## 3 Results and Discussion
### Splitting Tensile Strength  
Splitting tensile strength is an engineering property of concrete that is used in design features of construction elements such as those associated with the beginning and propagation of cracks, anchorage, and shear strength in structural members [3]. The splitting tensile strength not only represents the true tensile strength but also depicts the failure patterns of specimens under the action of loads (splitting load). The tensile strength test was carried out following ASTM C496/C496M-17 [40] on cylindrical specimens (150 \(\times\) 300 mm) at the ages of 7, 28, and 56 days after casting, and results are shown in Figure 5.  
It can be observed from the figure that the tensile strength is increasing for QFS-GPC samples until 15% replacement of SG by QRD (GPC-D); while a further increase in QRD, i.e., 20% (GPC-E), showed a decrease in tensile strength. From the test results at 7 days, the specimens of OPC, GPC-A, GPC-B, GPC-C, GPC-D, and GPC-E depicted 1.57 MPa, 1.45 MPa, 1.49 MPa, 1.56 MPa, 1.66 MPa, and 1.09 MPa split tensile strengths, respectively. Only the samples of GPC-D had shown higher early (7 days) and later age (28 and 56 days) tensile strengths than the OPC control specimens. The 7 days tensile strengths of GPC-A, GPC-B, GPC-C, and GPC-E are 7.6%, 5%, 1%, and 31%, respectively, lower than the control mix sample, while GPC-D has a 5.7% higher tensile strength than the control specimen at 7 days. However, the tensile strength tests at 28 and 56 days depicted 4.8% and 6.6%, respectively, lower strengths of GPC-D than the control OPC mix, which shows slightly  
Figure 4: The compressive strength values of control (OPC) and QFS-GPC samples at 7, 28, and 56 days. less than the target control OPC specimen; however, this can be further improved by incorporating fibers. Albeit the increment in the tensile strength is observed from mix GPC-A to GPC-D. The GPC-D mix with 15% QRD has 14.48% more split tensile strength than mix GPC-A having 0% QRD contents. At the age of 28 days, the tensile strength for the control OPC mix and GPC-A to E were observed as 1.98 MPa, 1.75 MPa, 1.82 MPa, 1.88 MPa, 2.08 MPa, and 1.64 MPa, respectively. There was a decrease in the tensile strength of GPC-A to E of 16%, 12.5%, 9.6%, 4.8%, and 21%, respectively, from the strength of the control OPC mix. However, GPC-D has the least difference (less than 5%) from the strength of the OPC specimen. Among the QFS-GPC mixes, the tensile strength of mix GPC-D is 13.14% more than GPC-A. Geopolymer concrete performs better in terms of compressive strength. However, the tensile strength of GPC depends on the initiation of cracks in the matrix. The previous study has reported that geopolymer concrete performs better in terms of tensile strength as compared to the ordinary Portland cement concrete [36; 48]. Another study reported that the ACI standard design code better predicts the tensile strength of geopolymer concrete. Use of up to 30% GGBS in geopolymer concrete increased the splitting tensile strength [36]. Similar upward trend in tensile strength in the current study was observed with up to 15%QRD in geopolymer concrete. At the age of 56 days, the splitting tensile strengths of the control mix and GPC-A to E were observed as 2.27 MPa, 1.93 MPa, 1.97 MPa, 2.03 MPa, 2.12 MPa, and 1.85 MPa, respectively. The tensile strengths of the GPC-A to E mixes were less than the control OPC mix by 15%, 13%, 10.6%, 6.6%, and 18.5%, respectively. There was an improvement in the tensile strength of all the QFS-GPC specimens from 7 to 28 and 56 days; however, the tensile strength has been observed to be less than the conventional concrete specimens at all ages except for GPC-D, which has slightly more strength at 7 days than the control OPC specimen. Furthermore, the trends of increases in tensile strengths are similar to that of the compressive strength results, where up to 15% replacement of SG by QRD has improved the strength.