Experimental Study on the Effect of Basalt Fiber and Sodium Alginate in Polymer Concrete Exposed to Elevated Temperature

: Polymer concrete contains aggregates and a polymeric binder such as epoxy, polyester, vinyl ester, or normal epoxy mixture. Since polymer binders in polymer concrete are made of organic materials, they have a very low heat and ﬁre resistance compared to minerals. This paper investigates the effect of basalt ﬁbers (BF) and alginate on the compressive strength of polymer concrete. An extensive literature review was completed, then two experimental phases including the preliminary phase to set the appropriate mix design, and the main phase to investigate the compressive strength of samples after exposure to elevated temperatures of 100 ◦ C, 150 ◦ C, and 180 ◦ C were conducted. The addition of BF and/or alginate decreases concrete compressive strength under room temperature, but the addition of BF and alginate each alone leads to compressive strength increase during exposure to heat and increase in the temperature to 180 ◦ C showed almost positive on the compressive strength. The addition of BF and alginate both together increases the rate of strength growth of polymer concrete under heat from 100 ◦ C to 180 ◦ C. In conclusion, BF and alginate decrease the compressive strength of polymer concretes under room temperature, but they improve the resistance against raised temperatures.


Introduction
Concrete is an old building material, in use for centuries. Concrete is widely used in the construction of civil engineering structures such as buildings [1,2], bridges [3,4], and other civil structures [5,6]. Reinforced concrete structures are vulnerable to high-temperature conditions, which greatly shortens the service life and hinders its applications [7]. The properties of the mix design parameters have a significant effect on the performance of concrete exposed to elevated temperature [8][9][10][11]. Several research studies have been carried out to improve the thermal stability of concrete exposed to elevated temperatures using various materials, such as fillers, nanoparticles, and fibers [12][13][14][15].
Sodium alginate (SA) is a well-known natural polymer that is extracted from cell walls of brown algae [16,17]. Recently, SA has received much attention in concrete applications due to self-healing behavior [18,19]. The influence of the SA on mechanical and flexural properties is still unclear and different studies achieved different results. Abbas and Mohsen [20] indicated that the addition of SA increased the fresh and mechanical properties of concrete. However, Heidari et al. [21] reported a decrease in mechanical properties by Table 1. A summary of the studies on the effect of alginates on mechanical parameters of concrete.
Ouwerx et al. [19] Alginate gel bead -• Properties of alginate significantly depend on polymer type and concentration.
Pathak et al. [16] Alginic acid and metal alginates -• Presence of metal ions impacted on the pore size distribution of alginates. • Different thermal behavior was observed in different metal alginates due to structural differences.
Polymeric concrete is a kind of concrete in which natural aggregates such as silica sand and gravel are bound together in a matrix with a polymer binder as a supplement or replacement of cement in concrete [25]. Polymeric concrete has higher mechanical strengths, chemical resistance, and ductility, compared with ordinary concrete (OC) [26,27]. Currently, three distinct types of polymeric concrete are studied that include polymer-Portland cement concrete (PPCC), polymer impregnated concrete (PIC), and polymer concrete (PC) [27].
According to American Concrete Institute (ACI 548.3R), in PC, the polymer is served as the sole binding material present in concrete [28]. However, filler materials such as silica fume and fly ash can be utilized along with aggregates to enhance mechanical properties and minimize building cost. PC can achieve about 80% of its 28 day compressive strength Processes 2021, 9,510 3 of 16 in one day, and compressive strength of 100 MPa can be attained [26,29]. Higher ductility after 60 • C [30] and no visible failure under compression for mixes containing epoxy or epoxy and filler of 30% of the total volume is also reported for PC [31]. An investigation by Golestaneh et al. [32] indicated an optimal amount of epoxy to reach the maximum compressive and flexural strength was 15% of the total volume, while Elalaoui et al. [33] suggested 13% to reach the highest physical and mechanical properties at the lowest cost. However, the higher value for the suggested optimal amount by Golestaneh et al. [32], even with 20% epoxy, may be due to the utilization of silica fume as filler to get the maximum tensile strength.
