Study On Improving Mechanical Properties And Constitutive Model Of Modified Magnesium Slag-based Filling Materials

Modified magnesium slag-based filling material is a new type of solid waste cementing filling material,which is mainly made by mixing and mixing magnesium slag,fly ash and coal gangue in different proportions with water.Magnesium slag and fly ash are used as cementing materials to replace cement in traditional cementing filling materials.The implementation of the concept can reduce the stacking of solid wastes such as magnesium slag and gangue,reduce the use of cement,save the cost of coal mine filling,and provide a green and efficient solution for resource utilization and coal mine filling.In order to explore the pore structure characteristics and mechanical properties of modified magnesium slag-based filling materials under different cement-sand ratio,slurry concentration and fly ash content.In this paper,13 groups of specimens with different proportions of modified magnesium slag-based filling materials were set,and the pore structure parameters and mechanical property parameters of the filling materials were obtained by NMR test and macro mechanical test respectively.Finally,according to the influence of initial defects such as internal pores on the mechanical properties of the modified magnesium slag-based filling material,the damage strengthening coefficient determined by porosity and average pore diameter was proposed,and the damage strengthening constitutive model of the modified magnesium slag-based filling body was established based on the damage strengthening coefficient.The research contents and results are as follows:(1)The cement to sand ratio,slurry concentration and fly ash content have great influence on the pore structure and mechanical properties of modified magnesium slag-based filling materials.Among them,the contrast ratio,concentration of slurry and the pore structure parameters of filling material is a negative correlation,and mechanics performance parameters appear positive correlation,that is to say,the contrast and slurry concentration,the greater the modified magnesium slag filling material of porosity and average pore diameter is smaller,the uniaxial compressive strength,residual strength and elastic modulus.(2)The content of fly ash can greatly affect the cementitious property of magnesium slag-fly ash cementitious material.The results show that when the cementitious material contains 40%fly ash,the pore development and mechanical properties of the modified magnesium slag-based filling material are the best.When the fly ash content is more than 40%,the pore size and porosity of the modified magnesium slag-based filling material become larger,and the mechanical properties become worse.(3)The pore structure of the modified magnesium slag-based filling material has a great influence on its mechanical properties,and there is a nonlinear relationship between the porosity and average pore size and the strength of the filling material.(4)The failure process of modified magnesium slag-based filling material under uniaxial compression is mainly caused by the appearance,expansion,convergence and increase of main cracks.Combined with the damage constitutive model,it can be seen that when the damage variable is about 0.25,the stress reaches the peak,the stress-strain curve shows a downward trend,the damage growth rate increases,and the filling material is prone to damage.(5)The constitutive model of the curve is obtained by theoretical model calculation compared with UCS test curve,the results show that the proposed modified magnesium slag base filling body damage constitutive model and the uniaxial compression test results are in good agreement,can effectively describe the modification of magnesium slag base filling body under uniaxial compression condition of damage evolution law and the development process of the stress-strain curve.