Abstract: In order to explore the safety of basalt fiber high strength concrete under multiple impact loads, the longitudinal wave velocity and internal pore structure of the specimen under different strain rates and impact times are measured by non-metallic ultrasonic analyzer and nuclear magnetic resonance test device. The dynamic compression test of the specimen was carried out by using the separated Hopkinson compression bar device with a diameter of 74 mm. The changes of longitudinal wave velocity, damage factor, T₂ spectrum, pore structure and stress-strain with impact pressure and impact times are analyzed. The test results show that the longitudinal wave velocity decreases with the increase of impact times, and the damage factor increases with the increase of impact times, and there is a good quadratic linear positive correlation between them. The T₂ spectrum of the specimen is mainly three peak type, and the increase of impact times will shift the spectrum to the right and increase the peak value. With the increase of impact times, the pore diameter and the number of pores increase, the porosity of the specimen increases, and the subsequent impact is more conducive to the expansion of cracks. The contents of micropores and mesopores in the specimen account for more than 95% of the total porosity. The impact load reduces the proportion of micropores and mesopores in the specimen, and increases the proportion of macropores and cracks. Under the action of multiple impact loads, the peak stress of the specimen will be reduced and the stress variable will be increased. There is a good quadratic function negative correlation between the impact times and the peak stress.

Key words: multiple impact loads, basalt fiber high strength concrete, longitudinal wave velocity, damage factor, pore structure, peak stress, composites