Empirical modelling of CO2 uptake by recycled concrete aggregates under accelerated carbonation conditions

In order to assess the potential CO2 capture ability of recycled concrete aggregates (RCAs) subjected to accelerated carbonation, an empirical prediction model has been developed in relation to carbonation conditions and the characteristics of RCAs. In this study, two sources of RCAs were used: RCAs from a designed concrete mixture and RCAs obtained from crushing of old laboratory concrete cubes. Two types of carbonation approaches were employed: (A) pressurized carbonation in a chamber with 100% CO2 concentration and (B) flow-through carbonation at ambient pressure with different CO2 concentrations. Four groups of RCAs particles with sizes of 20-10, 5-10, 2.36-5 and < 2.36 mm were then tested and evaluated. It was found that a moderate relative humidity, a CO2 concentration higher than 10%, a slight positive pressure or a gas flow rate of > 5 L/min were optimal to accelerate the RCAs carbonation. Moreover, the CO2 uptake of fine RCAs particles was faster than that of large RCAs particles. The developed model was able to predict the CO2 uptake in relation to relative humidity, particle size, carbonation duration and cement content of the RCA under the tested carbonation conditions.