65 Journal of Sustainable Architecture and Civil Engineering 2017/2/19 *Corresponding author: danute.palubinskaite@ktu.lt Alkaline Activation of Hybrid Cements Binders Based on Industrial by-Products Received 2017/03/27 Accepted after revision 2017/05/25 Alkaline Activation of Hybrid Cements Binders Based on Industrial by- Products JSACE 2/19 http://dx.doi.org/10.5755/j01.sace.19.2.17836 Vytautas Bocullo, Danutė Vaičiukynienė* Kaunas University of Technology, Faculty of Civil Engineering and Architecture Studentų st. 48, LT-51367 Kaunas, Lithuania Aras Kantautas Kaunas University of Technology, Faculty of Chemical Technology, Radvilėnų rd. 19, Kaunas 5025 Ruben P. Borg, Charlo Briguglio Department of Construction & Property Management, Faculty for the Built Environment Built Environment Building, Room 213, University of Malta, Msida, MSD 2080, Malta Journal of Sustainable Architecture and Civil Engineering Vol. 2 / No. 19 / 2017 pp. 65-73 DOI 10.5755/j01.sace.19.2.17836 © Kaunas University of Technology Introduction Environmentally friendly building materials are becoming increasingly relevant in civil engineering in view of their contribution toward sustainable development. This research is focused on hybrid geopolymer concrete (geopolymer with ordinary Portland-cement (OPC) additive) with the objective of analysing strength development. In this research, hybrid geopolymer concrete, manufactured using biomass bottom ash, fly ash and production waste from the manufacture of aluminium fluoride (silica gel) with 4 different amounts of OPC (0%, 5%, 10% and 15%) is studied. Each blend is cured at a temperature of 50 0C and the material is tested after 7, 14 and 28 days. X-ray powder diffraction and energy-dispersive X-ray spectroscopy were used as investigation methods. The purpose of research was to study the chemical composition and the strength development in hybrid geopolymer concrete made from OPC and the industrial by-products mentioned above. Keywords: alkali – activated cements, fly ash, geopolymer, hybrid concrete. Ordinary Portland-cement (OPC) is the most common building material in the world (Turner and Collins 2013)an alternative binder based on fly ash (a fine waste collected from the emissions lib- erated by coal burning power stations, but manufacturing OPC results in significantly high energy consumption, due to the high temperatures required. Production of 1 t of OPC produces nearly 1 t of CO2, which all in all accounts for around 7% of annual CO2 emissions (Turner and Collins 2013) an alternative binder based on fly ash (a fine waste collected from the emissions liberated by coal burning power stations. This is not only environmentally unfriendly due to the high carbon foot- print of the material, but can have significant economic disadvantages due to additional taxes on products (Turner and Collins 2013)an alternative binder based on fly ash (a fine waste collected from the emissions liberated by coal burning power stations. All of this encourages further research on alternative binders instead of OPC. Geopolymer concrete (GC) is a relevant alternative to OPC. Geopolymer concrete can significantly reduce the amounts of OPC consumed. In addition different production wastes (like fly ash, high furnace slag and any other waste material that has high quantities of SiO2 and Al2O3) can be utilized during manufactur- Journal of Sustainable Architecture and Civil Engineering 2017/2/19 66 ing of the concrete. Research suggests that GC has a higher resistance to fire, and improved per- formance at elevated temperatures (Abdulkareem et al. 2014)mortars and lightweight aggregate geopolymer concrete (LWAGC and in the case of acid attack (Ariffin et al. 2013). Recently more attention has been given to research in geopolymer concrete containing OPC as an additive. These cements form when blends containing low proportions of cement and high pro- portions (60-70 %) of mineral additions (slag, fly ash or metakaolin) are alkali activated. According to Posi et al. (2016) the incorporation of OPC enhances the strength development of lightweight geopolymer concrete with a slight increase in the density. Posi et al. determined the optimum OPC content as 10% OPC replacement level of fly ash. The optimum curing temperature curing proposed was 60 °C. Concrete with a density of 1400 kg/m3 and a strength of 14.5 MPa was obtained using a similar mix design with 10% OPC