| In the process of coal mining,there are many unsafe factors,among which gas is the most common risk factor.Gas accidents have brought great economic losses and casualties to the coal industry,In production operations,borehole drainage is usually used to reduce the gas content in coal seams,and the quality of hole sealing directly affects the gas drainage effect.Therefore,the research and development of a mining hole sealing material with excellent performance is of great significance to the safety production of coal mine.At present,the most common is the cement-based hole sealing material,which has the characteristics of strong geological adaptability,simple configuration process and high economy.However,there are also defects such as unstable setting time,low early strength,easy collapse and cracking in the later stage,which will lead to the failure of hole sealing gas leakage and greatly affect the gas drainage efficiency of the mine.In order to improve the defects of the above cement-based sealing materials,this paper carried out relevant experimental research,and improved their related properties by adding nano,polymer and inorganic materials.After the cement-based material is mixed with nano silicon carbide,due to the high surface activity and micro aggregate effect of nano materials,it can provide nucleation points for cement clinker,and a large number of hydration products gather,which is conducive to the continuous and stable progress of hydration process.At the same time,some air will be introduced into the cement material during mixing,forming micro pores in the cement during mixing,Nano materials can fully fill the pores,so as to reduce the porosity of cement and make its structure uniform and compact.When subjected to external force,all parts are uniformly stressed,resulting in better mechanical properties.To sum up,this paper first explores the influence of nano SiC on the performance of cement-based materials.The experimental precipitation cement ratio is set to 0.4,and 0.2%,0.3%and 0.4%nano SiC are added respectively.Through the comparison of experimental data,it is determined that when the content is 0.3%,the cement performance reaches the best,and its compressive strength at 1d,3d,7d and 28d reaches 10.780mpa,20.335mpa,32.004mpa and 43.735mpa respectively,Compared with the blank control group,it increased by 50.41%,17.16%,16.15%and 25.70%.Through microscopic analysis,it is observed that nano SiC particles fill the internal pores of cement to make its structure compact.In the early stage of hydration,spherical adsorption structure and aft crystal can be obviously observed to provide nucleation point for hydration reaction products,and a large number of hydration products gather to accelerate the hydration reaction rate.On the basis of the above experiments,the paper continues to explore the influence of nano SiC composite polymer PVA on the early performance of cement.The experiment concludes that when the content is 0.3%nano SiC+0.2%PVA,the performance of the sample is the best,and its compressive strength at Id,3d,7d and 28d is 15.441mpa,26.091mpa,34.273mpa and 48.673mpa respectively,which is 115.45%,50.33%,24.39%and 39.89%higher than that of the blank group at the same age.PVA can effectively disperse cement particles and reduce the agglomeration of nano SiC particles,making the hydration reaction more sufficient.In the cement,the bridging effect between polymers forms a high-density tension membrane structure,which increases the compressive and flexural properties of cement materials.The addition of PVA will change the fluidity of the slurry,resulting in the change of the movement rate of calcium ions and other ions,which will affect the formation of CH crystal morphology.Ch crystal planes extend in multiple directions,and different ch crystal planes grow interactively to form a curved stacked plate structure,resulting in greater structural strength.Lithium sulfate can be combined with nano-sic and PVA to form a new type of early strength agent in ternary composite system.The experiment shows that the cement performance is the best when the content is 0.3%nano SiC+0.2%PVA+0.4%Li2SO4.The compressive strength at Id,3d,7d and 28d were 23.100mpa,28.358mpa,35.197mpa and 48.635mpa respectively,which were increased by 222.31%,63.39%,27.74%and 39.78%respectively compared with the blank group.Due to the small radius and strong polarization of lithium ion,it has better penetration than other cations.In the early stage of hydration,CH and C-S-H produced by the reaction will form a hydration film to cover the surface of cement particles.PVA and nano SiC are interspersed to form a polymer film to wrap the hydration products,which weakens the promotion effect of hydration reaction,and lithium ion is easy to penetrate these membrane structures,After penetration,the same ion effect will promote the exchange of calcium ions outside the membrane,thus damaging the hydration membrane structure.At the same time,PVA is wrapped on the outer surface of cement particles,hinders the agglomeration of cement particles through the double electron layer effect,and carries nano SiC and lithium ions to adsorb on the hydration membrane,further promoting the damage of lithium ions to the hydration membrane structure and promoting the hydration reaction rate of cement.Figure[35]table[7]reference[75]... |
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