| Paste backfilling mining is effective manner to coal resources under village,water and road. With solid waste including gangue and coal as main rawmaterial, Cement paste backfilling (CPB) for coal mining is important way tosolve environmental pollution of solid waste. As a result, paste backfillingmining is important part of green mining. CPB is a key factor for fillingcontrolling subsidence effectively and monitoring and evaluating of filling effectis major step to improve cement paste filling system. On the basis of CPBresistivity property, this paper focuses on active characters of raw materials, theinfluence of raw materials content on the CPB properties, the relationshipbetween stress and electrical resistivity with the uniaxial loading, and evaluationof filling effect via high density-resistivity method by using experimentalmethod, theoretical analysis and numerical simulation. Some innovation resultsare discovered.In order to investigate the pozzolanic reaction degree and active ionsdissolution of gangue powder and fly ash in different concentration Ca(OH)2solution in48hours dissolving time. The mineral, micromorphology andinfrared spectrogram of residue in different dissolving time were analysed byX-ray diffraction (XRD), field emission transmission electron microscopy(FETEM) and Fourier Transform Infrared Spectrum (FT-IR), the active ionconcentration and conductivity of filtrate were measured by inductively coupledplasma optical emission spectrometer (ICP-OES) and conductivity meter. The results indicate that:1. The gangue has pozzolanic activity after grinding, thevariation trend ofAl3+、Fe3+、Si4+ions concentration appeared similar in1mol/Land0.1mol/L Ca(OH)2solutions with increasing dissolving time, it appearedtwo peaks at6and24hour; It resulted in dissolving active ions that change ofAl-O and Si-O bond energy from kaolinite in gangue, the longer time ganguedissolved, the more clearly change of bond energy appeared; Themicromorphology of gangue went through from bareness of flaky mineral, toadhesion of lamelliform Ca(OH)2crystal, and then precipitate of small activeparticle, finally generation of petals shape products transforming into needle-likeor pillar-like products; The conductivity of1mol/L and0.1mol/Lgangue-Ca(OH)2solution appeared decreasing tendency, the degree ofpozzolanic reaction in1mol/L Ca(OH)2solution appeared higher than in0.1mol/LCa(OH)2solution.2. The fly ash also has pozzolanic activity, it hassimilar variation of active Al3+、 Fe3+、 Si4+ions concentration in1mol L-1Ca(OH)2solutions compare to0.1mol L-1Ca(OH)2solutions with increasingdissolving time: concentration of Al3+、Si4+ions appears two peaks at6and24hour; Fe3+ion concentration appears decline; Conductivity of1mol L-1and0.1mol L-1fly ash-Ca(OH)2solution shows decreasing tendency, the degree ofpozzolanic reaction in1mol L-1Ca(OH)2solution appears higher than in0.1molL-1Ca(OH)2solution.The cement paste backfill (CPB) in coal mining is normally made ofgangue (particle size0-15mm), fly ash, cement and water. In this study, theeffects of the content (ranging from20%to60%) of fine gangue (0-5mm) andthe fly ash content on the microscopic characteristics, resistivity andcompressive strength of CPB were investigated at differengt curing times,respectively. The test results indicate that1. The strengths of the CPB, regardlessof the curing time, increased with fine gangue content changing from20%up to40%. Further increase in fine gangue introduced a decrease in the strength. This is due to the increase in products from hydration and pozzolanic reaction withfine gangue content and the microstructure change of CPB. Another observationis that, at3days, a general increasing trend of CPB resistivity was noted withfine gangue content, which could be attributed to a dense structure and low ionconcentration in pore solution caused by high fine gangue content. At28days,the resistivity of CPB decreased with increase in the fine gangue content, whichenhances interfacial transition zone effect and increases ion concentrations ofpore solution. Though fine gangue addition was found to minimize the criticalpore size of CPB at later curing stage, it seems not to dominate the resistivity ofCPB. Correlations between the resistivity and compression strength of CPBshow a concave pattern, which indicates using resistivity to derive strength ofCPB is not appropriate.2. The resistivity decreased with increasing fly ashcontent and compressive strength did not take obvious change. As increasingcuring time, compressive strength exhibited increased, which attributed tohigher content of pozzolanic products and lower content of large pores, theincrease resistivity due to the total concentrations of the ions in the pore solutiondecreased, moreover, pore network system was related to the ability oftransporting current. Using the method of least squares regression, thecompressive strength values were correlated with the resistivity value for CPBsamples. A linear relation with high correlation coefficient appeared to exitsbetween the compressive strength and resistivity for CPB samples.Traditional rock mechanics method was used in the test. This paperinvestigated stress-strain curve of CPB at early curing time for the nature andmine water curing condition when the specimen of CPB was in the process ofuniaxial loading. The four stage of deformation was also analyzed, the variationof pH value and conductivity of mine water was investigated. The effect of porestructure on the stress-strain-resistivity at different curing condition was studied.The function correlations of stress and resistivity under the different curingcondition at the front and behind of stress peak were provided, for the sake for calculating the resistivity of paste backfilling body.This paper presents the situation of Xinyang Collery, the component of pastefilling system, coal backfilling technology and raw material ratio. On the basisof the specific geological conditions of filling surface, resistivity of overlyingrock were determined. According to formula of early backfilling body strength,the resistivity of backfilling body at the different stage of mining was calculated.The feasibility of resistivity using in filling effect was discussed. Taking forwardmodeling software, resistivity models of backfilling body and overlying strata indifferent stages were established. In the process of filling mining, the variationof apparent resistivity curve shape and value was discovered by the apparentresistivity profile of inversion calculation, which plays an important role inassessing the backfill effect via high density resistivity. The field assessment forbackfill effect in Xinyang Collery was taken by resistivity evaluating fill effectmethod. Contrast to the forward and inversion numerical modeling results, itproved the feasibility of using resistivity to assess the backfilling effect. |
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