Effect of solid concentration and shear rate on shear-thickening response of high-performance cement suspensions

Flow performance, placement, and consolidation of concrete are mainly related to its rheology. Rheology of paste plays a key role on rheology of concrete. Cement pastes exhibit complex rheological behavior affected by several physical and chemical factors, including the solid concentration, type and dosage of high-range water-reducer (HRWR), cement characteristics, and shear history. An experimental investigation was carried out to investigate the effect of solid concentration, HRWR-cement combinations, and shear rate regime on pseudoplastic behavior of high-performance cement grouts. Grout mixtures proportioned with w/c of 0.30, various cement-HRWR combinations, 8% silica fume, and different limestone powder additions were investigated. Solid concentration and shear rate regime are shown to be key factors affecting shear-thickening response of concentrated cement-based suspension (i.e. low w/c). Concentrated high-performance grout mixtures are shown to exhibit shear-thickening behavior. The use of polycarboxylate HRWR acting by hindrance effect exhibited greater shear-thickening behavior compared to polynaphtalene type acting by electrostatic effect. The use of finer particles enhances the powder skeleton and ensures polydisperse systems, hence resulting in lower shear-thickening response. For concentrated cement-based suspensions, shear-thickening is due to disorder state, and at higher shear rate, hydrocluster formation is prevailing. (C) 2013 Elsevier Ltd. All rights reserved.