## 3 Mechanical Behaviors
### Dynamic Flexural Strength and Deflection after Elevated Temperature  
#### 3.2.1 Influence of Strain Rate  
Prismatic specimens (100 mm \(\times\) 100 mm \(\times\) 400 mm) were used to test the flexural strength, which was frequently used as a significant index to evaluate the bending resistance of concrete beams. The dynamic flexural strength represented the behavior of concrete beam subjected to impact loading suddenly. Dynamic flexural strength results of DSC after elevated temperature are shown in Table 8. The relation between strain rate, flexural strength, and DSRR for DSC (F3-F8) is plotted in Figure 8. Six prismatic specimens were produced in every case and the value of Table 8 was the average value of experimental data. As displayed in Table 8 and Figure 8, the dynamic flexural strength increased with the enhancement of strain rate when DSC specimens were exposed to the same elevated temperature. Figure 7: Experimental curves and predicted curves of DSC at room temperature in various strain rates. The vertical displacement of mid\(-\)span DSC was defined as the deflection measured by a dial gauge with the precision of 0.01 mm. The vertical deflection was used to evaluate the flexural toughness of DSC after elevated temperature, which represented the ability of vertical deformation of the DSC beam under loading. Dynamic deflection results of DSC after elevated temperature are shown in Table 9. It can be clearly found from Table 9 that the deflection of the DSC specimen after elevated temperature with the strain rate of \(1.25\times 10^{-5}\) s\({}^{-1}\) was much more than that of the specimen in \(3.57\times 10^{-7}\) s\({}^{-1}\). For instance, deflections of DSC (F3\(-\)F8) with DSRR of 0%, 20%, 40%, 60%, 80%, and 100% after 300 \({}^{\circ}\)C in \(1.25\times 10^{-5}\) s\({}^{-1}\) increased by approximately 30%, 16.8%, 35%, 8.7%, 15.2%, and 14.3%, respectively, compared to those of specimens with the strain rate of \(3.57\times 10^{-7}\) s\({}^{-1}\), which indicated that the deflection had a clear dependence of strain rate and increased with the enhancement of strain rate. This phenomenon may be analyzed as follow: The self\(-\)weight and flexural strength of DSC were responsible for the production of deflection. The self\(-\)weight and stiffness of DSC with the  
Figure 8: Relation between strain rate, flexural strength, and DSRR for DSC (F3\(-\)F8). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Group**} & **Fly Ash** & \multicolumn{8}{c}{**Dynamic Flexural Strength Results of DSC after Elevated Temperature (MPa)**} \\ \cline{3-11}  & **Replacement** & **DSRR** & \multicolumn{3}{c}{\(3.57\times 10^{-7}\) s\({}^{-1}\)} & \multicolumn{3}{c}{\(2.16\times 10^{-6}\) s\({}^{-1}\)} & \multicolumn{3}{c}{\(1.25\times 10^{-5}\) s\({}^{-1}\)} \\ \cline{3-11}  & **Ratio (\%)** & & & **300 °C** & **500 °C** & **700 °C** & **300 °C** & **500 °C** & **700 °C** & **300 °C** & **500 °C** & **700 °C** \\ \hline F1 & 0 & 0 & 2.44 & 1.11 & 0.44 & 2.75 & 1.34 & 0.64 & 3.01 & 1.36 & 0.72 \\ \hline F2 & 10 & 0 & 2.53 & 1.23 & 0.57 & 3.01 & 1.01 & 0.71 & 3.15 & 1.31 & 0.75 \\ \hline F3 & & 0 & 2.49 & 1.17 & 0.54 & 2.92 & 1.27 & 0.60 & 3.10 & 1.33 & 0.69 \\ F4 & & 20 & 2.88 & 1.26 & 0.65 & 3.04 & 1.29 & 0.68 & 3.20 & 1.37 & 0.74 \\ F5 & 20 & 40 & 3.16 & 1.32 & 0.68 & 3.34 & 1.64 & 0.98 & 3.42 & 1.70 & 1.05 \\ F6 & & 60 & 3.12 & 1.27 & 0.58 & 3.15 & 1.49 & 0.92 & 3.30 & 1.63 & 0.97 \\ F7 & & 80 & 2.90 & 1.24 & 0.50 & 3.12 & 1.40 & 0.86 & 3.24 & 1.53 & 0.88 \\ F8 & & 100 & 2.64 & 1.15 & 0.47 & 3.14 & 1.39 & 0.69 & 3.20 & 1.47 & 0.74 \\ \hline \end{tabular}
\end{table} 
Table 8: Dynamic flexural strength results of DSC after elevated temperature same DSRR were almost alike after exposure to the same temperature, so the value of deflection was mainly determined by the flexural strength. It is observed from Figure 8 the flexural strength of DSC exposed to elevated temperature increased with strain rate. Therefore, the deflection increased with strain rate.