The results indicate that, compared to OC, polymeric concrete exhibited fewer cracks that are probably due to the bound effect between fiber and matrix [34]. PC has higher strengths than OC [34][35][36] and, similar to the OC, with the addition of fiber, reduction in its workability is unavoidable [34]. Acceptable interface adhesion between fiber and polymeric matrix for fiber loading of 15% of the total volume resulted in high tensile and flexural strengths [37]. Understanding the behavior of concrete exposed to various temperatures is considered an important factor in meeting the safety and service life objectives in which structures are intended and designed. Three different temperature ranges are generally used in concrete studies that include low temperature (<0 • C), medium temperature (0-50 • C), and high or elevated temperature (<50 • C). The thermal response of concrete to elevated temperature mainly depends on constituents' characteristics and the mix composition [38]. Based on the applications and intended exposure condition, previous researches have considered various temperature ranges to evaluate the thermal response of concrete which can be classified as temperatures below 200 • C [39][40][41], below 600 • C [42][43][44], and below 1000 • C [45][46][47]. The value of 600 • C is generally selected because the interior of the concrete members will not exceed 600 • C in a short time. Higher temperatures (e.g., 1000 • C) are considered for the peak gas temperature of a fire that may reach a higher value [48], while the temperature lower than 200 • C is generally considered for members exposed to indirect fire heat.
The duration of exposure and heating rate are two other important factors that have been investigated in many research studies. Different heating durations are generally based on the recommendation by different specifications for maximum fire-resistance rating. For example, the fire resistance for column members in China fire design specifications is defined as 180 min (3 h) [48]. Alharbi et al. [49] indicated that duration of exposure has an effect on degradation of the stiffness while prolonged exposures can significantly reduce the strength of concrete. The heating speed caused by exposure to real fire is generally specified by fire standards (e.g., ISO 834 standard fire).
Investigation on the behavior of PC with basalt fiber has revealed that BF >1% reduces concrete strength [50]. On the other hand, the studies on epoxy/basalt polymer concrete showed enhancement of mechanical properties and more ductility under increasing temperature up to 100 • C [36]. Reis [30] observed that the epoxy mortars had higher sensitivity to temperature variations due to the heat distortion temperature of the resins [19]. Niaki et al. [51] demonstrated that basalt fiber improved the mechanical properties and increased the thermal stability of the PC subjected to different temperatures (up to 250 • C). Several research studies have been conducted to improve the durability of polymer concrete exposed to elevated temperatures [9]. Elalaoui et al. [52] proposed ammonium polyphosphate to be used as a constituent of the PC to improve the temperature resistance of the concrete. Niaki et al. [36] reported that adding crushed basalt aggregates into PC led to decreases in the highest maximum stress rapidly, but increases the yield displacement significantly due to temperature increase. Gorninski et al. [53] produced PC composites using waste alumina and showed that the addition of alumina flame retardant waste can efficiently improve the temperature resistance of the PC. The effect of using BF on concrete has been carried out by many researchers, and several experiments were conducted to study the influence of adding different proportions, diameter, and length of fibers in concrete. Jiang et al. [54] demonstrated that BF addition can considerably improve the tensile and flexural strength and toughness index of fiber reinforce concrete. It was indicated that adding BF had no obvious increase in compressive strength. Compared to other types of fibers such as polypropylene and glass fiber (GF) higher performance for splitting tensile, flexural strengths, crack resistance, ductility post cracking flexural response have been reported for BF [54][55][56][57]. Almost all previous researchers are agreed upon the fact that an increase in the fiber content and/or length decreases the workability of concrete and increases porosity [58]. Kabay [59] showed that increasing the length and/or volume of fibers reduces concrete workability. It was observed that void content has a higher impact on abrasion compared to compressive and flexural strength. The inclusion of fibers reduced compression strength and abrasive wear of concrete. The highest flexure strength was achieved in mixtures with 60% w/c. Dias and Thaumaturgo [34] studied the effect of BF in geopolymer concrete. It was indicated that BF in geopolymer concretes improved the flexural and splitting tensile strength compared to geopolymer concretes; however, the addition of 1.0% BF resulted in a 26.4% reduction in compressive strengths of cement concretes.
