Thixotropy Of Molybdenum Tailings Cement Slurry And Mechanical Properties Of Stone Body For Filling Hollow Goaf

The coal mine hollow goaf is a huge space left after the completion of underground coal resource mining.It is an unstable artificial geological structure that can degrade and lead to ground collapse,mine earthquakes and other mine hazards.The best way to deal with the goaf is the grouting filling method,but this method is easy to cause material waste,and due to its large fluidity and uncontrollable flow range,it is easy to cause problems such as poor filling compactness and large empty roof.In this study,a new grouting material suitable for cavitation goaf was developed by adding solid fine-grained molybdenum tailings to thixotropic cement slurry after smelting molybdenum ore,and through laboratory tests and model tests.The material takes advantage of the characteristics of thixotropic slurry,solves the difficulty of difficult control and accumulation of traditional grouting materials,and saves the amount of natural sand,which has good economic and social benefits.The following results were achieved:(1)The ratio of thixotropic molybdenum tailings cement slurry was designed by orthogonal experiment,the thixotropy,water evolution rate and compressive strength of the corresponding stone body were tested under different mixing ratios.The optimal ratio of molybdenum tailings cement slurry is as follows: the addition amount of positive adhesive is 6%,the water-cement ratio is 0.8,and the solid ratio(molybdenum tailings: cement)is6:4.The influencing factors of thixotropic coefficient are as follows: the amount of positive adhesive < solid ratio < water cement ratio;The size of the influencing factors of the rate of water separation: solid ratio < the amount of positive adhesive added < water cement ratio;The influencing factors of the compressive strength of the stone body are as follows: solid ratio < positive adhesive content < water cement ratio.(2)A new method to evaluate the thixotropic properties of thixotropic grout,namely the thixotropic coefficient method,is proposed.The ratio of the difference between the static yield stress after standing for 10 min and the difference between 180×(1+the percentage of positively charged glue added)and the static yield stress at the initial time is used to evaluate the thixotropic size of thixotropic grout.(3)The rheological characteristics of thixotropic molybdenum tailings cement mortar are analyzed.The shear rate,shear stress and viscosity of the optimal ratio conform to the power rate rheological model and power function relationship respectively.The shear stress and viscosity of the slurry increased with the increase of the amount of positive adhesive,decreased with the increase of water cement ratio,and increased with the increase of solid ratio.(4)The effects of positive adhesive amount,water cement ratio and solid ratio on mechanical properties of thixotropic molybdenum tailings cement mortar were analyzed.The axial compressive strength,static elastic modulus,splitting tensile strength,flexural strength and compressive strength after high temperature calcination of the grout stones increased first and then decreased with the increase of the amount of positive adhesive.All showed a decreasing trend with the increase of water cement ratio.Both showed an increasing trend with the increase of solid ratio.According to the known compressive strength,the prediction formulas of static elastic modulus,flexural strength,splitting tensile strength and compressive strength at high temperature are given.(5)The results show that the accumulation height of the cement slurry of thixotropy molybdenum tailings is positively correlated with the flow distance,and the flow distance of the slurry tends to slow down with the increase of the accumulation height.The function relationship among the accumulation height,grouting time and flow distance is fitted.The accumulation effect of the two groups with positive adhesive content of 6% and 10% is similar,and the slurry can be piled up to a certain height within a limited flow distance,which has a good accumulation effect compared with ordinary cement slurry.Therefore,thixotropic molybdenum tailings cement slurry has good development prospects and practical value in coal mine goaf treatment engineering.