UTILIZATION OF IMPEDANCE SPECTROSCOPY FOR STUDYING THE RETARDING EFFECT OF A SUPERPLASTICIZER ON THE SETTING OF CEMENT

The electrical resistivity and conductivity of cement pastes with diff erent dosages of a superplasticizer have been determined using impedan ce spectroscopy. The evolution of these parameters during the first 24 h after mixing indicates that the incorporation of the superplasticiz er leads to a retardation of the setting process, the significance of which increases with the dosage. It appears that the incorporation of the superplasticizer extends the dormant stage of hydration and delays the onset of the accelerating stage, without affecting its rate. Comp arisons are made with penetration measurements with the Vicat apparatu s. (C) 1998 Elsevier Science Ltd.