Effects of particle fractions on the Bingham yield stress and viscosity of fine-coarse particle suspensions

The rheological behaviors of highly concentrated fine particle suspensions (clay-silt-water mixtures) and coarse particle suspensions (coarse particles within a fine particle suspension) were investigated in this study. Experimental results demonstrated that the Bingham Fluid Model with two rheological parameters, Bingham yield stress and viscosity, well characterized the rheological behavior of fine particle suspensions at shear rates between 4 and 20 s^-1. The inclusion of coarse particles within a fine particle suspension induced an enhancement to the rheological parameters. The rheological parameters of a coarse particle suspension not only depend on its total particle fraction but also on its relative fine/coarse particle fractions. Empirical equations of these two parameters were proposed, quantitatively related to both fine and coarse particle fractions. Results indicated that the Bingham yield stress and viscosity are much more (an order larger) sensitive to changes in fine particle fraction than to changes in coarse particle fraction.