Today, the advancement of technology and the achievement of increasing innovations in the field of building materials have increased high-strength concrete (HSC) production. The use of this material has been increased due to economic and technical reasons in the construction of concrete sections. However, the more compressive strength of the concrete is, the more concrete becomes brittle and its tensile strength does not increase with increasing compressive strength. HSC is also more vulnerable to high temperatures due to its high density and low porosity compared to conventional concrete. Researchers have proposed different methods including the use of polypropylene fibres in concrete mix designs in order to overcome these defects of HSC. In this study, a new type of polypropylene fibres, called high performance synthetic macro polypropylene fibres (HPP), have been used in dosages of 1, 2 and 3 kg/m3 . Tests on hardened concrete include compressive strength, tensile strength and flexural strength at temperatures of 25, 100, 200 and 300 C. By adding 1 kg of fibres to HSC, its compressive strength, tensile strength and flexural strength increased up to 14, 17 and 8.5%, respectively. Furthermore, the greatest improvement in the mechanical properties of concrete exposed to high temperatures was obtained when 1 kg/m3 of fibres was added to HSC.
Construction and Building Materials 165 (2018) 631–638 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Effects of high temperatures on mechanical behavior of high strength concrete reinforced with high performance synthetic macro polypropylene (HPP) fibres Reza Abaeian, Hamid Pesaran Behbahani ⇑, Shahram Jalali Moslem Department of Civil Engineering, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran h i g h l i g h t s HPP Fibers did not have significant effect on the compressive strength of concrete Mechanical properties of HSC were enhanced when HPP fibers were added Addition of HPP fibers postponed the spalling of HSC when exposed to high temperatures Discussion about the optimum dosages of HPP fibers was made a r t i c l e i n f o Article history: Received 29 September 2017 Received in revised form January 2018 Accepted January 2018 Keywords: High strength concrete High performance synthetic macro polypropylene fibres (HPP) Fibre reinforced concrete High temperatures a b s t r a c t Today, the advancement of technology and the achievement of increasing innovations in the field of building materials have increased high-strength concrete (HSC) production The use of this material has been increased due to economic and technical reasons in the construction of concrete sections However, the more compressive strength of the concrete is, the more concrete becomes brittle and its tensile strength does not increase with increasing compressive strength HSC is also more vulnerable to high temperatures due to its high density and low porosity compared to conventional concrete Researchers have proposed different methods including the use of polypropylene fibres in concrete mix designs in order to overcome these defects of HSC In this study, a new type of polypropylene fibres, called high performance synthetic macro polypropylene fibres (HPP), have been used in dosages of 1, and kg/m3 Tests on hardened concrete include compressive strength, tensile strength and flexural strength at temperatures of 25, 100, 200 and 300 °C By adding kg of fibres to HSC, its compressive strength, tensile strength and flexural strength increased up to 14, 17 and 8.5%, respectively Furthermore, the greatest improvement in the mechanical properties of concrete exposed to high temperatures was obtained when kg/m3 of fibres was added to HSC Ó 2018 Elsevier Ltd All rights reserved Introduction Concrete is one of the most important and most popular building materials, featuring advantages such as plasticity prior to hardening, good compressive strength and the availability of its constituent materials Due to advances in technology, the use of high-strength concrete (HSC) has been increasing in recent years In parallel, many studies have been done to improve the weaknesses of this type of concrete, including its low tensile ⇑ Corresponding author E-mail addresses: (H.P Behbahani) hamidbehbahani@gmail.com, https://doi.org/10.1016/j.conbuildmat.2018.01.064 0950-0618/Ó 