Abstract: Based on the experimental study of the internal pore structure characterization of basalt fiber concrete with different lengths (0 mm, 6 mm, 12 mm, 18 mm) and the mechanical properties of splitting tension under different strain rates, the techniques of nuclear magnetic resonance and scanning electron microscope were used to analyze the T₂ spectrum distribution, pore size distribution, porosity and the bond between fiber and concrete. Dynamic splitting tests were carried out on basalt fiber concrete specimens of different lengths at different strain rates by using universal testing machine and split Hopkinson pressure bar, and the effects of fiber length and strain rate on the splitting tensile properties of concrete were analyzed. The results show that the T₂ spectrum curve of basalt fiber concrete is bimodal. The T₂ spectrum peak value and porosity of plain concrete specimen are the largest. The incorporation of fiber can effectively reduce the porosity of the specimen, and the effect is best when the length is 6 mm. The internal pores of the specimen are mainly micropores and small holes. The incorporation of fiber increases the proportion of micropores in the specimen, while the proportion of small holes decreases. As the strain rate increases, the specimen exhibits a strain rate strengthening effect, and the dynamic increase factor has a good logarithmic correlation with strain rate. The incorporation of fiber can effectively enhance the tensile strength of the specimen and reduce its ultimate strain. The effect is best when the fiber length is 18 mm. SEM result shows that the bond between basalt fiber and concrete material can effectively bear the load, reduce the crack expansion and enhance the resistance of the specimen to deformation.

Key words: basalt fiber, concrete, nuclear magnetic resonance, scanning electron microscope, SHPB, split tensile strength, ultimate strain