Bond Performance Evaluation of Deformed Rebars in Ultra-High Performance Concrete (UHPC)

Abstract

Ultra-High Performance Concrete (UHPC) is an advanced cementitious material with enhanced mechanical properties and higher resistance to aggressive ion penetration over High-Performance Concrete (HPC) and Normal Concrete (NC). For a decade, UHPC has been increasingly used in the civil engineering field. The bond performance between steel rebars and UHPC is the fundamental issue in reinforced UHPC structures. In this study, the bond performance of deformed rebars in UHPC was evaluated using pullout tests. Test parameters included the cover thickness (1d, 2d and 4.5d) and concrete type (UHPC, HPC and NC). Test results showed that the failure of pullout specimens was governed by rebar pulling out or cover splitting. Differing from HPC or NC, UHPC splitting failure was ductile due to the bridge action of steel fiber. The bond-slip curve of deformed rebars in UHPC contained the rising branch, descending branch with exponential characteristics and residual branch. The bond strength slightly increased as the cover increased. The bond strength of specimens with covers of 4.5d and 2d increased by 9.6% and 17.2% to those with a cover of 1d. When compared to HPC and NC, the bond strength of deformed rebars in UHPC improved by 90% and 157%, respectively. Moreover, the design recommendation on the development length of deformed rebars in UHPC was proposed.