Presented By: Jiong Hu, University of Nebraska-Lincoln
Description: While it is believed that recycled concrete aggregate (RCA) can be effectively incorporated into 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. Through a recently completed ACI CRC project, this study included a set of different test methods 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.