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

• Factors affecting rheology of paste are outlined and discussed.
• Factors affecting shear-thickening response of cement-based suspensions are identified and discussed.
• Shear-thickening behavior of concentrated cement suspension is observed.
• The behavior of new generation of superplasticizer acting by steric hindrance in concentrated cement suspensions is highlighted.

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.