The length and weight fraction of BF are two interactive factors that influence on mechanical and fresh properties of cementitious composites. Khan and Cao [60] investigated the mechanical properties of basalt-fiber-reinforced cementitious composites with four different fiber lengths (3,6,12, and 20 mm) and also with a combination of various lengths and contents. The results indicated that the compressive strength of basalt-fiber-reinforced cementitious composites containing fiber with the length of 6 and 12 mm is higher than that with 3 and 20 mm length. It was observed that short fibers in the matrix play a bridging role to limit the expansion of microcracks while longer fibers provided additional capacity to restrict the development of macrocracks. Amuthakkannan et al. [61] studied the effect of basalt fiber length and content on the mechanical properties of basalt-fiber-reinforced polymer matrix composites of the fabricated composites. It was shown that basalt fiber with the length of 10 mm and 50 mm provided better tensile strength than 4 mm and 21 mm in polymer matrix composites. It was indicated that shorter fiber lengths will create more fiber ends that act as stress concentration points, resulting in a faster failure at these points.
Almost all studies conducted on properties of fiber-reinforced cementitious materials indicated that increasing the fiber contents and/or length harms the workability and porosity of the fresh mix [58]. Reduction in the workability due to an increase in the fiber content requires higher water-to-cement ratio, which leads to higher porosity in the hardened concrete. Accordingly, fiber content is also a main parameter considered by previous researchers to control the fiber effect on the concrete properties. However, selecting an appropriate amount of fiber content to reach proper workability with expected mechanical properties for concrete is necessary. As shown in Table 2, the length of BF is varied from 3 to 30 mm while the fiber content is ranged from 0.05% to 5% of the volume fraction in the mixes. As it can be seen in the table, 2% is the most frequently used weight fraction in studies related to fresh and hardened concrete properties. Chopped fibers with shorter length are characterized with a more uniform distribution while longer lengths can better contribute with crack control. Ayoub et al. [62] stated that an increase in BF contents of the concrete mix leads to reduced compressive strength. However, 0.5% and 0.75% of BF content can slightly improve the compressive strength. The addition of 10% silica and BF can result in a higher tensile strength in high-performance concrete. BF content does not correlate with E-value. Fenu et al. [56] reported that the addition of GF and BF increased dynamic energy absorption at a high strain rate. Furthermore, it enhanced the post-peak behavior and static flexural strength of concrete. Shafiqh et al. [55] indicated that the addition of GF and BF enhanced strain capacity attaining of the concrete. Significant improvement was achieved in flexural response, ductility, and toughness by the inclusion of PVA fibers. However, no relation was found between BF addition and post-peak flexural behavior of concrete. Girgin 2016 [63] stated that the addition of GF resulted in a 35% reduction in the average strain capacity of concrete compared to the control specimens. The flexural strain capacity of BF was influenced by cement hydration in the matrix-fiber interface. Afroz et al. [67] studied the influence of BF fibers for sulfate and chloride resistance in concrete for longterm durability applications. It was shown that modified BF had better stability in the alkaline medium compared to non-modified ones. However, a slight reduction in the mechanical properties was reported for concretes reinforced with treated fibers.
Since polymer binders in polymer concrete are made of organic materials, they have a very low heat and fire resistance compared to minerals. Hence improving the thermal performance of the polymer concretes is of utmost importance for the construction industry. The limited information that exists in the literature indicates that application of SA in the concrete mixture could associate with self-healing of cracks and improving the fire, flame, and heat resistance of concrete while the inclusion of BF could enhance the energy absorption and ductile behavior of concrete that can prevent brittle fracture of structures. Several pieces of research have been conducted to study the effect of using SA and BF in cement concrete; however, such studies are limited when it comes to their applications in PC. To the author's knowledge, this study is the first that investigated the strength characteristic of SA-based BF-reinforced PC subjected to elevated temperature. After an extensive literature review, two experimental phases, including the preliminary phase to set the appropriate mix design, and the main phase to investigate the compressive strength of samples after exposure to elevated temperatures of 100 • C, 150 • C, and 180 • C, were conducted. A summary of the research on PC/PPCC with and without fiber reinforcement is presented in Tables 3 and 4, respecrively.  • BF was exposed to water, styrene butadiene rubber and superplasticizer that prevails in cementitious materials • BF >1% reduced concrete strength & basalt was degraded and degenerated by biochemical changes • In increased alkaline conditions, spalling of fibers was observed when exposed to the pH of 12 & further disintegration of fibers were noticed when exposed to polycarboxylate based superplasticizer and polymer matrix of styrene butadyene rubber at pH 12 • Further studies are required to enhance the structural stability of BF in the concrete matrix

