Effet du broyage sur la reactivité de l'anhydrite vis-à-vis de l'eau

In order to clarify the influence of grinding on anhydrite reactivity to water, the authors have ground natural and synthetic products in different ways and investigated the evolution of microstructure and the rate of the conversion: CaSO4 II → CaSO4·2H2O, as a function of grinding. Different parameters have been used to characterize the anhydrite microstructure; nevertheless, only the specific surface BET and very short-range disorder, defined by the 'disorder coefficient' (Cd), can affect the product reactivity. The most important results are the following: • - The grinding operation causes important changes in microstructure. The specific surface is always a function of the grinding time, given by the equation: y = axn + b. On the contrary, the Cd-value is a function of the grinding time given by the same equation only if the anhydrite is synthetic. For natural anhydrites, no simple correlation can be established. • - The reactivity of all ground products is a function of the specific surface BET given by the above equation. The same law also controls the dependence of synthetic anhydrites reactivity on Cd. • - The change in grinding energy does not affect the law of the reactivity dependence on the specific surface and Cd, but the grinding times must be changed proportionally in order to achieve the same values of specific surface BET.