## 3 Test Results and Analysis
### Influence Analysis of Temperature  
The appearance characteristics of the specimens after exposure to different temperatures when the fiber content is 0.2% are shown in the Figure 4.  
As can be seen from Figure 4, when the temperature was 200 \({}^{\circ}\)C, the specimen had a complete appearance without obvious peeling and damage, and the color was roughly the same as that at 20 \({}^{\circ}\)C. At 400 \({}^{\circ}\)C, the skin of specimen was slightly peeled off, and the color showed light gray. At 600 \({}^{\circ}\)C, the peeling of the epidermis was more obvious, with slight cracks on the surface and a reddish color. At 800 \({}^{\circ}\)C, the peeling of epidermis was obvious, the surface had obvious cracks, and the reddish color deepened. When the temperature was 1000 \({}^{\circ}\)C, the specimen was broken into pieces and the color was red. The specimen was completely destroyed under the effect of temperature. When the impact rate is 8.8 m/s and the fiber content is 0.2%, the crushing morphology of BFRC specimens after exposed to different temperatures are shown in Figure 5. It can be seen that the size of fragmentations became smaller and smaller as the temperature rose under impact loading. Figure 4: The appearance characteristics of the specimens after exposed to different temperatures. Figure 3: The variation rule between fiber content and stress peak strength. When the impact velocity is 8.8 m/s, the change curves between temperature and dynamic strength of BFRC specimens with different fiber content are shown in Figure 6.  
Figures 3, 5 and 6 shows that the dynamic peak stresses of BFRC specimens gradually reduced as the temperature rose. The dynamic strengths of the ordinary concrete specimens at 200 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C were 88%, 81.7%, 44% and 36.5% of that at room temperature, respectively. When the fiber content was 0.2%, its corresponding proportion respectively: 83.5%, 93%, 77.4%, 58.3%, indicating that elevated temperature has significant damage to the dynamic mechanical properties of concrete. Compared with ordinary concrete, BFRC has lower damage. When the temperatures ranged from 20 \({}^{\circ}\)C to 400 \({}^{\circ}\)C, the peak strength decreased less than 20% compared with room temperature, which was consistent with the variation law of concrete strength after high temperature under quasi-static loading in reference [26]. But when the fiber contents were 0.1-0.3% and temperatures ranged from 200 \({}^{\circ}\)C to 400 \({}^{\circ}\)C, the peak strength increased slightly. When the temperature reached 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the peak stress greatly reduced. According to the microscopic studies of concrete after elevated temperature [27; 28; 29; 30], it can be seen that when the temperatures were at 200-400 \({}^{\circ}\)C, micro-cracks and voids in the concrete caused by free water evaporation continued to develop, the C-S-H gel became decomposed simultaneously and the damage became more severe. But the interlock force between gels and aggregate became enhanced due to the contraction of C-S-H gel. In addition, the bridging effect of basalt fibers could limit and delay the development of micro-cracks and partially relieve stress concentration at the tips of cracks. Therefore, when the increase of crack resistance by fibers and interlock force exceeds the strength reduction caused by fracture development, the impact strength of specimens would increases under impact load. When the temperature exceeded 400 \({}^{\circ}\)C, the C-S-H gel became loose, calcium hydroxide and crystallization water inside concrete decomposed, cement mortar shrank significantly and aggregate expanded at the same time, the internal stress increased, the bonding surfaces between aggregate and cement mortar cracked. The above phenomena would lead to the destruction of the internal structure of concrete, and the strength would decrease sharply.