Improvement of Load Carrying Capacity of Concrete Pavement Slabs Using Macro Synthetic Fibers

: This study presents the results of an investigation of the effect of macro synthetic ﬁbers (MSF) reinforcement on the load carrying capacity of concrete pavement slabs. Six concrete slabs having dimensions of 800 × 800 × 50 mm 3 were prepared and tested under static loads at three different positions: interior, edge and corner of the slab. Three of the slabs were Portland cement concrete (PCC) and prepared as references. The other three slabs were macro synthetic ﬁber reinforced concrete (MSFRC). Mechanical properties examined in this study included compressive strength, splitting tensile strength, ﬂexural strength and modulus of elasticity and ductility of PCC and MSFRC. The ﬁndings showed that the addition of MSF to PCC improved the load carrying capacity of concrete pavement slabs. Test results obtained indicated that the ultimate load carrying capacity of MSFRC slabs was increased by 24%, 20%, and 23% for interior, edge and corner loading positions, respectively.


Introduction
Concrete pavement is subjected to repeated axle loads during its service life. Axle loads, which influence the rigid pavement, produce different stresses according to the different positions of the pavement [1]. The initiation of cracks may be caused due to the repeated application of axle loads along with the variation of temperature at the highly stressed positions. There are three critical positions: interior, edge and corner, which influence the structural performance of pavement [2][3][4][5][6]. The propagation of cracks through the concrete pavement-especially for these positions-causes fracture and failure, which can lead to loss of serviceability and unsafe driving conditions [6,7]. This occurrence is mainly because of the brittleness of concrete together with its small toughness and its low resistance to fatigue [7]. Therefore, researchers started to modify the concrete permanently, to enhance its comprehensive performance. They have found an effective and economic way of enhancement. By mixing of concrete and different types of fibers, a new type of building material with brilliant comprehensive performance is produced, namely fiber reinforced concrete (FRC) [8].
Many studies have been conducted in the last decades concerning the mechanical performance of FRC. It appears that the incorporation of fibers in the concrete mixture could considerably enhance the mechanical properties of concrete [9][10][11][12]. Furthermore, fibers have been used to enhance the cracking performance of concrete pavements, provide additional structural capacity and decrease the required slab thickness [13].
There are mainly four types of fibers that can be used to reinforce concrete: steel fiber, glass fiber, natural fiber and synthetic fiber [14]. Recently, synthetic fiber has been more famous due to its excellent comprehensive characteristics. Compared to other fibers, synthetic fiber has been widely used in engineering practice, with the properties of small density, appropriate price and easy dispersion in concrete [15]. Synthetic fiber can be made of polyolefin, aramid, acrylic and carbon [16]. Locally available crushed stone from the Suez Attaka quarry of sizes 20 mm and 10 mm in 50:50 proportion was used as coarse aggregate, and natural sand was used as fine aggregate. Table 2 shows the physical properties of coarse, fine aggregates and the Egyptian standard specifications [38]. For casting and curing purposes, potable water was used in PCC and MSFRC mixtures. The superplasticizer used in this study was polycarboxylic ether (PCE), provided by BASF, and complied with the ASTM C494 standard [39]. The superplasticizer was used to facilitate the dispersion of MSF in the concrete mixture, and to attain the desired workability for concrete [40].

Fibers
The synthetic fibers were chosen based on the present market trend and the findings of a literature review. The structural macro synthetic polypropylene fibers were found to be the most desirable and sustainable. The fibers were extruded from a natural PP homopolymer according to the ASTM C1116 [41] and EN 14889-2 [42] standards. The MSF used in this study were manufactured by BASF Construction Chemicals, Dubai, with a trade name Master fiber 249. The fiber manufacturer provided the material properties and dosage of the MSF, which can be found in the datasheet published on the BASF website [43]. These PP fibers were straight strips with a continuously embossed surface texture and were highly resistant to chemicals and alkali. Further details about the properties of MSF, as provided by the manufacturer [43], are reported in Table 3. Figure 1 shows the shape of the MSF used in this study. The synthetic fibers were chosen based on the present market trend and the findings of a literature review. The structural macro synthetic polypropylene fibers were found to be the most desirable and sustainable. The fibers were extruded from a natural PP homopolymer according to the ASTM C1116 [41] and EN 14889-2 [42] standards. The MSF used in this study were manufactured by BASF Construction Chemicals, Dubai, with a trade name Master fiber 249. The fiber manufacturer provided the material properties and dosage of the MSF, which can be found in the datasheet published on the BASF website [43]. These PP fibers were straight strips with a continuously embossed surface texture and were highly resistant to chemicals and alkali. Further details about the properties of MSF, as provided by the manufacturer [43], are reported in Table 3. Figure 1 shows the shape of the MSF used in this study.

