MONITORING THE SETTING OF CONCRETE BY INTERFEROMETRY OF ULTRASONIC CODA

Abstract

The properties of concrete at early age, its hardening andsetting phases, influence the properties of the whole struc-ture throughout its life. Traditional ultrasonic methodsmake possible the following of the concrete setting basedon low frequency signals, in order to limit the attenuationmainly due to the scattering of waves by the aggregates. Incontrast to traditional methods using coherent ultrasonicwaves [1], the Interferometry of Coda Wave (CWI), basedon the diffused ultrasonic field, makes possible an increasein sensitivity to changes in the microstructure of the con-crete. In this paper an energy characteristic of the CODA[2] is used to track the concrete and deduce continuouslyits Poisson’s ratio based on additional measured compres-sion wave velocity data. In this article, CWI tests were per-formed on a concrete formulation already widely studied inthe literature [1]. An experimental device is developped toregister viable measures 8 hours after casting. However,the interpretation of CWI measurements does not coincidewith the classical results until 20 hours after pouring. Theexistence of a spatial variation of the temporal evolution ofthe setting in the tested specimens is proposed to explainthe differences obtained in the early hours.In this article, the apparatus and the test conditions aredescribed. Finally, the results are presented and followedby a discussion.