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