CONTROL OF CONCRETE SKIN BY NONLINEAR ACOUSTICS AND SURFACE WAVES

Abstract

Concrete cover has an essential role in the life of a civilengineering structure. It faces to chemicals, environmentaland mechanical. It is important to know its aging conditionand its ability to perform its functions. Many techniquesare able to listen the first layer of material, but the ultra-sonic waves have the particularity to penetrate equivalentto the wavelength depths. These waves can be adjusted tovary the frequency monitoring depth. It then becomes pos-sible to propose the characterization of the material and itsgradients by Rayleigh waves. The parameters related tothe nonlinear acoustic are more sensitive to changes of thematerial as the velocity and attenuation obtained by linearacoustics. The level of non-linearity in the elastic responseof materials strongly depends on the level of damage bymicrocracking or different pathologies and their develop-ments such as alkali reaction or carbonation. We proposein this work a study of combining the nonlinear acousticwith the surface waves in order to auscultate the materialsurface to a predetermined depth. This technique offers areal possibility of test by a single face of a structure whichopens up possibilities for transposition on site. The ulti-mate goal is to make experiments on structures by exploit-ing natural vibrations such as the passage of a truck on abridge. It is done in collaboration with the University ofSherbrooke.