Study On Preparation And Properties Of Filling Material In Coal Mined Area

Coal mining for several years has left surprising mined areas,In order to prevent the surface subsidence,to ensure the safety of people's lives and property,the coal mined out underground voids need to be filled.Smelting metal magnesium to consume a lot of energy sources,so most of the metal magnesium plants built near the coal base.Magnesium slag is the waste residue produced during the smelting process of metal magnesium,most of the plants stacked or landfilled,which not only takes up land but also causes environmental pollution.This paper proposes that use magnesium slag to prepare low-cost filler material to fill the coal mined out underground voids.In this paper,two kinds of pastes with different properties were prepared with the main raw materials of magnesium slag for different areas of mined areas.The physical and chemical properties of the pastes were compared by physical property test,expansion amount measurement,XRD,SEM and so on.Then the optimal ratio of the filling was obtained.At the same time,a foaming agent was prepared to prepare a foamed concrete filling material that would satisfy the requirements of the general backfill.Through the above experimental data analysis,the following conclusions are drawn:(1)The compressive and flexural strength of the high strength magnesium slag paste decreases with the increase of the content of magnesium slag.The contents of C-S-H and Ca(OH)2 in the hydrated products were decreased with the increase of the content of magnesium slag.The proportion of magnesiumslag paste is 50% of magnesium slag content,10% of fly ash content,40% of cement content.The 3d compressive strength is 21 MPa,28d compressive strength is 42 MPa.The ratio of magnesium slag paste after curing for 200 d,the expansion rate is 0.44%,with micro-expansion.(2)The water-cement ratio of low-strength magnesium slag paste is relatively small,so the slurry fluidity is poor.Mixing the right amount of fly ash can improve the fluidity of the slurry,but with the increase of fly ash content,the compressive strength of the paste gradually decreased.The setting time of the paste is affected by the water-cement ratio.Comprehensive comparison of various factors on the performance indicators,choose the best plan for the cement content is 10%,ash slag ratio is 1:1.4,water-cement ratio is 0.32.In this ratio,the slurry fluidity is 19.8cm,the setting time is 17.5h,and the 28 d compressive strength is 16.19 MPa.(3)A complex type of foaming agent was prepared by using sodium dodecyl sulfate(K12)and calcium stearate.The foam multiple is 28,1h sinking distance is 1mm,1h bleeding capacity is 8ml.When the cement content is 10%,ash slag ratio is 1:1.4,water-cement ratio is 0.32,the foam content is 0.5m3/m3,the dry density of the prepared wet-density foamed concrete is about a half of the wet density.And the growth law of 28 d compressive strength and dry density accorded with the power function.In the SEM image of the foamed concrete sample can be seen when the wet density is large,the pore size is small and the thickness is uniform,all of which are independent closed holes.When the wet density is reduced,the pore size is significantly increased,the cellular is not uniform,and there are communication holes.From the foamed concrete sample pore size differential distribution curve can be seen on the wet density of 1700kg/m3 sample pore distribution is mainly concentrated in the 100 ~550nm,and the pore distribution of the samples with the wet density of 1400 ~1600kg/m3 are mainly concentrated in the range of 200 ~ 1500 nm.The compressive strength of the foamed concrete sample decreases generally with increasing porosity and average pore size.The effect of macroporous porosity on compressive strength is more important.