Research On The Influence Of Different Mineral Admixtures On The Performance Of Machine-made Sand Concret

With the rapid development of the civil engineering industry,the demand for concrete is increasing,and natural sand resources are increasingly scarce.Machinemade sand has gradually become an excellent substitute for natural sand.At present,the application research of machine-made sand concrete is one of the hotspots in the civil engineering industry.Guizhou Province is rich in manufactured sand resources.Compared with natural sand,it has defects such as poor particle gradation,polygonal shape and rough surface,which makes the concrete prepared by manufactured sand have the risk of segregation and bleeding.Concrete mineral admixture can replace part of cement and improve the working performance of the mixture.It has been widely used in the concrete industry.In this paper,four kinds of mineral admixtures are selected : fly ash,granulated blast furnace slag powder,steel slag powder and limestone powder.The effects of single and compound addition of mineral admixtures on the performance of machine-made sand concrete in Guizhou Province are studied.The main work and achievements are as follows1.The activity test shows that the activity index of fly ash and granulated blast furnace slag powder gradually increases with the increase of age,and the activity index of steel slag powder and limestone powder basically remains unchanged with the change of age.At 28 d,the activity index of granulated blast furnace slag powder is 107.09%,limestone powder is 77.21%,steel slag powder is 75.75%,fly ash is68.86%.2.When mixed alone,mineral admixtures have adverse effects on the early strength of machine-made sand concrete,which can enhance the strength in the middle and late stages,improve the internal structure,fill pores,reduce internal defects,and change the content and composition of hydration products.The comprehensive analysis shows that :(1)When the fly ash content is 5%,the granulated blast furnace slag powder content is 10%,the steel slag powder content is10%,and the limestone powder content is 5%,the mechanical properties are the best.Fly ash-6.2%(3d),5.6%(7d),3.7%(28d),granulated blast furnace slag powder-27.0%(3d),6.3%(7d),6.6%(28d),steel slag powder-1.3%(3d),17.8%(7d),0.7%(28d),limestone powder-5.5%(3d),15.9%(7d),5.3%(28d),splitting tensile strength increased by 5.6%,granulated blast furnace slag powder 9.9%,steel slag powder6.7%,limestone powder 7.7%,flexural strength fly ash increased by 3.7%,granulated blast furnace slag powder 20.0%,steel slag powder 25.0%,limestone powder 14.5%.3.When single-doped,mineral admixtures have adverse effects on the early strength of manufactured sand concrete,can enhance the strength in the middle and late stages,and can play a filling effect to improve the internal structure,fill pores,reduce internal defects,and change the content and composition of hydration products.Comprehensive analysis shows that :(1)When the fly ash content is 5%,the mechanical properties are the best,the compressive strength is increased by-6.2%(3d),5.6%(7d),3.7%(28d),the splitting tensile strength is increased by 5.6%,and the flexural strength is increased by 3.7%;(2)When the content of granulated blast furnace slag powder is 10%,the mechanical properties are the best,the compressive strength is increased by-27.0%(3d),6.3%(7d),6.6%(28d),the splitting tensile strength is increased by 9.9%,and the flexural strength is increased by 20.0%.(3)When the content of steel slag powder is 10%,the mechanical properties are the best,the compressive strength is increased by-1.3%(3d),17.8%(7d),0.7%(28d),the splitting tensile strength is increased by 6.7%,and the flexural strength is increased by 25.0%.(4)When the limestone powder content is 5%,the mechanical properties are the best,the compressive strength increases by-5.5%(3d),15.9%(7d),5.3%(28d),the splitting tensile strength increases by 7.7%,and the flexural strength increases by 14.5%.4.Through the compound mixing test between different proportions of mineral admixtures,it is concluded that compared with the single mixing of the two admixtures in the combination,the slump and expansion of the compound mixing are larger,and the mixture has better working performance.The early compressive strength of the composite mineral admixture is obviously improved,which can eliminate the adverse effect of single admixture on the early compressive strength.In addition to the decrease of compressive strength when fly ash and steel slag powder are mixed,the compressive strength of other combinations is improved compared with that of single admixture,and the is gradually reduced with the development of age.The composite superposition effect has not been effectively exerted in the splitting tensile strength and flexural strength,and there is a slight negative impact.Microscopically,the mineral admixtures are filled with each other,the structure is denser,and can promote the hydration reaction.The optimal ratio of fly ash : slag powder = 2:1,fly ash : steel slag powder = 1:2,fly ash : limestone powder = 2:1,slag powder : steel slag powder = 2:1,slag powder : limestone powder = 2:1,slag powder :limestone powder = 2:1,steel slag powder : limestone powder = 1:2.5.The results of frost resistance test,sulfate resistance test and shrinkage deformation test show that mineral admixtures can improve the frost resistance,erosion resistance and shrinkage deformation resistance of manufactured sand concrete when mixed alone,and the enhancement effect is better when mixed.