Tailoring the hardening performance and microstructure of calcium aluminate cement through carbonation curing

The hydration of calcium aluminate cement (CAC) generates metastable phases such as CAH10 and C2AH8, which subsequently transform into more stable products, leading to a reduction in strength and causing volumetric instability. The present study aims to alter the hydration pathway with improved mechanical strength and volume stability of CAC by carbonation curing with different temperatures and durations. The mechanical strength, dimensional changes, carbonation products, and microstructure were comprehensively investigated. The results reveal that carbonation curing converts the metastable hydration products C2AH8 and CAH10 of CAC directly into AH3 and calcium carbonate, primarily in the forms of amorphous CaCO3, calcite, and aragonite. Suitable early carbonation curing and subsequent water curing could increase CO2 uptake and carbonation depth, reduce total porosity, and optimize the pore structure. CAC subjected to 4 hours of carbonation curing at 20 °C exhibited excellent volume stability and significant enhancement of compressive strength up to 106 MPa with 90 days of subsequent water curing. A shorter carbonation duration leveraged the synergy between carbonation reactions and subsequent hydration to enhance the macroscopic performance of CAC significantly. This study offers new insights into innovative methods for mitigating the unstable transformation of hydrates in CAC by effectively utilizing and sequestering CO2.