The contaminated wastewater is producing negative impacts on the natural atmosphere as well as on human health. Therefore, such adverse impacts on the environment and human health could be avoided up to a certain limit by using wastewater in the concrete mix. Furthermore, to overwhelm the low tensile strength of plain concrete and the high carbon footprint of the cement industry, the use of glass fibers and fly ash to concrete is beneficial. In this study, mechanical properties such as compressive strength and split tensile strength as well as durability properties i.e., water absorption, chloride penetration, and resistance against H₂SO₄ of the recycled aggregate concrete incorporating with fly ash and glass fibers (FGRAC) have been studied under different curing ages by employing six types of wastewater for mixing purpose such as domestic sewage wastewater (DSW), fertilizer factory wastewater (FFW), textile factory wastewater (TFW), sugar factory wastewater (SFW), leather factory wastewater (LFW), and service station wastewater (SSW). One concrete mix was manufactured with potable water without adding glass fibers and fly ash for the comparative analysis. A one-way variance analysis (ANOVA) study was conducted at the five percent significance level to determine the value of discrepancy between the different properties of FGRAC mixes.

Ordinary Portland cement having grade 43 was employed for concrete production as per ASTM C150/C150M (50). The physicochemical properties of cement are presented in Table 1. F type fly ash taken from DIRK Pozzoplast was used in the present study. The chemical and physical properties of fly ash were reported in Table 1. The RCA was used by replacing 100% NCA. For this purpose, reinforced concrete columns and cylinders with ages of 1 to 2 years were crushed having a compressive strength ranging between 30 MPa and 45 MPa. The recycled aggregate with a maximum size of 12 mm was obtained. In this study, Lawrancepur sand was used according to ASTM C33/C33M-18 (51). The physical and chemical properties of sand and RCA are mentioned in Table 2 and the sieves analysis graphs of both materials are presented in Figure 1. The alkali-resistant glass fibers were employed in the present study having a tensile strength of 1800 MPa and a specific gravity of 2.65. Some of the main characteristics of glass fibers were reported in Table 3. The RAC was manufactured with six various types of wastewater based on their origins and potable water. The clean water was fully relieved by each wastewater type. The chemical examination of each type of wastewater was carefully performed and mentioned in Table 4. Besides, the chemical properties of wastewater were comprehensively tested in the Pakistan Council of Research in Water Resources.

To achieve an optimal saturation, the RCA was submerged in potable water for 10 minutes (58). Seven different types of FGRAC mixes i.e., potable drinking water mix (PW30-GF-100RCA), domestic sewage wastewater mix (DS30-GF-100RCA), fertilizer factory wastewater mix (FF30-GF-100RCA), textile factory wastewater mix (TF30-GF-100RCA), sugar factory wastewater mix (SF30-GF-100RCA), service station wastewater mix (SS30-GF-100RCA), and leather factory wastewater mix (LF30-GF-100RCA) were prepared. For comparative analysis, each of the FGRAC mixes was compared with the FGRAC mix prepared using potable water (PW) containing fly ash and glass fibers. The labeling of FGRAC mixes was done in such a way that the first two letters from the left side indicate the type of wastewater, the first digit from the left side indicates the percentage of fly ash, two letters at the middle indicate the addition of glass fibers, the digit from the right side indicates the 100% replacement of NCA with RCA, and three letters at the right side indicate recycled aggregate concrete (RAC).

A total of twenty-one cylindrical specimens (150 mm 300 mm) from each wastewater (constant quantity) were prepared for the determination of compressive strength and splitting tensile strength. Three samples for each wastewater at all ages were prepared and tested. A total of forty-two specimens (50 mm height and 100 mm in diameter) were developed for examining the waster absorption. For the determination of chloride ion migration, forty-two samples (100 mm in diameter and 100 mm in height) were also prepared. Whereas, sixty-three cube samples of size 100 mm were cast to explore the resistance of FGRAC concrete against sulfuric acid attack. The ingredients and quantities utilized for each FGRAC blend as shown in Table 5.

