Experimental Study of the Interfacial Shear Behavior Between NRC and UHPC in UHPC-Jacketing Rehabilitation of Concrete Bridges

Ultra-High-Performance Concrete (UHPC) jacketing is an effective and innovative strengthening method in the renovation projects of concrete bridges. In December 2021, the UHPC-jacketing method was first applied to rehabilitate a seriously damaged bridge in the Changzhou Bridge rehabilitation project in Guangzhou, China. However, the interfacial shear behavior between the Normal Reinforced Concrete (NRC) substrate and UHPC is a crucial factor for the effectiveness of the UHPC-jacketing strengthening method. Therefore, four push-out specimens were designed in this paper to investigate the effects of the embedded bolt diameter (12 mm and 16 mm) and construction method (cast-in-place UHPC layer (ZJ group) and precast UHPC panels with infilled high-strength mortar (GJ group)) on the shear behavior of the NRC–UHPC interface. The results indicated that with the increased bolt diameter from 12 mm to 16 mm, the first peak load (P1) rose from 920.17 kN to 1048.07 kN (+13.9%) in the ZJ group and from 838.08 kN to 1204.20 kN (+43.7%) in the GJ group. The residual loads (Pr) of the GJ group were smaller than those of the ZJ group, at 41.9% and 30.2% lower for bolt diameters of 12 mm and 16 mm, respectively. The construction method of high-strength mortar filling was significantly influenced by the bolt diameter, with a diameter of 16 mm required to fully utilize its shear resistance. Predictions from ACI 318-19 underestimated experimental shear capacity by 70.6% on average, while AASHTO (2017) and Fib provided accurate estimations (within 9.8–10.9% of experimental values).