Improving recycled concrete aggregates using flue gas based on multicyclic accelerated carbonation: Performance and mechanism

Utilizing flue gas from cement plants to treat the recycled concrete aggregates (RCAs) through accelerated carbonation is a new strategy for reducing carbon emission and improving the quality of RCAs. However, due to the low CO2 concentration, carbonation efficacy is always unsatisfactory. In this study, multicyclic carbonation treatment was performed to enhance the carbonation efficacy using flue gas as CO2 source. The key operation parameters including carbonation duration, gas pressure and cycle numbers were optimized, and the carbonation performance and mechanisms were evaluated. Results showed that treating the RCAs for six cycles within 24 h at gas pressure of 0.1 MPa could obtain satisfactory carbonation percentage. Microstructure analysis verified that, after multicyclic carbonation, large amount of calcium hydroxides were converted into calcium carbonates to reduce the porosity and promote the quality of RCAs. Furthermore, compared with non-carbonated recycled aggregate concrete, the compressive strength and flexural strength of concrete incorporating RCAs treated by flue gas increased by 25.2 % and 26.5 %, respectively. The present study proposes an innovative approach for improving the carbonation efficacy of flue gas as CO2 source.