeneity of all the finished mixtures (fig. 3). hariz et al., j. build. mater. struct. (2022) 9: 141-149 145 fig. 2. protocol of mixing cork concretes (tedjditi et al., 2020) fig. 3. cross section of reference and male cork concretes 4. testing procedures 4.1. workability workability of the developed virgin cork concrete mixtures was determined by using slump test. 4.2. plastic viscosity plastic viscosity tests were conducted using coaxial vane geometry rheometer. the rheometer is equipped with a heidolph agitator (fig. 5). plastic viscosity tests were carried out 10 min after finishing mixing procedure. the obtained raw results present a relationship between torque and rotational speeds. fig. 4. slump test fig. 5. rheological laboratory apparatus 4.3. mechanical properties mechanical properties of the prepared concretes were measured at the age of 7, 28 and 90 days. measurements of compressive strengths were carried out on cylindrical samples (110 mm in diameter and 220 mm in height). 146 hariz et al., j. build. mater. struct. (2022) 9: 141-149 fig. 6. compressive strengths test 5. results and discussion 5.1 workability figure 7 shows the workability of virgin cork. as can be seen, the presence of virgin cork used does not play an important role in the workability of the mixtures. the mixtures maintained approximately the same workability in the presence or absence of virgin cork. for example, the workability of reference concrete (containing 0% virgin cork) was (195-200) mm. however, this slack became (194-205) mm when the virgin cork was added. concrete has maintained a very wet texture fig. 7. workability of the different mixtures. 5.2. plastic viscosity figure 8 shows the evolution of the concrete viscosity with the addition of filler and virgin cork. the results indicated that the addition of filler and cork leads to a decrease in the viscosity of concrete. it is important to note that during the tests, the mixtures showed good homogeneity, that is, signs of separation were absent. (the viscosity of the plastic has decreased from 15 pa for reference concrete to 0.4 pa for oc-10f-25hc concrete). remarkable is the fact that with workability, the viscosity of the plastic decreases with the addition of filler and virgin cork. this decrease could be related to the lower value of filler adsorption than that of cement and the lower density of cork grains, allowing for less friction and less resistance to flow. it can also due to the reduction of paste volume with adding cork amount and which allows more freedom for cork particles to circulate in the mixture. hariz et al., j. build. mater. struct. (2022) 9: 141-149 147 fig. 8. evolution of the concrete viscosity with the addition of filler and virgin cork. 5.3. mechanical properties 5.3.1. compressive strength the compressive strength obtained at 7, 28 and 90 days for the mixtures produced are summarized in fig 9. each value represents the average of three different samples. despite the reduction in mechanical strengths compared to reference concrete, the results show that with the addition of virgin cork, the compressive strength decreases but increased slightly with the addition of filler which ranged between 6.3 and 12.7 mpa at 90 days compared to (6.28.3) mpa that tedjditi found at 28 days for the same proportion of cork (25%) (tedjditi et al., 2022). the results on compressive strength seem to indicate that the developed concretes are classified according to the rilem recommendation in class ii for lightweight concrete (table 7). these concretes can be used both for structural and insulating elements. fig. 9. the compressive strength at 7, 28 and 90 days. 148 hariz et al., j. build. mater. struct. (2022) 9: 141-149 table 7. recommendation of functional classification of lightweight concrete (rilem-lc2, 1978) class i ii iii type of light concrete (lc) structural lc structural & insulating lc insulating lc oven dry density (kg/m3) < 1800 for information only for information only compressive strength (mpa) > 15 > 3.5 > 0.5 coef. of thermal conductivity (w/m k) __ < 0.75 < 0.30 6. conclusions in this work, an experimental investigation on the potential of using virgin cork and filler to develop lightweight concrete intended for building applications was conducted. the experiments were carried out on six mixtures containing, in volume of aggregates: 0 and 25% of virgin cork granules with or without filler. in summary, the study unveils the following: in fresh state, by introducing virgin cork into concrete, the workability and the plastic viscosity were mostly the same. despite the remarkable reduction in mechanical strengths compared to reference concrete, virgin cork and filler composites presented good mechanical properties as structural materials. for instance, the compressive strength ranged between 5 and 12.7 mpa. according to the tentative recommendation of functional classification of lightweight concrete. to complement this research, we look forward to conducting future porosity, permeability and chloride diffusion experiments to ensure the durability of the studied concrete. 7. references brás, a., leal, m., & faria, p. (2013). cement-cork mortars for thermal bridges correction. comparison with cement-eps mortars performance. construction and building materials, 49, 315-327. caldas, m. m. (1986). ceroides da cortiça. dados preliminares para um estudo mais aprofundado. boletim ipf, 578, 339-342. de fátima júlio, m., soares, a., ilharco, l. m., flores-colen, i., & de brito, j. (2016). aerogel-based renders with lightweight aggregates: correlation between molecular/pore structure and performance. construction and building materials, 124, 485-495. directive, c. (2010). directive 2010/30/eu of the european parliament and of the council. indication by labelling and standard product information of the consumption of energy and other resources by energy-related products. off. j. eur. union, 153, 1-2. directive, e. e. (2012). eu energy efficiency directive 2012/27/eu. journal reference, 50(315), 1-56. eurolightconr1, (1988). definitions and international consensus report, european union – brite euram iii 1988 be96-3942/r1. fortes, m. a., & rosa, m. e. (1988). densidade da cortiça: factores que a influenciam. cortiça, 593, 65-68. garavaglia, v., & besacier, c. (2012). state of mediterranean forests, in: vivexpo, vives. gil, l. (2009). cork composites: a review. materials, 2(3), 776-789. gomes, m. g., flores-colen, i., manga, l. m., soares, a., & de brito, j. (2017). the influence of moisture content on the thermal conductivity of external thermal mortars. construction and building materials, 135, 279-286. gomes, m. g., flores-colen, i., melo, h., & soares, a. (2019). physical performance of industrial and eps and cork experimental thermal insulation renders. construction and building materials, 198, 786-795. knapic, s., oliveira, v., machado, j. s., & pereira, h. (2016). cork as a building material: a review. european journal of wood and wood products, 74(6), 775-791. merabti, s., kenai, s., belarbi, r., & khatib, j. (2021). thermo-mechanical and physical properties of waste granular cork composite with slag cement. construction and building materials, 272, 121923. hariz et al., j. build. mater. struct. (2022) 9: 141-149 149 pereira h., (2007). cork: biology, production and uses, elsevier. pereira, h. (1982). studies on the chemical composition of virgin and reproduction cork of quercus suber l. anais do instituto superior de agronomia, vol. 40, p. 17. rilem, l c2 (1978). functional classification of lightweight concrete. mater. struct, 11, 281-283. rodrigues, a. m., piedade, a. c., & braga, a. m., (2009). thermal behavior of buildings (in portuguese). edições orion, pp. 1–673. salem, t., fois, m., omikrine-metalssi, o., manuel, r., & fen-chong, t. (2020). thermal and mechanical performances of cement-based mortars reinforced with vegetable synthetic sponge wastes and silica fume. construction and building materials, 264, 120213. silva, s. p., sabino, m. a., fernandes, e. m., correlo, v. m., boesel, l. f., & reis, r. l. (2005). cork: properties, capabilities and applications. international materials reviews, 50(6), 345-365. silva, s. p., sabino, m. a., fernandes, e. m., correlo, v. m., boesel, l. f., & reis, r. l. (2005). cork: properties, capabilities and applications. international materials reviews, 50(6), 345-365. stefanidou, m. (2014). cement-based renders with insulating properties. construction and building materials, 65, 427-431. sudagar, a., andrejkovičová, s., patinha, c., velosa, a., mcadam, a., da silva, e. f., & rocha, f. (2018). a novel study on the influence of cork waste residue on metakaolin-zeolite based geopolymers. applied clay science, 152, 196-210. tedjditi, a. k., ghomari, f., belarbi, r., cherif, r., boukhelf, f., & bouhraoua, r. t. (2022). towards understanding cork concrete behaviour: impact of considering cork absorption during mixing process. construction and building materials, 317, 125905. tedjditi, a. k., ghomari, f., taleb, o., belarbi, r., & bouhraoua, r. t. (2020). potential of using virgin cork as aggregates in development of new lightweight concrete. construction and building materials, 265, 120734. tedjditi, a.k., (2021). cork concrete: optimization of formulation and thermal performance. doctoral theses university of tlemcen, algeria. j. build. mater. struct. (2022) 9: 110-121 original article doi : 10.34118/jbms.v9i1.2083 probabilistic slope stability analysis: a case study of ain bouzian landslide within north-east algeria ghedjati s 1,2,*, lamara m 2, houmadi y 3 1 faculty of earth science, seddik ben yahia university,jijel, algeria 2 laboratoire de génie civil et environnement (lgce),university of seddik ben yahia, jijel, algeria 3 smart structures laboratory, department of civil engineering, university center of ain temouchent, ain temouchent, algeria * corresponding author: samirlabo23@gmail.com received: 17-09-2021 accepted: 29-05-2022 abstract. the aim of this study is to carry out a probabilistic analysis of slope stability within homogenous soil profile of ain bouzian landslides located north-east algeria. this region suffers of many instability problems, which is aggravated during the construction of eastwest motorway. the random variables for the soil considered in this study are the young modulus e, cohesion c and friction angle φ. stochastic soil properties values are used to evaluate the reliability and to assess sensitivity of the system, for two hydrological conditions, with and without water table within the soil mass. the deterministic model is based on strength reduction method (srm) analysis using the finite difference code flac3d. key words: factor of safety; failure probability, probabilistic method, monte carlo simulation, strength reduction method. 1. introduction the problems of the landslides have emerged, since the human being begins to disrupt the delicate balance of nature. the building of massive projects (motorways, dams etc….) has generated often problems of slope instabilities. with the development of economic construction, more and more attention has been paid to the reasonable assessment of slope stability. at present, the deterministic methods of slope analysis can mainly be classified into two categories: one is the limit equilibrium method (lem); the other is numerical approaches, such finite element method (fem) or finite difference method (fdm) (yang et al., 2012).though, conventional deterministic slope analysis does not account for assessing uncertainty in an explicit manner and relies on conservative parameters. the account for this uncertainty in design need statistical definitions of material properties, probabilistic analysis, and global response quantified in terms of reliability and probability of failure (hicks, 2005). slope stability engineering is perhaps the geotechnical subject that most dominated by uncertainty. geological anomalies, inherent spatial variability of soil properties, scarcity of representative data, changing environmental conditions, unexpected failure mechanisms, simplifications and approximations adopted in geotechnical models, and human mistakes in design and construction are all factors contributing to uncertainty (el-ramly et al., 2002). probabilistic modeling of slope stability problems has been carried out since seventies, albeit mainly through the use of limit equilibrium methods combined with various statistical approaches (el-ramly et al., 2002).it is worth to notice that the monte carlo simulation (mcs) method is the most used technique to conduct probability studies. this methodology is wellknown to be very expensive because of the great number of calls; of the deterministic model, required for the probabilistic analyses (houmadi et al., 2012).in this paper, an efficient probabilistic method called collocation-based stochastic response surface method (csrsm) is used. this method is based on the approximation of the system response by a polynomial chaos ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 111 expansion (pce). it aims to replace a complex deterministic model by a meta-model which is an approximate explicit analytical formula. this makes it easy to apply mcs methodology on the meta-model without the need to call the original deterministic numerical model. beside the csrsm allows to rigorously calculating the contribution of each random variable in the variability of the system response using sobol indices (sudret, 2008; mollon et al., 2011). this is very important because one can detect the uncertain variables that have the major contribution in the variability of the system response, and thus can lead to a reduction in the number of uncertain parameters that should be handled by the geotechnical engineer. this paper is organized as follows: first, a brief review of collocation-based stochastic response surface method (csrsm) and the sensitivity analysis are presented. then a brief presentation of study area where landslide has occurred along with geological formation of the site. finally, deterministic and probabilistic analyses are presented. the study ends up with a conclusion on the main findings. 2. revue of strength reduction method (srm) in the last few decencies, there are two main types of slope stability analysis method, one is based on the rigid body motion of limit equilibrium method, and the second is based on the numerical approaches. the latter once are currently adopted in several well-known geotechnical software. the strength reduction method (srm) was first put forward by zienkiewicz et al. (1975), which developed in 1990s (griffiths and lane, 1999). griffiths and lane (1999) indicated that srm is a powerful alternative to the traditional limit equilibrium methods, and should be seriously considered by geotechnical practitioners. this approach is one of the most important slope stability analysis methods. among its main advantages it’s suitability in dealing with nonhomogeneous soil profiles and complicated slopes. by combining reduction theory and elasticplastic method to analyze the slope stability, the nonlinear constitutive relationship of rock and soil mass are considered, the critical failure surface is detected automatically from the localized shear strain; it requires no assumption on the inter-slice shear force distributions; and it is applicable to many complex conditions (zeng and xiao, 2017). srm is typically applied with mohr-coulomb failure criterion for computing factor of safety, by progressively reducing the original shear strength parameters in order to bring the slope to a state of failure. this method implemented in flac3d (fast lagrangian analysis of continua), it is a three-dimensional explicit finite-difference program, to carry out a series of simulation of three-dimensional formations of soil, rock or others. the process of strength reduction technique can be described as follows. for mohr-coulomb failure criterion, the shear strength τf is given: (1) where σn is the effective normal stress, c is the cohesion, and φ is the angle of internal friction. the reduced shear strength τm along the failure surface is expressed as follows: (2) by substituting, we get: ⁄ (3) after strength reduction the strength parameters can be expressed as respectively: (4) ( ) (5) 112 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 the value of is adjusted until the slope fails, whereas the ultimate is the factor of safety. (6) 3. methodology 3.1. the study area ain bouzian landslide is one of many instability problems encountered in skikda region, it is located halfway between the two cities, skikda to the north (47 km) and constantine to the south, within eastern part of northern algeria, which have been sighted alongside of the ain bouzian-el harrouch section of the east-west motorway as shown in (fig .1). fig .1. (a) ;( b) and (c) map of algeria study area-ain bouzian showing location of landslide (google earth 2021) ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 113 3.2. field investigation from a geological point of view (figs. 2, 3), the area is a part of the maghrebain chain (bouillin, 1986) with a complex geological formations, it is the buffer zone between the kabylides (the internal zones) to the north and the tellian over thrust (external zones) to the south (durand delga, 1969), this area is a paleogeographic boundary that has been active during mesozoic era. furthermore the region of ain bouzian as the mountains of the northern part of algeria has been affected by the alpine orogeny with large and highly complex tectonic movements which results from the additional effects at least three different tectonic phases: before the eocene, during middle to upper eocene and during the upper oligocene (fig.1). according to raoult (1974) and benabbas (2007), at the north slope of dj kantour from the national road 03 to the plain of oued neça is consists of the flysch-formations , mauritian flysch of the ziane type of turoniansenonian age (greenish yellow marls with centimeter levels of slightly carbonate sandstone pelites, and varicolored clays) . fig. 2. general sketch of the maghrebian chain and location of the study area (belayouni et al. 2012) fig. 3. geology and geotechnical investigation on a major slope failure on a est-ouest highway (ain bouzian) 3.3. experimental work the hydrogeological (piezometric measurement) and geotechnical investigations carried out in site lead to identify the causes and mechanism of instability: representative soil samples were 114 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 collected from different parts of the slope. these soil samples were prepared and tested in laboratory to determine the average values of material properties which are given in table 1. according to the core drilling and the observation of slope, the local geology is predominated by the presence of yellowish brown weathered argillite, clay soil and blue-gray fresh argillite highly fragmented. according to inclinometer measurement, the shape of the sliding surface is located approximately between the layers of fresh and rather altered argillites, within a depth of 17m below ground surface. according to piezometric measurement, the level of the water table is quite high, around 1.4m below ground level, which indicate the significant effect of water table presence on the triggering of landslide. 4. deterministic analysis in this section the results obtained for fos, by deterministic slope stability analysis, using both methods srm and lem, are presented for both cases, with and without water table. the physical and mechanical parameters of the soil (table 1) were determined through in situ and laboratory tests. using this data the numerical simulations for slope stability analysis were performed. the failure criterion adopted is the mohr-coulomb criterion in the study. in order to initialize ground stress conditions the elastic parameters should be specified, a high elastic modulus was chosen to ensure that the model reaches equilibrium in a short time period. table 1. mechanics parameters of the slope item γh [kn/m 3 ] c [kn/m 2 ] φ [°] e [mpa] ν soil 20 3e4 20 7.38 0.3 figure 4 represents the slope profile with a total height equal to 60 m with a varying inclination angle (43.53°,23.26° and 09°),the geometric size and boundary conditions are also illustrated. fig. 4. model to evaluate slope stability analysis. the result of safety factors for the slope, computed using the strength reduction method (srm) and limit equilibrium methods (lem), are grouped in table 2, for both case, the safety factors values obtained by the two approaches are almost similar, the major difference is less than 8%. as expected the factor of safety in the case of absence of water table is greater than those obtained for saturated cases, the large difference is around 16 % (srm), however all values are less than 1.5 which means that the slope, in its state, is unstable. table 2. fos calculated by lem and srm. cases studies srm ordinary bishop janbu morgenstern price with water table 0.92 0.938 0.954 0.938 0.954 without water table 1.10 1.017 1.072 1.008 1.039 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 115 5. collocation-based stochastic response surface method (csrsm) csrsm is a general and powerful method for probabilistic analysis (isukapalli et al., 1998; sudret , 2008; mollon et al., 2011; houmadi et al., 2012). csrsm aims to determine the full probability distribution function (pdf) of the system response by accounting for the uncertainties of the input parameters by their probability distributions. the evaluation of probability distribution of the system response must be performed as follows:  the number and positions of the collocation points in the standard space of random variables, depends on the order of the chosen polynomial chaos;  the collocation points must be transformed into physical space of random variables (non-normal and/or correlated);  each collocation point available in the physical space must be computed, using the corresponding deterministic mechanical model of the system response (by performing the monte carlo-simulation method on the pce);  the pdf of the approximated system response is subsequently computed, and the statistical moments of this distribution are deduced. two methods are available for computing the pc expansion coefficients, from selected deterministic evaluations of the model function, whose unknown coefficients are computed either by a regression approach or by a projection approach (isukapalli et al., 1998; mollon et al., 2011). note that the size p of the pce is given by: ( ) (7) thus, the number n of available collocation points that are result from all possible combinations of the roots depends on the number of the random variables m and order p of the chosen pce, ( ) . the number of points required for an acceptable solution is directly related to the invariability of the information matrix , which represents the generic terms. herein, ψis the matrix of size n p whose coefficients are given by: ( ) it is necessary to specify the choice of the experimental design x, the output random variable may be expressed by a pce as follows: ∑ ( ) (8) the unknown coefficients of the pce can be computed using the following equation: ∑ { ( ) ∑ ( ) } ( ) (9) in which a is a vector containing the unknown coefficients, y is a vector containing the system responses as calculated by the deterministic model at the different collocation points and is a matrix of size n*p whose elements are the multivariate hermite polynomials. in the regression method, it is necessary to specify the choice of the experimental design to improve the accuracy of the results. the optimal number of regression points, for any number of input random variable m and degree of pc expansion p which is smaller than the empirical rule is given by the following equation. ( ) ( ) in the following parts, csrsm is used for reliability and the global sensitivity evaluation of slope stability using meta-model. the computational deterministic model for slope stability is based on flac3d code. the polynomial chaos expansion (pce) can be performed, whose unknown coefficients are determined by a regression approach. 116 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 the monte carlo simulation gives the system response through the evaluation of corresponding pdf and failure probability pf which provide an accurate and intrinsic representation of safety factor fos. this can be carried out faster than the other numerical approach, due to the high efficiency of the pce. the coefficients of the pce are computed by solving the linear system of equations using matlab. 5.1 reliability analysis using csrsm probabilistic analysis is commonly adopted to quantify the uncertainties of input parameters by computing failure probabilities of system responses. precisely, input parameters are treated as random variables following prescribed distributions, thus the corresponding model response (slope safety factor in this case) is also a random variable, and hence reliability analysis is carried out. the limit state/performance function, g(x) is defined in terms of the basic random variables xi, and the functional relationship among them. the failure condition is defined as g (x)=fs–1;the function of the uncertain input parameters and the factor of safety fs is given by eq. (6). the “probability of failure”, is regarded as the probability of unacceptable values for the analytical and statistical models yielded by the performance function. in this study, reliability evaluation has been carried out, using monte-carlo simulations, which is expressed as: ∑ ( ( )) ( ) where nmc is the number of mcs samples. stochastic soil properties values presented in table 3 are used to evaluate the reliability and to assess sensitivity of the system, for the two hydrological conditions. table 3. stochastic soil properties on the slope stability analysis parameters mean coefficient of variation (%) distribution type e [mpa] 7.38 9.78 log-normal c [kn/m²] 3e4 18.50 log-normal φ [°] 19.76 13.45 log-normal to get a good estimate of probability of failure through this method, 100,000 simulations were performed. these values are then used for the study of the system reliability for slope stability analysis. the effect of the presence of groundwater on slope reliability is also investigated in this section. the position of the water table in the slope is indicated in the previous section (determinist analysis).as displayed in table 1 for both cases, we have the same statistical input values for soil properties. the obtained result for pdfs, of the corresponding safety factors (fos), are shown in table 4, for both hydrological conditions. it is clear that the pdfs shapes tend to be gaussian distribution. we can conclude that, the presence of the water table generates higher variability of safety factor (fos), which illustrated by an increase in the mean value around 15 %. meanwhile the water table in the soil mass induces a substantial increase in the pf (table 4) more than three times that obtained in the case of absence of water table. the corresponding difference in pfis significantly large around 67%. which means that the presence of water table within the soil mass increases safety factor uncertainty and failure risk for the slope. most results of the analysis are presented in table 4. table 4. slope reliability analysis for both case study and its statistical moments case study mean standard deviation skewness kurtosis cov (%) pf (%) with groundwater table 1.11 0.021 0.471 0.423 0.131 22.20 without groundwater table 0.94 0.016 0.536 0.5891 0.136 68.70 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 117 5.2. sensitivity analysis using csrsm global sensitivity analysis based on sobol indices, aims to quantify the effects of each input random variable on the response system variability as well their interaction (huber et al., 2011), through computing the sobol’ indices, which have proven to be the most efficient sensitivity measures for general computational models. sudret (2015) has proposed an original post-processing of polynomial chaos expansions for sensitivity analysis, which can be established analytically, using, the sobol’ decomposition of a truncated pc expansion y. once the pc basis has been set up , and the coefficients have been calculated, the series expansion will be post processed, in order to compute the statistical moments of the model response (mean value, standard deviation, etc.), and the probability density function. notice that the sum of all the sobol indices of a model is always equal to unity. it is now easy to derive sensitivity from the above representation. these indices, called pc-based sobol' indices and denoted by sui1…………is ,are defined as: ∑ [ ] (12) there are several methods for the quantification of the accuracy of the pce, that depends mainly on its order. the calculation of the coefficient of determination r2 is commonly used to control the quality of approximation, by normalizing the mean squared difference between the model and the surrogate (sudret, 2008). the coefficient of determination r², is calculated as follows: (13) where is given by: ( ⁄ )∑ [ ( ( ) ( ( ))] ( ) (14) and ( ) ∑ [ ( ( )) ̅] (15) ̅ ∑ ( ( )) (16) in these equations, j is number of collocation points used to evaluate the unknown coefficients of the pce. m, ξ is the standard normal random vector which is defined by j realization { ( ) ( ( ) ( ) ) ( ) ( ( ) ( ) )}. in this study, a global sensitivity assessment based on sobol indices, relative to the three random variables (e, c, φ ) for the system response represented by (fos), were performed using the monte carlo simulation (mcs) via a pce within csrsm. according to the numerical results, a pce order m=7 with corresponds coefficient of determination r2 ≈ 0,999 are obtained with the number of calls equals 209. 6. parametric study in order to investigate the effect of cov of certain random variables on the reliability and the sensitivity of the system response related to safety, a parametric study is carried out. the random variables for the soil considered in this study are the young modulus e, cohesion c and friction angle φ. so the cov of cohesion c and friction angle φincreased or decreased by 10%, the cov of young modulus e increased or decreased by 20%. the sensitivity of the system response is estimated, using sobol indices. three values of each input parameter are considered (table 3), and their effects on the possibility of slope failure are assessed for both cases with and without water table. 118 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 6.1. their effect on the pdf of factor of safety figures 5, 6 and 7 illustrate the pdf associated for each parameter variations in both cases with and without water table. from the first examination of pdf curves, we can observe, for both hydrological cases, the parameter variations have similar effects on the pdf shapes. the effect of variation of young modulus is trivial and all curves overlap, the system response almost remain the same. while for the other two parameters ( c, φ) when increasing cov(φ) or cov(c), the pdf curves shift away from being gaussian distribution, the corresponding pdf changes, associated with friction angle variations, are more significant. fig. 5. influence of the coefficients of variation of young modulus cov (e) on the pdfs of (fos) : (a) without groundwater; (b) with groundwater fig . 6. influence of the coefficients of variation of cohesion cov(c) on the pdfs of fos: (c) without groundwater; (d) with groundwater. ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 119 fig. 7. influence of the coefficients of variation of friction angle cov (φ) on the pdfs of fos: (e) with groundwater; (f): without groundwater. 6.2 effect of variability of geotechnical input parameters on sensitivity analysis based on methods of global sensitivity analysis and using sobol indices, a study is realized in order to quantify the influence of each input random variables onto the system behavior. the computation of the sobol indices is achieved by monte carlo simulation, using a combination of input random variable cov (φ and c ).the effect of the coefficients of variation on sobol indices are presented in figures 8 and 9 ,for cov (φ ) and cov (c)respectively and both hydrological conditions, (with and without water table). fig . 8. influence of the coefficients of variation of friction angle cov (φ ) on the sobol index of s (c) and s (φ ) for both cases. fig .9. influence of the coefficients of variation of cohesion cov (c) on the sobol index of s (c) and s (φ) for both cases. as we can see in figures 8 and 9, with the increases of cov (φ) and cov (c) for both models, it is clear that the random variable φ has higher effect on the system response; its weight in the variability is more than 80% for both hydrological cases. while the random variable of cohesion c has less effect with values around 13% and 18%, for both system responses, with and without water table respectively. the random variable of elastic modulus e has negligible influence onto the system responses for both cases. therefore we can conclude that the random variable φ 120 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 plays major role into the variability of system response in slope stability analysis, thus great care should be paid during geotechnical evaluation of this parameter. 7. conclusion collocation-based stochastic response surface method (csrsm) was applied for the probabilistic study of slope stability analysis problems within homogenous soil profile of ain bouzian landslide. it intends to investigate the system response, reliability of slope failure and global sensitivity due to soil parameters variability and correlations for two hydrological conditions. from the previous results and discussions we can draw the main conclusions:  the deterministic analysis shows that the slope is instable for both cases with and without water table; with the shape of critical failure surfaces are almost circulars. the results obtained from the two approaches for safety factor are practically similar and indicate the slope is instable.  from parametric study, with the increase of cov(c), the pdf curves of safety factor remain almost gaussian with an increase in the main values. whereas for an increase of cov(φ), the pdf curves tend to shift away from gaussian shape with a reduction in the main value of factor of safety. moreover we can put forward that :  the young modulus has no effect on the system response which is logic. in fact this parameter is an elastic propriety of the soil mass and can be input as a deterministic parameter.  the major contribution to the system responses is induced by the variation of friction angle.  the other strength parameter of the soil, the cohesion, has minor effect on the system response.  we can conclude that the presence of water table reduces the probability of failure pf when increasing cov(φ) and cov(c), while we get the opposite impact in the case of absence of water table.  from global sensitivity analysis based on sobol indices, we can realize that the contribution of each parameter (c and φ ) increases with the increase of its coefficients of variation and reduces the effect of the other parameter. however the angle of friction always has the major contribution on the system response. 