CAUSES OF THE DROP IN CONDUCTIVITY DURING THE HYDRATION OF GYPSUM PLASTER MIXES

The drop in electrical conductivity of a gypsum plaster mix without an y additives has been attributed quantitatively to the reduction in con centration of calcium and sulphate ions and to a drop in the free wate r. It has also been established that in addition to these at least one other influencing factor plays a prominent plant in the change in con ductivity. This includes the increase in specific surface area of the solid phase caused by the hydration. It was proved experimentally that the drop in conductivity of a gypsum plaster mix conforms closely in timing and extent to the increase in the degree of hydration. Conducti vity measurements therefore make it possible to determine the degree o f hydration of a gypsum plaster mix continuously and with comparativel y little expenditure.