Carbonation mechanism and cementation properties of recycled cement paste based on CO2 injection time and pressure

Current applications of recycled cement paste (RCP) carbonation mainly focus on using carbonized particles as filler materials or enhancing the adhesion of hardened cement paste to aggregates. However, there is limited research on the carbon dioxide (CO2) 2 ) sequestration effectiveness and strength improvement mechanisms of carbonized waste recycled concrete powder as a cementitious material. This study investigates the carbonation mechanism and cementation properties of RCP under various carbonation conditions. The phase composition and microstructural evolution of RCP are systematically analyzed through detailed characterization tests, exploring the impact of carbonation time and CO2 2 pressure on the mechanical properties of the RCP samples. These findings demonstrate that prolonged carbonation enhances the formation of calcium carbonate (CaCO3) 3 ) and crystalline silica (SiO2), 2 ), which in turn improves particle bonding and reduces porosity. Higher CO2 2 pressure results in increased carbonation products and tighter interparticle binding. Advanced nuclear magnetic resonance (NMR) analyses indicate that carbonation facilitates the transition of Al from six- to four-coordinated states and the polymerization of SiO4 4 tetrahedra, leading to enhanced structural cohesion. This study demonstrates the potential of carbonation in reshaping the cementitious properties of RCP, highlighting its environmental and economic benefits for recycling construction waste.