| In coal mines,gas issues show up during production.Thus,plenty of measures are taken to get ride of gas burst,in which the most notable is gas drilling drainage.However;the efficiency of drilling drainage is affected by the quality of sealing.At present,the most widely adopted sealing material is cement-based material for it cheap price and better effect Whereas,certain disadvantages exist despite of its advantages,which can not fully satisfy the demands of actual sealing.Namely,the early-strengthen can not meet the requirement in high humidity conditions in coal mine and its solidification and hardening time is relatively long,leading to low sealing effliciency.In the meantime,the shrinking phenomenon occurs after its solidification,which results in air leakage because of the voids.On account of those problems,modification treatment are made on cement-based sealing material,which can enhance the sealing quality.In this paper,experimental researches are made on sealing material.In the first place,a kind of compound agent are studied aiming at the first problem.Various of early-strengthening compound agents are confected by orthogonal experiment and their influence on the early-strength of cement-based sealing material is studied.Then,the hydration reaction of cement and its products are analyzed by means of scanning electron microscope,thermogravimetry and X ray diffraction.Additionally,its microstructure is studied and working mechanism is summarized.Throughout experimental research,the optimal combination is as listed below:0.5%Na2So4,0.5%NaCl,0.05%triethanolamine and 1%AMPS.This compound improves the strength of cement-based sealing material.In detail,the early compressive strength is 4.38 times higher than that of the baseline group in 1st day.And its strength increased to 2.19 times at the end of 3rd day,which indicates an obvious early-strengthening effect Besides、it mechanism is studied by scanning electron microscope,which shows that the compound early-strengthening agent only accelerates hydration process without changing the category of hydration products,further enhancing early-strengthen of cementSecondly,a kind of microencapsulated expanding agent investigated for the air leakage problem of cement-based sealing material.On the basis of microencapsulated technology,the expanding agent is microencapsulated with polyacrylamide as capsule wall and powdered aluminium as capsule-core.Thus,the balanced development of strength and expansion can be maintained at the same time.With a mixture of 1%expanding microencapsule,its expansion effect is evident that the delayed expansion time is about 4 hours and the ultimate expansion rate rises up to 35.2%compared to baseline group.Afterwards,the modified cement is analyzed by means of scanning electron microscope,showing that its has a integral structure and its hydration products are thick,which enables a rational utility of expansion energy.In addition,the early-strengthening component and expansion component are further compounded,resulting in early-strengthening expanding sealing material.Its component and proportion is as followed.Ordinary portland cement:water:sodium chloride:sodium sulfate:triethanolamine:AMPS:sodium aluminate:aluminum powder microcapsule,according to the mass percentage of 100:55:0.5:0.5:0.05:1.0:1.0:0.1 mixed.Moreover,the powdered aluminium microencspsule is manufactured by water,polyacrylamide and powdered aluminium as a mass ratio of 100:2:2.Consequently,the compressive strength enhances to 3.77 times than that of the baseline group in 1st day and 1.79 times at the end of 3rd day.Besides,its expanding time extends to 4 hours with its ration going up to 27.5%. |
PDF Full Text Request