2018 Elsevier Ltd All rights reserved hbehbahani@khuisf.ac.ir strength and ductility compared to its compressive strength [1,2] and its greater vulnerability at high temperatures among various types of concrete Studies show low resistance of concrete in high temperatures, so that exposure of concrete to high temperatures leads to cracking and explosive spalling Accordingly, the strength and modulus of elasticity of HSC drops significantly [3–9] Concrete may be exposed to high temperatures in cases such as the occurrence of fire in concrete structures, in the explosion of jet engines, in factories in the extraction and melting of metals, in some chemical plants where concrete is close to the furnace, and relatednuclear activities Adding fibres is the most widely known method to prevent spalling of HSC [10–17] Among fibres, adding polypropylene (PP) into HSC shows better performance in order to increase 632 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Table Technical specifications of studied HPP fibres compared with a typical PP fibre Type of Fibre Physical Shape Density (gr/cm3) Tensile Strength (MPa) Modulus of Elasticity (MPa) Melting Point (°C) Diameter (mm) Length (mm) HPP Typical PP Fiber Sinusoidal shape Straight 0.9 0.9–0.91 700 400–500 3800 3500 200 160–170 0.9 – 50 – Fig Physical shape of fibres (a) studied HPP fibres (b) typical type of PP fibres Table Concrete mix design of samples Type of Concrete Sample W/C Dmax (mm) Coarse Aggregate (kg/m3) Fine Aggregate (kg/m3) Cement (kg/m3) Fibre Content (kg/m3) Super Plasticizers (%) NC HSC HSC.1 HSC.2 HSC.3 0.4 0.35 0.35 0.35 0.35 19.5 19.5 19.5 19.5 19.5 1024 898 898 898 898 671 646 646 646 646 462 572 572 572 572 0 0.3 0.3 0.3 0.3 resistance of HSC at elevated temperatures [18–20] In addition, it caused improvement in the mechanical properties of HSC and its shrinkage control [21–27] Investigating the spalling phenomena for concrete by incorporating polypropylene fibres, Lura and Terrasi [18] found that spalling was substantially decreased by adding to the concrete small quantities (almost 0.1% by volume) of fibres made from a low melting-point polymer Noumowe [28] and Sahmaran et al [29] studied the mechanical and microstructure properties of HSC in face of high temperatures It was found that the pore structure at high temperature may have a considerable influence on the spalling behavior of the high strength polypropylene fibre concrete Polypropylene fibres are melted when exposed to high temperatures, and creating channels in concrete mass prevents the formation of high vapor pressure in concrete pores, which reduces the spalling of concrete In addition, the fibrous concrete cool slower than normal concrete, resulting in fewer cracks in cooling phase Other researches have studied properties of HSC with combination of Polypropylene and other fibres, e.g steel fibres in order to improve the mechanical properties of HSC [30,31] This study investigates the effects of adding a new type of polypropylene fibres, called high performance synthetic macro polypropylene fibres (HPP), on the mechanical properties of concrete at elevated temperatures up to 300 °C These fibres are made of polymer materials that have an especial sine-shape The physical shape of these fibres makes them superior for concrete mixture when compared with the common type of fibres In addition, compared to typical fibres, they also have a higher modulus of elasticity and tensile strength [32,33] Among advantages of this type of fibre are enhancing the concrete resistance to stress, fatigue, heat, and increase tensile, shear and flexural strength in concrete Table shows the differences between properties of HPP fibers and a common type of polypropylene fibers Their physical shapes are displayed in Fig The objectives of this research are (i) to obtain the effect of high temperatures on the mechanical properties of conventional normal concrete (NC) and HSC; (ii) to study the effect of adding polypropylene fibres with different dosages on mechanical properties of HSC; (iii) to examine mechanical behavior of high strength HPP fibre concrete at elevated temperatures up to 300 °C Test program and procedures 2.1 Concrete mix design and testing Two different types of concrete including normal concrete and HSC are used in this research with strength of 25 and 