Study of the shear thickening effect of superplasticizers on the rheological behaviour of cement pastes containing or not mineral additives

Fresh cement pastes, when dispersed by a superplasticizer acting mainly by electrostatic effect, present a viscosity that increases with the shear rate (shear thickening). When mineral additives are used, the intensity of the phenomenon depends on their nature: it can be amplified (metakaolin), unchanged (quartz, fly ashes) or reduced (silica fumes). According to the literature, shear thickening occurs when suspensions have a high solid concentration and when repulsive interactions are predominant. These conditions can be achieved in cement pastes owing to the dispersing action of superplasticizer. In that case, the shear thickening behaviour could be due to local mechanical actions created by the increased shearing forces. (C) 2000 Elsevier Science Ltd. All rights reserved.