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