Viscosity is a very complicated property, specially for slurries having finer particles (less than 75 microns in dia.) at higher concentrations (more than 15% by volume). However, viscosity for slurries consisting of coarser particles may be determined using Thomas correlation with fair degree of accuracy.

I have experience of measurement of rheological properties of fly ash-water slurries. The attached figure shows the particle size distribution for fly ash used in the experiments. The specific gravity and volumetric static settled concentration was measured as 2.1 and 50%, respectively. I measured the rheology of fly ash-water slurry at different volumetric solid concentrations ranging from 0 to 40% using a Weissenberg Rheogoniometer at temperature of 22 deg C. I observed that the slurry viscosity increases monotonically with increasing solid concentration. The rate of increase was larger at higher solid concentrations. I also observed that the slurry behaves as a Newtonian fluid up to a solid concentration of 17% (by volume) and above 17% (by volume), it behaves as a Bingham fluid. The viscosity of fly ash-water slurry was 47.7 cP and yield stress was 0.60 N/sq m at 40% concentration by volume.

Regards

D.R. Kaushal ■

PSD of fly-ash used in rheology measurements:

http://paniit.iitd.ac.in/~kaushal/id14.html ■