Research On Preparation And Application Of Reactive Powder Concrete Containing Waste Steel Fibers

Reactive powder concrete(RPC),as a typical representative of ultra-high performance concrete,has excellent mechanical properties and durability.And RPC increases its toughness and ductility by introducing steel fibers,which overcomes the problem of higher brittleness of concrete materials.However,compared with ordinary concrete,RPC has the problems of high production cost,complicated preparation process and large shrinkage.Although domestic and foreign scholars do a lot of research on the three major problems of reactive powder concrete,the high cost problem has not been solved well,which hinder the large-scale application of RPC.At the same time,the generation of scrap tire is huge.And recycling scrap tire has become the focus of the whole society.The scrap tire contains about 17%of the steel wire.Recycling the steel wire from scrap tire to replace steel fibers commonly used in RPC can reduce the production cost of RPC and recycle scrap tire resources.Based on this,this paper studies the use of waste steel fiber to replace the traditional copper-coated steel fiber to prepare reactive powder concrete.First of all,in order to obtain a better basic mix ratio,the performance of the active powder concrete formulated by the mainstream mix design methods such as the orthogonal experiment method and the Dinger-Funk continuous distribution theory was experimentally analyzed.The results show that different factors of orthogonal experiment have different effects on RPC flexural strength,compressive strength and fluidity.The Dinger-Funk continuous distribution model is easy to prepare RPC with good working performance,and when RPC is prepared from multi-component materials with a large amount of inert materials,"close packing of sand+Dinger-Funk continuous distribution of powder material"should be selected.Secondly,in order to confirm the possibility of using waste steel fiber to prepare RPC,the effects of waste steel fiber and copper-coated steel fiber on the physical and mechanical properties of reactive powder concrete were compared.Experimental results show that the effect of the waste steel fiber and copper-coated steel fiber on the physical and mechanical properties of RPC is basically the same,and has the same resistance to chloride ion erosion.Then,in order to improve the physical and mechanical properties of waste steel fiber reactive powder concrete,the influence of material composition and curing regime on the waste steel fiber reactive powder concrete was studied.It is expected that the physical and mechanical properties of the reactive powder concrete will be improved by optimizing the material composition and curing system.The results show that in terms of chemical admixtures,superplasticizers and viscosity reducers have some influence on the fluidity and strength of RPC,but defoamers and silica fume dispersants have almost no effect on RPC.The amount of silica fume and the incorporation method have an impact on the performance of RPC,the best use of fly ash and limestone powder is 5%,and limestone powder can partially replace quartz sand.The curing regime has a great influence on the mechanical properties,phase composition and microstructure of RPC.Compared with room temperature curing,RPC with high temperature curing has higher strength and denser microstructure.The optimal temperature for steam curing is 80~90?and the optimal curing time is 2~3 days.Pre-curing for 1~2 days can further improve the strength of RPC.Waste steel fiber RPC with compressive strength over 200MPa can be prepared by using the best mixture ratio obtained from experiments(quartz sand 1045kg/m~3,limestone powder 55kg/m~3,cement 800kg/m~3,silica fume 200kg/m~3,fly ash 40kg/m~3,water147kg/m~3 and steel fiber 208kg/m~3).Finally,in order to explore the engineering application effect of waste steel fiber reactive powder concrete,the manhole cover was prepared by using the waste steel fiber reactive powder concrete,and the performance and economic benefit of manhole cover were analyzed.The results show that Waste steel fiber reactive powder concrete can be used to prepare manhole covers of D400,which cost is as low as 105RMB.From the research results,it can be seen that it is feasible and potential to prepare RPC with waste steel fibers instead of copper plated steel fibers.