## 3 Mechanical Behaviors
### Dynamic Flexural Strength and Deflection after Elevated Temperature
#### 3.2.3 Influence of Temperature  
Flexural Strength and Deflection  
The relation between temperature and flexural strength of DSC (F3-F8) with different strain rates is shown in Figure 9. As seen from Figure 9 and Table 8, the flexural strength of DSC F5, compared with those exposed to 300 \({}^{\circ}\)C, showed an obvious reduction of 58.2% and 78.5%, 51.5% and 70.7%, and 50% and 69.3% when DSC F5 were exposed to 500 \({}^{\circ}\)C and 700 \({}^{\circ}\)C with the strain rates of \(3.57\times 10^{-7}\) s\({}^{-1}\), \(2.16\times 10^{-6}\) s\({}^{-1}\), and \(1.25\times 10^{-5}\) s\({}^{-1}\), respectively. These analyses showed the flexural strength of DSC decreased with temperature. This phenomenon was because the calcium silicate hydrates (C\(-\)H\(-\)S) and calcium hydroxides (Ca(OH)\({}_{2}\)) were decomposed with the temperature [51; 52]. The relation between the temperature and deflection of DSC (F3-F8) is presented in Figure 10. It can be illustrated from Figure 10 that the deflection of DSC gradually increased with the temperature. As shown in Figure 10, the deflections of DSC F8 at 500 \({}^{\circ}\)C and 700 \({}^{\circ}\)C were greater than those of  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{\ \begin{tabular}{c} **Fly Ash** \\ **Replacement** \\ **Ratio (\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **DSRR** \\ **(\%)** \\ \end{tabular}  } & \multicolumn{4}{c}{**\(\mathbf{3.57\times 10^{-7}\) s\({}^{-1}\)**}} & \multicolumn{4}{c}{\(\mathbf{1.25\times 10^{-5}\) s\({}^{-1}\)**}} \\ \cline{4-9}  & & & **300**\({}^{\circ}\)**C** & **500**\({}^{\circ}\)**C** & **700**\({}^{\circ}\)**C** & **300**\({}^{\circ}\)**C** & **500**\({}^{\circ}\)**C** & **700**\({}^{\circ}\)**C** \\ \hline F1 & 0 & 0 & 0.20 & 0.26 & 0.46 & 0.22 & 0.38 & 0.62 \\ \hline F2 & 10 & 0 &300 \({}^{\circ}\)C: 52.4% and 41.7% for 500 \({}^{\circ}\)C, and 162% and 167% for 700 \({}^{\circ}\)C with the strain rate of \(3.57\times 10^{-7}\) s\({}^{-1}\) and \(1.25\times 10^{-5}\) s\({}^{-1}\), respectively. This can be explained as follow: as the temperature increased, the evaporation and decomposition of grouts were gradually performed, which caused the decrease of compaction and increase of damage. The DSC of low compaction generated smaller deformation under a low impact loading in the four-point flexural test, compared to DSC with a high compaction. Moreover, the increase of damage decreased the stiffness of the DSC specimen. The increase of deflection also indicated that the failure gradually changed from brittle failure to plastic failure with the enhancement of temperature. Figure 10: Relation between the temperature and deflection of DSC (F3–F8) at different strain rate. Figure 9: Relation between temperature and flexural strength of DSC (F3–F8) at different strain rate. Apparent appearance is a significant visual indicator for buildings exposed to elevated temperatures, which can preliminarily evaluate the degree of damage. Apparent appearance includes appearance of color, crack, and damage. The apparent appearances of DSC F5 after elevated temperature are shown in Figure 11.  
As shown in Figure 10(a), the color of DSC specimen was dark grey and there were occurrences of some tiny cracks on the surface after 300 \({}^{\circ}\)C. Moreover, the impact sound was clunking. At 500 \({}^{\circ}\)C, the DSC specimen, with a slightly clear impact sound, turned into a light grey color and cracks became evident on the surface of the specimen. When the temperature went up to 700 \({}^{\circ}\)C, the color changed to light white and the width of cracks was larger. Besides, the impact sound turned to clear for DSC specimens. The change of color may be due to the effect of siliceous gravel. The siliceous gravel had many colors and the specimen showed different colors with different temperatures [53]. The different impact sounds were due to the change of compaction. The compaction of the DSC specimen decreased with the increase of temperature.