Experimental Study On Filling Material Properties Of Powdered Coal Ash Paste In Goaf

With the massive exploitation of coal resources in China,the goaf left behind by underground mineral resources exploitation and the large amount of waste left behind by coal combustion have become a serious problem facing the national environment.Therefore,making full use of waste filling materials to fill mined-out areas has become the basis of paste filling materials in coal mines.In this paper,fly ash and coal gangue waste as the base material,using the method of orthogonal test,first study the performance of paste filling material with fly ash as the base material without additives,and then compare the performance of paste filling material with fly ash and coal gangue as the base material with additives.Results The test showed that:(1)Under the condition of no additives:(1)The fluidity and viscosity of the powder coal ash paste filling material are mainly affected by the mass concentration of the slurry,and too small flow and too large viscosity are not conducive to the transport of the paste filling material;(2)The setting time of coal ash paste filling material is mainly affected by the content of fly ash.With the increase of fly ash content,the increase rate of setting time of pulverized coal ash paste backfill material slows down,and there is no negative value,and the initial setting time of pulverized coal ash paste backfill material increases.With the increase of cement content in different gradients,the increase and decrease of setting time of pulverized coal ash paste filling material are basically the same,and the initial setting time decreases first and then increases.The setting time of pulverized coal ash paste filling material can be shortened by increasing the appropriate cement content.(3)The early compressive strength of pulverized coal ash paste filling material is mainly affected by the cement content;(4)The late compressive strength of the filling material of coal ash paste is mainly affected by the content of fly ash.Through this test,it is concluded that the optimal ratio of coal ash paste filling material to fill goaf is fly ash: cement: sand:loess = 4:6:1:1,and the paste mass concentration is 68%.Under this ratio condition,the filling paste's fluidity and compressive strength effect are consistent.(2)Under the condition of additives:(1)The collapse degree of the pulverized coal ash paste filling material is mainly affected by the mass concentration of the filling slurry,and too small collapse and too large viscosity are not conducive to the transportation of the pulverized coal ash paste filling material;(2)The setting time of paste filling material is mainly affected by the mass concentration of slurry,and the accelerating agent has a great influence on the mass concentration of paste filling material.(3)With the increase of slurry mass concentration of the pulverized coal ash paste filling material,the change of compressive strength of the pulverized coal ash paste filling material at the early stage firstly showed negative growth and then increased,leading to the decrease of the compressive strength of the pulverized coal ash paste filling material at first and then increased.Through this test,it is concluded that the optimal ratio of coal ash paste filling material to fill goaf is fly ash: cement:coal gangue: fine sand: loess = 2:3:4:0.5:0.5,and the mass concentration is 75%.Compared with the non-additive powder coal ash paste filling material,the additive powder coal ash paste filling material uses coal gangue more effectively,shortening the setting time and improving the compressive strength.