Spectral analysis of radar surface waves for non-destructive evaluation of cover concrete

This paper presents the use of spectral analysis of radar surface waves for the non-destructive evaluation of cover concrete. With only two commercial coupled antennas centred around 1.5 GHz, an original measurement mode is proposed for obtaining dynamic wide angle reflection refraction profiles. It consists in taking several profiles at the same place using different distances between the two antennas. After separation of the air wave and surface waves, the wrapped phase spectrum is obtained for a given distance between two receiver positions by means of a Fourier transform. For a given position, the speed is calculated for each frequency from the known wave travel distance. The repetition of the processing for other positions gives the speed variation along a profile. Moreover, the dispersion analysis can provide further information on the humidity of the material. Tests on a dry concrete surface and after wetting provide reliable results which allow the two moisture contents to be distinguished. (C) 2003 Elsevier Ltd. All rights reserved.