A mixer at a speed of 20 revolutions/min (capacity of 0.15 m³) was used to mix concrete. A total of 10 minutes required for complete mixing. To achieve a homogenous mixture, the aggregate was mixed with water, fly ash, and cement in the first 5 minutes then added the remaining quantity of water and the glass fibers. For each wastewater mix, a slump test (as per ASTM/C143) was performed and its values ranging between 90 mm to 105 mm (59). For curing purposes, normal water was used in this study.

The properties such as compressive strength and split tensile strength for each RAC blend at different curing ages were tested. The compressive strength of specimens at 7, 28, and 90-days was tested according to ASTM C39 (60). On the other hand, the split tensile strength of specimens at 28 and 90-days was tested as per ASTM C496 (61). The strength properties such as chloride ion migration, water absorption, and acid attack were tested for all seven FGRAC blends. For the determination of water absorption, ASTM C1585 (62) was followed. All specimens at 28-days were placed at room temperature to find resistance against sulfuric acid (H₂SO₄) left to dry at 50 C° for 24 hours then immersing them in 4% H₂SO₄.

To find out how chloride ion penetrates, the specimens developed have been cured in water for 28 and 90-days, preceded by oven-drying at a temperature of 50°C for 24 hours. Following this, the specimens were cooled to normal temperature and then submerged in a solution of 4% NaCl for 56 days. The splitting of cylinders procedure was followed as per the ASTM C496 (61) and spraying with a 1N AgNO₃ solution into water. When AgNO₃ reacts chemically with chloride ions, AgCl is produced giving a silver color.

In this current investigation, the compressive strength for each of the six different FGRAC mixes was tested after 7, 28, and 90-days of curing as per ASTM C39 (60). Figure 2 reports the compressive strength of each varying FGRAC mix. Three developed samples of all RAC blends for each age group were placed compression test machine then their mean results were calculated. TF30-GF-100RCA mix recorded the maximum compressive strength while the DS30-GF-100RCA mix displayed the lowest compressive strength at all the various testing ages. A control mix (PW30-GF-100RCA) has been developed to conduct a relative study of the results of different FGRAC mixtures produced using different kinds of wastewater. At 7-days, the compressive strength shown by PW30-GF-100RCA was 18.45 MPa. The compressive strength at 28-days was 26 MPa which was improved by 29% when compared with the measurement at 7-days. The compressive strength was 31.36 MPa when checked at 90-days, which was 142% of the compressive strength observed at 7-days. Thus, the PW30-GF-100RCA mix with the testing age noted a significant rise in its compressive strength.

The compressive strength of concrete for the TF30-GF-100RCA mix improved dramatically when compared with PW30-GF-100RCA at all ages. At 7-days, the TF30-GF-100RCA blend showed a compressive strength of 22.4 MPa which was 17.6% higher as compared to the compressive strength of PW30-GF-100RCA at 7-days. After 28-days, the compressive strength of the TF30-GF-100RCA mix was increased by 135% having a value of 34.6 MPa which was 24.8% higher as compared to the compressive strength of the PW30-GF-100RCA mix. When bicarbonates and fluoride existing in TFW involves a reaction with Al₂O₃ remaining in ordinary Portland cement and thus proceed to calcium fluoroaluminate formation leading to the increased compressive strength of concrete. This mineral is extremely toxic, resulting in both fast setting and early hydration, which improved the performance (33). The high compressive strength of TF30-GF-100RCA than the control mix may also be ascribed to the addition of glass fibers and fly ash. Fly ash reduces the voids between fine particles and form CSH-gel after the chemical reaction of free CH and fly ash particles. Furthermore, the glass fibers provided the bridging effects between the particles of the TF30-GF-100RCA mix to improve the compressive strength.

The improved compressive strengths of FGRAC mixes developed with wastewater could be ascribed to the pozzolanic reactions between free fly ash and CH. Fly ash filled the voids between sand and cement, improved the bond of glass fibers with the binding matrix, and, finally, formed a gel (C-S-H-gel) giving a stronger bond. Furthermore, the ability of glass fibers to prevent the propagation of cracks also improved the compressive strength of FGRAC mixes to give comparable results with the control mix.

