Study On Gangue-Combustion Fly Ash Gunning Material

Coal is one of the main energy sources in China,but it brings many economic and environmental problems in the mining process.The use of coal gangue produced during coal mining power generation,is turning waste into treasure,an effective way to solve pollution.However,the ash content of coal gangue fuel is higher,the amount of fly ash produced by combustion is equivalent to 2 times of coal-fired power plant,and its quality is lower than three gray standards of the national building materials standard,which brings heavy economic and environmental burden to the coal mining enterprises for it's hard to effectively use.The problem of fly ash stacking will be solved,which could achieve circular economy and significantly reduce the cost of excavation,if using the activated low-quality fly ash to prepare gunning material for curing and support of shaft and roof at the nearby coal mine.The physical and chemical properties of gangue-combustion fly ash in Huangling were studied by means of particle size analysis,chemical analysis,scanning electron microscopy and X-ray diffraction analysis.Compared with coal-fired power plant fly ash,the particles of gangue-combustion fly ash were coarser,consisting of a large number of porous vitreous,amorphous carbon particles and a small amount of crystals,which had few spherical particles,and its crystal phase was mainly quartz,mullite and so on.It mainly contained SiO₂,Al₂O₃,CaO and Fe₂O₃ and other chemical composition,was low calcium ash,its loss on ignitionand water demand ratio were large,resulting in its poor quality,limited application.The activation effect of industrial grade Na₂SO₄,CaO and CaSO₄·2H₂O on gangue-combustion fly ash was studied by the experiment of mortar strength.The results showed that the order of activation effects was:Na₂SO₄>CaO>CaSO₄·2H₂O;and the effect of compound activation was better.Among them,the impact of CaO is largest on early and mid-term strength of the sample,followed by Na₂SO₄,and the impact of Na₂SO₄ is largest on later strength,followed by CaO.The optimum mix ratio of the activator was determined:CaO?4%?,Na₂SO₄?3%?and CaSO₄·2H₂O?0.7%?.In this paper,the activated gangue-combustion fly ash was used for the preparation of gunning material,and the effects of sand content,sand ratio,fly ash content,mass concentration and admixture on the working characteristics and compressive strength of gunning material were studied.The quality ratio of gunning material was determined as,cement:fly ash:sand:water=1:9:5:6.1,the content of polycarboxylate superplasticizer is 1.0%,sodium gluconate is 0.05%,NaAlO₂ is 4.5%and Na₂SO₄ is 2.7%.The consistency,fluidity,bleeding rate and setting time of the fresh mix were in accordance with the requirements of pipeline transportation,and cohesion and water retention were also good;The compressive strength of the specimen after stripping can respectively reach more than 0.4 MPa,1 MPa,2 MPa and 5 MPa at 8 h,3 d,28 d and 270 d ages.Therefore,working characteristics and compressive strength of gangue-combustion fly ash gunning material could meet the requirements of mine support.And its low cost,green environmental protection,would bring economic,environmental and social benefits.The influence of species and dosage of water reducing agent and retarder on the rheological parameters of gunning material was studied by using rotary viscometer.Shear stress of slurry was linearly related to shear rate,which was in accordance with the Bingham fluid model.Plastic viscosity decreased,eventually stabilized,with increasing shear rate.Yield stress and plastic viscosity decreased,eventually stabilized,with the increase of dosage of water reducing agent and retarder,indicating that there were saturated content while using the water-reducing agent and retarde.FLUENT was used to simulate the pipeline transportation process of gunning material,the influences of the inlet velocity on velocity distribution,pressure distribution and loss of resistance along the line were studied under the conditions that Pipe line is 2.6,and critical flow rate of self-flow transport and pumping was calculated as 1.5m/s by combining theory and simulation.Therefore,self-flow transport method was determined to be feasible.The application of gangue-combustion fly ash gunning material reduces the cost of mine excavation and support,and provides a feasible way to solve the problem of stacking and pollution of gangue-combustion fly ash.It is of great significance to circular economy,ecological protection and social sustainable development.