## 3 Test Scheme and Result Analysis
### Uniaxial Dynamic Impact Compression Test
#### 3.2.2 Dynamic Peak Intensity  
The relationship between peak stress and temperature was plotted based on the results of uniaxial dynamic compression tests at different impact air pressures (see Figure 8).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Temperature/\({}^{\circ}\)C** & **Specimen Code** & \begin{tabular}{c} **Impact Air** \\ **Pressure/MPa** \\ \end{tabular} & \
\begin{tabular}{c} **Peak** \\ **Stress/MPa** \\ \end{tabular} &
\begin{tabular}{c} **Peak Strain** \\ **Pressure/MPa** \\ \end{tabular} \\ \hline
25 & PC-25-1 & 0.3 & 48.7 & 0.0034 \\  & PC-25-2 & 0.4 & 49.9 & 0.0039 \\  & PC-25-3 & 0.5 & 52.4 & 0.0044 \\  & S1 PP0-2-25-1 & 0.3 & 71.1 & 0.0062 \\  & S1 PP0-2-25-2 & 0.4 & 69.7 & 0.0072 \\  & S1 PP0-2-25-3 & 0.5 & 71.8 & 0.0081 \\ \hline
100 & PC-100-1 & 0.3 & 50.4 & 0.0041 \\  & PC-100-2 & 0.4 & 51.7 & 0.0052 \\  & PC-100-3 & 0.5 & 52.9 & 0.0058 \\  & S1 PP0-2-100-1 & 0.3 & 71.1 & 0.0087 \\  & S1 PP0-2-100-2 & 0.4 & 72.8 & 0.0112 \\  & S1 PP0-2-100-3 & 0.5 & 75.6 & 0.0122 \\ \hline
200 & PC-200-1 & 0.3 & 51.6 & 0.0065 \\  & PC-200-2 & 0.4 & 53.3 & 0.0074 \\  & PC-200-3 & 0.5 & 54.2 & 0.0083 \\  & S1 PP0-2-200-1 & 0.3 & 79.6 & 0.0089 \\  & S1 PP0-2-200-2 & 0.4 & 78.3 & 0.0119 \\  & S1 PP0-2-200-3 & 0.5 & 81.4 & 0.0128 \\ \hline
400 & PC-400-1 & 0.3 & 40.9 & 0.0075 \\  & PC-400-2 & 0.4 & 43.1 & 0.0099 \\  & PC-400-3 & 0.5 & 44.9 & 0.0113 \\  & S1 PP0-2-400-1 & 0.3 & 63.8 & 0.0098 \\  & S1 PP0-2-400-2 & 0.4 & 67.0 & 0.0128 \\  & S1 PP0-2-400-3 & 0.5 & 69.0 & 0.0132 \\ \hline
600 & PC-600-1 & 0.3 & 30.2 & 0.0094 \\  & PC-600-2 & 0.4 & 31.8 & 0.0109 \\  & PC-600-3 & 0.5 & 33.4 & 0.0133 \\  & S1 PP0-2-600-1 & 0.3 & 49.2 & 0.0117 \\  & S1 PP0-2-600-2 & 0.4 & 51.6 & 0.0147 \\  & S1 PP0-2-600-3 & 0.5 & 54.0 & 0.0157 \\ \hline
800 & PC-800-1 & 0.3 & 17.0 & 0.0125 \\  & PC-800-2 & 0.4 & 18.6 & 0.0134 \\  & PC-800-3 & 0.5 & 19.2 & 0.0152 \\  & S1 PP0.2-800-1 & 0.3 & 33.5 & 0.0133 \\  & S1 PP0-2-800-2 & 0.4 & 35.6 & 0.0157 \\  & S1 PP0.2-800-3 & 0.5 & 36.5 & 0.0176 \\ \hline \hline \end{tabular} Note: “PC” indicates plain concrete, “S” represents steel fiber, and “PP” denotes polypropylene fiber; the number “0.2” of “S1 PP0.2” indicates the percentage of volume mixing.  
\end{table}
Table 5: Dynamic compression test results of specimens.  
Under the same impact air pressure, C40 plain concrete and HyFRC show a temperature enhancement effect within 25 \({}^{\circ}\)C-200 \({}^{\circ}\)C. With the increase in temperature, the compressive strength increases slightly. The reason is that in this temperature range, the internal microstructure of concrete will produce secondary hydration [24], and the mechanical properties will be improved. At the same time, the impact load has a compaction effect on the microcracks of the concrete material, which significantly reduces the number of primary bubbles and microcracks in the internal structure of the concrete, and the macroscopic performance is the enhancement of mechanical properties. At the temperature gradient of 200 \({}^{\circ}\)C-800 \({}^{\circ}\)C, the specimens exhibit a significant temperature damage effect, and their compressive strength decreases significantly with increasing temperature. The variation mechanism is basically consistent with static compression. However, another reason for the enhanced dynamic compressive strength is the compaction of microfractures in the concrete material by impact loading, significantly reducing the number of indigenous air bubbles and microcracks in the internal structure of the concrete. The HyFRC exhibits both positive and negative effects. The dynamic compressive strength of S1 PP0.2 HyFRC at 200 \({}^{\circ}\)C was the greatest, with an increase of 51.7%, 49.3%, and 50.2% in dynamic compressive strength compared to C40 plain concrete at impact air pressures of 0.3 MPa, 0.4 MPa, and 0.5 MPa, respectively. At an impact air pressure of 0.3 MPa and a temperature of 800 \({}^{\circ}\)C, the dynamic compressive strength of S1 PP0.2 HyFRC increased by 97.1% compared to C40 plain concrete.