Microsoft Word - numero_64_art_03_3910.docx D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 31 Effect of date palm and polypropylene fibers on the characteristics of self-compacting concrete: comparative study Dounia Derdour, Mourad Behim, Mohammed Benzerara Materials, Geomaterials and Environment Laboratory (LMGE), Faculty of Technology, Department of Civil Engineering, Badji Mokhtar- Annaba University, P.O. Box 12, 23000, Annaba, Algeria douniaderdour@hotmail.com; dounia.derdour@univ-annaba.dz mbehim@yahoo.fr; mourad.behim@univ-annaba.dz mohammed.benzerara@yahoo.com; mohammed.benzerara@univ-annaba.dz ABSTRACT. This article presents the results of a comparative experimental study on the influence of date palm fibers to replace polypropylene fibers used as reinforcement in self-compacting concrete (SCC). Indeed, the use of polypropylene fibers makes it possible to reduce the plastic shrinkage of concrete. Date palm fibers have mechanical characteristics (tensile strength and elasticity modulus) largely sufficient to replace polypropylene fibers. The use of natural fibers has several advantages, they are natural, renewable, have no effect on the environment and require little energy for their transformation unlike synthetic fibers. In this comparative study, polypropylene fiber is used as a control material and date palm fiber as a study material. The results obtained show that the two types of fibers decrease the fluidity and the compressive strength, increase the flexural strength and decrease the shrinkage. Date palm fibers delay the appearance of cracks more than polypropylene fibers. Date palm fibers guarantee the best results of SCC in fresh and hardened state. KEYWORDS. Self-compacting Concrete, Fibers, Workability, Mechanical behavior, Shrinkage, Environment. Citation: Derdour, D., Behim, M., Benzerara, M., Effect of date palm and polypropylene fibers on the characteristics of self-compacting concrete: comparative study, Frattura ed Integrità Strutturale, 64 (2023) 31-50. Received: 15.10.2022 Accepted: 12.01.2023 Online first: 15.01.2023 Published: 01.04.2023 Copyright: © 2023 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. INTRODUCTION he use of plant fibers as reinforcement in building materials has existed for a long time. Raw earth bricks reinforced with straw are an example. However, the transition from the traditional clay matrix to the cement matrix is relatively recent, yet plant fibers are locally available, renewable, less polluting [1–7] and require little energy for their transformation compared to synthetic fibers [8–12]. The reinforcement of mortars and concretes with fibers dates back to the beginning of the 19th century [13] and the use of vegetable fibers in these materials dates back to the seventies of the 19th century, when the first works aimed to replace asbestos fiber in the elements prefabricated [14]. Since then, many studies have been conducted on the use of plant fibers in cement matrix [15–18]. These works fall within the context of T https://youtu.be/UTlwrzd_kIA D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 32 sustainable development and are encouraged by Brundtland report [19] on the preservation of non-renewable natural resources. The most studied natural fibers, with the aim of replacing synthetic fibers in concretes and mortars are flax (linen) [20,21], bamboo [17], coconut [22,23] and hemp fibers [24]. Other natural fibers have also been studied, notably straw, sisal, jute, bagasse…etc. [25–31]. In Algeria, studies on the use of plant fibers in concrete and mortar are recent. These works concerning vegetable fibers that are available in Algeria such Diss [1,4–7], Alfa [7,32–34] and date palm fibers [4,7,35,36]. The number of date palms of different species is estimated at 18 million feet in Algeria, cultivated over an area of 165,000 hectares [4,37], generating more than 200 tons of waste deposited in landfill or burned [4,36]. In our study which aims at the elaboration of self-compacting fiber-reinforced concrete, we are interested in date palm fiber because