A Novel Test Method for Chloride Permeability of Ordinary Portland Cement Mortar Exposed to Salt Fog–Dry Cycles

In this study, the stationary chloride permeability of ordinary Portland cement mortar exposed to salt fog–dry cycles is investigated. An original salt fog–dry cycling test setup, comprising an outer upstream tank and four inner downstream reservoirs, is established to explore chloride transport behavior through the bulk material. Steady-state chloride flux is discovered from the chloride profile, which exhibits a linear concentration gradient in both the convection and diffusion zones, following months of salt fog–dry cycles. Based on experimental observations, this study proposes a double-broken-line model to mathematically represent the chloride profile. An equivalent diffusion zone is then proposed by considering the deposited convection factor. Correspondingly, the diffusion coefficient of the equivalent diffusion zone is determined using Fick’s first law. Considering the effects of water-to-cement ratio and fog temperature, the stationary chloride permeabilities range from 0.283 × 10−12 m2/s to 0.674 × 10−12 m2/s, which are generally consistent with field data for concrete exposed to salt aerosols/dry environments. Although chloride permeability is temperature-dependent and, to some degree, affected by mixture proportion, the researchers recognize the aggregate/sample size effect on the variance of diffusivity values. Recommendations are drawn to upgrade the chloride transport scenario for a reliable evaluation of coarse-sand mortar and concrete.