8. references belayouni, h., guerrera, f., martín, m. m., & serrano, f. (2012). stratigraphic update of the cenozoic subnumidian formations of the tunisian tell (north africa): tectonic/sedimentary evolution and correlations along the maghrebian chain. journal of african earth sciences, 64, 48-64. https://doi.org / 10.1016/j.jafrearsci.2011.11.010 benabbas, c. (2007). cartographie géologique et géomorphologique du tronçon autoroutier bbael harrouche, pour le compte du consortium cojaal (projet autoroute estouest (section est) (mars-août 2007), rapports et cartographie non publiés. bouillin, j. p. (1986). le bassin maghrebin; une ancienne limite entre l'europe et l'afrique a l'ouest des alpes. bulletin de la société géologique de france, 2(4), 547-558. durand delga, m. (1969). mise au point sur la structure du nord-est de la berbérie. publ. serv. carte géol. algérie, ns. bull. soc. géol. fr, 13(7), 328-337. el-ramly, h., morgenstern, n. r., & cruden, d. m. (2002). probabilistic slope stability analysis for practice. canadian geotechnical journal, 39(3), 665-683. https://doi.org/10.1139/t02–034 http://dx.doi.org/10.1016/j.jafrearsci.2011.11.010 https://doi.org/10.1139/t02%e2%80%93034 ghedjati s et al., j. build. mater. struct. (2022) 9: 110-121 121 griffiths, d. v., & lane, p. a. (1999). slope stability analysis by finite elements. geotechnique, 49(3), 387403. hicks, m. a. (2005). risk and variability in geotechnical engineering. geotechnique, 55(1), 1-2. houmadi, y., ahmed, a., & soubra, a. h. (2012). probabilistic analysis of a one-dimensional soil consolidation problem. georisk: assessment and management of risk for engineered systems and geohazards, 6(1), 36-49. https : // doi.org / 10.1080/17499518.2011.590090 huber, m., westrich, b., vermeer, p. a., & moormann, c. (2011, november). response surface method in advanced reliability based design. in budelmann, holst, proske: proceedings of the 9th international probabilistic workshop, braunschweig. institute of geotechnical engineering, university of stuttgart. isukapalli, s. s., roy, a., & georgopoulos, p. g. (1998). stochastic response surface methods (srsms) for uncertainty propagation: application to environmental and biological systems. risk analysis, 18(3), 351-363. https://doi.org/10.1111/j.1539-6924.1998.tb01301.x mollon, g., dias, d., & soubra, a. h. (2011). probabilistic analysis of pressurized tunnels against face stability using collocation-based stochastic response surface method. journal of geotechnical and geoenvironmental engineering, 137(4), 385-397. https://doi.org/10.1061/(asce)gt.19435606.0000443 raoult, j. f. (1974). géologie du centre de la chaîne numidique (nord constantinois, algérie). mém. soc. géol. fr., n.s., t. liii, n°121, 164 p., 62 fig., 11 pl.h.t. rapport interne, pp 1-31. sudret, b. (2008). global sensitivity analysis using polynomial chaos expansions. reliability engineering & system safety, 93(7), 964-979. https://doi.org/10.1016/j.ress.2007.04.002 sudret, b. (2015). polynomial chaos expansions and stochastic finite element methods, risk and reliability in geotechnical engineering, crc press, pp.265-300. yang x , yang g , yu t (2012). comparison of strength reduction method for slope stability analysis based on abaqus fem and flac3d fdm. applied mechanics and materials, 170-173, 918– 922. https://doi.org/10.4028/www.scientific.net/amm.170-173.918 zeng, j., & xiao, s. (2017). optimization algorithm of the strength reduction method for the stability analysis of slopes based on flac3d. the electronic journal of geotechnical engineering, 22(9), 3831-3843. zienkiewicz, o. c., humpheson, c., & lewis, r. w. (1975). associated and non-associated visco-plasticity and plasticity in soil mechanics. geotechnique, 25(4), 671-689. https://doi.org/10.1080/17499518.2011.590090 https://doi.org/10.1111/j.1539-6924.1998.tb01301.x https://doi.org/10.1061/(asce)gt.1943-5606.0000443 https://doi.org/10.1061/(asce)gt.1943-5606.0000443 https://doi.org/10.1016/j.ress.2007.04.002 j. build. mater. struct. (2016)3:43-54 https://doi.org/10.34118/jbms.v3i2.23 issn 2353-0057 effect of content and fineness of slag as high volume cement replacement on strength and durability of ultra-high performance mortar gupta s national institute of technology, jamshedpur, jharkhand, india. corresponding author: souradeepnus@gmail.com received : 30-08-2016 revised: 15-10-2016 accepted: 02-11-2016 abstract. replacement of cement by slag in ultrahigh performance concrete (uhpc) makes it a green material for building and construction application. however, slag hydrates slower which delay strength gain in uhpc which can be addressed by using slag of high fineness. in this study, cement is replaced by slag at 20% and 60% by weight. slag of three different fineness is used 400± 4 m2/kg, 556 ± 5m2/kg and 750 ± 5 m2/kg at constant water-binder ratio of 0.25 for all mixes. compressive and flexural strength were measured for mechanical performance while water penetration test and chloride migration test were conducted to enumerate durability. results show that early and late compressive strength and flexural strength is improved significantly by incorporation of slag with fineness 556 ± 5m2/kg compared to reference and slag of 400 m2/kg fineness. however, at similar fineness 20% slag incorporation is found to produce higher early strength compared to 60% slag although 90 day strength for both replacement percentages are similar. on durability aspects it is found that slag with fineness of 556 m2/kg and 750 m2/kg demonstrates significantly lower penetration depth and very high resistance to chloride migration at 28 day and 90 day age irrespective of slag replacement percentage. the study suggests that slag of high fineness (about 556m2/kg based on the study) and 20-60% cement replacement can significantly accelerate hydration and improve long term durability of uhpc mortar. key words: strength, durability, ultra high performance concrete, chloride migration, water penetration 1. introduction ultra-high performance concrete (uhpc) is gaining popularity in building and infrastructure construction due to its fast strength development and superior mechanical and durability properties compared to conventional concrete (pyo and el-tawil,2015, alkaysi et al.,2016). however, as every developed and developing economy is striving for sustainable construction and energy savings, the high energy consumption, material price and associated high co2 emission for uhpc are restricting it from wide application in building and construction sector. to reduce cement content in uhpc, granulated blast furnace slag (ggbs) is commonly used to replace part of cement. it is well known that ggbs due to its hydraulic property reacts with water and form calcium silicate hydrate. however, although ggbs can be activated by calcium hydroxide and gypsum, the rate of hydration of ggbs in concrete is low (regourd et al., 1983, binici et al., 2007, johari et al., 2011,kim et al.,2016) which results in slower strength development of uhpc. slower rate of strength development means that the designed strength would be achieved late which can delay removal of formwork and affect construction economy. especially in applications at places of adverse conditions, for example, marine construction or underwater foundations, rapid strength gain is critical to durability and life of concrete construction. one of the ways to speed up hydration and strength development in uhpc containing slag is to modify the fineness of ggbs. ggbs of variable fineness will offer different surface area for hydration reaction and influence the distribution of hydration products in the cement matrix which can impact strength and durability of uhpc. due to incorporation of fine slag particles, the rate of strength development of the concrete may be improved and the permeability of the concrete can be reduced due to reduced total pore volume, mailto:souradeepnus@gmail.com 44 gupta, build. mater. struct. (2016)3:43-54 pore connection and the better filling of the pores in the interfacial transition zone (itz). it was reported that ultra fine ggbs-blended (ufggbs) concrete showed reduction in creep value and drying shrinkage compared to opc concrete (li and yao, 2001).the addition of ufggbs results in a stronger structure and higher resistance to deformation caused by applied force (teng et al., 2013). moreover, the percentage of cement replacement by ggbs also influences strength development because of the difference in rate of hydration between cement and ggbs of normal fineness. typically, minimum of 20% of cement replacement by ggbs is practiced in construction industry although several researches have tried high cement replacement, up to 60 % to 80% (yazici, 2007, yazıcı et al., 2010). to boost up ongoing efforts to achieve sustainable construction, some green building codes and authorities including building and construction authority of singapore (bca) have made provision for replacement of 20% cement by ggbs to prepare greener concrete which will cut down on the use of raw materials and emission (cp65, 2008). the coupled effect of slag replacement and slag fineness on hardened properties of uhpc mortar is not widely studied. this study aims to explore the effect of content and fineness of slag on strength and durability of ultra-high performance concrete. to study the effect of slag fineness on mechanical strength and durability, mortar paste has been used in the study. ggbs of three different specific surface areas -400m2/kg, 556m2/kg and 750 m2/kg is added at two different cement replacement percentages 20% and 60% by weight. these two percentages of slag replacement are chosen to have significant difference in quantity of cement replacement in the mortar paste. it ensures that the difference in strength development and durability by incorporation of slag of different fineness in the uhpc mortar can be highlighted and studied. compressive and flexural strength tests have been conducted to study the rate of strength development at different ages of uhpc while water penetration test and chloride migration test are conducted to estimate durability of uhpc with different slag fineness and content. 2. experimental program 2.1 materials used ordinary portland cement (type 1) conforming to specification of astm c150, 52.5n has been used in the study. the physical properties, chemical composition and mineralogical composition of the cement using bogue calculation are mentioned in table 1. table 1. physical properties and chemical composition of opc properties ordinary portland cement used physical properties density(kg/m3) 3180 blaine fineness (m2/kg) 385 mean particle size (µm) 13.50 chemical composition (%) mgo 1.8 cao 63.5 so3 2.1 al2o3 5.4 sio2 20.8 na2o 0.59 chloride 0.005 mineralogical composition (%) c3s 58 c2s 20 c3a 2 c4af 14 gupta, j. build. mater. struct. (2016)3:43-54 45 the sand used is locally available river sand of fineness modulus of 2.54 and specific gravity of 2.65. the sand is dried in oven at 105 0c for 24 hours before sieving. only particle sizes below 600 µm is used in preparation of the mortar to allow better packing. the composition of ggbs used is presented in table 2. fineness of ggbs was determined by blaine permeability method. ggbs with three different fineness values were mixed 400± 4 m2/kg, 556 ± 5m2/kg and 750 ± 5 m2/kg respectively with mean particle sizes of 4.09µm, 2.10 µm and 1.45 µm respectively. 2.2 mix design and mixing procedure the total cementitous content used in the study is 800 kg/m3.the water to binder ratio (w:b) is maintained at 0.25 for all the mixes. as stated earlier, cement is replaced by 20% and 60% by weight of ggbs. for each replacement percentage, effect of three different ggbs fineness has been studied. a reference mortar (without ggbs) is prepared for comparison. the specimen terminologies are presented in table 3. table 2. chemical composition of blast furnace slag (ggbs) used in the study. chemical composition (%) ggbs (mass %) sio2 39 al2o3 6 fe2o3 0.75 cao 35 mgo 12 so3 1.10 k2o 0.4 table 3. mix design, description and terminologies mix name mix code cement (kg/m3) ggbs (kg/m3) sand (kg/m3) water-binder ratio superplasticizer (kg/m3) reference ref 800 0 1400 0.25 6.95 20% slag replacement with ggbs fineness of 400± 4 m2/kg g20f400 640 160 1400 0.25 6.15 20% slag replacement with ggbs fineness of 556± 5 m2/kg g20f556 640 160 1400 0.25 5.90 20% slag replacement with ggbs fineness of 750± 5 m2/kg g20f750 640 160 1400 0.25 6.20 60% slag replacement with ggbs fineness of 400± 4 m2/kg g60f400 320 480 1400 0.25 5.95 60% slag replacement with ggbs fineness of 556± 5 m2/kg g60f556 320 480 1400 0.25 5.73 60% slag replacement with ggbs fineness of 750± 5m2/kg g60f750 320 480 1400 0.25 6.05 2.2.1. preparation and casting of specimen the mortar mixes have been prepared in a 60l hobert mixer under the following steps: the first step of the mixing involves dry mixing of all the solid components which include cement, ggbs and sand. mixing water is then added during 15-20 seconds and the mixing is continued for another 3 minutes at medium speed. superplasticizer (adva 181 n manufactured by w.r.grace) is then added 46 gupta, build. mater. struct. (2016)3:43-54 to the mix and the composition was mixed for 1 minute before switching to high speed for next 1 minute. during mixing, the consistency of mixed mortar is checked by means of flow table test following astm c1437. all the mixes were prepared to achieve a uniform flow range between 150160 mm and the superplasticizer dosage was adjusted accordingly which is presented in table 3 for different mixes. after the flow test, the edges of the bowl are scraped the mixing was continued for 2 minutes. the mixture is finally mixed for three minutes at high speed. after mixing, the mortar was cast into respective mould placed on vibration table to achieve proper compaction. the specimens for strength and durability testing are demolded after 22-24 hours and cured under 25±1 0c and 95% relative humidity (rh) till the age of testing. compressive and flexural strength test of the mortars were carried out at age of 3 day, 7 day, 28 day and 90 day while water penetration test and chloride migration test were conducted at age of 28 day and 90 day. 2.3 tests methods 2.3.1. flow table test the workability of mortar can be estimated from its flowability. flow diameter was measured according to the procedure recommended by astm c1437. after 5 minutes of mixing some mortar was filled in truncated conical mould of 70 mm top diameter and 100 mm bottom diameter placed on flow table. once the cone was filled, the top part was leveled. then the mould was lifted and the mortar was allowed to flow. the subsequent diameter of the mortar is measured in two perpendicular directions and the average is reported as the final diameter. 2.3.2. compressive strength compressive strength test has been performed on cube specimens. the results have been recorded by using a compression testing machine ((dmg compression testing machine) operated at loading rate of 157 kn/min. before subjecting the specimens to test, the excess moisture is wiped off from the surface of the specimen. 2.3.3. flexural strength flexural load is obtained by a three point loading on to a calibrated flexural testing frame (instron) with displacement rate set at 0.50 mm/min. specimen of dimension 40x40x160 mm is used. the distance between the supports in the frame is fixed at 100mm. 2.3.4. depth of water penetration cylinder specimen (100mm (d) x200(h) mm) is used to measure depth of water penetration. after the curing period specimens have been allowed to dry in oven at 50 0c for 48 hours to ensure removal of moisture from pores of mortar. the surface of the specimens is then coated with epoxy to avoid any leakage from the sides during the test. the applied layer has been allowed to air dry for 24 hours before testing. penetration testing has been conducted on a calibrated water penetration apparatus (controls water permeability apparatus). water pressure of 6±0.5 bar was applied for about 72 hours. after 72 hours the specimens were split into two halves and the maximum penetration depth (in mm) has been recorded. 2.3.5. chloride migration coefficient nord test build 492 (nord test method, 1999) has been followed to determine chloride migration coefficient in the uhpc samples. three 50 mm specimens have been tested for each mix at a time. the specimens were obtained by cutting cylinder specimens by high speed concrete cutter. the specimen was exposed to two solutions on both side a 10% sodium chloride (nacl) solution on one side (cathode) and a 0.3 m sodium hydroxide (naoh) solution on the other side (anode). chloride ion was made to move into the specimen by application of an external potential across the gupta, j. build. mater. struct. (2016)3:43-54 47 specimen. after test duration the specimen was axially split across its circular cross section. the split surfaces were sprayed with 0.1 m silver nitrate (agno3) solution to determine the chloride penetration by measuring the silver chloride precipitates formed. the chloride migration coefficient can be calculated according to the equations mentioned in nord test build 492 (nord test method, 1999). the test details are shown in table 4. table 4. test details. curing regime type of specimen testing age(day) test conducted water 100 mm cube 3,7,28,90 compressive strength water 40x40x160mm prism 3,7,28,90 flexural strength water 100(d)x 200mm(h) cylinder 28,90 water penetration test water 50mm disc 28,90 chloride migration test 3. results and discussion 3.1. flowability of mortar it is observed from table 3, that superplasticizer dosage is reduced with increased cement replacement by slag. kim et al. (2016) reported similar findings that addition of slag as 50% cement replacement improved flowability by 34.4%. improvement in flow is due to reduction in water demand by slag particles compared to cement (karri et al.,2015; boukendakdji, 2009; kourounis et al.,2007). the reduced water demand is due to lower rate of slag hydration attributed to its mineralogical composition. cement replacement by slag also reduces the amount of ettringite produced during early stages of hydration which is responsible for improvement in flowability (samet et al., 2004). it is worth noting superplasticizer dosage is increased when slag of fineness 750m2/kg is incorporated compared to that in case of slag of lower fineness values. table 5 illustrates this finding. table 5. reduction in superplasticizer (sp) dosage with increasing fineness and replacement rate of slag. curing regime fineness(m2/kg) reduction in sp dosage compared to reference (%) difference in sp dosage (%) 20% slag replacement g20f400 vs. ref 11.51 g20f556 vs. g20f400 15.10 3.6 g20f750 vs. g20f556 10.79 -4.32 ( increased demand) 60% slag replacement g60f400 vs. ref 14.38 g60f556 vs. g20f400 17.55 3.16 g60f750 vs. g20f556 12.95 -4.60( increased demand) for example, in case of 20% replacement, while sp demand was reduced by 11.51% and 15.10% for slag fineness of 400m2/kg and 556 m2/kg respectively compared to reference. however, for slag of fineness 750m2/kg , sp dosage was reduced by 10.79% meaning increase in sp demand by 4.32% compared to slag of 556 m2/kg fineness. similarly trend can be observed in case of 60% slag replacement as well. this is attributed to increased interparticle friction when the density of fine particles increases around coarser cement and sand particles (rilem report, 2000). the increased surface area due to ultra-fine slag particles increase the contact area of friction between other 48 gupta, build. mater. struct. (2016)3:43-54 particles in the paste which offer resistance against flow resulting in reduction of flowability. particle friction in powder materials is difficult to reduce by increasing interparticle distance through addition of more water, especially in case of high performance mortar. thus to make up for water demand, higher amount of sp is needed to disperse the ultra-fine particles in the cement paste. however, one must be careful with increased demand for sp because high dosage may lead to segregation and bleeding. 3.2. compressive and flexural strength development of compressive and flexural strength of slag containing specimen and reference specimen is presented in fig. 1 and fig.2 respectively. it can be observed from the graphs that slag containing samples show higher compressive and flexural strength at 90 day than the reference (ref) although slight reduction in early strength and 28 day strength takes place due to high volume slag replacement. especially, mortar samples with slag of fineness 400 m2/kg show reduced 3 day, 7 day and 28 day strength irrespective of replacement percentage. it may be because of similar fineness of slag as that of cement (385 m2/kg, from table 1). fig 1. development of compressive strength strength development depends on packing density of mortar which also influence rate of hydration. improved packing means that voids between cement particles should be filled by finer slag particles. however, packing density in the bulk cement paste is not significantly improved because slag of higher fineness (400 m2/kg) compared to cement is used in this case as replacement. g20f556 mix achieved highest compressive and flexural strength at 7 day, 28 day and 90 day followed by g60f556. one can observe that when 60% of cement is replaced by ggbs, reduction of 3 day and 7 day strength takes place compared to reference and 20% replacement with same fineness. this can be attributed to slower hydration of slag and lesser rate of production of secondary calcium silicate hydrate. improvement in early compressive and flexural strength (3 day and 7 day) is observed when fineness of ggbs is increased to 556m2/kg. the percentage increase in early strength of 20% and 60% slag as cement replacement over reference mortar is reported in table 6. gupta, j. build. mater. struct. (2016)3:43-54 49 table 6. percentage improvement in compressive and flexural strength with slag fineness of 556 m2/kg over reference mortar % increase in compressive strength over reference mortar(ref) % increase in flexural strength over reference mortar (ref) 3 day 7 day 3 day 7 day g20f556 13.25 9.08 14.14 20.56 g60556 3.48 4.90 4.50 5 increase in fineness implies higher specific surface area of slag which allows faster hydration reaction. moreover, finer slag particles can act as micro-filler between cement and sand particles and provide nucleation sites to boost up hydration. however, as fineness is further increased to 750m2/kg, both g20f750 and g60f750 batches show reduction in strength. 90 day strength in case of ggbs of fineness 750m2/kg is almost similar to that of 400 m2/kg which implies that increase in fineness do not necessarily contribute to strength improvement. fig 2. development of flexural strength 28 day compressive strength is reduced by about 15% and 17% respectively for g20f750 and g60f750 than the maximum observed in each case which is for g20f556 and g60f556 respectively. similarly, reduction in flexural strength by 15% and 16% is observed in g20f750 and g60f750 than the maximum. reduction in strength due to addition of ultrafine ggbs particles is believed to be due to intense cohesiveness developed from high fineness of ggbs which prevented it from bonding properly with the matrix. ultrafine particles tend to have poor dispersion in the matrix due to physical van der waal's force of attraction between the particles which results in formation of weak spots in the matrix by particle agglomeration. particle agglomeration form localized voids in the paste. therefore decrease in strength could be believed to have resulted from too many voids and interfacial bond failure within the matrix. 3.3. water penetration depth depth of water penetration performed at 28 day and 90 day for reference and slag containing samples is reported in fig.3. samples containing 20% and 60% slag replacement show lower depth 50 gupta, build. mater. struct. (2016)3:43-54 of penetration at 28 day and 90 day compared to reference. all types of ggbs used in the study has higher fineness compared to cement which means that finer slag particles could block some continuous pore network in the matrix resulting in reduction of penetration depth. comparing the effect of slag content on depth of penetration, one can observe that 28 day penetration of g20f400 is lower than that of g60f400 while there is no significant difference between penetration depths between g20f556 and g60f556, and g20f750 and g60f750. it may be explained by reduction in capillary channels by fine ggbs particles irrespective of slag replacement at 28 day. however, the 90 day results follow a different trend. penetration depth in g20f556 and g20f750 is reduced by about 14% and 23.50% than g60f556 and g60f750 respectively. fig 3. depth of water penetration in reference and slag containing sample at different ages such observation may be attributed to coupled effect of hydration and pore-blocking by ggbs particles. slag has a slower rate of hydration and therefore a minimum percentage of slag hydrates at 28 day which is more complete at 90 day. when introduced at 20% cement replacement, more complete hydration of slag occurs at 90 day. physical densification of the microstructure takes place with the addition of fine ggbs and moreover, the pozzolanic reaction leads to the formation of secondary c–s–h. (elahi et al., 2010). the secondary c–s–h formation results in reduction of capillary and gel porosity of the mortar which explains reduction in penetration depth of 20% replacement samples compared to that in case of 60% replacement. influence of ggbs fineness on penetration depth in uhpc can be two foldthrough reduction of open porosity and increasing precipitation of calcium-silicate hydrate which makes the matrix dense. this effect can be observed when 20% of cement is replaced by slag. penetration depth at 28 day is reduced by about 18% in g20f556 compared to g20f400 although no further significant reduction took place in g20f750. higher surface area facilitates faster hydration reaction and therefore penetration depth in g20f556 is reduced than g20f400 at 28 day. however, the same cannot be said for g20f750 because this mix showed reduction in 28 day strength (from fig. 1). therefore, it can be concluded that reduction of water penetration at 28 day in g20f750 and g60f750 is primarily due reduction in open porosity through better particle packing by finer slag particles. however, at 90 day age g20f750 shows highest resistance to water penetration probably due to formation of secondary hydration products by pozzolanic reaction of slag resulting in denser matrix. gupta, j. build. mater. struct. (2016)3:43-54 51 3.4. chloride migration test non-steady state chloride migration coefficient of uhpc mortar is computed based on nt build 492 (nord test method, 1999) which is presented in table8. resistance of mortar against chloride penetration can be classified using the migration coefficient values (nilsson et al., 1998) as shown in table 7. table 7. classification of chloride resistance based on 28 day resistivity (nilsson, ngo and gjørv, 1998) chloride migration coefficient (dx10-12 m2/s) classification of resistance to chloride penetration >15 low 10-15 moderate 5-10 high 2.5-5 very high <2.5 extremely high all the mixes incorporating slag show reduction in chloride migration coefficient than the reference mortar at 28 day and 90 day age. the results show that as the fineness of slag increases there the migration coefficient is reduced. at 28 day and 90 day chloride migration coefficient of g20f556 is reduced by about 59% and 82% respectively compared to g20f400 although further increase in slag fineness do not show significant improvement. similar trend is observed in case of g60f556 which shows reduction in chloride migration coefficient by about 58% and 72% compared to g60f400 at 28 day and 90 day respectively. based on table 6 classification, resistance of g20f556, g20f750, g60f556 and g60f750 at 28 day and 90 day can be classified as very high and extremely high respectively. therefore, it can be concluded that incorporation of fine slag (minimum fineness 556 m2/kg based on this study) reduces pore connectivity and blocks migration of chloride ion into mortar. it is also worth noting that chloride migration coefficient significantly reduces beyond the curing age of 28 day although development of compressive and flexural strength slows down which is also supported by teng et al. (2013). it may be due to deposition of secondary hydration products at localized zones around the slag particles due to pozzolanic reaction which breaks the continuity of pore network. table 8. computed chloride migration coefficient from rapid chloride migration test samples age(day) chloride migration coefficient (dx10-12 m2/s) ref 28 13.61 90 11.48 g20f400 28 10.14 90 7.30 g20f556 28 4.14 90 1.21 g20f750 28 4.18 90 1.25 g60f400 28 10.10 90 8.21 g60f556 28 4.21 90 2.25 g60f750 28 4.37 90 2.43 52 gupta, build. mater. struct. (2016)3:43-54 3.5. comparison of mechanical and durability properties of mortar with respect to replacement rate and fineness of slag fig.4 presents the strength and durability properties at 28 day of ultrahigh performance mortar with respect to different fineness values of slag and cement replacement rates. while compressive strength is plotted on primary vertical axis, flexural strength, depth of penetration and chloride diffusivity are plotted on secondary vertical axes (right y-axis). it can be observed from fig.4 that g20f556 offers the highest 28 day strength although depth of water penetration and chloride diffusivity are similar to that of g20f750. it has earlier been discussed that while strength development is related to microstructure of mortar paste, transport properties are more sensitive to pore connectivity of the matrix (wang et al., 2014). strength is influenced by the composition and the microstructure of the specimen. several factors including water to cement ratio, aggregates grading, age and curing condition, admixtures, can influence strength because they will influence the hydration degree and microstructure of the specimen. higher hydration means filling up of pore spaces by solid hydration products resulting in increase in strength. fig 4. comparison of properties of ultrahigh performance mortar at 28 day with respect to cement replacement rate and fineness of slag therefore, microstructure of mortar is the main factor influencing strength. in this study, for a particular cement replacement rate, all the specimens were made with the same cement, sand and water, using the same w/c ratio and sand to cement ratio. the only difference was addition of slag of variable fineness. therefore, it may be implied that slag of higher fineness is beneficial for improving transport properties of ultrahigh performance mortar while slag of 400m2/kg fineness performs best from the perspective of strength development at both 20% and 60% cement replacement rate. comparing the effect of replacement rate on strength and durability properties, one can observe that the strength development is lower in case of 60% replacement. however, the difference between penetration depth and chloride diffusivity is not as significant as difference between strength development at both replacement rates. such observation results due to introduction of fine slag particles which will reduce porosity of mortar regardless of rate of strength gain. therefore, from the results it can be implied that 60% replacement of cement by slag is feasible gupta, j. build. mater. struct. (2016)3:43-54 53 where faster strength development is not a stringent requirement, which will be more economic and sustainable from the perspective of reduction in associated carbon emission. 4. conclusion based on the outcome of the study, the following conclusions can be drawn: a) although water demand is reduced with increase in cement replacement percentage, slag of higher fineness tends to increase water demand because of more interparticle friction around cement grains and sand particles. b) deployment of slag with higher fineness, about 556m2/kg, significantly improves early strength and 28 day strength of uhpc mortar when added to replace 20% and 60% of cement. however, the effect on early strength diminishes when slag of very high fineness, about 750m2/kg is used although 90 day strength is similar to that of reference mortar. c) depth of water penetration is significantly reduced with increase in slag fineness up to 750 m2/kg. unlike mechanical strength, resistance of water penetration is found to be directly proportional to fineness of slag due to ability of fine particles to reduce porosity of matrix. lowest penetration depth at 28 day and 90 day is observed in case of 20% cement replacement of slag fineness 750 m2/kg . d) uhpc mortar with slag of fineness 556 m2/kg irrespective of replacement percentage showed very high and extremely high resistance to chloride migration at 28 day and 90 day. unlike mechanical strength, resistance to chloride migration is observed to be significantly affected by age beyond 28 day, increasing from 28 day to 90 day age of specimen. e) it can be concluded from this study that about 20% slag replacement with high fineness, about 556 m2/kg may be optimal to develop early strength and improve long term mechanical and durability performance. from the results, it can be justified the application of uhpc with 20% cement replacement by slag of high fineness can be an ideal material for construction and repair under adverse conditions and short turn-around time. 5. references alkaysi, m., el-tawil, s., liu, z., and hansen, w. (2016). effects of silica powder and cement type on durability of ultra-high performance concrete (uhpc). cem. concr. compos., 66, 47-56. astm (2007). standard test method for flow of hydraulic cement mortar, standard specification c1437-07, astm, west conshohocken, pennsylvania. astm (2016e1). standard specification for portland cement, standard specification c150/150m, astm, west conshohocken, pennsylvania. binici, h., temiz, h., and köse, m. m. (2007). the effect of fineness on the properties of the blended cements incorporating ground granulated blast furnace slag and ground basaltic pumice. construction and building materials, 21(5), 1122-1128. boukendakdji, o., kenai, s., kadri, e., and rouis, f. (2009). effect of slag on the rheology of fresh selfcompacted concrete. construction and building materials, 23(7), 2593-2598. cp65(2008). design guide of high strength concrete. building and construction authority (bca) sustainable construction series 3. elahi, a., basheer, p., nanukuttan, s., and khan, q. (2010). mechanical and durability properties of high performance concretes containing supplementary cementitious materials. construction and building materials, 24(3), 292-299. johari, m. m., brooks, j., kabir, s., and rivard, p. (2011). influence of supplementary cementitious materials on engineering properties of high strength concrete. construction and building materials, 25(5), 26392648. 54 gupta, build. mater. struct. (2016)3:43-54 karri, s. k., rao, g. r., and raju, p. m. (2015). strength and durability studies on ggbs concrete. ssrg international journal of civil engineering (ssrg-ijce), 2(10),34-41. kim, h., koh, t., and pyo, s. (2016). enhancing flowability and sustainability of ultra high performance concrete incorporating high replacement levels of industrial slags. construction and building materials, 123, 153-160. kourounis, s., tsivilis, s., tsakiridis, p., papadimitriou, g., and tsibouki, z. (2007). properties and hydration of blended cements with steelmaking slag. cem. concr. res., 37(6), 815-822. li, j., and yao, y. (2001). a study on creep and drying shrinkage of high performance concrete. cem. concr. res., 31(8), 1203-1206. nilsson, l., ngo, m., and gjørv, o(1998). high-performance repair materials for concrete structures in the port of gothenburg. proc., second international conference on concrete under severe conditions: environment and loading, 1193-1198. nt build 492 (1999). concrete, mortar and cement-based repair materials: chloride migration coefficient from non-steady-state migration experiments. nordtest method. pyo, s., and el-tawil, s. (2015). capturing the strain hardening and softening responses of cementitious composites subjected to impact loading. construction and building materials, 81, 276-283 regourd, m., thomassin, j., baillif, p., and touray, j. (1983). blast-furnace slag hydration. surface analysis. cem. concr. res., 13(4), 549-556. rilem (2000).self-compacting concrete. state-of-the-art report. rilem report, 23(2000), 150. samet, b., and chaabouni, m. (2004). characterization of the tunisian blast-furnace slag and its application in the formulation of a cement. cem. concr. res., 34(7), 1153-1159. teng, s., lim, t. y. d., and divsholi, b. s. (2013). durability and mechanical properties of high strength concrete incorporating ultra fine ground granulated blast-furnace slag. construction and building materials, 40, 875-881. wang, j., soens, h., verstraete, w., and de belie n.(2014).self-healing concrete by use of microencapsulated bacterial spores. cem. concr. res., 56(1), 39-52. yazici, h. (2007). the effect of curing conditions on compressive strength of ultra high strength concrete with high volume mineral admixtures. building and environment, 42(5), 2083-2089. yazıcı, h., yardımcı, m. y., yiğiter, h., aydın, s., and türkel, s. (2010). mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag. cem. concr. compos., 32(8), 639-648. j. build. mater. struct. (2022) 9: 57-73 original article doi : 10.34118/jbms.v9i1.1606 issn 2353-0057, eissn : 2600-6936 hydration behaviour and characteristics of binary blended metakaolin cement pastes j.a. apeh department of building, federal university of technology, minna, nigeria. * corresponding author: apehjoe@futminna.edu.ng received: 14-12-2021 accepted: 08-03-2022 abstract. cement production consume large amount of energy to form clinker and carbon dioxide (co2) emitted into the atmosphere causing global warming. to mitigate this challenge, the use of metakaolin (mk) as supplementary cementitious material cannot be over emphasized. this study evaluated the use of metakaolin (mk) on hydration development of mk--pc blended cements and strength of mortars. the mk with a blaine fineness of 7883 cm2/g was used to replace portland cement (pc) at a level of 0, 5, 10, 15, 20, 25 and 30 % by mass of pc at a constant w/b ratio of 0.50 to prepare blended cements. hydration development of blended cement and compressive strength of mortars were investigated using chemically bond water and free-lime contents and strength tests respectively. x – ray diffraction (xrd) and scanning electron microscopy (sem) techniques were also utilised in the analysis of pozzolanic reaction and hydration products. test results indicates that water of consistency, setting times for the mixes increased with increase in mk contents, influence of mk on the chemically bond water and free lime contents of the blended cements were due to its filler and dilution effects and pozzolanic reaction. the cumulative non-evaporable water and free-lime contents increased by partial replacement of pc with mk due to pc hydration and pozzolanic reaction. the tested mortar prepared with blended cements with 30 % pc replacement with mk shows a retardation of strength development with a low value at early ages (7 days) and increased in growth at later ages (28 days). the compressive strength of tested mortar for 90 days curing age for the blended mortar is 31 n/mm2 close to that of control mortar (35 n/mm2). the results obtained from xrd and sem analysis indicated increase in calcium hydroxide (ch) consumption and calcium silicate hydrate (c-s-h) formation in blended cement pastes with curing time. the pc replacement with mk induced changes in microstructures of blended cement paste and chemical composition of hydration products. these results are potentials for modelling the behaviour of mk-pc blended cements. key words: metakaolin, compressive strength, non-evaporabl e water, hydration behaviour and free lime content. 