Effect of operational factors on reproducibility of yield stress measurement based on the vane method for cemented paste backfill

Abstract

• Precise measure of yield stress is critical for CPB and vane method is widely used. • The reproducibility is subject to instrumental, analytical and operational influence. • Various vane positions, standing times and rotation speeds were tested. • A satisfactory reproducibility requires consistent preparation and operation. • A lower rotation speed facilitates a closer result to the true value. • Equilibrium time of 1 min and rotation speed of 0.1 rpm are suggested for CPB. Precise determination of yield stress with the desired reproducibility is critical for cemented paste backfill (CPB). An overview of the instrumental, analytical and operational factors was carried out to evaluate the key factors in CPB measurement using the vane method. Therewith the effects of vane inserted depth (10 to 40 mm), standing time (0 to 6 min), and rotational speed (0.05 to 5 rpm) were tested. The results show that an increased rotation speed or prolonged standing time leads to higher measured values and poorer reproducibility. The ESEM images indicate that larger yield stress values correspond to denser microstructures and the deterioration in structural homogeneity leads to pronounced deviation in results. Increasing the rotation speed enhances the role of viscous resistance and leads to an overestimation of yield stress. It is recommended that a consistent operation should be followed with the vane centered in the sample, resting for less than 1 min, and rotating below 0.1 rpm.