Experimental investigation on bond performance of UHPFRC wet joint by direct tension test

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is applied to joint nodes with its excellent mechanical properties, which helps to improve the force transfer performance of UHPFRC structures. The strength of the connections is dependent on the adhesion and friction between the connected materials in the bridge design procedure. This research aims to identify the adhesion performance between UHPFRC and UHPFRC under different interfacial roughening methods. To this end, the maximum tensile stress and the load–displacement curves of UHPFRC wet joints treated by high-pressure water jet roughening, uniform plastic formwork roughening, embedded wire mesh roughening, manual mechanical roughening, and epoxy resin were obtained via direct tension tests. The test results indicate that the bond strength of UHPFRC wet joints can reach 22.36%-68.06% of the tensile strength after different interfacial treatments, among which the roughening methods using high-pressure water jet significantly improve the bond performance of UHPFRC wet joints, followed by the roughing method of uniform plastic formwork and embedded steel wire mesh. Physical roughening treatment has less effect on the stiffness of UHPFRC wet joints and exhibits a typical brittle failure mode. A tensile constitutive model in the elastic phase of the UHPFRC wet joint interface and the simplified interfacial tensile stress-relative displacement model were proposed. Finally, the performance of the interfacial adhesion parameters was appraised by finite element modeling. The finite element analysis showed a good agreement with the experimental results.