it has asperities with significant roughness and interesting mechanical characteristics depending on varieties according to the regions of the date palm. Tensile tests measurement shows that date palm fibers presents an average tensile strength of 80-200 MPa, Young modulus of 2-10 GPa and elongation 2-10 mm [7,11,36,38,39]. It also has very significant water absorption, which limits cracking at a young age by reducing plastic shrinkage. The use of fibers in concrete makes it possible to confer a better resistance to the propagation of cracking, to reduce the fragility of the material, to improve the tensile strengths, to bending and to shocks as well as the improvement of ductility [11,35,40]. The objective of this study is the valorization of date palm fiber as reinforcement in self-compacting concrete. This is to replace the polypropylene fiber traditionally used. SCC is extremely fluid and its placement in the formwork does not require vibration [41]. This characteristic is obtained by using a super plasticizer, a large volume of paste varying from 300 to 400 (l/m³) limiting the quantity of coarse aggregates and their size [42], thus making them more susceptible to shrinkage [43] and cracking. Seven SCC are formulated, a reference SCC noted (RSCC) (without fibers), three control SCC with polypropylene fiber noted (PPSCC6, PPSCC9 and PPSCC12) and three study SCC with date palm fiber noted DPSCC6, DPSCC9 and DPSCC12). The fiber dosages are 600, 900 and 1200 g/m3. The results obtained on the PDSCC were compared with those obtained from the PPSCC in the fresh state (slump flow, filling ability and stability) and in the hardened state (compressive, flexural strength, shrinkage, and capillary water absorption). The use of date palm fibers in comparison with polypropylene synthetic fibers in SCC could constitute an interesting alternative on the environmental and the technic-economic levels. MATERIALS USED AND EXPERIMENTAL METHODS Materials: Cement he cement used in this study is a compound Portland cement CPJ-CEM II 42.5 comes from the Hdjar Essoud cement plant (Skikda, eastern Algeria) resulting from a simultaneous grinding of clinker (80%), granulated slag (20%) and gypsum (5%) conforming to the standard NA 442 [44]. The physic-mechanical characteristics of cement is given in Tab. 1. Characteristics Units Values Apparent density g/cm3 1.02 Absolute density g/cm3 3.01 Normal consistency % 28 Start of take h/min 2/37 End of take h/min 4/12 Refusal to the sieve 0.08 mm % 5 Table 1: Physic-mechanical characteristics of cement [45,46]. Materials: Aggregates Two sands are used in this study: a fine siliceous sand, coming from Ouargla region (eastern Algeria) and a quarry sand resulting from the crushing of limestone rocks from Skikda region. Two fractions of gravel used in this work: (3/8) and (8/16) resulting from the crushing of limestone rocks from Skikda. The physical characteristics of the study aggregates are shown in Tab. 2 and the particle size composition is represented by Fig. 1. T D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 33 Characteristics Units Silica sand Quarry sand Gravel 3/8 Gravel 8/16 Apparent density (NF EN 1097-3) kg/m³ 1620 1690 1450 1590 Absolute density (NF EN 1097-3) kg/m³ 2590 2790 2700 2680 Fineness modulus (XP P 18-540) % 1.89 3.09 / / Sand equivalent (NF EN 933-8) % 89.7 88 / / Los Angeles test (P 18-573) % / / 20 20 Micro Deval test (NF EN 1097-1) % / / 9.29 9.29 Table 3: Characteristics of aggregates [47–51]. Figure 1: Granulometric curves of the aggregates used (NF P 18-560) [52]. Materials: Limestone Filler The limestone filler used in this study is a calcium carbonate in powder form (derived from limestone rock waste and ground to a fineness greater than that of cement) with a CaC03 content equal to 98%. Its trade name is Bexcar 10N by SNC Bexcar Benbrahim in El-Khroub, Constantine (eastern Algeria). Tabs. 4 and 5 give the physical properties and chemical composition of the limestone filler used. Elements CaO Al2O3 SiO2 Fe2O3 MgO Na2O Cl- K2O SO3 P.A.F Content (%) 55 0.11 0.50 0.06 0.20 