Study on time-dependent characteristics of rheological parameters on high-concentration slurry in treatment of coal mining subsidence area

In order to accurately grasp the size and shape of deposits formed by high-concentration slurry in the gob, it is of great significance to study the rheological characteristics of the high-concentration slurry over time for the grouting filling in the gob. This paper makes a preliminary study of the effects of cement as cementitious materials and standard sand as aggregates on the rheological properties of high concentration filling slurry under a series of samples with different bone-cement ratios and time. The test results show thatwhen the shear rate is increasing from 0 to 60 s-1, the shear stress and apparent viscosity of the slurry will suddenly increase to a certain value and then decrease. In the process of decreasing the shear rate from 60 to 0 s-1, shear stress and apparent viscosity of the slurry decrease linearly. When the shear rate increases, the corresponding shear stress and apparent viscosity are greater than that when it decreases, and the slurry has significant thixotropy. When the shear rate decreases from 60 to 0 s-1,the slurry conforms to the Bingham model, and the shear rate reduction process satisfies the actual working conditions of high concentration slurry filling the gob.Using the Bingham model to obtain the plastic viscosity and yield stress of the slurry at different times, it was found that as the standing time increases, the yield stress and plas tic viscosity of the high-concentration slurry increase as a whole, and the thixotropy increases as a whole. Under the same standing time, the more the proportion of aggregate, the greater the plastic viscosity and yield stress of the slurry. The rheological properties of high-concentration slurry over time are mainly affected by the tricalcium silicate reaction. The acicular hydrated calcium silicate directly affects the viscosity, yield stress and thixotropy of high-concentration slurry over time. Within 2 hours, the bridging effect of acicular hydrated calcium silicate between the sand particles increases the viscosity, yield stress and thixotropy of the high-concentration slurry. When the water-cement ratio is constant and the cement hydration reaction is constant, the more aggregate, the thinner the film formed by the cement slurry on the aggregates, and the more needle-like hydrated calcium silicate is generated between the aggregates. According to the experimental data, the formulas of plastic viscosity and yield stress with time are fitted, which provides a certain basis for the setting of key parameters in the subsequent high-concentration slurry filling process.