Research And Development Of Coal Gangue Foam Concrete And Its Performance

In 2022,China’s total coal production exceeded 4.56 billion tons,accounting for 52percent of the world’s total.Coal gangue is a solid waste from coal mining,accounting for15-20%of coal output.When discharged directly to the surface as a waste pile,it will occupy a large area of land and cause environmental pollution.Coal seam fire is a major disaster in coal mine production.In order to prevent coal spontaneous combustion,it is necessary to build sealing walls in local areas such as leaky roadway and goaf in working face.Therefore,a kind of coal gangue foamed concrete for coal mine is developed in this paper.In this paper,cement,coal gangue and fly ash are used as cementitious materials,and physical foaming method is used to study the coal gangue foamed concrete.Through single factor experiment and orthogonal design experiment,the influences of foam content,water-binder ratio,coal gangue content and fly ash content on dry density,compressive strength,water absorption and mobility of coal gangue foamed concrete are systematically studied,and the excellent performance of coal gangue foamed concrete is obtained.On this basis,Image Pro Plus software was further used to study the influence of foam content,water-binder ratio and fly ash content on the pore structure of coal gangue foamed concrete,and the influence of coal gangue content on the micromorphology of foamed concrete was studied by SEM scanning electron microscopy and XRD tests.Finally,the filling effect of coal gangue foamed concrete is verified by industrial field test.The results show that:(1)In the single factor experiment,with the increase of foam content,the compressive strength and dry density of foamed concrete tend to decrease.With the increase of water-binder ratio,the 7d compressive strength,28d compressive strength and dry density of foamed concrete showed a decreasing trend.With the increase of coal gangue replacing cement,the dry density of foamed concrete gradually increases,and the 7d compressive strength and 28d compressive strength both increase first and then decrease.With the increase of fly ash replacement amount,the 7d compressive strength of foamed concrete gradually increases,the 28d compressive strength first increases and then decreases,and the dry density first decreases and then increases.(2)The orthogonal experiment results show that the foam content is the key factor affecting the 28d compressive strength and dry density of foamed concrete,and the water-binder ratio is the key factor affecting the water absorption of foamed concrete.The optimal mixing ratio was determined as water-binder ratio 0.7,coal gangue content 30%,fly ash content 20%and foam content 20 kg/m~3.(3)The porosity and average pore diameter of foamed concrete increase with the increase of foam content,and increase with the increase of water-binder ratio.With the increase of fly ash content,it first decreases and then increases.The porosity roundness of foamed concrete firstly increases and then decreases with the increase of foam content,firstly decreases and then increases with the increase of water-binder ratio,and firstly decreases and then increases with the increase of fly ash content.(4)The microscopic morphology shows that the appropriate addition of coal gangue can promote the secondary hydration of cement,increase the hydration products,effectively improve the pore structure of foamed concrete,reduce the average pore diameter of pores,reduce the proportion of large pores,reduce the perforating pores in foamed concrete,and reduce the connectivity between pores.When the coal gangue content is 30%,the average pore diameter is 260μm,the average pore area is 0.434mm2,the roundness is 1.57,and the average Feret diameter is 0.288,indicating the best pore properties.(5)Through the designed filling scheme and filling process,the filling of the simulated roadway of Yankuang Energy Mine rescue brigade in the experimental roadway of the former military-type mine rescue brigade of Yankuang Group was completed.The results show that the foamed concrete material filling effect is good,the air tightness and strength are up to the standard,and the site filling operation is smooth,which verifies the feasibility of foamed concrete filling isolation in local sites of mine.