A Combined method of AC Impedance Measurement and BE Inverse Analysis for Detecting Corroded Rebar in Concrete Structure

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An effective boundary element inverse analysis method was developed to detect the corrosion location and corrosion rate of rebars in a concrete structure. This method consists of two steps. The outlines of these steps are shown below.The first step is the effective non-destractive detection of corrosion locations by combining potential measurement and boundary element inverse analysis. The boundary element inverse analysis method for this step was developed based on the boundary element direct corrosion analysis method, which had been developed before. In this inverse method, the corroded part in the rebar net was approximated as a circle, i.e., the part of the rebars in the circle is taken to be corroded. The radius r and the coordinates (x, y) are taken as design variables, and the difference between the measured and calculated values of potential is taken as the cost function robe minimized. The polarization characteristics of the corroded and non-corroded parts are assumed to be gi … More ven. The minimization is performed through use of the Simplex method. The usefulness of the method was demonstrated by solving an example problem.The second step is the identification of the corrosion rate of the corroded part which was detected in the first step. The identification of the corrosion rate is performed by improving the AC impedance method. A boundary element inverse analysis was utilized to improve the AC impedance method. At first, it was verified experimentally that the potential in the concrete domain is described with the Laplace's equation. The potential at any point in the concrete domain can be calculated by solving the Laplace's equation with the boundary element method.Then, an inverse problem was formulated in which the location and the complex impedance (corrosion rate can be obtained from the complex impedance) of corroded part on the surface of a rebar are estimated from a small number of potential data measured on the surface of a concrete structure. The cost function to be minimized in the inverse problem is a function of difference between the measured and calculated values of potential. The validity and efficiency of the proposed method were demonstrated with an example in which a prismatic concrete block specimen with an embedded piece of rebar was used. Less