Title:
Noninvasive Surface Measurement of Corrosion Impedance of Reinforcing Bar in Concrete—Part 2: Forward Modeling
Author(s):
Jieying Zhang, Paulo J. M. Monteiro, and H. Frank Morrison
Publication:
Materials Journal
Volume:
99
Issue:
3
Appears on pages(s):
242-249
Keywords:
corrosion; reinforcing bar; test
DOI:
10.14359/11969
Date:
5/1/2002
Abstract:
The corrosion state of a reinforcing steel bar in concrete can be characterized by the electrical impedance of the interface between the steel bar and the concrete. The experimental part of this study has shown that changes in the interfacial impedance that are diagnostic of the rate and extent of the corrosion can be measured indirectly with an array of current and voltage electrodes on the concrete surface. The measured impedance, however, depends on the electrical resistivity of the concrete, and the depth and diameter of the steel reinforcing bar, as well as the interfacial properties. To relate the measured impedance directly to the interfacial properties, a closed-form solution to the governing Poisson’s equation was developed and programmed for the potentials from arbitrary current sources in the vicinity of the reinforcing bar. The solution uses an impedance boundary condition for the complex impedance at the steel-concrete interface. The response of an arbitrary corrosion state can be simulated in this model by embedding the appropriate complex, frequency-dependent impedance at the interface and computing the voltage/current response that would be measured for an arbitrary placement of electrodes on the concrete surface. To simulate the experimental findings, this paper presents the modeling results by various interfacial impedances but constant concrete resistivity and constant geometry of the steel reinforcing bar. This simulation confirms that important parameters of the interfacial impedance controlling corrosion kinetics such as polarization resistance and double layer capacitance are clearly observed in the measured surface data.