Shear properties of the interface between ultra-high performance concrete and normal strength concrete

Many properties of ultra-high performance concrete (UHPC) are superior to those of normal strength concrete (NSC) - including high strength, toughness, and durability, which makes UHPC a promising repair material for damaged NSC structures. The good bonding and shear resistance of the UHPC-NSC interface may enhance the mechanical properties and ensure the impermeability of repaired concrete structures. Eight sets of interface shear push-out tests were conducted in this study. The shear properties of different UHPC-NSC interface treatments, including shallow chiseling, deep chiseling, interfacial adhesives, rebar exposing, grooving, drilling, and post-installed steel studs, were evaluated and discussed. The results demonstrated that the shear strength of the interface was improved by increasing the concrete strength and surface roughness degree. The ranking of the shear strength of interfacial treatments from the highest to the lowest is as follows: post-installed studs, rebar exposing, high roughness (deep chipping), grooving, low roughness (shallow chipping), and holes drilling. In terms of failure modes, the treatments of chipping, the interfacial adhesive, the exposure of rebar, and the drilling of holes demonstrated brittle interface shear failures, whereas the treatments of grooving and post-installed steel studs showed ductile interface shear failures. Finally, a comprehensive method was proposed to calculate the shear strength of the UHPC-NSC interface, taking several effects into account, including the interface cohesion, mechanical interlocking between concrete and rebars, the UHPC grooved joints, and the dowel action of UHPC. The calculated results were in good agreement with the experimental results, indicating that a reliable prediction of the shear strength of the UHPC-NSC interface could be achieved through the proposed model. (C) 2020 Elsevier Ltd. All rights reserved.