Abstract
Flow curves (data on shear stress vs. shear rate) were obtained for Na-montmorillonite suspensions at solid ratios up to 2.6% from steady-state shear experiments with cone-plate viscometer. These results exhibited typical pseudo-plastic flow pattern with some yield stress, and were expressed by a Herschel-Bulkley model.
Yield stresses τ0 were estimated from the flow curves, and they revealed high dependency on solid ratio φ0, such that τ0 changed according to the 7th power of φ0. Then extrapolation of this relationship to higher solid ratio leaded accurate correspondence to the liquid limit test data for Na-montmorillonite paste. This result indicated that the relationship between τ0 and φ0 could explain plastic flow properties of samples over the wide range of water content from suspension paste to liquid limit.
It was also examined from theoretical viewpoint by the Michaels and Bolger model. Assuming a uniform and parallel arrangement of clay particles and adopting the van-der-Waals attractive force as an inter-particle force factor in that model, we calculated theoretical values for yield stresses of Na-montmorillonite. They showed good agreement qualitatively with the measured tendency although calculated values were less than 10-5 of measured ones.
