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Ultrasonic monitoring of P-wave and S-wave transmission velocity for setting time determination of mortar

par Carette, Jerome ;Lambrette, Nicolas;Meskens, Benjamin;Viaene, Xander;Staquet, Stéphanie
Référence Concrete Innovation Conference(11-06-2014: Oslo), Proceedings of CIC2014 international conference
Publication Publié, 2014-06-11

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Résumé :

The final setting time of mortar, or t0, corresponds to the time when its mechanical properties such as Young’s modulus or tensile strength start to develop. In the precast concrete industry or in a construction site, the knowledge of t0 allows a safe early formwork removal. This parameter is also essential for modeling purposes, especially as regards to the very early age behaviour of concrete structures. Until now, the most used standardized methods developed for the setting time detection are destructive and non-continuous. Manual measurements have to be made regularly on several samples throughout the whole test, until final set has occurred. The ultrasonic pulse velocity (UPV) measurement is a well-established method which permits to follow the evolution of fresh concrete throughout its setting process. The early age evolution of cement-based materials properties can be correlated with UPV measurements. Most of these correlations imply the measurement of P-waves, due to the easy implementation of such tests compared to the S-waves propagation monitoring. However, ultrasonic S-waves seem to be better indicators of the mechanical setting of cement-based materials, since they are more sensitive to the solid matrix connectivity than P-waves. This study proposes a new methodology, based on the UPV measurements of P- and S-waves, and isothermal calorimetry, to determine the final setting time of mortars containing various rates of substitution of Portland cement by thermal power station fly ash (TFA) and Municipal Solid Waste Incineration (MSWI) Electrostatic Precipitator fly ash (EFA). The S-waves velocity and dynamic elastic properties seem to be the most accurate indicators of the setting process, since they are closely related to the shear modulus development at early age, and allow capturing microstructural evolutions that usual UPV methods do not detect.