0.08 0.27 0.01 0.06 42.5 Table 4: Chemical composition of limestone filler according to the producer. D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 34 Characteristics Units Limestone Apparent density kg/m³ 790 Absolute density kg/m³ 2700 Fines content (refusal to the 0.08 mm sieve) (%) 4.3 Blaine Specific Surface (cm2/g) Table 5: Intrinsic characteristics of the limestone fillers used. Materials: Adjuvant The adjuvant used is a water-reducing plasticizer under the name "VISCCOCRETE 3045" manufactured by the Algerian company SIKA. It is non-chlorinated, ready-to-use adjuvant and based on modified poly-carboxylates, which comes in the form of a brown liquid. It makes it possible to obtain a long rheology maintenance (>1H30), whose physical and chemical characteristics are given in Tab. 6. Adjuvant VISCCOCRETE 3045 Physical state Liquid Color Chestnut Density 1.11±0.02 pH 5±1 Cl ion content ≤0.1% Na2O ion content 36.04±1.8% Table 6: Physical and chemical properties of plasticizer used according to the producer [53]. Materials: Polypropylene fibers The polypropylene fibers used are marketed by the Algerian company “SIKA” (Fig. 2). Polypropylene fibers are used as a control fiber in the composition of self-compacting concrete reinforced with polypropylene fiber (PPSCC). The technical characteristics of polypropylene fibers are given in Tab. 7. Figure 2: Polypropylene fibers. D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 35 Characteristics Units Polypropylene fibers Color - White Diameter μm 25 (±10%) Length mm 12 (±10%) Density g/cm³ 0.91 Tensile strength N/mm² 300-400 Fusion point °C 160-170 ignition point °C 570 Elongation % ≥ 120 Number of fibers per kg 120×106 Young's modulus kN/mm 3 Table 7: Technical characteristics of polypropylene fibers used [54]. Materials: Date palm fibers mesh The date palm fibers used in this study come from palm trees at Ouargla region (eastern Algeria). The fibers are naturally woven date palm surface fibers. They are formed by the superposition of three trellis plates. They are extracted from the trunk of the palm in plate form. The preparation of fibers consists of separating fibers pads into fibers, which are cut to the desired length as shown in Fig. 3. The cutting of the fibers is done in a shredder with parallel-cut knife mill. The length of the fiber depends on the shredding speed (adjustable) [55]. Figure 3: Preparation of date palm fibers mesh. The length of the date palm fibers can be cut according to the need, in this study it is equal to that of the polypropylene fiber (12 mm). Date palm fibers are not uniform in diameter but it varies from 0.4 to 0.6 mm and the same fiber can have a diameter variation of 0.4 to 0.5 µm as shown in Fig. 4. Fibers diameters measurements were performed using optical microscope imaging (Fig. 5). Figure 4: Measurement of date palm fibers diameter by optical microscope imaging. D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 36 Figure 5: Optical microscope imaging used for measurement palm date fibers diameter. The direct tensile test on the date palm fibers per unit, length of 60 mm was carried out using a ZWICK Roell press tensile machine with a maximum capacity of 20 kN (Fig. 6a). In our study, we followed the same protocol used by Benzerara, M. et al [4]. It is an experimental test protocol because there is no specific standard published. The stress-strain curve is shown in Fig. 6b. The Tabs. 8 and 9 present respectively the physic-mechanical characteristics and chemical composition of fibers used. (a) (b) Figure 6: The direct tensile test on date palm fiber mesh: (a) loading device and (b) tensile curve. The water absorption coefficient of date palm fibers was determined according to a procedure drawn from several works [1,7,35,36,56]. Besides the water absorption value at 24 hours, we also determined the absorption kinetics. Six fiber samples were dried in an oven at 60°C to constant mass before being immersed in water at room temperature. Samples are removed from the water at 5, 10, 15, 30, 60 minutes and 2, 4, 8 until 24 