Materials
Materials including aggregates, BF, SA, and two-part epoxy resin for this experiment were provided by a local supplier. Basalt fiber, SA, and epoxy resin were productions originally from the U.S., Iran, and Germany, respectively. Triplicate cubic concrete samples of 50 × 50 × 50 mm were tested for the compressive strength of each mix composition. According to ASTM C117 and E11, the aggregates for the mortar were sieved through sieve number 4 to provide relatively fine aggregates of size less than 4.75 mm. The fineness modulus of the used aggregates was 2.72. Size distribution curve for aggregate used in the present research is shown in Figure 1. The review of the literature presented in Table 2 showed that the length of the BF considered in the table for production of polymer and Processes 2021, 9, 510 9 of 16 cementitious composites is ranged from 6 to 45 mm. Shorter chopped lengths fibers are more effective for appropriate fiber distribution while longer chopped lengths are more effective in crack bridging action [68].
PC. In this study, the content of the chopped BF in the mortar mixtures was considered 2% of the total volume, which is consistent with the literature. BF is another admixture in the composite to improve the thermal resistance of the composite. Nonetheless, the addition of BF into the mixtures may improve the fresh properties of the composite, it reduces the compressive strength of the hardened mortar specimens. In order to restrict the adverse effect and take advantage of BF in improving thermal resistance and rhetorical properties, a lower proportion of SA compared to that used in literature was incorporated. BF amount used in this study occupied only 0.1% of the total mortar volume. The geometrical and mechanical properties of the BF used in the present study are shown in Table 5. The fine fraction of aggregates 0-150 μm were excluded. Two-part epoxy resin with a specific weight of 1.1 gr/cm 3 was used in the experiment. In this process, a low viscous epoxy, known as saturant resin (Part A) and hardener (Part B), was mixed to obtain a homogeneous mixture. Epoxy resins are the most widely used PC compounds [69]. Epoxy concrete is composed of two parts of the epoxy and aggregate blend. The curing of the epoxy resin systems is an exothermic reaction. The aggregates were checked to be dry and free of dirt, debris, and organic materials using In order to achieve the objectives of this study and in light of the findings reported in previous studies, together with the literature review discussed in the introduction section, the average length of the chopped BF in the mortar mixtures is considered 10 mm for this study. Moreover, the amount of investigated fiber content reported in previous studies and literature review is ranged between 0.15% and 2% of the total volume of the PC. In this study, the content of the chopped BF in the mortar mixtures was considered 2% of the total volume, which is consistent with the literature. BF is another admixture in the composite to improve the thermal resistance of the composite. Nonetheless, the addition of BF into the mixtures may improve the fresh properties of the composite, it reduces the compressive strength of the hardened mortar specimens. In order to restrict the adverse effect and take advantage of BF in improving thermal resistance and rhetorical properties, a lower proportion of SA compared to that used in literature was incorporated. BF amount used in this study occupied only 0.1% of the total mortar volume. The geometrical and mechanical properties of the BF used in the present study are shown in Table 5. The fine fraction of aggregates 0-150 µm were excluded. Two-part epoxy resin with a specific weight of 1.1 gr/cm 3 was used in the experiment. In this process, a low viscous epoxy, known as saturant resin (Part A) and hardener (Part B), was mixed to obtain a homogeneous mixture. Epoxy resins are the most widely used PC compounds [69]. Epoxy concrete is composed of two parts of the epoxy and aggregate blend. The curing of the epoxy resin systems is an exothermic reaction. The aggregates were checked to be dry and free of dirt, debris, and organic materials using sieving and oven drying. The mix proportion of the saturant resin and hardener with the trading name of Araks FK20 was as per the guidelines of the manufacturer. Generally, epoxy formulations are skin sensitizers, and handling precautions should be taken carefully [69]. In order to determine the general proportions of selected materials in the experimental study, two amounts of 13% and 15% of the total mortar volume were used for epoxy content in the mix design stage. SA occupied 0.1% of the total mortar volume.
The curing time and temperature for PC are affected by parameters such as the epoxy formulation, mix proportions of PC composition, and mass volume. Generally, PC mortar cures in hours after casting while complete curing of the cement-based materials takes days or weeks.

