Optimizing concrete properties with carbonated recycled concrete aggregate: a sustainable approach

This study explores the potential of carbon dioxide sequestration to enhance the properties of recycled concrete aggregate (RCA) through accelerated carbonation techniques. Carbonated RCA (CRCA) was incorporated into concrete mixtures with two water–cement ratios (0.55 and 0.42), targeting compressive strengths of 30 MPa and 40 MPa, respectively. RCA particles (5–20 mm) were carbonated under 1 bar pressure for 2 and 3 h. Key physical properties including aggregate crushing value (ACV), aggregate impact value (AIV), and water absorption (WA), were evaluated for both RCA and CRCA. Results showed that CRCA significantly improved concrete workability and strength compared to untreated RCA. Specifically, CRCA reduced ACV, AIV, and WA by 2.8%, 2.3%, and 1.5%, respectively, indicating better aggregate quality. In 30 MPa concrete, compressive strength increased by 16% with 100% CRCA and by 9.6% with 50% CRCA; for 40 MPa concrete, the improvements were 18% and 12%, respectively. Similar trends were observed for split tensile strength. Microstructural analyses (XRD, FTIR, TGA, DSC, SEM) confirmed that carbonation at 1 bar for 2 h provided optimal RCA modification. These findings suggest that accelerated carbonation of RCA can substantially improve concrete performance, offering practical benefits for sustainable construction practices.