## 5 Results and Discussion
### Splitting Tensile Strength  
Figure 10 illustrates the splitting tensile strength of HSC containing various contents of fibres, NS and SP. The splitting tensile strength depends on the tensile strength of the matrix and the adhesion between cement and aggregates. As seen in Figure 10, increasing the value of SF resulted in raising the tensile strength of HSC. Using SP improves the splitting  
Figure 8: Influence of fibres on the compressive strength of HSC (**a**) SF and (**b**) PPF.  
tensile strength of HSC; however, the positive effect of SF on this property dropped by adding SP at more than 5%. Moreover, using 10% SP with no NS has a negative impact on the splitting tensile strength of HSC. On the other hand, using NS enhances the tensile strength of HSC. Almost the same improvement influence of SP and NS on the splitting tensile strength of concrete was reported by previous studies [10; 11; 12; 13]. [PERSON] and [PERSON] [62] showed that the splitting tensile strength of concrete substantially improved with the use of low SP content, while by increasing SP content, the splitting tensile strength gradually declined. The pozzolanic activity of SP is the main reason for improving the splitting tensile strength of HSC [63; 64]. Moreover, the negative impact of using 10% SP dropped by raising the SF content. As seen in Figure 10, the tensile strength of HSC raised by nearly 15%, 20%, 26%, 30% and 37% by adding 0.1%, 0.2%, 0.3%, 0.4% and 0.5% SF, respectively. Besides, the tensile strength increased by about 65.5%, 86.4%, 88%, 92.6% and 104% when 0.1%, 0.2%, 0.3%, 0.4%, respectively, and 0.5% SF with 2% NS and 10% SP were employed. [PERSON] and [PERSON] [53] showed that the SP particles size is an important property to improve the mechanical characteristics of concrete due to filling porous and creating a strong ITZ.  
In addition, using PPF resulted in improving the tensile strength of HSC. Furthermore, using PPF compensates for the negative influence of using SP at more than 5%. Furthermore, the impact of SF on the improvement of the tensile strength of HSC was greater than that  
Figure 10: Influence of fibres of the splitting tensile strength of HSC (**a**) SF and (**b**) PPF.  
Figure 9: Impact of the fibres on the compressive strength of HSC containing NS and SP (**a**) SF and (**b**) PPF.  
of PPF. The higher tensile strength of fibres, in comparison with concrete paste and the bridging role of fibres, are the main reasons why SF and PPF improve the splitting tensile strength of HSC [61]. Therefore, this property was improved by 7%, 10%, 18%, 25% and 31% by adding 0.1%, 0.2%, 0.3%, 0.4% and 0.5% PPF, respectively. Moreover, using both 2% NS and 10% SP with 0.1%, 0.2%, 0.3%, 0.4% and 0.5% PPF enhanced the splitting tensile strength of HSC by approximately 56.8%, 66.8%, 79.6%, 87% and 102%, respectively. Besides, [PERSON] et al. [52] stated that the use of low SP content improved the splitting tensile strength of concrete and it was further enhanced when SF was also added.  
The effect of fibres on the splitting tensile strength of HSC can also be observed in Figure 11. Using either SF or PPF considerably improves the tensile strength of HSC.