Mix Designs and Preparation of Specimens
The experimental study was conducted in two phases, one aimed to obtain appropriate proportions and the other is to investigate the main objective of this research. In the first phase of the experimental program, two epoxy concrete mixes made of aggregate and epoxy resin without the inclusion of BF and SA were tested. The results of the compressive strength for the epoxy resin contents of 13% and 15% were 41.9 MPa and 39.7 MPa. For the second phase, different mix designs of PC were determined to have aggregate, epoxy resin, FB, and SA in the composition of the mix. The resin amount, in the PC mix designs, was constant and equal to 13% of the total concrete volume. The mix design for SA-based BFreinforced mortar subjected to 0 • C and elevated temperatures of 100 • C, 150 • C, and 180 • C is presented in Table 6. Zero temperature in these tables that is room-curing temperature without heating was a reference before heating of samples. The hardened mortar specimens were exposed to three elevated temperatures of 100 • C, 150 • C and 180 • C for a duration of three hours. Then, the compressive strength of samples was tested and compared for each mix design under raised temperature conditions. To test compressive strength, PC samples were placed in the oven for three hours under the intended temperature after 7 days of curing. In order to prevent cooling shock, samples were left at room temperature to cool down gradually before applying compressive load in the testing machine.

Compressive Strength Testing
The compressive strength tests of the specimens were carried out according to ASTM C109-08. For each mixture, three 50 × 50 × 50 mm cubic specimens of each mix were tested after 3 days. In order to determine the ultimate load-carrying capacity under pure compression, the axial compressive load was applied continuously with a rate of 2.4 kN/sec according to ASTM C31 by a compression machine with 2000 kN capacity. The load was applied until the rupture of the specimen which means that the failure of the specimen at the point, the reading of the load in kN, and stress in MPa were recorded from the dial gauge.

Result and Discussions
Compressive tests were performed to investigate the temperature resistance of PC mortar and the effect of the inclusion of chopped BF and SA on the mechanical strength of PC. The results of the ultimate load-carrying capacity of the mortar specimens for different mix designs are shown in Table 7. The result shows that incorporation of BF and/or SA into PC reduced the compressive strength to 33.8, 34.3, and 35.3, which is consistent with the observation published by Dias and Thaumaturgo [34] and Niaki et al. [36], that BF reduces the compressive strength of PC.

Compressive Strength Testing
The compressive strength tests of the specimens were carried out according to ASTM C109-08. For each mixture, three 50 × 50 × 50 mm cubic specimens of each mix were tested after 3 days. In order to determine the ultimate load-carrying capacity under pure compression, the axial compressive load was applied continuously with a rate of 2.4 kN/sec according to ASTM C31 by a compression machine with 2000 kN capacity. The load was applied until the rupture of the specimen which means that the failure of the specimen at the point, the reading of the load in kN, and stress in MPa were recorded from the dial gauge.

Result and Discussions
Compressive tests were performed to investigate the temperature resistance of PC mortar and the effect of the inclusion of chopped BF and SA on the mechanical strength of PC. The results of the ultimate load-carrying capacity of the mortar specimens for different mix designs are shown in Table 7. The result shows that incorporation of BF and/or SA into PC reduced the compressive strength to 33.8, 34.3, and 35.3, which is consistent with the observation published by Dias and Thaumaturgo [34] and Niaki et al. [36], that BF reduces the compressive strength of PC.

