Copious studies have discovered a phenomenon that a chloride concentration peak appears on the surface of concrete under cyclic drying-wetting environments. In such cases, the chloride diffusion coefficient (D) obtained through directly fitting the standard error function of Fick's second law is no longer accurate. e more reliable D obtained by the method proposed by Andrade is employed in this research to investigate the influence of pore structure on chloride penetration rate of pastes. e results show that both the effective coefficient (D eff ) and the apparent coefficient (D app ) increase with total porosity, the most probable pore size, and water absorption porosity, suggesting that the increase of the three pore structure parameters accelerates chloride penetration rate under cyclic wetting-drying condition. e increase of the three parameters makes more room available and eases the difficulty for salt solution to enter the matrix and thus leads to the augmentation of chloride transporting in matrix.

Chloride transport under wetting and drying environment is very complicated. A lot of research has reported maximum phenomena in chloride profiles under such environment. Considering the fact that most specimens in which chloride maximum was detected before either had inhomogeneous surface (might be influenced by skin effect) or were exposed to natural environment (might be influenced by rain washing), this study aims to reveal chloride distribution under mere wetting and drying condition in cement-based materials. The chloride distribution results in the surface layer of specimens with different water to binder ratio (W/B) detected by silver nitrate titration method (SNT), ion chromatography method (IC)and electric probe micro analysis (EPMA) present a fact that: maximum phenomena occur in all specimens under four wetting-drying regimes, no matter in paste or mortar, in free or total chloride, and whether with slag (SL) and fly ash (FA) or not. It suggests that mere wetting and drying action can incur chloride maximum phenomenon without the attendance of skin effect and rain washing, though sometimes confined by the accuracy of testing method, the position of maximum phenomenon can not be presented.