Structural breakdown and build-up in bentonite dispersions

An experimental study on the rheology of bentonite aqueous dispersions is presented. The viscoelastic response of the system as a function of the pH has been studied. Solid-like behaviour has been observed in all cases. Stress sweeps in dynamic tests have shown that the extent of the linear viscoelastic region and the consistence of the systems are pH dependent. The viscosity of the dispersions depends on the steady shear rate and the time of shearing. It is shown that the dispersions show thixotropic viscosity, i.e., shear thinning with a long relaxation time as a unique function of shear. An experimental approach for viscosity decay at constant shear rate for step-up experiments and viscosity increase at constant shear rate for step-down experiments is tested. The rate parameters for the decay and increase of the viscosity are found to be a power-law function of the shear rate.