## 3 Experimental Results and Discussion
### Dynamic Compressive Strength
#### 3.3.4 The Dynamic Constitutive Model of Basalt Fiber-Reinforced Concrete  
In this section, the dynamic compressive strength-temperature constitutive model of basalt fiber-reinforced concrete exposed to various high temperatures and different cooling methods under the dynamic load rate of 5.8 m/s is established as Equation (4):  
\[\text{f}=\text{t}_{1}+\text{t}_{2}+\text{t}_{3}\text{T}^{2}+\text{t}_{3}\text{T }^{3} \tag{4}\]  
f--Compressive strength (Mpa).  
T--Temperature (\({}^{\circ}\)C).  
Based on the Equation (4), the constitutive model of basalt fiber-reinforced concrete after air cooling was shown in Figure 25 and its fitting parameters were recorded in Table 18.  
Figure 24: The failure patterns of basalt concrete using the water-cooling method.  
Figure 25: The constitutive model of basalt fiber-reinforced concrete after air cooling.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameters** & \(\mathbf{t_{1}}\) & \(\mathbf{t_{2}}\) & \(\mathbf{t_{3}}\) & \(\mathbf{t_{4}}\) \\ \hline basalt fiber-reinforced concrete & 51.84 & 0.087 & \(3.6\times 10^{-4}\) & \(2.3\times 10^{-7}\) \\ \hline \end{tabular}
\end{table}
Table 18: The fitting parameters of dynamic compressive strength of basalt fiber-reinforced concrete after air cooling.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameters** & \(\mathbf{t_{1}}\) & \(\mathbf{t_{2}}\) & \(\mathbf{t_{3}}\) & \(\mathbf{t_{4}}\) \\ \hline basalt fiber-reinforced concrete & 52.25 & 0.05 & \(-4\times 10^{-4}\) & \(3.4\times 10^{-7}\) \\ \hline \end{tabular}
\end{table}
Table 19: The fitting parameters of dynamic compressive strength of basalt fiber-reinforced concrete after water cooling.  
Figure 26: The constitutive model of basalt fiber-reinforced concrete after water cooling.  
compressive strength decreases and the peak strain increases with the increase of the temperature for the same strain rate state. At the same temperature, the dynamic compressive strength increases with the increase of the loading rates.  
Figure 27: The comparison figures of the stress–strain curves of the two concretes.  
In addition, the dynamic compressive strength of basalt fiber-reinforced concrete is better than ordinary concrete at every temperature on the whole; that is to say, the addition of basalt fiber in concrete can effectively increase the toughness of concrete and improve the dynamic compressive strength of concrete.  
The comparison figures of the temperature-strength curves of ordinary concrete and basalt fiber-reinforced concrete are shown as follows:  
Figure 28 shows that the strength of the two concretes increases with the increase of the temperature and reaches peak strength when the temperature reaches 200 \({}^{\circ}\)C. After, the strength both of basalt fiber-reinforced concrete and ordinary concrete begins to decrease continuously. This is attributed to the rehydration of lime accompanied by a volume increase, which converts the CaCO\({}_{3}\) into CaO and causes cracking and crumbling of concrete materials at high temperatures.  
However, under the same temperature and loading rate, the strength of basalt fiber-reinforced concrete is bigger than ordinary concrete. This also confirms that the addition of basalt fiber to concrete can significantly increase the dynamic compressive strength of concrete.