Performance studies on recycled aggregate concrete with treated recycled aggregates

Excessive construction activities generate huge quantities of waste that are disposed of in nearby sites, leading to environmental degradation. Recycling the concrete fractions of construction wastes for their utilization as aggregates has been predominant among industrialists and researchers in recent years. However, the smearance of cement mortar on the recycled aggregates affects the concrete properties. Fewer treatments were developed to remove the weak cement mortar or seal the micro-pores on the adhered cement mortar of recycled aggregates. This paper investigates the comparative efficiency of acid and carbonation treatment on recycled coarse aggregate (RCA) properties and its behaviour on recycled aggregate concrete (RAC). The RCA was treated with HCl acid at 0.1 mol/L, 0.5 mol/L, and 0.8 mol/L and CO₂ at 0.1 bar, 0.2 bar, and 0.4 bar and tested for their physical properties, and the concrete mixtures with treated recycled aggregates were tested for fresh and hardened properties. It could be observed that the properties of RAC were affected owing to the smearance of weak mortar, whereas for the concrete with carbonated (RACc) and chemically treated aggregates (RACa), the concrete properties tended to improve. The strength of RAC was 28.59% less than that of normal aggregate concrete (NAC), whereas the strength of RACc and RACa was enhanced by 16.44% and 9.7% compared to that of RAC at 28 days. The water absorption of RAC was 47.51% more than that of NAC, whereas the water absorption of RACa and RACc was 28.67% and 33.75% lesser than RAC. Pre-soaking the RCA with acids removes the adhered mortar due to its acidic activity. In contrast, in carbonation, the CO₂ reacts with the Ca(OH)₂ on the cement mortar to form CaCO_3, filling the micro-cracks in the cement mortar on the RCA.

Graphical abstract