Study On The Effect Of Fly Ash And Silica Fume On The Physical And Mechanical Properties Of Recycled Concrete

With the development of the economy,the land occupied by construction waste is increasing.In the process of repair and reconstruction of traditional buildings,a large amount of construction waste will be generated,causing environmental pollution and waste of resources.Research on the performance and application of recycled concrete can promote the effective use of solid waste,accelerate the development of green recycling,reduce environmental pollution and waste of land resources,and reduce construction costs.The research on the influence of fly ash and silica fume on the performance of recycled concrete provides an effective technical approach for the resource utilization of waste concrete.It has shown great application prospects today when our country is vigorously advocating sustainable development.This thesis studies the performance of recycled concrete,mainly introduces the current research status of waste concrete and recycled aggregate concrete at home and abroad,and systematically analyzes the influence of admixtures（silica fume/fly ash）and recycled aggregates on the performance of recycled concrete.It also analyzes the current shortcomings of recycled concrete and looks forward to its future prospects.In order to explore the influence of the proportion of fly ash,silica fume and recycled aggregates on the physical properties,mechanical properties and corrosion resistance of recycled concrete,this experiment adjusted different amounts of fly ash,silica fume,and recycled bone.In this experiment,22 sets of parallel experiments were designed by adjusting the proportions of fly ash,silica fume,and recycled aggregate to compare and analyze the effects of different proportions of admixtures on the physical properties of recycled concrete such as slump,water absorption,and softening coefficient,and the mechanical properties such as 7d/28d compressive strength,28d flexural strength,and the corrosion resistance of recycled concrete.The result shows:（1）Among the effects on the slump of recycled concrete,both recycled aggregate and silica fume reduce the slump,while fly ash increases the slump up to 62mm.Impact on the water absorption rate of recycled concrete,silica fume reduces the water absorption rate of concrete,and when the mixing amount is 10%,the lowest is reduced to 0.51%,while fly ash and recycled aggregate both increase the water absorption rate,and when the mixing amount of fly ash is 15%,the water absorption rate is 1.36%.Silica fume increases the softening coefficient of concrete first and then decreases.The highest value is 0.892 when the content of silica fume is 8%,and fly ash decreases the softening coefficient of concrete first and then increases.The lowest point is when the content of fly ash is 15%.The softening coefficient is0.821,and the content of recycled aggregate makes the concrete softening coefficient continue to decrease.（2）The influence of silica fume on the compressive strength of concrete 7d and 28d is first increased and then gradually decreased.When the content of silica fume is 8%,it is the inflection point.At this time,the compressive strengths of 7d and 28d are 30.8MPa and37.2MPa,respectively.The compressive strength of fly ash to concrete 7d and 28d first decreases and then increases.When the content is 15%,the corresponding compressive strength values of 7d and 28d are 25.2MPa and 30.2MPa,respectively.The increase of recycled aggregate content will gradually reduce the compressive strength of concrete 7d and28d.Both fly ash and silica fume can increase the sulfate resistance and corrosion resistance of concrete compared with the initial value.When the fly ash content is 20%,the sulfate corrosion resistance coefficient of concrete is 0.97,and when the silica fume content is 10%,the coefficient is 0.96.The incorporation of recycled aggregate gradually weakens the sulfate resistance of concrete.When the amount of recycled aggregate is 40%,the sulfate corrosion resistance coefficient of concrete is 0.96.（3）After silica fume and fly ash are compounded,due to the"balling"effect of fly ash and the fine particles of silica fume can form a complementary effect,they can give full play to their respective lubrication,compact pores,and secondary hydration effects,and improve the performance of concrete.Physical and chemical properties,compact the pores of the concrete,improve the impermeability of the concrete.The silicate gel formed by silica fume and fly ash after the alkali-activated reaction further increases the strength of concrete,which can better prevent the penetration of SO4^2-in the concrete,to improve the ability of the recycled concrete to resist sulfate erosion.Compared with single admixture,compound admixture has better various mechanical properties,which can better improve all aspects of concrete performance...