Effect surface treatment of recycled concrete aggregate on properties of fresh and hardened concrete

The inferior properties of the recycled concrete aggregate (RCA), as compared with the natural aggregate, are caused by the presence of the porous residual mortar with numerous micro-cracks, which is attached to the original aggregates. The inferior qualities of RCA have limited its use in structural concrete production. Thus, this study investigated the feasibility of combining two different methods of surface treatment to enhance the properties of coarse RCA. This treatment process involves soaking coarse RCA at low acid concentrations to remove loose particles on the RCA surface and then impregnating the RCA with a calcium silicate (CS) solution. The results revealed that the combined method significantly improved the physical properties of coarse RCA. CS provided a coating layer on the RCA and functioned as a microfiller that can refill and treat the cracks and pores on the RCA surface. In addition, the CS particles on the RCA surface caused a pozzolanic reaction during concrete hardening that could improve the microstructure of concrete by strengthening the bonds between RCA and the cement paste and consequently further enhancing the compressive strength of concrete.