Interfacial shear behavior between prefabricated Strain-Hardening Ultra-High-Performance Concrete (SH-UHPC) and cast-in-place concrete

Strain-Hardening Ultra-High-Performance Concrete (SH-UHPC) serves as an ideal material for creating durable stay-in-place permanent formwork systems, streamlining the construction process and enhancing structural durability. The interfacial shear behavior is the key factor when applying UHPC permanent formwork. This study investigated the interfacial shear behavior of prefabricated UHPC and cast-in-place concrete through push-out tests. The failure process and mechanism of the UHPC/concrete interface were analyzed based on the digital image correlation method. The influencing factors included the number, height, and shape of shear key, matrix fiber content, and loading direction. Three typical failure modes were identified: pure interface failure, combined interface and cast-in-place concrete side failure, and concrete splitting failure. It was found that the dimensions of UHPC teeth critically influence the interfacial shear capacity. The triangular-shaped UHPC teeth were observed to optimize stress distribution and increase shear strength. A strategic inter-tooth spacing that maximized interfacial shear capacity was also identified. Most importantly, with the appropriate configuration of UHPC teeth, the UHPC/concrete interfacial shear strength could exceed the shear strength of ordinary concrete block. The findings of this study are useful for the design and applications of UHPC/concrete composite structures made by prefabricated UHPC and cast-in-place concrete.