Research On Coal Gangue Used In Concrete’s Coarse Aggregate

Coal gangue is a waste rock made during the mining and washing of coal that contains carbon.Large accumulations not only occupy more space but also cost more to maintain.There won’t be any land to pile up under the current policy,which forbids the establishment of permanent coal gangue yards,severely limiting the sustainable growth of the social economy.Thus,it is critical to establish a new method for the efficient and extensive use of coal gangue.In this thesis,three kinds of coal gangue in Changcun Coal Mine are compared in terms of macro-morphology,micro-morphology,water absorption,crushing value,chemical composition,mineral composition,lithofacies,industrial index,thermodynamic property,environmental protection performance and durability,and the coal gangue coarse aggregate with good performance is selected to prepare concrete.On the working performance and mechanical qualities of coal gangue concrete,the impacts of admixture type,coal gangue gradation,sand ratio,and other parameters were examined.Coal gangue concrete’s resilience was examined.Investigations were done into how coal gangue coarse aggregate and concrete’s characteristics would change after being treated with slurry.The microscopic mechanism was then investigated and evaluated using XRD,SEM,and microhardness.The results show that the main chemical composition of coal gangue is SiO₂ and Al₂O₃,and the mineral composition is quartz,muscovite and kaolinite.The carbon content ranges from 2.1%to 10.9%,and the calorific value is between 490～3647 k J·kg^-1.The microstructure is layered and scaly,and the compactness is general;large crushing value,high water absorption,poor durability;the concentration and radioactivity of heavy metal ion leaching solution of coal gangue meet the specification requirements.The working performance and mechanical properties of the whole coal gangue coarse aggregate concrete are better when the anti-adsorption slow-release type admixture is used;when the coal gangue gradation is combined in a ratio of4.75mm～9.5mm:9.5mm～19mm=3.25:6.75 and the sand ratio is 48%,the working performance and mechanical properties of the concrete are better;the whole coal gangue coarse aggregate can prepare concrete with C40 and below strength grade,but can not prepare concrete with C40 and above strength grade.It is mostly caused by the coarse coal gangue aggregate’s low hardness and high crushing value.Concrete damage results from coal gangue crushing as strength grade rises.Compared with limestone concrete,the impermeability of coal gangue concrete is reduced by 20%,the frost resistance is reduced by 33%,and the strength loss rate after dry-wet cycle is increased by 7.2%.The analysis of XRD and SEM shows that the crystallization of hydration products is damaged and the diffraction intensity is reduced after dry-wet and freeze-thaw cycles.Secondly,the coal gangue aggregate is seriously damaged by erosion,and the joint damage of slurry and coal gangue aggregate leads to poor durability of coal gangue concrete.The performance of coal gangue coarse aggregate is improved by pretreatment of coal gangue coarse aggregate,and the effect of superfine ore powder is the best.The correlation between coal gangue coarse aggregate performance and concrete performance is strong;the performance improvement of coal gangue coarse aggregate after wrapping slurry is to weaken the damage of water to clay minerals;the improvement of coal gangue concrete performance lies in the improvement of aggregate and interfacial transition zone performance.