Monolithic and non-monolithic interface shear performance of ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is being increasingly considered as a construction material for struc-tural applications. When considering these applications, the load transfer across monolithic and non-monolithic interfaces must be adequately designed. However, due to the physical and mechanical differences between UHPC and conventional concrete, it becomes apparent that existing design provisions developed for conventional concretes may not be appropriate. To address this need, 13 S-shaped interface shear pushoff specimens were tested. These cases included six monolithic specimens with varying steel micro-fiber contents and interface reinforcement ratios and seven non-monolithic specimens with varying surface preparations and interface reinforcement ratios. The proposed predictive models for monolithic UHPC interface shear behavior, which consider the clamping pressures provided by both the steel reinforcement and UHPC, remain applicable when steel micro-fiber contents are increased to 4 %. Existing capacity models for conventional concrete may need to be modified when UHPC is paired at an interface with conventional concrete since, in some cases, the interface shear resistance may be reduced.