Study On Preparation And Properties Of Cement-fly Ash Composite Materials For Leakage Blocking In Mine

Coal spontaneous combustion in goaf is one of the major natural disasters seriously endangering mine safety production.Sealing and controlling air-leakage is the key to prevention of coal spontaneous combustion.As mining stress changes resulting from mining depth increase,the coal mine area such as small coal pillar appear fractures and cracks in large area of under pressure disturbance,which not only causes air leakage channels in adjacent goaf,but also seriously increases the risk of coal spontaneous combustion in goaf.However,the commonly used organic leakage blocking material is put in the coal mine problem such as heat,easy to promote coal spontaneous combustion;inorganic leakage blocking material such as cement-guniting material gelling time is not controllable,large-scale application of the high cost.Therefore,it is particularly important to develop a kind of leakage blocking material with low cost,good leakage blocking and strengthening effect,adjustable gelling time.On the basis of summarizing cement-based inorganic plugging material and combining with the national demand for the utilization of solid waste of fly ash,this paper developed a cement-fly ash composite material.The research results are as follows:The hydration mechanism of cement,fly ash and water glass of cement-fly ash composite materials are studied,including the solid phase reaction theory and solution theory of cement,the theory of pozzolanic reaction of highly active substances in fly ash,the effect of sodium silicate on quick-setting and strengtheing of cement clinker and alkaline excitation effect of fly ash,analyzing the interaction between composite components,proving an important reference for improving the reaction efficiency of composite materials.The influences of single factors,such as water cement ratio,sodium silicate content and fly ash content,on the properties of the gelation time,fluidity,concretion ratio and bleeding ratio of cement-fly ash composites were studied and analyzed.On this basis,orthogonal tests were designed to optimize the ratio of the three factors.The range analysis results show that when the water-cement ratio is 0.6,the fly ash content is 30%,and the sodium silicate content is 3%,the gelling time of cement-fly ash composite material can be controlled at about 30min,which can meet the practical needs of the project.Rheological properties of cement-fly ash composites were studied,the rheological constitutive equation of the cement-fly ash composite material was established,the change law of cement-fly ash composite material viscosity with shearing time was studied,and the velocity distribution and pressure drop equations of cement-fly ash composite material.Steady-state rheological experiments show when the shear rate is from 0.1s^-1 to 100s^-1,the cement-fly ash composite material show obvious shear thinning characteristics;through the fitting experiment results,it is found that the cement-fly ash composite material belongs to the pseudoplastic fluid,and the constitutive equation of the preferred cement-fly ash composite material in this article is obtained.The effect of shear time on the rheological properties of cement-fly ash composite material was studied.It was found that the viscosity of composite material increased with the extension of shear time,which provides the basis for the field leakage and diffusion range.When the cement-fly ash composite material flows in a kilometer pipeline at a speed of 20m³/h,it is laminar flow movement,and its pressure drop is 1.0778MPa.The reinforcement performance and air plugging performance of cement-fly ash composite materials are studied.The universal testing machine was used to test and analyze the compressive strength of different grouting amounts（180ml,200ml,220ml）,different particle sizes of broken coal（<5mm,5～20mm,>20mm）and different ages（3d,7d,14d,28d）.The experimental results showed that the compressive strength of consolidated body at different ages increases with the increase of grouting amount and particle size of broken coal.At the same time,the plugging air leakage of cement-fly ash composite material were studied by using eself-made plugging wind testing device.The negative pressure of the vacuum chamber reduced by-3.23KPa to-15.63KPa after cover crushing coal using cement-fly ash composite material,which suggested the cement-fly ash composite material seeps and diffuses through the broken coal,covers,wrapping and finally consolidating the broken coal as a whole,and has a more obvious effect of plugging the leakage wind.Aiming at the phenomenon that the small coal pillars appear fracture development or lamping phenomenon and serious air leakage between 3106 return airway and 3104 goaf in Menkeqing Coal Mine,it is proposed to use cement-fly ash composite material to wrap the broken coal body and block the air leakage.This paper contains 47 figures,16 tables and 88 references.