Research On Concrete Deterioration Detection Based On Nonlinear Ultrasonic Features

Because of the nonlinearity of concrete material, the traditional ultrasonic method which is based on the linear wave theory, can not detect the characteristics of materials' internal structure and is not sensitive to micro-cracks detection, its limitation on identification and quantification of the material degradation exists. Studies show that the nonlinear ultrasonic features are more obvious after the concrete damaged. Thereby, it is worthy to identify and quantify the degradation damage of concrete materials by its nonlinear ultrasonic features. Meanwhile, the ultrasonic signal is nonlinear and nonstationary, the traditional signal processing methods most based on the premise of linear and stationary, so the traditional methods have some limitations. Therefore, using nonlinear and nonstationay method is very beneficial to nonlinear ultrasonic features of materials.Based on nonlinear ultrasonic theory, this paper uses Hilbert-Huang Transform to process ultrasonic signal and extract the nonlinear acoustic features so as to quantify the degradation of the concrete materials. Then the deterioration of the concrete materials is estimated. The main content and the conclusions are as follows:The characteristic of current ultrasonic signal processing methods is presented and its boundedness on nonlinear and nonstationay signals is analyzed. The principle, implementation steps and the characteristics of Hilbert-Huang Transform to process signal is discussed.Based on the principle of Hilbert-Huang, the signal processing program and numerical simulation has been work out, the results show that IMF components discomposed by EMD can reflect the features of time scales of signal better. In the meantime, the nonlinear attenuation characteristics that the signals showed are obvious and coincided with classical nonlinear wave theory, which proved the effectiveness of the method and procedure.This paper adopts the method of HHT to process the tested signals of nonlinear ultrsonic high order harmonic, the filtering method based on marginal spectrum is put forward because of the features of marginal spectrum, and is used to process the tested signals. Results show that the denoising effect with this method is obvious. The process of deterioration and damage of concrete due to the alkali-silica can be described by the parameters of instantaneous frequency, instantaneous amplitude and the nonlinear ultranosic parameter, so to some extent, identifying and quanlifying the accumulative deterioration and damage of concrete can be realized.