Research On Mechanical Properties Of Fly Ash Geopolymer Paste Backfill Material

Fly ash and coal gangue are common bulk solid wastes.If not treated well,they will cause serious air and water resources pollution.In China,hundreds of millions of tons of fly ash and coal gangue are produced every year,which has a serious negative impact on cleaner production.Fly ash contains active A1₂O₃ and SiO₂,which can be made into geopolymer cementing material for use after chemical excitation.Therefore,a new type of paste backfill material called geopolymer cemented coal gangue-fly ash backfill?GCGFB?is prepared by using fly ash geopolymer as cementing material and coal gangue as aggregate,which can make use of solid waste in large quantities to carry out cleaner production and protect environment.The test used fly ash geopolymer composite cementitious material as cementing material,coal gangue and unexcited active fly ash as aggregate.The mix proportion design was carried out by orthogonal design method,and the optimal mix proportion GCGFB is microscopically scanned by scanning electron microscopy?SEM?and energy dispersive spectrdmeter?EDS?.Uniaxial compressive strength?UCS?test and the white light digital speckle correlation method?DSCM?were combined to analyze the deformation law of the filling body.Finally,the uniaxial creep test was used to establish the creep model.The research results show that:?1?In the process of GCGFB preparation,a new mixing technique of mixing a small amount of fly ash with cement,slag and a small amount of water and then adding aggregate and remaining fly ash was proposed.This process can effectively excited the activity of fly ash.Using this new mixing technique and through the orthogonal mix proportion analysis,it was concluded that the optimal mix proportion is when the mass fraction is 80%,the cementing material dosage is 150 kg/m³,the sand rate is 75%and the fly ash dosage is 20%;?2?According to SEM and EDS microscopic scanning,calcium silicate hydrate gel and calcium silicate aluminate hydrate gel formed in the early stage were found.The formation of amorphous hydrated calcium aluminate gel coated ettringite and calcium carbonate formed flocculation structure between aggregate particles.After that,GCGFB slurry entered into the state of agglomeration-crystal structure;?3?UCS test and DSCM were adopted for the experiment.In the early stage of loading,the horizontal displacement,vertical displacement and maximum shear deformation of GCGFB were small and evenly distributed.With the progress of loading,the deformation localization zone gradually appeared,and when it reached the post-peak,the deformation localization zone further expanded gradually.In the stage from the initiation of deformation localization to the peak strength,the growth rate of poisson ratio of GCGFB increased significantly.After the peak growth rate significantly slowed down and appeared unstable fluctuations growth changes.The deformation energy density of GCGFB decreased slowly after the peak and the rate of decline decreased gradually.Different from the sharp decline of post-peak deformation energy density of high-strength rocks,the collapse time of deformation energy density of GCGFB was much longer than that of high-strength rocks;?4?According to uniaxial creep test data,an improved fractional Burgers creep model was established.Based on the creep test data,the mathematical model of GCGFB under uniaxial creep was established by mathematical method.The model parameters were determined by fitting.The results of creep model and mathematical model were in good agreement with the test data.There are 45 graphs,18 tables and 90 references in this paper.