## 3 Experimental Results and Discussion
### Dynamic Compressive Strength
#### 3.3.2 Effect of High Temperature on Dynamic Compressive Strength  
The dynamic compressive temperature-strength curves of ordinary concrete and basalt fiber-reinforced concrete at various heating temperatures are shown as follows (Figure 20):  
It can be seen from the Figure 20 that the dynamic compressive strength of ordinary concrete and basalt fiber-reinforced concrete increases first and reaches a peak when the temperature increases to 200 \({}^{\circ}\)C. After, with the further increase of the temperature, the dynamic compressive strength of concrete declines rapidly. When the temperature reaches 400 \({}^{\circ}\)C, the compressive strength of concrete is less than at 25 \({}^{\circ}\)C. When the temperature reaches 800 \({}^{\circ}\)C, the ordinary concrete and basalt fiber-reinforced concrete loses the bearing capacity.  
When the loading rate is 5.8 m/s, compared with room temperature (25 \({}^{\circ}\)C), the dynamic compressive strength of ordinary concrete improves by 31.3%, 33.7%, 53.4%, and 84.8% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively, while the dynamic compressive strength of basalt fiber-reinforced concrete improves by 43.3%, 11.6%, 50.2%, and 75.7% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively. When the loading rate is 7.8 m/s, compared with room temperature (25 \({}^{\circ}\)C), the dynamic compressive strength of ordinary concrete improves by 25.5%, 25.5%, 44.8%, and 83.6% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively, while the dynamic compressive strength of basalt fiber-reinforced concrete improves by 13.6%, 25.8%, 46.6%, and 80.8% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively. When the loading rate is 9.8 m/s, compared with room temperature (25 \({}^{\circ}\)C), the dynamic compressive strength of ordinary concrete improves by 28.3%, 18.5%, 38.3%, and 79.4% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively, while the dynamic compressive strength of basalt fiber-reinforced concrete improves by 25.7%, 19.4%, 48%, and 76% at 200, 400, 600, and 800 \({}^{\circ}\)C, respectively.  
When the temperature is less than 200 \({}^{\circ}\)C, a thermal strengthening effect is observed. At this stage, free water escapes constantly, and due to thermal expansion and cold contraction, the tiny cracks of concrete are reduced with the expansion of the aggregate and vapor increases the internal pressure. With the increase of the dynamic loading, the internal cracks of concrete are pressed and the stress concentration of the concrete is decreased; therefore, the strength of the concrete is improved. When the temperature exceeds 200 \({}^{\circ}\)C, the bound water inside the concrete begins to precipitate, and the interaction of the cement in the concrete is enhanced. Due to the concrete thermal expansion, the coefficients of the coarse aggregate and additives are different, and a lot of thermal damage to the joint of the  
Figure 20: The dynamic compressive temperature–strength curves of two concrete.  
concrete is caused. Under the influence of these two factors, the strength of the concrete decreased and is less than at room temperature. When the temperature reaches 600 \({}^{\circ}\)C, the hydrate, like NaOH, of the concrete begin dehydration and produce NaO, the volume is expanded, and the fractures in the concrete are developed further. When the temperature reaches 800 \({}^{\circ}\)C, the strength of the aggregate in concrete is lost and the concrete becomes completely loose.