Effects of UHPC age and interfacial treatment on structural behavior of post-cast UHPC joints in prefabricated wall-base slab assemblies

Structural behavior of post-cast Ultra-high-performance concrete (UHPC) joints connecting prefabricated wall and base slab under cyclic loading was investigated in this study, focusing on the effects of UHPC curing age (1, 3, and 28 days) and interfacial treatment. Previous research has primarily examined these factors in isolated small-scale tests, while this study evaluates their impact on full-scale prefabricated components at multi-joint interfaces under complex stress conditions. Quasi-static tests revealed that early-age UHPC (1–3 days) achieved sufficient bond strength and load-bearing capacity to resist wind load during construction and enable rapid construction, with the 3-day UHPC joint (WU-3d) showing 38.7 % higher cracking load and 25.1 % higher yield load than the 1-day counterpart (WU-1d). At full curing (28 days), UHPC joints significantly enhance loadbearing capacity and pre-failure seismic resilience compared to monolithic normal concrete (NC) wall, exhibiting an 8.5 % increase in ultimate strength and 12 % higher energy dissipation capacity. Numerical models, validated by experimental results, accurately captured key failure modes, including hysteretic behavior, interfacial debonding, and rebar fracture. Such a validation is nontrivial, as it does not involve any fitting parameters. Parametric analyses demonstrated that midrough interfacial treatments optimized the balance between loadbearing capacity (28.9 % increase) and energy dissipation of prefabricated components, whereas excessive bonding (rough interfaces) caused premature crushing of NC.