Study On Basic Mechanical Properties Of Modified Steel Slag Micro-powder Concrete

Steel slag is a by-product formed by the reaction of steelmaking raw materials with various fluxes and slagging materials in the smelting process.Generally,120-210 kg steel slag is produced with each ton of steel produced.Over the years,the green concept of sustainable development has penetrated into all walks of life,and due to the complex composition of steel slag,large output,processing difficulties and other characteristics,there are various matter in the all-round utilization of steel slag.And the application of steel slag in concrete industry is a feasible way for comprehensive utilization of steel slag.In this paper,steel slag micro-powder with a specific surface area greater than450 m²/kg is obtained from steel slag after mechanical grinding,which is mixed into cement cementitious material as an admixture to produce concrete.Then zeolite powder is added and curing condition is changed.Through various mechanical property tests and microscopic analysis,the effect of zeolite powder and hydrothermal curing on the mechanical properties of steel slag concrete is studied,and the mechanism of activation of zeolite powder and hydrothermal curing on steel slag is explored.The experimental design replaces cement with 10%,20%,and 30%steel slag micro powder,and zeolite powder with 0%,20%,and 40%steel slag micro powder.The mixture is then designed with natural artificial watering for 28 days and constant temperature 35℃hydrothermal curing for 7 days,followed by natural artificial watering for 21 days.A total of 20 experimental groups are designed to conduct mechanical performance tests on concrete,Analyze the influence of zeolite powder and hydrothermal curing conditions on the mechanical properties of steel slag micro powder concrete with different dosages.Further microscopic analysis of concrete was conducted through XRD（X-ray diffraction）and SEM（scanning electron microscopy）experiments to explore the hydration activity excitation mechanism of steel slag in concrete.The study concludes that:（1）Without the addition of zeolite powder,the mechanical properties of concrete show a continuous decline trend with the increase of steel slag micro powder dosage.The cube compressive,splitting tensile,axial compressive strength,and static modulus of elasticity of the test-piece all show a steep decrease at first,then do a gradual increase.The flexural strength continuous decrease.（2）With the addition of zeolite powder,the mechanical properties of concrete are significantly improved with the increase of zeolite powder content.Among them,when using steel slag micro powder to replace cement by 30%and adding zeolite powder with 40%steel slag micro powder quality,the cube compressive strength,splitting tensile strength,flexural strength,and axial compressive strength all exceeded the blank group,especially the axial compressive strength improved the most significantly.（3）The mechanical properties of concrete were significantly improved after changing from 28 days of ordinary natural artificial watering to 7 days of constant temperature 35℃water bath curing,and then 21 days of natural artificial watering curing.（4）Two formulas for the relationship between compressive strength and static elastic modulus of concrete cubes were proposed based on the formulas proposed in the reference literature.After comparison,it was found that polynomial fitting had better results.（5）Through analysis of variance,it was found that both the amount of steel slag micro powder,zeolite powder,and curing conditions have a significant impact on the mechanical properties of the experimental group.However,the interaction effect between the two is relatively low,and the interaction effect of the three cannot be considered.（6）Through XRD and SEM experimental analysis,it was found that the activity of steel slag micro powder is low,the hydration rate is slow,and the degree of hydration is low,resulting in a low overall hydration degree of concrete.However,after curing in 35℃hydrothermal,it has been improved,which helps to promote the hydration reaction.The compactness and flatness are better,and it can form a more compact and complete cement stone structure.The hydration products such as C-A-S-H and C-S-H have increased.The addition of zeolite powder can only partially participate in hydration and provide excessive Si O₂,which cannot fully participate in the hydration reaction to generate C-S-H and C-A-S-H,and most of them exist in the quartz state.The reason why the addition of zeolite powder can improve the mechanical properties of concrete is because the particle size of zeolite powder is much smaller than that of cement,steel slag powder,etc.,which is conducive to filling the gaps and cracks in concrete and increasing its strength.