Review of the Interfacial Bonding Properties between Ultrahigh-Performance Concrete and Normal Concrete

As a high-quality building material exhibiting excellent toughness and durability, ultrahigh-performance concrete (UHPC) is increasingly being used in the construction industry and as building reinforcement. During the reinforcement of existing concrete structures with UHPC, their interface is the weakest part of a structure. Interface bonding ensures the operation of two types of materials together. However, existing studies rarely report the bonding of the UHPC–normal concrete (NC) interface. Herein, the existing test methods and interface bonding mechanisms are summarized. Subsequently, the differences among relevant design codes are investigated by comparing different theoretical formulas. Important influencing factors of the reinforcement method, namely, interface roughness, fiber type and content, interface agent type and content, moisture content, existing concrete strength, cementitious material content, curing conditions, freeze–thaw cycles, and chloride ions, are also considered. Further, the enhancement mechanism of the characteristics of the UHPC–NC interface is clearly described. Finally, the shortcomings and application prospects of the interfacial bonding properties are highlighted.