Experimental characterization of concrete-to-concrete interface shear strength design-oriented constitutive parameters

In concrete composite systems, the shear strength between concrete layers cast at different times determines the mechanical performance of the structure. Different mechanisms are identified as potential shear-transfer actions through the concrete interface, namely cohesion, friction, and dowel action in case of shear reinforcement crossing the interface, and their role on the shear strength is largely determined by the shape and roughness of the interface. Codes provide formulation to predict the shear strength based on cohesion and friction variables depending on roughness parameters. However, the mechanical approach for the interface shear strength is not well-established yet and, as a result, the design-oriented expressions proposed by codes for determining the strength of composite structural members are under continuous review. In the present study, shear strength of concrete composite elements with different surface textures representative of precast and in-situ concrete constructions -left as-cast surface, resin treatment surface, indented surface and surface with bolts- was assessed. To that aim, a comprehensive experimental programme consisting on push-off tests on small-scale and large-scale specimens was conducted. Based on the test results, the coefficients of concrete cohesion and friction for the different textures were determined, assessing the possible scale effect of the mechanical performance. The experimental shear strength obtained for various cases was compared with the code provisions, showing consistent agreement.