USE OF DIFFUSION ANALYSIS OF ULTRA SONIC WAVES TO CHARACTERIZE THE DAMAGE OF CONCRETE

Abstract

Damage to concrete arises, for a wide range of patholo-gies, as microstructural changes associated with the onsetand progression in number and size of microcracks. In amore advanced stage, macrocracks are developing andprogressing to the collapse of the structure. To prevent thislast point, it is important for CND to detect upstream andas soon as possible early signs of damage. In the presenceof obstacles in the propagation medium, the ultrasonicwaves are scattered and the obtained signals are extendedand then consist of a superposition of waves. For high lev-els of scattering, coherent wave is then no longer observedand the diffusion theories used to describe the evolution ofthe energy in the medium. By a 2D approximation, it is pos-sible to determine the diffusivity parameter D, dissipations and the Arrival Time of the Maximum Energy ATME thatare characteristic of the energy evolution. Concrete is theseat of an important multiple scattering related to the for-mulation but also related to damage. Relative variations ofthe observable in energy diffusion (D, s and ATME) allowto characterize the evolution of damage in the material. Weshow an experimental study of these parameters evolutionon samples with the same composition at various stages ofdamage. The potential of these techniques as solutions ofNon-Destructive Testing is encouraging and prospectsassociated are identified.