Ultra-high performance concrete (UHPC) has been demonstrated to be a realistic alternative to less maintenance and significantly longer service life due to its better mechanical properties and low permeability. The bond performance of the deformed steel bar embedded in UHPC is critically important for the safety of the UHPC structures. This paper conducted an experimental investigation on the bond behavior of deformed steel bars and UHPC. The impacts of loading method, UHPC strength, steel fiber type and content, rebar diameter, and cover thickness were studied. The testing results revealed that the specimens failed in three modes: pull-out, splitting + pull-out, and cone failure. The main factors affecting the bond strength are UHPC compressive strength, cover thickness, and fiber characteristics. The peak slip of rebar-UHPC increases with cover thickness and rebar diameter. Finally, an analytical model of the bond stress-slip relationship between the UHPC and deformed steel bar is obtained, which is in suitable agreement with the test results.

With superior mechanical properties and workability, ultra-high-performance concrete (UHPC) has been utilized extensively in engineering projects. To gain a comprehensive understanding of the bond behavior of UHPC or ultra-high-performance fiber-reinforced concrete (UHPFRC), researchers studied the factors influencing the bond-slip between rebar and UHPC or UHPFRC over the past few years. The literature-proposed ultimate bond strength formulas and the bond-slip constitutive model between rebar and UHPFRC are analyzed and compared. Based on the bond test database of UHPFRC, the results indicate that UHPFRC strength, relative concrete cover thickness, relative bond length, and steel fiber volume content are the primary parameters influencing the ultimate bond strength between rebar and UHPFRC. In the bond-slip constitutive model, the nonlinear ascending and linear descending model is more accurate than other models. This paper concludes by discussing the shortcomings in UHPC or UHPFRC bond research and predicting the future research trend.