Stray current induced chloride ion transport and corrosion characteristics of cracked ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a strong, durable, and corrosion-resistant material that is poised to revolutionize construction in complex environments, such as the deep sea and underground. However, the formation of cracks of UHPC during service and the occurrence of stray currents in underground stations and tunnels greatly accelerate the transport of chloride ions, posing a threat to the safety of underground con-struction. Here, we used the rapid chloride migration (RCM) method to study the effect of stray current in cracked UHPC. Essentially, electric field accelerates chloride ion transport in cracks by increasing ion transport in the uncracked zone. The wider the crack, the more severe the corrosion of steel fibers, which affects the pore structure of UHPC and leads to an increase in the diffusion coefficient in the uncracked area. In addition, area normalization was employed to precisely monitor the chloride ion concentration in the cracks, which was validated by numerical simulations. Finally, microscopy and atomic force microscopy (AFM) showed that larger crack widths led to deeper corrosion and more severe steel fiber corrosion in UHPC. These results have important implications for the durability design of UHPC structures in stray current environments.