Determination of the bulk elastic moduli of various concretes by resonance frequency analysis of slabs submitted to impact echo
Résumé
The presented study aims at evaluating the bulk elastic Young's modulus of six different concrete mixes as a function of porosity and water content. The impact echo method consists of a frequency analysis of ultrasonic waves generated by the impact of a steel ball. It is commonly used to measure the thickness of large concrete slabs, to detect voids in concrete structural elements considered as infinite. This method was employed on reduced size slabs (0.5 x 0.25 x 0.12 m(3)). As a consequence, it was necessary to identify the frequencies corresponding to resonance modes or pseudo-stationary modes. This modal analysis was performed with simplified models (for beam in particular) and used to extract the dynamic Young's modulus E-dyn and the Poisson's ratio. The results are then analysed. The E-dyn-modulus, inverted for all concrete mixes, is compared to static Young's modulus E-stat, measured by destructive testing, to the porosity and to the water content of the specimens.