Study on Chloride Permeability and Chloride Ion Transport of Fiber-Reinforced Cementitious Composite Repair System

The durability degradation of concrete structures in marine and urban underground environments is largely governed by chloride-induced corrosion. This process becomes significantly more severe under the coupled action of external loading and drying–wetting cycles, which accelerate chloride transport and structural deterioration. However, the existing research often isolates the effects of mechanical loading or environmental exposure, failing to comprehensively capture the synergistic interaction between these factors. This lack of understanding of chloride ingress under simultaneous mechanical and environmental loading limits the development of reliable service life prediction models for concrete structures. In this study, a self-made loading system was employed to simulate this coupled environment, combining external loading with 108 days of drying–wetting cycles. Chloride profiles were obtained to assess the combined effects of stress level, water/binder ratio, and fiber content on chloride penetration in fiber-reinforced cementitious composites (FRCCs). To further extend the analysis, a Crank–Nicolson-based finite difference approach was developed for the numerical assessment of chloride diffusion in concrete structures after repair. This model enables the point-wise treatment of nonlinear chloride concentration profiles and provides space- and time-dependent chloride concentration distributions. The results show that using an FRCC as a repair material significantly enhances the service life of chloride-contaminated concrete structures. The remaining service life of the repaired concrete was extended by 36.82% compared to the unrepaired case, demonstrating the clear practical value of FRCC repairs in aggressive environments.