Influencing Factors of Steel States in Concrete Based on Electrochemical Impedance Spectroscopic Measurements

To cope with the premature deterioration of reinforced concrete structures caused by chloride-induced corrosion, the corrosion rate is required to be estimated and the transport parameters calculated. The electrochemical impedance spectroscopy (EIS) technique can evaluate steel corrosion behaviors at different frequencies. However, its capacity to interpret the impedance response of the system (steel embedded in concrete) is still challenged. Although concrete is a good barrier used to secure structural performance, one of the main obstacles associated with electrical measurements relates to the cases in which concrete contains unexpected or invisible variables, such as changes in pore structure induced by the continuous hydration process. In addition, the fact that steel embedded in concrete is controlled during experiments is technically challenging. Due to these limitations, various circuits have been proposed to explain the corrosion behavior of steel in concrete. EIS measurements are very sensitive to small perturbations. During the analysis process of EIS data, it is possible to introduce unexpected errors attributed to variables; thus, the estimated corrosion values based on the analysis rate may be misleading. To overcome the limitations, it is necessary to confirm the impedance responses first in controlled variable cases. In this study, EIS measurements were conducted for active/passive states of steel in concrete in various conditions to minimize variable errors which are likely induced by operators.