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 rat e (shear thickening). When mineral additives are used, the intensity of the phenomenon depends on their nature: it can be amplified (metakaolin), unch anged (quartz, fly ashes) or reduced (silica fumes). According to the liter ature, shear thickening occurs when suspensions have a high solid concentra tion and when repulsive interactions are predominant. These conditions can be achieved in cement pastes owing to the dispersing action of superplastic izer. In that case, the shear thickening behaviour could be due to local me chanical actions created by the increased shearing forces. (C) 2000 Elsevie r Science Ltd. All rights reserved.