Linear and non-linear rheological behaviour of cement and silica suspensions. Effect of polymer addition

Oil well cement pastes and model silica suspensions demonstrate similar rheology: in oscillatory shear, beyond a critical stress, a sharp transition is observed between gel and liquid behaviour. In creep tests, an apparent yield stress and shear-thinning are followed by the appearance of shear thickening. The minimum viscosity measured in steady shear is close in value to the complex viscosity obtained from oscillatory measurements. The observations can be explained by the formation of liquid trapping aggregates whose compactness may be estimated by fitting the Tsenoglou model, and whose cohesion is reflected in the rigidity of the gel and in the critical strain (or stress) of gel dissolution. Substituting cement or silica particles by polymer redispersible powder causes a decrease of the storage modulus in the gel state and a lower viscosity, while leaving the general features of the flow curve unchanged. Decrease in material rigidity may be due to a weaker inter-particle attraction generated by the polymer presence. The decrease in viscosity is explained by a lessening of water entrapped within the aggregates, which now contain polymer particles which are less hydrophilic than either cement or silica.