Kinetics and structure analysis of CO2 mineralization for recycled concrete aggregate (RCA)

Abstract

CO2 mineralization of solid waste in the construction industry for green concrete production is a promising approach for economically storing CO2 and recycling solid waste. Recent investigations have underscored the significance of CO2 sequestration and the augmentation of RCA performance engendered by the holistic reaction processes. While there is a pronounced interest in the optimization of macroscopic reaction conditions (e.g., temperature, pressure, etc.), the exploration and enhancement of the reaction kinetics stage often remains under explored. This study employed a reaction kinetics model to quantify the reaction rate unveiled two distinct reaction stages within the mineralization reaction. Early evaporation and pore formation established the groundwork for the diffusion mechanism of gas product layers in the middle and later stages, emphasizing the crucial role of water in connecting solid ion leaching and gas dissolution-diffusion in the reaction. The water content of the reaction has an optimal value (4%–6%), smaller particle size correlates with a higher optimal water content. Pre-soaking with a calcium hydroxide (CH) solution or suspension was employed to improve mineralization reaction kinetics, resulting in RCA with improved pore characteristics and strength. The crushing index decreased by 28.8% and 21.8%, the water absorption rate decreased by 11.1% for both coarse and fine RCA, and the cumulative total porosity of fine RCA decreased by 17.6%. This research aims to broaden the applications of waste concrete in the CO2 capture, utilization and storage (CCUS) industry and produce low-cost, extensively processed, and high-strength RCA products while contributing to sustainable CO2 management.