1. introduction cement production consume large amount of energy to form clinker and carbon dioxide (co2) emitted into the atmosphere causing global warming. from the cement industry alone, its contribution to global emission of green house gases especially co2 is 8 – 10 % (mehta, 2002; suhendro, 2014). it has been roughly estimated that one ton of portland cement (pc) produced released one ton of co2 into the air. it is more worrisome being the third most energy-intensive industry (shafigh et al, 2012) and this has raised serious environmental challenge in the built environment. to mitigate this, steps have been taken and the most effective is the reduction of clinker production by using supplementary cementitious materials (scms) during production or directly by replacement of cement at the building site. however, to make any meaningful impact in the reduction of co2 emission associated with cement production, maximum proportion of the admixture(s) should be used in cement, so as to lower the clinker content of the final product and the use of blended cements in general construction should be increased. the work of 58 apeh, j. build. mater. struct. (2022) 9: 57-73 (ecosmart, 2008) has shown that globally, if just 30 % of cement used was replaced with scms, this will considerably reverse the rise of co2 emissions from cement production. the works of (li and ding, 2003; antoni et al., 2012; moser et al., 2010) have shown that scms such as blast-furnace slag (bfs), fly-ash, (fa), silica fume (sf), ground limestone (gls) and metakaolin (mk) have been used in binary blends of portland cement (pc) used in civil and engineering constructions, thereby achieving energy cost savings, environmental protection and attaining special technical requirements such as durability. as a counter measure to reduce the amount of co2 generation and emission into the air, cement blended with mk is also required. mk (al2sio2o2), is a highly amorphous dehydration product of kaolinite, al2 (oh)4 sio2. kaolinite is the mineralogical term that is applicable to kaolin clays. kaolin is a fine, white clay mineral that has been traditionally used in the manufacture of porcelains. when thermally activated between 600 to 850oc, a substantial loss of water occurs in its constituents which leads to a new arrangement of its crystal lattice structure giving birth to a phase transition called metakaolin, metakaolin has a highly disordered and amorphous character with high pozzolanicity. its recrystallization occurs forming mullite leading to loss in pozzolanicity when activated beyond activation temperature range aforementioned (badogiannis et al., 2005). the kaolin disintegrates maintaining a small part of alo6 octahedral, while the rest is transformed to more amorphous and reactive tetraand pentacoordinated units (abo-el-enein et al 2014). these units of alumina on reaction with calcium hydroxide (ch) produces additional alumina containing phases such as c4ah13, c2ah8 and c3ah6 (saikia et al., 2006). mk, an scm when it partially replaces cement in concrete reacts with calcium hydroxide (ca(oh)2, a byproduct of hydration reaction of cement resulting to additional c-s-h gel which increase strength of concrete as shown in equation (1) and (2). (1) (2) as seen from equation (1), when cement reacts with water, it becomes hydrated and that part of water becomes chemically bound. the degree of hydration, (α) is defined as the ratio of the hydrated cement to the original cement content. the work of (powers and brownyard, 1948) showed that the maximum amount of chemically bound water required for the system is about one quarter of the weight of cement. hence the dire need for proper adoption of water – binder ratio that will not lead to excess water in the system. as the hydration process continues, there is growth of hydration products in form of crystals from the cement gels produced. the hydration of plain cement is in two phases; dissolution and precipitation. cement dissolves into the mix water releasing ions forming aqueous solution or pore solution. cement minerals, c3a and c3s being highly soluble forms higher concentration than other minerals. this increase in concentration continues until it becomes supersaturated. this means that the pore solution has a higher tendency to combine with other compounds to form new solid phases than to remain dissolved (wild and khatib, 1997). the c3a and c3s eventually combined with other compounds/ions and water to form new hydrated products different from the cement minerals which is precipitated. this is the precipitation stage of cement hydration. as new products are precipitated, the concentration of c3a and c3s in the solution are reduced and the solution is no longer supersaturated. then more c3a and c3s get dissolved in the solution in an attempt to reach supersaturated state again, thus leading to another stage of formation of new precipitated products. this circle continues to repeat itself until the entire cement mix is fully hydrated. similarly, from equation (2), ca (oh)2, a byproduct of cement hydration reacts with mk to form more c-s-h and thus improve strength of concrete. these two reactions form the basis for hydration behaviour of mk blended cement which requires more in depth study. in the work of (oriel and pera, 1995), mk was used as partial replacement of pc at 0, 5, 10 and 15 % and ch consumption, strength development were determined in mk-pc pastes and apeh, j. build. mater. struct. (2022) 9: 57-73 59 mortars employing tga analysis. test results showed minimum value of ch at 14 days curing which was attributed to an apparent fact that more ch is being removed from the paste by reaction with mk than is being generated by the cement hydration which was due to a peak in pozzolanic activity of mk. however, after 365 days of curing, substantial amount of ch was still left, even in the paste with 15 % replacement of pc by mk. this shows that for total consumption of ch produced by pc, a higher level of pc replacement by mk in excess of 15 % is required which depend on purity of mk and quantity of ch produced by the pc which in turn, a function of pc composition and w/b ratio. the study further showed that compressive strength of mk-pc cement pastes was enhanced at all ages and for all substitution levels. the work of (wild et al., 1997) showed that for mk-pc paste with a w/b of 0.5 and cured in lime-saturated water at room temperature between 30 to 40 % of mk is required to remove all the ch in mk-pc paste. the specific surface of mk can also enhance the strength of mk-pc cement paste. (wild et al., 1996), established that when the specific surface area of mk increased from 12,000 to 15,000 m2/kg, the age at which maximum strength enhancement occurs is reduced. other reports in literature indicates the influence of mk on the strength of mk-pc concretes which exhibited strengths slightly greater than sf-pc mixtures at the same levels of cement replacements by pozzolans. in such works as (wild et al., 1996), they established that three factors that influence the contribution of mk to concrete strength include filler effect (which is immediate), acceleration of pc hydration (which occurs within the first 24 hours) and the pozzolanic reaction (which occurs between the first 7 to 14 days) for all mk levels between 5 % and 30 % (hamdy et al., 2018). the work of dave et al. (2016) on hydration characteristics of metakaolin pozzolanic cement pastes shows that when pc was replaced with 20 % mk content, there was increase in the standard water of consistency, acceleration in the initial setting time and high compressive strength at early ages. this may not be unconnected with the additional pozzolanic reaction coupled with pc hydration and the specific surface area of mk. the work of (olubajo et al., 2020) also confirmed that the high specific surface area of mk due to its fineness increase the setting time of the mk-pc paste even at low replacement levels, hence its use as partial replacement of pc for better performance of advanced concrete. (shafigh and nurudin 2010), in their work on ternary blended cement reported that with increase of mk content from 5 to 25 % at constant rha content, water consistency of the ternary cement paste experienced a variation as mk was increased up to 25 % at constant rha up to 10 %. but at 10 % constant rha, as mk content increases, water demand of the cement paste gradually increased. these changes could be attributed to pozzolanic reactions. the study further showed that a maximum compressive strength of 40.5 n/mm2 was obtained at 60 days curing duration when pc was replaced by mk at 15 % at 5 % rha constant. this was attributed to the high silica/alumina contribution to the matrix by mk inclusion, the calcium/silica (c/s) ratio in the matrix. in the work of (el-gamal et al., 2017), they investigated the degree of hydration of pc and pc/fly-ash (fa) paste samples conditioned at different relative humidity. test results showed that varying relative humidity affects compressive strength and degree of hydration considerably. at varying relative humidity, pc-fa pastes showed better compressive strength than pc pastes samples. the work of (suprenant and papadopoulos, 1991) investigated the hydration characteristics and compressive strength of hardened cement pastes containing nano metakaolin and nano-metakaolin containing silica fume. test results showed higher compressive strength values for pcnmk blends compared with pc control values, but the values of free lime content for all pc-nmk blended cement pastes are lower than those of pc control values especially at later ages showing that reactions still continued. for the mk-pc composite cementitious system, because of the simultaneous presence of cement hydration and mk ash reaction, the amount of non-evaporated water and calcium hydroxide (ch) which are cement water hydration products cannot be used to evaluate the degree of hydration of the individual components. to achieve this accurately, (lam et al., 2000) used the selective dissolution by hydrochloric acid (hcl) to test the degree of reaction of fly ash cement. 60 apeh, j. build. mater. struct. (2022) 9: 57-73 in the same vein, (bentz, 2000) studied the hydration process of facement composites and measured the degree of reaction of fa in composites materials by determining the chemically combined water and using selective dissolution by hydrochloric acid. the work of (wild et al., 1996) also showed that the same feat can be achieved for two different blended cement-fa systems using the same selective dissolution approach but with ethylene diamine tetra acetic acid (edta) combined with sodium hydroxide (naoh), diluted naoh solution and portlandite content. from these studies, it showed that degree of hydration of blended cements can be determined from the values of its chemically bonded water and free lime content for both constituents of the composites employing the selective dissolution approach. the influences of mk cement on hydration and microstructure development can be seen through its chemical and physical effects. chemically by the pozzolanic reaction and physically by nucleation, dilution and filler effects as well as synergetic chemical interactions between mk and pc. the works of (caldrone et al., 1994) and (el-diadamony et al., 2018) showed that the main effects of mk on cement hydration is the immediate filler effect, the nucleation effect that accelerates the cement hydration occurs in the first 24 hours and the pozzolanic reaction which occurs in the first two to fourteen days. nucleation and filler effects of mk on cement hydration is directly related to its surface area. this is because the finely divided particles promote surface adsorption and provide precipitation sites which results in improving the degree of hydration. it is strongly believed that the mechanism of nucleation of mk is derived when the hydrates adsorbs on the surface of mineral grains of mk which catalyses the nucleation process by lowering the energy barrier for growth as opined by (el-diadamony et al., 2018). the nucleation process is influenced by the high fineness (high surface area), rate of substitution of mk and its affinity for cement hydration (naik et al., 2001). since mk particles are finer than that of pc, it readily provides nucleation sites for cement hydration. this fact is strengthened by the work of (clarridge, 2011) which showed that the use of mk at 10 to 15 % substitution of pc by mass first acts as a nucleating agent that accelerates the rate of pc hydration, secondly by providing a surface which enables the hydrating products to adsorb on the mk particle surface. the dilution effect of mk particles on pc pastes occurs when pc is substituted with mk leading to its decrease in the system. this is related to an increase in the effective water-to-cement ratio of the system binder. the presence of mk particles consequently enhanced pc hydration early by providing more nucleation sites for more hydration to take place and at later stages, more hydration by pozzolanic reactions with ch from pc hydration. (bs en 196-3, 1995) showed that the dilution effect of mk is more pronounced when it is used at 15 – 20 % replacement level of pc. at this level of substitution, there is more mk particles in the system and with its high surface area, higher rate of reaction is prompted and sustained only if there is more water but with w/b ratio being constant, no additional water is available to lubricate and sustain the rate of reaction which then stalls the reaction leading to decrease in strength. microstructure of cement paste consists of the capillary and gel pores. capillary pores are long continuous pores that exist within the un-hydrated cement paste and the gel pores are very small dimension and occurs within the reacted products. as hydration reaction progresses, this decrease the volume of the capillary pores because of the increase in pc gels or crystals. the capillary pores in the system consequently diminishes in size, gradually shortens until the connection between them is ceased. this means that the microstructure of the pastes changes as the degree of hydration changes or progresses which requires investigation. other factors also affect the setting and hardening of pc and blended cement pastes such as consistency, setting time, compressive strength and the nature of the cement mix (kakali et al, 2001). generally, degree of hydration of pc pastes can be determined by calculating the amount of ca (oh)2 in the paste, quantity of chemically bound water, fraction of un hydrated cement, liberated heat of hydration and strength of the hydrated cement. among these methods, estimation of the amount of ca (oh)2 content is mostly used. this can be achieved by using solvents to extract the apeh, j. build. mater. struct. (2022) 9: 57-73 61 ca (oh)2 from the paste, by quantitative x – ray diffraction method and by thermal analysis. when cement and other pozzolanic materials react with water for initiation of hydration reactions, they form hydration products that chemically bind water. evaporable or free water remains dispersed throughout the pore structure and allows for further hydration of cementing materials. the doh of any cement paste, α is a function of the non-evaporable water, wn, initial mass of cement present in the sample and k which represents the mass of chemically combined water needed to fully hydrate one grain of cement as shown in equation (3): (3) (astm c 191, 2008), developed an expression in relation to equation (3) for doh of a binary, ternary or quaternary mix. this was adopted and used for the study. the study evaluated the hydration behaviour and characteristics of pc paste, pc blended pastes with varying amounts of mk in terms of compressive strength, chemically combined water and free lime content at varying ages of hydration. the study also investigated the effect(s) of mk content on the fresh properties of the cement pastes, the use of xrd and sem to investigate the hydration products of some selected samples. 2. materials and method 2.1. materials portland cement (pc) used for the study was obtained from a local dealer of dangote cement company, nigeria, of grade cem 1-42.5n. mk used for the study is a product from dehydroxylation of kaolin obtained from madagali, yobe state, nigeria and thermally activated at 750oc at 10o c/min for 2 hours at the central services laboratory, national cereals research institute, badeggi, niger state, nigeria. it was cooled to room temperature in a desiccator ground with a local mill and sieved through a 75μm sieve. choice for the calcination temperature was based on the work of (ambroise et al., 1985). calcination below 700o c results in poor reactive mk while calcination above 850o c leads to crystallization which reduce its reactivity (abo-elenein et al., 2014). preliminary tests were conducted on the materials and the physical and chemical properties are shown in table 1. the mineralogical composition of mk is as shown in figure 1. the main mineral and amorphous alumino-silicate phase is quartz. the amorphous phase is formed due to reactions between sio2 and al2o3. fig. 1. xrd pattern of mk 62 apeh, j. build. mater. struct. (2022) 9: 57-73 2.2. preparation of samples six different blended cement mortar mixes were prepared with a mix ratio of 1:3.the sample mixes were prepared, substituting pc with 5 % stepwise increase up to 30 % of mk. mixing of the dry constituents mechanically was attained with a local mill for one hour so as to attain homogeneity, then kept in air tight plastic containers for further investigation. the mortar specimens were then mixed in standard mixer for about 5 minutes continuously, poured into 25 mm cubic steel moulds, left to set at ambient temperature and at about 86 % relative humidity for 24 hours, de-moulded and cured for 90 days immersed in water. maximum replacement of pc with mk was 30 % by weight for all mixtures. composition of binders is shown in table 2. table 1. mix proportion for mortar table 2: mix proportion for mortar materials (kg/m3) s/no mix id pc mk sand water w/c 1 pc 186.00 114 93 0.5 2 5mk – pc 176.70 9.30 13 10mk – pc 167.40 18.60 4 15mk – pc 158.10 27.90 5 20mk – pc 148.80 37.20 6 25mk – pc 139.50 46.50 7 30mk – pc 130.20 55.80 2.3. method 2.3.1. consistency and setting times tests for consistency and setting times of pc and pc-mk pastes were conducted in accordance with bs en 1963 provisions. the values of consistency, setting times (initial and final) of the pastes were determined using the vicat apparatus in accordance with (kondo et al. 1975) and (astm c 618-00, 2000) provisions. the water of consistency as well as setting times of the prepared pastes were directly determined using equation (4). ⁄ (4) where wc is the water of consistency, l is the amount of water required to produce a suitable paste and w is the mass of binder sample. the initial setting time is the time taken to reach the initial set while the final setting time is the time taken to attain final setting of paste. 2.3.2. compressive strength the required water of consistency was used to mix the pc and pc-mk blended dry mixtures to obtain fresh mortar pastes and then cast in 50 x 50 x 50 mm moulds, vibrated and then kept under room temperature and relative humidity of about 86 % for 24 hours. thereafter, the specimens were de-moulded and cured for 7, 14, 28, 56 and 90 days respectively. the specimens were tested for compressive strength for the aforementioned cured ages. three cubes of the hardened pastes were tested for compressive strength and average value recorded for each age. 2.3.3. degree of hydration of pc and pcmk fragments from the crushed specimens of the hardened cement pastes were ground, dried for 30 minutes and sieved through a 75μm sieve. the hydration reaction was stopped by immersion in a mixture of (1:1) methanol to acetone for about 30 minutes. with the aid of the ground dried sample, kinetics of hydration was evaluated on the basis of chemically combined water, (wn), at different ages of hydration. using the ignition loss test at 1100oc for two hours, the chemically apeh, j. build. mater. struct. (2022) 9: 57-73 63 combined water content was determined using equation (5).the test was repeated twice for each sample and the mean value recorded. (5) where wo is dried sample mass at 110oc and wi is ignited sample mass at 1100oc, pcloi is loss on ignition of pc. with known value of wn % and inserted in equation (3), doh for pc paste was determined for all ages. however, for pc-mk blended pastes, equation (6) (asttm c 191, 2008) was used as thus stated. ⁄ = ⁄ [ {1 – loigu} + {1 – loimk}] (6) where, btot is total mass of cementing binders, ⁄ is ratio of gu to total binder used, ⁄ is ratio of mk to total binder used, loigu and loimk is the loss – on – ignition values of gu and mk, gu is initial mass of general use cement (pc), binder, m110oc is mass of binder when oven dried, m1100oc is mass of binder when ignited. similarly, using the glycerol/ethanol extraction approach the free lime content, (%), was determined and the mean value for two repeated test values for each sample was recorded. (said-mansour, et al., 2011; amin et al., 2012). the fragments of the end products were prepared and the phase compositions of the formed hydrates was investigated with an x-ray diffraction (xrd) analysis technique using a philips pw 1050 diffractometer. data from the analysis was obtained with the aid of an xrd software (pdf21 data base on cd-release, 2005). microstructure of the hardened blended cement mortar was studied with the aid of sem inspect s equipped with an edx analyser. 3. results and discussion 3.1. physical and chemical properties of constituent materials 3.1.1. physical properties table 2 showed the physical and chemical properties of pc and mk. table 2. physical and chemical properties of materials materials physical properties pc (wt %) mk (wt %) specific gravity (g/cm 3 ) 3.15 2.52 blaine fineness (cm2/g) 3045 7483 loss on ignition (loi) 2.98 1.22 chemical composition calcium oxide, cao % 64.19 0.39 silicon dioxide, sio2 % 19.57 54.30 aluminum oxide, al2o3 % 5.47 38.30 ferric oxide, fe2o3 % 3.24 4.28 magnesium oxide, mgo % 2.01 0.08 manganese oxide, mno % 1.25 sodium oxide, na2o % 0.26 0.12 potassium oxide, k2o % 0.45 0.50 so3 2.74 0.22 the results of the average specific gravities indicated that pc has a value of 3.15 and mk has a value of 2.52. the specific surface area of pc is 3045 cm2/g and that of mk is 7483, more than twice that of pc. this means that mk particles is much finer than pc particles, thus occupy more space than pc and more volume of it is obtained when used to replace pc in mortar or concrete. 64 apeh, j. build. mater. struct. (2022) 9: 57-73 3.1.2. chemical properties from table 2, sum of sio2 + al2o3 + fe2o3 (saf) = 96.88 % which exceeds 70 % for mk thus satisfied (abo-el-enein et al., 2014) provisions value for mk is more than twice that for pc indicating high specific surface area which enhances mk reactivity. specific gravity of mk (2.52) less than that for pc (3.15) makes it a filler which also aids reaction. 3.2. standard consistency and setting times 3.2.1. standard consistency of pc and mk-pc pastes water of consistency (wc), and setting times for pc and mkpc pastes containing mk at varying proportions is shown in figure 2a and 2b. for neat pc paste, it is 33 %. the water of consistency of mk-pc pastes is higher than that for pc paste. addition of mk increased the water for normal consistency. this may be attributed to the high reactivity of mk, amorphous structure and higher specific surface area of mk particles which required more water of hydration compared with that for pc which does not require such quantity of water. from figure 2a, the standard water of consistency, wc, increases with increase in mk content. this is fruitful as it facilitates more reactions between mk particles and primary hydrates of pc. the increase of mk content by 10 % increase the water of consistency by 1.52 % and by 30 % mk content, increases wc by 9.01 %. the increase in wc by 9.01 % when mk replaced pc up to 30 % is due to the aforementioned factors. 3.2.2. setting time initial and final setting times for the mk-pc pastes is shown in figure 1b as prolonged compared with pc value. fig. 2a. normal consistency, wc for varying metakaolin content. the initial setting times (is) and final setting times (fs) increased steadily with increase in replacement level of pc with mk. this is due to reduction of c3s and c3a in pc which is responsible for acceleration of the chemical reaction which in turn determines the initial and final setting times of the paste. this is also due to the coating effect of the particles on the cement grains as well as the formation of ettringite (end product due to reaction between ch and 0 5 10 15 20 25 30 33 33.5 34 34.5 35 35.5 36 w a te r o f c o n s is te n c y (w n ) metakaolin content (%) wc apeh, j. build. mater. struct. (2022) 9: 57-73 65 c3ah6). generally, the setting of mk-pc blended pastes is not consistent with increase in mk content as can be seen in figure 2b. at an increase of 5 % mk content, wc increased by 1.5 % and at 30 % increase of mk content, wc increased by 9.01 %. hence, the increase of mk content levels as a replacement of pc in mk-pc cements is not proportional to increase in wc of the blended cements. this is in consonance with the work of (badogiannis et al., 2005). fig. 2b. ist and fst of pc/mk-pc pastes; nb. ist is initial setting time, fst is final setting time. 3.3. compressive strength figure 2 showed the compressive strength test results for pc and mk-pc hardened mortar pastes. it is observed that compressive strength of pc paste increased steadily with increase in hydration period, but for mk-pc pastes, it is less up to 21 days. this is due to the fact that it is the hydration of pc due to its c3s and c2s contents which mainly contributed to hydration products (c-s-h) which are responsible for strength increase at this stage. this is more in pc pastes than in mk-pc pastes due to reduction in pc content. also, the mk particles becomes the precipitation sites for the early hydration of c-s-h and ch which hinders pozzolanic reaction, furthermore, the strong dependency of the breaking down of glass phase on the alkalinity of the pore water which could only attain the high ph of 12 after some days of hydration. but at 28 days and beyond, increase in strength of mk-pc pastes improved, equalled and even surpassed that of pc values. this is because, in addition to the strength from pc hydration, in mk-pc pastes, mk reacted with calcium hydroxide (ch), by-product of pc hydration to form more c-s-h which increased the strength of the mk-pc pastes (amin et al., 2012). it is further observed that strength in mk– pc pastes is maximum in mix 15mk– pc paste for all ages as compared with other mixes. this can be attributed to pc hydration and pozzolanic reactions between mk and ch, silica and alumina (sio2 and al2o3) ions from mk which dissolved readily in solution to react with c3s and c3a ions from pc to form more c-s-h and c-s-a-h as precipitations when solution saturation is attained (abo-elenein et al., 2013). the strength decreased at 20mkpc paste up to 30mk–pc paste at all ages. this is due to dilution effect; more ca++ ions from addition of mk and less sio2, due to reduction in pc content resulting in unbalanced c++/si ratio in the solution which led to reduction in strength for both 20mk-pc and 30mk-pc pastes. 0 5 10 15 20 25 30 40 60 80 100 120 140 160 180 200 220 240 in it ia l/ fi n a ls e tt in g ti m e s (m in s ) metakaolincontent(%) ist fst 66 apeh, j. build. mater. struct. (2022) 9: 57-73 fig. 3. compressive strength versus age for pc /pc-mk pastes 3.4. chemically combined water (wn) and free lime content (%) figure 4 showed the results of chemically combined water for pc and mk-pc pastes studied. it has been observed that for pc paste, wn, steadily increased for all hydration ages which can be attributed to progressive hydration reaction of pc. it also showed that hydration rate is high from point of mixing to a few days, slowed down due to shielding from cement grains by initially formed hydration products and the rate of hydration gradually picked up again and steadily increased to 90 days as can be seen from the fairly flat shape of the graph between 28 to 90 days. the wn content for most mk-pc pastes are high compared with that for pc paste and the highest value obtained was for 15mk-pc paste as from 28 to 90 days. similarly (figure 4), the values of the free lime content (%) obtained from the pc paste studied increased continuously with increase in hydration age while for mk-pc pastes increased and then decreased at later ages. for the pc paste, the continuous increase in free lime content (%) with increase in hydration age is due to continuous release of ch from the pc hydration even up to later ages. however, for mkpc pastes, it increased up to about 60 days of hydration and then decreased. this is due to increase in ch content from pc hydration which is more than its consumption by the pozzolanic reaction (mk + ch) at ages up to 60 days. but at later ages, the consumption of ch through pozzolanic reaction becomes higher than that obtained from hydration reaction which led to decrease in free lime (%) content for mk – pc pastes compared with values of pc paste. the work of gupta and vyas (2018) has shown that increase in the percentage of pozzolanic material used to replace pc in pc blended pastes is shown by a marked decrease in the values of free lime (%) content. 0 10 20 30 40 50 60 70 80 90 0 5 10 15 20 25 30 35 c o m p re s s iv e s tr e n g th (n /m m 2 ) hydration age(days) pc 5mk-pc 10mk-pc 15mk-pc 20mk-pc 25mk-pc 30mk-pc apeh, j. build. mater. struct. (2022) 9: 57-73 67 fig. 4. chemically combined water (wn) versus hydration age for all pastes fig. 5. free lime content versus hydration ages for all pastes 3.5. mineralogical analysis figures 6 – 7 presents the xrd patterns of neat pc and mk-pc blended cement pastes with 0, 10, 20 and 30 % mk content after 28 and 90 days of curing. the spectra in the region of 2ɵ between 10o and 60o were used to investigate the change in hydration products of neat pc and blended cements with curing age. the diffraction peaks of pc and the blended cements at different ages show similar collections. from the figures, it can be shown that the main minerals are alite, a, which is c3s, belite, b, c2s, quartz, q which is sio2, calcium silicate hydrates (c-s-h), calcium 0 20 40 60 80 100 120 0 2 4 6 8 10 12 14 16 18 20 c h e m ic a lly b o n d e d w a te r w n ( % ) hydration age (days) pc 5mk-pc 10mk-pc 15mk-pc 20mk-pc 25mk-pc 30mk-pc 0 10 20 30 40 50 60 70 80 90 0 1 2 3 4 5 6 7 8 f re e l im e c o n te n t (% ) hydration age (days) pc 5mk-pc 10mk-pc 15mk-pc 20mk-pc 25mk-pc 30mk-pc 68 apeh, j. build. mater. struct. (2022) 9: 57-73 hydroxide (ch) and calcium aluminate silicate hydrate (cash). alite (c3s) and belite (c2s) are primary minerals found in pc. calcium hydroxide or portlandite (ch) is generated during hydration of pc and present in solution with the primary minerals, c3s and c2s in the pastes. during hydration of pc, c3s and c2s reacts with water, producing calcium silicate hydrate (c-sh) and calcium hydroxide (ch). in figure 6, the hydration of pc produced ch whose intensity peaks can be observed around 2 theta of 18.00o, 34.10o, 47.17o and 50.81o respectively. for the pc-mk mixes, it exhibits lower intensity peaks at 90 days curing (figure 7) due to additional pozzolanic reactions which consumes ch to form more c-s-h and also due to replacement of pc by mk which in turn leads to reduction of the clinker phase (c3s and c2s), resulting to lower generation of ch. as curing or hydration age increases up to 180 days or more, ch intensity peaks reduces drastically or disappears completely because they are used to produce more c-sh. the maximum intensity peaks for c-s-h at 28 days of curing were observed at around 2 theta of 29.09o for all the mixtures. the formation of c-s-h gel generally dominates the mechanical performance of concrete matrix. from the study, it can be observed that the pc-mk blended mixtures exhibited higher intensity peaks of c-s-h gel than that for pc mix. this is due to the cs-h production from pc hydration in addition to c-s-h produced due to pozzolanic reaction between mk and ch. fig. 6. xrd pattern for mixes pc, 10pc-mk, 20pc-mk and 30pc-mk for 28 days similarly, the calcium aluminate in the mk reacts with water producing calcium aluminate silicate hydrate (c3ah6). the mineral phase of cash was found in the form of gismondine at around 2 theta 33.15o. their intensity peaks were found to be significantly lower at 28 days of curing than at 90 days (figure 7). the peaks of gismondine were found to be higher for pc-mk blended mixtures than for pc mix, which might be due to the presence of high aluminate phases in the mk ash. the work of gupta and vyas (2018) show that the presence of high aluminate phases of the mullite (aluminium silicon oxide) phase in mk ash reacts with ch to form cash or gismondine. also, its formation along with csh gel partially enhance the densification of cement paste (tang et al, 2016). apeh, j. build. mater. struct. (2022) 9: 57-73 69 fig. 7. xrd pattern for mixes pc, 10pc-mk, 20pc-mk and 30pc-mk for 90 days. it is an established fact that the amorphous silica, which is the reactive component in pozzolanic materials like mk reacts with ch to produce additional hydrate products. from the study, the diffraction peaks of alite (c3s) as a and belite (c2s) as b can be seen in the opc mix only around 2 theta 29.5o and 54o respectively while q (sio2) which is quartz appeared mainly at 23o and 28o which increases with increase in mk content (highest in mk30 mix) for all the mixes labelled; opc, mk10, mk20, and mk30, representing control pc, 10 %mk, 20 % mk and 30 %mk at 28 and 90 days curing duration as shown in figures 6 – 7 respectively. in each figure, ch intensity decreases gradually as aforementioned with both curing age and percentage replacement level of mk. this indicates that the incorporation of mk yields the pozzolanic reaction which proceeded even after 90 days curing duration, producing c-s-h and cash which further increase the strength of the mortar. this accounts for the diminishing of the ch intensity peaks. 3.6. microstructural analysis the chemical compound that affects the hcp of pc and pc-mk pastes performance and the changes in the microstructure due to the presence of mk were investigated by sem. after compressive strength test and hydration behaviour in terms of non-evaporable water, free lime water content, the core of the cross section areas of the test specimen was prepared and coated with gold for 30 seconds, then observed under aforementioned sem equipment so as to study the evolution of the microstructure due to the presence of mk in the blended cement and pc control. test results are produced images of the distribution and volume of pores and the morphology of particles in the hcp for the specimens. sem micrographs of pc and blended cement at 28 and 90 days hydration age are shown in figures 8 and 9. test result for pc specimen (figure 8) shows that pc particles have an irregular polygonal shape with sizes ranged from less than 5 μm to 15 μm. on the other hand (figure 9), mk particles are elongated likemicrofibers and some like flakes with a rough surface. the pc-mk hcp image is finer than that for the pc. the image shows pc mix at 28 days curing as a matrix with a crystalized ch and poorly crystallized c-s-h gel and pores occupying considerable volume in the matrix, though forming a compact microstructure. however, with partial replacement of pc with mk as shown in figure 8b at 90 days, the paste showed more dense and compact though in homogeneous microstructure. with development of more cement hydration and pozzolanic reaction, the 70 apeh, j. build. mater. struct. (2022) 9: 57-73 microstructure of blended cement becomes denser with further formation of more c-s-h and c3ah6 gels. also, only a few ch with irregular shapes have been detected in the blended cement pastes instead of the ch crystal with hexagonal plate structure as in pc paste. this is attributed to the consumption of ch by mk during the pozzolanic reaction. the result indicates that the characteristics of the pc-mk blended cement has the potential to enhance the properties of pc while in service. this is because mk is a pozzolan with a specific surface area of about 12,000 m2/kg, specific gravity of 2.50 g/cm3 compared with pc with a specific surface area of 373 m2/kg, specific gravity of 3.15g/cm3 for pc. this shows that mk has very small particles and hence can enhance pc in two fundamental mechanisms: (a) by filling of interstitial pores inside the skeleton mesh of pc matrix, thereby improving the density and strength as well, and (b) by contribution to more strength through pozzolanic reaction with ch liberated during pc hydration. fig. 8. sem micrograph for the hardened neat pc after 28 days of hydration fig. 9. sem micrograph for the hardened pc-mk30% paste after 90 days of hydration 4. conclusion hydration and strength development of blended cement with mk were investigated using chemically combined water, free-lime content and compressive strength tests,. xrd, sem apeh, j. build. mater. struct. (2022) 9: 57-73 71 techniques were applied in the analysis of pozzolanic reaction and hydration products. from the results of compressive strength tests, and that obtained from analysis of the hydration products using aforementioned techniques, the following conclusions were drawn: 1. test results on the mechanical characteristics showed that for all curing ages the pc strength were higher up to 21 days compared with blended strength values, but at 28 days upward, strength of blended cements equal and even surpassed control values due to additional strengths from pozzolanic reactions. 2. standard consistency in mkpc binders increased with increase in replacement level of the pc with mk due to its high water requirement, its high specific surface area and its degree of reactivity. 3. there is a remarkable modification observed in the hydration product of ch, csh gel and cash on the cement matrix containing the blended cement as shown in the xrd test results. 4. the incorporation of mk improves the densification of the blended cement matrix as shown in the sem analysis test results. it further showed a remarkable impart of mk on the formation of the hydration products, its ability to form better bonding with paste content which leads to improvement in the mechanical performance of mk blended cement mixture. 5. the chemical and morphological changes observed in the developed binders was achieved through microstructural analysis. based on the mechanical and microstructural characteristics, mk content up to 25 % as a replacement of pc can be utilized in the production of mortar of concrete for construction. conflicts of interest: the author declares no conflict of interest. 5. references abo-el-enein, s. a., amin, m. s., el-hosiny, f. i., hanafi, s., elsokkary, t. m., & hazem, m. m. (2014). pozzolanic and hydraulic activity of nano-metakaolin. hbrc journal, 10(1), 64-72. ambroise, j., murat, m., & pera, j. (1985). hydration reaction and hardening of calcined clays and related minerals v. extension of the research and general conclusions. cement and concrete research, 15(2), 261-268. amin, m. s., abo-el-enein, s. a., abdel rahman, a., & alfalous, k. a. (2012). artificial pozzolanic cement pastes containing burnt clay with and without silica fume: physicochemical, microstructural and thermal characteristics. journal of thermal analysis and calorimetry, 107(3), 1105-1115. antoni, m., rossen, j., martirena, f., & scrivener, k. (2012). cement substitution by a combination of metakaolin and limestone. cement and concrete research, 42(12), 1579-1589. astm c 191 (2008). standard method for normal consistency and setting of hydraulic cement. astm annual book of astm standards. astm c 618-00 (2000). specification for coal fly ash and raw calcined natural pozzolans for use as a mineral admixture in portland cement concrete. astm international, west conshocken, pa. badogiannis, e., kakali, g., & tsivilis, s. (2005). metakaolin as supplementary cementitious material: optimization of kaolin to metakaolin conversion. journal of thermal analysis and calorimetry, 81(2), 457-462. bentz, d. p. (2000). influence of silica fume on diffusivity in cement-based materials: ii. multi-scale modeling of concrete diffusivity. cement and concrete research, 30(7), 1121-1129. bs en 196 – 3 (1995). methods of testing cement; determination of setting time and soundness. british standard institution, london. 