Inhomogeneities of carbonation depth distributions in recycled aggregate concretes: A visualisation and quantification study

The carbonation depths nonuniformly distribute in recycled aggregate concrete (RAC) because it has two kinds of mortars and three kinds of interfacial transition zones; but the inhomogeneity of the distribution is underestimated. Hereby, the inhomogeneities in RACs prepared with modelled industrially-produced and laboratory produced recycled coarse aggregates (RCAs) were visualised and quantified using a proposed method. Afterwards, the influences of RCA types, RCA replacement ratios and strengthening methods of RCA on the average carbonation depths, their errors and the maximum carbonation depths were examined. The results showed that the carbonation depth distributions of RACs presented clear inhomogeneities. Utilising the CO2 curing technology for RCA might not reduce the inhomogeneities; but light effects can be observed through selecting a proper RCA or using a nano-SiO2 slurry soaking method for RCA. Reducing the maximum carbonation depth of RAC by selecting an appropriate RCA was more effective compared with by using the nano-SiO2 slurry soaking method. Besides, predicting the carbonation degree of RAC by using the maximum carbonation depth was more conservative than by using the average carbonation depth.

Automated summary

This study demonstrates the inhomogeneities of carbonation depths in recycled aggregate concrete and investigates the effects of RCA types, replacement ratios, and strengthening methods on carbonation depths. The results indicate that selecting appropriate RCA can effectively reduce carbonation depths, while the nano-SiO2 slurry soaking method has a less significant effect. Additionally, predicting carbonation degree using maximum carbonation depth is a more conservative approach.