Influence of volume fraction and orientation of fibers on the pullout behavior of reinforcement bar embedded in ultra high performance concrete

An experimental investigation was carried out to evaluate the effect of fiber volume fraction (Vf) and fiber orientation on the pullout behavior of steel reinforcement bar embedded in Ultra High Performance Concrete (UHPC). The experiments were performed using pullout specimens under tensile stresses and low concrete cover. It was found that the peak pullout load increased with the increase in Vf. When Vf was kept constant at 2%, it was observed that the specimens with perpendicular and parallel fiber orientation with respect to the rebar direction recorded the highest and the lowest pullout load, respectively. Finally, an empirical model equation was developed to predict the bond strength values.