Understanding the role of different phases in γ-C2S based carbonatable clinkers

Accelerated carbonation of carbonatable clinkers into building products is an effective way of CO₂ utilization. However, due to insufficient understanding on the phase characteristics of carbonatable clinkers, there is still a lack of guidance on the selection and design of carbonatable clinkers. In this study, three γ-C₂S based carbonatable clinkers were designed and synthesized, covering the carbonation active phase, the unavoidable C₂AS and amorphous glass phases when using industrial feedstocks. The differences in the carbonation activity, mechanical properties and microstructure were compared. Results show that the uncarbonated phases have a significant impact on the mechanical properties of carbonated matrix. The presence of unreacted γ-C₂S with self-pulverization induced cleavage planes and the amorphous glass phase with poor binding to the adjacent calcium carbonate crystals leads to reduced compressive strength. The carbonation reactivity of γ-C₂S formed in composite system is significantly higher than that of pure γ-C₂S. Benefiting from the higher degree of carbonation, carbonatable clinkers only need to contain >40 wt% of γ-C₂S to obtain comparable compressive strength as the pure γ-C₂S system.