Fracture Mechanisms of Polymer Cement Mortar: Concrete Interfaces

Abstract

Laboratory tests, including splitting tension, three-point bending, and direct shear tests, were conducted on polymer cement mortar (PCM)-concrete composite specimens with various degrees of interface roughness (Ra). The PCM-concrete bond strength, fracture energy, and fracture surface were investigated qualitatively. The failure mode and the condition of the fracture surface significantly affected the interface bond strength and fracture energy. The bond strength and fracture energy were found to increase with increasing interface roughness until the fracture location shifted from the PCM-concrete interface to within either the PCM or the concrete. The interface roughness has a greater influence on the interface fracture energy and the flexural strength than on the tensile and shear strengths. Considering the single mode (Mode I or Mode II) bond and fracture properties, as well as retrofitting costs, a roughness index of approximately 1 mm (0.9≤Ra≤1.1 mm) is proposed as the optimum value of interface roughness, and the corresponding recommended treatment is water-jetting (WJ) to a depth of 2–2.5 mm. Finally, an interfacial tension softening model that takes into account the effects of fracture energy, tensile strength, and failure mode is presented.