Another Dimension to Slump

Estimating the rheological properties of a paste using convenient methods such as the slump technique are common practice within the industry. However, the universality of comparing slump heights to estimate the flow properties for different paste products has been questioned (Clayton et al., 2003; Paterson, 2002). The dispute relates to the fact that two paste products may in fact exhibit similar slump heights, but may not share the same shear yield strength since their densities may be different. This discrepancy is catered for by the method of Pashias et al. (1996) in which the shear yield stress can be conveniently calculated from the slurry density and the slump height. However, certain paste rheological behaviours are observed which appear puzzling and which cannot be explained on the basis of particle size and slurry density alone. The chemical conditions of pastes (particularly those containing clay minerals) have profound effects on the colloidal interactions of the suspended solids and hence on the rheological behaviour of pastes (Vietti, 2004; Dunn, 2005). This paper demonstrates that different slump heights may be observed for a kimberlite paste containing smectite at one material density, but varying paste chemical conditions.