Chloride enrichment induced by magnetic field of stray current and coupled deterioration mechanism in concrete under salt freeze–Thaw conditions
Jing Ge, Huaxia Zhuang, Fei Xu, Xuesong Han, Yunhong Zhan, Xingyu Meng, Hua Wei, Wenxun Qian
Abstract
Rail transport engineering and high-voltage transmission and transformation projects in high-latitude coastal and saline-alkali regions face harsh conditions caused by stray current–salt freeze–thaw coupling corrosion. This study adopted a novel perspective focusing on the magnetic field effect of stray current and designed experiments to evaluate the frost resistance and chloride ion erosion of concrete under coupled conditions. Using X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and theoretical calculations, the study revealed the fundamental characteristics and mechanisms of concrete deterioration. After 250 freeze-thaw cycles in 3% NaCl, the mass loss rate at a stray current density of 80 mA/dm² was 1.35 times higher than that without stray current, indicating severe surface spalling. Chloride ion diffusion coefficients increased by up to 49% under 80 mA/dm² stray current after 200 cycles, and water-soluble chloride ion content at 10–20 mm depth rose by 81% compared to the no-current condition. Moreover, mortar deterioration on the surface of the concrete is more pronounced than that near the steel bars. The magnetic field generated by stray current alters the migration paths of chloride ions, causing localized accumulation. MIP tests showed that the volume of harmful pores (>200 nm) in surface mortar increased by 19% under stray current, intensifying the chloride gradient and spalling risk. XRD and SEM-EDS analyses confirmed accelerated Ca²⁺ leaching, Friedel’s salt formation, and carbonation, all contributing to surface degradation. These findings demonstrate that the magnetic field effect promotes directional chloride migration, chloride enrichment, and phase transition stress amplification, revealing a deterioration chain: directional migration → local enrichment → stress amplification → surface damage. This research provides a mechanistic basis for improving the durability of reinforced concrete structures in stray current–salt freeze–thaw environments.