| Many environmental issues were caused during the process of coal production, such as worked-out area subsidence, coal gangue and fly ash piling. Paste backfill technology was an important part of green mining technology. But it had some deficiencies, such as the poor adjustability in performance, the lacking science in material mixture ratio, the high cost in backfill materials, etc. Therefore, the research of foam paste backfill materials prepared by coal solid wastes was proposed to overcome or improve the deficiencies of paste backfill materials, which might provided the basis for the preparation of high performance backfill materials. Firstly, the activity of fly ash was stimulated by chemical methods, the effect of activator kinds, contents and curing age were mainly considered, the hydration products and microstructure were analyzed by XRD and SEM. Secondly, the influence of the ratio of raw materials on the working performance was explored using the single-factor test method. Finally, taking the long-term compressive strength as the indicator, the main proportioning parameters of foam paste backfill materials were optimized by using the method of orthogonal test, and its microstructure was also analyzed.Research of fly ash activation stimulation showed:1)Compared with CaCl2, KOH, the compressive strength of fly ash-cement cementations material could significantly increase by adding Na2SO4. Its compressive strength increased with the increase of curing period and Na2SO4. When the content of Na2SO4was3%,7d compressive strength of specimens was increased by37.3%and the28d compressive strength increased by82.4%;2)XRD, SEM and EDS analysis showed that there was a lot of needle bar AFt and CSH in fly ash-cement cementations material with3.0%Na2SO4. The hydration of fly ash particles was in good condition.Research on working performance of foam paste backfill materials showed:1)The fluidity increased with the increase of the ratio of water to materials, coal gangue, water reducing agent, and decreased with the increase of foaming agent, bentonite. The tendency of the fluidity of foam paste backfill materials with different contents of fly ash and coal gangue showed slight difference in different water conditions;2)The setting time increased with the increase of the ratio of water to materials, fly ash, coal gangue, foaming agent, and first decreased and then increased with the increase of accelerating agent Na2SiO4, bentonite had little effect on the setting time;3)The dry density decreased with the increase of the ratio of water to materials, fly ash, coal gangue, foaming agent, and first decreased and then increased with the increase of bentonite;4)When the content of bentonite was2.0-4.0%, the pore structure and apparent molding effect were significantly improved.The strength and optimization research of foam paste backfill materials showed:1)The factor order influenced the compressive strength of foam paste backfill materials was as follow:foaming agent> coal gangue> fly ash> the ratio of water to materials.2)The optimization result of foam paste backfill materials was:0.65-0.75the ratio of water to materials,55～65%fly ash,1:0.6～1:0.8the ratio of cementitious materials to coal gangue,2.0～3.0%foaming agent,3.0%bentontie,6.0%accelerating agent,3.0%activator agent,1.5%water reducing agent, some lime and gypsum. Under this condition, foam paste backfill materials could got a better comprehensive performance, its fluidity was16.5～20.0cm, dry density was300-450kg/m3, the initial and final setting time was50～350min and175-550min,28d compressive strength was larger than0.5MP, and apparent molding effect was better;3)With the increase of the dry density, pore microstructure showed a certain regularity. The aperture changed bigger, pore distribution changed more heterogeneous, pore wall changed thicker, hydration products changed more compact, a lot of AFt and CSH generated gradually, the hydration particles formed a coherent whole. |
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