###### Abstract  
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 methods are combined depending on the purpose of the study. The applied current or premixed chloride methods yield fast results compared with wet/dry cyclic regimes. Meanwhile, wet/dry cyclic methods are more realistic than those used in other methods. Steel exposed to a simulated pore solution can observe corrosion products directly and can reduce the required time for corrosion initiation [12; 13; 14], but this method is difficult to fully simulate the inhomogeneity of concrete.  
Various techniques have been used for corrosion measurements based on the use of (a) destructive methods, such as the mass loss technique, and (b) nondestructive methods, such as the half-cell potential technique and the DC (direct current) and AC (alternating current) polarization techniques. Nondestructive methods fascinate engineers compared with destructive methods [15]. The half-cell potential technique is extensively used to detect steel corrosion in concrete [16], but it is inappropriate for the quantification of the amount of corrosion. Polarization techniques, such as the linear polarization and galvanostatic/potentiostatic methods, are preferred for measurements of the corrosion rate of steel. In linear polarization, the estimation of ohmic resistance and the determination of the Tafel constant \(B\) are the main issues. It is difficult to archive a steady state rapidly using galvanostatic/potentiostatic methods due to the polarization phenomenon. In addition, it is hard to apply a proper current to avoid unintended corrosion using the galvanostatic method [11]. Electrochemical impedance spectroscopic (EIS) measurements as another polarization technique seem to be the most reliable in evaluating the corrosion rate, as repeatable measurements using AC sources are available. However, there are limitations attributed to sensitivity measurements [17], such as ambiguous responses at low frequencies [5] and interpretation difficulties [18; 19]. To improve the applicability of EIS in measuring the corrosion of steel in concrete, it is necessary to first identify various influencing factors on the measurement.  
Accordingly, the main aim of this study is the confirmation of the effects of variables (contact solution/contact pressure in a concrete-sponge-electrode system, counter electrode size, and location) on EIS data (based on measurements), and the achievement of improvements in the interpretation of an impedance spectra. Therefore, this study investigates the effects of these variables on high-frequency responses accounting for concrete properties.