Mixing, Casting and Curing Procedure
A pan mixer (MATEST manufacturer, Treviolo, Italy) with a capacity of 0.1 m 3 was used for mixing. To cast all the specimens, two batches were prepared with the same mix proportions. The first batch was used to cast all PCC specimens, while the second batch was used to cast all MSFRC specimens. The ratio of water to cement (w/c) used in PCC and MSFRC mixtures was 0.45. A mixture without any MSF was prepared as a control. To produce PCC, the process of mixing began with the dry mixing for 30 s of the coarse and

Mixing, Casting and Curing Procedure
A pan mixer (MATEST manufacturer, Treviolo, Italy) with a capacity of 0.1 m 3 was used for mixing. To cast all the specimens, two batches were prepared with the same mix proportions. The first batch was used to cast all PCC specimens, while the second batch was used to cast all MSFRC specimens. The ratio of water to cement (w/c) used in PCC and MSFRC mixtures was 0.45. A mixture without any MSF was prepared as a control. To produce PCC, the process of mixing began with the dry mixing for 30 s of the coarse and fine aggregates. Then, the cement was added to the mixture and blended for 1 min. Subsequently, for 30 s, a liquid mixture of water and SP was poured into the mixture. To attain the desired workability for concrete, the obtained mixture was then stirred for 2 min.
In the other mixture, MSF were added to the PCC at a constant dosage of 6 kg/m 3 corresponding to a volume fraction (V f ) of 0.66%. This dosage was selected, as (a) the dosage suggested by the manufacturer to attain appropriate performance [43], and (b) based on previous studies [44][45][46][47][48]. Table 4 shows the proportions of the concrete mixture. In the MSFRC mixture realized as part of this study, the same proportions were retained for the concrete matrix. The amount of SP was remained the same for PCC and MSFRC mixtures at 1.0% of the cement weight to assess the influence of MSF on the concrete mixture workability. MSF were typically added to the ready-mix concrete in the batch plant, and the produced concrete was easy to pump and implement [49]. In this study, MSF were added after mixing aggregates, cement, and water. Then, for 2 min, the mixture was thoroughly mixed to ensure uniform distribution. Two minutes of additional mixing was sufficient for the appropriate dispersion of MSF in the mixture without leading to a "balling" influence [50]. For each mixture, the fresh properties of concrete were measured after the mixing procedure. Six timber formworks were prepared for molding of concrete slabs. Figure 2 shows the concrete slabs prepared for this study. All slabs were cast on the same day and were compacted using mechanical vibrators (MATEST manufacturer, Treviolo, Italy). The slabs were cured for 28 days after 24 ± 2 h from the casting. To prevent losing moisture from the concrete, the slabs were covered with hessian blankets during the curing process. Additionally, to minimize the effects of ambient air, the slabs were covered with two layers of plastic sheets.
ability. MSF were typically added to the ready-mix concrete in the batch plant, and the produced concrete was easy to pump and implement [49]. In this study, MSF were added after mixing aggregates, cement, and water. Then, for 2 min, the mixture was thoroughly mixed to ensure uniform distribution. Two minutes of additional mixing was sufficient for the appropriate dispersion of MSF in the mixture without leading to a "balling" influence [50].
For each mixture, the fresh properties of concrete were measured after the mixing procedure. Six timber formworks were prepared for molding of concrete slabs. Figure 2 shows the concrete slabs prepared for this study. All slabs were cast on the same day and were compacted using mechanical vibrators (MATEST manufacturer, Treviolo, Italy). The slabs were cured for 28 days after 24 ± 2 h from the casting. To prevent losing moisture from the concrete, the slabs were covered with hessian blankets during the curing process. Additionally, to minimize the effects of ambient air, the slabs were covered with two layers of plastic sheets.
In addition to the slabs, PCC and MSFRC specimens were also cast for the companion mechanical tests. For each mixture, the fresh concrete was cast into cubic molds of size 100 mm, cylindrical molds with the dimensions of 150 mm diameter by 300 mm height, and prismatic molds having a size of 100 × 100 × 500 mm 3 , as shown in Figure 3. The specimens were cast in two layers and vibrated on a vibrating table for 25 s per layer. To avoid moisture loss, the specimens were covered with plastic sheets after casting. Then, the specimens were kept under standard laboratory conditions for 24 ± 2 h until demolding. Subsequently, the specimens were placed in a curing tank (23 ± 2 °C and 95% ± 5% relative humidity (RH)) until testing. All tests were performed at 28 days.   In addition to the slabs, PCC and MSFRC specimens were also cast for the companion mechanical tests. For each mixture, the fresh concrete was cast into cubic molds of size 100 mm, cylindrical molds with the dimensions of 150 mm diameter by 300 mm height, and prismatic molds having a size of 100 × 100 × 500 mm 3 , as shown in Figure 3. The specimens were cast in two layers and vibrated on a vibrating table for 25 s per layer. To avoid moisture loss, the specimens were covered with plastic sheets after casting. Then, the specimens were kept under standard laboratory conditions for 24 ± 2 h until demolding. Subsequently, the specimens were placed in a curing tank (23 ± 2 • C and 95% ± 5% relative humidity (RH)) until testing. All tests were performed at 28 days. Coatings 2021, 11, x FOR PEER REVIEW 6 of 18

