Durability Performance of Polypropylene Fiber-Reinforced Concrete in Sulfate Environments

To address the durability issues of fiber-reinforced concrete (FRC) in sulfate environments, this study investigates the macroscopic performance and microstructural evolution of polypropylene fiber systems (fine polypropylene fibers FPF 0.8 kg/m 3 , coarse polypropylene fibers CPF 6 kg/m 3 ) under a 150-day wet–dry cyclic sulfate attack test in a 5% sodium sulfate (Na 2 SO 4 ) solution. The synergistic reinforcement mechanisms of FPF and CPF were analyzed. The results indicate that the hybrid fiber group (B5: 0.8% FPF + 8% CPF) exhibited the best performance, with a mass loss rate of only 1.49%, a compressive strength of 38.8 MPa, and a relative dynamic modulus retention of 83.3% after 150 days of sulfate exposure. Fine fibers played a crucial role in inhibiting microcrack initiation, while coarse fibers were more effective in controlling the propagation of macrocracks. Their synergistic effect reduced pore connectivity and delayed sulfate ion penetration, enhancing sulfate resistance. The log-normal distribution model was employed to quantify the nonlinear characteristics of strength deterioration (coefficient of determination > 0.93), while microscopic analysis confirmed that the fiber network effectively mitigated stress accumulation and interfacial damage. This study provides a multiscale synergistic reinforcement strategy for the design of FRC in sulfate environments, significantly improving the durability and service life of concrete structures.