hours. The fibers were superficially wiped with an absorbent paper in order to eliminate the water adsorbed on their surfaces then weighed. The masses were determined with an accuracy of 0.001g. The water absorption coefficient of fibers is determined by Eqn. (1): 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 10 T en si le s tr en gh t [ M P a] Allongement [mm] D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 37   w d abs d M M W      x 100 M (1) Wabs: Water absorption (%) Mw: Wet mass (g) Md : Dry mass (g) Characteristics Units Values Diameter mm 0.40 - 0.50 Length mm 1.2 Absolute density g/cm3 1.58 Apparent density g/cm3 0.28 Water Absorption at 5 min % 60 Water Absorption at 24 hours % 110.57 Tensile strength MPa 94.73 Elongation at crack mm 9.13 elasticity modulus GPa 2.05 Table 8: Characteristics of date palm fibers used. Compositions Cellulose Hemicellulose Lignin Ash Proportions (%) 32 – 35.8 24.4 – 28.1 26.7 – 28.7 7 Table 9: Chemical composition of Date Palm fiber mesh [19]. The result on the water absorption kinetics of date palm fibers presented in Fig. 6 is similar to those found by [35,36]. The fibers have two absorption phases: The first has a fairly high slope, which characterizes the initial water absorption, corresponding to the filling of the largest pores. After 5 minutes of total immersion under water, an absorption coefficient of 63.58% was noted. The second absorption phase with a low slope corresponds to the filling of the smallest pores. The water absorption coefficient was 110.67% after 24 hours of preservation of the date palm fibers under water. However, total saturation was not reached, the fibers were kept under water at 48, 72 and 96 hours corresponding to 115.14%, 121.53% and 126.29 % water absorption coefficients respectively. This absorption capacity of date palm fibers is due to their porous structure as shown in Fig. 7. Figure 7: Water absorption kinetics of date palm fibers. 0 20 40 60 80 100 120 0 1 2 3 4 5 W at er a b so rp ti on ( % ) Time (h 1/2) D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 38 Scanning electron microscope (SEM) observation of the cross section of a date palm fiber (Fig. 8) shows high porosity. Indeed, it consists of a set of tubular shape microfibers with an average diameter of 10 μm (Fig. 8a), which explains its high water absorption capacity. Its exterior surface is characterized by roughness (Fig. 8b) that could improve its grip with the cement matrix. (a) (b) Figure 8: Date palm fiber mesh scanning electron microscope observations: (a) cross section and (b) exterior surface. METHODS Compositions of SCC he Japanese method developed by Okamura, H et al [41] was used for the formulation of the various SCC. This study concerns seven SCC: reference non-fiber SCC (RSCC), which served as the basis for the compositions of the six fibered SCC. Three control SCC are reinforced with polypropylene fiber (PPSCC6, PPSCC9 and PPSCC12) and three study SCC fibered with date palm fiber (DPSCC6, DPSCC9, DPSCC12). Three fiber dosages were used 600, 900 and 1200 g/m3 length of 12 mm. Tab. 10 groups the compositions of the SCC to study. Concretes Constituents Unit RSCC Polypropylenes fiber Date palm fiber PPSCC6 SCC PP9 PPSCC12 DPSCC6 DPSCC9 DPSCC12 Cement (kg/m3) 350 350 350 350 350 350 350 Limestone filler (kg/m3) 200 200 200 200 200 200 200 Water (kg/m3) 200 200 200 200 200 200 200 silica sand (kg/m3) 384 384 384 384 384 384 384 Quarry sand (kg/m3) 284 284 284 284 284 284 284 Gravel (3/8) (kg/m3) 490 490 490 490 490 490 490 Gravel (8/16) (kg/m3) 460 460 460 460 460 460 460 Plasticizer (kg/m3) 6.6 6.6 6.6 6.6 6.6 6.6 6.6 Fibers (g/m3) 0 600 900 1200 600 900 1200 W/C / 0.57 0.57 0.57 0.57 0.57 0.57 0.57 W/F / 0.36 0.36 0.36 0.36 0.36 0.36 0.36 Table 10: SCC composition. T D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 39 Mixing sequences: The constituents are mixed in a concrete mixer with an inclined axis with a capacity of 30 liters. In this work, we followed the same mixing protocol used by several research [36,57–61] as follows: the date palm fibers