Compressive Strength Testing
The compressive strength tests of the specimens were carried out according to ASTM C109-08. For each mixture, three 50 × 50 × 50 mm cubic specimens of each mix were tested after 3 days. In order to determine the ultimate load-carrying capacity under pure compression, the axial compressive load was applied continuously with a rate of 2.4 kN/sec according to ASTM C31 by a compression machine with 2000 kN capacity. The load was applied until the rupture of the specimen which means that the failure of the specimen at the point, the reading of the load in kN, and stress in MPa were recorded from the dial gauge.

Result and Discussions
Compressive tests were performed to investigate the temperature resistance of PC mortar and the effect of the inclusion of chopped BF and SA on the mechanical strength of PC. The results of the ultimate load-carrying capacity of the mortar specimens for different mix designs are shown in Table 7. The result shows that incorporation of BF and/or SA into PC reduced the compressive strength to 33.8, 34.3, and 35.3, which is consistent with the observation published by Dias and Thaumaturgo [34] and Niaki et al. [36], that BF reduces the compressive strength of PC.

Compressive Strength Testing
The compressive strength tests of the specimens were carried out according to ASTM C109-08. For each mixture, three 50 × 50 × 50 mm cubic specimens of each mix were tested after 3 days. In order to determine the ultimate load-carrying capacity under pure compression, the axial compressive load was applied continuously with a rate of 2.4 kN/sec according to ASTM C31 by a compression machine with 2000 kN capacity. The load was applied until the rupture of the specimen which means that the failure of the specimen at the point, the reading of the load in kN, and stress in MPa were recorded from the dial gauge.

Result and Discussions
Compressive tests were performed to investigate the temperature resistance of PC mortar and the effect of the inclusion of chopped BF and SA on the mechanical strength of PC. The results of the ultimate load-carrying capacity of the mortar specimens for different mix designs are shown in Table 7. The result shows that incorporation of BF and/or SA into PC reduced the compressive strength to 33.8, 34.3, and 35.3, which is consistent with the observation published by Dias and Thaumaturgo [34] and Niaki et al. [36], that BF reduces the compressive strength of PC.

Compressive Strength Testing
The compressive strength tests of the specimens were carried out according to ASTM C109-08. For each mixture, three 50 × 50 × 50 mm cubic specimens of each mix were tested after 3 days. In order to determine the ultimate load-carrying capacity under pure compression, the axial compressive load was applied continuously with a rate of 2.4 kN/sec according to ASTM C31 by a compression machine with 2000 kN capacity. The load was applied until the rupture of the specimen which means that the failure of the specimen at the point, the reading of the load in kN, and stress in MPa were recorded from the dial gauge.

