Pseudo-coating model for predicting chloride diffusion into surface-coated concrete in tidal zone: Time-dependent approach

There are three fundamental physical types for repairs by surface treatment on concrete, i.e., coating, penetrant, and sealer. Due to the inconsistency in using the penetrant-based model in a previous study, three limitations occur. To avoid the limitations, this paper proposes a simple pseudo-coating model embedded in a Fick-based time-dependent approach for modeling the performance of surface-coated concrete in the tidal zone subjected to chloride attack. In addition, the time-dependent regression equation is also developed and combined in computation. To validate the approach, the chloride diffusion predicted by the developed approach is compared to that measured in the previous study. From the study, it is found that the nonlinear and linear surface chloride functions are suitable for uncoated and coated concrete, respectively. The sensitivity analysis shows that the chloride content in concrete is most sensitive to the time-dependent parameter in the surface chloride functions. The surface coating can either decrease or increase initial surface chloride, and the deterioration rate of the surface coating depends on coating materials. By considering the change of the surface chloride after surface treatment, two criteria are proposed to assess the lifetime of coating materials, i.e., equivalent amount of surface chloride, and equivalent instantaneous slope of surface chloride. And, the lifetime is calculated and compared to other literatures. The service life extension of concrete structures with different surface coatings is also compared. The benefit of combining the repair by surface coating with the durability design by increasing concrete cover is also shown.