72 apeh, j. build. mater. struct. (2022) 9: 57-73 caldrone, m; giuber, k; burg, r, (1994). high reactivity metakaolin. a new generation mineral admixture concrete international 16(11),37-40. clarridge, e. (2011). an investigation of the hydration of steam-cured ternary and quaternary cement blends. a phd. thesis, department of civil engineering, university of toronto, canada. dave, n., misra, a. k., srivastava, a., & kaushik, s. k. (2016). experimental analysis of strength and durability properties of quaternary cement binder and mortar. construction and building materials, 107, 117-124. ecosmart concrete. (2008). environmental impact–cement production and the co2 challenge. canada: ecosmart foundation. el-diadamony, h., amer, a. a., sokkary, t. m., & el-hoseny, s. (2018). hydration and characteristics of metakaolin pozzolanic cement pastes. hbrc journal, 14(2), 150-158. el-gamal, s. m. a., amin, m. s., & ramadan, m. (2017). hydration characteristics and compressive strength of hardened cement pastes containing nano-metakaolin. hbrc journal, 13(1), 144-121. gupta, l. k., & vyas, a. k. (2018). impact on mechanical properties of cement sand mortar containing waste granite powder. construction and building materials, 191, 155-164. hamdy, d., ahmed, a., amer, t.m.s., samir, h. (2018). hydration and characteristics of metakaolin pozzolanic cement pastes. hbrc journal, 14,150–158. kakali, g., perraki, t. h., tsivilis, s., & badogiannis, e. (2001). thermal treatment of kaolin: the effect of mineralogy on the pozzolanic activity. applied clay science, 20(1-2), 73-80. kondo, r., abo-el-enein, s. a., & daimon, m. (1975). kinetics and mechanisms of hydrothermal reaction of granulated blast furnace slag. bulletin of the chemical society of japan, 48(1), 222-226. lam, l., wong, y. l., & poon, c. s. (2000). degree of hydration and gel/space ratio of high-volume fly ash/cement systems. cement and concrete research, 30(5), 747-756. li, z., & ding, z. (2003). property improvement of portland cement by incorporating with metakaolin and slag. cement and concrete research, 33(4), 579-584. mehta, p. k. (2002). greening of the concrete industry for sustainable development. concrete international, 24(7), 23-28. moser, r. d., jayapalan, a. r., garas, v. y., & kurtis, k. e. (2010). assessment of binary and ternary blends of metakaolin and class c fly ash for alkali-silica reaction mitigation in concrete. cement and concrete research, 40(12), 1664-1672. naik, t. r., singh, s. s., & ramme, b. w. (2001). time of setting influenced by inclusion of fly ash and chemical admixtures: in the 7th international conference on fly ash, silica fume, slag and natural pozzolans in concrete canmet/aci); proceedings, vol 1 ed. by v.m. malhotra; july 22-27, 2001, madras, india, 393 – 413. olubajo, o. o., makarfi, i. y., ibrahim, m. s., ayeni, s., & uche, n. w. (2020). a study on ordinary portland cement blended with rice husk ash and metakaolin. path of science, 6(1), 3001-3019. oriol, m., & pera, j. (1995). pozzolanic activity of metakaolin under microwave treatment. cement and concrete research, 25(2), 265-270. powers, t. c., & brownyard, t. l. (1948). studies of the physical properties of hardened portland cement. portland cement association. said-mansour, m., kadri, e. h., kenai, s., ghrici, m., & bennaceur, r. (2011). influence of calcined kaolin on mortar properties. construction and building materials, 25(5), 2275-2282. saikia, n., kato, s., & kojima, t. (2006). thermogravimetric investigation on the chloride binding behaviour of mk–lime paste. thermochimica acta, 444(1), 16-25. shafigh, n. and nurudin, m.f. (2010). degree of hydration of opc and opc/fa pastes dried in different relative humidity. concrete research letters, 1(3), 2010, 81– 89. apeh, j. build. mater. struct. (2022) 9: 57-73 73 shafigh, p., jumaat, m. z., mahmud, h. b., & abd hamid, n. a. (2012). lightweight concrete made from crushed oil palm shell: tensile strength and effect of initial curing on compressive strength. construction and building materials, 27(1), 252-258. suhendro, b. (2014). toward green concrete for better sustainable environment. procedia engineering, 95, 305-320. suprenant, b. a., & papadopoulos, g. (1991). selective dissolution of portland-fly-ash cements. journal of materials in civil engineering, 3(1), 48-59.. tang, s. w., cai, x. h., he, z., shao, h. y., li, z. j., & chen, e. (2016). hydration process of fly ash blended cement pastes by impedance measurement. construction and building materials, 113, 939-950. wild, s., & khatib, j. m. (1997). portlandite consumption in metakaolin cement pastes and mortars. cement and concrete research, 27(1), 137-146. wild, s., khatib, j. m., & craythorne, m. j. (1997). strength development of mortar containing metakaolin. in proceedings of the 5th international conference on modern building materials, structure and techniques, pp. 58-63. wild, s., khatib, j. m., & jones, a. (1996). relative strength, pozzolanic activity and cement hydration in superplasticised metakaolin concrete. cement and concrete research, 26(10), 1537-1544. j. build. mater. struct. (2016)3: 31-42 https://doi.org/10.34118/jbms.v3i1.22 issn 2353-0057 the effect of coal bottom ash (cba) on mechanical and durability characteristics of concrete khan r a * and ganesh a department of civil engineering, dr b r ambedkar national institute of technology jalandhar * corresponding author : rizwankhan1@gmail.com abstract. the present paper would contribute to the efforts being made in the field of concrete technology towards development of concretes possessing good strength and durability properties along with economic and ecological advantage. in the present study it was found that with increase in amount of coal bottom ash, standard consistency, initial and final setting time increase at the same time workability of concrete decreases. early age strength is less for bottom ash concrete compare to control mix, but as the age increases they show good improvement in strength due to pozzalanic reaction. optimum dosage is observed to be 10% grinded bottom ash (gba) which shows about 14 % more strength compared to control mix at 56 days. also 20% replacement by gba gives results comparable to control concrete. gba concrete shows more resistance to acid attack compared to original bottom ash (oba). mix m7 with 30 % replacement by gba shows highest resistance to acid attack. with the increase in amount of bottom ash water absorption capacity of concrete increases, also as the age increases for all the mix water absorption capacity decreases. it was also found that at optimum dosage i.e at 10% replacement of cement with gba it is also economical and also less amount of co2 is emitted that mean it is also environmental friendly compared to control mix. key words: coal bottom ash, workability, mechanical, durability. 1. introduction natural resources of aggregate, due to high consumption in construction fields, are getting depleted rapidly. therefore, in the present conditions of inadequate resources of aggregate and development in concrete industry, it becomes crucial and necessary to detect ideal substitute material in durable concrete for aggregate. the environmentally-friendly solution is to use lowcost industrial residues or solid wastes in the production of concrete. in so doing, in spite of a decrease in the amount of industrial wastes sent to landfills, the impacts of the depletion of natural resources, and sever environmental hazards, this is a positive advance in sustainable development and opens new market opportunities. bottom ash (ba) is one of the renowned industrial wastes produced at the bottom of coal furnaces. it is originated from agglomerated ash particles that are not finer and lighter to be found in the flue gasses. the chemical composition of ba includes heavy metals and arsenic. due to this fact, the stockpiled piles of ba in ponds pose health hazards to human and the environment by spreading hazardous components and contaminating adjacent soil and underground water. therefore, it becomes essential to recycle effectively and reuse ba due to deficiency of natural resources, economic problems and enormous negative impacts on the environment (nikbin et al., 2016). ba is produced by combustion of coal. ba before and after being grounded was used as replacement of cement and its physical and chemical properties were studied, it was found that compressive strength of mortar containing 20-30% of ba as cement replacement was much less than that of cement mortar at all ages, but at 60 days ba concrete has more strength (jaturapitakkul and cheerarot, 2003). grinded ba for different periods was used as replacement of cement and its mechanical properties, ecological and economical substation was studied. it was found that usage of ba in concrete industry help in reducing energy demand as well as co2 emission; it also reduces the price of concrete by 10% (bajare et al., 2013). utilization of ba as fine and coarse aggregates in high-strength concrete was studied. firstly, the chemical and physical mailto:hkhater4@yahoo.com 32 khan and ganesh, j. build. mater. struct. (2016)3:31-42 characteristics of ba particles, such as chemical compositions, specific gravity and sem images, were investigated. further experiments were conducted by replacing fine and coarse ba with normal sand and gravel varying in percentages. the effect of fine and coarse ba on the flow characteristics and density of concrete mixture was investigated in the aspect of particle shapes and paste absorption of ba. mechanical properties, such as compressive strengths and modulus of elasticity and flexural strength of high-strength concrete with ba were evaluated. it was found that the slump flow of fresh concrete was slightly decreased when coarse ba was replaced 100% of normal coarse aggregates, while fine ba did not affect the slump flow. moreover, it also showed that both of fine and coarse ba aggregates had more influence on the flexural strength than compressive strength. flexural strength of concrete almost linearly decreased as the replacement ratio of the fine and coarse ba was increased (kim and lee, 2011; kim et al., 2014). investigations were carried out on the use of ba waste as sand replacement and cement with fly ash. concrete specimens were prepared incorporating 0, 20, 50, 75 and 100% of ba replacing sand and 20% of coal fly ash by mass, as a substitute for ordinary portland cement. results revealed that concrete workability reduced when ba content increased replacing sand. on the other hand, at the early age of 28 day, no significant effect was observed in compressive, flexural and tensile strengths of all concrete samples. after curing at 91 and 180 day ages, compressive strength of both the experimental and control concrete samples increased significantly but remained almost similar. however, flexural and splitting tensile strengths of the experimental mix containing 75% ba and 20% fly ash exceeded much more than the control sample. moreover, drying-shrinkage of experimental concrete mixtures containing 50%, 75% and 100% ba and 20% fly ash was lower than the control mix. it is concluded that those experimental concrete mixes can be used in several structures (foundations, sub-bases, pavements, etc.) which will minimize the cost, energy and environmental problems to a great extent (rafieizonooz et al., 2016). influence of the use of coal bottom ash (cba) as a replacement for natural fine aggregates on the properties of concrete in the fresh state is also studied by the researcher. tests for water loss through bleeding and the determination of the setting times and plastic shrinkage, were carried out in order to evaluate the material in the presence of ba, as well as on the water consumption of concretes produced with ba is also discussed. the results showed that in the fresh state the concretes produced with the ba are susceptible to water loss by bleeding and the higher the percentage of ba used as a natural sand replacement the lower the deformation through plastic shrinkage. with increase in quantity of ba there is a slight delay for maximum temperature peak to be reached, the results also showed that the setting time is affected by the presence of ba in the concrete (andrade et al., 2009). fresh properties of concrete like bleeding, workability, hardened properties like compressive test, splitting tensile test, modulus of elasticity, chemical resistance, density of concrete permeable pore space and water absorption, x-ray diffractogram, and sem morphology of concrete containing ba as fine aggregate were studied, workability of ba concrete was found to decrease on use of cba, water loss from bleeding decreased, permeable pore space increased in early age and reduced with the progress of curing age, water loss through air drying increases up to 50% replacement and from 75% it decreases, compressive strength reduces in early age and after 28 days curing strength increases, splitting tensile strength of concrete improved at all the curing ages on use of cba as fine aggregate. (siddique et al., 2014; siddique, 2013; singh and siddique, 2014). strength and drying shrinkage of concretes with the natural sand replaced with furnace ba by mass were studied at fixed water cement ratios and fixed slump ranges. the results showed that, at fixed water cement ratios, the compressive strength and the drying shrinkage decreases with the increase of the furnace ba sand content. however, at fixed workability, the compressive strength was comparable with that of the control concrete, while the drying shrinkage increased with the increase of the furnace ba content beyond 30% replacement level. nevertheless, 30% of the natural sand can be beneficially replaced with the furnace ba without detrimentally affecting drying shrinkage properties of the concrete (bai et al., 2005). moisture kinetics aspects of composite granular material samples composed of natural sand and ba from thermoelectric power stations and the use of this material in the production of durable concretes, in relation to water transport, are discussed. the evaluations of the phenomenon of water absorption by khan and ganesh, j. build. mater. struct. (2016)3:31-42 33 capillarity and the loss of water through air drying until hygroscopic equilibrium were carried out; the results showed that due to the high porosity of ba, the water absorption by capillarity along with the absorption velocity were higher in the compositions with greater ba content. the values for moisture equilibrium from air drying, absorption from capillarity and sorptivity obtained in the hydroscopic equilibrium tests, carried out on the same samples after absorption, were also higher in the samples with ba. these samples also requited a longer drying time (andrade et al., 2007). pozzolanic properties of a cba were investigated. plain pastes containing equal amounts of calcium hydroxide and ba were prepared and analysed at different ages for their strength and the calcium hydroxide consumption, it was found that at early ages, ba does not react with calcium hydroxide. its pozzolanic reaction proceeds slowly and accelerates gradually to become very interesting after 28 days and especially after 90 days. the strength activity indexes measured on mortars are sufficiently important to allow the use of ba in concrete. an adequate grinding improves the pozzolanic activity of the ba, when cba is ground for 6 h in a laboratory ball mill; the 28-day strength activity index is increased by 27% (cheriaf et al., 1999). properties of concrete made with portland cement, nine mixtures with 12.5%, 25% and 50% of replacement of cement by fly ash, rice husk ash and limestone filler; two with (12.5 + 12.5)% and (25 + 25)% of fly ash and rice husk ash. all the mixtures were prepared with water/binder ratios of 0.35, 0.50, and 0.65. the results show that the pozzolanic and physical effects have increased as the mineral addition increased in the mixture, being higher after 91 days than after 28 days. when the results for the same strength values are compared, it was observed that the filler effect increased more than the pozzolanic effect. the pozzolonic effect was stronger in the binary and ternary mixtures prepared with rice husk ash in proportions of 25% or higher. the binary mixtures of rice husk ash showed better performance than the fly ash material, although the ternary mixtures have reached better overall results (isaia et al., 2003). physical, chemical, mineralogical and thermal properties of the cenospheres obtained from an ash lagoon. cenospheres quantity depends on the carbon and iron contents present in the ash. cenospheres are being used in different industrial applications, mainly due to their low density, high strength, and good thermal properties. results have shown that alumina and quartz are the most predominant minerals present in the cenosphere sample. these particles are noticed to be almost uniform in size (kolay and singh, 2001). ba was used up to 25% as a partial substitute for the portland cement. in order to be able to reduce the unburned carbon content, cba was treated by three different processes (particle size classification, heavy medium separation and electrostatic separation). results show that compared to other pre-treatment methods such as the heavy medium separation and electrostatic separation methods, the crushing-screening method was found to be a more useful method for lowering the carbon content of the cba. compressive and flexural strengths of specimens cured at 56 day increase with increasing amount of ash replacement up to 15%, the maximum substitution rate of cba was determined as 10%. when 10% of cba is replaced by cement, the compressive strength of cba-concrete increases (kurama and kaya, 2008; kurama et al., 2009). study of the literature shows that not much work has been reported on replacement of cement with ba. so in this paper we tried to study the effect of ba on mechanical and durability properties of concrete, as well as the economical and ecological study were done to know how much cost and co2 emission is reduced. 2. experimental procedures 2.1. materials ordinary portland cement (opc) from a single lot was used throughout the course of the investigation. the physical properties of the cement were determined from various tests conforming to indian standard is: 1489-1991(part-1). all the tests were carried out as per recommendations of is: 4031-1988. cement was carefully stored to prevent deterioration in its properties due to contact with the moisture. 34 khan and ganesh, j. build. mater. struct. (2016)3:31-42 crushed angular granite from a local source was used as coarse aggregate. river sand was used as fine aggregate. the specific gravity and fineness modulus was 2.55 and 2.94 respectively and it belongs to zone ιι of grading as shown in fig.1. fig 1. sieve analysis of fine aggregates. ba from nearby cement factories is used in this study. in this study we used two types of ba, original bottom ash (oba) without grinding is used in first set, ba that is grinded in los angeles abrasion test machine for 30 minutes is used in second test. sieve analysis is carried out for both oba and grinded bottom ash (gba) and the difference is shown in fig.2. fig 2. comparison between oba and gba using sieve analysis taking 100gms of each. 2.2. preparation of mixes different mixes were prepared and compared with control mix. mix proportions are shown in table 1.the mix design has been prepared as per bureau of indian standards guidelines is : 10262-2009. khan and ganesh, j. build. mater. struct. (2016)3:31-42 35 table 1. mix proportion per m3. mix cement (kg/m3) oba (kg/m3) gba (kg/m3) w/b water (kg/m3) fine aggregate (kg/m3) coarse aggregate (kg/m3) m1 438 0 0 0.45 198 630.89 1099.3 m2 394.2 43.8 0 0.45 198 630.89 1099.3 m3 350.4 87.6 0 0.45 198 630.89 1099.3 m4 306.6 131.4 0 0.45 198 630.89 1099.3 m5 394.2 0 43.8 0.45 198 630.89 1099.3 m6 350.4 0 87.6 0.45 198 630.89 1099.3 m7 306.6 0 131.4 0.45 198 630.89 1099.3 3. results and discussion 3.1. workability workability is considered to be that property of plastic concrete which indicates its ability to be mixed, handled, transported and most importantly, placed with a minimum loss of homogeneity. more precisely, it defines that it can be fully compacted with minimum energy input. there should be no sign of any segregation or bleeding in a workable concrete. the workability of all the mixes of concrete used in this work was controlled by conducting slump test. w/b ratio was kept constant 0.45 for all the concrete mixes. the workability results of different concrete mixes were shown in table 2. it shows that as the replacement of cement with ba increases, the workability of concrete mix decreases compared to control mix. it also shows that the addition of gba decreases the workability more as compared to oba. it may be due to the fact that gba is finer than oba which absorbs more water thereby reducing the workability. table 2. workability values for different concrete mixes. mix no description slump (mm) 1 100%opc+0%oba+0%gba 107 2 90%opc+10%oba+0%gba 101 3 80%opc+20%oba+0%gba 96 4 70%opc+30%oba+0%gba 91 5 90%opc+0%oba+10%gba 99 6 80%opc+0%oba+20%gba 93 7 70%opc+0%oba+30%gba 88 3.2. standard consistency the object of conducting this test is to find out the amount of water to be added to the cement to get a paste of normal consistency, i.e., the paste of a certain standard solidity, which is used to fix the quantity of water to be mixed in cement before performing tests for setting time, soundness and compressive strength. the standard consistency test was carried out as per indian standards is:4031-part4 1988. the standard consistency results for different mixes are given in table 3. it was found that the standard consistency of paste increases with increase in replacement of cement with ba, this is even more when gba is added. standard consistency increases because ba absorbs water. gba absorbs more water than oba therefore standard consistency is more for gba than oba at the same cement replacement level. table 3. standard consistency values of different mixes. mix no description standard consistency (%) 1 100%opc+0%oba+0%gba 31 2 90%opc+10%oba+0%gba 31 3 80%opc+20%oba+0%gba 32 4 70%opc+30%oba+0%gba 32 5 90%opc+0%oba+10%gba 32 6 80%opc+0%oba+20%gba 33 7 70%opc+0%oba+30%gba 34 36 khan and ganesh, j. build. mater. struct. (2016)3:31-42 3.3. setting time in order that the concrete may be placed in position conveniently, it is necessary that the initial setting time of cement is not too quick and after it has been laid, hardening should be rapid so that the structure can be made use of as early as possible. the initial set is a stage in the process of hardening after which any cracks that may appear will not re-unite. the concrete is said to be finally set when it has obtained sufficient strength and hardness. the setting time for different mixes is given in table 4. the mix to test setting time was prepared by taking the corresponding standard consistency values from the table 3. from the obtained standard consistency values the amount of water that is to be added to cement is calculated. as the replacement of cement with ba increases initial and final setting time increases. initial and final setting time of cement depends on reaction of cement, so as the cement is replaced with ba the cement that is present for reaction decreases so it is taking more time for initial and final setting time. there is no much difference between adding oba and gba in both the cases they are nearly same. table 4. setting time of different mixes. mix no description initial setting time (minute) final setting time (minute) 1 100%opc+0%oba+0%gba 65 315 2 90%opc+10%oba+0%gba 75 370 3 80%opc+20%oba+0%gba 90 417 4 70%opc+30%oba+0%gba 105 465 5 90%opc+0%oba+10%gba 75 360 6 80%opc+0%oba+20%gba 85 420 7 70%opc+0%oba+30%gba 105 470 3.4. compressive strength test results of cement mortar the tests were conducted on cube of size 70.5mm x 70.5mm x 70.5mm. the cement sand mortar of the ratio 1 : 3 containing (p/4 + 3)% water was prepared and placed in moulds. specimens were taken out from curing tank at the age of 7, 14, 28, 56 and 90 days of curing. surface water was then allowed to drip down. specimens were then tested on 200 tonnes capacity compression testing machine. the position of cube while testing was at right angles to that of casting position. axis of specimens was carefully aligned with the centre of thrust of the spherically seated plates. the load was applied gradually without any shock and increased at constant rate of 3.5 n/mm2/minute until failure of specimen takes place. the average of three samples was taken as the representative value of compression strength for each batch of mortar. the compressive strength was calculated by dividing the maximum compressive load by the cross sectional area of the cube specimens. thus the compressive strength of different specimens was obtained. the test specimens are stored in place free from vibrations, in most air of at least 90% relative humidity and at a temperature of 27 degree centigrade for 24 hours from the time of addition of water to the dry ingredients. after this period, the specimens are marked and removed from the moulds and unless required for the test within 24 hours, immediately submerged in clean and fresh water and keep there until taken out just prior to test. the water or solution in which the specimens are submerged, are renewed every seven days and are maintained at a temperature of 27 degrees centigrade. the specimens are not to be allowed to become dry at any time until they have been tested. the specimens are tested at 7, 14, 28, 56 and 90 days of curing. the compressive strength test results of all the mixes at different curing ages are shown in fig.3. in the first 28 days the strength of the ba cement mortar mix is less compared to control mix, because there is less cement in ba cement mortar mix compared to control mix. after 28 days the difference is gradually reduced because pozzolanic reaction starts and calcium hydroxide reacts with the ba and the strength increases. cement mortar with gba has more strength than that with oba, because gba is more fine compared to oba (fig.2). cement mortar is dense in gba compared to oba so initial strength is more for gba mortar. after 28 days pozzolanic reaction takes place, in gba pozzolanic reaction is more compared to oba because it is finer. khan and ganesh, j. build. mater. struct. (2016)3:31-42 37 fig 3. compressive strength (mpa) results of all mortar mixes at different curing age. 3.5. compressive strength test results of concrete the tests were conducted on cube of size 150mm x 150mm x 150mm. specimens were taken out from curing tank at the age of 7, 14, 28, 56 and 90 days of curing. surface water was then allowed to drip down. specimens were then tested on 200 tonnes capacity compression testing machine (ctm). the position of cube while testing was at right angles to that of casting position. axis of specimens was carefully aligned with the centre of thrust of the spherically seated plates. the load was applied gradually without any shock and increased at constant rate of 3.5 n/mm2/minute until failure of specimen takes place. the average of three samples was taken as the representative value of compression strength for each batch of concrete. the compressive strength was calculated by dividing the maximum compressive load by the cross sectional area of the cube specimens. thus the compressive strength of different specimens was obtained. the test specimens are stored in place free from vibrations, in most air of at least 90% relative humidity and at a temperature of 27 degree centigrade for 24 hours from the time of addition of water to the dry ingredients. after this period, the specimens are marked and remove from the moulds and unless required for the test within 24 hours, immediately submerged in clean and fresh water or saturated lime solution and keep there until taken out just prior to test. the water or solution in which the specimens are submerged, are renewed every seven days and are maintained at a temperature of 27 degrees centigrade. the specimens are not to be allowed to become dry at any time until they have been tested. the specimens are tested at 7, 14, 28, 56 and 90 days of curing. the compressive strength test results of all the mixes at different curing ages are shown in fig.4. it shows the variation of compressive strength of concrete mixes w.r.t control mix after 7, 14, 28, 56 and 90 days respectively. in the first 28 days strength of the ba concrete is very less compared to control mix concrete. in the first 28 days pozzolanic reaction doesn’t start so early strength is due to the cement in the mix. in bottom ash concrete there is less cement compared to control mix so the strength of bottom ash concrete is less compared to control mix at 28 days. gba is finer compared to oba, so gba is densely packed in concrete compare to oba, so strength of gba concrete is more than oba concrete in the initial age. after 28 days ba concrete gains more strength compared to control mix and the difference between them is reduced because of pozzolanic reaction of bottom ash with calcium hydroxide. after 28 days gba concrete gains more strength than oba concrete because pozzolanic reaction is more in gba concrete. at 56 days strength of the gba concrete at 10% replacement (m5) is more than the control mix (m1) because of pozzolanic reaction. but at the same 10% replacement oba 38 khan and ganesh, j. build. mater. struct. (2016)3:31-42 concrete (m2) is having less strength because it is coarser than gba and having more voids than gba, pozzolanic reaction in oba is less. at 56 days strength of the m6 and m7 is less compared to m5, strength of m3 and m4 is less than m2, because pozzolanic reaction is slow and it requires calcium hydroxide to form pozzolanic reaction, since this mixes have less cement and more ba there is less calcium hydroxide available at that time so resulting in less strength. fig 4. compressive strength (mpa) results of concrete at different curing ages. 3.6. acid resistance test the concrete cubes of 150 mm size were cast for finding the mass loss due to the acid attack. the prepared cubes were cured in water for 28 days after which they were immersed in 1% h2so4 and the solution ph is maintained same (ph 2.0) for all the 90 days of curing. the initial mass and the mass of concrete specimens after the immersion period of 28, 56 and 90 days were measured for finding the mass loss due to the deterioration of concrete specimens. the average value of three specimens was considered for assessment. table 5-8 show effect of acid attack on compressive strength of concrete. from table 5-8 it was observed that m7 mix is having highest resistance against weight loss in 1% h2so4 solution at all curing ages, and m2 mix is showing less resistance at all curing ages compared with control mix. it was observed that as the bottom ash content increases resistance against weight loss in h2so4 increases. from above table it can also be observed that percentage loss in strength is less for m7. further, itwas also found that concrete containing gba has more resistance than oba. table 5. effect of acid attack on compressive strength of concrete after 28 days. sl. no. mix identity weight of cubes before and after immersion (kg) % loss in weight compressive strength (n/mm2) compressive strength after acid attack (n/mm2) % difference in compressive strength before after 1 m1 2.579 2.544 1.35 38.45 32.62 15.16 2 m2 2.578 2.549 1.124 35.9 33.3 7.24 3 m3 2.501 2.478 0.92 30 28.6 4.66 4 m4 2.522 2.502 0.79 27.85 27.2 2.33 5 m5 2.583 2.555 1.084 43 39.4 8.37 6 m6 2.493 2.471 0.882 35.8 34.5 3.63 7 m7 2.4675 2.461 0.263 33.5 33.3 0.59 khan and ganesh, j. build. mater. struct. (2016)3:31-42 39 table 6. effect of acid attack on compressive strength of concrete after 56 days. table 7. effect of acid attack on compressive strength of concrete after 90 days. table 8. percentage increase in the resistance of bottom ash concrete against the weight losses in comparison with ordinary concrete mixes. mix type % of ba 1% h2so4 solution 28 days immersion period 56 days immersion period 90 days immersion period m1 0.0% --- m2 10% oba 0.226 0.297 0.371 m3 20% oba 0.43 0.494 0.473 m4 30% oba 0.56 0.658 0.966 m5 10% gba 0.266 0.404 0.396 m6 20% gba 0.468 0.505 1.049 m7 30% gba 1.087 .828 1.899 3.7. water absorption test the concrete cubes of 100 mm size were cast for finding the water absorption by oven drying at 110oc. the cubes of size 100 mm were cast and cured for 28, 56 and 90 days. after curing they are removed and surface dried and weight is measured it is taken as w1 and then it is dried in oven for 24 hours and weight is measured and again dried in oven until we get the constant weight that is taken as w2. the test results are shown in table 9. it was observed that as the ba content increases the water absorption capacity of concrete is increased initially. at 90days it was observed that ba concrete is absorbing less water than 28days. sl. no. mix identity weight of cubes before and after immersion (kg) % loss in weight compressive strength (n/mm2) compressive strength after acid attack (n/mm2) % difference in compressive strength before after 1 m1 2.5725 2.532 1.574 38.9 31.4 19.25 2 m2 2.5825 2.5495 1.277 37.55 33.7 10.25 3 m3 2.545 2.5175 1.08 33.25 31.45 5.41 4 m4 2.5635 2.54 0.916 29.3 27.75 5.3 5 m5 2.6065 2.576 1.17 43.6 39.3 9.76 6 m6 2.4785 2.452 1.069 38.1 36.25 4.8 7 m7 2.547 2.528 0.746 36.7 36.1 1.6 sl. no. mix identity weight of cubes before and after immersion (kg) % loss in weight compressive strength (n/mm2) compressive strength after acid attack (n/mm2) % difference in compressive strength before after 1 m1 2.5155 2.4445 2.8225 40.1 30.8 22.97 2 m2 2.631 2.5665 2.451 41.2 34.6 15.825 3 m3 2.575 2.5145 2.3495 37.6 34.5 8.244 4 m4 2.5865 2.5385 1.8557 34.2 31.4 7.94 5 m5 2.4315 2.3725 2.4264 44.45 37.9 14.68 6 m6 2.5385 2.4935 1.7727 41.5 38.25 7.83 7 m7 2.5465 2.523 0.9228 39.75 38.83 2.3 40 khan and ganesh, j. build. mater. struct. (2016)3:31-42 table 9. water absorption of concrete. mix type % of ba water absorption of concrete (%) 28 days immersion period 56 days immersion period 90 days immersion period m1 0.0% 6.13 5.55 4.6 m2 10% oba 6.53 5.63 4.97 m3 20% oba 6.31 6.27 4.55 m4 30% oba 6.99 6.99 4.24 m5 10% gba 6.48 5.88 4.97 m6 20% gba 6.26 5.84 4.76 m7 30% gba 6.47 6.19 4.73 3.8. economic and ecological study in this study the test results obtained from compression test are compared with the normal opc concrete mix of that particular strength. the cement that is saved by adding ba is calculated. cost of the cement that is saved is the economic benefit in case of replacement with ordinary ba. in case of gba economic benefit is cost of cement that is saved minus grinding cost. from the compressive strength test results shown in fig.4, comparing the results of ba concrete with control mix it was observed that 10% replacement of cement with gba is showing good results so it has been taken as sample to check whether it is economical or not. in this study cost comparison of making 10% gba concrete with control mix is done. in this mix’s amount of coarse aggregate, fine aggregate and water remains same so there is no effect of them on change in cost of concrete. cost is affected only by change in cement content. assuming the cost of transportation is same for both cement and ba the below calculations are done. cost of one bag of cement is rs.350 and each bag contains 50 kg of cement. commercial electricity tariff is taken as rs.7 per unit. cba is grained in los angeles abrasion test machine or 30 minutes. each time only 8 kg is taken for grinding. power used by los angeles abrasion test machine is 1hp i.e it used one unit of power per one hour. in control mix 438 kg of cement was used. in 10% gba replacement mix 394.2 kg of cement was used and 43.8 kg of gba. from table 10 it can be observed that for every one m3 of concrete we save rs.287.44. 10%gba concrete was economical than control mix. further emission of co2 depends on the type of procedure used to make cement, generally we take 1 ton of cement production emits 1 ton of co2. carbon dioxide emitted for electricity used in grinding is negligible, so co2 emitted is directly related to amount of cement used. from the study it was observed that for every one m3 of concrete 4.38 kg of co2 emission is reduced per metre cube of concrete when gba is used instead of cement. table 10. cost (in rs.) of mix per m3. control mix 10% gba mix cement used (kg) 438 394.2 cost of cement (rs) 3066 2759.4 gba used (kg) 43.8 cost for gba (rs) 19.16 total cost (rs) 3066 2778.56 4. conclusions 1. the results show that as the cement replacement with ba increases standard consistency increases. addition of gba increases the standard consistency more compared to oba. also initial and final setting time increases as the cement replacement with ba increases. it is observed that gba and oba show nearly same effect. 2. it was found that as the bottom ash content increases in the concrete workability decreases. for the same amount of bottom ash in gba workability decreases more compared to oba. khan and ganesh, j. build. mater. struct. (2016)3:31-42 41 3. it was observed that addition of ba reduces strength initially but later age strength was found to be more compared to control mix. addition of gba gives more strength compared to oba concrete at all the ages. addition of 10% gba shows more strength compared to control mix at 56 days and 90 days. 4. optimum dosage is observed to be 10% gba which shows about 14 % more strength compared to control mix at 56 days. also 20% replacement by gba gives results comparable to control concrete. it may be due to the fineness of gba as compared to oba. 5. the durability of concrete from the aspect of resistance to acid attack on concrete increases by replacing the cement with ba. it was observed that replacement of cement with gba gives more resistance to acid attack as compared to oba. 6. concrete containing ba was found to absorb more water compare to ordinary concrete. as the curing age progress water absorption capacity of concrete before and after replacement with ba decreases. 7. it was observed that at optimum dosage i.e at 10% replacement of cement with gba concrete is economical and co2 emission also decreased that means it is environment friendly compare to control mix. 5. references andrade, l. b., rocha, j. c., & cheriaf, m. (2007). aspects of moisture kinetics of coal bottom ash in concrete. cement and concrete research, 37(2), 231-241. andrade, l. b., rocha, j. c., & cheriaf, m. (2009). influence of coal bottom ash as fine aggregate on fresh properties of concrete. construction and building materials, 23(2), 609-614. bai, y., darcy, f., & basheer, p. a. m. (2005). strength and drying shrinkage properties of concrete containing furnace bottom ash as fine aggregate. construction and building materials, 19(9), 691697. bajare, d., bumanis, g., & upeniece, l. (2013). coal combustion bottom ash as microfiller with pozzolanic properties for traditional concrete. procedia engineering, 57, 149-158. cheriaf, m., rocha, j. c., & pera, j. (1999). pozzolanic properties of pulverized coal combustion bottom ash. cement and concrete research, 29(9), 1387-1391. is 10262 2009. concrete mix proprtioning guidelines, 9bhadur shah zafar marg, new delhi, 110002. is 1489-1,1991. specification for portland pozzolona cement, manak bhavan, 9bhadur shah zafar marg, new delhi, 110002. is 4031 part-4 1988. determination of consistency of standard cement paste, manak bhavan, 9bhadur shah zafarmarg, new delhi, 110002. is 4031,1988.methods of physical tests for hydraulic cement, manak bhavan, 9bhadur shah zafar marg, new delhi, 110002. isaia, g. c., gastaldini, a. l. g., & moraes, r. (2003). physical and pozzolanic action of mineral additions on the mechanical strength of high-performance concrete. cement and concrete composites, 25(1), 69-76. jaturapitakkul, c., & cheerarot, r. (2003). development of bottom ash as pozzolanic material. journal of materials in civil engineering, 15(1), 48-53. kim, h. k., & lee, h. k. (2011). use of power plant bottom ash as fine and coarse aggregates in highstrength concrete. construction and building materials, 25(2), 1115-1122. kim, h. k., jang, j. g., choi, y. c., & lee, h. k. (2014). improved chloride resistance of high-strength concrete amended with coal bottom ash for internal curing. construction and building materials, 71, 334343. 