Bonding Performance of Steel Rebar Coated with Ultra-High-Performance Concrete

In this study, to improve the bond performance of reinforcing bars fixed inside concrete, a pullout test using ultra high-performance concrete (UHPC) and structural steel fibers was conducted and a model that could predict the performance was also presented. After creating a UHPC layer on the rebar surface, the specimens were prepared along with three types of structural fibers. The structural fibers with different shapes were mixed up to 0.2%, 0,4%, 0.6%, 0.8%, 1% and 2% to analyze their effects on the bond failure at the interface. As a result of the experiment, the pullout resistance ability of the specimen thinly coated with UHPC maintained high residual stress due to the steep section reaching the maximum load, increased the maximum pullout load, and delayed the bond failure during the extraction process. As a result of the cross-sectional examination of the specimen, the coating of UHPC was strongly attached to the rebar surface and the bond surface was broken through sliding at the interface (UHPC–ordinary Portland concrete (OPC)). It was found that the increase in the structural fiber significantly improved the pulling-out resistance at the interface. The proposed model based on the existing Cosenz–Manfredi–Realfonzo (CMR) and Bertero–Popov–Eligehausen (BPE) prediction models was found to be in good agreement with the experimental results.