69 (MPa) 633 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Fig Studied fresh concrete containing HPP fibres Fig A view of used electric oven Chemical analysis Blaine (cm2/gr) SiO2 (%) Al2O3 (%) Fe2O3 (%) CaO (%) MgO (%) SO3 (%) Compressive strength (MPa) Effects of adding HPP fibres on properties of HSC were studied at three different dosages of 1, and kg per cubic meter of concrete The mix design to achieve HSC was in accordance with DOE method [34] and is presented in Table Naming the samples was done in such a way as to represent the type of sample HSC represents high strength concrete and the number after that indicates the fibre content in a cubic meter of HSC NC represents the normal concrete Concrete samples were tested at day and day 28, and three samples were made for each design The experiments carried out in this study are compressive strength test in accordance with B S 1881: Part 116 standard, splitting tensile strength test according to ASTM C496/C496 M-04 regulation, flexural strength test following ASTM C293 The samples were exposed to three different temperatures of 100, 200 and 300 °C according to ISO-834 standard using oven The electric oven used in this study is shown in Fig The number and type of studied specimens and testing procedure are presented in Table Different methods are used to make fibre reinforced concrete Type of work, facilities and equipment are among the factors that are important in choosing production methods It should be noted that in any method of production of fibre reinforced concrete, the distribution of fibres in a mixture should be homogeneous to prevent fibres from balling The balling or conglobation of fibres during the mixing process depends on several factors, with the most important parameter being the aspect ratio Other factors that affect the fibre distribution include fibre percentages, grain size, aggregate size and quantity, the ratio of water to cement, mixing method Higher amount of aspect ratio, volume percentage of fibres, and size of the aggregates increased the tendency for balling The fibre concrete mixing design is similar to other concrete and for a specified mixture, the slump decreases with increasing fibre content For a uniform distribution of fibres in the mixture, the proper performance of the concrete is important Additives materials may be used to create air bubbles, water reduction and shrinkage control In Fig 3, an illustration of the studied fresh fibre reinforced HSC is presented Table Properties of used cement 80 69 3200 ± 100 20.7 ± 0.3 5.2 ± 0.2 4.6 ± 0.2 65 ± 0.5 1.8 ± 0.2 2.2 ± 0.4 64 59 60 40 25 24 50 23 21.5 20 0 50 100 150 200 250 HSC NC 300 Temperature (°C ) Fig Effects of high temperatures on NC and HSC samples 2.2 Materials The cement used in this research was the production of Ardestan cement plant with the shown properties in Table In order to make experimental samples, a washed sand from Isfahan flood plain was used with a fineness modulus of 1/3 in accordance with ASTM C-125 standard The sand used in this study was mountainous materials in Isfahan with a maximum size of 19.5 mm, specific gravity of 2.68 gr/cm3 and bulk density of 1500 kg/m3 In this research, super plasticizer Dynamon SP 5600, without any chlorine based on formulations containing advanced polycarboxylate molecular chains, is used to provide the required Table Number and type of concrete samples for testing Total number of samples Type and Sample size (cm) Type of test Temperature (°C) 24 96 96 96 Cube: 10 Â 10 Â 10 Cube: 10 Â 10 Â 10 Cylinder: 15 Â 30 Prism: 10 Â 10 Â 50 Compressive strength test of NC Compressive strength test of HSC Tensile strength test of HSC Flexural strength test of HSC 25, 100, 200, 300 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Table Results of the slump test on fresh concrete NC HSC HSC.1 HSC.2 HSC.3 Slump (cm) 10 10 9.5 Compressive Strength (MPa) Type of Sample 70 68 69 68.64 66 66.12 64 7.2 7.1 6.9 6.8 6.7 6.6 6.5 6.4 6.3 6.2 7.09 6.8 6.71 6.5 HSC 62 60 60.2 58 HSC.1 HSC.2 HSC3 Type of Sample Fig The effect of HPP fibres on the flexural strength of HSC 56 54 HSC HSC.1 HSC.2 HSC3 Type of Sample Fig The effect of HPP fibres on compressive strength of HSC 12.7 Tensile Strength (MPa) Flexural Strength (MPa) 634 12.5 exposed to high temperatures In Section 3.2, the results of adding