By using FFW to produce FGRAC mixes, the compressive strength attained at 7-days was higher and lesser at 28 and 90-days associated with PW30-GF-100RCA. At 7-days, the FF30-GF-100RCA mix exhibited a compressive strength of 21.2 MPa that is 13% higher than the compressive strength of PW30-GF-100RCA at 7-days. The compressive strength of the FF30-GF-100RCA mix was increased by 15.6% at 28-days having a value of 25.2 MPa. It was further decreased by 7.8% at 90-days when compared with PW30-GF-100RCA but it showed 12.9% higher strength than at 28-days. This drop in the compressive strength of FF30-GF-100RCA mix at 28 and 90-days of testing occurred because of an increased quantity of COD as well as BOD at 5-days in FFW (63).

When DSW has been used for mixing, the compressive strength of concrete decreased considerably. At 7-day testing, the compressive strength was observed 11.9 MPa, at 28-days testing it was 18 MPa, and at 90-day testing, it was 15.3 MPa. The average compressive strengths were 35%, 30%, and 51% lower than the strengths reported in the same order by the PW30-GF-100RCA mix at testing days of 7, 28, and 90. The uniformity of the mixing water has a significant effect on concrete strength. Consequently, the concrete strength for DS30-GF-100RCA is lower than PW30-GF-100RCA. While at 28-days of testing, this strength of the DS30-GF-100RCA mix increased to 34.3% and it shows a reduction of up to 15% at testing days of 90. This reduction in the strength of the DS30-GF-100RCA mix can be due to the existence of many organic matters in DSW that reacts with cement ingredients and thus result in reducing the strength of concrete. Due to the large amount of sulfate found in DSW, the compressive strength of the DS30-GF-100RCA mix is decreased after 90-days of testing.

When SSW was used for mixing, then the compression capacity of concrete was affected to a slight extent. It had shown compressive strengths of 16.9 MPa in 7-days, 23.9 MPa in 28-days, and 29.8 MPa in 90 test days. These compressive strengths were in similar accordance with that of the PW30-GF-100RCA mix and on average 8.4%, 8%, and 4.8% were lower than compressive strengths displayed by the PW30-GF-100RCA mix at the testing days of 7, 28, and 90. These negligible variations indicate that the concrete compressive strength has no noticeable effect when SSW is used for mixing. The reason is that SS30-GF-100RCA has shown a decline in strength at all test ages which can be due to the existence of BOD and COD in excessive amounts. The concrete compressive strength decreased at 7-days by using SFW comparison to the PW30-GF-100RCA mix, which subsequently increased to 43.9% after 28-day testing. SF30-GF-100RCA mix has shown increased strength because of the long setting time of cement paste and the larger surface area of cement particles (64). Compared with the PW30-GF-100RCA mix, the concrete compressive strength decreased by 5% at 90-days. This drop in the compression capacity can be due to the availability of C₃S in cement triggering the hydration process to delay (65, 66). Figure 3 represents the comparative strengths of all RAC blends at 7, 28, and 90 test days.

When LFW was used for mixing, then the compression capacity of concrete was affected to a slight extent. It had shown compressive strengths of 16.7 MPa in 7-days, 29.9 MPa in 28-days, and 30.5 MPa in 90 test days. These compressive strengths were in similar accordance with that of the PW30-GF-100RCA mix and on average 9.5%, 3.3%, and 7% lower than compressive strengths displayed by the PW30-GF-100RCA mix at the testing days of 7, 28, and 90. These negligible variations indicate that the concrete compressive strength has no noticeable effect when LFW is used for mixing. The reason is that LF30-GF-100RCA has shown a decline in strength at all test ages that may be associated with a large amount of COD and BOD in LFW. The improved compressive strengths of FGRAC mixes fabricated with wastewater could be ascribed to the pozzolanic reactions between free CH and fly ash. Fly ash filled the voids between sand and cement, improved the bond of glass fibers with the binding matrix, and, finally, formed a gel (CSH-gel) giving a stronger bond. Furthermore, the ability of glass fibers to prevent the propagation of cracks also improved the compressive strength of FGRAC mixes to give comparable results with the control mix.