and curing temperature set at 60 °C. García-Lodeiro et al. reviewed the fundamental chemistry governing these new reactive systems. The authors also analyses the nature of the reaction products formed and their compatibility under different reaction conditions (2012). In the research the reaction mechanism involves a number of stages in which the original gels form in the OPC hydration, C-S-H gel and the gel precipitated in the alkali activation of alumi- nosilicates, N-A-S-H gel, evolve to C-A-S-H and (N,C)-A-S-H respectively (Inés García-Lodeiro et al. 2012). Pangdaeng et al. (2014) stated that the use of OPC as additive had improved the properties of high calcium fly ash geopolymer. The strength increased due to the formation of additional C–S–H and C–A–S–H gel. Curing conditions significantly affected the properties of geopolymers. C-S-H/N-A-S-H mix of gels precipitating, did not precipitate in a pure state. Rather their compo- sition was affected by the presence of dissolved species. In the presence of aluminium C-S-H gel development was as follows: C-S-H → C–(A)–S–H → C-A-S-H, whilst in the presence of calcium, N-A-S-H gel evolved as follows: N-A-S-H → (N,C)-A-S-H → C-A-S-H. This last conversion is not complete in these systems because the amount of calcium present is thought to be insufficient (I. García-Lodeiro, Fernández-Jiménez, and Palomo 2013). Nath and Sarker (2015) used OPC to improve the setting and early strength properties of low cal- cium fly ash geopolymer concrete cured at room temperature. In the research they concluded that the presence of OPC accelerated the geopolymerisation reaction and the compactness of the gel increased with an OPC content (P. Nath and Sarker 2015). Shinde and Kadam (2016) reported that GC with OPC gives better compressive strength when compared to GC cured at ambient temperature. In this article the development of strength and the chemical composition of hybrid GC with OPC and additive from biomass bottom ash (BMBA), coal fly ash (FA) and production waste of alumin- ium fluoride (PW) is studied. The aim of the research is to analyse how additional OPC affects the chemical composition and the development of strength during the first 28 days. The mineral composition of the material was analysed through X-ray diffraction (XRD) using on the “D8 Advance” diffractometer (Bruker AXS, Karlsruhe, Germany). The device parameters were set as follows: tube voltage - 40 kV; current - 40 mA The X-ray beam filter - Ni 0.02 mm, scanning range 2θ = 3–60°. Diffraction patterns were recorded in a Bragg-Brentano geometry using a fast counting detector “Bruker LynxEye” based on silicon strip technology. Samples for chemical composition analysis (XRD) were prepared separately without aggregate to avoid peaks that belong to minerals such as quartz in the sand aggregate. These samples were prepared keeping the same proportions and molar ratios as for the mortar samples and kept in same curing conditions. The XRF analysis of raw materials were performed on the fluorescence spectrometer “S8 Tiger” (Bruker AXS, Karlsruhe, Germany) operating at the counter gas helium 2 bar. The compressive and flexural strength of mortar samples was deter- mined using a hydraulic machine “ToniTechnik 2020” at 7, 14 and 28 days. The mechanical properties including compressive and flexural strength of samples were determined in accordance to BS EN 196- 1:2005. The sample size, load rate and other experimental parameters refer to the standard. Methodology 67 Journal of Sustainable Architecture and Civil Engineering 2017/2/19 SiO2 and Al2O3 sources Three different industrial by-products, were used as raw materials. All materials used were a– source of SiO2 and Al2O3; main components of geopolymer chains. The raw materials used were the following: biomass (timber) bottom ash (BMBA), coal fly ash (FA) and AlF3 Production waste (PW). BMBA was sourced from a Lithuanian biofuel boiler house. This type of ash contains large amounts of CaO. The XRD analysis for this material (Fig. 1) shows peaks of mullite and quartz and also the halo peak at 2θ 25o – 35o indicates the presence of amorphous SiO2. Its chemical composition is given in table 1. Materials Fig. 1 XRD analysis 0 10 20 30 40 50 60 In te ns ity , a . u . 