fibres on workability of HSC are discussed Section 3.3 presents the effects of HPP fibres on mechanical properties of HSC, including compressive strength, tensile strength and flexural strength Finally, mechanical behavior of HSC with addition of HPP fibres at designated high temperatures are described in Section 3.4 12.5 3.1 Compressive strength of ordinary concrete and HSC against heat HSC3 The results of the compressive strength test on ordinary concrete and HSC samples are demonstrated in Fig at temperatures of 100 °C, 200 °C, and 300 °C It should be noted that the heated samples were tested after removal from the oven, followed by cooling to ambient temperature of about 25 ± °C It was seen that the strength of both NC and HSC reduced when exposed to high temperatures The compressive strength of normal concrete in the face of heat was reduced with a slight slope and reduced by 4%, 8%, and 14% when exposed to temperatures of 100, 200 and 300 °C, respectively Compressive strength of HSC decreased significantly such that its strength reduced up to 7.2%, 14.5%, and 27.5% after exposure to 100 °C, 200 °C and 300 °C, respectively This proves that the HSC is more susceptible to spalling than normal concrete at high temperatures 12.3 12.2 12.1 11.9 12 12 HSC HSC.1 11.7 11.5 HSC.2 Type of Sample Fig The effect of HPP fibres on splitting tensile strength of HSC performance for high-strength concrete This product is manufactured in accordance with type F, G ASTM C-494 and EN 934-2 standards 3.2 Effects of adding HPP fibres on workability of fresh HSC Results and discussion This part is categorized into four sections Section 3.1 presents results of compressive strength test on NC and HSC specimens The slump test was used in order to measure workability of concrete samples Table indicates the slump value of different types of samples Fig Cracking mechanism of a HSC specimen with fibre under flexural strength test 635 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Table Testing results of HSC specimens with fibres in different temperatures Temperatures (°C) 7-day 28-day change (%) 7-day 28-day change (%) 7-day 28-day change (%) HSC 25 100 200 300 54 50 47 42 69 64 59 50 – À7.2 À14.5 À27.5 25 100 200 300 12 11 10 8.5 – À1.4 À2.9 À5.1 4.1 3.5 3.2 2.9 6.5 5.2 4.8 4.3 – À1.9 À2.5 À3.2 HSC.1 25 100 200 300 54 53.9 51 47 68.6 65 63 59 – À5.2 À8.2 À14.0 25 100 200 300 12 12 11 10.5 – 0.0 À1.5 À2.2 4.2 3.8 3.4 3.2 6.7 6.3 5.5 5.0 – À0.6 À1.7 À2.5 HSC.2 25 100 200 300 52.5 48 44 42 66.1 60.7 59.8 55 – À8.2 À9.5 À16.8 25 100 200 300 12.2 12.2 11.5 11 – 0.0 À1.1 À1.8 4.3 3.9 3.7 3.4 6.8 6.2 5.6 5.2 – À0.9 À1.8 À2.4 HSC.3 25 100 200 300 46.4 43.5 39 37 60.2 56.5 51.3 50 – À6.1 À14.8 À16.9 25 100 200 300 12.5 12.5 12 11.5 – 0.0 À0.8 À1.7 4.4 4.1 3.8 3.6 7.1 6.5 6.0 5.8 – À1.0 À1.8 À2.2 Compressive strength (MPa) Tensile Strength (MPa) 75 70 65 60 55 50 45 Tensile strength (MPa) 25 100 200 300 HSC.0 HSC.1 HSC.2 Flexural Strength (MPa) 13 12 11 10 25 Temperature (° C) 100 200 300 Temperature (° C) HSC.0 HSC.3 Fig 28-day compressive strength of HSC with different dosages of fibres in different temperatures According to mentioned table, the amount of concrete workability reduced by adding HPP fibres and it continued to reduce by increasing amount of fibres However, addition of kg HPP fibres had no significant effect, reducing workability by only 5% 3.3 Effect of adding HPP fibres on mechanical properties of HSC Fig presents the compression test results performed on the HSC specimens with different dosages of HPP fibres The results showed that the compressive strength of the HSC had negligible change by adding kg fibres The compressive strength decreased with increasing fibers content; however, this reduction is not significant Addition of fibres into HSC led to decrease by 4.3%, and 12.7% in compressive strength of mixtures with fibre content of kg and kg, respectively Similarly, reduction in compressive strength of concrete due to addition of different types of polypropylene fibres was obtained in other studies, e.g [27,35] This reduction could be attributed to the presence of voids due to the addition of HPP fibre and the existence of weak interfacial bonds between the HPP fibers and cement particles [36] Fig shows the effect of adding HPP fibres on 28-day splitting tensile strength of HSC As