are pre-wet for 5 minutes in 10% of the volume of total water. This pre-wetting is necessary to reduce water migration from the cement paste to fibers. The aggregates, cement and limestone filler are mixed dry for 60 seconds. Introduction of granular fractions into concrete mixer, in descending order, followed by the addition of fines (cement and addition, the fibers were mixed with a quantity of fines). Keeping the concrete mixer running, added 75% of the total volume of water and mixed for 2 minutes. The adjuvant were diluted in the remaining 25% of water added to the mixture and followed by a final mixing during 2 minutes. Storage conditions for test specimens After the manufacture of the test specimens, the molds are covered with a plastic sheet and kept in a humid chamber at room temperature 20°C for 24 hours. Once removed from the mold, the specimens are kept until the moment of the test as follows: the specimens for the mechanical characterization tests were stored in baths filled (saturating humidity) with distilled water (pH= 7, T = 20 ±2 °C, RH = 100%) [62–64] and kept for periods of 2, 7, 14 and 28 days, as well as to control the transfer properties of the SCC and fiber-reinforced SCC. The specimens for the shrinkage tests were kept in a standardized room at a temperature of 20°C and 50% relative humidity [7,61]. Characterization of SCC in the fresh state The characterization of the SCC in the fresh state was carried out using standard tests. Workability and T500 tests (Fig. 9a) are determined by the Abrams cone-spreading test described in standard NF EN 12350-8 [65]. The mobility of SCC in a confined environment and its ability to cross an area with heavy reinforcement is measured by the L-box test (Fig. 9b) described in standard NF EN 12350-10 [66]. Resistance to segregation is carried out with the sieve stability test (Fig. 9c) described in standard NF EN 12350-11 [67], air content test (Fig. 10a) according to standard NF EN 12350-7 [68] and apparent density measurement (Fig. 10b) according to standard NF EN 12350-6 [69]. (a) (b) (c) Figure 9: workability study of SCC by the tests: (a) Abrams cone spreading and T500 tests, (b) Filling power tests (the L box) and (c) Segregation stability test. Characterization of SCC in hardened state Compressive and in flexural Strength, measurements of cracking time, shrinkage and capillarity water absorption according to the procedure given by reference [40], were realized on SCC in the hardened state. Strength tests The compressive strength was evaluated using cubic specimens of dimensions 10×10×10 cm3 according to standard NF EN 12390-3 [70]. The flexural strength was evaluated using prismatic specimens of dimensions 7.7.28 (cm) according to standard NF EN 12390-5 [71]. The specimens are kept under water at a temperature of 20±2 °C and tested in compressive D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 40 using a hydraulic press with a capacity of 2000 KN (Fig. 11a) and in flexural using a hydraulic press with a maximum capacity of 150 KN (Fig. 11b), at 2, 7, 14, 28 and 90 days. The result of each test in compressive and in flexural corresponds to the average of three values for each deadline. (a) (b) Figure 10: (a) determination of the entrained air with aerometer and (b) measure of concrete density in the fresh state. (a) (b) Figure 11: Hydraulics presses: (a) compression test and (b) three points bending test. Shrinkage test The experimental protocol for the shrinkage test was carried out in accordance with standard EN P 15-433 [72]. The shrinkage-measuring device is shown in Fig. 12. The specimens used are prisms of dimensions 7×7×28 cm3 fitted with metal studs at their ends. 24 hours after pouring, the specimens are removed from the mold and kept in a climatic chamber at a temperature of 20 ± 2 (°C) and a relative humidity (H≥50%). The shrinkage measurements are carried out on three specimens for each SCC and at the times of 1, 2, 3, 7, 14, 28, 50 and 90 (days). Capillary water absorption The test was carried out according to the procedure recommended by [73] shown in Fig. 13. The specimens used are cylindrical in shape and have dimensions 11×5 cm2. After curing for 28 days under water at a temperature of 20 ± 2 °C, the specimens are dried at a temperature of 80°C until constant mass. The side surfaces of the specimens are coated with resin to prevent evaporation of water absorbed during the test, then immersed in the water of the container to a maximum height of 3 mm. At each deadline, the specimens are taken out of the container, wiped with a damp sponge, weighed and then D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 41 placed back in the container. The capillary absorption coefficient is determined by relation (2) at the following times: 0.25, 0.5, 1, 2, 4, 8 and 24 hours.   t 0 t M  M Ca     A (kg/m2) (2) Cat: capillary absorption coefficient at (t) time (kg/m2). Mt: Mass of specimen at (t) time (kg). M0: Initial mass of specimen (kg). A : Specimen section (m²). (a) (b) Figure 12: Shrinkage device: (a) retract-meter calibration and (b) shrinkage measurement. (a) (b) Figure 13: capillary water absorption measurement: (a) capillary water absorption test [40] and (b) capillary water absorption device. D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 42 RESULTS AND DISCUSSION Influence of natural and synthetic fibers on the properties of SCC in the fresh state Workability The introduction of fibers into the SCC causes a resistance to flow, which translates into a reduction in the self-compacting characteristics, proportionally to the rate of fiber drawing (Fig. 14) in accordance with several researches [74–79]. (a) (b) (c) (d) Figure 14: Effect of fiber rate on: (a) Slump flow, (b) speed flow (T500), (c) L-BOX test and (d) segregation resistance. The non-fibered concrete (RSCC) shows no blockage (Fig. 15a). The PPSCC causes a blockage at the level of the steel bars in L-box (Fig. 15b) greater than that caused by the date palm fibers (Fig. 15c). This behavior can be explained by the fact that the number of polypropylene fibers (PPN) is very high equal to 120×106 (fibers/kg) [54], compared to that of date palm fibers (DPN), experimentally determined equal to 35×104 (fibers/kg). Air content and apparent density It is established that the incorporation of fibers in the concrete results in an increase in the entrained air content and a decrease in the apparent density (Fig. 16) with the increase in the fiber dosage. Indeed, the fibers create additional porosity in the concrete at the interface (cement matrix – fiber). The PPSCC and DPSCC have occluded air volumes greater than that of RSCC and apparent densities lower than that of RSCC, in proportion to the fiber dosage, which is in agreement with several researches [36,38,61,80,81]. However, the DPSCC develops a lower volume of occluded air than that of the PPSCC. This behavior can be explained by the fact that for the same fiber dosage, the number of polypropylene fibers is much 0 100 200 300 400 500 600 700 800 0 600 900 1 200 Sl u m p f lo w ( m m ) Fiber rate (g/m3) RSCC PPSCC PDSCC 0 1 2 3 4 5 0 600 900 1 200 Sp ee d f lo w T 50 0 (s ec on d ) Fiber rate (g/m3) RSCC PPSCC PDSCC 0 0,2 0,4 0,6 0,8 1 1,2 0 600 900 1 200 H 2/ H 1 Fiber rate (g/m3) RSCC PPSCC PDSCC 0 2 4 6 8 10 12 14 16 18 0 600 900 1 200 Si ev e se gr eg at io n ( % ) Fiber rate (g/m3) RSCC PPSCC PDSCC D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 43 higher than that of date palm fibers. Thus, with a greater number of fibers, the probability of trapping air bubbles is greater, also increasing the volume of occluded air and therefore decreasing the density of PPSCC compared to DPSCC. (a) (b) (c) Figure 15: L-Box test of concretes: (a) RSCC, (b) PPSCC12 and (c) DPSCC12. (a) (b) Figure 16: Effect of fiber rate on: (a) air content of SCC and (b) density of SCC. Influence of natural and synthetic fibers on mechanical behavior of SCC in the hardened state Influence on compressive and flexural strengths According to Figs. 17 and 18, it is found that the dosage of 600 g/m3 recommended by the manufacturer of the polypropylene fiber guarantees optimal