Abstract: To investigate the combined effects of loading rate and water saturation on the mechanical properties and failure mechanisms of basalt fiber reinforced concrete, non-metallic ultrasonic detectors and other devices were used to measure porosity, water saturation, and longitudinal wave velocity of the specimens. Compression tests were performed on saturated and dry specimens under different strain rates, using a universal testing machine and a split Hopkinson pressure bar with a diameter of 74 mm. The impacts of strain rate and water saturation on peak stress, elastic modulus, longitudinal wave velocity, and stress-strain relationships were also analyzed. Results showed that the porosity of basalt fiber reinforced concrete ranged from 1.89% to 3.05%, and a positive linear correlation was observed between the porosity of the specimens and their saturation levels. Water saturation accelerated the propagation of longitudinal waves inside the specimens. Under static loading conditions, the peak stress of saturated specimens was 8.6% lower than that of dry specimens, while the peak stress and elastic modulus of both types of specimens increased with increasing strain rates. Results also revealed a significant strain rate effect on specimens, with stress increase more pronounced in saturated specimens compared to dry ones. When the strain rate reached 130 s^-1, the stress levels in dry and saturated specimens were largely consistent. However, at a strain rate of 160 s^-1, the peak stress of saturated specimens was 11.4% higher than that of dry specimens. The elastic modulus showed a similar behavior to the strength. Water saturation led to erosion and degradation of the concrete as well as dynamic coupling strengthening effects between the water and fiber. Under static loading, softening effects of water and crack extension due to hydrostatic pressure at the crack tip reduced the ability of specimens to resist external loads. Under dynamic loading, negative pressure within pores and the Stefan effect hindered crack extension and the failure of the specimens. The critical strain rate corresponding to the same stress levels for both dry and saturated specimens was found to be 130 s^-1.

Key words: fiber concrete, strain rate, water saturation, porosity, longitudinal wave velocity, peak stress, dynamic coupling strengthening