Shear behaviour of interface between normal-strength concrete and UHPC: Experiment and predictive model

Ultra-high performance concrete (UHPC) has various excellent mechanical properties and durability which make it as a suitable repair material for bridge decks repair. However, the bond shear strength between UHPC and concrete substrate is still considered as knowledge gap in the literature. In this investigation, the bond shear properties of UHPC–NSC were systematically investigated using single side shear test, and the shear bond strength and bond failure mode were obtained. Different factors including surface roughness, steel fibre type, and substrate strength which affect the bond strength of UHPC–NSC were discussed. The results suggested that for the as cast substrate surface, bond failure occurred at the interface and the floating pulp layer adhered to UHPC. For specimens with a rough surface, the debonded interface showed that the coarse aggregate on the rough surface adhered to the UHPC. There was a linear relationship between the area of substrate adhered to the UHPC overlay and the bond shear strength. The substrate roughness has a significant influence on bond strength, while the steel fibre type has only a slight influence on bond strength. Bond strength mechanical model were built to predict the interfacial shear strength. The calculated results are in good agreement with the experimental results, indicating that the model can reliably predict the UHPC–NSC interface shear strength.