Study On The Preparation Of Dry-mixed Mortar By Steel Slag Micronized Powder And The Effect Of Performance

The impact of fluctuations in the ecological environment on human life is enormous.Global attention has been paid to environmental issues caused by climate change and energy depletion,and smelters,as high energy consumption and high pollution industries,are the focus of attention.Currently,China’s steel production ranks first in the world,accounting for more than half of the global production.The steel slag after steelmaking is irregularly stacked in the open air,causing a series of problems such as environmental pollution,land occupation,resource waste,and so on.In order to improve the resource utilization rate and added value of steel slag,it is necessary to strengthen the exploration of the mineral properties and comprehensive utilization approaches of steel slag.In China,converter steel slag is mainly used,and its ultra-fine cementitious material is one of the main research directions in the building materials industry.In this paper,the steel slag from the converter,which has been crushed,screened,and multistage magnetic separation,is selected for grading grinding.The steel slag micropowder is prepared by adjusting the working parameters of the ball mill through experiments.High quality dry mixed mortar is prepared by using mechanically activated steel slag micropowder in conjunction with slag micropowder to replace cement with single or multiple admixtures.The basic properties and hydration products of dry mixed mortar with different strength grades are studied and analyzed.The grinding experiment determines the operating parameters of the experimental ball mill by controlling single factor variables:the ball to material ratio is 3:1,the initial mass of steel slag is 2000 g,and the rotational speed is 2400r/min.Under this condition,grinding for 100 min has the highest efficiency.According to the mechanical activation results,from the results of particle size distribution and specific surface area of fine powder obtained by grinding converter steel slag at different times,the specific surface area of steel slag fine powder will increase with the increase of grinding time.In the test,after grinding for 100 minutes,it can reach 789 m²/kg.The mineral similarities of converter steel slag with different particle sizes mainly include dicalcium silicate（C₂S）,tricalcium silicate（C₃S）,mullite（3Al₂O₃·2Si O₂）,black calcium iron ore（2Ca O·Fe₂O₃）,and a small amount of inert oxide（RO phase）,which can be used as a substitute for cement paste to prepare cementing materials.Firstly,four strength grades of dry mixed mortar,M5,M7.5,M10,and M15,were prepared using steel slag powder mixed with 0%,10%,20%,30%,and 40%respectively.Through comparative tests,it was found that adding more than 30%steel slag powder would increase the water demand in the mortar and worsen its workability.However,the addition of steel slag powder increases the mortar density,which is conducive to ensuring the construction performance and significantly enhances the compressive strength in the later stage.Using orthogonal experimental design,steel slag and slag powder were combined to prepare commonly used dry mixed mortar with M7.5 grade strength.The influence of different factors on mortar strength was explored and the optimal mix ratio was obtained.According to the results of range and variance analysis,the degree of influence of various factors varies at different ages,but the overall performance shows that the greater the mass ratio of steel slag to slag powder,the more conducive it is to early hydration for 3 days,while the most significant factor affecting the degree of hydration for 28 days in the later stage is the specific surface area of steel slag powder,and the compressive strength of mortar test blocks mixed with cement is better than that of mortar test blocks prepared with cement.In addition,the SEM test of hydration products at different ages found that the amount,size and structure of C-S-H gel and CH crystals formed in the later stage of the mortar prepared by the composite of steel slag and slag powder were significantly better than those of the mortar mixed with steel slag powder alone.