Enhancing Performance and Reducing Environmental Impact of Concrete with Replacement of Recycled Concrete Aggregate Treated with Various CO 2 Pressures

Recent studies have demonstrated that the carbonation treatment of recycled concrete aggregate (RCA) could enhance its properties by the conversion of adhesive paste to stronger and denser products. In addition, the use of RCA and the sequestration of CO₂ during the CO₂-treatment process can help to reduce the carbon footprint of concrete. This study assesses the performance of recycled aggregate concrete (RAC) developed from CO₂-treated RCA. RCAs obtained from over 20 old highway and airfield pavements were treated under different pressures (5, 10, 20, 40, and 60 pounds per square inch [psi]) of CO₂. The physical and mechanical properties of RCA were then examined. The complete substitution of natural coarse aggregate was carried out using both untreated and treated RCA, followed by an assessment of the resulting RAC’s fresh, mechanical, and durability properties. Furthermore, the environmental performance of concrete incorporating untreated and treated RCA was evaluated. The experimental findings revealed that the CO₂ treatment pressure had a significant influence on RCA characteristics, leading to notable improvements in the mechanical and durability properties of RAC. Results demonstrated that by employing CO₂ treatment at pressures of 20, 40, and 60 psi, concrete incorporating complete RCA replacement can achieve properties comparable to concrete with natural aggregate. Moreover, the RAC produced using CO₂-treated RCA demonstrated a reduced CO₂ equivalent when compared with concrete incorporating natural aggregate or untreated RCA. These findings underscore the potential of CO₂-treated RCA as a viable and environmentally friendly alternative to natural aggregate for sustainable concrete production.