MECHANICAL CHARACTERIZATION OF HETEROGENEOUS MATERIALS DURING SETTING

The vibroscope, a non destructive vibratory test at low frequency (100 Hz-1 kHz) is presented in this article. It was developed in order to study the theological evolutions of crude cellular concrete during setting. This highly heterogeneous material changes from a bubbly fluid to a porous solid in four hours. The action of the vibroscope consists of sending shea impulses of compressional waves into the material at regular intervals. The recorded signals allow the calculation of the celerity and the damping coefficients as well as the ratio of normal stresses in two orthogonal directions. From celerity measurements, the transition between fluid and solid state of the cellular crude paste is determined. The three quantities measured are analyzed and are then related to the mechanical properties of the material by an inverse analysis. The latter is based on the assumption that the paste behaves as a suspension of gas bubbles in a viscoelastic medium. From this analysis, the evolution with lime of the values of the theological parameters can be calculated. Finally it is shown that the vibroscope can be adapted to the study of other heterogeneous materials during setting.