Influence of carbonation on “maximum phenomenon” in surface layer of specimens subjected to cyclic drying-wetting condition

Numerous researches have reported that there is a tendency chloride content first climbs to the maximum then declines with depth increasing in the surface layer of concrete under cyclic drying-wetting environments, which is temporally called 'maximum phenomenon' in this paper. This research focuses on the impact of different carbonation conditions on this phenomenon for both pastes and mortars. The distribution of chloride suggests that coupled effect of carbonation and capillary suction/moisture evaporation is more likely to lead to the formation of maximum phenomenon than the merely effect of capillary suction/moisture evaporation. Furthermore, analysis of pore structure and phase composition reveals that this particular phenomenon is directly related to the release of bound chloride fixed in Friedel's salt triggered by carbonation. In addition, the forming process of maximum phenomenon is proposed in the end based on Friedel's salt decomposition under cyclic drying and wetting condition.