| Roadside cemented filling technology of gob-side entry retaining using gangue cemented backfill materials to replace coal pillar,significantly reduce the loss of coal resources and the workload of roadway excavation,and effectively use gangue to reduce the source of mine waste.Under the long-term action of overlying rocks,the gangue cemented backfill materials beside the lane is easily damaged and deteriorated,so it is still a fundamental challenge to achieve the low cost and low carbon path of cemented backfill materials and achieve sufficient strength.Therefore,this thesis takes the direct alkali-activated gangue to strengthen cemented backfill material as the entry point,and takes the substitution of alkali-activated gangue to reduce the cement consumption and realize the dual-carbon path as the guidance,and comprehensively uses the research methods such as test,theoretical analysis and numerical simulation to deeply explore the macro and micro characteristics and creep modification mechanism of alkali-activated gangue cemented backfill materials.The main achievements are as follows:(1)The effects of activator content,activator ratio and curing age on the stressstrain behavior,volumetric strain,dilatancy deformation,compressive strength,acoustic emission response characteristics and ultrasonic response characteristics of gangue cemented backfill materials were investigated by uniaxial compression,acoustic emission monitoring and ultrasonic detection tests.Based on the coupling relations among the activator content,activator ratio,curing age and ultrasonic wave velocity and compressive strength,a prediction model of compressive strength of gangue cemented backfill materials with eleven decision parameters was proposed.The decision parameters of the prediction model were optimized by gravity search algorithm and the prediction accuracy of the model was evaluated.(2)With the assistance of experimental methods such as microscopic scanning,energy spectrum analysis,pressurised mercury test,X-ray diffractometer and thermogravimetric analyzer,the influence of the activator content,the activator ratio and the curing age on the microstructural characteristics,pore parameters,phase composition and the weight of heat loss of the gangue cemented backfill materials were investigated.The types of hydration products of gangue cemented backfill materials under alkali-activated were analyzed,the hydration reaction degree of gangue cemented backfill materials under different influencing factors was quantitatively evaluated,and the influence mechanism of activator content,proportion of activator and curing age on mechanical properties of gangue cemented filling materials was revealed from a microscopic perspective.(3)A hydration molecular model of alkali-activated gangue cemented backfill materials was established using LAMMPS molecular simulation framework,and the whole process of nucleation molecular fracture evolution under tensile action was reconstructed.The effects of changes in calcium ion substitution and calcium-silicon ratio induced by alkali-activated on the tensile strength,failure mode,stress distribution and energy distribution characteristics of the molecular model were analyzed.The molecular fracture mechanism of alkali-activated hydration products was revealed.(4)The influence of the content and ratio of activator on the creep characteristics of gangue cemented backfill materials was investigated by uniaxial compression creep test,and the critical conditions of creep damage/creep hardening of the alkali-activated gangue cemented backfill materials were established.A discrete element model of gangue cemented backfill materials considering both creep load stress corrosion and alkali-activated creep hardening was constructed,and the mesostructural evolution of alkali-activated gangue cemented backfill materials throughout the creep process was reproduced.There are 111 figures,24 tables and 223 references in this dissertation. |
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