*4.1. Average Strain Rate of 7.5 s*−*<sup>1</sup>*

Table 3 shows the macro morphology of UR50 ultra-early-strength cement-based specimens after impact compression at different stages when the impact velocity is 5 m/s (the average strain rate is 7.5 s−1) in three repeated experiments. It can be seen from the table that at an impact velocity of 5 m/s, the specimens were damaged under the impact compression stress wave. The specimen ruptured into a number of larger fragments, indicating that the ultra-early-strength cement-based material has a greater impact compression brittleness. Under the low strain rate, the overall fracture will occur, but under the same strain rate conditions, ordinary concrete will generally not fail. The stress–strain curve and the average stress–strain curve obtained by repeating the experiment three times at an impact velocity of 5 m/s are shown in Figure 5.

**Figure 5.** Stress–strain curve of 5 m/s.


**Table 3.** Test results at an impact velocity of 5 m/s.
