Study On The Influence Of Filling Performance Of Coal-Refuse-Based Composite Materials

As a by-product of coal mining and washing,the output of coal refuse increases rapidly with the growth of coal consumption.The accumulation of coal refuse occupies a large amount of land resources,causing serious waste of resources and environmental pollution.How to efficiently use coal refuse has received extensive attention.Using coal refuse as filling material to backfill goaf can effectively control surface subsidence,reduce the movement of overlying strata,improve the recovery rate of coal resources,realize green filling mining of coal mines,and promote the comprehensive utilization of coal refuse.In this paper,coal gangue and fly ash are taken as the research objects.Based on the analysis results of their physical and chemical properties,the effects of cement+fly ash content,gangue aggregate gradation and slurry mass concentration on the setting time,bleeding rate,slump expansion and compressive strength of filling materials are studied,and the ratio of filling materials is optimized.The strengthening effect of magnetic field on the filling performance of coal gangue matrix composites was studied,and the dissolution effect of heavy metals in the filling body was analyzed.The strengthening mechanism of magnetization on the filling properties of coal gangue matrix composites was revealed by means of X-ray diffractometer,scanning electron microscope and energy spectrometer,thermogravimetric analyzer,contact angle meter,mercury porosimeter and infrared spectrometer.The main results are as follows:（1）Select activators Na₂SiO₃,Na₂SO₄and NaCl and the dosage is 0.75%,1.5%and 2.25%,respectively;The dosage of cement and fly ash is 29%,with fly ash:cement=3:1;The aggregate grading is:the proportion of particles with particle sizes below 5 mm,5-10 mm,and 10-15 mm is 40%,31%,and 29%,respectively;The mass concentration of the slurry is 78%.The composite filling material ratio is cement:fly ash:coal gangue:water=7.25%:21.75%:49%:22%,and the resulting composite material has better performance in all aspects.（2）Magnetic field activated water can significantly improve the performance of filling slurry and filling body.Under the conditions of a water flow velocity of 4 L/min and a magnetic induction intensity of 1.2 T,the initial and final setting times of the filling material were shortened by 13.6%and 3%,respectively,and the compressive strength of the filling material increased by 15.7%after 28 days.Magnetic field activation reduces the cement content,which can be reduced by 1.5%under the condition of meeting the general filling compressive strength requirement of 5 MPa.（3）On the one hand,magnetic field activation can disrupt the C-S-H chain in the cement flocculation structure and release a large amount of free water,reducing viscosity.At the same time,the contact angle between the aqueous solution and the aggregate decreases,enhancing wettability,improving the slurryability and flowability of the slurry;On the other hand,it can improve the pore structure,reduce porosity,reduce harmful pore content,and improve the compressive strength of the filling body（4）The concentration of heavy metal ions in the leaching solution of the filling body is within the range specified by national standards,and will not cause pollution to groundwater;Adding an activator and magnetized water to the filling material can better solidify heavy metal ions;The hydrated calcium silicate gel and ettringite have high ion exchange energy in the development process,and have good solidification effect on heavy metals.