## 3 Experimental Results and Discussion
### Basic Physical Parameters
#### 3.2.1 Effect of High Temperature on Static Compressive Strength  
The trend of the two concretes' strength at a high temperature is similar. For air cooling, the experiment results are shown in Tables 6 and 7.  
Although the overall trend of the strength of the two concretes decreases with the temperature increasing, the concrete strength increases when the temperature increases within 25-200 \({}^{\circ}\)C and reaches a peak when the temperature reaches 200 \({}^{\circ}\)C. The concrete  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature/\({}^{\circ}\)C** & **Hight/mm** & **Mass/g** & **Strength/Mpa** \\ \hline  & 100.0 & 1072 & 32.3 \\
25 & 99.8 & 1067 & 30.8 \\  & 99.7 & 1064 & 31.6 \\ \hline  & 100.4 & 978 & 36.9 \\
200 & 100.3 & 995 & 34.7 \\  & 99.7 & 987 & 37.8 \\ \hline  & 99.5 & 962 & 23.9 \\
400 & 100.3 & 1003 & 19.6 \\  & 99.3 & 952 & 23.6 \\ \hline  & 99.2 & 948 & 16.1 \\
600 & 99.7 & 900 & 15.7 \\  & 99.5 & 910 & 14.9 \\ \hline  & 100.4 & 807 & 8.6 \\
800 & 99.6 & 810 & 7.4 \\  & 100.5 & 836 & 7.5 \\ \hline \end{tabular}
\end{table}
Table 6: The static compressive strength of ordinary concrete in air cooling.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature/\({}^{\circ}\)C** & **High/mm** & **Mass/g** & **Strength/Mpa** \\ \hline  & 100.3 & 1072 & 37.5 \\
25 & 99.6 & 1057 & 35.7 \\  & 99.9 & 1065 & 34.8 \\ \hline  & 99.8 & 995 & 43.0 \\
200 & 100.7 & 995 & 42.6 \\  & 99.4 & 992 & 39.7 \\ \hline  & 99.9 & 987 &  
strength begins to decrease with the further increase of the temperature. When the temperature reaches 400 \({}^{\circ}\)C, the strength of ordinary concrete decreases 25% than the strength at room temperature while the strength of basalt fiber-reinforced concrete decreases 7.2% than the strength at room temperature. When the temperature reaches 600 \({}^{\circ}\)C, the strength of ordinary concrete decreases 49.3% compared to the strength in room temperature while the strength of basalt fiber-reinforced concrete decreases 53.1% compared to the strength at room temperature. When the temperature reaches 800 \({}^{\circ}\)C, the strength of ordinary concrete decreases 75.8% compared to the strength at room temperature while the strength of basalt fiber-reinforced concrete decreases 68.9% compared to the strength at room temperature.  
The reason for this phenomenon is that, when the temperature is less than 200 \({}^{\circ}\)C, the cracks inside concrete are fewer because of thermal expansion and cold contraction; therefore, the static compressive strength is improved. With the further increase of the temperature, the bound water inside the concrete begins to precipitate, and the static compressive strength decreases rapidly. When the temperature reaches 800 \({}^{\circ}\)C, the CaCO\({}_{3}\) inside the aggregate of cement paste begins to resolve into CaO, so that the concrete loses its bearing capacity.  
The failure patterns of the two kinds of concrete subjected to high temperatures under air cooling are shown as follows:  
At room temperature and 200 \({}^{\circ}\)C, the two concretes were subjected to axial pressure, and concrete specimens without confining pressure extended along the longitudinal and the discontinuous tension failure was increased. With the increase of compression, the cracks gradually penetrated and caused the surface to break, and spalling occurred locally, causing the concrete to lose its bearing capacity. When the temperature increased further, the bound water in the concrete began to precipitate, the internal cracks gradually developed and penetrated, and concrete showed failure patterns of \"/\", \"V\", and \"X\".