Experimental Study On Mix Proportion Of Coal Gangue Reactive Powder Concrete

In response to the year-by-year increase in coal gangue production in my country and the urgent need for environmental protection in mining areas,the national "Key Points of Coal Gangue Comprehensive Utilization Technology Policy" emphasizes that the treatment method of coal gangue should focus on harmless treatment and resource utilization.Therefore,it is necessary to explore the economical and efficient processing technology according to the material characteristics of coal gangue itself,combined with regional development needs,and develop products and technologies that can be widely used in production practice,so as to improve the comprehensive utilization level of coal gangue.In order to obtain grade C20～C30 coal gangue reactive powder concrete(coal gangue RPC),this paper selected coal gangue,river sand,cement,fly ash,silica fume,limestone powder,fiber and high efficiency water reducing agent as raw materials,and carried out the experimental study on the proportion of coal gangue RPC.The following conclusions are drawn:(1)The particle gradation,chemical composition,mineral composition and microstructure of the aggregate were tested,and it was concluded that compared with river sand,coal gangue aggregate had lower density,lower self-strength,uneven particle distribution,and larger specific surface area.The micropores are relatively developed,rich in clay minerals,and have the characteristics of strong water absorption.(2)The influence of cement/fly ash,cement/silica fume,gel aggregation ratio and fiber content on the fluidity,compressive strength and flexural strength of gangue RPC in orthogonal test was studied by trend chart analysis,range analysis and variance analysis.And selected a group of dominant mix ratio,namely coal gangue/cement/fly ash/silica fume is 12:3:2:1,polypropylene fiber content is 3 kg/m3.The flexural strength of gangue RPC with the mixture ratio is 4.17 and 4.69 MPa at 7 and 28-day ages,and 16.49 and 24 MPa at 7 and 28-day ages,respectively.(3)Coal gangue of the orthogonal experiment show the RPC mix optimization is applied to aggregate after replacing test,through the different rate of coal gangue to replace the RPC fluidity of close packing degree evaluation,testing,the compressive and flexural strength test,water absorption and porosity test,fiber content test and hydration products test,microstructure observation and interface features,The performance difference between gangue aggregate and conventional natural aggregate in RPC was compared.A group of dominant proportions was selected,that is,the content of coal gangue,river sand,cement,fly ash,silica fume,limestone powder and steel fiber were 925 kg/m3,309 kg/m3,312 kg/m3,223 kg/m3,125 kg/m3,89 kg/m3 and 160 kg/m3,respectively.The flexural strength of gangue RPC at 7,14 and 28 days is 16.55,22.43 and 9.68 MPa,respectively.The compressive strength at 7,14 and 28 days is 39.58,43.91 and 48.32 MPa,respectively.(4)In terms of water-binder ratio,a large water-binder ratio(between 0.5 and 0.6 in the orthogonal test)can guarantee the flow performance of gangue RPC and prevent the shrinkage of its later strength to a certain extent,but also lead to a large porosity and low strength of gangue RPC.However,the small water-binder ratio(0.29-0.42 in aggregate substitution test)is easy to cause the expansion stress caused by hydration reaction in coal gangue RPC in the later curing period,resulting in the development of micro-cracks in RPC and the phenomenon of strength shrinkage.Therefore,for gangue RPC,it is very important to choose a more appropriate water-binder ratio.