Fresh Properties
The slump, air content and fresh density were calculated immediately after the mixing process according to the ASTM C143 [51], ASTM C231 [52], and ASTM C138 [53] standards, respectively.

Compressive Strength Test
The compressive strength tests were conducted on three 100 × 100 × 100 mm 3 cubic specimens for each mixture at 28 days according to the EN 12390-3 standard [54]. The compression testing machine used was an ELE (Engineering Laboratory Equipment) of capacity 2000 kN. For each mixture, the average of three compressive strength values was reported.

Splitting Tensile Strength Test
The splitting tensile test is well known as one of the simplest and most dependable tests for the indirect evaluation of concrete tensile strength [55]. The splitting tensile strength tests were conducted on cylindrical concrete specimens of 150 mm diameter and 300 mm height at 28 days according to the ASTM C496 standard [56]. The load was applied continuously at a constant rate up to failure using a universal testing Schmadzumachine of capacity 500 kN. The failure load was reported to calculate the splitting tensile strength by following Equation (1), and three specimens were used to calculate the average strength.

Flexural Strength Test
Flexural strength, sometimes also known as modulus of rupture (MOR), is like an evaluation of tensile strength in bending. The flexural strength tests were conducted on 100 × 100 × 500 mm 3 prism test specimens at 28 days, according to the ASTM C293 standard [57]. For each mixture, three specimens were prepared, and the average values were recorded. The set-up consists of two supporting rollers, spaced by 400 mm, and one loading roller placed in the middle. The flexural test was conducted using a universal testing Schmadzu-machine of capacity 500 kN. Equation (2) was used to calculate the flexural strength of the concrete specimens.

Fresh Properties
The slump, air content and fresh density were calculated immediately after the mixing process according to the ASTM C143 [51], ASTM C231 [52], and ASTM C138 [53] standards, respectively.

Compressive Strength Test
The compressive strength tests were conducted on three 100 × 100 × 100 mm 3 cubic specimens for each mixture at 28 days according to the EN 12390-3 standard [54]. The compression testing machine used was an ELE (Engineering Laboratory Equipment) of capacity 2000 kN. For each mixture, the average of three compressive strength values was reported.

Splitting Tensile Strength Test
The splitting tensile test is well known as one of the simplest and most dependable tests for the indirect evaluation of concrete tensile strength [55]. The splitting tensile strength tests were conducted on cylindrical concrete specimens of 150 mm diameter and 300 mm height at 28 days according to the ASTM C496 standard [56]. The load was applied continuously at a constant rate up to failure using a universal testing Schmadzu-machine of capacity 500 kN. The failure load was reported to calculate the splitting tensile strength by following Equation (1), and three specimens were used to calculate the average strength.

