This article presents the effects of basalt-polypropylene fibers on the compressive strength and chloride ion resistance of concrete with matrix strength grades C30, C40, and C50. Test results indicated that hybrid fibers can effectively improve the compressive strength of concrete; that the maximum increases in compressive strength of C30, C40, and C50 concrete were 9.18%, 5.06%, and 7.13%, respectively; and that the effect of basalt fiber on compressive strength was greater than that of polypropylene fiber. A suitable quantity of hybrid fibers can effectively improve the chloride ion resistance of concrete. The enhancement was greatest for C50 concrete, in which the chloride diffusion coefficient was reduced by 77.8% compared to the reference concrete. The chloride diffusion coefficient of basalt-polypropylene fiber–reinforced concrete has a strong positive correlation with the coulomb electric flux. However, the hybrid fibers have adverse effects on the compressive strength and chloride ion resistance of concrete when the quantity of fibers is excessive. Therefore, considering the compressive strength and chloride ion resistance of concrete, the total volume fraction of hybrid fibers should not exceed 0.15%.

This study investigates the effects of basalt–polypropylene fibers on the compressive strength and splitting tensile strength of concrete and calculates the fractal dimension of the pore structure of concrete by using a fractal model based on the optical method. Test results reveal that hybrid fibers can improve the compressive strength and splitting tensile strength of concrete, and the synergistic effect of the hybrid fibers is strongest when the contents of basalt fiber (BF) and polypropylene fiber (PF) are 0.05% each, and that the maximum increments in compressive strength and splitting tensile strength are 5.06% and 9.56%, respectively. The effect of hybrid fibers on splitting tensile strength is greater than on compressive strength. However, hybrid fibers have adverse effects on mechanical properties when the fiber content is too high. The pore structure of basalt–polypropylene fiber-reinforced concrete (BPFRC) exhibits obvious fractal characteristics, and the fractal dimension is calculated to be in the range of 2.297–2.482. The fractal dimension has a strong correlation with the air content and spacing factor: the air content decreases significantly whereas the spacing factor increases with increasing fractal dimension. In addition, the fractal dimension also has a strong positive correlation with compressive strength and splitting tensile strength. Therefore, the fractal dimension of the pore structure can be used to evaluate the microscopic pore structure of concrete and can also reflect the influence of the complexity of the pore structure on the macroscopic mechanical properties of concrete.