Effects of Different Carbonation Treatment Methods for Recycled Concrete Aggregate

Compared to natural aggregates, recycled concrete aggregates (RCAs) which are derived from construction and demolition (C&D) waste exhibit inferior properties, such as lower density and higher water absorption. Accelerated carbonation was an effective approach to enhance the properties of RCA. This study conducted a comparative analysis on the property enhancement of both coarse recycled concrete aggregate (CRCA) and fine recycled concrete aggregate (FRCA) by utilizing four carbonation approaches: conventional carbonation, CH spraying with conventional carbonation, wet carbonation, and two-step wet carbonation. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) analysis, and CO₂ uptake comparison were used to investigate the microstructural properties of the RCA. Furthermore, we also evaluated the compressive strength of mortar specimens with four different replacement ratios and the density and water absorption values of different carbonation-treated aggregates. The experimental findings revealed the following: (1) All of the accelerated carbonation approaches were more effective for FRCA than CRCA due to a higher adhered mortar content. (2) The pretreatment of CH spray provided external Ca²⁺ which improved the carbonation efficiency and therefore significantly enhanced the property of FRCA. (3) Liquid–solid phase carbonation achieved higher carbonation efficiency in the inner pore areas of the adhered mortar, resulting in a high CO₂ uptake and microstructure densification compared with conventional gas–solid phase carbonation.