Carbonation resistance study and inhomogeneity evolution of recycled aggregate concretes under loading effects

Abstract Carbonation-load coupling effects can aggravate the inhomogeneity of recycled aggregate concrete (RAC) which contains old attached mortar (OAM) and new added mortar (NAM). In this study, these mortars are first distinguished using an iron oxide. Afterwards, accelerated carbonation coupled with four-point bending effects are applied on the RAC samples, and the carbonation depths in compressive, load-free and tensile zones are compared. The loading rate equals to 40% RAC flexural strength. The microstructures of the mortars in different zones are then compared. Moreover, a computing method for the steel corrosion zone widths of the RACs is proposed after the figures determined using the OAMs and NAMs in different zones as samples are compared. The results show that the carbonation depths of RACs present a significant difference which is more remarkable compared with natural aggregate concrete. Besides, the load shows significant impacts on the mortar microstructure and steel corrosion zone width. Specifically, the effect of tensile stress on OAMs is more obvious than that on NAMs, but there is no such difference in compressive zone. Furthermore, using the OAMs in tensile zone as the samples concludes the highest steel corrosion zone width which is suggested to be used to evaluate the carbonation service life of RAC structures for avoiding the overestimation of structure safety.