resistance at any age. It can be noted that the compressive strength of RSCC reached 58 MPA at 90 days. Reinforcement of the SCC by the fibers leads to a noticeable improvement in the resistance to bending compared to the RSCC as demonstrated by different researches. Date palm fibers guarantee the best results compared to polypropylene fibers, this can be explained by the influence of the surface condition of the rough date palm fiber (Fig. 8) which ensures better adhesion with the cementitious matrix [7,36,61] in relation to the surface state of the polypropylene fiber which is smooth. The compressive strength of the studied concrete is more or less altered; this is related to the increase in the porosity of the concrete (entrained air). It is assumed that it is not the fibers directly that reduce the resistance but rather the occluded air entrained by them. The incorporation of fibers into the concrete leads to a reduction in the compressive strength (Fig. 17). 0 0,5 1 1,5 2 2,5 3 3,5 0 600 900 1 200 A ir c on te n t (% ) Rate fiber (g/m3) RSCC PPSCC PDSCC 2280 2300 2320 2340 2360 2380 2400 0 600 900 1 200 A p p ar en t d en si ty ( kg / m 3 ) Rate fiber (g/m3) RSCC PPSCC DPSCC D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 44 The fibers modify the porous network of the concrete leading to the formation of pores and more heterogeneity of the structure of the material, in particular at the interface fiber – cementitious matrix that disturbs the compactness of the concrete. This additional porosity obviously leads to a drop in the compressive stress. In addition, a decrease in the densities of the concrete is observed with the increase in the fiber dosage (Fig. 16b). The results found are in agreement with various researches on the use of plant fibers in the cement matrix. [11,35,36,61,74,76,81]. Fiber orientation is an essential parameter to activate the transfer of the load to the fiber [4,5]. In bending, the orientation of the fibers was perpendicular to the load and to the crack propagation [1,34]. Fibers ligate the cracks and prevent their propagation in the cementitious matrix, which increases the bending stress of the fiber material [7,32]. However, in compression, the orientation of the fibers was parallel to the load and to the cracks propagation. In this case, fibers do not have an effective role in terms of their stresses [61,82]. Figure 17: Effect of polypropylene and Date Palm fibers on compressive strength. Figure 18: Effect of polypropylene and Date Palm fibers on flexural strength. 0 10 20 30 40 50 60 RSCC PPSCC DPSCC PPSCC DPSCC PPSCC DPSCC 0 600 900 1200 C om p re ss iv e st re n gt h ( M P a) Fiber rate (g/m3) 2 days 7 14 28 90 0 1 2 3 4 5 6 7 8 9 10 RSCC PPSCC DPSCC PPSCC DPSCC PPSCC DPSCC 0 600 900 1200 F le xu ra l s tr en gt h ( M P a) Fiber rate (g/m3) 2 days 7 14 28 90 D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 45 Shrinkage The volume of paste in self-compacting concrete is relatively high, which leads to the appearance of cracks, especially at a young age due to drying shrinkage [83]. The results of the shrinkage measurements (Fig. 19) show that the use of fibers makes it possible to reduce shrinkage. This reduction depends on the dosage and the nature of the fibers. These results are validated by several works [36,83]. Date palm fibers are more effective than polypropylene fibers due to their rough surface. Figure 19: Effect of polypropylene and Date Palm fiber on shrinkage of SCC. Capillary water absorption Fig. 20 presents two absorption phases: the first phase is relatively fast, extends up to 8 hours and corresponds to the filling of the largest pores. The second phase is slower and corresponds to the filling of the smallest pores. The introduction of fibers into concrete generates additional porosity at the interface fiber-cement matrix [36,84]. This explains the increase in capillary absorption, which is in agreement with the literature [39,80,85]. Chikhi, M et al [39] emphasizes that the introduction of date palm fibers in a new composite (gypsum-date palm fibers) increases