Research on the Bonding Performance of UHPC–NC Interfaces With Different Sizes of Grooves

The interfacial treatment between normal concrete (NC) and ultra-high–performance concrete (UHPC) is crucial to ensure bonding strength. Grooving is an effective method to treat the UHPC–NC interface, but the shear properties and failure modes at the composite interface remain under-investigated. This study focuses on the bonding performance of different groove designs (width, spacing, and angle) at the UHPC–NC interface, and push-off tests with 15 specimens were carried out to evaluate the strength and stiffness. Furthermore, a finite element model (FEM) and calculation methods were validated with the experimental study to reveal the bonding strength, and a parametric study on the groove depth was also carried out. The interface treated by grooves increases 3.32 and 2.48 times in strength and stiffness compared with specimens bonded by epoxy resin adhesive. The results also show that failing at the interface and NC matrix made up a majority of the failure modes. The shear strength of the UHPC–NC interface increased with the width and decreased with the space between the grooves. Grooves with 10 mm width, 100 mm space, 25 mm depth, and right angle were recommended. This paper will lay a foundation for the surface preparation of UHPC strengthening NC bridges.