Cemented paste backfill (CPB) is considered to be a concentrated suspension in which tailings are bonded together by the hydraulic binder and water, and it has a high solid volume concentration (≥50 vol.%). Although the shear thinning and thickening of CPB has been extensively reported in literature, the shear history effects have been ignored in previous studies. In this paper, by using rheometer and Focused Beam Reflectance Measurement, the relationship between the rheological properties and microstructure of the paste under different shear histories was studied. The results have shown that at a low shear rate, CPB revealed shear thinning, low yield stress and low index parameters; while exhibited shear thickening, high yield stress and high consistency index when at high shear rates of shear history. This agreed with the general trends shown in the FBRM analysis. It was proposed that the action of shear is beneficial to particle dispersion, whereas a high shear rate history tends to promote the aggregation of particles. It was revealed that both shear thinning and thickening of paste are related to the situation of particles (flocculation, dispersion and aggregation), and shear history effects play an important role in rheological properties of CPB.

Nowadays, the cemented paste backfill mining method is widely used in mines. Since the temperature of the mine increases with increasing mining depth, the influence of temperature on the mechanical properties of cemented paste backfill (CPB) require attention. To address the problem of less research on paste performance in high temperature environments, uniaxial compressive strength tests of CPB at different temperatures were performed, and it was observed that temperature had a significant effect on the CPB strength. The CPB strength at a curing temperature above 40 °C deteriorated in the later curing time period, CPB at 65 °C was “crisp”, and the strength was lower than 40 °C in 3~28 days. Microscopic tests, such as thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) analysis, of the samples found that the coarsening of the pore structure of CPB was the main reason for the decrease in the strength caused by the increase in temperature. The effect of curing temperature on the deformation characteristics of CPB was studied. Different curing temperatures had a greater impact on the stress-strain curve and elastic modulus, and there was a linear relationship between the elastic modulus and strength. Finally, based on MATLAB, a back propagation (BP) neural network model of strength under different curing temperature conditions was established. Compared with the actual value and the predicted value, the average absolute error was less than 0.2 MPa, and the average relative error was less than 6%. This prediction model had a high accuracy. The research results provide a good reference significance for the strength design of CPB.

The influence of the mass concentration and particle size distribution on rheological parameters and slump was investigated by analyzing the mixture of overflow tailings (OT) and classified tailings (CT). The correlation between the rheological parameters, slump and characteristic value of the tailings particle diameter was discussed. Finally, the ratio parameters of a mixed tailings filling slurry were optimized using a lead–zinc mine in Guangdong, China as the engineering background. The results showed a quadratic decrease in the slump of the tailings slurry as the mass concentration increased, while the slump decreased with a decreasing particle size. With the increase in the mass concentration, the yield stress of the tailings slurry follows a quadratic function, while the plastic viscosity exhibits linear growth. The influence of tailings fine particles on the sensitivity of the yield stress and plastic viscosity to the mass concentration is reduced as their content increases. The yield stress and plastic viscosity of the tailings slurry exhibit a quadratic function decrease and linear growth as the slump increases. The slump of the tailings slurry is related to the particle size characteristic value and the mass concentration of the slurry. The correlation coefficient between the yield stress and the aggregate characteristic particle size increases most obviously at d₁₀~d₅₀, and the increase in the characteristic particle size will enhance the correlation between the yield stress and particle gradation. The correlation coefficient between the plastic viscosity and aggregate particle gradation parameters exhibits an initial increase followed by stabilization with an increasing characteristic particle size, with the most significant increase observed at d₁₀~d₅₀.

Rheological properties, such as the yield stress, viscosity, and thixotropy, are related to the microstructure of cemented paste backfill (CPB). To highlight the relationship, two instruments were combined to measure the changes in the microstructure and the rheological properties of CPB simultaneously. In this way, the particle/agglomerate size distribution characterized by the focused beam reflectance measurement (FBRM) and the rheological factors measured by the rheometers could be directly linked. The results show that when under shearing, the intrinsic network structure of CPB responds to the shear-induced stresses with the interference of interparticle forces, leading to changes in the rheological behavior. Shear thinning can be found in CPB suspensions with a microstructure that is either loose interconnection or random. With an increase in the shear rate, random collisions among particles become organized in the flow, lowering the yield stress and viscosity. However, when the shear rate exceeds a certain threshold value, the rheological parameters change as a result of shear thickening. The results of this study contribute to better understanding of the complex rheological behavior of CPB.