Result and Discussions
Compressive tests were performed to investigate the temperature resistance of PC mortar and the effect of the inclusion of chopped BF and SA on the mechanical strength of PC. The results of the ultimate load-carrying capacity of the mortar specimens for different mix designs are shown in Table 7. The result shows that incorporation of BF and/or SA into PC reduced the compressive strength to 33.8, 34.3, and 35.3, which is consistent with the observation published by Dias and Thaumaturgo [34] and Niaki et al. [36], that BF reduces the compressive strength of PC.  Figure 2 shows the variation in the compressive strength of different mix designs compared to the reference state. The analysis of the results obtained by the compressive strength test of the samples maintained at room temperature revealed that the addition of BF and SA to the reference mix design decreased compressive strength. A lower decrease in compressive strength was observed for the mortar mix containing sodium alginate (SA) compared to those with only alginate. The samples with sodium alginate pose lower compressive strength due to the amount and size of voids in the structure of the hardened composite compared to the control mortar [24]. This weakening of compressive strength may ascribe to forming voids by the addition of the fibers into the matrix, which is in agreement with test results by Reis [30], Kabay [59], and Sun et al. [66]. However, the observation during uniaxial compressive loading indicated that the inclusion of FB leads to the absorption of a large amount of plastic energy before failure that is indicated also in other research studies. He and Lu [70] and Donker and Obonyo [71]. The analysis of the results obtained by the compressive strength test for polymer mortar containing BF and SA revealed that the addition of BF and SA to the reference mix design enhanced compressive strength growth in elevated temperatures. The cure of an epoxy resin is an exothermic process; however, the observation of an experimental investigation on curing temperature of epoxy resin conducted by Lahouar et al. [72] reported absorption of energy between 20 • C and 80 • C representing an endothermic peak due to possible phase change in curing state of the resin. Variations in the compressive strength after heating of the PC containing either BF or SA alone or both together indicate improving the effectiveness of these additives. The obtained results are not in agreement with those of either two works of Reis et al. [35] and [30], indicating a sharp increase (up to 50%) or drastic drop of compressive strength due to temperature elevation. the results obtained by the compressive strength test for polymer mortar containing BF and SA revealed that the addition of BF and SA to the reference mix design enhanced compressive strength growth in elevated temperatures. The cure of an epoxy resin is an exothermic process; however, the observation of an experimental investigation on curing temperature of epoxy resin conducted by Lahouar et al. [72] reported absorption of energy between 20 °C and 80 °C representing an endothermic peak due to possible phase change in curing state of the resin. Variations in the compressive strength after heating of the PC containing either BF or SA alone or both together indicate improving the effectiveness of these additives. The obtained results are not in agreement with those of either two works of Reis et al. [35] and [30], indicating a sharp increase (up to 50%) or drastic drop of compressive strength due to temperature elevation. The negative percentage for variation of compressive strength of MPT specimens is in agreement with previous studies that indicated the adverse effect of elevated temperature on the hardened specimens. The increase in the variation of compressive strength in MPBT, MPAT, and MPBAT supports the finding of this research that the addition of BF and SA enhances the compressive strength of PC. The highest positive influence by raised temperature is corresponding to the mixture including SA alone that with an increase in the temperature from room temperature to 100 °C then 150 °C and finally to 180 °C, growth in the compressive strength became 21.08%, 29.45%, and 30.61%, respectively. A lower increase of the compressive strength of the BF-reinforced PC is due to the entrapped voids because of fiber addition. The obtained results about enhanced temperature resistance of SA-based mortar specimens also conform to the finding of DeBrouse [23]. MPT   The negative percentage for variation of compressive strength of MPT specimens is in agreement with previous studies that indicated the adverse effect of elevated temperature on the hardened specimens. The increase in the variation of compressive strength in MPBT, MPAT, and MPBAT supports the finding of this research that the addition of BF and SA enhances the compressive strength of PC. The highest positive influence by raised temperature is corresponding to the mixture including SA alone that with an increase in the temperature from room temperature to 100 • C then 150 • C and finally to 180 • C, growth in the compressive strength became 21.08%, 29.45%, and 30.61%, respectively. A lower increase of the compressive strength of the BF-reinforced PC is due to the entrapped voids because of fiber addition. The obtained results about enhanced temperature resistance of SA-based mortar specimens also conform to the finding of DeBrouse [23].
Utilization of both BF and SA together in the PC has been with a lower increase from room temperature to 100 • C until 180 • C, compared to the individual application of these materials. However, it can be seen that heating of PC for 3 h under 180 • C resulted in strength reduction, while together or individual effectiveness of BF and SA in the PC is remarkable on the improvement in the compressive strength after heating for all the three temperatures. From Table 6, the highest compressive strength for samples of PC after 3 days of air curing was higher than the cement concrete samples. A comparison between the obtained compressive strength of polymer and cement concretes with BF and SA indicated that the elevated temperature had a greater influence on polymer concrete than that of cement concrete. The rate of increase was around 20% for polymer concrete, while it was around 5% for cement concrete for temperature rise from room temperature to 180 • C.
Polymer concrete samples after failure under compression test are shown in Figure 3. It should be demonstrated that PC samples exhibited no obvious crack on the surface when the applied load was released after failure under compression. The produced polymer concrete can be considered as a composition of two phases of polymer mortars and aggregates. Through applying the load displacement into the specimens, it was observed that the failure was initiated by the creation of interphase microcracks between polymer mortars and aggregates. By increasing the compressive load, longitudinal cracks were propagated along the jaws' direction, which was similar to those that happen in normal concrete. It was observed that the time between crack initiation and total failure of the specimens was lower than that of cementitious concrete specimens [24,73].
remarkable on the improvement in the compressive strength after heating for all the three temperatures. From Table 6, the highest compressive strength for samples of PC after 3 days of air curing was higher than the cement concrete samples. A comparison between the obtained compressive strength of polymer and cement concretes with BF and SA indicated that the elevated temperature had a greater influence on polymer concrete than that of cement concrete. The rate of increase was around 20% for polymer concrete, while it was around 5% for cement concrete for temperature rise from room temperature to 180 °C.
Polymer concrete samples after failure under compression test are shown in Figure  3. It should be demonstrated that PC samples exhibited no obvious crack on the surface when the applied load was released after failure under compression. The produced polymer concrete can be considered as a composition of two phases of polymer mortars and aggregates. Through applying the load displacement into the specimens, it was observed that the failure was initiated by the creation of interphase microcracks between polymer mortars and aggregates. By increasing the compressive load, longitudinal cracks were propagated along the jaws' direction, which was similar to those that happen in normal concrete. It was observed that the time between crack initiation and total failure of the specimens was lower than that of cementitious concrete specimens [24,73]. The compressive load was applied until the mortar specimens of each mix reached their ultimate load-bearing capacity and failure occurred. High plastic deformation of the polymer concrete was observed corresponding to the applied load.

