Non destructive non contact air-coupled concrete cover evaluation by ultrasound surface waves using an automated device

Many reinforced concrete structures are suffering from deterioration occurring earlier than their expected service life. The first barrier against attacks of external environmental agents is the concrete cover. The damage mechanisms depend on the microstructure of the cover concrete. This microstructure can be assessed with various measurements. The paper presents the automated device designed for the non destructive control of the concrete using the ultrasonic surface waves. The measurements are carried out without any contact with tested sample. The increase of signal level, required for such solution, is obtained using the frequency swept signals, so called “chirps”. The recorded signals are processed using special software which permits to obtain the attenuation and the velocity dispersion of surface waves. These parameters can be next used in order to determine the parameters of concrete cover. Especially the inversion of velocity dispersion characteristics using the approaches developed for the multichannel analysis of surface waves (MASW) technique, enables to evaluate the variations of shear velocity as a function of the concrete cover depth. The potential possibilities of this approach are shown on an example of laboratory measurements carried on the cement slab especially manufactured, displaying the increasing porosity as a function of depth, and on the example of in-site measurements carried out in order to evaluate the depth of deterioration of a concrete platform in maritime port.