Elucidating factors on the strength of carbonated compacts: Insights from the carbonation of γ-C2S, β-C2S and C3S

Accelerated carbonation presents a promising approach for enhancing the early strength of cement-based materials while simultaneously sequestering CO₂. This study examines the carbonation of γ-C₂S, β-C₂S, and C₃S compacts to identify the critical factors influencing strength development over extended curing periods. Analysis of the evolution of mechanical properties, microstructure, and phase assemblages reveals three key factors: 1) Degree of carbonation, which directly correlates with the density of the compacts; 2) Crystalline form and crystal size of calcium carbonate, influencing the strength of the crystal interface; and 3) Silica gels, which act as a phase boundary, with hydration products forming in the later stages of β-C₂S carbonation potentially affecting strength. The findings indicate that calcite promotes rapid strength gain in the early stages, while aragonite contributes to long-term performance. The presence of hydration products within the silica gel phase boundary may explain the observed strength reduction in β-C₂S compacts during extended carbonation. These insights provide valuable guidance for optimizing the design and application of carbonated cement-based materials for sustainable construction.