Degradation of ultra-high-performance concrete and reinforced concrete under coupled effect of subway stray current and chloride-rich groundwater

The degradation behaviour of ultra-high-performance concrete (UHPC) and conventional reinforced concrete (RC) under accelerated stray-current corrosion was investigated. Cube and prism specimens, both plain and reinforced, were subjected to direct current to simulate the subway stray-current environment. The evolution of current, cumulative charge passed and mechanical properties was recorded, and the corrosion morphology of the embedded steels was analysed. The results showed that the RC (grade C50) exhibited severe electrochemical activity and rapid strength loss, with over 80% reduction in compressive strength and 95% in flexural strength after 14 days of current exposure. In contrast, the UHPC displayed only slight degradation owing to its dense microstructure and stable steel–matrix interface, which effectively limited ion migration and localised corrosion. The findings highlight UHPC’s superior electrochemical stability and mechanical performance under stray-current environments, providing technical guidance for the performance design of RC structures in metro and tunnel systems.