can be seen, addition of kg fibres did not affect the tensile strength of HSC The tensile strengths of HSC HSC.1 HSC.2 HSC.3 Fig 10 28-day tensile strength of HSC with different dosages of fibres in different temperatures Flexural Strength (MPa) Compressive Strength (MPa) Type of Sample 25 100 200 300 Temperature (° C) HSC.0 HSC.1 HSC.2 HSC.3 Fig 11 28-day flexural strength of HSC with different dosages of fibres in different temperatures specimens containing higher content of fibres were higher than those of the HSC specimens without fibres When the splitting occurred and was sustained, the HPP fibres bridging the split parts of the specimens acted over the stress transfer from the matrix to the fibres, and gradually supported the full tensile stress The transferred stress enhanced the tensile strain capacity of the concrete matrix, and thus improved the tensile strength of 636 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Fig 12 View of the channels created by the melting of the fibres in the cube sample the fibrous mixtures over the non- fibrous concrete mixture counterpart Fig displays the results of 28-day flexural strength test of HSC specimens with different contents of fibres The results show that using fibres increases the flexural strength of HSC Adding different contents of kg, kg and kg fibres into HSC caused increase in flexural strength up to 3.1%, 4.6% and 9%, respectively It could be due to bridging mechanism of fibres which prevent the growth of cracks and reduce crack width Fig shows the cracking mechanism of a fibrous HSC sample under flexural test Overall, through observing the mechanical properties of HSC equipped with HPP fibres, it can be obtained that the addition of fibres caused reduction in compressive strength of HSC; however, this reduction is negligible when kg fibres were added Tensile strength and flexural strength of concrete increased by addition of fibres imen reinforced by fibres and the channels formed on the sample are observed The results are in agreement with other studies Porosity of HSC increases with addition of fibres, resulted in reducing vapor pressure in the pores in the deeper concrete areas and control cracking In addition, the melted polypropylene fibres due to high temperatures cause the creation of channels in the concrete mass that allows water vapor to evacuate, releasing pore pressure, gradually reducing the temperature, and decreasing the cracks in the cooling phase [8,22,37–39] Finally, it should be mentioned that results of previous section showed addition of kg/m3 HPP fibres did not sacrifice workability and compressive strength of the concrete while increasing the flexural strength of the HSC Thus, it could be concluded that the optimum dosage of addition of HPP fibres into concrete is kg/m3, which not only improves the mechanical properties of the HSC, but also caused higher resistance of the HSC at elevated temperatures up to 300 °C 3.4 Effects of adding HPP fibres on properties of HSC exposed to high temperatures Conclusion HSC specimens without fibre and with fibres were put inside the furnace and heated to temperatures of 100, 200 and 300 °C The samples were naturally cooled to reach ambient temperature The results of measurement of compressive strength, tensile strength and flexural strength of HSC with different dosages of fibres in different temperatures are recorded in Table and depicted in Figs 9–11 All of experimentally obtained results are provided in detail and presented in Appendix A Generally, it can be seen that the concrete samples lost their strength when exposed to high temperatures Non-fibrous HSC were damaged more than fibrous concrete With respect to Table 6, the plain HSC experienced drops in compressive strength up to 7.2%, 14.5% and 27.5% when exposed to temperatures of 100, 200 and 300 °C, respectively However, compressive strength of HSC.1 reduced 5.2, 8.12 and 14% when exposed to temperatures of 100, 200 and 300 °C, respectively In addition, Table reveals that the specimens with content of kg fibres showed better performance in the face of high temperatures compared to other specimens containing higher amount of fibre Fig 12 shows an exterior of heated HSC spec- This paper investigated effects of different dosages of HPP fibres on mechanical behavior of HSC The effects of high