Flexural Strength Test
Flexural strength, sometimes also known as modulus of rupture (MOR), is like an evaluation of tensile strength in bending. The flexural strength tests were conducted on 100 × 100 × 500 mm 3 prism test specimens at 28 days, according to the ASTM C293 standard [57]. For each mixture, three specimens were prepared, and the average values were recorded. The set-up consists of two supporting rollers, spaced by 400 mm, and one loading roller placed in the middle. The flexural test was conducted using a universal testing Schmadzu-machine of capacity 500 kN. Equation (2) was used to calculate the flexural strength of the concrete specimens. where F b = flexural strength (MPa), P = failure load (N), l = specimen span (mm), b = specimen width (mm) and h = specimen height (mm).

Modulus of Elasticity Test
Modulus of elasticity is an important mechanical property used to evaluate the behavior of concrete [58]. Modulus of Elasticity was calculated by averaging the test results of three 150 × 300 mm 2 cylindrical specimens for each mixture at 28 days according to the ASTM C469 standard [59]. In this test, the cylindrical specimens were subjected to compressive loading in the longitudinal direction. The axial stress of the specimens during the compression test was determined as the ratio of the applied compressive force to the specimens' cross section, and their axial strain was also calculated through measurement of the axial deformation at the mid-height. Table 5 presents the details of PCC and MSFRC slabs. Six concrete slabs, having dimensions of 800 × 800 × 50 mm 3 , were prepared and tested under a static load. Three of the slabs were PCC slabs and taken as references. The other three slabs were MSFRC slabs. The slabs were divided into three groups according to the position of the applied load. Each group consisted of two slabs (PCC and MSFRC slabs). The load was applied at the interior of the slabs for the first group. The load was applied at the edge of the slabs for the second group. For the third group, the slabs were tested by applying the load at the corner of the slab. The number of six concrete slabs chosen in this study was to test one slab for one position for PCC and MSFRC slabs as simulated in a study performed in 1998 [60], and another one in 2018 [61]. They studied the behavior of concrete pavement slabs with one slab for each case of the loading position with consideration the ratio of side dimension to thickness, more than 15 times that complied with concrete pavement design assumptions reported by the Portland cement association (PCA) [62].

Slabs Loading Test
The labelling of PCC and MSFRC slabs is summarized in Table 5. The first letter in the table is PCC slabs (P) (reference) and fiber reinforced concrete slabs (F). The second letter on the label refers to the position of the applied load, which are interior, edge and corner labelled as (I), (E) and (C), respectively. For example, the MSRFC slab which was loaded at the edge of the slab is labelled as (FE).
To simulate a subgrade soil with a specific modulus of subgrade reaction, steel springs were used under a layer of recycled rubber with a 20 mm thickness that was used to ensure the uniform distribution of stress overall springs. A displacement control testing machine was used to calculate the springs' modulus of reaction or spring constant in compression by recording the applied loads with the regarding displacements. The average modulus of subgrade reaction of the springs was 37 MPa/m. Figure 4 shows the concrete slab loading frame. The load was monotonically applied by a hydraulic jack of capacity 1000 kN. A circular steel disk with a 100 mm diameter was placed between the hydraulic jack and the slab. The load was applied until the collapse load of the slab was reached. A steel frame was used to fix the concrete slabs with spring support while applying the load. The steel frame contained three steel angles with dimensions of Coatings 2021, 11, 833 8 of 17 50 × 50 × 5 mm 3 and one steel strip to fix the fourth side of the slab. Figure 5 shows the test set-up for the three load cases. support while applying the load. The steel frame contained three steel angles with dimensions of 50 × 50 × 5 mm 3 and one steel strip to fix the fourth side of the slab. Figure 5 shows the test set-up for the three load cases.
The parameters measured during the monotonic testing were the slab vertical deflection and the applied load. The deflection that occurred at the loaded area was measured by linear variable displacement transducers (LVDTs). The maximum applied load which caused the collapse of the slab was defined as the ultimate load carrying capacity. The load versus deflection curves were plotted for different loading positions for each slab.   support while applying the load. The steel frame contained three steel angles with dimensions of 50 × 50 × 5 mm 3 and one steel strip to fix the fourth side of the slab. Figure 5 shows the test set-up for the three load cases. The parameters measured during the monotonic testing were the slab vertical deflection and the applied load. The deflection that occurred at the loaded area was measured by linear variable displacement transducers (LVDTs). The maximum applied load which caused the collapse of the slab was defined as the ultimate load carrying capacity. The load versus deflection curves were plotted for different loading positions for each slab.  The parameters measured during the monotonic testing were the slab vertical deflection and the applied load. The deflection that occurred at the loaded area was measured by linear variable displacement transducers (LVDTs). The maximum applied load which caused the collapse of the slab was defined as the ultimate load carrying capacity. The load versus deflection curves were plotted for different loading positions for each slab.