Figure 4 demonstrates the split tensile behavior of various FGRAC mixes that have been manufactured using different wastewater types. The specimens were tested following ASTM C496 (61). The PW30-GF-100RCA mix displayed an average tensile strength of 2.45 MPa at 7-days, 2.85 MPa at 28-days, and 3.46 MPa at 90-days, respectively indicating that the PW30-GF-100RCA mix displayed a split tensile strength of 117% at 90-days compared to its strength at 28-days. The TF30-GF-100RCA mix showed significantly higher split tensile strength whereas the DS30-GF-100RCA mix showed the lowest strength. The TF30-GF-100RCA mix displayed improved split tensile strengths of 2.84 MPa after 7-days, 3.6 MPa after 28-days and 4.1 MPa at 90-days that were 13.7%, 20.8%, and 15.6% greater than the PW30-GF-100RCA mix tested at various days, respectively. The tensile strength displayed by the TF30-GF-100RCA mix was greater as the TFW has lesser bicarbonates amounts relative to other wastewater types. After all, the rise in bicarbonates contributes to reduced tensile strength (67). The improved split tensile behavior of FGRAC mixes may be attributed to the pozzolanic reactions between free fly ash and CH. Fly ash forms the C-S-H-gel and fills the small voids between the fine aggregates and binder particles. Furthermore, the ability of glass fibers to prevent the propagation of cracks and to produce the bridging effect also improved the split tensile strength of FGRAC mixes to give comparable results with the control mix PW30-GF-100RCA.

The FF30-GF-100RCA mix indicated split tensile strengths of 2.36 MPa at 7-days, 2.68 MPa at 28-days, and 3.17 MPa at 90-days, respectively. This indicates that the split tensile strengths were reduced by 3.6% at 7-days, by 5.9% at 28-days, and by 8.4% at 90-days associated with the control mix when FFW was used for mixing. The tensile strengths demonstrated by the DS30-GF-100RCA mix were small with falls of 8.9% at 7-days, 7% at 28-days, and 9.8% at 90-days as compared with the PW30-GF-100RCA mix. The SF30-GF-100RCA mix displayed split tensile strengths of 2.34 MPa at 7-days, 2.71 MPa at 28-days, and 3.29 MPa at 90-days with a reduction of 4.5% at 7-days, 5.0% at 28-days, and 4.8% at 90-days, respectively. The decreases in split tensile strengths displayed by diverse FGRAC mixes (i.e. FF30-GF-100RCA, DS30-GF-100RCA, SS30-GF-100RCA, and SF30-GF-100RCA) can be due to the excess of total suspended solids, COD, and BOD in such kinds of wastewater (68). The concrete displays a reduction in the tensile strength when the volume of chloride increases (69). This is due to the presence of large quantities of chloride. These FGRAC mixes have lower pH values. The reduction of the pH value is responsible for reducing the strength of the split tensile (70).

Figure 5 shows the comparison between the relative percentage of split tensile strengths produced by various FGRAC mixes and that reported by the PW30-GF-100RCA mix for different age groups. The LF30-GF-100RCA mix displayed enhanced split tensile strengths of 2.89 MPa after 7-days, 3 MPa after 28-days, and 3.4 MPa at 90-days that were on average 15.2% and 5.6% greater than the PW30-GF-100RCA mix experienced at 7 and 28-days, respectively. While this mix presented a 2% lower value of split tensile strength at 90-days compared with the PW30-GF-100RCA mix. The tensile strength displayed by the LF30-GF-100RCA mix was greater as the LFW has lesser bicarbonates amounts relative to other wastewater types because the rise in bicarbonates results in the reduced tensile behavior of concrete (67).

Being a durability parameter, the water absorption calculates the number of pores that are moisture-accessible in concrete. If water absorption is extreme, it will cause reinforcement corrosion which leads to the penetration of numerous toxic chemicals and when react with cement additives thus completely change the characteristics of concrete. Figure 6 indicates the water absorption shown by different RAC blends. Nearly all the specimens displayed relatively higher water absorption levels. This may be due to higher water absorption levels for RCA (7.7%). When the findings were analyzed, they demonstrated that the different types of wastewater had no significant impact on concrete water absorption as shown in the literary works (71).

