Distinguishing between new and old mortars in recycled aggregate concrete under carbonation using iron oxide red

Abstract

During the preparation of samples for testing the micro-structure of cement-based materials with recycled aggregate, the old mortar attached to the recycled aggregate is difficult to distinguish from the new mortar. In this study, we attempted to use iron oxide red to distinguish these two kinds of mortars in carbonated concrete with recycled aggregate from laboratories and demolished buildings respectively. First, the influence of iron oxide red on the strength and carbonation depth values of the mortar, and on its micro-structure were investigated. Additionally, the properties of new mortar and old mortar coloured by iron oxide red in recycled aggregate concrete under carbonation were studied. The results showed that adding iron oxide red did not affect the strength values, carbonation depth values, and corresponding micro-structure of the mortar. Moreover, iron oxide red can clearly distinguish the new mortar and old mortar in carbonated concrete with recycled aggregate from laboratories and demolished buildings respectively. The properties of these two kinds of mortars showed some differences. Therefore, further research should give more attention to the effect of the distinctions based on sampling location on the experimental results, such as the complete carbonation zone and semi-carbonation zone widths.