Chloride binding capacity of pastes influenced by carbonation under three conditions

This research investigates the influence of carbonation on chloride binding capacity under three conditions varying in the sequence and way of carbonation-chloride contact: I, hardened pastes first carbonated then contacted with chloride; II, hardened pastes first contacted with chloride then carbonated; III, pastes inner-introduced with chloride during casting, hardened and then carbonated. The results indicate that, before carbonation, the bound chloride content of pastes inner-introduced with chloride is slightly higher than that of pastes first hardened then contacted with chloride because more Friedel's salt is formed through the former way. And during the carbonation process, the remaining bound chloride content mainly depends on the content of un-carbonated C-S-H gel. And based on the content of it before total carbonation, the content of residual bound chloride in samples under condition I is higher than that under the other two conditions after the same carbonation time. After complete carbonation, the bound chloride content under the three conditions all approximates to zero, which indicates that carbonation makes paste lose chloride binding capacity completely.