42 khan and ganesh, j. build. mater. struct. (2016)3:31-42 kolay, p. k., & singh, d. p. (2001). physical, chemical, mineralogical, and thermal properties of cenospheres from an ash lagoon. cement and concrete research, 31(4), 539-542. kurama, h., & kaya, m. (2008). usage of coal combustion bottom ash in concrete mixture. construction and building materials, 22(9), 1922-1928. kurama, h., topcu, i. b., & karakurt, c. (2009). properties of the autoclaved aerated concrete produced from coal bottom ash. journal of materials processing technology, 209(2), 767-773. nikbin, i. m., rahimi, s., allahyari, h., & damadi, m. (2016). a comprehensive analytical study on the mechanical properties of concrete containing waste bottom ash as natural aggregate replacement. construction and building materials, 121, 746-759. rafieizonooz, m., mirza, j., salim, m. r., hussin, m. w., & khankhaje, e. (2016). investigation of coal bottom ash and fly ash in concrete as replacement for sand and cement. construction and building materials, 116, 15-24. siddique, r. (2013). compressive strength, water absorption, sorptivity, abrasion resistance and permeability of self-compacting concrete containing coal bottom ash. construction and building materials, 47, 1444-1450. siddique, r., aggarwal, p., & aggarwal, y. (2012). influence of water/powder ratio on strength properties of self-compacting concrete containing coal fly ash and bottom ash. construction and building materials, 29, 73-81. singh, m., & siddique, r. (2014). strength properties and micro-structural properties of concrete containing coal bottom ash as partial replacement of fine aggregate. construction and building materials, 50, 246-256. j. build. mater. struct. (2016)3:55-67 https://doi.org/10.34118/jbms.v3i2.24 issn 2353-0057 durability of concrete using marble mining waste kore s.d. *, vyas a.k. department of civil engineering, malaviya national institute of technology, jaipur, rajasthan-302017, india. * corresponding author: suudarshankore123@gmail.com received : 30-09-2016 revised: 09-11-2016 accepted: 20-11-2016 abstract. the aim of the study was to study behavior of concrete containing marble mining waste under aggressive environment. waste from marble mining and processing industries was used in concrete as coarse aggregate in combination with conventional coarse aggregate. the particle packing density approach was followed to design the concrete mix and 75% conventional coarse aggregate was replaced by aggregate obtained by crushing waste from marble mining waste. the water-cement ratio was fixed 0.45 for all the mixes. properties of concrete under aggressive environment such as chloride ion penetration, resistance to sulphates were evaluated. the test results revealed that, resistance to chloride ion penetration and sulphate attack increased as compared to control concrete. overall the results supported by microstructure analysis indicate that there is no significant adverse effect on the use of marble waste as a coarse aggregate on the durability properties of concrete. the results of fire study reveal that, concrete with marble waste performs better than control concrete up to a temperature of 800 ºc. key words: marble mining waste, cement concrete, durability. 1. introduction the ornamental stone industries are the backbone to the economy of rajasthan state, india. approximately 95% of production of marble in india is from rajasthan state alone (msme, 2009; marble, 2013). in the state of rajasthan around 4000 marble mines and about 1100 processing units are operated. these mines and industries produce lot of waste in the form of pieces of irregular size of stones and powder/slurry. the waste generated during the mining operation is approximately 50% of the overall production (minor minerals, 2014; msme, 2009). according to jain et al. (2015) in india the solid waste generation per annum is around 48 million tons. the percentage of marble waste, as generated during mining has been estimated approximately 50% of total mass (msme, 2009). this waste produced is huge in quantity and a little part of it is used in small scale in manufacture of tiles and statues and rest is dumped on open land, roadsides forestland, pasture lands and agricultural fields leading to widespread environmental pollution and loss of fertile top soil. such wastes adversely affect vegetation in nearby area and create lot of environmental and health problems to the people in nearby area. this industrial waste has been used by many researchers in infrastructure development works for easy and effective disposal. hebhoub et al (2011) conducted studies on use of marble waste in the form of fine and coarse aggregate in concrete with water-cement ratio of 0.5. he reported that, workability decreased with increase in replacement level in the range of 0% to 100% for all the formulations. compressive strength of concrete mix increased by 16% to 25% at 75% replacement of conventional aggregate by marble aggregate. in a study conducted by andré et al (2014), marble waste was used in different percentages (20% to 100%) as replacement for conventional aggregates. it was reported that, workability and compressive strength of concrete mix marginally decreased as the replacement level increased. they also reported that, water absorption and depth of carbonation of concrete containing marble aggregate showed similar results to that of control concrete. whereas the water absorption by immersion and depth of carbonation, the performance of concrete mailto:suudarshankore123@gmail.com 56 kore and vyas, j. build. mater. struct. (2016)3:55-67 containing marble aggregate shows similar trend to that of control concrete. the results obtained by andré et al. (2014) are in the line of the results obtained by hebhoub et al. (2011). marble waste used as a 100 % replacement for natural coarse aggregates in concrete with a constant watercement ratio 0.4 in a study conducted by binici et al. (2008). fine aggregate used in their study was river sand and ground blast furnace slag. it was reported that, compressive strength, flexural strength, splitting tensile strength and young’s modulus of elasticity of concrete, prepared with ground blast furnace slag as fine aggregate and marble waste as coarse aggregate was 3% and 6%, respectively, higher than that of concrete with river sand as fine aggregate and marble waste as coarse aggregate. another study conducted by binici et al. (2007) reported, compressive strength of concrete mix containing marble dust and control concrete after immersion in 10% sodium sulphate solution was reduced by 15% and 58%, respectively. in a study by abdul mageed et al. (2014) marble waste was used as a complete replacement for conventional coarse aggregate. they reported that, the physical and mechanical properties of concrete improved. the workability of concrete mixes increased by 50% due to smooth flat surface and low water absorption of marble aggregate. it was also reported that, the compressive and flexural strength of concrete containing marble aggregate increased by 29.62% and 11.44% as compared to that of control mix. kore and vyas (2016-a) conducted studies on use of marble waste as a partial replacement for conventional coarse aggregates in different percentages (0% to 100%) in low strength concrete mixes designed as per bureau of indian standards (bis) guidelines. from this study it was observed that, the workability of all the concrete mixes increased with increase in replacement level. the compressive strength of the concrete mixes increased by 35% and 26%, respectively at 80% and 100% replacement level of conventional coarse aggregate. martins et al. (2014) reported that, coarse aggregate from marble waste can be used as a partial replacement for conventional coarse aggregate to improve the mechanical properties of concrete. they also reported that, the workability of all concrete mixes increased by 4.16%, 2.08%, 9.34% and density marginally decreased by 0.28%, 1.49% and 4.21% at 20%, 50% and 100% replacement level respectively. with regard to compressive and tensile strength, both marginally decreased by 5.2%, 2.3%, 6.2% and 10.4%, 6.1%, 1.0% respectively but this decrease was approximately 10% and found to be insignificant. it was also reported that, concrete mixes prepared using marble waste showed reduction in abrasion resistance by 9.3%, 18.1% and 26.8% at 20%, 50% and 100% replacement level. in the present study, concrete mixes were designed keeping a constant water cement ratio of 0.45 and maximum packing density of aggregates. durability properties of concrete supported by microstructure have been discussed. 2. experimental study 2.1. characterization of materials portland pozzolana cement used in this study fulfills the requirement of bis:1489 (1991). the marble waste used in this study was brought from the mining areas, then it was fed into crusher to obtain the desired gradation suitable for coarse aggregate. the fine aggregate, conventional coarse aggregate and aggregate produced from marble mining waste conform to grading zone ii as per bis 383 (1997). the nominal maximum size of conventional coarse aggregate and marble aggregate used was 20 mm. the particle size distributions of aggregates are shown in figure 1. the physical properties of fine and coarse aggregates used in this study are presented in table 1. the chemical compositions of coarse aggregates are presented in table 2. in order to achieve desired slump of 75 mm, a third generation poly-carboxylate based super-plasticizer rheobuild 522 nd confirming to bis:9103 (1999) was used. from table 1 it was observed that, water absorption of marble mining waste is less that of conventional aggregate. the values obtained in los angeles test are within the limits as per bis: 2386 (1963). kore and vyas, j. build. mater. struct. (2016)3:55-67 57 table 1. physical properties of aggregates. aggregate type specific gravity water absorption (%) by weight grading zone los angeles abrasion value (%) coarse conventional aggregate 2.78 0.54 as per table 2 of bis 383 25.88 fine aggregate 2.66 2.0 zone ii as per table 4 of bis 383 coarse aggregate from marble mining waste 2.88 0.05 as per table 2 of bis 383 34.87 table 2. chemical compositions as percentage of oxides in marble maste and natural aggregate. component marble mining waste (%) natural aggregate (%) sio2 3.75 53.70 cao 33.12 4.83 mgo 17.91 2.01 fe2o3 0.13 10.66 al2o3 traces sulphate content loi 45.07 5.08 fig 1. particle size distribution of aggregates. 2.2. concrete mix proportioning the concrete mix was designed by particle packing density approach (kore and vyas, 2016-b). coarse aggregate consist of 75% fraction from marble waste and 25% conventional aggregate as per best results obtained by the authors in trial mixes. all the concrete mixes were prepared with a 0 10 20 30 40 50 60 70 80 90 100 0.01 0.1 1 10 100 p e r c e n ta g e p a s s in g o f a g g r e g a te sieve size (mm) fine aggregate natural aggregate marble aggregate 58 kore and vyas, j. build. mater. struct. (2016)3:55-67 constant water-cement ratio of 0.45. mix proportion of concrete was based on achieving maximum packing density of all aggregate by trials conducted in the laboratory. it was found that, mixing of 60% coarse aggregate and 40% of fine aggregate resulted in maximum packing density of aggregate. the voids were estimated to be 23% in the dry aggregate mixture. then cement paste 10% in excess of voids was mixed to the aggregate in concrete mixer in order to get desired workability in the range of 75 mm to 100 mm. the mixture proportions are given in table 3. table 3. mix proportion. mix paste content in excess of voids (%) water (l) cement (kg) sand (kg) coarse aggregate (kg) natural aggregate aggregate from marble mining waste 20 mm 10 mm 20 mm 10 mm c1 10 157 348 800 720 481 c2 10 154 343 805 181 121 544 362 note: mix designated by c1 shows control mix and mix designated by c2 shows concrete mix containing 75% marble aggregate and 25% conventional coarse aggregate. both the concrete mixes were designed by packing density approach. 2.3. sample preparation and test methods cubes of size 100×100×100 mm were cast (bis:516, 1959) to determine chloride penetration, carbonation, resistance to sulphates and resistance to fire respectively. all the specimens were demoulded at the age of 24 ± 1 h and thereafter, were cured in water tank at room temperature up to 28 days. after 28 days specimens were taken out from the water, dried in oven at temperature of 60± 5 c for 24 ± 1 hr. the specimens removed from the oven are allowed to cool down to room temperature and these dried specimens were used for further test. 2.3.1. permeability in order to assess the porosity in concrete, water permeability test was conducted as per german standard din-1048 (1991). the concrete specimens were kept in oven to achieve the constant weight. the concrete specimens were taken out from the oven after 24 h ±1hr and cooled down to room temperature. the weight of the specimens was measured. these specimens were exposed to a constant water pressure of 0.5 n/mm2 acting normal to the mould-filling direction, for a period of 72 hr. the pressure is maintained for 72 hr. with periodic monitoring. after 72 hr. the specimens were taken out from the setup and split in to two pieces. the depth of penetration is measured. 2.3.2. chloride penetration test the chloride penetration test was conducted on 28 days cured (100×100×100 mm) concrete specimens. the silver nitrate spraying method was followed to study the depth of penetration (baroghel-bouny et al., 2007-a; 2007-b). the concrete cubes were soaked in 4% nacl solution and taken out from the solution after 28, 56 and 91 days of interval. these cubes were broken in to two pieces and the 0.1n silver nitrate solution was sprayed on the broken pieces. the sprayed silver nitrate reacts with the free chloride ions present on the concrete surface and form a white precipitate of silver chloride. in the places where the free chlorides are absent, agno3 reacts with hydroxide to form a brown precipitate of silver oxide (ago). thus, the boundary of color change indicates the depth of chloride penetration as shown in figures 2 (a) and 2 (b). kore and vyas, j. build. mater. struct. (2016)3:55-67 59 (a) mix c1 (b) mixc2 fig 2. images of chloride ion penetration of concrete. 2.3.3. resistance to sulphate attack the resistance to sulphate attack was evaluated as per astm c 267-01(2006). the concrete specimens were immersed in 10% dilute magnesium sulphate solution. the change in weight and compressive strength of concrete specimens was determined after 28, 56, 91, 180 and 300 days. 2.3.4. micro structural analysis the x-ray diffraction method was adopted for the identification of most probable phases of control concrete and concrete with marble waste. 2.3.5. fire exposure the impact of fire on the performance of concrete was investigated. the gas fired furnace was used for the experimentation. the test was carried out on the cube size specimens of 100×100×100 mm and the temperatures range is set to be 200ºc, 400ºc, 600ºc and 800ºc (li et al., 2004). when specimens inside the furnace reached the peak temperature, fire was stopped, immediately and these specimens were taken out from furnace and allowed to cool down at room temperature. the compressive strength test was conducted on the specimens after it reached to room temperature. 3. results and discussion 3.1. compressive strength the variations in the compressive strength of concrete mixes with different curing ages are shown in figure 3. the reduction in compressive strength of concrete mix c2 was in the range of 5% 10% as compared to that of control mix. but this reduction is considered as insignificant. however this is due to presence of inadequate fractions finer than 10 mm in marble aggregate. another possible reason is round shape of marble aggregate as compared to conventional coarse aggregate at similar water-cement ratio. both the factors are responsible for fall of compressive strength in c2 mix. 60 kore and vyas, j. build. mater. struct. (2016)3:55-67 fig 3. variation in compressive strength of concrete. 3.2. permeability the permeability of concrete depends on interconnectivity of pores in the concrete. the permeability of c2 mix reduced by 8% as compared to that of control mix c1. the aggregates which are flaky, elongated, angular, and unfavorably graded particles lead to higher voids content than, cubical, rounded, and, well graded particles (de larrard, 2009; quiroga and fowler, 2004). possible reason for reduction in permeability of concrete mix c2 was, better packing of aggregate due to cubical and round shape of marble aggregate. reduced permeability indicates increased durability of concrete mixes with marble waste. fig 4. variation in depth of water penetration. fig 5. variation in depth of chloride of concrete penetration 3.3. chloride penetration silver nitrate spray test was used to measure the depth of chloride ion penetration. the depth of penetration was obtained by measuring the average depth in three samples. the variations in the results of depth of chloride ion penetration are shown in figure 5. 24.04 22.95 32.93 31.14 39.00 37.67 46.04 41.61 0 5 10 15 20 25 30 35 40 45 50 c1 c2 c o m p r e s s iv e s tr e n g th i n n / m m 2 type of mix 7 days 28 days 90 days 180 days 93 86 82 84 86 88 90 92 94 c1 c2 d e p th o f p e n e tr a ti o n ( m m ) type of mix c1 c2 8.33 7.67 9 8.67 10.67 10 0 2 4 6 8 10 12 c1 c2 d e p th o f c h lo r id e p e n e tr a ti o n i n (m m ) type of mix 28 days 56 days 91 days kore and vyas, j. build. mater. struct. (2016)3:55-67 61 it can be seen from the figure 5 that, the depth of chloride ion penetration at 28 days of the concrete mix c2 was reduced by 8.6%, 3.8% and 6.7% in comparison to that of c1 mix at 28 days, 56 days and 91days, respectively. the significant reduction in the depth of chloride ion penetration was observed in the concrete mix c2. this reduction was due to presence of al2o3 in the marble aggregates as shown in table 2. the presence of alumina favors the formation of aluminate hydrates, which fixes the chloride ions and forms insoluble compounds (andré et al., 2014). the same fact was reported by binici et al. (2008) in their study. 3.4. resistance to sulphates the effect of magnesium sulphate on the compressive strength of concrete specimens was studied. the results of variation in compressive strength of concrete specimens after immersion in 10% dilute magnesium sulphate solution at different ages are shown in figure 6. fig 6. compressive strength of concrete after immersion in magnesium sulfate solution. note: *without sulfate attack it can be seen from figure 6 that, initially the compressive strength of concrete specimens increased up to immersion period of 91 days. thereafter decrease in the strength was observed as the immersion period extended to 300 days. initial increase in strength was due to filling of pores by ettringite. exposure of test specimens beyond 91 days shows reduction in compressive strength. this reduction in compressive strength was due to excessive formation of gypsum and ettringite which causes expansion and disruption of the concrete as shown in figure 9. during the test up to 91 days of immersion period no spalling or cracks on test specimens were observed except a few white patches of sulphate compounds. however after 91 days of immersion in solution, erosion and cracks on surface of the concrete were observed as seen in figure 7, figure 8 and figure 9. 32.93 36.7 37 37.07 31.63 21.33 31.14 35.47 36.33 37.57 33.06 22 0 5 10 15 20 25 30 35 40 28* 28 56 91 180 300 c o m p r e s s iv e s tr e n g th i n n / m m 2 curing age in days c1 c2 62 kore and vyas, j. build. mater. struct. (2016)3:55-67 (a) mix c1 (b) mix c2 fig 7. after 91 days of immersion in 10% magnesium sulphate solution. (a) mix c1 (b) mix c2 fig 8. after 180 days of immersion in 10% magnesium sulphate solution. (a) mix c1 (b) mix c2 fig 9. after 300 days of immersion in 10% magnesium sulphate solution. 3.5. xrd phase identification the powder sample of concrete mixes after 180 days of immersion in 10% magnesium solution was taken from the concrete specimens to know the most possible phases of the compounds formed during the entire immersion period. the x-ray diffraction pattern of concrete mix c1 and mix c2 are shown in figures 10(a) and 10(b). kore and vyas, j. build. mater. struct. (2016)3:55-67 63 10 20 30 40 50 60 70 80 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200           in te n si ty 2copper cu) quartz  portlandite  calcium silicate hydrate calciumalumimiun silictae hydrate brownmilleronite,syn     (a) mix c1 10 20 30 40 50 60 70 80 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500                       in te n s it y 2 copper cu quartz calcite dolomite ettringite magnesium silicate magnesium sulphate brownmilleronite calcium silicate hydrate       (b) mix c2 64 kore and vyas, j. build. mater. struct. (2016)3:55-67 fig 10. xrd of concrete after exposed to 10% mgso4 solution at 180 days. from the analysis it was observed that, the major compounds dolomite and ettringite are found in concrete containing marble aggregate i.e. mix c2. dolomite is a calcium magnesium carbonate with a chemical composition of camg (co3)2. formation of dolomite is due to presence of higher content cao and mgo in the marble aggregate as shown in table 2. the bond between aggregate and cement paste is improved due to presence of dolomite resulting in increase in compressive strength of concrete mix c2. this fact was also reported by heboub et al. (2011). 3.6. scanning electron microscope (sem) analysis the sem study was conducted on the concrete specimens immersed in magnesium sulphate solution over a period of 180 days as shown in figures 11(a) and 11(b). (a) mix c1 (b) mix c2 fig 11. sem micrographs of concrete mixes after 180 days of immersion in 10% magnesium sulphate solution. [e=ettringite, ch= calcium hydroxide, csh =calcium silicate hydrate, v= voids] the sem images of concrete mix c1 and c2 show the formation of ettringite, csh gel, ch crystals and voids present in the concrete. the needle shaped crystals of ettringite are seen in both the mixes. the voids seen in the concrete mix c2 are less as compared to that of control mix. the formation of these voids was due to weakening of cement matrix by entry of solution and formation of errtingite (neville, 2004). the formation of ettringite causes volume expansion within the voids resulting in spalling (mehta and monteiro, 2001) and finally cracks were formed on the surface of the concrete. because of this reason concrete losses it’s mass and strength. 3.7. compressive strength after exposure to fire the impact of fire on the compressive strength of concrete specimens is shown in figure 12. gradual decrease in compressive strength of all concrete mixes is clearly seen as the temperature increases. the compressive strength of concrete mix c1 decreased by 15%, 17%, 31% and 42% on the other hand in mix c2 it decreased by 11%, 17%, 25% and 44% at 200 ºc, 400 ºc, 600 ºc and 800 ºc respectively. the loss in compressive strength at 200 ºc is due to evaporation of free moisture which reduces the cohesive forces. further increase in temperature results in more loss in compressive strength due to breaking of some siliceous aggregate. beyond 573 ºc some chemical changes in the cement and phase transformation in aggregate takes place. at this temperature the decomposition of calcium hydroxide into calcium oxide starts (mendes et al., 2011) and chemically bound water from the c-s-h gel evaporates results in shrinkage of cement paste and formation of micro-cracks and cracks (hager, 2013). better performance of c2 mix at 600ºc is due to the fact that kore and vyas, j. build. mater. struct. (2016)3:55-67 65 marble remains stable up to 600ºc and it decomposed in cao and co2 beyond temperature of 700ºc. continuous heating of test specimens cause further fall in strength of c2 mixes around 800ºc as marble aggregate start deteriorating. the breaking of calcium carbonate into calcium oxide takes place after 660 ºc with the release of carbon di oxide. the reaction is endothermic, which absorbs heat and delay temperature rise in concrete. the calcined minerals are better insulator. the release of carbon di oxide from the surface of the concrete in considerable volume forms as inert insulation layer which retard the further rise of temperature (astm, 1956). this may be the reason for better performance of concrete containing marble aggregate (mix c2) exposure to fire. the cracks formed due to shrinkage of cement paste get widen with increase in temperature and weakens the cementaggregate bond resulting in failure of concrete showing higher loss in compressive strength. fig 12. compressive strength of concrete after exposure to fire. 3.8. cost analysis and benefits of using marble mining waste the cost analysis of the control concrete and concrete containing marble mining waste is shown in table 4. table 4. total material cost for production of 1 m3 of concrete in (inr). mix water cement sand natural aggregate marble aggregate total material cost (rs.) c1 1949/425/488/2862/ c2 1920/425/98/317/2760/ from the table 4, it can be seen that, the overall production cost of concrete mix c2 reduced by approximately 7%. on the other hand the cost of natural aggregate saved by 75% as compared to that of control mixes. in view of test results obtained it is clearly understood that, using aggregate from marble waste in place of conventional aggregate, the properties of concrete mixes are not adversely affected. the variation in properties lies in a narrow range of +5% to -5%. the benefit shall be in terms of cost saving of concrete product and more important would be utilization of waste in that locality. another saving would be saving in cost of disposal of waste. such unaccounted gains keep the environment clean. 32.93 28.07 27.47 22.83 19.13 31.14 27.53 25.87 23.30 17.33 0 5 10 15 20 25 30 35 ambient temp 200 400 600 800 c o m p r e s s iv e s tr e n g th n / m m 2 temperature ºc c1 c2 66 kore and vyas, j. build. mater. struct. (2016)3:55-67 4. conclusions in this paper concrete mixes containing marble mining waste as coarse aggregate were studied and it can be concluded that, a) the compressive strength of concrete mixes prepared using marble mining waste are nearly equal to that of control concrete. b) reduction in permeability by 8% of concrete produced using marble mining waste is the indication for better durability in the future. c) the reduction in the depth of chloride ion penetration by 8% at 28 days was observed in the concrete mix containing marble aggregate. d) the concrete containing marble aggregate shows marginally better performance as compared to that of control concrete when concrete is exposed to sulphates. e) after exposure to fire at different temperatures the loss in compressive strength of concrete mix c2 showed nearly same trend as that of control mix c1. overall the results of this study show that, marble waste can be used as aggregate in adverse environment without notable adverse effect in concrete mixes. 5. references abdul mageed, a., hassan, k., mohamed, a., & ahmed, s. (2014). an experimental study on the availability of solid waste of mines and quarries as coarse aggregate in concrete mixes, journal of engineering sciences, assiut university, 42 (3), 876–890. andré, a., de brito, j., rosa, a., & pedro, d. (2014). durability performance of concrete incorporating coarse aggregates from marble industry waste. journal of cleaner production, 65, 389-396. astm (1956). significance of tests and properties of concrete and concrete aggregates. astm special technical publication, n°169, philadelphia, pa. astm c267-01(2006), standard test methods for chemical resistance of mortars, grouts, and monolithic surfacings and polymer concretes, astm international, west conshohocken, pa, 2006, www.astm.org. baroghel-bouny, v., belin, p., maultzsch, m., & henry, d. (2007-a). agno3 spray tests: advantages, weaknesses, and various applications to quantify chloride ingress into concrete. part 1: non-steady-state diffusion tests and exposure to natural conditions. materials and structures, 40(8), 759-781. baroghel-bouny, v., belin, p., maultzsch, m., & henry, d. (2007-b). agno3 spray tests: advantages, weaknesses, and various applications to quantify chloride ingress into concrete. part 2: non-steady-state migration tests and chloride diffusion coefficients. materials and structures, 40(8), 783-799. binici, h., kaplan, h., & yilmaz, s. (2007). influence of marble and limestone dusts as additives on some mechanical properties of concrete. scientific research and essays, 2(9), 372-379. binici, h., shah, t., aksogan, o., & kaplan, h. (2008). durability of concrete made with granite and marble as recycle aggregates. journal of materials processing technology, 208(1), 299-308. bis:1489 (1991), specification for portland pozzolana cement(part-1), bureau of indian standards. new delhi, india. bis:2386 (1963). methods of test for aggregates for concrete (part-iv), bureau of indian standards. new delhi, india. bis:383 (1997). specification for coarse and fine aggregates from natural sources for concrete. bureau of indian standards. new delhi, india. bis:516 (1959). specification for methods of tests for strength of concrete, bureau of indian standards, new delhi, india. http://www.astm.org/ kore and vyas, j. build. mater. struct. (2016)3:55-67 67 bis:9103 (1999). specification for concrete admixture, bureau of indian standards. new delhi, india. de larrard, f. (2009). concrete optimisation with regard to packing density and rheology. in 3rd rilem international symposium on rheology of cement suspensions such as fresh concrete, p 8. din-1048 (1991). en-testing concrete, determination of depth of penetration of water under pressure in hardened concrete, berlin, germany. hager, i. (2013). behaviour of cement concrete at high temperature. bulletin of the polish academy of sciences: technical sciences, 61(1), 145-154. hebhoub, h., aoun, h., belachia, m., houari, h., & ghorbel, e. (2011). use of waste marble aggregates in concrete. construction and building materials, 25(3), 1167-1171. jain, n., garg, m., & minocha, a. k. (2015). green concrete from sustainable recycled coarse aggregates: mechanical and durability properties. journal of waste management, article id: 281043, p8. kore, s. d., & vyas, a. k. (2016-a). impact of marble waste as coarse aggregate on properties of lean cement concrete. case studies in construction materials, 4, 85-92. kore, sd., & vyas, ak. (2016-b). packing density approach for production of cost effective and durable concrete, in: proceedings of the international conference on advances in concrete technology materials and construction, pp. 71–77. li, m., qian, c., & sun, w. (2004). mechanical properties of high-strength concrete after fire. cement and concrete research, 34(6), 1001-1005. marble (2013). indian minerals yearbook, partiii : mineral reviews. 52nd edition final release, government of india ministry of mines, indian bureau of mines. martins, p., brito, j. d., rosa, a., & pedro, d. (2014). mechanical performance of concrete with incorporation of coarse waste from the marble industry. materials research, 17(5), 1093-1101. mehta, pk., & monteiro pjm. (2001). concrete, microstructure, properties and materials. second edition, p239. mendes, a., sanjayan, j. g., & collins, f. (2011). effects of slag and cooling method on the progressive deterioration of concrete after exposure to elevated temperatures as in a fire event. materials and structures, 44(3), 709-718. minor minerals (2014). department of mines & geology, udaipur office wise report, available at: www.dmgraj.org/docs/stat2014-15.xls. msme (2009). status report on commercial utilization of marble slurry in rajasthan. development institute, govt. of india, ministry of micro, small & medium enterprises, p36. neville, a. (2004). the confused world of sulfate attack on concrete. cement and concrete research, 34(8), 1275-1296. quiroga, p. n., & fowler, d. w. (2004). the effects of aggregates characteristics on the performance of portland cement concrete (no. icar 104-1f,). international center for aggregates research, university of texas at austin. http://www.dmg-raj.org/docs/stat2014-15.xls http://www.dmg-raj.org/docs/stat2014-15.xls j. build. mater. struct. (2016)3:15-30 https://doi.org/10.34118/jbms.v3i1.21 issn 2353-0057 effect of limestone powder as a partial replacement of crushed quarry sand on properties of self-compacting repair mortars benabed b 1,*, soualhi h 2, belaidi ase 1, azzouz l 1, kadri e 2 and kenai s 3 1 civil engineering laboratory, university of laghouat, 03000, algeria. 2 l2mgc laboratory, university of cergy-pontoise, 95000, france. 3 geomaterials laboratory, university of blida, 09000, algeria. * corresponding author: b.benchaa@mail.lagh-univ.dz , b_benchaa@yahoo.fr abstract. self-compacting repair mortars (scrm) are particularly desired for the rehabilitation and repair of reinforced concrete structures. the properties of scrm can be improved by using chemical, mineral, polymer and fiber additives. in limestone quarries, considerable quantities of limestone fine powder are obtained during the process of crushing rock. these fine powders are being collected and their utilization is a big problem from the aspects of disposal, environmental pollution and health hazards. the introduction of limestone powder as cement and sand replacement present interesting possibilities to reduce the cement cost production, co2 emission and the conservation of natural resources. the effects of limestone powder content in crushed sand on the properties of scrm are not studied. an experimental study was undertaken to find out the effect of limestone powder content on fresh and hardened properties of scrm. scrm mixtures were prepared using crushed sand partially replaced with limestone powder at varying percentages up to 30%. results indicate that the limestone powder as sand replacement significantly improves the fresh and hardened properties of scrm with a content ranging from 10 to 15%. the use of limestone powder in repair mortar and concrete application would offer technical, economical and environmental advantages for concrete producers. key words: crushed sand, limestone powder, self-compacting repair mortar, concrete repair. 