2, deg. FA PW Q CC CC Q Q CA CCCA CA Q Q Q BMBA Z Z M M M MM M Z M M M Q Q Q A AAAA AA A AAA AA A A AA Q Q T T T T TTT T OPC B S BSB D D D D D Coal burning FA is one of the most popular raw materials for geopolymer concrete due to its near perfect chemical composition: FA contains large amounts of SiO2 and Al2O3. These oxides form minerals of quartz and mullite according to the XRD analysis. Amorphous SiO2 forms a halo peak at 2θ 20o – 30o. Since annual FA output is over 500 Mt it is important to utilize this waste rather than landfill it. The chemical compositions of this material are given in table 1. AlF3 production waste consists of SiO2·nH2O, where SiO2 is in the amorphous state. AlF3 production waste is a silicahexaflouride acid neutralisation product. This acid is obtained from the manufac- ture of phosphoric acid. The silicahexaflouride process reaction (1) is as follows: (1) The XRD analysis shows that the material consists of crystalline AlF3 · 3.5 H2O (Fig. 1). The “halo” peak at 2θ 20o – 30o in the XRD analysis indicates the presence of amorphous SiO2. The chemical composition is presented in table 1. Notes: A - AlF3 · 3.5H2O, M – mullite, Q – quartz, T – alite, D – belite, B –Brownmillerite, S – Bassanite, Z - Anorthoclase, CA – calcium oxide, CC – calcium carbonate. Journal of Sustainable Architecture and Civil Engineering 2017/2/19 68 Table 1 Chemical composition of raw materials (XRF Analysis) Oxide amount, % Oxide amount, % FA BMBA PW OPC FA BBF PW OPC CaO 3.683 48.978 0,42 57.4 ZrO2 0,147 0,039 0 0.016 SiO2 49.468 22,39 72,23 14.3 SO3 0,921 0 0 4.70 Na2O 0,945 0,281 0 0 ZnO 0,05 0,041 0 0 Al2O3 27.452 2.509 5,68 3.63 TiO2 1.658 0,328 0 0.231 MnO 0,063 0,347 0 0.0428 CuO 0,027 0,02 0 0 MgO 1.699 8.286 0 2.36 NiO 0,031 0 0 0 K2O 4.539 8.686 0 1.33 PbO 0,038 0 0 0 Fe2O3 7.379 2.179 0,66 3.29 Cl 0 0,04 0 0 BaO 0,436 0,161 0 0 Rb2O 0 0,024 0 0 P2O5 1.310 5.048 0 0.392 F 0 0 21,01 0 SrO 0,106 0,06 0 0.0817 Aggregate Standard BS EN 196-1 sand was used as aggre- gate for mortar. Standard sand is natural siliceous sand consisting mostly of rounded particles with silica content of at least 98%. Sand is thoroughly washed, dried and accurately graded. The grading range is provided by manufacturer and presented in Table 2. Table 2 Grading range of aggregate Size in mm Cumulative retained, % 2,00 0 1,60 7 ± 5 1,00 33 ± 5 0,50 67 ± 5 0,16 87 ± 5 0,08 99 ± 1 Portland-cement Portland-cement is used as additive to contribute through additional C-S-H gel in the geopolymer concrete system (Yip et al. 2008). This is expected to improve the mechanical properties (flexural and compressive strength). In this research CEM I 42.5 R is used. The XRD analysis shows the presence of alite, belite, brownmillerite and bassanite – typical clinker minerals (Fig. 1). In this research prisms (size 40 x 40 x 160 mm) were tested for the flexural and compressive strength. There were 9 prisms produced for each batch and these were tested after 7, 14 and 28 days. During the experimental period, the prisms were kept in the oven at a temperature of 50 °C. An elevated temperature is proven to have a positive effect on geopolymerisation (S. K. Nath et al. 2014). The composition of the mixtures is presented in Table 3. Results and discussion Additional OPC additive had different effects on the samples produced using different materials (Fig. 2, Fig. 3). In most of the cases OPC additive contributed significantly in improving the com- pressive (Fig. 3) and flexural strength (Fig. 2) especially when the raw material was FA and PW. The s control mix (0 % OPC) of the FA samples achieved 5.75 MPa flexural (Fig. 2a) and 29.67 MPa compressive strength (Fig. 3a) after 28 days. Samples with 5% OPC additive achieved 6.02 MPa flexural (Fig. 2b) and 44.60 MPa compressive (Fig. 3b) strength. Furthermore, within 14 days these samples reached 93% of the final flexural and 98% of the final compressive strength, while control samples reached only 59% and 61% respectively. FA samples with 15% substitute of OPC gained the biggest strength: after 28 days flexural strength was 8.02 MPa and compressive strength 50.99 69 Journal of Sustainable Architecture and Civil Engineering 2017/2/19 Table 3 Mixtures composition Mixture design Mix 1 Mix 2 Mix 3 Mix 4 FA Geoplymer Aggregate, g 1350.00 Water, g 244.46 NaOH, g 171.85 FA, g 740.04 703.04 666.04 629.04 OPC, g 0.00 37.00 74.00 111.01 SiO2/Na2O molar ratio 2.70 2.61 2.52 2.43 Al2O3/SiO2 molar ratio 0.33 0.32 0.32 0.32 CaO/SiO2 molar ratio 0.08 0.14 0.21 0.28 BMBA Geoplymer Aggregate, g 1350.00 Water, g 