Unveiling the synergistic effects of stray current and high hydraulic pressure on chloride transport in ultra-high-performance concrete

Abstract

Ultra-high-performance concrete (UHPC) is a promising material for constructing future deep underground spaces owing to its exceptional toughness and durability. Nevertheless, the potential impact of stray currents and high hydraulic pressure on the durability of UHPC in deep underground electric projects (such as subways and electric railways) remains elusive. Moreover, existing experimental setups are inadequately equipped to simulate these extreme conditions. To address this challenge, we developed a novel designed ultra-deep underground corrosion simulation system to study the synergistic effects of high hydraulic pressure and stray currents on the chloride ion transport in UHPC. The results indicate that stray currents cause the corrosion of steel fibers, which in turn elevates the porosity of UHPC(rising from 1.45 % to 2.96 %). This porosity increase enhances the hydraulic conductivity of UHPC, intensifying the impact of high hydraulic pressure on chloride ion transport. The extreme gradient boosting (XGBoost)model revealed that stray current is the dominant factor affecting chloride ion transport, contributing to approximately 83 % of the impact. Numerical simulations demonstrated that the omission of steel fiber corrosion leads to an underestimation of chloride ion transport speed. Finally, a time-dependent model for the effective diffusion coefficient of chloride ions was developed. Based on the measured data, it was found that accounting for the coupled effects of high hydraulic pressure and stray currents increases the cover layer thickness from 17 mm to 57 mm. This study provides valuable guidance for the durability of deep underground UHPC structures.