Rheological yield stress measurement of mine paste fill material

This thesis addresses rheological characterization of mine tailings and paste materials as saturated solid-liquid or homogenous mixtures. Thickened tailings and paste fill can be classified as viscoplastic or time-independent non-Newtonian fluid material. Viscoplastic fluids deform plastically when the applied shear stress is less than a critical stress, which is known as "yield stress". When the shear stress exceeds the yield stress this type of fluid flows like a viscous material with finite viscosity.;There is also a method for calculating the yield stress from slump height. Any geometry of slump moulds, cone or cylinder, with different dimensions can be applied in this method. The standard conical slump test is basically used for controlling the workability of fresh concrete. This method was then modified for yield stress and viscosity calculation of cemented mixtures. These slump tests can be categorized as in-situ methods of yield stress measurements.;Several rheometery and in-situ experiments were carried out to measure the yield stress of two mine tailings samples in this study. A rheometer was used in controlled shear rate and controlled shear stress modes for yield stress measurements with the vane method. The results were satisfactory for cemented and non-cemented mixtures. The effect of mixing time on the yield stress of material combined with cement was also assessed using the vane method. No significant difference emerged between increased yield stress of the mixtures after 4 minutes and 12 minutes of mixing.;The accuracy of calculated yield stress values using in-situ methods was also determined by drawing comparisons between these series of data and actual yield stresses measured using a rheometer. Modified conical slump tests overestimated the values of yield stress and did not obtain reliable data for viscosity calculation of the mixtures.;In terms of pipeline design for transportation of mine tailings or paste material, one of the most important rheological parameters that must be measured would be yield stress. There are numerous techniques and equipment that can be used for rheological characterization and specifically for yield stress measurements. Literature review shows that the vane method is one of the best rheometery techniques for determining the yield stress of homogeneous fluids directly.