Fresh Concrete Properties
The fresh properties of PCC and MSFRC mixtures were measured, and the results are reported in Table 6. The addition of fibers is well known to have a major effect on PCC workability [63]. In this study, the amount of water and SP remained the same for PCC and MSFRC mixtures to assess the effect of MSF on MSFRC workability. From Table 6, it can be noted that the slump of 112 mm was obtained for the PCC, and once the MSF were added, the slump reduced by 27.6% compared with that of PCC. This reduction in slump can be because of the use of fibers that can create a network structure in the concrete mixture, consequently preventing the mixture from segregation and flow [63]. Furthermore, because of the large surface area of fibers, fibers can absorb cement paste to wrap around, consequently increasing the viscosity of the concrete mixture and reducing its workability [64]. In the case of air content, as reported in Table 6, the added MSF participated in the increase of air content. PCC showed air content of 1.7%, and MSFRC showed higher air content of 1.9%. During the mixing process, fibers can entrap more air [65]. The large specific surface area of the fibers and their trend to sometimes conglomerate can also participate in the increase of air entrapment [66].
The densities of PCC and MSFRC were 2389 and 2332 kg/m 3 , respectively, as reported in Table 6. The density of MSFRC was reduced by 58 kg/m 3 than that of PCC. Consequently, the density of MSFRC was reduced by 2.4% as compared to that of PCC. The less density of MSFRC than that of PC is due to the existence of less density of MSF [37]. Moreover, the above-mentioned increase in air content may have a slight impact on the density [65]. Figure 6 presents the results of compressive strength of PCC and MSFRC specimens at 28 days. Each mixture achieved the target compressive strength of 30 MPa. The 28-day compressive strength of PCC was 34.6 MPa. With the incorporation of MSF, the compressive strength was not significantly influenced, which was minor reduced by about 4% compared with that of PCC specimens. In previous studies [24,67], researchers reported a 6%-13% decrease in compressive strength of concrete due to the addition of other types of MSF. This decrease could be because of the existence of voids due to the incorporation of MSF and the presence of weak interfacial bonds between MSF and cement particles [68]. Moreover, this reduction may be due to the influence of MSF on decreasing the mixture density [51].

Compressive Strength
There was a change in the failure mode of the specimens when MSF were added. The failure mode significantly changed from brittle to ductile. The cubic specimens did not crush but held their integrity up to the end of the test due to the bridging effect of fibers [49,69].

Splitting Tensile Strength
The results of the splitting tensile strength at 28 days are presented in Figure 7. As can be noted from the results, the splitting tensile strength of MSFRC specimens was increased when compared with that of PCC specimens. The results clarified that the incorporation of MSF enhanced the splitting tensile strength of MSFRC specimens by about 20.5%, in comparison with that of PCC specimens. In previous studies [70,71], researchers reported a 12%-16% increase in splitting tensile strength of concrete with the addition of other types of MSF. Coatings 2021, 11, x FOR PEER REVIEW 10 of 18