Conclusions
In order to investigate the effectiveness of the addition of BF with the natural source and/or SA as a waste material to reduce the strength degradation of polymer concretes after exposure to raised temperatures of 100 °C, 150 °C, and 180 °C, an experimental program was conducted in two phases including primary study and main study. The addition of BF and/or SA decreases concrete compressive strength under room temperature, but the addition of BF and SA each alone leads to compressive strength increase during exposure to heat. An increase in the temperature to 180 °C showed an almost positive effect on the compressive strength. The highest positive influence by raised temperature is corresponding to the mixture including SA alone that, with an increase in the temperature from room temperature to 100 °C then 150 °C and finally to 180 °C, growth in the compressive strength became 21.08%, 29.45%, and 30.61%, respectively. The addition of BF and SA both together increases the rate of strength growth of polymer concrete under heat from 100 °C to 180 °C. In view of these conclusions, the addition of BF and SA results in a decrease of compressive strength of polymer concretes under room temperature, but it is obvious that these materials are positive to improve the resistance of PC. However, the most important outcome of this research may be a natural source of BF and waste material SA to prevent PC compressive strength degradation under elevated temperature. Increase of compressive strength up to 30%, that when noticed to the  The compressive load was applied until the mortar specimens of each mix reached their ultimate load-bearing capacity and failure occurred. High plastic deformation of the polymer concrete was observed corresponding to the applied load.

Conclusions
In order to investigate the effectiveness of the addition of BF with the natural source and/or SA as a waste material to reduce the strength degradation of polymer concretes after exposure to raised temperatures of 100 • C, 150 • C, and 180 • C, an experimental program was conducted in two phases including primary study and main study. The addition of BF and/or SA decreases concrete compressive strength under room temperature, but the addition of BF and SA each alone leads to compressive strength increase during exposure to heat. An increase in the temperature to 180 • C showed an almost positive effect on the compressive strength. The highest positive influence by raised temperature is corresponding to the mixture including SA alone that, with an increase in the temperature from room temperature to 100 • C then 150 • C and finally to 180 • C, growth in the compressive strength became 21.08%, 29.45%, and 30.61%, respectively. The addition of BF and SA both together increases the rate of strength growth of polymer concrete under heat from 100 • C to 180 • C. In view of these conclusions, the addition of BF and SA results in a decrease of compressive strength of polymer concretes under room temperature, but it is obvious that these materials are positive to improve the resistance of PC. However, the most important outcome of this research may be a natural source of BF and waste material SA to prevent PC compressive strength degradation under elevated temperature. Increase of compressive strength up to 30%, that when noticed to the cement amount with the energy-wasting process to be produced, is a very valuable finding.