Geometrical, physical, mechanical, and compositional characterization of recycled concrete aggregates

Recycling, being one of the strategies in minimizing waste, offers three benefits: it lessens the demand for new resources, reduces transportation and production energy costs, and beneficially reutilizes waste, which would otherwise be lost in landfill sites. While it is believed that recycled concrete aggregate (RCA) can be effectively incorporated in new concrete, its use is limited, mostly due to the absence of effective characterization of RCA. Current specifications and characterization methods mostly include only basic parameters such as specific gravity and absorption, which are not necessarily representing critical properties such as mechanical properties, residual mortar content, and freeze/thaw resistance. Many test methods that are currently used for RCA are either not suitable for RCA or present human error in the procedure and thus not accurate and repeatable. The goal of this study is, therefore, to develop a testing protocol to characterize RCA effectively. A set of different test methods were used in this study to evaluate RCA collected from various sources. Test methods to identify aggregate crushing value and residual mortar content were modified to accurately characterize a variety of RCA without excessive variability introduced by human factors. The freeze-thaw resistance test with a modified data analysis protocol proved to be capable of differentiating the level of air-entrainment of parent concrete. Aggregate shape and texture were shown to significantly impact the void content of an aggregate granular matrix. A better understanding of RCA physical, mechanical, and compositional properties was achieved, which is critical in designing new concrete and evaluating the effect of RCA on new concrete. The success of the study will greatly encourage the use of RCA in daily concrete production and ultimately lead to a cleaner and more sustainable concrete production.