On the impact of cathodic polarization on the chloride threshold for carbon steel in concrete

This study examines the influence of the steel potential E on the chloride threshold CT for carbon steel reinforcement embedded in concrete. Building upon the authors’ previous findings in alkaline solutions, this study uses realistic concrete conditions, providing a quantitative model for concrete systems. Concrete specimens with embedded rebars were exposed to a cyclic wetting–drying regime using NaCl solution while being subjected to varying levels of cathodic polarization until corrosion initiation occurred. The results suggest that CT remains largely independent of potential above a threshold potential ET0 but increases progressively at more cathodic potentials. The relationship can be expressed as $$C_{{\text{T}}} = 1.30{ }\% /{\text{cem wt}}.{\text{for }}E \ge - {16}0 \ {\text{m}}V_{{{\text{SCE}}}}$$and $$C_{{\text{T}}} = 1.30 \cdot 10^{{\frac{ - 160 - E}{{520}}}} \% /{\text{cem wt}}.{\text{for }}E < - {16}0 \ {\text{m}}V_{{{\text{SCE}}}},$$corresponding to a cathodic potential shift of 520 mV/dec required for a tenfold increase in CT. The increase in CT is likely attributed to both intrinsic and extrinsic mechanisms: intrinsic effects involve beneficial modifications of the passive layer composition induced by cathodic polarization, while extrinsic effects arise from chloride migration and hydroxide generation near the steel surface. The results emphasize the role of polarization-induced spatial variability in corrosion initiation. Incorporating this behavior into predictive corrosion models could significantly enhance service life assessment of reinforced concrete structures.