327.53 NaOH, g 95.78 BMBA, g 740.04 703.04 666.04 629.04 OPC, g 0.00 37.00 74.00 111.01 SiO2/Na2O molar ratio 2.24 2.21 2.17 2.13 Al2O3/SiO2 molar ratio 0.07 0.07 0.07 0.07 CaO/SiO2 molar ratio 2.34 2.41 2.47 2.54 PW Geoplymer Aggregate, g 1350.00 Water, g 244.46 NaOH, g 214.00 PW, g 740.04 703.04 666.04 629.04 OPC, g 0.00 37.00 74.00 111.01 SiO2/Na2O molar ratio 3.33 3.20 3.06 2.93 Al2O3/SiO2 molar ratio 0.05 0.05 0.05 0.05 CaO/SiO2 molar ratio 0.01 0.05 0.1 0.15 MPa, which amounts to an additional 20 MPa (Fig. 3d) when compared to samples without ad- ditional OPC. Similar observations can be noticed in samples with 15% OPC additive (Fig. 2d and Fig. 3d). Only samples with 10% OPC substitute did not present improvement with respect to the compressive strength, for reasons yet to be understood (Fig. 3c). The decrease of compressive strength can occur due to modified zeolite in the system. The mod- ified hydrosodalite possesses, the great surface and water absorption and the early strength of hardened cement paste might decrease when zeolite percentage increases (Janotka, 1995). BMBA samples didn’t develop additional compressive strength or in some cases even experi- enced a reduction in compressive strength on addition of OPC in the blends. In general, with some exceptions, samples lost flexural strength while compressive strength remained the same as for the control sample. Geopolymer with BMBA gained most of its strength within the first 7 days and later compressive and flexural strength remained the same irrespective on whether additional OPC was used or not. PW samples with the OPC substitute, similarly to FA samples FA, gained additional compres- sive and flexural strength. But unlike samples with FA, PW samples experienced an increase in strength (flexural and compressive) with a 5% OPC substitute. However higher levels of substi- tution of OPC did not contribute more to the mechanical properties (flexural and compressive strength). Nevertheless, PW samples were noted to be the weakest in general, among the materi- Journal of Sustainable Architecture and Civil Engineering 2017/2/19 70 Fig. 2 Flexural strength of hardened binder: (a) – 0% OPC, (b) – 5% OPC, (c) – 10% OPC, (d) – 15% OPC Fig. 3 Compressive strength of hardened binder, (a) - 0% OPC, (b) – 5% OPC, (c) – 10%, (d) – 15% OPC a c b d a c b d 71 Journal of Sustainable Architecture and Civil Engineering 2017/2/19 als tested, even with the gain of additional compressive and flexural strength due to the OPC sub- stitute. Exceptions were noted at 7 days for flexural strength with 10 % OPC substitute – the only time when PW samples showed larger flexural strength than FA and BMBA samples, and at 14 a Fig. 4 XRD analysis of hardened binder. (a) Fly ash; (b) biomass bottom ash; (c) AlF3 production waste (silicagel) days with 5 % OPC sub- stitute (Fig. 2c), where PW samples were stron- ger than BMBA samples (Fig. 2b). Separate hardened ma- terial samples without aggregate were prepared in order to determine the chemical composition of the binder through XRD analysis. Two composi- tions of each raw ma- terial were selected to be tested – without OPC (control) and with 15% OPC substitute (the max- imum substitute in this experiment) to see what difference additional OPC contributes to, with re- spect to the chemical composition in hardened samples. Samples with FA and 15% OPC additive result- ed in the largest gain in compressive and flexural strengths. XRD analysis of the binder showed that additional OPC formed C-S-H, which should have contributed to strength development, because it is the prima- ry binding agent in OPC concrete (Fig. 4a). Despite C-S-H forma- tion in hardened binder samples of BMBA, con- crete samples didn’t gain strength in most of the cases. This phenome- non could be explained through the formation of b c Notes: Z – sodium zeolite (31-1271); M- mullite (84-1205), A – alite (13-272), K – calcium silicate hydrate (33–306), Q – quartz (78–1252), CA – portlandite (44-1481), CC – calcite (81-306), C – fluorite (2-1203), N – villiaumite (36–1455, D – larnite (33-302). Journal of Sustainable Architecture and Civil Engineering 2017/2/19 72 portlandite (Ca(OH)2) – the portlandite peaks in the XRD showed the presence of this compound (Fig. 4b). This is a relatively weak compound and doesn’t contribute to strength development. It is possible that the larger quantity of CaO (48.98%) contributed, to