the porosity. The dosage and the nature of the fibers influence the capillary water absorption of the SCC. The DPSCC are characterized by lower coefficients than those of PPSCC. The dosage of 600 g/m3 seems to be the best dosage. Figure 20: Effect of polypropylene and Date Palm fiber on capillary water absorption. D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03 46 CONCLUSION he study of the influence of date palm fibers as reinforcement in self-compacting concretes replacing polypropylene fiber, on the properties in the fresh and hardened states has made it possible to draw the following conclusions:  Date palm fibers are characterized by a porous and highly hydrophilic microstructure.  The use of fibers leads to an increase in the content of occluded air in the SCC, which is lower with date palm fibers than with polypropylene fibers.  The self- compacting parameters of SCC are modified with the introduction of the two types of fibers but remain within the domain of SCC.  The apparent density of concrete decreases more with polypropylene fibers than with date palm fibers.  The introduction of fibers into the SCC leads to a decrease in compressive strength. The bending strength is significantly improved; hence, the date palm fiber guarantees the best results both in compression and in flexion.  Polypropylene fibers significantly reduce shrinkage and the best result is obtained with date palm fibers.  The results obtained are encouraging. Date palm fibers could replace polypropylene fibers in the development of fiber SCC, due to the environmental, technical and economic advantages . ACKNOWLEDGMENTS he authors thankfully acknowledge Materials, Geomaterials and Environment Laboratory (LMGE-Annaba) of Badji Mokhtar Annaba University (Algeria) providing of equipment required for behavioral testing. NOMENCLATURE SCC: self-compacting concrete. RSCC: reference self-compacting concrete (without fibers). PPSCC: polypropylene self-compacting concrete. DPSCC: date palm self-compacting concrete. PPSCC6: self-compacting concrete with 600 grams of polypropylene fibers. PPSCC9: self-compacting concrete with 900 grams of polypropylene fibers. 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Cergy Pontoise University, France. << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. Stvoreni PDF dokumenti mogu se otvoriti Acrobat i Adobe Reader 5.0 i kasnijim verzijama.) /HUN /ITA /JPN /KOR /LTH /LVI /NLD (Gebruik deze instellingen om Adobe PDF-documenten te maken die zijn geoptimaliseerd voor prepress-afdrukken van hoge kwaliteit. De gemaakte PDF-documenten kunnen worden geopend met Acrobat en Adobe Reader 5.0 en hoger.) /NOR /POL /PTB /RUM /RUS /SKY /SLV /SUO /SVE /TUR /UKR /ENU (Use these settings to create Adobe PDF documents best suited for high-quality prepress printing. Created PDF documents can be opened with Acrobat and Adobe Reader 5.0 and later.) >> /Namespace [ (Adobe) (Common) (1.0) ] /OtherNamespaces [ << /AsReaderSpreads false /CropImagesToFrames true /ErrorControl /WarnAndContinue /FlattenerIgnoreSpreadOverrides false /IncludeGuidesGrids false /IncludeNonPrinting false /IncludeSlug false /Namespace [ (Adobe) (InDesign) (4.0) ] /OmitPlacedBitmaps false /OmitPlacedEPS false /OmitPlacedPDF false /SimulateOverprint /Legacy >> << /AddBleedMarks false /AddColorBars false /AddCropMarks false /AddPageInfo false /AddRegMarks false /ConvertColors /ConvertToCMYK /DestinationProfileName () /DestinationProfileSelector /DocumentCMYK /Downsample16BitImages true /FlattenerPreset << /PresetSelector /MediumResolution >> /FormElements false /GenerateStructure false /IncludeBookmarks false /IncludeHyperlinks false /IncludeInteractive false /IncludeLayers false /IncludeProfiles false /MultimediaHandling /UseObjectSettings /Namespace [ (Adobe) (CreativeSuite) (2.0) ] /PDFXOutputIntentProfileSelector /DocumentCMYK /PreserveEditing true /UntaggedCMYKHandling /LeaveUntagged /UntaggedRGBHandling /UseDocumentProfile /UseDocumentBleed false >> ] >> setdistillerparams << /HWResolution [2400 2400] /PageSize [612.000 792.000] >> setpagedevice