Abstract: A chloride concentration peak is prone to occur in the chlorideprofiles of concrete subjected to dying-wetting cycles. This research mainly investigated the influence of different water cement ratios ( W/C) on the occurring of chloride concentration peak. Besides, the appropriate calculating method of diffusion parameters was proposed for such chloride profiles with a concentration peak. The experimental results indicate that the peak value of chloride content (Cmax) presents a hysteric relation with increasing W/C, while the position where Cmax appears increased linearly with increasing W/C. Furthermore, the method of excluding the chloride content increasing part and starting from the position where Cmax appears to fit the chloride content phase is the proper way to obtain diffusion parameters of chloride profiles with a concentration peak. In addition, the method, excluding the increased content of chloride ions before the peak value and setting the exposure distance respective to the peak value as the zero point, was applied to obtain diffusion coefficient of chloride profile.

Key words: cement paste;wetting and drying cycle;peak value of chloride concentration;chloride diffusion coefficient;surface chloride concentration