Détermination de la résistance à la compression du béton d'après la vitesse transversale de propagation des ultrasons et les méthodes combinées qui en découlent

Abstract

On expose les résultats d'une recherche, qui permettent de formuler un jugement sur le degré de corrélation entre la résistance du béton à la compression et ses caractéristiques aux ultrasons, soit la vitesse de propagation des ultrasons par impulsons d'ondes transversales, une caractéristique complexe composée de la vitesse d'impulsion des ondes transversales et de la vitesse d'impulsion des ondes longitudinales, le module d'élasticité dynamique en compression et en tractionE _bu du béton, le module d'élasticité dynamique transversaleG _bw, ces relations étant comparées avec la relation employée jusqu'alors pour déterminer la résistance du béton, et la vitesse de propagation des ultrasons par impulsion d'ondes longitudinales.

Summary

This research is founded on new knowledge of the possibility of measuring the propagation time of transverse ultrasonic waves in concrete and on a measurement method devised by the author. This uses the measured and theoretical characteristics of concrete obtained by the ultrasonic method, that is to say the velocity of propagation of transverse ultrasonic waves vt, the dynamic modulus of elasticity in compressive and tensile loading E_bw, the dynamic modulus of transverse elasticity G_bw, determined on the bases of their ultrasonic parameters, the velocity of propagation of longitudinal waves and a complex characteristic composed of two pulse velocities (v_t and v_L).

Extensive study of the degree of correlation between the compressive strength and the two characteristics of concrete mentioned above led the author to formulate the following statements: Correlations R=F (v_t), R=f₂(E_bw), R=f₃(G_bw) and the multiple correlation R=F₁(v_t, v_L) show an analogous degree of correlation which is always higher than the correlation R=f₁ (v_L) used up till now.

From the practical point of view, the result is that to determine the strength of a concrete in a building or a structural member, it suffices to measure the propagation time of transverse ultrasonic waves and to apply R=f(v_t) expressed by a regression equation. Introducing other parameters (velocity of longitudinal ultrasonic waves, the concrete density and the Poisson ratio) which implies undertaking additional measurements, will no longer give rise to appropriate effects.

By varying the aggregate content and the concrete density at certain points in the concrete, it is possible to reach greater accuracy in the determination of compressive strength of concrete with the correlation R=f₃(G_bw).