Study On Strengthening Mechanism And Application Of CO₂ Mineralized Solid Waste Backfill Materials

Coal resource mining causes a series of problems such as overburden movement and surface building collapse,while the mining and application of coal resources generate a large amount of solid waste and CO₂ gas.In response to the above problems,this thesis investigates the development of CO₂ mineralized solid waste backfill materials（CFGB）from the viewpoint of rock stratum control,solid waste treatment,energy saving and emission reduction.The transportability and mechanical properties of CFGB under different fly ash-coal gangue ratios are analyzed,the strengthening mechanism is analyzed from the microscopic perspective,and the overburden and surface deformation characteristics of CFGB under different backfill rate conditions are revealed,and the main results are as follows:（1）The slump and extension,water bleeding rate and setting time of CFGB are optimized and analyzed.Compared with N-CFGB（no CO₂,other conditions remain unchanged）,and show a decreasing trend with increasing fly ash admixture and decreasing coal gangue admixture.CFGB belongs to non-Newtonian solid-liquid two-phase flow slurry,and its rheological model is fitted to Herschel-Bulkley model（H-B model）,with shear thinning characteristics.（2）The mechanical properties of CFGB and N-CFGB were compared and analyzed.The compressive strength of CFGB was higher than that of N-CFGB,and the strength of the backfill material could be improved after the CO₂ reaction.In addition,the early strength of CFGB is stronger,and the compressive strength increases with age,and the more obvious the effect of age on strength when increasing the fly ash content and decreasing the gangue ratio.At the same age,the strength of CFGB increases with the increase of the proportion of flyash-gangue content,and the strength increase is more pronounced at the later stage.（3）The microscopic morphology and the types of hydration and mineralization products of CFGB were analyzed to reveal the strengthening mechanism of CFGB.C-S（A）-H gel,Silica gel,Ca CO₃ and other hydration and mineralization products generated in CFGB were attached to the surface of aggregate particles such as fly ash and gangue,and filled in the pores of the aggregate.The loose pore structure of the backfill body is transformed into a dense and cemented structure,so as to form an overall network skeleton and provide strength for CFGB.The CO₂ absorption of CFGB is 3.98 mg/g-CFGB based on the TG test results.（4）FLAC3D was used to simulate the application of CFGB backfill materials,and the overburden migration and surface deformation characteristics under two mining modes of collapsed longwall caving mining and CFGB backfill mining were analyzed.Increasing the backfill rate is an effective way to improve the control of surface deformation.When the backfill rate is above 70%,the surface deformation parameters are lower than the standard of Class I buildings,which can protect the surface structures above the mine site.There are 54 figures,12 tables and 100 references in this thesis.