temperatures on properties of non-fibre and fibrous HSC was also studied Normal concrete was found to be less damaged than HSC when exposed to high temperatures The addition of HPP fibres to HSC improved the tensile strength and flexural strength of HSC which could be due to distribution of tensile stresses and the prevention of growth of cracks in concrete Addition of HPP fibres reduced compressive strength of HSC which could be due to fibre compression and reduction in concrete condensation However, this reduction was negligible when kg of fibres were added Adding more than kg/m3 of fibres caused significant reduction in workability of fresh concrete as well It could be concluded that the best improvement in properties of HSC was achieved by adding content of kg/m3 fibres The addition of HPP fibres to HSC improved the behavior of concrete when exposed to high temperatures HSC exposed to heat at a temperature of 300 °C experienced compressive strength reduction of about 28% while a 14% reduction was found in concrete containing kg/m3 HPP fibres 637 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 Appendix A Following tables display the experimentally obtained results for concrete specimens in detail Table A.1 The 7-day test results of HSC specimens with fibres in different temperatures ⁄ Type of Sample Temperatures (°C) Compressive strength (MPa) Tensile strength (MPa) Flexural strength (MPa) NSC 25 100 200 300 16.16 15.06 14.96 13.94 15.87 15.11 15.01 14.07 16 14.97 14.98 14 N.A.⁄ N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A HSC 25 100 200 300 53.67 50.2 46.76 41.9 54.33 49.8 46.84 41.6 54 50 47.37 42.5 9.94 8.99 7.86 6.96 10.01 8.98 8.07 7.03 10.03 9.07 8.067 7.012 4.1 3.49 3.19 2.88 4.15 3.53 3.27 2.93 4.07 3.5 3.16 2.89 HSC.1 25 100 200 300 54.24 53.85 52 47.45 53.76 54 50 46.55 54 53.9 51 47 9.98 10 8.99 8.625 10.07 9.978 8.92 8.573 10.03 9.996 9.07 8.596 4.25 3.79 3.37 3.2 4.16 3.83 3.4 3.3 4.21 3.78 3.45 3.12 HSC.2 25 100 200 300 51.7 48.63 44.4 42.6 52.83 47.446 43.6 41.2 52.95 48 44 41.9 10 9.98 9.17 8.69 9.99 9.99 9.24 8.79 10.11 10 9.19 8.63 4.21 3.91 3.7 3.43 4.26 3.866 3.78 3.35 4.14 3.625 3.63 3.44 HSC.3 25 100 200 300 47 43.2 39.1 37.1 45.7 43.5 39.3 36.8 46.54 43.8 38.6 37.2 10.59 10.479 9.54 8.84 10.49 10.489 9.48 8.79 10.44 10.498 9.48 8.765 4.51 4.15 3.79 3.58 4.43 4.09 3.77 3.65 4.26 4.062 3.85 3.56 N.A.: Not Available Table A.2 The 28-day test results of HSC specimens with fibres in different temperatures ⁄ Type of Sample Temperatures (°C) Compressive strength (MPa) Tensile strength (MPa) Flexural strength (MPa) NSC 25 100 200 300 25.02 24.02 23.06 21.5 24.97 23.95 22.944 21.54 25.01 24.04 22.97 21.47 N.A.⁄ N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A N.A HSC 25 100 200 300 68.92 64.4 59.3 50.18 69.35 64 58.89 50 68.67 63.6 58.78 49.83 11.94 10.94 9.94 8.53 12.15 11 10.05 8.48 12.06 11.08 9.99 8.49 6.41 5.26 4.75 4.36 6.63 5.16 4.82 4.27 6.47 5.18 4.83 4.29 HSC.1 25 100 200 300 68.2 65.23 62.95 58.8 68.6 65 62.73 58.97 69 64.81 63.3 59.25 12.071 11.91 11.12 10.65 11.94 12 10.88 10.55 12.02 12.1 10.97 10.33 6.69 6.26 5.48 4.89 6.62 6.34 5.536 4.96 6.78 6.32 5.51 5.17 HSC.2 25 100 200 300 66.25 61.46 59.95 55.1 66.2 60.4 59.6 55 65.87 60.3 59.78 54.86 12.18 12.21 11.49 10.98 12.19 12.17 11.37 11.01 12.23 12.21 11.66 11.018 6.85 6.14 5.632 5.13 6.83 6.19 5.6 5.11 6.74 6.28 5.57 5.37 HSC.3 25 100 200 300 60 56.3 51.47 50.16 60.15 56.5 51.5 50.11 60.5 56.8 50.85 49.8 12.494 12.5 11.94 11.49 12.502 12.488 11.99 11.39 12.53 12.49 12.12 11.63 7.17 6.54 5.93 5.97 7.068 6.47 5.92 5.64 7.06 6.49 6.15 5.78 N.A.: Not Available 638 R Abaeian et al / Construction and Building Materials 165 (2018) 631–638 References [1] H.P Behbahani, B Nematollahi, A.R Mohd Sam, F Lai, Flexural behavior of steel-fiber-added-RC (SFARC) beams with C30 and C50 classes of concrete, Int J Sustain Concstr Eng Technol (2012) 54–64 [2] J.-H Lee, Influence of concrete strength combined with fiber content in the residual flexural strengths of fiber reinforced concrete, Compos Struct 168 (2017) 216–225 [3] G Sanjayan, L Stocks, Spalling of high-strength silica fume concrete in fire, Mater J 90 (1993) 170–173 [4] U Diederichs, U Jumppanen, U Schneider, High 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and creating channels in concrete mass prevents the formation of high