How carbonation curing influences ca leaching of Portland cement paste: Mechanism and mathematical modeling

Carbonation curing provides a promising method for both CO2 sequestration and strength improvement of cement-based materials. To date, there is little knowledge about the influence of carbonation curing on Ca leaching resistance of cement-based materials due to the occurrence of both physical and chemical transformation. It was the first time that Ca solid-liquid equilibrium curves were experimentally established for cement pastes with different carbonation degrees in this paper. Experimental results demonstrated that on the one hand, carbonation curing improves the leaching resistance of cement paste by sequestrating Ca in insoluble CaCO3; on the other hand, potential negative effects may occur due to the accelerated decalcification and increased solubility of C-S-H after carbonation curing. Results of 29SR NMR showed that both carbonation curing and Ca leaching can increase the Si chain length and polymerization degree of C-S-H. Additionally, a modified mathematical model was established to simulate the leaching process of carbonation-cured cement paste and it was also verified by energy-dispersive spectroscopy (EDS) results. Therefore, the long-term leaching resistance of cement-based materials is possibly degraded by the carbonation curing treatment.