Study On High Aeolian Sand Filling Material For Water Conservation Mining In Ecologically Fragile Area

The resource of shallow coal seam in west china is affluent.However,The large scale exploitation of it will seriously exert undesirable influence on local environment.Reducing the cost of filling materials is the key to the promotion of strip filling and water saving technology.Aeolian sand in west china is abundant.Therefore,the study of high sand filling material is the foundation of low cost filling and mining.Besides,the research has important theoretical meaning and practical value.The physical and chemical properties of aeolian sand were studied by means of laser particle size analysis,chemical analysis,scanning electron microscopy and X-ray diffraction analysis.The results show that the particle size of the aeolian sand is irregular,the edges are many and the surface is rough.The D50 represents 500 ?m.The sand that has a narrow particle size distribution and a fineness modulus between 1.21 and 1.36 can be classified as fine sand;The sand that has a 2.27 % average sediment percentage and a unevenness coefficient between 2.2 and 2.4 belongs to ill aggregates.But adding fly ash(D50 = 12.74?m)and cement(D50 is 19.73?m)will increase its ill gradation.Aeolian sand can be used for making high sand filling material that is filled with flexible strip on coal mine roadway.The effects of the ratio of mortar ratio,fly ash percentage,mass concentration,additive percentage and type on conveying performance and compressive strength were studied.Additionally,the microstructures and the mechanism of the admixture of high sand filling materials were studied by scanning electron microscopy(SEM).High sand filling material with mortar ratio 1:14 was made for meeting the requirments of strip filling properities.Finally,it was confirmed that the mass ratio of cement,fly ash and aeolian sand was 1: 2: 14,that the mass concentration was 84%,that the naphthalene superplasticizer was1.5%,that the sodium type was coagulant 3% and that triethanolamine type early strengthagent is 0.04%.As the results shows,the increasing mass concentration is not conducive to the filling of paste fluidity but decreases filling paste bleeding rate and initial setting time.It can enhance early strength.However,the long-term strength decreased.As a result,the decreasing long term strength will increase the aeolian percentage,which gives rise to poor filling paste fluidity and high bleeding rate.Eventually,It has little influence on condensation time.For same amount,the compressive strength increases with increasing age.The addition of fly ash increases the flowability of the paste and reduces the bleeding rate,which can delay the setting time and the optimum amount of fly ash.With the increase of fly ash content,the compressive strength of each age gradually increased.When the fly ash content increased to greater than 1:2,its long term strength(90d and 180d)decreased.The incorporation of concrete admixture can effectively control the performance of the filling material.The effect of polycarboxylate superplasticizer is better than that of naphthalene super plasticizer,but it has certain inhibitory effect on cement hydration.Sodium sulfate and triethanolamine,a early strength agent,increases the 8h intensity of filling material.But the sodium sulfate remarkably reduces the long term intensity of filling material.If adding setting acelerator to it,its condensaton time will be largely shortened and the early strength will be increased at the cost of long-term strength.So,stir fastener dosage should be strictly controlled.In general,the ratio of plasticity,bleeding rate and coagulation time to meet the performance requirements of strip filling and transportation are better than those of the high sand filling material with the ratio of sand to sand ratio of 1:14.The stability and water retention are better.The compressive strength of the test piece can reach 0.338 MPa and 2.16 MPa respectively for 8 h and 28 d respectively,which can meet the requirements of the compressive strength of the filling body,provide the economical filling material ratio for the strip filling and water conservation.It is importantly significant for ecologically fragile mining area in northern Shaanxi and Ordos to do water presevered mining.