The experimental investigation of width of semi-carbonation zone in carbonated concrete

• Reaction zone of carbonated concrete is determined to chemical component change.
• The partially carbonated zone width was greater than that of pH value variation.
• Carbonated concrete is divided into four zones.
• Carbonation process of concrete is classified into three stages.

An accelerated carbonation experiment was carried out under artificial environment with high CO2 dosing to investigate the concentration distributions of the Ca(OH)2 and CaCO3 by chemical analysis methods as well as the pH value profiles. The results indicate that the distributions of phase components are not consistent with that of the pH value in corresponding zone of carbonated concrete. The cross section of carbonation concrete shows complete carbonation zone, semi-carbonation zone with variable pH value, semi-carbonation zone with constant pH value, and non-carbonation zone. In the light of formation sequence of semi-carbonated zone and completely carbonated zone, the development process of concrete carbonization is divided into three stages: (1) from the beginning of carbonation to the point when pH on concrete surface starts to decrease; (2) from the point when pH on concrete surface starts to decrease to the point when the alkaline component is depleted; (3) from the point when the alkaline component is depleted to any time.