Influence of curing temperature on the carbonation products and mechanical performance of reactivated cementitious materials

Recycling demolition concrete is a vital strategy for advancing the sustainability of the construction industry. In this study, recycled concrete fines were thermally activated at 800 ℃ to produce carbonatable reactivated cementitious materials (RCM). RCM has a distinct phase composition from that of Portland cement, and its carbonation hardening mechanism varies with curing conditions. This work examines the effect of carbonation temperature (20°C to 80°C) on the phase evolution, microstructure, and mechanical properties of RCM. Thermally activated RCM was found to consist mainly of α′_H-C₂S, β-C₂S and γ-C₂S, which successfully promote efficient carbonation. The highest compressive strength of 53.3 MPa was achieved at 40°C and was attributed to a dense matrix formed by well-crystallized CaCO₃ crystals and calcium-modified silica gel. At higher temperatures, calcium carbonate polymorphs shifted: calcite decreased, vaterite increased, and aragonite appeared at 60°C. Morphological changes in CaCO₃ were observed, ranging from scalenohedral calcite at 20°C to rhombohedral forms at elevated temperatures. Additionally, the polymerization of calcium-modified silica gel intensified with temperature. Carbonated RCM achieves an 84% reduction in net CO₂ emissions relative to conventional Portland cement (96 kg CO₂ eq/t), offering a promising low-carbon pathway for repurposing construction waste.