Carbonation degree evaluation of recycled aggregate concrete using carbonation zone widths

Evaluating the carbonation degree of concrete using the carbonation zone width provides more accurate results than using the carbonation depth determined via pH indicators. In this study, a testing and calculation method for the carbonation zone widths of recycled aggregate concrete (RAC) was developed. The method was applied after the old mixed mortar (OMM) and new mixed mortar (NMM) were distinguished using iron oxide. The effects of the type and replacement ratio of the recycled coarse aggregate, carbonation period, and sampling location on the carbonation zone widths of the RAC were investigated. Furthermore, the mathematical relationships between the carbonation depths and carbonation zone widths were analysed. The results indicated that the carbonation zone widths were significantly larger than the carbonation depths. Additionally, using samples of OMM and NMM yielded significantly different results. Therefore, selecting a larger carbonation zone width can avoid overestimation of the carbonation service life of concrete structures. Furthermore, polynomial and logarithmic functions were suggested for the calculations of the carbonation zone widths when selecting NMM and OMM samples, respectively. This study is useful for engineers because the findings can assist in evaluating the carbonation degree of concrete and the carbonation service life of structures according to the carbonation depth.