Electrical Impedance (NDE)

We developed a nondestructive surface measurement method to detect the corrosion state of reinforcing bars embedded in concrete. Complex impedance spectra from the reinforced concrete were able to distinguish different metal / concrete interfaces. For mineral exploration in geophysics, it has been long recognized that characteristics of the complex impedance spectra from earth materials with distributed metallic conductors are controlled by the electrochemical reactions at the metallic/ionic interface.

The surface measurement method employs four-electrode array consisting of two currents and two potential electrodes to measure electrical responses from subsurface targets. The input signal is a sine wave current with a small magnitude I and a frequency . The recorded output signal is a voltage response V( t) with a phase shift to that of the current. Apparent complex impedance Z with the dimension of ohm.m, which has both real Re (in-phase) and imaginary Im (quadrature) components.

The surface measurement method allows keeping the concrete protection cover intact and doing mapping around different locations. The dependence of impedance spectra on different corrosion state can provide bases for corrosion process interpretation and prediction. Such dependence is able to give an insight into the corrosion mechanism of reinforcing bars in concrete.

References

P.J.M. Monteiro, F. Morrison and W. Frangos, Non-Destructive Measurement of Corrosion State of Reinforcing Steel in Concrete , ACI MATERIALS JOURNAL, NOV-DEC, V95 N6:704-709, (1998).

J. Zhang, P.J.M. Monteiro, and F. Morrison, Non Invasive Surface Measurement of the Corrosion Impedance of Rebar in Concrete. Part I: Experimental Results ACI MATERIALS JOURNAL, MAR-APR, 2001, V98(N2):116-125.