1. introduction self-compacting repair mortars (scrm) are particularly desired for the rehabilitation and repair of reinforced concrete structures (courard et al, 2002; felekoğlu et al, 2006). the selfcompactability of repair mortar may provide considerable advantages such as reducing the repair construction time and labor cost, enhancing the filling capacity in highly congested structural members (khayat and morin, 2002; felekoğlu et al, 2007; o’flaherty and mangat, 1999). with the development of new generation high range water reducer admixtures, to obtain high filling rates is possible even for complex molding systems (o’flaherty and mangat, 1999). in structural repairs, the repair material should provide the targeted mechanical properties (poston et al, 2001). the physical, mechanical and durability properties of scrm can be improved by using chemical, mineral, polymer and fiber additives. for instance, producing of self-compacting mortars with the use of chemical additives, decreasing shrinkage and permeability and using mineral additives increased compressive strength (edamatsu et al, 1999; khayat and guizani, 1997; yurugi et al, 1995; khayat, 1998; zhu and gibbs, 2005; sonebi and bartos, 1999). as it is well known, there is a wide range of cementitious mortars based on cement and components similar to those of concrete. the composition of mortar could sometimes consist of more than one type of cement (i.e. special cement; like ultra-fine alumina cement) together with additions (i.e. silica fume, slag or fly ash), aggregates (normal, lightweight and special types, fillers), admixtures such as superplasticizers. the use of industrial by-products such as silica fume offers a low-priced solution to the environmental problem of disposing these industrial wastes. the viscosity of cement-based material can be enhanced by decreasing the water/cementitious material ratio or using viscosity-modifying agent. it can also be improved by mailto:b.benchaa@mail.lagh-univ.dz mailto:gueddouda_mk@yahoo.fr 16 benabed et al. j. build. mater. struct. (2016)3:15-30 increasing the cohesiveness of the paste through the addition of fillers such as limestone (khayat, 1999). however, excessive addition of fine particles can result in a considerable increase in the specific area of the powder, which in turn can result in an increase of water demand to achieve the required consistency. on the other hand, for fixed water content, high powder volume increases interparticles friction due to solid-solid contact. this may affect the ability of the mixture to deform under its own weight and pass through obstacles (nawa et al, 1998). for improving strength and durability properties, limestone powders produce a more compact structure by pore-filling effect. in the case of silica fume and fly ash, it also reacts with cement by binding ca(oh)2 with free silica by a pozzolanic reaction forming a non-soluble csh structure (o’flaherty and mangat, 1999). the influence of finely ground limestone and crushed aggregates dust on the properties of selfcompacting concrete (scc) mixes in the fresh and hardened state was comprehensively studied by bosiljkov (2003). the utilization of sands rich in fines like limestone quarry dust may be a second alternative source of fillers. these sands may also enhance the cost effectiveness of scc, by reducing the demand for external filler addition. the use of quarry dust in scc is expected to offer significant economic benefits to quarries and concrete producers (naik et al, 2005). in crushed fine aggregate production process and depending on the quality of aggregate and crushing process, a high fraction of fine aggregate may sometimes be very fine (guimaraes et al, 2007). this portion can be as high as 10% to 15% by weight of total aggregate production. this very fine material may contribute as viscosity improver in scc production (johansen et al, 1999; johansen et al, 2001). however, the quality of sands rich in fines should be carefully investigated before the use in concrete application. in case of normal concrete, the proportion of fines in sands is usually rather limited. fine fraction of sand may affect the properties of scc in an either positive or negative way (topçu and uğurlu, 2003). high content of dust in aggregate increases the fineness and the total surface area of aggregate particles, where surface area is measured in terms of specific surface, i.e. the ratio of total surface area of all particles to their volume. aggregates with higher specific surface area require more water in the mixture to wet the particles surface adequately and to maintain a specific workability (johansen et al, 1999; johansen et al, 2001; topçu and uğurlu, 2003; nehdi et al, 1996). obviously, increasing water content in the mixture will affect the quality of concrete. the effect of inclusion of limestone fines in crushed sand on fresh and hardened mortar and concrete has been a major research topic for many years. it was found that up to 15% of limestone fines do not affect strength performance of limestone concrete manufacture (bonavetti and irassar, 1994; chi et al, 2004). it has been established that 12–18% of fines could be allowed in sand without harmful effects on the physical and mechanical properties of mortar and concrete (bonavetti and irassar, 1994; chi et al, 2004; benabed et al, 2012; bouziani, 2013; bouziani et al, 2014; benabed et al, 2014). the durability of a concrete repair can depend on many factors. those most often considered are cement reactivity with environment, low permeability, diffusion coefficient of species such as sulfate ions and compressive strength. the water absorption is also very important factor affecting durability such as freezing and thawing. the use of mineral additives may provide a way of improving the durability of scrm depending on the type and amount of mineral additive used. in addition, in the absence of self-compactability the success of mortars depends on the compaction degree supplied at application site. ferraris et al. (2001) studied on the effect of addition of fine grounded materials with a comprehensive literature survey. they have concluded that the selection of a fine mineral admixture for improved concrete workability is not a trivial problem. at present, this selection cannot be predicted from the physical or chemical characteristics of the powders and can only be determined using the properly designed tests. no detailed investigation has been done to study the effect of crushed limestone powder on properties of self-compacting mortars or scc. in this research work, some part of sand is replaced with crushed limestone powder at quantities up to 30%, keeping all the other ingredients and proportions constant. the effect of varying the limestone powder content on the benabed et al. j. build. mater. struct. (2016)3:15-30 17 rheological properties of fresh scrm was investigated using slump flow, flow time and viscosity measurements. the corresponding effect on mechanical properties of hardened scrm was studied in terms of the compressive strength and flexural strength at ages of 3, 7 and 28 days. the water absorption capacity of scrm was also assessed at age of 28 days. 2. materials and methods 2.1. materials all mixtures were prepared using a portland cement cem i type with a strength class of 42.5. the chemical and physical properties of cement and limestone powder are given in table 1. table 1. chemical and physical properties of cement and limestone powder. chemical analysis (%) cement limestone powder sio2 21.7 1.0 cao 65.7 52.6 mgo 0.7 2.1 al2o3 5.2 0.2 fe2o3 2.7 0.2 so3 0.6 0.07 mno k2o 0.4 0.04 tio2 0.01 na2o 0.7 0.06 ci 0.01 loss of ignition 0.3 43.63 physical properties specific density 3.15 2.7 fineness (m²/kg) 300 350 compressive strength at 28 days (mpa) 44 the mineralogical composition of limestone powder was determined by x-ray diffraction and is presented in figure 1 indicating that calcite mineral is the main component of limestone powder. fig 1. x-ray diffraction of limestone powder. 18 benabed et al. j. build. mater. struct. (2016)3:15-30 in order to determine the surface characteristics of the limestone powder, scanning electron microscopy (sem) was performed and typical secondary electron image is presented in figure 2. as seen on this figure, limestone powder presents angular shapes with rough surface texture. crushed limestone sand (cs) was used in this investigation. the physical properties and sieve analysis results of cs are given in table 2. moreover, sem image of this sand is given in figure 3. sem investigation reveals the angular shape of the crushed sand grains. fig 2. sem of limestone powder. fig 3. angular shape of crushed sand grains in sem view. table 2. sieve analysis and physical properties of cs. sieve size (mm) cumulative passing (%) 2 100 1.25 87.15 1 80.43 0.8 72.79 0.5 56.22 0.2 36.10 0.16 26.5 0.125 20.58 0.063 5.93 0.05 4.5 physical properties specific density 2.68 unit weight (kg/m3) 1541 fineness modulus 2.21 sand equivalent (%) 71 absorption (%) 5 benabed et al. j. build. mater. struct. (2016)3:15-30 19 a polycarboxylates type of third generation high range water reducing superplasticizer (sp) was used to achieve the desired fresh properties of scrm. the solid content, ph and specific gravity of sp are respectively, 30%, 6 and 1.07. 2.2. mixture proportions and mixing procedure the mixture proportions were based on okamura’s method, with improvements made on the methods of selecting the fine aggregates content. the sand to mortar (s/m), the water to cement (w/c) and the superplasticizer to cement (sp/c) ratios were selected by a simple evaluation test for assessing the stress transferability of fresh scrm as recommended by edamatsu et al. (2003). the self-compactability of mixtures was obtained by increasing the sp dosage. sp requirement of all mixtures to reach the slump flow value of 280±20 mm were determined as suggested by domone et al. (1999). scrm were prepared with crushed limestone sand which was partially replaced by limestone powder at varying percentages of 0, 5, 10, 15, 20, 25 and 30%. for all mixtures, s/m and w/c ratios were kept constant. the mixture proportions are given in table 3. in the production of scrm, the mixing process was kept constant to supply the same homogeneity and uniformity in all mixtures. the consisted of mixing the fine aggregates with cement for half a minute before adding 70% of necessary water during 1 min, then adding the remaining 30% of water containing sp during another 1 min. the mixing procedure continues for 5 min, after that the whole mix was kept settling for 2 min before remixing for just half a minute. table 3. mix proportions of scrm made with various limestone powder contents. w/c s/m cement (kg/m3) crushed sand (kg/m3) limestone powder (%) limestone powder (kg/m3) water (kg/m3) sp (%) 0.4 0.5 697 1340 0 0 279 0.6 1273 5 67 1205 10 135 1139 15 201 1072 20 268 1005 25 335 938 30 402 2.3. test methods 2.3.1. fresh scrm tests tests carried out on fresh scrm involved mini slump flow and v-funnel flow time. the apparatus for the mini-slump flow test of self-compacting mortar consisted of a mould in the form of frustum of cone, 60 mm high with a diameter of 70 mm at the top and 100 mm at the base as shown in figure 4. the cone was placed at the centre of a steel base plate, and was filled with scrm with no compaction but finished with a trowel. immediately after filling, the cone was lifted, the scrm spreads over the table and the average diameter in mm of the spread measured. the scrm spread was visually checked for any segregation or bleeding. the v-funnel test was used to select a suitable water to powder ratio in the mix design (okamura et al., 1993). the v-funnel as shown in figure 4 was filled with 1.1 litres of scrm, the gate was then opened and stopwatch simultaneously started. the watch was stopped when light first appeared, looking down into the v-funnel from above. the flow time (in sec) was then recorded. 2.3.2. viscosity measurements viscosity measurements were performed on scrm using a brookfield dv-ii model viscometer as shown in figure 5. it is a rotational viscometer with a smooth-walled concentric cylinder so that 20 benabed et al. j. build. mater. struct. (2016)3:15-30 at low stress values, wall slip (nearly yield stress) occurs resulting in inaccurately low yield stress measurements. slip appeared to be more influential at low strain rates, thus resulting unusual low viscosity. fig 4. typical dimensions of mini-spread flow cone and mini-v-funnel apparatus (felekoğlu et al., 2006). however, a decrease in the influence of slip was observed at higher rotational speeds. therefore, the viscosity measurements were conducted at different rotational speeds and time dependent viscosity measurements were performed (felekoğlu et al., 2006). fig 5. viscometer used. the measurements based on the viscosity were realized at the nine rotational speeds (0.5, 1, 2, 4, 5, 10, 20, 50 and 100) at 0 minutes after mixing. for this, the fresh mortar was prepared and placed into the pot of the viscometer. pre-mixing was performed by increasing the rotational speed from zero to 60 rpm within 120 sec. the viscometer was terminated when the highest rotational speed was achieved. after that, a full cycle of increasing rotational speed by 9 steps benabed et al. j. build. mater. struct. (2016)3:15-30 21 from 0.5 to 100 rpm and back to rest with another 9 steps was performed. the average of viscosity readings determined at upwards and downwards of each rotational speed steps were recorded (felekoğlu et al., 2006). 2.3.3. compressive and flexural strength the tests of compressive and flexural strengths of hardened scrm were determined at 3, 7 and 28 days. after the completion of initial fresh scrm tests, mixtures were poured into steel moulds without any vibration and compaction. specimens were demoulded 24 hours after casting. after demoulding, specimens were cured in lime water at a temperature of 20 °c until age of testing. the flexural strength was conducted on 40x40x160 mm specimens by three-point bending test and the compressive strength was performed on the resulting halves from the flexural strength test. 2.3.4. water absorption to find out the absorption of scrm, specimens of 40x40x160 mm were dried at a temperature of approximately 105°c for 72 hours, and this dry weight was designated as m0. after final drying, cooling and weighing, the specimens were immersed in water at approximately 20°c for 24 hours. then the specimens were taken out and their surfaces were dried by removing surface moisture with a towel, and weighed. this final saturated-surface dry weight was designated as weight m1. the absorption of scrm was calculated as following: absorption (%) = (m1 – m0)/m0 (1) 3. results and discussions 3.1. fresh properties of scrm results of slump flow test are given in figure 6. from this figure, it is evident that, as the percentage of limestone powder in scrm increases, the slump flow increases for limestone powder content of up to 10% and then decreases for higher powder contents. this could be explained by the increase in the fineness and specific surface area of the crushed sand due to the increase in fines content and hence more water is required to wet the surface of particles and consequently flowability decreases. fig 6. slump flow test of scrm made with various limestone powder contents. v-funnel flow times of fresh scrm test results are given in figure 7. it can be seen from this figure that while the limestone powder content of fresh scrm increases, the flow time of fresh scrm increases. it is observed that when limestone powder content is 10 %, the scrm achieved a better flowability. however, for limestone powder content more than 10%, a loss of flowability 22 benabed et al. j. build. mater. struct. (2016)3:15-30 was obtained. this matches with the slump flow results in figure 6. limestone powder is usually used for improving the workability and reducing the bleeding of mortar (erdoğan, 1997). it should also be noted that limestone powder provides cohesiveness and plasticity of a mortar. fig 7. v-funnel flow time test of scrm made with various limestone powder contents. the highest v-funnel flow time was obtained for limestone powder content of 30%. the reason for this behaviour can be attributed to the fineness of limestone powders, since they were greater than cement particles (felekoğlu et al., 2004). this suggests that the physical effect of the limestone powder on the properties of the fresh mortar depends on the water/cementitious material ratio and the addition percentages of limestone powders. generally, the obtained results that the replacement of crushed sand by limestone powder strongly influences the flow resistance; it may increase or decrease the fresh properties of scrm. 3.2. viscosity variation in the viscosity of scrm according to the rotational speed and limestone powder content is given in figure 8. as seen in this figure, the scrm with limestone powder content had consistently higher viscosity values than those without dust. the highest viscosity values were derived from 30% of limestone powder content. it was also observed that the high rotational speed reduced the viscosity of all mixtures whatever the powder content. fig 8. viscosity of scrm with various limestone powder contents at different rotational speeds. benabed et al. j. build. mater. struct. (2016)3:15-30 23 this result was in good agreement with the findings of other studies reported in the literature in that replacing portland cement with limestone filler at different replacement levels gave a marked increase in the viscosity of scrm when compared of the control mixture (felekoğlu et al., 2006). tang et al (2000) mentioned about the effect of fly ash on viscosity increase and proposed that the fly ash can increase the energy demand in order to reach sufficient workability. the behaviour of all scrm can be classified as pseudo-plastic. in other words, the viscous behaviour is evident for low rotational speeds, while at higher speeds, the flowable behaviour becomes dominant. an example of the curve obtained of viscosity change of scrm at different rotational speeds is illustrated in figure 9. fig 9. the fitted equation curve of viscosity of scrm at different rotational speeds. the results of viscosity measurement show that the behaviour of all mixtures is similar and can be best fitted with the power low model: µ = aγb (2) µ = the viscosity in centipoise (cp); γ = the rotational speed in revolutions per minute (rpm); a and b = constants of the best fit equations. the equation constants and regression coefficients of the best fit equations are presented in table 4. table 4. the equation constants and regression coefficients of the best fit curves. limestone powder content (%) 0 5 10 15 20 25 30 equation constants a 1245 1680 778.5 117.5 227.7 185.7 404.4 b -0.9 -1.02 -1.00 -0.52 -0.57 -0.49 -0.59 r2 0.95 0.99 0.99 0.94 0.94 0.93 0.95 from this table, the regression coefficients (r2) were superior than 0.90 for all scrm indicating a good exponential correlation. felekoglu et al (2006) proposed a similar equation representing the variation of viscosity at different rotational speeds of scrm containing fly ash and limestone fillers. in order to understand the possible mechanism of different mineral and inert admixtures on time-dependent viscosity, it is also important to characterize the micro-shape, surface texture, angularity and particle size distribution of powders. for this purpose, sem images of limestone powders were investigated and presented in figure 2. 24 benabed et al. j. build. mater. struct. (2016)3:15-30 the limestone powders have a more angular and coarse structure, which can significantly change the viscosity of scrm. another factor affecting the fluidity of mixes is the zeta potentials of powders. limestone powders have positive zeta potentials. it can be concluded that particle size distribution, micro-shape, surface structure and zeta potential changes are better parameters for rheological characterization of cement–powder–superplasticizer dispersion systems (felekoğlu et al., 2006). 3.3. correlation between fresh properties and viscosity a plot was made between the v-funnel flow time and slump flow and viscosity measurements at 10 rpm rotational speed in figures 10 and 11. the relationships between the flow time and viscosity correlate in certain case and have a linear tendency for both v-funnel time and slump flow and viscosity. however, the coefficient of correlation seems not very higher. the values of correlation coefficients for v-funnel flow time (r2 = 0.75) and for slump flow (r2 = 0.70). similar results were also reported by other researchers (felekoğlu et al., 2006; güneyisi et al., 2009). fig 10. relationship between v-funnel flow time and viscosity of scrm. fig 11. relationship between slump flow and viscosity of scrm. figures 10 and 11 show respectively that by increasing the viscosity, v-funnel time increases and slump flow decreases. as it is known, v-funnel and slump flow tests measure the flowability of self-compacting mortar and concretes. in fresh state, when the yield stress is exceeded, flow benabed et al. j. build. mater. struct. (2016)3:15-30 25 start and the shear stress will increase linearly with an increase in strain rate, as defined by viscosity as a measure of the ease of flow (felekoğlu et al., 2006). 3.4. compressive and flexural strength the results of compressive strength at 3, 7 and 28 days are shown in figure 12. it can be seen that the compressive strength at 3, 7 and 28 days increases to a maximum at limestone powder content of 10%. for limestone powder content higher than 10%, the compressive strength decreases. this is probably due to insufficient cement paste to coat all the crushed sand particles, which consequently leads to a decrease in compressive strength. for specimens without or with only 5% limestone powder, there are not enough fine particles to fill all voids between cement paste and crushed sand particles and hence, lower compressive strength values as compared to specimens with 10 % of limestone powder content. fig 12. compressive strength at 3, 7 and 28 days of scrm made with various limestone powder contents. figure 13 shows also the relation of limestone powder content and flexural strength, which represents the average of three tests for 3, 7 and 28 days. it can be seen that the flexural strength increases to a maximum at limestone powder content of 10%. as the limestone powder content exceeds the value of 10%, the flexural strength decreases. fig 13. flexural strength at 3, 7 and 28 days of scrm made with various limestone powder contents. similar arguments as mentioned above for compressive strength can be applied also for flexural strength (benabed et al., 2012). 26 benabed et al. j. build. mater. struct. (2016)3:15-30 mortar is, of course, a mixture of the paste and aggregate, and it is the interface between these that is of interest. for the flexural strength could be supposed that it is more sensitivity of the transition zone between aggregate and matrix. especially, as the bending load on the mortar increases, cracking will start in this zone, and subsequently propagate in to the hardened cement paste until crack paths are formed through the mortar. the increase in strength in systems of mortars containing pozzolanic materials play an important role in improving the aggregatepaste bond through the densification of the transition zone and formation of more calcium silicate hydrates (shannag, 2000). in this study, the use of limestone powder in scrm that they have worsening effect on the interfaced due to the lower pozzolanic activity. thus they have reducing effect of the mortar strength. in literature, limestone powder was described neither cementitious nor pozzolanic materials. therefore, it is accepted that limestone powder contributes little to the strength of mortar (erdoğan, 1997). as expected, the lowest flexural and compressive strength at 28 days was obtained for 30% of crushed sand by weight was replaced by limestone powder. this result shows that limestone powder appropriate to improve deformability, but it is not completely effective on mechanical properties. however, includes substitutions of crushed sand with limestone powder (10 %) to positive effect on the mechanical strength. the increase in strength can be explained with pore-filling effect of limestone powder and also provided suitable nucleus for hydration and by this way catalyzing the hydration (gürol, 1999). additionally, limestone powders reacted with c3a phase of cement and supplied the formation of monocarboaluminate that partially takes part of ettringite; thus, increase at early strength values (türker et al., 2004). however, it seems that no additional hydration reactions take place to enhance the long-term strength of pastes incorporating limestone fillers. fig 14. correlation between flexural and compressive strength of scrm made with various limestone powder contents at all ages. figure 14 plots the relationship between flexural and compressive strength of scrm made with various limestone powder fines content at all ages, which gives a good linear correlation with a coefficient of correlation (r2 = 0.95). figure 15 shows the results of sem observation at 28 days of hardened scrm containing 15% of limestone powder. the sem image shows the good adhesion between the paste cement and the sand grains, which may lead to increase the mechanical strength. the existence of limestone powder in the cementitious matrix enhances the hydration reaction, as a result, the obtaining of dense structure. benabed et al. j. build. mater. struct. (2016)3:15-30 27 fig 15. sem view of hardened scrm containing 15% of limestone powder at age of 28 days. 3.5. water absorption the results of water absorption of scrm made with various limestone powder contents at age of 28 days are shown in figure 16. according to figure 16, the absorption percentage of scrm decreased for limestone powder contents from 0 to 15%, and then it started to increase for 20, 25, and 30% of limestone powder contents. limestone powder acts as filler in the scrm and contributes to reduce the absorption of concrete. however, increasing the limestone powder content more than 15% causes an increase in absorption, which is a parallel leading with compressive strength. fig 16. water absorption percentages of scrm made of various limestone powder contents at age of 28 days. this situation may bring out the opinion that limestone powder could not form to block capillary pores sufficiently (by the supplementary csh structure and filler effect) at 28 days. filling the voids in a packed system may improve the arrangement of particles in the system, ensuring a better contribution of the interfaced to achieve adequate prevent on the scrm absorption (yahia et al., 2005). figure 17 plots the relationship between water absorption and compressive strength of scrm made with various limestone powder fines content at age of 28 days, which gives a good linear correlation with a coefficient of correlation (r2 = 0.94). this relation suggests that with the decrease in water absorption of scrm, the scrm is expected to have a high compressive strength. 28 benabed et al. j. build. mater. struct. (2016)3:15-30 fig 17. correlation between water absorption and compressive strength of scrm made with various limestone powder contents at age of 28 days. 4. conclusions the influence of limestone powder up to 30% as crushed sand replacement of scrm fresh and hardened properties was investigated. based on the results of this investigation, the following conclusions can be drawn: 1. the slump flow time of scrm decreased whereas v-funnel flow time increased with the increase in limestone powder content beyond of 10%. 2. the viscosity of scrm increased with the increase in limestone powder content. the viscous behaviour of scrm is evident for low rotational speeds, while at higher speeds, the flowable behaviour becomes dominant. 3. increasing the limestone powder content up to 10 % improved the compressive strength of scrm. for higher limestone powder content, the compressive strength decreased gradually. a similar result was obtained for the flexural strength. 4. a good correlation exists between flexural strength and compressive strength at different curing times. 5. the minimum value for water absorption was obtained when the limestone powder content is 15%. limestone powder contents higher than 15% increased the water absorption of scrm. 6. a linear correlation exists between compressive strength and water absorption with a high coefficient of correlation. 7. crushed sand with 10 to 15% of powder can be used successfully in production of scrm with good rheological and strength properties. 8. the use of crushed quarry sand and limestone powder in self-compacting concrete and scrm application would offer technical, economical and environmental advantages for concrete producers. 5. recommendations for future work in the framework of this study, only one water/cement (w/c) ratio was adopted. however, a possibility of change in the properties of scrm by varying w/c ratio may be expected since the addition of superplasticizer (sp) is varied by w/c ratio. therefore, more experiments with other w/c ratios or other types of powders and sp may be useful as a further study. benabed et al. j. build. mater. struct. (2016)3:15-30 29 6. references benabed, b., azzouz, l., kadri, e. h., kenai, s., & belaidi, a. s. e. (2014). effect of fine aggregate replacement with desert dune sand on fresh properties and strength of self-compacting mortars. journal of adhesion science and technology, 28(21), 2182-2195. benabed, b., kadri, e. h., azzouz, l., & kenai, s. (2012). properties of self-compacting mortar made with various types of sand. cement and concrete composites, 34(10), 1167-1173. bonavetti, v. l., & irassar, e. f. (1994). the effect of stone dust content in sand. cement and concrete research, 24(3), 580-590. bosiljkov, v. b. (2003). scc mixes with poorly graded aggregate and high volume of limestone filler. cement and concrete research, 33(9), 1279-1286. bouziani, t. (2013). assessment of fresh properties and compressive strength of self-compacting concrete made with different sand types by mixture design modelling approach. construction and building materials, 49, 308-314. bouziani, t., bédérina, m., makhloufi, z., & hadjoudja, m. (2014). mixture design approach to evaluate fresh properties of scc made with various sands. journal of building materials and structures, 1(1), 1-9. chi, c., wu, y., & riefler, c. (2004). the use of crushed dust production of self-consolidating concrete (scc), recycling concrete and other materials for sustainable developement, editors tony c. liu christian meyer. aci international sp-219. courard, l., darimont, a., degeimbre, r., willem, x., geers, c., & wiertz, j. (2002). repairing concretes with self-compacting concrete: testing methodology assessment. in: proceedings of first north american conference on the design and the use of self-consolidating concrete (scc), chicago, u.s.a, pp: 267-274. domone, p. l., & jin, j. (1999). properties of mortar for self-compacting concrete. in proceedings of the 1st international rilem symposium on self-compacting concrete, pp: 109-120. edamatsu, y., nishida, n., & ouchi, m. (1999). a rational mix-design method for self-compacting concrete considering interaction between coarse aggregate and mortar particles. in proceedings of the first international rilem symposium on self-compacting concrete, stockholm. sweden, pp: 309-320. edamatsu, y., sugamata, t., & ouchi, m. (2003). a mix-design method for scc based on mortar flow and funnel tests. in: proceedings of 3rd international rilem symposium on scc, reykjavik, iceland, pp: 345-355. erdoğan, t. y. (1997). admixtures for concrete. first edition, middle east technical university press. felekoğlu b., türkel s., & baradan, b. (2004). the effect of powder type on the fresh and mechanical properties of self-compacting concrete, turkish ready mixed concrete association, march–april, pp. 67–77, (in turkish). felekoğlu, b., tosun, k., baradan, b., altun, a., & uyulgan, b. (2006). the effect of fly ash and limestone fillers on the viscosity and compressive strength of self-compacting repair mortars. cement and concrete research, 36(9), 1719-1726. felekoğlu, b., türkel, s., & altuntaş, y. (2007). effects of steel fiber reinforcement on surface wear resistance of self-compacting repair mortars. cement and concrete composites, 29(5), 391-396. ferraris, c. f., obla, k. h., & hill, r. (2001). the influence of mineral admixtures on the rheology of cement paste and concrete. cement and concrete research, 31(2), 245-255. guimaraes, m. s., valdes, j. r., palomino, a. m., & santamarina, j. c. (2007). aggregate production: fines generation during rock crushing. international journal of mineral processing, 81(4), 237-247. güneyisi, e., gesoğlu, m., & özbay, e. (2009). effects of marble powder and slag on the properties of selfcompacting mortars. materials and structures, 42(6), 813-826. gürol, g. (1999). components for economic concrete, cement/water/fine and coarse aggregate/chemical and mineral admixtures. j. des. constr, 164, 66-74. 30 benabed et al. j. build. mater. struct. (2016)3:15-30 johansen, k. i., mortsell, e., & lindgard, j. (1999). effect of adding natural fine sand rich in fines on the fresh concrete properties. nordic concrete research-publications, 22, 65-76. johansen, k., & busterud, l. (2001). low grade scc with secondary natural sand rich in fines. in second international rilem symposium on scc, tokyo, pp: 303-308. khayat, k. h. (1998). use of viscosity-modifying admixture to reduce top-bar effect of anchored bars cast with fluid concrete. materials journal, 95(2), 158-167. khayat, k. h. (1999). workability, testing, and performance of self-consolidating concrete. aci materials journal, 96, 346-353. khayat, k. h., & guizani, z. (1997). use of viscosity-modifying admixture to enhance stability of fluid concrete. aci materials journal, 94(4), 332-340. khayat, k. h., & morin, r. (2002). performance of self-consolidating concrete used to repair parapet wall in montreal. in: proceedings of first north american conference on the design and the use of selfconsolidating concrete (scc), chicago, u.s.a, pp: 475-481. naik, t. r., kraus, r. n., chun, y. m., canpolat, f., & ramme, b. w. (2005). use of limestone quarry byproducts for developing economical self-compacting concrete,” published at the canmet. in aci international symposium on sustainable developments of cement and concrete, toronto, canada, pp: 313-336. nawa, t., izumi, t., & edamatsu, y. (1998). state-of-the-art report on materials and design of selfcompacting concrete. in international workshop on self-compacting concrete, pp: 160-190. nehdi, m., mindess, s., & aïtcin, p. c. (1996). optimization of high strength limestone filler cement mortars. cement and concrete research, 26(6), 883-893. o’flaherty, f. j., & mangat, p. s. (1999). influence of constituents on the properties of self-compacting repair materials. in proceedings of the first international rilem symposium, pp: 263-274. okamura, h., maekawa, k., & ozawa, k. (1993). high performance concrete. gihoudou pub, tokyo. poston, r. w., kesner, k., mcdonald, j. e., vaysburd, a. m., & emmons, p. h. (2001). concrete repair material performance—laboratory study. materials journal, 98(2), 137-147. shannag, m. j. (2000). high strength concrete containing natural pozzolan and silica fume. cement and concrete composites, 22(6), 399-406. sonebi, m., & bartos, p. j. m. (1999). hardened scc and its bond with reinforcement. in self-compacting concrete: proceedings of the first international rilem symposium held in stockholm, sweden, pp: 275-289. tang, c. w., yen, t., & chen, k. h. (2000). the rheological behavior of medium strength high performance concrete. in second international symposium on cement and conc. tech., 2, 50-57. topçu, i. b., & uğurlu, a. (2003). effect of the use of mineral filler on the properties of concrete. cement and concrete research, 33(7), 1071-1075. türker, p., yeşilkaya, a., & yeğinobalı, a. (2004). the hydration process and microstructural development of limestone portland cements. cem. concr. world, 48(8), 50-66. yahia, a., tanimura, m., & shimoyama, y. (2005). rheological properties of highly flowable mortar containing limestone filler-effect of powder content and w/c ratio. cement and concrete research, 35(3), 532-539. yurugi, m., sakai, g., & sakata, n. (1995). viscosity agent and mineral admixtures for highly fluidized concrete. proceedings, concrete under severe conditions, environment and loadings, 2, 995-1004. zhu, w., & gibbs, j. c. (2005). use of different limestone and chalk powders in self-compacting concrete. cement and concrete research, 35(8), 1457-1462. j. build. mater. struct. (2023) 10: 16-26 original article doi : 10.34118/jbms.v10i1.2614 issn 2353-0057, eissn : 2600-6936 ceramic bricks using pistachio shells as controlled porosity former nancy quaranta 1,*, marta caligaris 1, miguel unsen 1, hugo lópez 1, gisela pelozo 1,2, adrián cristóbal 3 1 environmental studies group, national technological university. colón 332 (2900) san nicolás, argentina. 2 industrial engineering department, frsn, utn. colón 332 (2900) san nicolás, argentina. 3 intema, conicet, national university of mar del plata. j.b. justo 4302 (7600) mar del plata, argentina. * corresponding author: nquaranta@frsn.utn.edu.ar cic researcher received: 03-11-2022 accepted: 18-03-2023 abstract. the present work studies the use of pistachio shells as a porosity-forming raw material in the manufacture of ceramic bricks. it focuses on the characteristics of the ceramic pieces obtained with different residual biomass contents (from 5 to 20% by volume). the specimens were shaped by uniaxial pressure of 25 mpa, and then were treated at 950°c for 3h. based on the results obtained it is possible to conclude that the use of this residual biomass, as a pore former in the ceramic industry is feasible. the proportion of added biomass that generates the best characteristics and properties in the final product is 10%. up to this percentage of aggregate, ceramic pieces with very good macroscopic and microscopic characteristics are obtained, with porosity and flexural strength values that meet market requirements for this type of product. optical microscopy technique has been used to carry out a detailed analysis of the shape and size of the formed pores, which is a specific objective of this work. it has been observed that for contents of 5 and 10% biomass, the shape of pores is similar to the shape of the particles of added pistachio shells, while for higher contents (15 and 20%) it is different with elongated characteristics. in relation with the size of the pores, at lower contents is around 60% of the original particles size, and for the higher percentages of biomass, they are larger, indicating that agglomerates of particles are formed and when combusted, produce that porosity characteristics. key words: residual biomass, pistachio shells, lightweight ceramics, pore characteristics. 1. introduction the present work corresponds to the study of pistachio shells as a raw material in the manufacture of ceramic bricks. it focuses on the characteristics of the clay used and the ceramic pieces obtained with different residual biomass contents. the properties of the obtained bricks in relation to the market requirements for this type of materials are also analysed. this waste is a lignocellulosic material, which means that it is mainly formed by cellulose, hemicellulose and lignin, or biopolymers with similar structure complexity. its behaviour in biomass-energy processes has been studied since by calcination it exhibits decomposition and combustion reactions, which release significant amounts of energy (hosseinzaei et al., 2022). the pyrolysis processes of this biomass have been extensively studied, both as a bulk material and as a source of various biopolymers that compose it (acikalin et al., 2012; peters, 2011). in the last decade there have been numerous investigations aimed at the valorization of agricultural wastes for diverse uses (bhuyan, 2020). in the case of pistachio shells, they have been studied for various applications, such as activated carbon production (niksiar et al., 2017; niksiar et al., 2018; foroushani, 2016), heavy metal adsorption (banerjee et al., 2019; cheng, 2022), source of other compounds like essential oils (marett et al., 2017; kasiri et al., 2018; mohammadi et al., 2019), catalyst supports manufacture (taghizadeh et al., 2018), etc. the studies on complete pyrolysis of this biomass have found relatively low calorific capacities when compared with those of coal traditionally used for that purpose, but interesting http://www.oasis-pubs.com/ mailto:nquaranta@frsn.utn.edu.ar quaranta et al., j. build. mater. struct. (2023) 10: 16-26 17 intermediate products have been determined when the pyrolysis is performed in certain controlled pressure and temperature conditions. one such intermediate product is known as psc, pistachio shell carbon, and has been successfully used as a heavy metal biosorbent (siddiqui et al., 2017). dolatabadi et al. (2021) for example, have used pistachio shell based activated carbon as an economical and promising treatment for the removal of insecticides from groundwater. in relation to the use of pistachio shells as a structural material, due to its fibrous constitution, it has been studied as a reinforcement of polymeric matrices (koodalingam, et al., 2020; thiagarajan et al., 2021). also, tekin et al. (2021) have analysed pistachio shell ash as supplementary cementitious material in the construction industry. the authors have found that the presence of graphitic structures in the ashes contributed to the early strength properties of cement. besides, 10% ash incorporation improved the cement compressive strength values by 17% at long times, and for short periods, strength values were found to be satisfactory at even 20% aggregate. in the case of ceramic materials, their physical and mechanical properties depend largely on the raw materials used in their manufacture. one of these properties is porosity, which is usually managed during industrial production by incorporating organic additives derived from petroleum. when combusted, they generate pores, which lighten the bricks and provide insulating properties, although the use of these pore-forming agents implies an increase in the cost of the products. in recent years, some agro-industrial residues have been studied as porosity-forming materials in bricks because they present very high weight losses due to combustion, leaving very small proportions of inorganic material (ash) which is incorporated into the brick matrix (bories et al., 2014; al-fakih et al., 2019; martín-morales et al., 2018; ukwatta and mohajerani, 2017; raut et al, 2011; quaranta et al., 2020; pelozo et al., 2022; quaranta et al., 2023). the results obtained in preliminary studies, in relation to the characteristics of the pistachio shells for the formation of porous matrices have allowed determining that there is a high feasibility of its use. suitable particle sizes can be obtained in a simple way, and its combustion occurs in a wide temperature range, which would not affect the structure of the ceramic piece during the formation process. in addition, its combustion is complete, with production of co2 and water, with negligible concentrations of co. the amount of ash produced, which would be incorporated into the ceramic matrix is very small, so the properties of the ceramic material would not be modified by its presence. the only consideration to take into account is that the residual powder material has eco-toxic characteristics in relation to the development of sensitive plant species such as ryegrass, so special care must be taken during the storage process in the company. the main objective of this research is to achieve the manufacture of lightweight ceramic bricks with the incorporation of pistachio shells, and in particular their use as a controlled porosity former. the characteristics of the obtained bricks and their properties in relation to the market requirements will be analysed. a specific objective of this work is to study the shape and size of the obtained pores in relation to the size and shape of the aggregated biomass particles. 