Study on improvement of carbonation resistance of alkali-activated slag concrete

Carbonation resistance of Alkali-Activated Slag (AAS) concrete is poor. The main reason is that the main hydration product of AAS is calcium silicate hydrate and no calcium hydroxide crystal exits. Two technical approaches were used to improve carbonation resistance of AAS concrete. One method is to add some components that can react with CO32−, so Ca(OH)2, Zn(OH)2 and ZnCl2 were added to AAS concrete mixture to absorb CO2. The other method is to increase the diffusion resistance of CO2 in concrete, so air-entraining agent and CaSO4·2H2O were added to AAS concrete. The results show that CaSO4·2H2O slightly increases and ZnCl2 obviously reduces the pH value of solid dispersed phase. Other additional components have little effect on the basicity of solid dispersed phase. The carbonation degree of AAS concrete is significantly reduced by Ca(OH)2 and CaSO4·2H2O within the carbonation ages from 3 days to 28 days. Additional components have little effect on the compressive strength of AAS concrete and also have little effect on the hydration and carbonation products of AAS cement.