Piwakowski, Bogdan; Ecole Centrale de Lille; France
Ciccarone, C.; IEMN CNRS École Centrale de Lille; France
Drelich, R.; Institute of Mechanics and Applied Computer Science, Kazimierz Wielki University; Poland
Li, J.; Ecole Centrale de Lille; France
Piiwakowski, B.; Ecole Centrale de Lille; France
Session: Civil Infrastructure 2
Time: 16:20 - 16:40
In recent decades, considerable efforts have been made to develop air-coupled ultrasonic transducers for the purposes of radiating/receiving ultrasonic signals directly into/from air. This enables the development of so called non-contact ultrasonic testing methods which do not require any physical contact with the tested object (i.e. using air as a coupling medium). They are of particular interest for fast scanning applications, where coupling (physical contact) between the ultrasonic transducers and tested materials must be avoided.
The paper presents the automated scanner designed for the non destructive control of concrete using ultrasonic surface or plate waves. The measurement consists in signal recording by means of the non contact receiver moving along measured sample. The signal is radiated by a non contact emitter and can cover the sonic and ultrasonic frequency band, ranging from 10 to 50 kHz, just assuring the surface wave penetration in concrete between 5 to 25 cm.
Because of the relatively high damping in concrete and because of very low transmission coefficient between air and concrete, in order to improve the signal /noise ratio, the chirp technique is used. The scanner is, portable and can be used in a laboratory and as well as in site.
The acquired multi-channel spatio-temporal signal is processed in order to obtain the ultrasonic group velocity, the velocity dispersion characteristics and the ultrasonic attenuation versus frequency.
The potential possibilities of this approach are shown at an example of in situ measurements carried out in the frame of the French ENDE research project aiming in the concrete wall characterisation and in the cracks detection.