Bonding performance of the grooved interface between ultrahigh performance concrete and normal concrete

•The shear test was conducted to study the bond behavior between UHPC prefabricated and NC post-cast.•Effects of NC strength and groove density on UHPC-NC bond behavior were investigated.•The deformation and shear strain were monitored using a non-contact 3D speckle strain measurement and analysis system.•Grooving methods of interface preparation develops a good interface bond.•Mathematical models to estimate grooved interface cohesion following Mohr-Coulomb theory are built. When a diseased tunnel is reinforced by a UHPC-NC composite structure, the grooved interface has good bonding performance to ensure that the UHPC precast pipe co-works well with postcast NC. In this paper, the bonding properties of the UHPC-NC grooved interface were investigated by both slant shear tests and double-sided shear tests. Two factors, i.e., NC strength and groove density, are mainly considered. The results showed that the slant shear sample failed in the form of interface failure + NC failure or NC failure. The failure mode of the double-sided shear test was that the NC groove at the interface was cut off. The higher the NC strength is, the greater the shear strength of the interface. The increasing groove density leads to a high bond strength of the double-sided shear specimen, but the strength of the slanted shear specimen is basically unchanged. According to the failure mode of two-sided shear test, the shear bearing mechanism of UHPC-NC grooved interface is obtained, and the cohesion calculation formula of UHPC-NC slot interface is established. The results might provide a reference for design and construction of the interface of the UHPC-NC composite structure for tunnel reinforcement.