## 3 Results and Discussion
### Residual Flexural Tensile Strength  
Residual flexural tensile strength of the concrete is another key parameter governing the behavior of the fiber-reinforced SCC after heating to high temperatures. It should be indicated that flexural tensile strength tests are performed on the prismatic specimens after the fire resistance test. Figure 13 and Table 5 present that residual flexural tensile strength of SCC specimens without and with fibers is compared with varying target temperatures. It is observed that specimens with SF maintain higher residual flexural tensile strength in comparison to plain specimens without fibers. This is mainly because of the bridging effect of randomly dispersed SF cross cracks existing inside the concrete. However, for specimens with a single PF, no clear impact on the residual flexural tensile strength was observed. This may be attributed to the melting of PF and the formation of interconnected pores. Regarding combined fiber-reinforced specimens consisting of PF and SF, a great  
Figure 12: Reduction coefficient for residual compressive strength of fiber-reinforced SCC at different temperatures: (**a**) SF-SCC and (**b**) PF-SCC. increase in residual flexural tensile strength compared with plain specimens was observed. The inclusion of SF plays a key role in enhancing the residual flexural tensile strength after PF has melted. In the present study, for specimens with SF, there is a critical temperature of 200 \({}^{\circ}\)C influencing the residual flexural tensile strength. When the temperatures are lower than 200 \({}^{\circ}\)C, the residual flexural tensile strength of the concrete can be increased significantly with the incorporation of SF. The more SF used in concrete, the higher the residual flexural tensile strength obtained. For instance, Figure 13a shows that in comparison to the flexural tensile strength at room temperature, the inclusion of 20 kg/m\({}^{3}\), 40 kg/m\({}^{3}\), and 50 kg/m\({}^{3}\) SF can enhance the flexural tensile strength of fiber-reinforced SCC by 6%, 7%, and 15%, respectively, after heating to the high temperature of 200 \({}^{\circ}\)C. However, when the target temperatures were beyond the temperature of 200 \({}^{\circ}\)C, unlike the slower loss of compressive strength, a sharp reduction in the residual flexural tensile strength was observed. It is observed that the tensile strength of the concrete shows higher sensitivity to cracks induced by high temperature to concrete, whether on a macroscale or a microscale [54, 55]. Regarding specimens incorporating single PF or cocktail fibers, Figure 14b shows that no critical temperature exists, while a significant reduction in the residual flexural tensile strength is obtained as the target temperatures increase. After heating to the high temperature of 600 \({}^{\circ}\)C, only 17% to 25% of the flexural tensile strength of all the fiber-reinforced SCC specimens at room temperature is reserved. In summary, as demonstrated in Figure 13, regarding the ability of concrete types in preserving the residual flexural tensile strength, SF specimens show the best performing concrete types, which are followed by the cocktail fiber specimens and then followed by PF specimens and plain specimens. The incorporation of SF in the concrete plays a significant role in preserving the residual mechanical properties. However, because of the low melting temperatures of PF, the melting and vaporizing of them occurs in heating procedures. Figure 13: Flexural tensile strength of fiber-reinforced SCC subjected to different temperatures: (**a**) SF and (**b**) PF + SPF. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Temperature/\({}^{\circ}\)C** & **NC** & **PF1** & **PF2** & **SF20** & **SF40** & **SF50** & **SPF201** \\ \hline
20 & 5.73 & 6.08 & 5.48 & 7.60 & 8.43 & 8.14 & 6.75 \\
200 & 5.43 & 4.70 & 5.93 & 8.09 & 9.05 & 9.37 & 5.74 \\
400 & 2.29 & 2.16 & 4.06 & 5.83 & 7.35 & 9.37 & 5.01 \\
600 & 0.95 & 1.06 & 3.11 & 2.81 & 3.88 & 4.95 & 1.66 \\ \hline \hline \end{tabular}
\end{table}