Sustainable bridge strengthening techniques with UHPC overlay systems for jointless structures

This study evaluates the performance of ultra-high-performance concrete (UHPC) overlay systems for jointless bridge structures with respect to mechanical properties, durability, field behavior, and numerical response. The research combined laboratory testing, pilot-scale field applications, and finite element analysis to assess the effectiveness of two UHPC mixtures: a standard mix and a fly ash-modified mix. The standard UHPC achieved a compressive strength of 162 MPa, whereas the fly ash-modified mix reached 156 MPa. The corresponding flexural strengths were 23.0 MPa and 21.5 MPa, indicating a 6.5% reduction for the fly ash-modified mixture. Both mixes also exhibited bond strengths exceeding the requirements of GB/T 50728 -2011, the Chinese technical specification for UHPC strengthening of concrete structures, by 125%, demonstrating strong adhesion to the prepared concrete substrate. The results further showed that UHPC overlays improved load distribution, limited crack development, and enhanced resistance to thermal and environmental actions in the tested jointless bridge section. Overall, the findings indicate that UHPC overlay systems can improve the structural response and durability of jointless bridge sections, while the fly ash-modified mixture offers a potential route for reducing cement use without substantial loss of mechanical performance.