Effect of shear key arrangement on the bonding properties of prefabricated UHPC-NC interface

In order to study the bond-slip behavior of the interface between prefabricated ultra-high performance concrete (UHPC) and normal concrete (NC), 12 sets of UHPC-NC bond specimens were tested using double-sided shear tests with the density and spacing of shear studs on the prefabricated UHPC surface as the experimental parameters. The results show that, after the shear studs being installed on the formwork, there are three main failure modes of the specimens, namely (a) shear failure of UHPC-NC bond surface and UHPC shear studs; (b) shear failure of UHPC-NC bond surface and simultaneous shear and peeling failure of UHPC shear studs; and (c) shear failure of UHPC-NC bond surface and axial compression failure of NC matrix. The density and distribution interval of shear studs have a significant impact on the shear strength of UHPC-NC bond surface, especially the shear stud density. The shear strength on the bond surface increases parabolically with the density of shear studs. Under the same density of shear stud, the specimens with larger distribution interval of shear stud have a 19.04%-41.74% increase in shear strength on the bond surface, compared to the specimens with smaller distribution interval. On the basis of existing models and experimental results, a calculation formula for the shear strength of prefabricated UHPC-NC bond surface is established. It considers the failure modes of bond surface and the shear testing methods. The calculated results are in good agreement with the experimental values. This can provide a reference for the interface design of UHPC-NC composite specimens.