2. experimental program the raw materials used for the manufacture of bricks are treated by means of drying (100°c for 4h) and grinding processes, in order to obtain the suitable particle size distribution according to the design carried out, taking into account the procedures used in ceramic brick production companies. the grinding of the materials was carried out using a ball mill for 30 minutes for the clay, and a ring mill for 2 minutes for pistachio shells. the ground materials (clay and pistachio shells) were sieved to obtain particles smaller than 1 mm, which will be used for the formation of the compacts. the analysis of the particle sizes distribution was made according to the astm standards, with a zonytest equipment. the process was carried out using 500 g of dry material, maintaining 18 quaranta et al., j. build. mater. struct. (2023) 10: 16-26 continuous vibration for 10 minutes. the material retained on each sieve was then determined. table 1 shows the correspondence between the standardized mesh used and the passing particle size. table 1. astm mesh number and particle size correspondence. astm mesh 10 18 35 60 120 170 200 325 plate sieve opening [m] 2000 1000 500 250 125 88 74 44 < 44 the materials used for the production of ceramic specimens were characterized by various techniques: optical microscopy (om), scanning electron microscopy (sem), dispersive x-ray analysis (eds), differential thermal and thermogravimetric analysis (dta-tga), x-ray diffraction (xrd) and weight loss on ignition (loi). optical observations were made with a zeiss-axiotech equipment with a donpisha 3ccd camera. sem analyses were carried out with a philips 515 scanning electron microscope, with dispersive energy analyser (edax-phoenix). the chemical analysis was performed with dispersive energy analyser edax-phoenix. dta-tga essays were made with a shimadzu dta-50, teg-50, with ta50 wsi analyser, using heating rate of 1°c/min, in temperature range ambient-1100°c, in air atmosphere. the clay weight loss on ignition was carried out with a laboratory oven at 800°c for two hours, with a heating rate of 5°c/min, on samples of 20 grams. the green compacts are formed from these ground materials with different volume percentages of pistachio shells (biomass), and the obtained samples will be identified as follows: • p0: bricks without biomass • p5: bricks with 5% biomass incorporated • p10: bricks with 10% biomass incorporated • p15: bricks with 15% biomass incorporated • p20: bricks with 20% biomass incorporated several samples (bricks) were produced from each composition, in order to carry out different tests and properties analysis in a reproducible way. the sample p0, without incorporated biomass, is taken as a reference sample. for the bricks preparation, 80 g of clay, the corresponding volume percentage of the biomass, and finally 8% by weight of water on the total mixture, were used. the dry materials are mixed until homogeneous mixture before incorporating the water, and the moisture is added slowly, trying to avoid the formation of lumps, since the clay has hydrophilic surface characteristics greater than those of pistachio shells. once the mixtures are obtained, the specimens are shaped by uniaxial pressure of 25 mpa, using a hydraulic press, cific brand, in moulds of 70mm x 40mm, resulting thicknesses of c.a. 15mm. the compacts obtained with different percentages of residue are arranged to dry at room temperature, in an aerated place for 24-48 hours, constituting the so-called green bodies, and then at 100°c (24h). for the sintering of the bricks, the pieces are heat treated at 950°c for 3 hours, at a heating rate of 1°c/min. this stage is carried out in an electric oven (orl brand) following a heating curve similar to the one used regularly by companies that produce ceramic bricks. the products obtained after the firing process were characterized with various techniques: permanent volumetric variation (pvv), weight loss on ignition (loi), apparent porosity (p), optical microscopy (om) and flexural strength (mor). the objective of applying these techniques is to determine the properties of these materials, in order to evaluate if they meet the market requirements in their performance in service. quaranta et al., j. build. mater. struct. (2023) 10: 16-26 19 pvv determination is carried out by measuring the length, width and thickness dimensions of each sample, before and after firing, calculating the volumes in each case and the volume variation that occurred due to the firing process. the test to determine loi is carried out by making the difference in weight of each brick, before and after firing, and averaging the values of the five samples of each composition. the porosity of the samples was determined according to the astm c20-0 standard. to do this, small pieces of the brick are cut using a precision diamond saw, taking samples from the central and external regions of the bricks. this is due to a greater macroscopically presence of pores observed in the internal zone than in the superficial one, and the standard yields a single porosity value, so this procedure is carried out in order to avoid errors in the determinations. optical microscopy analyses were used to observe the microstructure of the bricks, the presence of cracks or micro cracks inside the material, and the size, shape and distribution of the present pores. the preparation of the samples for om observation is carried out firstly by embedding in resin, extracting the air by means of a vacuum pump, to allow the resin to enter the exposed pores. this allows the next stage (polishing) to be performed correctly, avoiding shelling during this process. the specimens were polished using a two-plate automatic polisher (praxis brand) with water-based sic paper of different grain sizes (400 to 1500), and the final finish was performed with polishing cloths and 6m and 1m diamond pastes. the flexural test was carried out with a universal testing machine on scale samples, according to the relationships established in the astm c67-03a standard. the main objective of this study is to analyze the mechanical behaviour of these materials, when subjected to a pure bending stress. in this way, the modulus of rupture (mor) of the bricks was determined. 3. results and discussion 3.1. raw materials characterization table 2 presents the chemical analysis of the used clay, expressed as percentage of the elements, without taking into account in this calculation the carbon and oxygen content determined in the samples, which could be part of organic matter, or inorganic compound (carbonates). the determined composition of the biomass is 70.4% c and 29.6% o. table 2. eds analysis of the used clay. element mg al si k ca fe clay composition [%] 4.5 26.7 58.4 5.7 1.5 3.2 the weight loss on ignition of the clay was 1.12% and for pistachio shells was 98.2%. the x-ray patterns of pistachio shells is presented in figure 1. four reflection peaks are observed at values of 16.7, 21.7, 34.7 and 44.4, which have been assigned to microcrystalline cellulose. other authors, in work done with sisal fibres (benítez-guerrero et al., 2014), have obtained similar spectra. mtibe et al. (2015) have also observed these reflection peaks in cellulose and cellulose nanofibers extracted from residues of the corn industry. the x-ray pattern of the clay shows the presence of iron oxide in the hematite structure (fe2o3), silicon oxide in the quartz structure (sio2), potassium feldspar (xalsio8), iron (fe) and aluminium oxide (al2o3). the diffractogram have been analysed taking into account the pcpdfwin international centre for diffraction data 2000 database. 20 quaranta et al., j. build. mater. struct. (2023) 10: 16-26 fig 1. xrd of grounded pistachio shells. the result of the dta-tga test is shown in figure 2. the presence of two exothermic peaks in the dta at 335°c and 450°c is observed. the latter is a wide peak that covers approximately 130°c (from 370°c to 500°c). the tga curve presents a first gentle slope of weight loss up to approximately 227°c, and then two other zones in the ranges 227°c-270°c and 280°c-460°c. these two zones would indicate different reactions probably corresponding to the combustion of hemicellulose, cellulose and lignin, with their corresponding weight losses. these compounds are present in the vast majority of agro industrial biomass (manals cutiño et al., 2011). fig 2. dta-tga of pistachio shells. the clay sample shows a typical dta-tga curve for this type of material, with continuous weight loss between 200°c and 700°c. this can be assigned to various reactions, up to 400°c a slow endothermic dihydroxylation reaction of the clay and up to 700°c the combustion of the organic material present. in the 850°c-950°c range, a peak in the dta curve without weight loss was recorded. this can be assigned to the phase transformation reaction of the alumino-silicates present in the sample, which is a reversible reaction. 3.2. ceramic bricks production figure 3 shows the results of the particle size distribution of the materials used to make the ceramic bricks. it can be seen that more than 50% of the clay has a particle size greater than 250µm and the rest is evenly distributed among the sizes of the selected sieves. in the case of pistachio shells, approximately 75% of the sample has sizes greater than 500µm. this 0 300 600 900 -100 0 100 200 300 450 temperature [°c] d t a [ a .u .] 335 0 5 10 15 20 t g a [ m g ] ____tga ____dta quaranta et al., j. build. mater. struct. (2023) 10: 16-26 21 granulometric distribution is adequate to achieve a good homogenization of the mixtures of both materials at the beginning of the production of the bricks. fig 3. particle size distribution of the used raw materials. figure 4 shows the aspect of the green pieces obtained after the drying process at room temperature. it is possible to appreciate that as the amount of biomass added increases, the surfaces of the bricks appear rougher, and the edges and corners appear less defined. as mentioned above, all sintered samples have been produced at 950°c. the obtained compacts are also shown in figure 4. a homogeneous reddish colour in all samples can be observed. in addition, a greater porosity in the bricks is notable as the amount of incorporated residue increases. in the samples with higher residue contents (15% and 20%), slight shattering of the structure can be observed on edges and corners. similar results have been obtained in previous works, in the production of porous ceramic bricks using other residual biomass such as corn cobs (quaranta et al., 2023) and peach pits (quaranta et al., 2020). martín-morales et al. (2018), analyzing the behavior of ceramic bricks obtained with aggregates of various biomasses (rice husks, almond shells, olive pits, olive wood and olive pruning) have determined that the best macroscopic characteristics and properties were obtained for biomass proportions by volume between 7.5% and 15%. fig 4. green bricks (left) and bricks obtained at 950°c (right). the pvv values of the analysed samples indicate that a contraction occurred in all of them, which increases as the residue content increases with a maximum value of 7.9% for the sample with 20% residual biomass incorporated, as can be seen in table 3. negative values indicate shrinkage processes. table 3. properties of the ceramic bricks. element p0 p5 p10 p15 p20 ppv [%] -6.6 -7.2 -7.3 -7.5 -7.9 loi [%] -9.4 -13.9 -17.2 -20.1 -24.1 porosity [%] 19.2 28.3 29.4 33.2 37.0 mor [mpa] 9.1 6.2 6.1 4.3 5.3 the values of weight loss on ignition (loi) of the compacts are also presented in table 3. the results show that the higher the residue added, the higher the value of this parameter is, as expected, since the added biomass combusts inside the brick during firing, with the consequent 22 quaranta et al., j. build. mater. struct. (2023) 10: 16-26 weight loss. negative values indicate the weight percentage of the samples that has decreased after heat treatment. table 3 also shows the porosity values of these fired compact samples. it can be seen that as the residue content increases, the porosity of the bricks also increases, being the maximum value recorded 37 %. this has a relationship with the loi results mentioned above. however, this increase in porosity does not present a direct proportional relationship, since as the weight loss increases due to biomass combustion, the porosity also increases but in minor proportions, taking into account the p/loi values. in table 4 the p/loi values are presented, as well as the following relations: p/pvv and loi/pvv. these calculations have been made because it has been observed that for samples produced with the addition of biomass, all these values are related by the expression (1). although this expression is not fulfilled for the case of the reference bricks, without added biomass. p/pvv p/loi  loi/pvv (1) table 4. relationship between porosity, loi and pvv. sample property p0 p5 p10 p15 p20 p [%] 19.2 28.3 29.4 33.2 37.0 loi [%] 9.4 13.9 17.2 20.1 24.1 pvv [%] 6.6 7.2 7.3 7.5 7.9 p/loi 2.0 2.0 1.7 1.7 1.5 p/pvv 2.9 3.9 4.0 4.4 4.7 loi/pvv 1.4 1.9 2.4 2.7 3.1 (p/pvv p/loi) 0.9 1.9 2.3 2.7 3.2 the mechanical properties of the compacts were evaluated by testing the flexural strength. table 3 shows the modulus of rupture (mor) of each of the analysed samples. it can be seen that the inclusion of pistachio shells in the samples produces a decrease in flexural strength, with respect to the clay reference sample. as the percentage of residue in the sample increases, the flexural strength decreases, with the exception of the sample with 20% incorporated residue, which has a slightly higher mor than p15 sample. it is known that a general reduction of the mechanical properties in these kind of materials can be caused by the presence of pores, as well as other microscopic imperfections such as surface or internal cracks, which act as notches or stress points. in the case of ceramic bricks, mor values are influenced by diverse parameters such as porosity values, permanent volumetric variation, weight loss on ignition and presence of superficial or internal microcracks. depending on these parameters and their combinations, more or less resistant matrices can be obtained. in the case of these samples these combinations may have occurred leading to a slight higher resistance value for the sample p20 compared with p15. however, the p20 macroscopic characteristics observed, in particular the edges and corners shelling, indicate that at these percentages of residue, the quality of the products is not good. in argentina, although there are regulations that establish how to perform the determinations of this mechanical property, there is no required market value of flexural strength. for this reason, the values obtained in this work are compared with the value established for astm c410-60 standard, for industrial floor bricks, where the required mor value is 5.2 mpa. optical microscopy analysis was used to study the internal structure of these bricks, in particular to determine the shape and size of the formed pores, and the presence of internal cracks. figure 5 presents images taken from different samples using the same 100x magnification. the difference in the shape and size of the pores in samples that have important proportions of residue, compared with the p0 sample, without residue, is remarkably observed. quaranta et al., j. build. mater. struct. (2023) 10: 16-26 23 as can be seen in the figure 5, in the bricks without biomass aggregate, p0, a homogeneously distributed porosity is observed, with rounded pores of small sizes that do not exceed 0.1 mm. samples p5 and p10 present a homogeneous distribution of pores with various sizes that reach values of 0.4 mm, although the most abundant are 0.3 mm pores. in these samples, the pores present irregular shapes, similar to those observed in the particles of the ground pistachio shells, as can be seen in the image shown in figure 6. fig 5. om images of the samples with different contents of pistachio shells. fig 6. sem image of ground pistachio shells. 24 quaranta et al., j. build. mater. struct. (2023) 10: 16-26 taking into account that approximately 70% of the ground biomass is constituted of 0.5 mm particles, and that the most abundant pore size observed is 0.3 mm, it can be inferred that during brick firing, the biomass particles that combust generate pores of sizes corresponding to 60% of the size of the particles that give rise to them. in the samples with higher percentage of pistachio shells, p15 and p20, the pores size is greater than the particles size used for this residue, observing pores of up to 2 mm. the shape of these pores is irregular and elongated compared with those observed in p5 and p10. this would be indicating that during mixing with the clay, and due to the high percentage of residue added, the biomass particles agglomerate, distributed in a non-uniform way, generating pores corresponding to these agglomerates during the firing process. fig. 7. sem image showing microcracks presence in p20 sample. it is also possible to observe in sample p20, the presence of numerous internal microcracks in the structure of the brick matrix, which would explain the increase in flexural strength observed in relation to p15 sample, because these microcracks may initially be acting as stress absorbers. in sample p15 microcracks can also be observed in the matrix, although they are smaller and in less quantity. figure 7 shows a micrograph of p20 where these microcraks can be observed. some studies on pore-forming materials in ceramics found in the literature (feng et al, 2013; sarikaya & dogan, 2013), mention the relationship between the shape of the aggregated particles and the pores formed, but they are generally organic compounds produced by chemical synthesis, with well-defined homogeneous characteristics, and not from residual materials as in this case. studies such as the one in this work where the pore former is a ground biomass, that is, where the particles have a preferential shape according to their structure, have not been found in the literature. the pistachio shell biomass used in this work is considered to be of medium density. pelozo et al. (2022) have carried out a comparative study of ceramic bricks produced with 10% volume aggregates of different biomasses (corncob, peanut shells, pistachio shells, olive pits, etc.), using similar particle sizes, the same heat treatment, and general experimental conditions. the results indicated that the porosity of the samples is directly related to the density of the biomass used, and therefore, the other properties of the bricks are also influenced by this parameter. taking into account the obtained results, for pistachio shells under the conditions described in this research, the proportion of added biomass that ensures the use of the greatest amount possible while maintaining the macroscopic characteristics and properties of the ceramic products within those market requirements was 10% by volume. 4. conclusions based on the analysis of the results obtained during the development of this study, and taking into account the characterizations of the used materials, it is possible to conclude that the use of pistachio shells, as a pore former in the ceramic industry is feasible. quaranta et al., j. build. mater. struct. (2023) 10: 16-26 25 the proportion of added biomass that generates the best characteristics and properties in the final product is 10%. at this percentage of aggregate, significant quantities of residual materials are used, and also ceramic pieces with very good macroscopic and microscopic characteristics are obtained, with porosity and flexural strength values that meet market requirements for this type of product. a detailed analysis of the shape and size of the formed pores has been carried out using an optical microscope. it has been observed that for contents of 5 and 10% biomass, the shape of the pores is similar to the shape of the particles of ground pistachio shells, while for the higher contents (15 and 20%), it is much longer. on the other hand, the size of the pores at lower contents is around 60% of the original size of the particles, and for the higher percentages of biomass, they are much larger. this would indicate that in this case of higher contents, agglomerates of particles are formed and when combusted, lead to that porosity characteristics. 5. references acikalin, k., karaca, f. & bolat, e. (2012). pyrolysis of pistachio shell: effects on pyrolysis conditions and analysis of products. fuel, 95, 169-177. al-fakih, a., mohammed, b.s., liew, m.s. & nikbakht, e. (2019). incorporation of waste materials in the manufacture of masonry bricks: an update review. journal of building engineering ,21, 37–54. banerjee, m., basu, r. k. & das s. k. (2019). adsorptive removal of cu(ii) by pistachio shell: isotherm study, kinetic modelling and scale-up designing-continuous mode. environmental technology & innovation, 15, art. 100419. benítez-guerrero, m., lópez-beceiro, j. & sánchez-jiménez, p. (2014). comparison of thermal behavior of natural and hot-washed sisal fibers based on their main components: cellulose, xylan and lignin. tg-ftir analysis of volatile products. thermochimica acta, 581, 70-86. bhuyan, n., narzari, r., gogoi, l., bordoloi, n., hiloidhari, m., palsaniya, d., deb, u., gogoi, n. & kataki, r. (2020). valorization of agricultural wastes for multidimensional use. chapter 2. current developments in biotechnology and bioengineering, 41-78. bories, c., borredon, m.e., vedrenne, e. & vilarem, g. (2014). development of eco-friendly porous fired clay bricks using pore-forming agents: a review. journal of environmental management, 143, 186–196. cheng, t., li, j., ma, x., zhou, l., wu, h. & yang, l. (2022). alkylation modified pistachio shell-based biochar to promote the adsorption of vocs in high humidity environment. environmental pollution, 295, art. 118714. dolatabadi, m., naidu, h. & ahmadzadeh, s. (2021). a green approach to remove acetamiprid insecticide using pistachio shell-based modified activated carbon; economical groundwater treatment. journal of cleaner production, 316 (2021) art. 128226. feng, y.; wang, k.; yao, j.; webley, p.; smart, s.; wang, h. (2013). effect of the addition of polyvinylpyrrolidone as a pore former on microstructure and mechanical strength of porous alumina ceramics. ceramics international, 39, 7551-7556. foroushani, f. t. & tavanai, h. (2016). an investigation of the effect of kmno4 on the pore characteristics of pistachio nut shell based activated carbon. microporous mesoporous materials, 230, 39-48. hosseinzaei, b.; hadianfard, m.; aghabarari, b.; garcía rollán, m.; ruiz-rosas, r.; rosas, j.; rodríguezmirasol, j.; cordero, t. (2022). pyrolysis of pistachio shell, orange peel and saffron petals for energy production. bioresource technology reports, 19, 101209. kasiri, n. & fathi, m. (2018). production of cellulose nanocrystals from pistachio shells and their application for stabilizing pickering emulsions. international journal of biological macromolecules, 106, 10231031. koodalingam, b., senthikumar, p. & rajesh babu, s. (2020). study of mechanical properties of the polymer matrix composite materials using pistachio shells. material today proceedings, 33 (7), 2912-2916. 26 quaranta et al., j. build. mater. struct. (2023) 10: 16-26 manals cutiño, e., penedo medina, m. & giralt ortega, g. (2011). thermogravimetric and thermal analysis differential different vegetable biomasses. tecnología química, 32 (2), 180-190. marett, j., aning, a. & foster, e. j. (2017). the isolation of cellulose nanocrystals from pistachio shells via acid hydrolysis. industrial crops and products, 109, 869-874. martín-morales, m. ; eliche-quesada, d. ; lópez-alonso, m. ;martín-pascual,j. ; pérez-villarejo,l. ; ruizpadillo, d.p. ; zamorano, m. (2018). comportamiento de ecoladrillos con inclusión de biomasas residuales. tecnología, ciencia y educación, 11, 61-79. mohammadi, m., ghorbani, m., del beigbabaei, a., yeganehzad, s. & sadeghi-mahoonak, a. (2019). investigation effects of extracted compounds from shell and cluster of pistachio nut on the inactivation of free radicals. heliyon, 5, e02438. mtibe, a., linganiso, l., mathew, a., oksman, k., john, m. & anandjiwala, r. (2015). a comparative study on properties of micro and nanopapers produced from cellulose and cellulose nanofibers. carbohydrate polymers, 118, 1-8. niksiar, a. & nasernejad, b. (2017). activated carbon preparation from pistachio shell pyrolysis and gasification in a spouted bed reactor. biomass and bioenergy, 106, 43-50. niksiar, a. & nasernejad, b. (2018). modeling of gasification reaction to produce activated carbon from pistachio shells in a spouted bed. biomass and bioenergy, 119, 97-108. pelozo, g., caligaris, m. & quaranta, n. (2022). ceramic bricks incorporation agro-industrial wastes: influence of biomass characteristics. procc. waste management and circular economy 2022, p13. (www.iswmaw.com). peters, b. (2011). prediction of pyrolysis of pistachio shells based on its components hemicellulose, cellulose and lignin. fuel processing technology, 92, 1993-1998. quaranta, n.; unsen, m.; lópez, h.; cristobal, a. (2020). porous ceramic bricks from clay and peach pits mixtures. revista tecnología y ciencia, 18 (38), 37-49. quaranta, n., varoli, r., caligaris, m. & cristóbal, a. (2023). use of corncob as controlled porosity former in ceramics. revista tecnología y ciencia. 21 (46), 1-17. raut, s.; ralegaonkar, r.; mandavgane, s. (2011). development of sustainable construction material using industrial and agricultural solid waste: a review of waste-create bricks. construction and building materials, 25, 4037-4042. sarikaya, a.; kogan, f. (2013). effect of various pore formers on the microstructural development of tapecast porous ceramics. ceramics international, 39, 403-413. siddiqui, s. h. & ahmad, r. (2017). pistachio shell carbon (psc) – an agricultural adsorbent for the removal of pb(ii) from aqueous solution. groundwater for sustainable development, 4, 42-48. taghizadeh, a. & rad-moghadam, k. (2018). green fabrication of cu/pistachio shell nanocomposite using pistacia vera l. hull: an efficient catalyst for expedient reduction of 4-nitrophenol and organic dyes. journal of cleaner production, 198, 1105-1119. tekin, i., dirikolu, i. & gökce, h. (2021). a regional supplementary cementitious material for the cement industry: pistachio shell ash. journal of cleaner production, 285, art. 124810. thiagarajan, a., velmurugan, k. & sangeeth p. (2021). synthesis and mechanical properties of pistachio shell filler on glass fiber polymer composites by varim process. materials today proceeding, 39 (1), 610-614. ukwatta, a.; mohajerani, a. (2017). leachate analysis of green and fired-clay bricks incorporated with biosolids. waste management, 66, 134-144. j. build. mater. struct. (2016) 3: 68-84 https://doi.org/10.34118/jbms.v3i2.25 issn 2353-0057 effect of inclusion of crumb rubber on the unconfined compressive strength and wet-dry durability of cement stabilized clayey soil yadav j s*, tiwari s k department of civil engineering, malaviya national institute of technology jaipur, india * corresponding author: jitendershine@gmail.com received : 21-11-2016 revised: 19-12-2016 accepted: 26-12-2016 abstract. in the present study, the effect of inclusion of waste crumb rubber and cement on the unconfined compressive strength and wet-dry durability of clayey soil has been investigated. crumb rubber and cement were added to clayey soil at ranges of 2.5%-10% and 3%-6% respectively. the results of the investigation revealed that the incorporation of crumb rubber influenced the unconfined compressive strength, axial strain at failure, energy absorption capacity and wet-dry durability of the cement-stabilized clay. the study reveals that as the content of crumb rubber in the cement-stabilized clayey soil increases the unconfined compressive strength decreases but prosperously changes the behavior of the cement-stabilized clay from brittle to ductile. the axial strain corresponding to peak axial stress and energy absorption capacity of the specimens can be increased by limiting the content of crumb rubber up to 5%. the weight loss of the cement-stabilized clay mixed with crumb rubber increases as the content of crumb rubber increases. with the prolongation of the curing period, the weight loss of cement-stabilized clay mixed with crumb rubber decreases. further, the weight loss of 90 days cured specimens of clayey soil incorporated with 6% cement and crumb rubber up to 5% meets the recommendation of the material to be used in construction of road pavements as a base, sub-base, and shoulder. most importantly, the utilization/disposal of this hazardous waste material reduces its impact on environment and health. key words: crumb rubber, cemented clay, compaction, unconfined compressive strength, energy absorption capacity, durability, xrd, sem. 1. introduction the industrialization and urbanization have been the two worldwide phenomena in the present century. though these are the necessity of the society, nevertheless their negative impacts on the environment and social life cannot be demitted. the major ill effect of these global processes is the production of large quantities of industrial wastes (such as incineration ash, plastic waste, rice husk-ash, fly ash, waste rubber tires etc.) and the problems related to their safe disposal and management. the safe and profitable disposal of these wastes is one of the greatest challenges before of industries. disposal of discarded waste tires is one of the primus problem faced by the industries and government of many country because it has a momentous share in the solid waste. about 1.5 billion tires are produced in a year, throughout the world and per annum almost 1000 million tires reach the end of their useful life. in india, a phenomenal increase in the number of automobiles has been noticed. in year 2010-11, the total production of tires was 124.3 million and became 146.1 million in the year 2014-15 (atma, 2015) the common practice used for the disposal of the waste tire such as stockpiles, landfills and burning are considered as a big danger to the health of humans and ecological systems. the stockpiling provides breeding sites for mosquitoes and rodent, whereas heaving of the ground has been faced with landfills disposal of waste tires. the poisonous gasses liberated by the burning of the waste tire, when used as a fuel in the industry causes serious health hazards to the population living nearby that area. although, many countries have banned the use of tires as a fuel for the industries. indian government restricted the import of used /retreaded tires since mailto:jitendershine@gmail.com yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 69 april 2006. still, the disposal of discarded waste tires is one of the major problems faced by the nations. therefore, timely action regarding the safe disposal of waste tires is necessary, keeping in view the environmental problems and health hazards associated with it. one of the common and feasible ways to utilize these waste products is to explore their use in the construction of roads, highways, embankments and a fill material. due to rise in population and an increase in infrastructure growth in metropolitan areas, there is a dramatic increase in the prices of land and lack of suitable sites for development. therefore, now-a-days construction is also being carried out on marginal sites having extremely poor ground conditions like soft clays that were earlier considered unsuitable due to their poor strength and high compressibility. such soils, when loaded, cause excessive settlements and early failure of structures. it is a challenge to the geotechnical engineer to improve the mechanical properties of the clayey soil by using stabilization and reinforcement techniques at a reasonable cost. the problems associated with the disposal of waste tires and stabilization of problematic soft/weak soils has encouraged the authors to do this investigation. the use of discarded waste tires as an engineering material is gaining popularity among civil engineering fraternity due to its low density, high strength, hydrophobic nature, low thermal, conductivity, durability, resilience and high frictional strength, which are essential from the geotechnical engineering perspective. astm d6270-98 lays guidelines pertaining to use of waste tires in civil engineering. 2. background the incorporation of waste rubber tire affects the properties of the clayey soils. various investigators (al-tabbaa et al., 1997; cokca and yilmaz, 2004; akbulut et al., 2007; robani and chan, 2008; ho and chan, 2010; cabalar et al., 2014; srivastava et al., 2014; wang and song, 2015; beena et al., 2016) had studied the effect of inclusion of waste rubber tire on the unconfined compressive strength of the cohesive soils. al-tabbaa et al. (1997)observed a decrease in unconfined compressive strength of kaolin, bentonite and kaolin-lime with the inclusion of shredded tyre of sizes 1-4 mm, 4-8 mm and 8-12 mm ranging between 2% to 20% by weight. a loss of 19.3%, 15.6%, and 9% (approx.) in ucs of kaolin, kaolin-lime, and bentonite containing 2% tyre of size 1-4 mm was reported as compared to untreated soil samples. whereas, inclusion of 10% tyre of size 1-4 mm led to a loss of 43.1%, 40.7%, and 30.6% (approx.) in the ucs of kaolin, kaolin-lime, and bentonite clay. cokca and yilmaz (2004) reported about 35 times reduction in the unconfined compressive strength of fly ash–rubber–bentonite mixtures as rubber increases from 0% to 10% and bentonite decreases from 10% to 0%. the inclusion of tire fibres of length 10mm up to 2% increases the unconfined compressive strength of the clay was reported by akbulut et al. (2007). robani and chan (2008) had treated the soft soil with 5% cement content and tire chips (passing 2mm sieve) varying from 5% to 15%. the unconfined compressive strength the soil incorporated with cement (5%) and tire chips (5%) was found to be more than the cement treated soil. the elastic properties of the cement treated soft soil could be increased with the inclusion of tire chips. ho and chan (2010) concluded that the inclusion of rubber chips in the cemented kaolin specimens reduces the unconfined compressive strength but were able to increase axial strain corresponding to peak axial stress. a loss of 6.7%, 15.25%, and 23.7% (approx.) was noticed in ucs of kaolin clay stabilized with 2% cement and incorporated with 5%, 10% and 15% rubber chips as compared to cement stabilized kaolin clay. similarly, a lowering of 19.6%, 38.2%, and 43.17% (approx.) in ucs of cemented kaolin clay containing 4% cement and 5%, 10% and 15% rubber chips was reported. guleria and dutta (2012) observed the decrease in the unconfined compressive strength of the fly ash-limegypsum mixture with increase in dry/wet tire chip content (5% to 15%) citing two possible reasons: (i) non polar nature of rubber, which entrap air during the mixing and (ii) negligible load taking ability of rubber as compared to the hardened mix. kim and kang (2013) had noticed a gradual increment in the unconfined compressive stress of clayey soil with increased strain after reaching a yielding stress with the increase in rubber content. the elastic compression of the crumb rubber was attributed as a reason for such behavior. cabalar et al. (2014) carried out 70 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 an investigation on the unconfined compressive strength of clay stabilized with lime (0%, 2%, 4% and 6% by dry weight) and tyre buffing (0%, 5%, 10% and 15% by dry weight). the addition of lime was found to increase the unconfined compressive strength but the inclusion of tyre buffing reduces the strength of the specimens. the inclusion of 5%, 10%, and 15% tire buffing led to a loss of 63.8%, 72.2%, and 77.8% in ucs of clay containing 6% lime as compared to unrubberized clay stabilized with 6% lime. hambirao and rakaraddi (2014) had noticed an increase in the unconfined compressive strength of the cement stabilized clayey soil with the addition of shredded rubber tyre chips up to 5%, thereafter it decreases. prasad et al. (2014) had found an improvement in the unconfined compressive strength of two different soil samples by addition of crumb rubber (425 µm to 600-µm size) up to 10% and 15%, further addition leads to decrease in the strength. an approximately 60% improvement the undrained cohesion value of black cotton soil with the inclusion of coarse size (4.75 mm passing -2 mm retaining) shredded tyres waste as compared to pure soil was reported by srivastava et al. (2014). otoko and pedro (2014) observed that the addition of shredded tyres of length 10 mm to 20 mm up to 5% leads to increase the ucs values of cemented soil. wang and song (2015) had incorporated different fineness of crumb rubber (30/40, 60/80mesh) in clayey soil stabilized with 7% and 20% cement content and observed that inclusion of crumb rubber resulted in a decrease in the compressive strength. the inclusion of 5%, 10%, 15%, and 20% crumb rubber of size 30/40 mesh in clay stabilized with 20% cement and cured for 91 days led to a reduction of 7.3%, 18.5%, 18.5%, and 31.4% respectively in the compressive strength of cement stabilized clayey soil. similarly, a reduction of 14.2%, 14.2%, 24.2%, and 31.4% was reported in the compressive strength of same mixtures with the inclusion of crumb rubber of size 60/80 mesh. the bad connection between non-polar rubber particles and polar cemented clay particles leads to the creation of voids in the matrix and reduces the strength consequently. the unconfined compressive strength of the rubberized cemented clay was found to be almost independent of the size of rubber particles. beena et al. (2016) investigated the effect of different size and content of crumb rubber on the unconfined compressive strength of clayey and silty soils. they found maximum unconfined compressive strength with the inclusion of crumb rubber between 2% to 4% regardless of the size of crumb rubber. the unconfined compressive strength of clayey soil decreases with the increase in the size of crumb rubber used, whereas it increases with the increase in the size of crumb rubber in case of silty soils. only one study is available in the existing literature on the effect of inclusion of waste rubber tires on the durability characteristic of soils. guleria and dutta (2013) reported that with the increase in the content of tire chips in fly ash-lime –gypsum mixtures the weight loss increases. the dissimilar thermal expansion of tire chips and fly ash-lime-gypsum mixtures during the drying cycle caused a reduction in the bond between the tire chips and mixture, which leads to increase in the weight loss of mixture incorporated with higher rubber content. the review of preceding literature evident that the adequate research has not yet been carried out on strength and durability characteristics of the cement stabilized clay incorporated with waste crumb rubber. the modified proctor tests were conducted in conformity with is : 2720 (1983) to obtain the maximum dry density (mdd) and optimum moisture content (omc) of the composite prior to unconfined compressive strength and durability tests. 