Splitting Tensile Strength
The results of the splitting tensile strength at 28 days are presented in Figure 7. As can be noted from the results, the splitting tensile strength of MSFRC specimens was increased when compared with that of PCC specimens. The results clarified that the incorporation of MSF enhanced the splitting tensile strength of MSFRC specimens by about 20.5%, in comparison with that of PCC specimens. In previous studies [70,71], researchers reported a 12%-16% increase in splitting tensile strength of concrete with the addition of other types of MSF. Even if the MSF have significant tensile strength, the brittle concrete is not designed to withstand the tensile force, and therein crack initiation is still restricted by the quality of the cement matrix, the peak load usually occurred when the main crack happened in the concrete. However, after the crack occurred, the effect of fiber bridging could provide an important role in restricting the fast growth of the crack. Consequently, MSF did not

Splitting Tensile Strength
The results of the splitting tensile strength at 28 days are presented in Figure 7. As can be noted from the results, the splitting tensile strength of MSFRC specimens was increased when compared with that of PCC specimens. The results clarified that the incorporation of MSF enhanced the splitting tensile strength of MSFRC specimens by about 20.5%, in comparison with that of PCC specimens. In previous studies [70,71], researchers reported a 12%-16% increase in splitting tensile strength of concrete with the addition of other types of MSF. Even if the MSF have significant tensile strength, the brittle concrete is not designed to withstand the tensile force, and therein crack initiation is still restricted by the quality of the cement matrix, the peak load usually occurred when the main crack happened in the concrete. However, after the crack occurred, the effect of fiber bridging could provide an important role in restricting the fast growth of the crack. Consequently, MSF did not Even if the MSF have significant tensile strength, the brittle concrete is not designed to withstand the tensile force, and therein crack initiation is still restricted by the quality of the cement matrix, the peak load usually occurred when the main crack happened in the concrete. However, after the crack occurred, the effect of fiber bridging could provide an important role in restricting the fast growth of the crack. Consequently, MSF did not clearly enhance the PC splitting tensile strength, but it significantly participated in the crack restricting [65].
Behaviors of distinct failure of concrete specimens were noticed after the test of splitting tensile. The PCC specimen displayed the obvious brittle failure as shown in Figure 8. However, after the addition of MSF, the failure behavior of the MSFRC specimen was varied; the failure was gradual, and the two parts were not fully separated. The morphology of the fracture confirmed that the MSF can bridge the crack and keep the concrete specimen to carry significant load after the occurrence of the first crack. crack restricting [65].
Behaviors of distinct failure of concrete specimens were noticed after the test of splitting tensile. The PCC specimen displayed the obvious brittle failure as shown in Figure 8. However, after the addition of MSF, the failure behavior of the MSFRC specimen was varied; the failure was gradual, and the two parts were not fully separated. The morphology of the fracture confirmed that the MSF can bridge the crack and keep the concrete specimen to carry significant load after the occurrence of the first crack.  In previous studies [72,73], researchers reported a 13%-17% increase in flexural strength of concrete with the addition of other types of MSF. It may be due to the bridging mechanism of MSF which restrained cracks growth and decreased crack width.   In previous studies [72,73], researchers reported a 13%-17% increase in flexural strength of concrete with the addition of other types of MSF. It may be due to the bridging mechanism of MSF which restrained cracks growth and decreased crack width. crack restricting [65].

Flexural Strength
Behaviors of distinct failure of concrete specimens were noticed after the test of splitting tensile. The PCC specimen displayed the obvious brittle failure as shown in Figure 8. However, after the addition of MSF, the failure behavior of the MSFRC specimen was varied; the failure was gradual, and the two parts were not fully separated. The morphology of the fracture confirmed that the MSF can bridge the crack and keep the concrete specimen to carry significant load after the occurrence of the first crack.  In previous studies [72,73], researchers reported a 13%-17% increase in flexural strength of concrete with the addition of other types of MSF. It may be due to the bridging mechanism of MSF which restrained cracks growth and decreased crack width.   Figure 10 displays the cracking mechanism of concrete specimens under the flexural test. It was observed that the PC specimen broke at the maximum load into two parts, displaying brittle behavior. Brittle behavior is permanently related to PCC [74]. The specimen cracked and collapsed almost suddenly when the first crack occurred, with very little deformation and no preceding warning. On the other hand, in the MSFRC specimen, the failure progressed with bending, but without any sudden collapse as observed in the PCC specimen. The load was transferred to the MSF when the concrete failed. The MSF restrained the growth of cracks and consequently delayed the failure [75].

