Improving concrete resistance to low temperature sulfate attack through carbonation curing

Carbonation curing of concrete can accelerate cement hydration and convert gaseous CO2 into embedded calcium carbonates. However, it’s commonly understood that concrete containing high amounts of calcium carbonates, as in the case of Portland limestone cement (PLC), is highly susceptible to low temperature sulfate attack. Therefore, this study investigated whether the same vulnerability applies to carbonation-cured concrete prepared from either ordinary Portland cement or PLC. It was found that calcium carbonates introduced through carbonation improved sulfate durability, unlike the compromising limestone additive in PLC. This was demonstrated by resilience against sulfate-induced spalling, expansion, and strength reduction. Gypsum, thaumasite and brucite were detected in severely damaged hydrated PLC specimens upon low temperature sulfate exposure. However, they were not found in the carbonated PLC specimens. Enhanced resistance to low temperature sulfate attack was attributed to reduction in permeability; consumption of calcium hydroxide; and decrease in the pH value of the pore solution.