Enhancing the Mechanism of Inert Fillers on Carbonation Properties of γ-Calcium Silicate Compacts

Carbonation curing was demonstrated as a promising method to mitigate carbonation emissions in the cement industry, and the utilization of inert fillers showed a significant enhancement in the carbonation efficiency of cementitious materials. This study focuses on the carbonation reactivity, carbonation degree, mechanical properties, and microstructure evolution of carbonated γ-C2S composites containing limestone powder (LS) and quartz powder (QZ) while elucidating the underlying mechanisms. Results revealed that the incorporation of limestone powder and quartz powder is conducive to the CO2 diffusion, promoting the γ-C2S carbonation as well as improving the mechanical properties via the nucleation effect and dilution effect. The introduction of inert fillers significantly extended the phase-boundary-controlled stage and prolonged the sustained carbonation period, thereby enhancing the carbonation efficiency of γ-C2S particles. A significant increase in degree of carbonation was found with the quartz powder addition up to 30% and limestone powder addition up to 50%. Moreover, the addition of limestone powder facilitated the precipitation and the growth of calcite, while the incorporation of quartz powder promoted silica gel formation. Uniformly distributed carbonation products reinforced the interfacial transition zone between carbonation products and unreacted particles, densifying the microstructure and reducing the porosity, thereby facilitating the development of mechanical performance. The compressive strength of the γ-C2S compact containing 10% limestone powder reached the highest compressive strength (150.58 MPa) after 48 h of carbonation. This study offers a unique method for developing a low-carbon mineral, inert-filler-containing carbonated system for high-performance carbonated materials.