this and that there was not enough SiO2 to react. BMBA contains only 22.39 % of SiO2, while FA contains 49.47%. Despite the fact that PW mortar samples were significantly the weakest, just like FA samples PW samples gained additional strength. The XRD analysis of the binder revealed the additional formation of zeolites and C-S-H gel in the system (Fig. 4c). The raw material consists mainly of amorphous SiO2 (over 70%) and only a fraction of CaO (0.42%). According to the results obtained, it can be concluded that OPC can be effectively used in geopoly- mer concrete as additive to increase the mechanical properties of concrete, whilst noting specific issues. The following observations are presented: _ Part of the raw materials used for geopolymer concrete could be substituted with OPC. The presence of OPC increases the flexural and compressive strength. The biggest strength gain was observed after 28 days with FA samples: geopolymer concrete samples reached 29.67 MPa compressive strength and those with 15% additive of OPC increased strength up to 50.99 MPa. _ Samples with 5% OPC additive gained strength more rapidly: after 14 days, 98% of its final strength was reached, while samples without OPC reached only 61%. _ The decrease in compressive strength could be caused by the formation of modified zeolite, which, according to literature, increases water absorption. _ Analysis of the chemical composition revealed that OPC forms C-S-H gel – the primary bind- er in ordinary concrete. In PW samples, additional OPC resulted in the formation of zeolites. _ If raw material has relatively small amount of SiO2 and contains a lot of CaO, which is often the case with type C fly ash, the addition of OPC can result in a decrease in strength in the sample, because of the formation (Ca(OH)2). In general, the research indicated that out of the three industrial by-products considered, the FA performed significantly better. While the geopolymer binder performed satisfactorily, the addition of OPC as a partial replacement of geopolymer binder resulted in significant increase in mechan- ical properties of the material. Conclusions Abdulkareem, O. A. et al. Effects of Elevated Tem- peratures on the Thermal Behavior and Mechan- ical Performance of Fly Ash Geopolymer Paste, Mortar and Lightweight Concrete. Construction and Building Materials, 2014; 50: 377–87. https://doi. org/10.1016/j.conbuildmat.2013.09.047 Ariffin, M.A.M. et al. Sulfuric Acid Resistance of Blended Ash Geopolymer Concrete. Construction and Building Materials, 2013; 43: 80–86. https://doi. org/10.1016/j.conbuildmat.2013.01.018 Pornnapa Kasemsiri b, Prinya Chindaprasirt c García-Lodeiro, Fernández-Jiménez I., A., Palomo A. Variation in Hybrid Cements over Time. 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Construction and Building Materials, 2013; 43: 125–30. https:// doi.org/10.1016/j.conbuildmat.2013.01.023 VYTAUTAS BOCULLO PhD Student Kaunas University of Technology, Faculty of architecture and civil engineering, department of building Materials Main research area Alkali activated and geopolymer concrete Address Studentų st. 48 LT51367 Kaunas, Lithuania Tel.+37068248654 E-mail: Vytautas. bocullo@ktu.edu DANUTĖ VAIČIUKYNIENĖ Professor Student at Kaunas University of Technology, Faculty of architecture and civil engineering, department of building Materials Main research area Zeolites, Alkali activated and geopolymer concrete, By- products of chemical industry Address Studentų st. 48 LT51367 Kaunas, Lithuania E-mail: Danute. paliubinskaite@ ktu.edu ARAS KANTAUTAS Assoc. Professor Kaunas University of Technology, Department of Сhemical Technology Main research area Building materials, Supplementary cementitious materials, zeolite synthesis. Address Radvilėnų av. 19 LT5025 Kaunas, Lithuania E-mail: aras.kantautas@ ktu.lt RUBEN PAUL BORG Senior Lecturer University of Malta Main research area Concrete, Cement Bound Materials Address Department of Construction & Property Management, Faculty for the Built Environment, Built Environment Building, Room 213, University of Malta, Msida, MSD 2080, Malta Tel. (+356) 79055680 E-mail: ruben.p.borg@ um.edu.mt CHARLO BRIGUGLIO Student University of Malta Main research area Concrete Address Department of Construction & Property Management, Faculty for the Built Environment, Built Environment Building, University of Malta, Msida, MSD 2080, Malta About the authors