Flexural Strength
test. It was observed that the PC specimen broke at the maximum load into two parts, displaying brittle behavior. Brittle behavior is permanently related to PCC [74]. The specimen cracked and collapsed almost suddenly when the first crack occurred, with very little deformation and no preceding warning. On the other hand, in the MSFRC specimen, the failure progressed with bending, but without any sudden collapse as observed in the PCC specimen. The load was transferred to the MSF when the concrete failed. The MSF restrained the growth of cracks and consequently delayed the failure [75].  Figure 11 presents the results obtained for the modulus of elasticity of PCC and MSFRC specimens. According to Figure 11, an increase in the 28-day modulus of elasticity was observed by 6% for MSFRC specimens as compared to PCC specimens. In a previous study [42], researchers observed a 3% increase in the modulus of elasticity of concrete reinforced with another type of MSF. By adding MSF, because of their embossed surface, a strong coherence was developed in the concrete specimen, which in turn improved the modulus of elasticity of the MSFRC with respect to the PCC [42]. Furthermore, MSF arrested the original shrinkage cracks in the concrete and hence reduced the strain induced under compression loading, and then enhanced the modulus of elasticity of MSFRC [76,77].

Modulus of Elasticity
The performance properties of plain concrete pavement were obtained for different values of elastic modulus of concrete ranging from 24 to 35 GPa [78]. Concrete with a higher elastic modulus behaved in a better way to deal with the loading stresses as compared with concrete with lower elastic modulus [78]. Therefore, the improvement in elastic modulus can be beneficial in concrete pavement design. It can be beneficial to increase the ultimate load capacity of PCC slabs, if the same thickness of PCC slabs will be used with reinforcement of MSF for the same service life [79].  Figure 11 presents the results obtained for the modulus of elasticity of PCC and MSFRC specimens. According to Figure 11, an increase in the 28-day modulus of elasticity was observed by 6% for MSFRC specimens as compared to PCC specimens. In a previous study [42], researchers observed a 3% increase in the modulus of elasticity of concrete reinforced with another type of MSF. By adding MSF, because of their embossed surface, a strong coherence was developed in the concrete specimen, which in turn improved the modulus of elasticity of the MSFRC with respect to the PCC [42]. Furthermore, MSF arrested the original shrinkage cracks in the concrete and hence reduced the strain induced under compression loading, and then enhanced the modulus of elasticity of MSFRC [76,77].   Table 7. The ductility of the tested concrete slabs is one of the investigated parameters in this study. It is defined as the ability of the specimen to resist the applied load from the start of loading until the failure occurred. It was determined by calculating the area under the applied load versus the deflection curve (Figures 12-14), as listed in Table 7.

Slabs Loading
The interior applied load versus deflection curves of PCC and MSFRC slabs, which were tested by applying a load at the interior of the slabs, labelled as slabs PI and FI, respectively, are shown in Figure 12. During the application of load, the ultimate applied The performance properties of plain concrete pavement were obtained for different values of elastic modulus of concrete ranging from 24 to 35 GPa [78]. Concrete with a higher elastic modulus behaved in a better way to deal with the loading stresses as compared with concrete with lower elastic modulus [78]. Therefore, the improvement in elastic modulus can be beneficial in concrete pavement design. It can be beneficial to increase the ultimate load capacity of PCC slabs, if the same thickness of PCC slabs will be used with reinforcement of MSF for the same service life [79].  Table 7. The ductility of the tested concrete slabs is one of the investigated parameters in this study. It is defined as the ability of the specimen to resist the applied load from the start of loading until the failure occurred. It was determined by calculating the area under the applied load versus the deflection curve (Figures 12-14), as listed in Table 7. The essential mechanism allowing for an increased collapsed load for MSFRC slabs was associated with the ability of fibers to engage a large proportion of the concrete slab in carrying and distributing load even after the occurrence of cracking [21].

