A.C.J. de Korte and H.J.H. Brouwers Ultrasonic sound speed of hydrating calcium sulphate hemihydrate; part 2, the correlation of sound velocity to hydration degree

In this article the sound velocity through a mix is correlated to the hydration degree of the mix. Models are presented predicting the sound velocity through fresh slurries and hardened products. These two states correspond to the starting and finishing point of the hydration process. The present research shows that a linear relation between the amount of hydration-product (gypsum) formed (Smith et al., 2002) and sound velocity can be used to describe this process. To this end, the amount of hydration-product formed is determined by the using the equations of Schiller (1974) for the hydration process and of Brouwers (2010) for the volume fractions of binder, water and hydration products during the hydration process. The presented model shows that the induction time and gypsum growth rate are linear related to the water/gypsum-ratio. Introduction In part 1, the ultrasonic speed measurements were compared with theoretical predictions for both the fresh slurry and the fully hydrated material. Based on these results we are now able to predict two points during the hydration process, namely the starting and completion of the hydration. Currently, the process in between these two stages has not been described yet. This article addresses the hardening stage as well as a model to relate the hydration degree to time. Relation between hydration degree and sound velocity Smith et al. /1/ describe the relation between hydration mechanism and ultrasonic measurements in aluminous cement. They provide a correlation between hydration degree and ultrasonic measurements. This correlation reads