## 3 Results and Discussion
### Flexural Strength  
The flexural strength of the OPC and GPC specimens was evaluated by the third point loading test on prism specimens (100 \(\times\) 100 \(\times\) 500 mm) following ASTM C78/C78M-21 [41]. It was performed to find the modulus of rupture (MOR) of prism specimens at the age of 28 and 56 days. The shape and texture of binders and aggregates can affect the flexural strength of concrete [28]. [PERSON] (2010) reported that the impact of binder and aggregate shape and texture is more obvious in the modulus of rupture test than the cylindrical split tensile or uniaxial compression tests [49]. He ascribed that the presence of stress gradient behavior delays the process of cracking specimens, which leads to the ultimate failure. The results of the flexural strength test of all the groups are shown in Figure 6. The trend of increasing strength observed in the GPC mixes is similar to the compressive and tensile strength results. The flexural strength of the OPC mix is 2.62 MPa at 28 days, while the GPC-A, GPC-B, GPC-C, GPC-D, and GPC-E have 2.45 MPa, 2.53 MPa, 2.64 MPa, 2.87 MPa, and 2.31 MPa, respectively. The control OPC mix has 6.49%, 3.44%, and 11.83% more flexural strength at 28 days than the GPC-A, GPC-B, and GPC-E, respectively, whereas GPC-C and GPC-D have 0.64% and 6.11% more flexural strength than the control OPC mix specimens at 28 days. It can be observed from Figure 6 that the flexural strength of GPC-D is the maximum among all the OPC and GPC mix specimens at 56 days. The flexural strength of the GPC-D mix is 15%, 10%, 7%, and 20% higher than the GPC-A, GPC-B, GPC-C, and GPC-E, respectively. The control OPC mix has 14.41%, 11.03%, 7.63%, and 4.24% higher flexural strength than GPC-E, GPC-A, GPC-B, and GPC-C, respectively. The replacement of QRD up to 15% has resulted in increasing the flexural strength of all GPC mix specimens. The flexural strength of GPC-B, GPC-C, and GPC-D at 56 days  
Figure 6: The flexural strength of the control (OPC) and QFS-GPC specimens at 28 and 56 days. is 3.81%, 7.62%, and 14.92% higher than the GPC-A (without QRD content). The rough and angular texture crushed particles such as QRD [50] produce the concrete with higher flexural strength than with the rounded shape constituents. The physical and chemical bond developed by the angular shape particles is stronger than the bond developed by the rounded particles [49; 51]. [PERSON] et al. (2013) and [PERSON] et al. (2012) also found that the replacement of QRD with sand increases the strength properties of concrete [52; 53]. A reduction in the flexural strength was observed with increasing the QRD content beyond 15% (GPC-E). This decrease in flexural strength is due to the incomplete hydration of excess lime (CaO) contents (present in QRD) in the alkaline medium to make Ca(OH)\({}_{2}\) and an incomplete geopolymerization process [44; 45; 47]. Geopolymers had shown better mechanical properties at lower exposure temperatures. However, the reduction increases after high temperature exposure [54]. For ascertaining properties at elevated temperature, cubic specimens (of dimensions 150 mm \(\times\) 150 mm \(\times\) 150 mm) were prepared for each mix type. After 56 days of ambient curing, the specimens were heated in an automatic controlled electric furnace of 1000 \({}^{\circ}\)C capacity under two temperature settings, i.e., 400 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, for 1 h following ASTM E 119-20 [49]. After heating to the required temperature, the specimens were cooled at room temperature. Then, the residual compressive strength was determined following BS EN 12390-3: 2019 [39]. The weight of each cubic specimen before and after exposure to elevated temperature was obtained to find the weight loss due to exposure at the relevant elevated temperature.