Abstract
As an extension of previous studies on the dilute solid-liquid suspensions, this paper describes the rheological behavior of suspension at very high concentrations, the sludge. An unconfined compression (uniaxial compression) was applied for cylindrical block of Na Bentonite-water sludge. Various hystereses of stress or strain were applied until the block was ruptured. Before the rupture, the deformation was viscoelastic and the non-recoverable part of strain depended on the hysteresis. The rupture stress depended only on the concentration, and was independent of the hysteresis of stress or strain. The rupture strain varied with the hysteresis and the concentration and it was always less than 0.1. The modulus plotted against the rupture stress for sludge laid on the extension of the line for the modulus plotted against the yield stress for dilute suspensions. It was concluded that the rupture of sludge corresponds to the yielding of suspension, though the former is viscoelastic before rupture and the latter is elastic before yielding. In the creep test, the strain response, immediately after the loading, was elastic, and then becomes viscoelastic. These responses could be represented by a four-element model if the obvious non-linearity at the initial stage of creep is ignored. The initial properties were recovered again by keeping the material at rest; thus the sludge has a thixotropic nature.