Conclusions
Based on the results of this study, the following conclusions can be drawn: 1. Adding MSF to the concrete mixture led to reduced workability of the fresh concrete. 2. It was observed that concrete density was not mainly affected by the addition of MSF.
3. The addition of MSF caused a slight increase in air content as compared to the PCC. 4. The addition of MSF did not have a considerable effect on compressive strength, as by adding MSF to the concrete mix, a 4% decrease in compressive strength was observed. 5. The splitting tensile strength, flexural strength and elastic modulus of MSFRC at 28 days were increased by 20.5%, 33% and 6%, respectively, compared with that of PPC. 6. The load carrying capacity of the PCC slab was improved considerably by the addition of MSF. 7. The load carrying capacity of the MSFRC slab was higher than the PCC slab by about 24% for interior loading, 20% for edge loading and 23% for corner loading. 8. The ductility of the MSFRC slab was higher than the PCC slab by about 43% for interior loading, 26% for edge loading and 33% for corner loading. 9. In general, the results obtained and the observations made in this study proposed that concrete incorporating MSF could be used with satisfactory mechanical properties to increase the load carrying capacity and ductility of rigid pavement slabs. The interior applied load versus deflection curves of PCC and MSFRC slabs, which were tested by applying a load at the interior of the slabs, labelled as slabs PI and FI, respectively, are shown in Figure 12. During the application of load, the ultimate applied load of slab PI was 735 kN. Meanwhile for slab FI, the ultimate load was 971 kN. This achieved an increase in the load carrying capacity of slab FI by about 24% more than slab PI. In addition, this achieved an increase in the ductility of slab FI by about 43% more than slab PI. The recorded deflection that occurred for slab PI was 13.1 mm. Meanwhile for slab FI, the maximum deflection was 16.7 mm.
For PCC and MSFRC slabs, which were tested by applying a load at the edge of the slab, named as slabs PE and FE, respectively, Figure 13 presents the edge applied load versus deflection curves that occurred at the loaded area. The ultimate applied load was 587 kN for slab PE. For slab FE, the ultimate load was 732 kN. This increase attained improvement in the load carrying capacity of slab FE by about 20% more than slab PE. In addition, this increase attained improvement in the ductility of slab FE by about 26% more than slab PE. The deflection of slabs PE and FE was 25.5 and 27.6 mm, respectively. Figure 14 shows the curves of corner applied load versus deflection that occurred at the loaded area for PCC and MSFRC slabs, which were tested by applying a load at the corner of the slabs, named as slabs PC and FC, respectively. The ultimate applied load was 668 kN for slab PC. For slab FC, the ultimate applied load was 868 kN. This achieved an increase in the load carrying capacity of slab FC by about 23% more than slab PC. In addition, this achieved an increase in the ductility of slab FC by about 33% more than slab PC. The maximum deflection was 29.2 mm for slab PC and 31.3 mm for slab FC.
The essential mechanism allowing for an increased collapsed load for MSFRC slabs was associated with the ability of fibers to engage a large proportion of the concrete slab in carrying and distributing load even after the occurrence of cracking [21].

Conclusions
Based on the results of this study, the following conclusions can be drawn:

1.
Adding MSF to the concrete mixture led to reduced workability of the fresh concrete.

2.
It was observed that concrete density was not mainly affected by the addition of MSF. 3.
The addition of MSF caused a slight increase in air content as compared to the PCC. 4.
The addition of MSF did not have a considerable effect on compressive strength, as by adding MSF to the concrete mix, a 4% decrease in compressive strength was observed.

5.
The splitting tensile strength, flexural strength and elastic modulus of MSFRC at 28 days were increased by 20.5%, 33% and 6%, respectively, compared with that of PPC.

6.
The load carrying capacity of the PCC slab was improved considerably by the addition of MSF. 7.
The load carrying capacity of the MSFRC slab was higher than the PCC slab by about 24% for interior loading, 20% for edge loading and 23% for corner loading. 8.
The ductility of the MSFRC slab was higher than the PCC slab by about 43% for interior loading, 26% for edge loading and 33% for corner loading. 9.
In general, the results obtained and the observations made in this study proposed that concrete incorporating MSF could be used with satisfactory mechanical properties to increase the load carrying capacity and ductility of rigid pavement slabs. Informed Consent Statement: Not applicable.

Data Availability Statement:
All data presented in this study are available within this article.