| ABSTRACT: | USE OF RAYLEIGH WAVE METHODS TO DETECT NEAR SURFACE CONCRETE DAMAGE
R. Al Wardany 1,2,, J. Rhazi1, G. Ballivy1, J.L. Gallias2, K. Saleh3
1Research Group on NDT and Instrumentation Université de Sherbrooke, Sherbrooke, Canada; 2 Laboratoire
de Modélisation, Matériaux et Structures Université de Cergy-Pontoise, Cergy-Pontoise, France; 3 Research
Institute of Hydro-Québec Varennes (Québec), Canada
Massive concrete structures, like dams, are often subjected to aggressive agents. Weathering actions,
chemical attacks, abrasion and other degradation processes, can act simultaneously on the concrete surface
and minimise its durability. The maintenance and rehabilitation of the near surface damaged concrete zone,
require a good evaluation of its degradation depth. The use of Rayleigh waves in non invasive methods,
appear to be the most promising approach for the determination of concrete stiffness profile. Rayleigh waves
propagate in cylindrical wave fronts, parallel to the concrete surface, with elliptical particle motion. Their
amplitudes decrease exponentially with depth, and most of the energy propagates in a thickness equal to the
wavelength. In this paper, applications of recent multistation Rayleigh wave methods were presented.
Experiments have been conducted on large volume concrete blocks (8 m3). Different typical near surface
defects common to the downstream wall of concrete dams were induced in these blocks. Voids,
heterogeneous layering, deterioration simulating freeze-thaw damage and horizontal fissuring, have been
very well detected. Results show that this new technology can be applied on existing full scale concrete
structures.
|