Prediction of chloride concentration with elevation in concrete exposed to cyclic drying-wetting conditions in marine environments

Abstract

Chloride ions are generally considered one of the most significant factors in the corrosion of steel bars in reinforced concrete (RC) structures exposed to alternate drying-wetting marine environments. When RC structures are exposed to cyclic drying-wetting conditions, such as in the marine tidal zone, the chloride concentration distributions in RC structures along the elevation direction changes due to the influence of various drying-wetting ratios. In the study presented here, an indoor exposure experiment for chloride transport in concrete specimens under different conditions of drying-wetting ratios is employed to explore the chloride concentration distributions along the elevation of an RC structure. The elevation related to the peak value of the chloride concentration, which corresponds to the most unfavourable drying-wetting ratio for the RC structure, is determined. On the basis of the tested chloride concentration results, the variation of the time-dependent models of surface chloride concentration and apparent chloride diffusion coefficient with elevation are established for an RC structure. Furthermore, an empirical model of chloride diffusion based on Fick’s second law is developed and adopted to predict the chloride concentrations in concrete at an arbitrary elevation and exposure time. The accuracy of this prediction model of chloride diffusion is validated in terms of the experimental chloride measurements.