Effect of CO2 Curing on the Physical Properties of Recycled Coarse Aggregate with Different Attached Mortar Contents

The effects of carbon dioxide (CO2) curing conditions (temperature, relative humidity and CO2 curing time) on the physical properties of recycled coarse aggregate (RCA) with varying attached mortar (AM) contents were studied. Before and after CO2 curing, the physical properties in terms of the apparent density, water absorption and crushing value of RCA were tested and the quality of RCA was determined. Besides, scanning electron microscope was used to observe the microstructure of RCA. Results show that the physical properties variation of RCA with higher AM content are more significant, and the quality of RCA with lower AM content is easier to be upgraded during CO2 curing. The physical properties of RCA with 40.8% AM content are earlier stable than that with no less than 44.5% AM content during CO2 curing. The optimal temperature and relative humidity are 50 °C and 55% for CO2 curing, respectively. CO2 curing is incapable of upgrading the quality of RCA with AM no less than 50.6%. The quality of RCA with 44.5% AM content can be upgraded only under the optimum CO2 curing conditions. Under relative humidity higher than 40% and the CO2 curing time more than 12 h, CO2 curing upgrades the quality of RCA with 40.8% AM content.