Progress of Carbonation in Chloride Contaminated Concretes

Concretes used in marine environment are generally under the cyclic effect of CO2 and chloride ions (Cl-). To date, the influence of carbonation on ingress of chloride ions in concretes has been widely studied; in comparison, study on the influence of Cl- on the progress of carbonation is limited. During the study, concretes were exposed to independent and combined mechanisms of carbonation and chloride ingress regimes. Profiles of apparent pH and chloride concentration were used to indicate the progress of carbonation and ingress of Cl- in concretes. From the apparent pH profile, a carbonation front and a carbonation boundary were characterized according to profile of consumed hydroxyl ions (OH-). Results show that carbonation was significantly slowed down due to the existence of Cl-, viz. the depth of carbonation boundary was decreased; the profile of consumed OH- became modest; the carbonation front for different mixes presented slightly different trends. For the sound concretes, carbonation generated microcracks on concrete surface and increased permeation properties; for the chloride contaminated concretes, due to the limited extent of carbonation, permeation properties did not present obvious difference.