Shear friction performance between high strength concrete (HSC) and ultra high performance concrete (UHPC) for bridge connection applications

Ultra high performance concrete (UHPC) has been typically used as grout material in the bridge connections or as a repairing material in the bridge deck applications due to outstanding mechanical properties, especially, superior bond strength with precast concrete. However, shear stresses due to mechanical, shrinkage, environmental loads, or any combination, usually develop at the interface between the two materials. Therefore, the interface should have enough capacity for these stresses at both early ages and during the service life. In this study, the interface bond performance between precast high strength concrete (HSC) and cast in place (UHPC) was examined under direct shear using the push-off test. The contribution of the shear reinforcement (SR) to the load transfer, before and after interface failure, was investigated. Results from this study were also compared with the predicted values from codes provisions. The test results indicate that UHPC has superior adhesion to the precast concrete, which exceeded the adhesion value of the monolithic surface specified by the provisions. A bond strength versus displacement model is proposed based on data analysis and could be used in the modeling of HSC-UHPC interface under a shear stress state. The shear reinforcement placed across the interface played a key role in reducing the slip at the interface before interface failure. The shear capacity from standard codes is highly conservative and could be used in the design.