Effect of casting defects on interfacial shear bonding performance between UHPC and NC substrate subjected to static and cyclic loading

Abstract

The interface, as a critical area of the strengthening system, is susceptible to casting defects induced by construction techniques, surface unevenness of the concrete substrate, and external loading during service life, leading to significant deterioration of structural durability and strengthening effectiveness. UHPC-NC interface push-out experiments considering interfacial defect area, surface condition, and loading type were carried out. The effect of casting defects on the bonding behavior of UHPC-NC interface was investigated in terms of shear strength, ductility coefficient, and maximum slip. Additionally, a parametric analysis was performed using a validated finite element model to examine the influence of key variables on the shear performance of interface defects. Results from the push-out tests indicated that the three main failure modes were observed, including NC substrate failure, mixed failure of the NC substrate and interface, and defect interface failure. Interfacial defects significantly weakened the shear performance of the UHPC-NC push-out specimens, including a reduction of 20.35–51.11 % in shear strength and 2.50–65.7 % in ductility coefficient. However, as the interfacial defects increased, the maximum slip increased accordingly caused by stress redistribution and weakening of interfacial bonding. Notably, the shear performance of the low-roughness specimen (MHW80) exhibited a higher sensitivity to interfacial defects. Finally, the shear strength prediction model considering the contribution of various factors such as interfacial cohesion, friction, and dowel action was derived. The excellent correlation between the experimental results and the predicted values of this model was presented.