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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.

Chloride ingression into reinforced concrete (RC) is currently considered an important reason behind the deterioration of RC structures exposed to aggressive environments. Previous studies have been mostly devoted to investigations on the one-dimensional transport characteristics of chloride in concrete; however, for the RC structures exposed to marine environment, the corners and edges of various components are often subjected to two-dimensional chloride penetration. Moreover, concrete is generally considered a typical heterogeneous material because of its coarse aggregate being randomly distributed in a cement paste. Both the two-dimensional chloride diffusion behaviour and the heterogeneity of concrete materials have large influences on the chloride concentration distribution in concrete. For the investigations in this paper, using the coarse aggregate volume fraction (CAVF) to quantify the heterogeneity of concrete materials, an indoor experiment for exploring the two-dimensional chloride diffusion behavior of concrete under real-time tidal cycles in a marine environment was carried out. The two-dimensional chloride diffusion concentrations within concrete specimens cast using different CAVFs of Vca = 0, 0.2, 0.3, 0.4, and 0.5 were tested at various exposure periods of t = 30, 70, 100, 140, and 180 days. The decreased percentages for the tested two-dimensional chloride diffusion concentrations increased with increasing CAVF, and the percentage values decreased from −4.95%, −5.22%, −6.29%, and −7.46% to −65.52%, −73.68%, −91.56%, and −97.22% for Vca = 0.2, 0.3, 0.4, and 0.5 in relation to Vca = 0 in the diagonal sample holes of the concrete specimens, respectively. The quantitative influence of Vca = 0.5 on the two-dimensional chloride diffusivity showed an average reduction of approximately 50.79% for each exposure period in relation to the specimen values for Vca = 0. On the basis of the two impact factors related to the exposure period (If (t)) and the CAVF (If (Vca)), a time-dependent model for predicting the two-dimensional chloride diffusion concentration in concrete by accounting for the heterogeneity of concrete materials was developed and compared with those determined by the meso-scopic numerical simulation method and physical experiment. The comparisons exhibited that the two-dimensional chloride concentrations assessed by the model and numerical simulation were almost within a ±20% error margin, validating the accuracy, correctness and reasonability of the prediction model developed in this paper.