Rheology of a gypsum suspension in the presence of different superplasticizers

In this work, the rheological properties of suspensions of micron-sized gypsum particles dispersed in water were studied in the presence of different fluidizer molecules. The yield stress and the shear moduli were measured versus the volume fraction in the presence of these molecules. Using the same polyelectrolyte with different molecular weights the dependence of yield stress versus the gyration radius of the polymer was investigated; also different sizes of the gypsum particles allowed to check the size dependence of the yield stress. A particular attention was brought to the change of the thickness of the polymer layer with the volume fraction. From a model, which relates the steric interaction between the two polymer layers to the yield stress and shear modulus, an important compression of the polymer layer with the volume fraction was found. At higher volume fractions a dynamic jamming transition was observed at a critical volume fraction of 0.485 which does not depend on the presence of the fluidizer molecule. Unexpectedly the fluidizer makes this transition to happen at lower shear rates although the yield stress has disappeared.