Shear Friction in Single-Generation and Multigeneration Recycled Aggregate Concrete

Knowledge of shear friction material properties is central to the design of reinforced concrete elements. These shear friction properties are impacted by components of concrete mix design that impact the roughness of a cracked plane, including the strength of the mortar and aggregates. In this paper, 72 shear friction tests are undertaken on multigeneration recycled aggregate concrete that successively crushes and reuses concrete to make three generations of aggregate. The results of these tests are brought together with 314 existing shear friction test results on virgin and recycled aggregate concrete to develop a new unified model to predict the shear capacity of initially uncracked concrete. The results of the modeling show that even after multiple generations of recycling aggregate, no significant decline occurs in the shear strength of concrete and that the shear strength is most strongly influenced by the confining stress. The analysis of the test results across multiple studies identifies critical areas for future research, including the need for better reporting of actual confining stresses and the reporting of crack widths to allow for a more complete understanding of behavior.