2008 Volume 19 Issue 3 Pages 51-60
The Nondestructive evaluation technique by thermography is increasingly being used as a tool for the maintenance of the concrete structures. In most applications, the evaluation of only the location and shape of defects on planes is expected, therefore, no method has been developed for evaluating the depth of defects. This paper describes a method that evaluates the three-dimensional shape of delaminations. After heating the target area, thermographies are taken sequentially. Then, temperature curves obtained at each pixel during convected cooling are analyzed by the Fourier series expansion. By Fourier analysis, it is shown that the phase delay of the temperature curve contains information on the depth of defect. In addition, the phase differences between the areas with and without defects have peak values at a specific period of processing the data. This specific period is related to the depth of the defects. Delaminations are introduced into the concrete specimen by applying expansion pressure from an inserted tube. It is found that the three-dimensional shape of the delaminations can be evaluated by the proposed technique.