Experimental and numerical investigation of the mechanical behavior of interfaces between cementitious materials

For interfaces between cementitious materials, as encountered between substrate concrete and concrete overlays, commonly only the pull-off strength is determined. By contrast, in the present work a fracture-mechanics based characterization of the mechanical interface behavior is performed. To this end the tensile strength and the shear strength as well as the mode I and mode II specific fracture energies and the softening behavior of such interfaces are determined by small-scale tests. They consist of three-point bending tests, modified torsion tests and splitting tests, focusing on three different interface surface preparations, i.e., high pressure water jetting, steel brushing and smooth cleaning of the interface surface. From the test results softening functions for mode I and mode II softening behavior are determined by an inverse parameter identification scheme. For considering the interface behavior in numerical simulations the cohesive zone model for interfaces, proposed by Caballero and Carol, is modified with respect to the experimentally observed shear dominated failure at the macro-scale. The performance of the interface model is demonstrated by numerical simulations of a three-point bending test and a modified torsion test.