Effects of the tensile properties of UHPC on the bond behavior

In recent studies, Ultra-high Performance Concretes (UHPC) have been shown to exhibit significantly better bond with steel reinforcement compared to conventional concrete. However, the influence of the fundamental tensile properties of UHPC on the bond behavior has not been evaluated. The present study addresses this knowledge gap by investigating the bond behaviors of three UHPC materials. Two of these materials exhibit typical UHPC behavior with different tensile strengths, and the third material is a highly ductile UHPC with tensile strain capacity of about 6.6%. Through double-pullout experiments, it was found that higher tensile strength of UHPC led to a significant improvement in the average bond strength (τ_av); however, the tensile strain capacity did not have any significant effect on τ_av. The τ_av increased by about 50 to 64% for various materials with increase in the cover thickness from 1.5d to 2.5d due to better confinement. On the other hand, τ_av decreased by approximately 34% with increase in the embedment length from 3d to 8d with a cover thickness of 1.5d, and it decreased by about 40% with increase in embedment length from 2d to 6d with a cover thickness of 2.5d. The experiments were complemented with finite element analyses, which provided key insights into the bond stress distribution in embedded rebars.