The effects of carbonation conditions on the physical and microstructural properties of recycled concrete coarse aggregates

Abstract

In this research, the effects of carbonation conditions on the physical, mechanical, microstructural anddurability properties of recycled concrete aggregate (RCA) are investigated. The results suggest thatregardless of the carbonation conditions, carbonation of RCA under wet moisture condition or moist car-bonation atmosphere results in no meaningful drop in water absorption or porosity. However, carbona-tion of RCA (preconditioned at 95% relative humidity) in the absence of external source of water vaporresults in significant drops in water absorption (up to 27%), porosity (27%), micro-Deval wear factor (40%regression) and freeze–thaw resistance (77% regression). Carbonation of RCA under optimal conditionswas found to densify the exterior surface of hydrated cement within the RCA grains through progressivedeposition of carbonates on the exterior of RCA grains. Carbonation also transforms the transition zonebetween the old cement and aggregates and results in formation of a dark rim around alite and belitegrains indicating reactivation of the residual unhydrated cement fraction.