Different FGRAC mixes reported a reduction in the properties of water absorption with time. The water absorption shown by the PW30-GF-100RCA mix was 12.5% at 28-days and 9.2% at 90-days, representing the decline in moisture content over time. As compared to PW30-GF-100RCA, the water absorption shown by the TF30-GF-100RCA mix was lower. The moisture content was 99% at 28-days and 98% at 90-days equated to PW30-GF-100RCA. The decline in water absorption may be attributed to a reduction in the amount of chloride, as the volume of chloride rises, the concrete density lessens with reduced strengths plus enhanced porosity in concrete (69).

When tested at 28 and 90-days, correspondingly, the water absorption values of the FF30-GF-100RCA mix were 9.7% and 16.5% higher than that of PW30-GF-100RCA. The DS30-GF-100RCA mix displayed moisture content that is the highest with 14.6% at 28-days, 12% at 90-days that have been 14.7%, and 23.9% higher than with the PW30-GF-100RCA mix. The large quantities of organic wastewater existing in DSW contribute to the establishment of large numbers of small pores resulting in higher water absorption. The water is consumed by such waste during the mixing process and then emitted during concrete casting, which increases the ratio of water to cement (W/C) and thus decreases the concrete density (72). When tested at 28 and 90-days correspondingly, the water absorption values of the SS30-GF-100RCA mix were 8% and 22.8% higher than PW30-GF-100RCA. Water absorption was enhanced by 11% at 28-days, and by 17% at 90-days while mixing with SFW. While using LFW in the mixing of concrete, water absorption enhanced by 6.5% and 11.7% at 28 and 90-days, respectively as related to the control mix. As previous studies have shown, water absorption has been increased by using various forms of wastewater in concrete mixes (33). The reduced water absorptions of FGRAC mixes may be attributed to the reason that the addition of fly ash helps to reduce the water absorption of concrete by filling the voids between the fine aggregates and the binder matrix but the addition of glass fibers and the use of RCA increases the water absorption due to high water absorption of RCA and the enhancement in the length of microchannels in the microstructure of concrete (44).

In this study, chloride penetration of concrete is studied using 4% NaCl. The method used to calculate this parameter is the penetration of ions color in millimeters penetrated by the chloride ions into the concrete microstructure. Figure 7 indicates the values of chloride ions penetration for all types of FGRAC mixes. The highest chloride penetration values were given by the FFW, which is rich in chloride iron and sulfate ions.

The control mix portrayed a chloride penetration of 11.87 mm at 28-days, and 7.45 mm at 90-days. At 28 and 90-days, the TF30-GF-100RCA mix displayed chloride penetration that was 12.6% higher and 18.9% higher than PW30-GF-100RCA. This depicts the TF30-GF-100RCA mix as more vulnerable to oxidation and steel bar corrosion. Also, penetration of chloride indicated by the FF30-GF-100RCA blend was 14.23 mm in 28-days and 10.41 mm in 90-days. Chloride ion penetration is also enhanced by the pretty low pH value of FFW (70). The increased values of chloride penetration to FGRAC mixes may be ascribed to the high water absorption of RCA and the addition of glass fibers causing a balling and bridging effect between the binder matrix leaving more voids to absorb chloride ions. But the addition of fly ash is advantageous to resist the penetration of chloride ions by filling the microstructure of concrete.

Fewer iron quantities in the DSW resulted in the chloride penetration values being close to the control mix. The chloride penetration shown by the SS30-GF-100RCA blend was 13.37 mm and 9 mm at 28- and 90-days, which is 11.2% and 17.2% higher on average than PW30-GF-100RCA values. The SF30-GF-100RCA mix demonstrated chloride penetration values close to those of the SS30-GF-100RCA mix. Similarly, the LF30-GF-100RCA mix depicted higher values of chloride ion penetration (12.24 mm at 28-days and 9.64 mm at 28-days) that were 3% and 22.7% higher than the control mix at 28 and 90-days, respectively. Hence, the chloride ion penetration represented by DSW was the lowest from all forms of wastewater tested, which indicates that it is less prone to corrosion.

