Advancing UHPC for structural strengthening: critical gaps and a roadmap from empirical application to intelligent design

Abstract Ultra-high-performance concrete (UHPC) has attracted increasing attention in structural strengthening due to its exceptional strength, toughness, and durability. This paper critically reviews recent advances in UHPC applications for strengthening structural members and systems, with emphasis on material behavior, interface performance, strengthening mechanisms, and structural responses. Existing studies demonstrate that UHPC can effectively enhance load-bearing capacity, ductility, fatigue resistance, and crack control through thin-layer overlays, jacketing, and hybrid strengthening systems. These improvements are primarily attributed to UHPC’s dense microstructure and fiber-bridging effect. However, several critical challenges still hinder reliable engineering applications, including insufficient understanding of long-term interface degradation under coupled environmental and mechanical actions, limited analytical models for complex stress states, and the lack of unified design and construction standards. Future research should focus on time-dependent interface constitutive models, performance-based design approaches, lifecycle durability assessment, and intelligent monitoring technologies. Advancing these aspects will promote the transition of UHPC strengthening from component-level enhancement toward systematic and sustainable infrastructure rehabilitation.