3. materials used 3.1. soil the soil sample was taken jaipur city in india. some physical properties such as atterberg limits, specific gravity, maximum dry density and optimum moisture content of the soil were determined in conformity with indian standards. table 1 illustrates the results of the tests. the soil is classified as cl (clay with low plasticity) according to the indian standard soil classification system is : 1498 (1970). the clay contains illite and quartz as predominant minerals along with some content of kaolinite. yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 71 table 1. physical attributes of soil soil properties indian standard used values specific gravity is:2720 (part 3)-1980 2.69 liquid limit (%) is:2720 (part 5)-1985 34.2 plastic limit (%) is:2720 (part 5)-1985 24.8 plasticity index (%) is:2720 (part 5)-1985 9.4 maximum dry unit weight (kn/m3) is:2720 (part 8)-1983 16.35 optimum moisture content (%) is:2720 (part 8)-1983 20.89 swelling pressure (kpa) is:2720 (part 41)-1977 70.12 3.2. crumb rubber the crumb rubber obtained from s&j granulate solution having the particle size between 0.8-2 mm was used in this investigation. fig 1 reveals the gradation curve of crumb rubber. it shows that crumb consists of mainly sand-sized particles. fig 2 illustrates the waste crumb rubber used in the investigation. the chemical composition as provided by the supplier is tabulated in table 2. 0.01 0.1 1 10 0 10 20 30 40 50 60 70 80 90 100 p er ce nt ag e fi ne r by w ei gh t (% ) seive size (mm) crumb rubber fig 1 gradation curve of crumb rubber fig 2. crumb rubber used in the study table 2. chemical composition of crumb rubber test results ash content, % 5.11 carbon black content, % 28.43 acetone extract, % 9.85 volatile matter, % 0.56 hydrocarbon content, % 56.05 polymer analysis sbr 3.3. cement ordinary portland cement (opc-43 grade) was used in this investigation. the physical properties determined in accordance with related indian standard. table 3 illustrates the physical properties of cement. table 3. physical properties of cement properties indian standard used values fineness is: 4301-1 (1996) 3.5 specific gravity, g is: 4301-11 (1988) 3.12 standard consistency, % is: 4301-4 (1988) 39 initial setting time, minutes is: 4301-5 (1988) 35 final setting time, minutes is: 4301-5 (1988) 600 soundness (expansion, mm) is: 4301-3 (1988) 4 72 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 4. experimental procedure 4.1. proportion of ingredient and preparation of mixture the soil sample obtained from the field was first air-dried and then pulverized to crush the lumps. the soil was mixed with crumb rubber and cement ranged from 2.5%-10% and 3%-6% by the weight of soil respectively. the general expression for the total dry weight (w) of clay– cement –crumb rubber mixture is: w =ws+ wc+ wr (1) where: ws, wc, and wr is the weight of soil, cement, and crumb rubber respectively. table 4 illustrates the details of mixtures and their proportions by dry weight on which the unconfined compressive strength and wetting-drying durability tests were conducted. for the sake of convenience and better understanding of the results, the codification of the mixes is used. the symbol s is used for clayey soil. c1 and c2 denote the 3% and 6% cement content. similarly, r1, r2, r3, and r4 notation indicates 2.5%, 5.0%, 7.5% and 10.0% crumb rubber content, respectively. the required quantities of clayey soil and crumb rubber were mixed together in a laboratory mixer and stored in air tight plastic bags. cement was incorporated at the time of formation of samples for unconfined compressive strength and durability tests. then, as per the optimum moisture content obtained from modified proctor test for each mix, the required amount of water was added. special care was taken for the homogeneity and uniformity of the mixes at each stage of mixing. table 4. test mixtures and soil, rubber, and cement percentages sample soil rubber sample soil rubber cement sample soil rubber cement percentage (%) percentage (%) percentage (%) s 100 0 c1 97 0 3 c2 94 0 6 r1 97.5 2.5 c1r1 94.5 2.5 3 c2r1 91.5 2.5 6 r2 95 5 c1r2 92 5 3 c2r2 89 5 6 r3 92.5 7.5 c1r3 89.5 7.5 3 c2r3 86.5 7.5 6 r4 90 10 c1r4 87 10 3 c2r4 84 10 6 4.2. test conducted 4.2.1. compaction test during design of an engineered fill, testing performed to determine shear, consolidation, permeability, or other properties requires test specimens to be prepared by compacting the soil at a prescribed molding water content to obtain a predetermined unit weight. compaction of soils increases their density, shear strength, bearing capacity but reduces their void ratio, porosity, permeability, and settlements. the modified proctor tests were conducted on the various combinations as illustrated in the table 4 to determine the maximum dry density (mdd) and optimum moisture content of the mixtures as per is : 2720 (part viii)-1983. the compaction on each sample was completed within 20 minutes of completion of mixing. 4.2.2. unconfined compressive strength test the unconfined compression strength test is used to determine the cohesion and shear strength of soil. it is an index for checking the short-term stability of foundation and slopes. it was carried out on various combinations as presented in table 4. unconfined compressive strength tests were carried out in accordance with is : 2720 (1991) on the specimens of 38.1 mm dia. and 76.2 mm length prepared at the maximum dry density (mdd) and optimum moisture content (omc) of modified proctor by static compaction method. the cylindrical mould of size 38 mm diameter and 76 mm length, with additional detachable collars were used to prepared the specimens by compressing the mould statically under uniform rate of deformation of 1.25mm/ min approximately till the specimen just reached the desired dimension as per is : 4332 (1968). the yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 73 specimens were then extracted by using sample extractor. after that samples were wrapped in the air tight polythene bags and kept in a humidity controlled room (27oc temperature and 96% humidity) for a curing period of 7, 14, and 28 days (as shown in fig 3(a)). the samples obtained after completion of age of curing were placed in strain-controlled unconfined compressive strength apparatus and axial strain was applied at a rate of 1 mm/min (as revealed in fig 3(b)). (a) (b) fig 3. (a) specimens cured in humidity-controlled room (b) setup for unconfined compressive strength tests 4.2.3. wetting-drying durability test the most crucial parameter to assess the suitability of any construction material is its durability for their use. the durability of cement –stabilized soils can be predicted by tube suction, 7-day unconfined compression strength, wetting–drying cycles and freezing–thawing cycle’s tests. in this investigation, the traditional wetting –drying cycles tests were performed in conformity with is : 4332 (1968) for securing the durability of the proposed composite in the adverse environmental conditions. the test specimens of volume 1000cc were prepared at their mdd and omc and extracted from the mould by using sample extractor as shown in fig 4(a) and 4(b). the samples so obtained were wrapped in the plastic sheet and placed in the humidity control room for curing period of 7, 28, 90, and 180 days (as revealed in fig 4(c)). after the completion of the curing age, the specimens were exposed to twelve alternate wetting and drying cycles. each wetting and dry cycle consisted of 5 hours of soaking in potable water at room temperature (as illustrated in fig 4(d)) and 42 hours of heating in an oven at 70 0c (as shown in fig 4(e)). total four specimens for each combination were prepared and out of four specimens, two specimens were brushed parallel to the longitudinal axis of specimens to measure the weight loss upon scratching after each wet and dry cycle. the rest two specimens were used to determine the change in the dimensions and moisture content. according to portland cement association (pca) and bhattacharja and bhatty (2003), the weight loss of the specimens after 12 cycles of wetting and drying should not exceed 14% for granular soils of low plasticity and 7% for cohesive clays of their original mass. however, these recommendations of pca were found to be too stringent as per some other studies. 20% and 30% loss in mass have been recommended for the cement stabilized materials to be used as base, sub-base, and shoulder for construction of roads as per irc: sp: 89 (2010). 74 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 (a) (b) (c) (d) (e) fig 4. the sequential steps of the preparation of samples for wetting and drying durability testing from: (a) to (e). 4.2.4. mineralogical and microscopical studies the most probable phases of the mineral present in c1 and c2 after curing were determined by the x-ray diffraction studies. a panalytical x’pert pro powder diffractometer (type 11141934) having copper electrodes that act as the source of radiation (cu-kἀ radiation, 40 kv40 ma) was used. the specimens were scanned from 2θ= 10.020 to 79.9800 with step scanning at 0.02°/0.5 s. the mineralogical phases present in the mixtures were identified by x’pert high score equipped with jcpds pdf-2 database (icdd 2003). the particle morphology of mixes was analyzed from micrographs obtained with the aid of scanning electron microscope (nova nano fe-sem 450 (fei)). the samples were prepared in the same way as for the ucs tests. they were cured for 28 days and then oven dried. the freshly cut specimen of 1 cm x 1cm x 1 cm were viewed under sem to establish the change in the microstructure due to addition of cement and rubber in the mixes. 5. results and discussion 5.1. compaction test table 5 shows the results of modified proctor test conducted on the various mixtures as illustrated in table 4. the inclusion of rubber in the clayey soil leads to lowering in the maximum dry density (mdd) of clay as indicated in table 5. for example, the maximum dry density of the clay is 16.35 kn/m3, which reduces to 16.14 kn/m3 to 14.82 kn/m3 with the addition of 2.5% to yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 75 10% rubber content. the decrease in the density of the clay is the possibility due to the reduction in clay content and low specific gravity of rubber. the introduction of cement in the rubberized clay results into the further reduction in mdd of a mixture. for example, for sample r2, the mdd is 15.67 kn/m3, which decreases to 15.57 kn/m3, and 15.15 kn/m3 respectively for sample c1r2 and c2r2. the decrease in the mdd of the mixture with the inclusion of cement may be due to increasing in the void ratio resulted by the base exchange aggregation and flocculation phenomenon. the optimum moisture content (omc) of the clay is 20.89%, which reduces to 20.45%, 19.38%, 18.96%, and 18.38% with the addition of 2.5%, 5%, 7.5%, and 10% rubber, respectively. the reduction in the omc of clay with the incorporation of rubber is the result of low water absorption capacity of rubber. however, the addition of cement in the rubberized clay increased the omc of the mixtures. the water content of sample r2 is 19.38%, which enhances to 19.58% and 19.78% with the addition of 3% and 6% cement in the mix. the additional water required for the hydration process of cement may be attributed as the reason behind the increase in omc of the mixtures. table 5. maximum dry density and optimum moisture content of the mixtures. sample mdd (kn/m3) omc (%) sample mdd (kn/m3) omc (%) sample mdd (kn/m3) omc (%) s 16.35 20.89 c1 16.25 21.28 c2 16.18 21.86 r1 16.14 20.45 c1r1 15.84 20.35 c2r1 15.65 20.56 r2 15.67 19.38 c1r2 15.57 19.58 c2r2 15.15 19.78 r3 15.15 18.96 c1r3 15.05 19.05 c2r3 14.89 19.58 r4 14.82 18.38 c1r4 14.64 18.58 c2r4 14.47 18.78 5.2. unconfined compressive strength test 5.2.1. stress-strain response the stress-strain response of the clay mixed with 2.5%-10% crumb rubber is shown in fig 5(a). the stress-strain curves for the rubberized clay stabilized with 3% and 6% cement cured for 28 days are shown in figs 5(b) and 5(c). a study of fig 5(a) reveals that the peak axial stress of clay mixed with rubber increases marginally up to 5% inclusion of crumb rubber, thereafter it starts decreasing. for example, for clay specimen s, the peak axial stress is 60.62 kpa, which increases to 61.87 kpa and 63.71 kpa, when 2.5% and 5.0% crumb rubber is incorporated in it and decreases to 55.67 kpa and 48.47 kpa, with the inclusion of 7.5% and 10.0% rubber content. these results are found similar to srivastava et al. (2014). exanimation of figs 5(b) and 5(c) reveal that the peak axial stress of cement stabilized clay increases with increase in the cement content and decreases with increase in the rubber content. for example, the peak axial stress of specimen c1r1 is 201.89 kpa which increases to 366.13 kpa for specimen c2r1 and the peak axial stress of specimen c1r1 is 201.89 kpa, which decreases to 168.96 kpa and 122.14 kpa respectively for specimen c1r3 and c1r4. the decrease in the peak axial stress may be attributed to the (i) entrapping of air because of non-polar nature of rubber (guleria and dutta, 2011; wang and song, 2015), (ii) soft aggregate like behavior of rubber (guleria and dutta, 2011), (iii) negligible load carrying capacity of crumb rubber (wang and song, 2015). the failure strain of clay stabilized with 3% and 6% cement is 3.29% and 4.61% respectively, which is much smaller than uncemented rubberized clay. a marked stiffness and brittleness is observed in cement-stabilized clay, which is similar to the observation made by tang et al. (2007) and yadav and tiwari (2016). with the inclusion of rubber in the cement-stabilized clay the sudden drop of strength after attaining peak stress becomes gradual. the incorporation of rubber reduces the brittleness of the response of cement-stabilized clay and changes the behavior of the composite from brittle to ductile by lowering the rate of loss of post-peak strength. it is possibly due to (i) the lower young’s modulus of elasticity of the crumb rubber as compared to cemented clay specimens (guleria and dutta, 2011), (ii) tire chips are elastic in nature and prevented from generating and growing cracks by the elastic reaction, which is 76 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 generated from tire chips during compression (yoshio et al., 2008), (iii) elastic compression of the crumb rubber, which leads to the strain softening after reaching the peak axial strain (kim and kang, 2013), (iv) crumb rubber acts as a reinforcement which enhances soil ability to restrain cracking (shahin and hong, 2010). the failure strain of the cement stabilized clay containing rubber contain up to 5% is found to be more than the other percentages of rubber content. for example, the failure strain of specimen c1r2 is 5.92%, where as for the specimens c1r1, c1r3 and c1r4 are 3.29%, 5.26%, and 4.61% respectively. 0 2 4 6 8 10 12 0 10 20 30 40 50 60 70 a x ia l s tr e s s ( k p a ) axial strain (%) s r1 r2 r3 r4 (a) 0 2 4 6 8 10 0 50 100 150 200 250 a x ia l s tr e s s ( k n /m 2 ) axial strain (%) c1 c1r1 c1r2 c1r3 c1r4 (b) 0 1 2 3 4 5 6 7 0 100 200 300 400 a x ia l s tr e s s ( k n /m 2 ) axial strain (%) c2 c2r1 c2r2 c2r3 c2r4 (c) fig 5. stress-strain response of clayey soil samples containing (a) 2.5% to 10% rubber; (b) containing 2.5% to 10% rubber and 3% cement after 28 days of curing; (c) containing 2.5% to 10% rubber and 6% cement after 28 days of curing. 5.2.2. energy absorption capacity the energy absorption capacity is defined as an area of the stress-strain curve upto maximum axial stress at failure as indicated in fig 6(a). fig 6(b) show the variation of energy absorption capacity of clayey soil mixed with cement and waste crumb rubber with age of curing. the energy absorption capacity of the rubberized clay containing 6% cement content is found to be more in comparison with rubberized clay containing 3% cement at all curing period. for example, 28 days cured specimen of c1r1 is 3.73 kj/m3, which increases to 9.63 kj/m3 for yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 77 specimen c2r1. the energy absorption capacity of the claycrumb rubber mixtures stabilized with 3% cement decreases with the incorporation of more than 5% rubber content. for example, the energy absorption capacity of specimen c1r2 is 4.64 kj/m3, which decreases to 3.82 kj/m3, and 2.733 kj/m3 for specimen c1r3 and c1r4 respectively. whereas the energy absorption capacity of mix c2r1 and c2r2 is found almost similar i.e. 9.63 kj/m3 and 9.40 kj/m3, and decreases for specimen c2r3 and c2r4.with prolongation of the curing period, the energy absorption capacity of the composites increases. for example, 7 days cured specimen of c2r1 has energy absorption capacity of 8.21 kj/m3, which increases to 9.03 kj/m3 and 9.87 kj/m3 with an increase in the curing period to 14, and 28 days. 0 7 14 21 28 0 3 6 9 12 e n e rg y a b s o rp ti o n c a p a c it y ( k j /m 3 ) curing period (days) c1 c1r1 c1r2 c1r3 c1r4 c2 c2r1 c2r2 c2r3 c2r4 (b) fig 6. (a) schematic diagram for energy absorption capacity (b) energy absorption capacity curing period of the mixes. 5.2.3. unconfined compressive strength the unconfined compressive strength test results of cement stabilized clay mixed with different crumb rubber content and cured for 7, 14 and 28 days are shown in figs 7(a) and 7(b). the unconfined compressive strength of the clay increases with the addition of cement. for example, 28 days ucs of the clay containing 3% cement (specimen c1) is 222.05 kpa, which is approximately 3.7 times greater than clay (specimen s). it is due to the formation of hydration product in the cemented clay mixture, which leads to the strengthening of the specimens. similarly, the unconfined compressive strength of the clay containing 6% cement is found to be approximately 6.73 times more than clay specimens. the unconfined compressive strength of the clay increases with the increase in cement content. it is due to the increase in relative cement per grain contacts points. the unconfined compressive strength of the cement-stabilized clay incorporated with crumb rubber decreases with the increase in rubber content. for example, the ucs of 28 days cured the specimen c1 is 222.05 kpa, which decrease to 168.96 kpa, 122.14 kpa and 96.22 kpa for specimens c1r2, c1r3 and c1r4 respectively. similarly, the ucs of specimen c2 is 405.07 kpa, which decreases to 333.85 kpa, 251.36 kpa and 217.17 kpa for specimens c2r2, c2r3 and c2r4 respectively. these observations are found contrary to results reported by hambirao and rakaraddi (2014). fig 7 reveals that ucs of the cement stabilized clay containing crumb rubber increases with prolonging the age of curing. for example, 7days ucs of specimens c2r2 is 248.40 kpa, which increased to a value of 321.30 kpa and 333.85 kpa after 14 days, and 28 days of curing respectively. it is possibly due to the formation of more hydration products with prolongation of the age of curing. the rate of loss of unconfined compressive strength of cement stabilized clayey soil containing rubber content more than 5% is found more. for example, a loss of 19.4% in ucs is observed for specimen c1r2 as compared to c1r1 and 78 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 38.33% for specimen c1r3 as compared to c1r2. at higher rubber content, the rate of loss of strength is more, which is possible due the (i) governances of the interaction between the rubber to rubber particle, rather than rubber to cemented clay particles (cabalar and karabash, 2015); (ii) difficulty in packing of lightweight rubber particles at higher rubber content create voids (benazzouk et al., 2007); (iii) sliding of the rubber particle, which is not restricted by the interfacial mechanical interaction between rubber and cemented clay particles; (iv) loss of friction and bonding in the mixtures (kim and kang, 2013). 7 14 21 28 0 50 100 150 200 250 u c s ( k p a ) curing period (days) c1 c1r1 c1r2 c1r3 c1r4 (a) 7 14 21 28 0 50 100 150 200 250 300 350 400 450 u c s ( k p a ) curing period (days) c2 c2r1 c2r2 c2r3 c2r4 (b) fig 7. unconfined compression test of the combination. 5.2.4. cracking pattern the vertical cracks were observed in the cement-stabilized specimens as evident from fig 8(a), which was responsible for the brittle behavior and no post-peak strength of the mix. the cracking pattern of cement-stabilized clayey soil specimens incorporated with crumb rubber was observed to have multiple or staggered cracks as shown in fig 8(b) and 8(c). these multiple/staggered cracks enable the specimen to bear the post-failure load. the multiple cracking is possibly due to (i) lower young modulus of rubber compared to cemented clay (guleria and dutta, 2012), (ii) development of elastic reaction under the compression load in crumb rubber (yoshio et al., 2008). it empowers the specimens to have high deformability and energy absorption capacity. fig 8. (a) vertical cracking in cemented clay specimen, (b) & (c) multiple/staggered cracking in cemented clay specimen containing rubber. yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 79 5.3. wet-dry durability test the continuous wetting and drying impact the serviceability and performance of rubberized cemented clay. the durability of the composite depends upon the pore structure, tensile strength, inter-particle friction and cohesion of the materials. the test result of the wet-dry durability in term of weight loss for 7, 28, 90, and 180 days cured specimens are plotted against the number of cycles in fig 9. clay-crumb rubber samples were unable to resist the first cycle of the process and disintegrated completely. similarly, 7 days cured samples of clay containing 3% cement and 2.5%-10.0% crumb rubber could not maintain the volumetric integrity and fail, along with samples of clay containing 6% cement and 7.5% and 10% crumb rubber before the completion of wet and dry process as illustrated in fig 9(a). while rubberized clay containing 6% cement and 2.5% and 5% crumb rubber is successful to endure the complete 12 cycles of wetting and drying. on prolonging the curing period of the specimens before subjected to wet and dry cycle, all the specimens are able to survive the complete process of durability test (except for c1r3, c1r4 and c2r4 specimens) as shown in fig 9(c) and 9(d). 0 2 4 6 8 10 12 100 80 60 40 20 0 w e ig h t lo s s ( % ) number of cycles c1 c1r1 c1r2 c1r3 c1r4 c2 c2r1 c2r2 c2r3 c2r4 (a) 0 2 4 6 8 10 12 100 80 60 40 20 0 w e ig h t lo s s ( % ) number of cycles c1 c1r1 c1r2 c1r3 c1r4 c2 c2r1 c2r2 c2r3 c2r4 (b) 0 2 4 6 8 10 12 100 80 60 40 20 0 w e ig h t lo s s ( % ) number of cycles c1 c1r1 c1r2 c1r3 c1r4 c2 c2r1 c2r2 c2r3 c2r4 (c) 0 2 4 6 8 10 12 100 80 60 40 20 0 w e ig h t lo s s ( % ) number of cycles c1 c1r1 c1r2 c1r3 c1r4 c2 c2r1 c2r2 c2r3 c2r4 (d) fig 9. weight lossnumber of cycles of (a) 7 days, (b) 28 days, (c) 90 days, and (d) 180 days cured specimens. fig 10 shows the variation of weight loss of the specimens with the curing period after completion of 12 wetting and drying cycles. the weight loss of clay mixed with cement decreases with the increase in cement content. for example, for 180 days cured specimen c1, the weight loss is 29.68%, which decreases to 15.02% for the specimen c2. the weight loss of cemented clay incorporated with rubber increased consistently with the increasing rubber content. for 80 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 example, the weight loss of 90 days cured specimen c1 is 38.20% which increased to 49.47% and 55.84% for the specimen c1r1 and c1r2 respectively. the disparate thermal elaboration between rubber and cemented clay during the drying cycle causes the deficiency in the bond strength between crumb rubber and cemented clay. further, the abrasive action of wire brush which was applied after the drying cycle leads to void formation and increases the weight loss (guleria and dutta, 2013). fig 10 shows that the weight loss of specimens containing 3% cement and varying percentages of rubber is higher than that of specimens containing 6% cement and varying percentages of rubber. for example, the weight loss of 49.47% and 55.84% for the specimens c1r1 and c1r2 at 90 days decreased to 25.0% and 30.38% for the specimens c2r1 and c2r2 respectively. the weight loss of rubberized cemented clay specimens decreases with the prolongation of curing period. for example, a weight loss of 45.6% for the specimen c2r1 cured for 7 days decreased to 33.67%, 25.0%, and 17.77%, respectively with the prolongation of the curing period to 28, 90, and 180 days. 0 30 60 90 120 150 180 0 10 20 30 40 50 60 70 w e ig h t lo s s ( % ) curing period c1 c1r1 c1r2 c2 c2r1 c2r2 c2r3 c2r4 fig 10. weight losscuring period of the composites after completion of 12 wetting and drying cycles. according to irc: sp: 89 (2010), the weight loss up to 20% and 30% have been allowed during the wet-dry durability test for cement stabilized material to be used as base, sub-base, and shoulder for road construction. only specimens c2, c2r1, and c2r2 satisfy this criterion of maximum allowable weight loss. therefore, up to 5% inclusion of crumb rubber in clayey soil containing 6% cement is worthwhile from durability aspect. however, more research is required to address the recommendation of pca for the use of proposed composite as road pavement material. fig 11. photographs of the composite cured for180 days during wetting and drying cycles. yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 81 5.4. mineralogical and microscopical studies 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 700 800 in te n s it y ( c o u n ts ) angle (2 theta) xrd c1 1 silica 2 c-s-h 3 calcium silicate 4 calcium carbonate 5 calcium silicate carbonate 6 calcium aluminum silicate hydrate 7 gypsum 8 manganite 9 hercynite 10 dolomite 1, 3,10 1,4 1,8 1,22,7 6 6 6 5 4 89 (a) 10 20 30 40 50 60 70 80 0 100 200 300 400 500 600 700 800 in te n s it y ( c o u n ts ) angle (2 theta) xrd c2 1 silica 2 c-s-h 3 calcium silicate 4 calcium carbonate 5 calcium silicate carbonate 6 calcium aluminum silicate 7 magnesium carbonate 8 magnesium hydroxide 9 hercynite 1,3,5 2 1,6 1 1,4 2 7,8,9 (b) fig 12. xrd pattern of (a) c1, and (b) c2 cured for 28 days. fig. 12(a) and 12(b) shows the xrd pattern of c1 and c2 after 28 days of curing. the crystalline phase present are identified from the peaks in the pattern. due to the inclusion of cement in the clay, changes in the mineralogical composition of mixes are observed. several new peaks of calcium silicate hydrate (c-s-h), calcium aluminium silicate hydrate, calcium carbonate, calcium silicate, calcium silicate carbonate, etc. are visualized. these new peaks confirm the cementing products of hydration and pozzolanic reactions between the clay and cement minerals. there is a reduction in the peaks intensity of quartz from 715.59 to 691.08 respectively, for c1 and c2 indicate the cementitious reactions taken place between the composite leading to the formation of hydration products. kaolinite is completely exhausted which leads to the formation of cessation of the pozzolanic reaction and additional cementitious products. the formation of these cementitious products improved the strength of the composite by enhancing the binding action of cement matrix. fig. 13(a) (e) shows the sem images of the mixtures. the dark portions are assumed voids in the matrix and fibrous crystals indicate c-s-h gel. due to compaction large clay cluster, reduces to small clusters, which lead to reduce the pore space as indicated in fig. 13(a). fig. 13(b) (c) shows micrograph of cement-treated clay specimens (c1 and c2) after 28 days curing. the sem images of c1 are similar to untreated soil sample because lesser amount of cement content as compared to soil mass. as the content of cement increases, the hydration product increases. the increase in the cementitious products fills the pores spaces and enhances the inter-cluster bonding strength as shown in fig. 13(c). the reaction product formation could be clearly observed in the fig. 13(d). the reaction product may be hydrated product like c-s-h and are most likely responsible for the increase in the strength of cement stabilized samples. at the interface of rubber and cement matrix, a gap can be visualized in fig. 13(e) along with micro cracks in the c2r2 specimen. the poor interaction between rubber and cemented clay leads to cracking and ultimately results into reduction in strength of the composite. 82 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 (a) clay (b) c1 (after 28 days) (c) c2 (after 28 days) (d) c-s-h gel (e) c2r2 (after 28 days) fig 13. sem of (a) clay (b) c1 (c) c2 and (d) c-s-h gel (e) c2r2 6. conclusions in the present paper, unconfined compressive strength, and wet-dry durability characteristics of the clayey soil incorporated with crumb rubber and cement were investigated. the conclusions of the investigation are as follows: 1. both maximum dry density and optimum moisture content of the clay decreases with the addition of crumb rubber, whereas inclusion of cement in the rubberized clay leads to decrease in the density and increase the optimum moisture content of the mixtures. 2. the inclusion of crumb rubber in the cement-stabilized clayey soil reduces the ucs. the decrease in ucs was on the higher side with the incorporation of rubber more than 5%. 3. the brittle behavior of the cement-stabilized clay has prosperously overcome with the inclusion of rubber by lowering the rate of loss of post-peak strength. 4. the cement stabilized clay soil mixed with various percentages of crumb rubber has shown an increase in energy absorption capacity by incorporation of rubber content up to 5%. 5. the clayey soil samples mixed with crumb rubber could not show enough durability and disintegrate during the first wet-dry cycle. 6. the weight loss of the clayey soil specimen mixed with cement can be decreased with the inclusion of the higher amount of cement and with the increasing the curing period. 7. the incorporation of rubber (2.5% to 10%) increases the weight loss of cementstabilized clay. 8. the weight loss of 90 days cured specimen of clay incorporated with 6% cement and rubber content up to 5% is observed closure to requirements of irc:sp:89-2010. yadav and tiwari, j. build. mater. struct. (2016) 3: 68-84 83 9. calcium silicate hydrate (c-s-h), calcium aluminium silicate hydrate, calcium carbonate, calcium silicate, calcium silicate carbonate etc minerals are found in the c1 and c2 specimens from xrd analysis. the formation of cementation products became more dense and compact as cement content increases. 10. from the sem images, the c-s-h gel formation is clearly seen in the cemented clay rubber mixture, which is the main governing force in the composite. 11. the presence of gap between the rubber and cemented clay is an indication of weak interfaces resulting into strength reduction in the composite. the results of tests presented in this research paper have confirmed that the inclusion of crumb rubber and cement in the clayey soil effects unconfined compressive strength and wet-dry durability properties. the results reveal that the crumb rubber up to 5% can be significantly incorporate with cement-stabilized clayey soils. the proposed composite can be a good material for use in base, sub-base, and shoulder in road construction having low traffic volume and lightweight fill material behind the retaining wall. the enormous utilization of waste crumb rubber for improving geotechnical properties uncemented/cemented clay helps to solve the health and environmental problems associated with the disposal of this hazardous waste. 7. references akbulut, s., arasan, s., kalkan, e. (2007). modification of clayey soils using scrap tire rubber and synthetic fibers. appl. clay sci. 38, 23–32. al-tabbaa, a., blackwell, o., porter, s.a. (1997). an investigation into the geotechnical properties of soiltyre mixtures. environ. technol. 18, 855–860. astm d 6270 98, standard practice for use of scrap tires in civil engineering applications. atma (2015). traction, a newsletter of automotive tyre manufacturers association, 5(4),1-16. available online in: http://www.atmaindia.org/pdf/traction-newsletter-aug-2015.pdf beena, a., binod, t., janak, k. (2016). geotechnical properties of clays modified with recycled crumb rubber, in: geotechnical and structural engineering congress 2016. pp. 1404–1413. benazzouk, a., douzane, o., langlet, t., mezreb, k., roucoult, j. m., & quéneudec, m. (2007). physicomechanical properties and water absorption of cement composite containing shredded rubber wastes. cement and concrete composites, 29(10), 732-740. bhattacharja, s., bhatty, j. (2003). comparative performance of portland cement and lime in stabilization of moderate to high plasticity clay soils. portl. cem. assoc. cabalar, a. f. and karabash, z. (2015). california bearing ratio of a sub-base material modified with tire buffings and cement addition, journal of testing and evaluation, 43(6), 1–9. cabalar, a.f., karabash, z., mustafa, w.s. (2014). stabilising a clay using tyre buffings and lime. road mater. pavement des. 15, 872–891. cokca, e., yilmaz, z. (2004). use of rubber and bentonite added fly ash as a liner material. waste manag. 24, 153–164. guleria, s.p., dutta, r.k. (2011). unconfined compressive strength of fly ash – lime – gypsum composite mixed with treated tire chips. j. mater. civ. eng. 23, 1255–1263. guleria, s.p., dutta, r.k. (2012). effect of addition of tire chips on the unconfined compressive strength of fly ash-lime-gypsum mixture. int. j. geotech. eng. 6, 1–13. guleria, s.p., dutta, r.k. (2013). durability and leachate analysis of fly ash–lime-gypsum composite mixed with treated tire chips. journal of geoengineering, 8(2), 33-40. hambirao, g.s., rakaraddi, p.g. (2014). soil stabilization using waste shredded rubber tyre chips. iosr j. mech. civ. eng. 11, 20–27. ho, m., chan, c. (2010). the potential of using rubberchips as a soft clay stabilizer enhancing agent. mod. appl. sci. 4, 122–131. 84 yadav and tiwari., j. build. mater. struct. (2016) 3: 68-84 irc:sp:89 (2010). guidelines for soil and granular material stabilization using cement lime &fly ash, published by indian roads congress, new delhi. is : 1498( 1970).classification and identification of soils for general engineering purposes, bureau of indian standards, new delhi (reaffirmed 2007). is : 2720 (1980). methods of test for soils, determination of water content-dry density relation using heavy compaction, part viii, bureau of indian standards, new delhi (reaffirmed 2011). is : 2720 (1991). methods of test for soils, determination of unconfined compression test, part x, bureau of indian standards, new delhi (reaffirmed 2006). is : 4332 (1968). methods of test for stabilized soils,part iv wetting and drying and freezing and thawing tests for compacted soil-cement mixtures. kim, y.t., kang, h.s. (2013). effects of rubber and bottom ash inclusion on geotechnical characteristics of composite geomaterial. mar. georesources geotechnol. 31, 71–85. otoko, g.r., pedro, p.p. (2014). cement stabilization of laterite and chikoko soils using waste rubber fibre. int. j. eng. sci. res. technol. 3, 130–136. prasad, a.s., ravichandran, p.t., annadurai, r., rajkumar, p.r.k. (2014). study on effect of crumb rubber on behavior of soil. int. j. geomatics geosci. 4, 579–584. robani, a.r., chan, b.c.m. (2008). unconfined compressive strength of clay stabilized with cement-rubber chips. in: seminar on unconfined compressive strength of clay stabilized with cement-rubber chips, uthm. shahin, m., hong, l. (2010). utilization of shredded rubber tires for cement-stabilized soft clays, in: ground improvement and geosynthetics proceedings of the geoshanghai international conference (2010). pp. 181–186. srivastava, a., pandey, s., rana, j. (2014). use of shredded tyre waste in improving the geotechnical properties of expansive black cotton soil. geomech. geoengin. 9, 303–311. tang, c., shi, b., gao, w., chen, f., cai, y. (2007). strength and mechanical behavior of short polypropylene fiber reinforced and cement stabilized clayey soil. geotext. geomembranes 25, 194–202. wang, f. c., & song, w. (2015). effects of crumb rubber on compressive strength of cement-treated soil. archives of civil engineering, 61(4), 59-78. yadav, j.s., tiwari, s.k. (2016). behaviour of cement stabilized treated coir fibre-reinforced clay-pond ash mixtures. j. build. eng. 8, 131–140. yoshio mitarai, yoshiaki kikuchi, kazuya yasuhara, jun otani, t.n. (2008). the ductility of cement treated clay with added scrape tire chips and the change of its permeability under shear deformation. japanese society civ. eng. 64, 181–196 (in japanese).