Rhelogycal behaviour of cement pastes with addition of silica fume, nanosilica and polycarboxilic dispersant

This article shows the results of an investigation about the effect of silica fume (SF), nanosilica (NS) and superplasticizer (SP) addition on the rheological behavior of CP V ARI RS cement pastes. Cement pastes with different content of SF (0 to 10 wt%) and 1.0 wt% NS were compared to REF (without mineral addition). For all samples studied (REF, NS and SF), SP ranged 0 to 0.5 wt% relative to cement. A rheometer with concentric cylinders geometry was used and the maximum shear rate of 100 s(-1) was applied. When SP is added into the mixtures, the hysteresis area, plastic viscosity and yield stress decreased. The latest was more affected than plastic viscosity. When SF was added, the yield stress did not change significantly, except in samples with 10 % SF and SP between 0.1 to 0.3 wt%. In relation to plastic viscosity, the difference was not visualized. However, NS influences more the plastic viscosity than REF and SF. The Bingham model describes properly the rheological behavior of mixtures at intermediate values of shear stress, while the Herschel-Bulkley model are more adequate at high and low values of shear stress.