Abstract: The damage degree, pore structure and energy dissipation of basalt fiber reinforced concrete under different stress levels are studied based on experiments. Non-metallic ultrasonic detector is used to measure 0σ_m, 0.15σ_m, 0.3σ_m, 0.45σ_m, 0.6σ_m variation of longitudinal wave velocity and damage factor under five different stress levels. The T₂ spectrum distribution, pore size distribution and porosity of specimens under different stress levels were studied by NMR test. Combined with the universal press machine, the uniaxial compression test of the specimen is carried out, and the variation laws of stress-strain curve, peak stress and energy dissipation are analyzed. The results show that the basalt fiber concrete specimen will be damaged under stress, the specimen height decreases with the increase of the applied stress level, and the longitudinal wave velocity first increases slightly and then decreases. The integrity of the specimen is enhanced under the action of low stress level,and the specimen is damaged under the action of high stress level, and the greater the stress, the higher the damage degree. The peak value of T₂ spectrum of test piece is the lowest under the action of 0.3σ_m stress level and the peak value of T₂ spectrum is the highest under the action of 0.6σ_m stress level. The porosity of the specimen first decreases and then increases with the increase of stress level. The internal pores of the test piece mainly exist in the form of micropores and mesopores. Under the action of low stress level, the original cracks in the test piece are compressed, the mesopores in the test piece are transformed into micropores, and the total porosity decreases. Under the action of high stress level, the test piece is damaged and deformed under the action of stress, the internal crack pore diameter increases and the porosity increases. The addition of basalt fiber increases the plastic deformation capacity of concrete, and the peak stress decreases with the increase of action stress level, and the decrease amplitude increases significantly. The dissipated energy per unit volume of the specimen decreases with the increase of the stress level, and the mechanical damage degree increases slightly with the increase of the stress level. Under the stress damage, the elastic deformation capacity of the specimen decreases and the energy dissipation rate increases.

Key words: stress damage, basalt fiber concrete, longitudinal wave velocity, damage factor, porosity, peak stress, energy dissipation, composites