Study On Preparation And Microstructure Characteristics Of Modified Magnesium Slag-based Backfill Material

As a new type of cementitious material,modified magnesium slag can be reasonably and effectively applied to mine backfill,which is of great significance to the sustainable development of the mining industry.Therefore,the exploration and research of modified magnesium slag-based backfill materials is imperative.The modified magnesium slag-based backfill material uses modified magnesium slag and fly ash as a binary cementing system and aeolian sand as fine aggregate to prepare a new type of solid waste backfill material.This design concept conforms to the principles of environmental protection,solid waste utilization,and economy and practicality,and can provide a green way for the selection of mining backfill materials.In this study,a series of researches were carried out on the preparation and performance evaluation of modified magnesium slag-based cementitious materials and the microstructure characteristics of modified magnesium slag-based backfill materials by using a combination of laboratory experiments and theoretical analysis.First,the basic properties of modified magnesium slag-based cementitious materials are studied,and the strength and slump of the two important indicators are evaluated using non-dimensional analysis and multiple linear regression analysis,and the optimal plan is selected and mixed with aeolian sand.The pore structure evolution law and mechanical properties of modified magnesium slag-based backfill materials are studied,and the relationship between fractal dimensions,pore structure parameters,and uniaxial compressive strength are explored.Finally,by observing the morphology and analyzing the hydration products,Reveal the mechanism of pore structure and macroscopic mechanical strength changes.The main conclusions drawn are as follows:(1)The basic performance of the modified magnesium slag cementitious material is greatly affected by the water-cement ratio and the amount of fly ash.Among them,the uniaxial compressive strength decreases with the increase of water-cement ratio,and shows a trend of first increase and then decrease with the increase of fly ash content;with the increase of water-cement ratio,the slump increases,and the initial and final setting time are delayed by about 3h.And 2.25h,with the increase of fly ash content,the initial and final setting time was delayed by 6h and 7.5h,respectively,and the slump increased,but the increase became smaller.(2)Using non-dimensional analysis and comparison,the fly ash content is the main factor affecting the strength of the cementitious material,and the water-cement ratio is the main factor affecting the slump of the cementitious material.And discuss the interaction of different independent variables on uniaxial compressive strength and slump,estimate the parameters of the independent variables,establish a regression model,and use SPSS to perform binary linear regression analysis to obtain linear regression equations under different curing times.The predicted value and the measured value are linearly fitted,combined with the actual proportioning scheme,and finally the optimal blending amount of fly ash is 15%and the water-cement ratio is 0.40.(3)The uniaxial compressive strength of the modified magnesium slag-based backfill sample is positively correlated with the mass concentration,and negatively correlated with the aeolian sand content.Taking 28 days as the maintenance standard,the aeolian sand content is 60%.The mass concentration is 80%and 82%,the uniaxial compressive strength reaches 3.425MPa and 4.145MPa,respectively,the aeolian sand content is 40%and 50%,and the uniaxial compressive strength reaches 5.776MPa and 4.574MPa respectively,meeting the requirements of mine backfill Mechanical strength requirements.(4)The critical pore size and threshold pore size will migrate to a smaller pore size range as the mass concentration increases and the amount of aeolian sand decreases.The harmful large pores gradually change to harmless small pores,and the pore structure is refined,and the pore size distribution and porosity performance Consistency;there is no obvious functional relationship between fractal dimension and porosity.There is a good correlation between fractal dimension and characteristic pore size and uniaxial compressive strength.Among them,fractal dimension and characteristic pore size are both negatively linearly correlated with single The axial compressive strength is positively correlated;in addition,the porosity has a negative linear relationship with the uniaxial compressive strength.(5)Using microscopic morphology and hydration product analysis,we can observe flocculent C-S-H gel,layered Ca(OH)2,fine needle-shaped AFt and unhydrated fly ash particles,etc.;with XRD Test methods such as FTIR,TGA,etc.qualitatively analyze the diffraction peak intensity of hydration products,the migration of chemical bonds,and the change characteristics of mass loss.