This study examined the mass loss of test samples at 28, 90, and 120-days after soaking them in 4% of the H₂SO₄ solution. Figure 8 indicates the mass losses caused by each of the FGRAC mixes. The highest degradation was observed by the FF30-GF-100RCA mix.

The degradation of the TF30-GF-100RCA mix is quicker than the control mix. TF30-GF-100RCA mix reported mass losses of 6.28% after 28-days, 13.11% after 90-days, and 16% after 120-days, which were 30.2%, 23.3%, and 15.8% higher than the PW30-GF-100RCA mix. The FF30-GF-100RCA mix reported mass losses of 7.3% at 28-days, 14.89% at 90-days, and 17.86% at 120-days that were 40%, 32.5%, and 24.5% higher than the PW30-GF-100RCA mix. The largest mass loss of the FF30-GF-100RCA mix can be linked to the lowest pH value (73, 74). Concrete deterioration is thus largely influenced by the pH value of both acid and wastewater mixing (75). Also, the greater mass loss can be due to the sulfate-rich FFW. The DS30-GF-100RCA mix exhibited higher degradation in the initial stages, but the degradation became identical to that of PW30-GF-100RCA at 90 and 120-days. The SF30-GF-100RCA mix displayed mass losses of 5.2% at 28-days, 12% at 90-days, and 15.4% at 120-day testing that were higher due to the sulfuric acid (H₂SO₄) invasion. The mass loss of LF30-GF-100RCA was observed to be 5.2%, 11%, and 14.4% at 28, 90, and 120-days, correspondingly. These mass losses were 15.6%, 9.2%, and 6.1% higher than that of the PW30-GF-100RCA mix. So, we can say that with the use of all the various forms of wastewater examined, the degradation of concrete becomes more rapid. Figure 9 records the relative mass losses of diverse concrete mixes at various testing ages due to an acid attack as compared with the control mix. The increased values of mass losses of FGRAC mixes may be attributed to the addition of glass fibers causing a bridging effect between the binder matrix leaving more voids to absorb chloride ions. But the addition of fly ash is advantageous to resist the acid attack by filling the microstructure of concrete.

Tables 6-10 demonstrate the ANOVA analysis at a significance level of 5% used to assess the importance of the discrepancies between the various durability properties of the FGRAC mixes at 90-days and the mechanical behavior at 28 testing days. The FGRAC mix was split into six groups of wastewater concrete mixes (TF30-GF-100RCA, FF30-GF-100RCA, DS30-GF-100RCA, SS30-GF-100RCA, SF30-GF-100RCA, and LF30-GF-100RCA) and a control mix PW30-GF-100RCA. A comparison was made between FGRAC mixes and the control mix (PW30-GF-100RCA) to explain the impact of the experimental outputs precisely.

The findings of the ANOVA test indicate that different FGRAC mixes did not show a substantial difference at 28-days of testing (P = 32.9% and F ˂ F _crit ) between their compressive strengths at 28-days of testing, showing that the types of wastewater tested directly did not influence the compressive strength of FGRAC. On the other hand, for the results of the tensile test, these FGRAC mixes did not display any substantial difference between them (P = 95.4% and F ˂ F _crit ), water absorption test (P = 18.64% and F ˂ F _crit ), and sulfuric acid attack test (P = 22.8% and F ˂ F _crit ). The results of the chloride penetration of different FGRAC mixes have also shown no difference with F ˂ F _crit which indicates that the aspects of wastewater explored in FGRAC mixing did not influence the results of the chloride penetration.

The statistical analysis of the durability and mechanical properties of FGRAC mixes portrayed that the compressive and tensile strengths are not influenced by using different types of wastewater examined in the present work. Similarly, no significant differences in the durability properties of FGRAC mixes (water absorption, chloride penetration, and concrete mass loss due to acid attack) were observed. This statistical analysis shows that the examined types of wastewater can be employed for the mixing of concrete without meaningly affecting the mechanical and durability behavior of concrete.