The durability of steel-reinforced concrete is a serious problem that concerns the whole world. It is well known that the corrosion of steel rebar in concrete is strongly influenced by the conditions of cover concrete, namely, water absorption, neutralization and chloride ion permeation. There are some literatures regarding the electrochemical tests, which are mainly measurements of corrosion potential and polarization curves, to evaluate corrosion of rebar in concrete [1,2]. Sagues et al. [3] reported the operation of a macroscopic Kelvin Probe (KP) for contactless measurement of concrete surface potentials. Dawson et al. [4] applied an electrochemical impedance spectroscopy (EIS) to the investigation of corrosion of rebar in concrete because the charge transfer resistance can be determined from the impedance spectrum.

Figure 1 shows the scheme of Nyquist plot of electrochemical impedance of steel-reinforced concrete. For example, a capacitive loop related to the time constant of charge transfer resistance and electric double layer capacitance at rebar/concrete interface is observed in the low frequency range. The capacitive loop in the middle frequency range is related to the electric nature of rust or oxide layer formed on rebar surface [5].  McCarter et al. [6] reported that capacitive loop in the high frequency range originated form the dielectric property of concrete absorbing water. In this presentation, we introduce some configurations of electrodes (or probes, sensor) to measure an impedance spectrum of steel-reinforced concrete. And we will discuss the corrosion behavior of rebar in concrete by analyzing the conditions of concrete and rebar/concrete interface by EIS.

References:

[1] ASTM C 876-91 (Reapproved 1999): Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete, Annual Book of ASTM standards, Vol. 03.02, pp. 457-462, 1999.

[2] M.J. Dugarte, A.A. Sagues, Corrosion, 70 (2014) 303-317.

[3] A.A. Sagues, M.T. Walsh, Corrosion Science, 56 (2012) 26-35.

[4] J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrosion/78, No-125 (1978).

[5] J. M. Deus, B. Diaz, L. Freire and X. R. Novoa, Electrochimica Acta, 131 (2014) 106-115.

[6] W. J. McCarter and S. Garvin, J. Phys. D: Appl. Phys., 22 (1989) 1773-1776.