Effect of carbonated recycled coarse aggregates on the mechanical and durability properties of concrete

The carbonation treatment seems to be an efficient process to increase the quality of recycled concrete aggregate (RCA) and to improve the hardened properties of concrete, especially the mechanical ones, as already demonstrated in several studies. However, research on durability properties of concrete obtained with carbonated RCA is still limited and do not allow to properly optimize the concrete mix design to effectively gain environmental advantages. In this work, mechanical and durability tests were performed on three different concretes, made with a water/cement ratio equal to 0.5, and either fully natural aggregates, or with a partial replacement with RCA or carbonated RCA (cRCA). RCA and cRCA were obtained by crushing respectively old alkaline and old carbonated concretes, and a further carbonation treatment was also performed on a fraction of cRCA. From results, a limited improvement in compressive strength, electrical resistivity, water absorption and sorptivity was observed in concrete made with cRCA with respect to concrete with RCA, whilst a significant decrease of the chloride diffusion coefficient was obtained. Despite the improvements obtained with respect to concrete with untreated RCA, the mechanical and durability performances of cRCA concrete remained on average lower than concrete made with natural aggregate.