Prediction on CO2 uptake of recycled aggregate concrete

Carbonation of concrete is a process which absorbs carbon dioxide (CO2). Recycled aggregate concrete (RAC) may own greater potential in CO2 uptake due to the faster carbonation rate than natural aggregate concrete (NAC). A quantitative model was employed to predict the CO2 uptake of RAC in this study. The carbonation of RAC and the specific surface area of recycled coarse aggregates (RCAs) were tested to verify accuracy of the quantitative model. Based on the verified model, results show that the CO2 uptake capacity increases with the increase of RCA replacement percentage. The CO2 uptake amount of 1 m3 C30 RAC within 50 years is 10.6, 13.8, 17.2, and 22.4 kg when the RCA replacement percentage is 30%, 50%, 70%, and 100%, respectively. The CO2 uptake by RCAs is remarkable and reaches 35.8%–64.3% of the total CO2 uptake by RAC when the RCA storage time being 30 days. Considering the fact that the amount of old hardened cement paste in RCAs is limited, there is an upper limit for the CO2 uptake of RCAs.