Authors: Wickens, J

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Wickens, J 2023, 'Potential errors in paste fill rheology measurements', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: Proceedings of the 25th International Conference on Paste, Thickened and Filtered Tailings, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 859-871,

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Depending on the mining method being used, the required unconfined compressive strength (UCS) of paste fill can vary between 500 to 5000 kPa at 28 days. In order to achieve these upper limit UCS targets, high concentration cemented paste backfill must be placed underground, sometimes at significant distances from the backfill plant. The understanding of the flow behaviour (rheology) of these mixtures is therefore vital from a reticulation design and operational point of view. There are many methods to determine the rheology of paste fill mixtures. Vane yield stress, along with bob and cup rotational viscometer measurements (yield stress and viscosity), are the most widely used methods due to the relatively simple test procedures and limited sample size required, but there are drawbacks to each method. Vane yield stress measurement will only provide the design engineer with yield stress values, not viscosity. Bob and cup rotational viscometer measurements will provide the design engineer with yield stress and viscosity, but one may experience slip at the wall of the rotational viscometer’s bob at high concentrations, which will skew the test results. To overcome the issue of slip at high concentration paste fill mixtures when using a bob and cup rotational viscometer, pipe loop tests can be conducted in at least two pipe diameters to accurately measure the rheology of these high concentration paste fill mixtures. This paper will discuss typical test results where the measurements of the bob and cup rotational viscometer underpredicted the yield stress and overpredicted the viscosity when the results were compared to a pipe loop test campaign completed on the same material.

Keywords: unconfined compressive strength, paste fill, rheology, yield stress, slip

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