The effect of coarse crushed concrete aggregate on the durability of structural concrete

The use of crushed concrete aggregates (CCA) (formerly referred to as recycled concrete aggregate (RCA)) is increasing, particularly for low-grade applications, where quality is of less importance. In higher value applications, such as structural concrete, further research has been required to understand the effect of coarse CCAs on the mechanical properties and durability performance. This research investigated the effect of coarse CCA in CEM I and CEM III/A structural concretes. The resistance to water and chloride ion ingress in terms of surface resistivity, sorptivity and rapid chloride migration were evaluated in this study, together with compressive strength to determine compliance with characteristic and target mean strengths. From this limited study - which forms part of a wider research project - results indicate that a higher proportion of CCA is detrimental to the resistance to water and chloride ion ingress, possibly due to the higher water absorption characteristics of the aggregates as suggested in literature. The incorporation of GGBS however, significantly improves the durability performance, possibly due to the reduced porosity of the cement matrix, improved quality of the interfacial transition zone (ITZ) between the recycled aggregates and cement matrix and an increased chloride binding effect. From the results it is recommended that a structural CEM III/A concrete incorporating coarse CCA up to 60% may be a viable option for future sustainable construction projects.