Wideband Microwave Imaging of Concrete for Nondestructive Testing

Abstract

Radar has the potential of becoming a powerful and effective tool for the nondestructive testing of concrete structures. An advancement of the method can be achieved through the understanding of the interaction between electromagnetic waves and concrete, and the identification of optimum radar measurement parameters for probing concrete. For the determination of optimum parameters, systematic radar measurements are needed in tandem with the implementation of proper signal processing techniques for imaging. This paper presents the results of such radar measurements, which are made using a wideband imaging radar with different frequency ranges. Inverse synthetic aperture radar is used for the measurements of laboratory-size concrete specimens having three different types of internal configurations. The signal processing algorithms implemented to obtain two-dimensional and three-dimensional imagery of concrete targets from radar measurements are also discussed. For the concrete specimens and measurement setup used in this study, 2–3.4 GHz waveforms are found to be adequate for the concrete thickness measurement, 3.4–5.8 GHz waveforms are adequate for the detection of delamination, and 8–12 GHz waveforms are adequate for the detection of inclusions embedded inside concrete.