Local bond slip behavior of steel reinforcing bars embedded in ultra high performance fibre reinforced concrete

The local bond stress slip behavior is a fundamental property required for the analysis and design of concrete structures at both serviceability and at ultimate limit. The addition of fibers has been shown to significantly improve the bond between normal strength concrete and steel reinforcement but little work has investigated the bond between reinforcing and ultra high performance fibre reinforced concrete (UHPFRC). In this paper a series of 69 pull tests are carried out on UHPFRC with either short straight or long hooked steel fibers including mixes where the two fiber types have been blended. The results of this study were combined with the results from existing literature to regress a material model for the bond slip behavior between UHPFRC and ribbed steel reinforcing bars. Importantly, it is shown that models for normal strength fiber reinforced concrete cannot be extrapolated to UHPFRC.