EIS response and applicability assessment of equivalent circuit models for reinforcement corrosion in chloride-contaminated concrete

Purpose This study aims to systematically evaluate the corrosion mechanisms and the applicability of equivalent circuit models (ECMs) for steel reinforcement in five concrete systems with varying chloride contents and curing ages. By combining electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques, it establishes a reliable correlation between LPR and EIS data and assesses the protective efficacy of mineral admixtures and corrosion inhibitors, providing a basis for durable concrete design in chloride-rich environments. Design/methodology/approach This study prepared five concrete systems (A, F, FG, FGS, FGX) with varying chloride contents (0–1.5% by binder mass) and curing ages (3, 7 and 28 days). Electrochemical tests were conducted using a three-electrode system and a CS2350M potentiostat. LPR measurements provided polarization resistance (Rp), while EIS data were fitted with ECMs to extract parameters like charge-transfer resistance (Rct). Data reliability was ensured through cross-validation between LPR and EIS results and linear regression analysis. Findings The study revealed a dynamic transition in corrosion mechanisms from charge-transfer control (3 days) to diffusion dominance (28 days) with increasing chloride concentration and age. ECMs evolved accordingly, achieving high accuracy (fitting error 10%). A strong linear correlation between Rp and Rct was observed under charge-transfer control but weakened under diffusion control. Hybrid systems (FG/FGS/FGX) demonstrated superior chloride resistance. The FGS system (with internal inhibitor) showed the best performance, maintaining low corrosion current density even at 1.5% chloride, due to synergistic “matrix immobilization-interface inhibition.” Originality/value The establishment of a dynamic “material-age-mechanism” correlation model reveals chloride-induced corrosion transition pathways, while quantification of the metakaolin-inhibitor synergy provides new insights into designing durable chloride-contaminated concrete.