Effect of Extended Carbonation Curing on the Properties of γ-C2S Compacts and Its Implications on the Multi-Step Reaction Mechanism

Accelerated carbonation of the cement-based materials has attracted worldwide attention due to the advantages of rapid strength gain and CO2 sequestration. This work was designed to investigate the mechanism of γ-C2S compacts under extended carbonation curing to further develop the accelerated carbonation technology. Based on the variation of the mechanical properties, microstructure, and the phase assemblages through the extended carbonation, a multi-step reaction mechanism is proposed in this work. The process can be divided into three stages: phase-boundary-controlled stage; product layer CO2 diffusion-controlled stage; and CO2 diffusion and calcium ion dissolution-controlled stage. Correlation between the calcium carbonate polymorph and the controlling factors is also investigated, in which the high calcium ion concentration is beneficial to the formation of calcite. Meanwhile, the stepwise pressurization curing regime based on the multi-steps is proposed to increase the strength obviously, which further verifies the mechanism of multi-step reactions.