On the frictional contribution to the viscosity of cement and silica pastes in the presence of adsorbing and non adsorbing polymers

This paper is devoted to the role of hydrodynamic lubrication in the flow of dense suspensions of non-Brownian cement or silica particles. The role of hydrodynamic lubrication is ambiguous since it is primarily a source of viscous dissipation but, by preventing direct contact between particles and friction, it may facilitate flow. We show that in the concentration and shear rate regimes investigated here direct contact friction between cement or silica particles is contributing to the overall energy dissipation. Addition of water-soluble polymers, either adsorbing or not adsorbing, was used as a mean to control friction. We show that, independently of the adsorption capacity of the polymer, it is the non adsorbed polymer which, thanks to hydrodynamic lubrication, prevents direct contacts and reduces the overall energy dissipation. This leads to the counterintuitive situation where by increasing the interstitial fluid viscosity, the suspension viscosity is decreased. When hydrodynamic lubrication is no longer able to avoid direct frictional contact, dilatant and shear-thickening behaviors set in.