Research On Preparation Mechanism Of Steel Slag Beads And Its Application To Fine Aggregate Of Concrete

The low utilization rate of steel slag and the shortage of sand aggregate resources are two big problems faced by the society.Using steel slag as a substitute of sand aggregate has double significance to improve the utilization rate of steel slag and solve the crisis of using shortage.At present,steel slag used as aggregate has some problems such as poor stability,high iron content and high crushing cost.It is found that the steel slag beads treated by air quenching are close to river sand aggregate in performance and are a good substitute for aggregate.However,a series of practical problems exist in air quenching process of steel slag,such as poor slag fluidity and difficulty in ferromagnetic separation.Therefore,it is necessary to deeply study the preparation mechanism of steel slag beads and its influence on the performance of concrete.The mechanism of granulation was further analyzed by simulating the process of air quenching granulation of steel slag,which provides reference for the granulating production parameters setting.Based on the optimization of slag fluidity and bead properties,the furnace slag was used as the modifier,and the hot slag of electric arc furnace remelting cold slag was used to simulate the factory hot slag for granulation test.The influence of different process parameters on the effect of air quenching of steel slag and the performance of steel slag beads was studied,and the effect of replacing river sand fine aggregate directly with steel slag beads without treatment on concrete performance was analyzed,The concrete grade and the best replacement rate suitable for steel slag beads were determined,and the purpose of waste utilization was achieved.The air quenching granulation process of liquid steel slag was simulated by using Fluent software,and the influence rules of slag flow velocity,air velocity and nozzle height on airflow velocity field around slag droplet,slag droplet temperature field and flight distance in flight space are explained in combination with flight curve,and the change trends of temperature and liquid phase ratio of slag droplet at different injection distances are analyzed.Through the simulation of the heat transfer and solidification process of slag droplets,the mechanism of the influence of different relative air speed and different slag particle sizes on the heat transfer and solidification of slag droplets is revealed.The increase of relative air speed will improve the cooling rate,but when the relative air speed is higher than 50 m/s,the cooling rate of slag droplets is not significantly improved.The particle size is reduced from 2 mm to 0.5 mm,the cooling efficiency of slag droplets is greatly improved,and the cooling rate is increased from43℃/s to 320℃/s.The granulation effect was optimized by adjusting the slag composition and process parameters.After composition reconstruction,the slag alkalinity decreases,the liquidus shifts to the low temperature zone,and the viscosity of reconstructed steel slag decreases,effectively expanding the slag air quenching temperature range.The granulation experiment of remelting steel slag in electric arc furnace shows that the air quenching rate of steel slag gradually increases and the bead forming rate of air quenching gradually decreases with the increase of the addition ratio of tempering agent;the increase of air quenching pressure and nozzle Mach number can improve the bead forming effect of steel slag air quenching;the higher the slag discharge temperature is,the better the slag fluidity is.The larger the temperature range of air quenching is,the better the effect of steel slag air quenching to form beads is.The optimum conditions for air quenching of steel slag into beads are as follows:the addition amount of blast furnace slag is15%～25%（Ca O/Si O₂value is 2.08～1.88）,the air quenching pressure is 0.30～0.35 MPa,nozzle Mach number are 1.4 and 1.6,slag-discharging temperature is higher than1600℃,both the air-queching rate and the bead rate of steel slag can reach 80%.According to the requirements of fine aggregate,the The performance analysis of steel slag beads prepared with different additives under better process conditions was analyzed.The results show that composition reconstruction changes the physical and chemical properties of slag beads.With the increase of the proportion of blast furnace slag added,the color of steel slag beads becomes lighter,the shape becomes longer and flaky,the smoothness degree increases,and the strength and sphericity become worse;after air quenching and granulation,the XRD peaks of steel slag beads become more dispersed.The mineral composition changes from the minerals such as melilite,magnetite and limonite before quenching and tempering to amorphous glass body with a small amount of dicalcium silicate,magnesium oxide and other minerals.The content of free calcium oxide in the granulated slag gradually decreases,and the stability is improved.The steel slag beads with the addition ratio of 15%of the conditioning agent are selected as the substitutes for river sand,and the substitution rates are 0,20%,35%,and50%to prepare concrete.The results show that the variation trend of slump is C30>C40>C50 under the same replacement rate of steel slag beads;after steel slag beads are replaced,only the compressive strength of C30 concrete is significantly improved;with the increase of substitution rate,the tensile strength of the three grades of concrete increases first and then decreases,and the flexural strength of C30 and C40 concrete increases continuously.In comprehensive consideration,steel slag beads are suitable for C30 concrete,and the optimal replacement rate is 20%～35%.In C30 concrete,after 200freeze-thaw cycles,with the increase of substitution rate,35%～50%steel slag bead concrete has the best freeze-thaw resistance,the corrosion resistance coefficient of concrete gradually decreases,and the sulfate resistance declines;at the same carbonization time,the maximum carbonization resistance is reached when the substitution rate is 20%～35%.Figure 84;Table 33;Reference 113.