The Performance Of Ultra-fine Fly Ash Prepared By Steam Kinetic Energy Mill And Its Application In Reactive Powder Concrete

Reactive powder concrete（RPC）is a new type of cement-based composite material with ultra-high mechanical properties,excellent durability and good volume stability,and has broad application prospects.However,due to the large amount of cement in RPC and the high price of silica fume,the production cost of RPC is high,which severely restricts its application in the construction industry.Therefore,in this paper,aiming at the high production cost of RPC,fly ash from a wide range of sources and low prices is used as a high-quality mineral auxiliary material to replace part of cement and silica fume,which reduces the production cost while ensuring the mechanical properties of concrete.By studying the performance difference of ultra-fine fly ash prepared by two different grinding processes,the multi-stage particle size ultra-fine fly ash with better comprehensive performance is applied to RPC,and the blending of ultra-fine fly ash RPC is studied.The specific design method,and the law of the close packing model,the amount of silica fume and the amount of fly ash that affect the mechanical properties and microscopic properties of the slurry.The main conclusions are as follows:（1）The activity of fly ash increases significantly as the particle size decreases.The ultrafine fly ash with a D₅₀ of 5.14μm prepared by mixing with 30%steam kinetic energy mill has an activity index of 104.5%.The mineral composition and chemical composition of ground fly ash of different particle sizes are not much different,and the particle size distribution and particle morphology have more significant effects on its activity.The particle size distribution width of the ultrafine fly ash particles prepared by the steam kinetic energy mill is narrower,the particle size distribution curve is also smoother,and its activity is also significantly higher than that of the ultrafine fly ash prepared by the ball mill.（2）Based on the close packing model,by designing the mix ratio of RPC,and based on the compressive strength of the prepared RPC,it is determined that the best mix ratio of the ultrafine fly ash RPC cementing material under this system is cement:silicon Ash:FA0:SFA1:SFA2=0.55:0.09:0.06:0.12:0.18.After 28 days of standard curing,the RPC material with a compressive strength of 145.3 MPa was successfully formulated,reaching the sixth strength level of RPC-RPC140.At the same time,it also shows that by mixing 36%fly ash with multi-stage particle size,instead of 36%cement and silica fume,while ensuring the performance of RPC,it can reduce its production cost,which is conducive to making RPC better.Of the application to construction projects.（3）The mechanical properties of RPC specimens are not only related to the accumulation effect of solid particles,but also affected by the hydration activity of the composite cementing material.The addition of fly ash with multi-stage particle size can not only ensure the packing density of solid particles,but also It can maximize the hydration reaction of the system and promote the formation of gel products,thereby reducing the porosity of the slurry and leading to an increase in compressive strength.（4）With the increase of silica fume content,the compressive strength of RPC gradually decreases.The increase in the content of silica fume reduces the substantial water-binder ratio of the slurry,which results in the slower hydration reaction of the slurry,the decrease of gel formation,and the increase of porosity.With the increase of fly ash content,the compressive strength of RPC first increases and then decreases.This is because at low water-to-binder ratio,excessive cement consumption will only cause more cement clinker in the system to fail to hydrate,and will not greatly promote the hydration reaction of the slurry.Instead,the slurry is due to active fillers.The decrease of sulphate causes the porosity to increase and the compressive strength to decrease.Moreover,there is no obvious interface transition zone between the fly ash particles and the cement matrix,and it is firmly bonded to the matrix,which has a good promotion effect on the compactness of the slurry structure and the strength of the concrete.