Study On Silicon Source Substitution Effect Of Alkali-Activated Steel Slag Based On Powder Strengthening Route

With the background of accelerating the realization of the"dual carbon"goal in the field of building materials,researchers improve the activity of steel slag by alkali-activation,and prepare alkali-activated steel slag cementitious materials,in order to solve the environmental problems caused by low utilization rate and stacking of steel slag at present,and further improve the utilization efficiency of steel slag.Most of the existing studies use sodium silicate to prepare alkali activated materials,and the performance of alkali activated steel slag strongly depends on the dosage of sodium silicate,but the cost of sodium silicate and the carbon footprint of the preparation process are high.In order to solve this problem,this paper takes the preparation of green alkali-activated steel slag cementitious materials as the research goal,and takes the powder strengthening route as the entry point,and puts forward the idea of preparing silicon source-substituted alkali-activated steel slag cementitious materials.The substitution effect of silicon-rich raw materials was explored,and the optimal alternative silicon source-silica fume was determined.The hydration mechanism,drying shrinkage mechanism and sulfate erosion mechanism of silica fume-substituted alkali-activated steel slag were analyzed,and finally the principle of preparing silica fume-substituted alkali-activated steel slag cementitious material was formed.The research results are as follows:（1）The mechanical properties of alkali-activated steel slag and the composites of steel slag and auxiliary precursors were tested,and the microstructure was characterized by means of X-ray diffraction（XRD）,thermogravimetry（TG-DTG）,infrared spectroscopy（FT-IR）and scanning electron microscopy-energy dispersion spectra（SEM-EDS）.The order of strengthening ability of slag,fly ash and silica fume was obtained from the mechanical properties;Based on the analysis of hydration products,the powder strengthening mechanism of alkali-activated steel slag was revealed;Based on the cost and environmental factors,the idea of preparing silicon source substituted alkali-activated steel slag cementitious material is put forward.（2）The effect of alternative silicon sources was studied by mean of mechanical properties and microstructure characterization（XRD,FT-IR,SEM-EDS）,and the order of the activity of waste glass powder,rice husk ash,diatomite earth,analytical purity of diatomite rarth and silica fume with activator parameters were obtained.Based on the selection of silica fume as alternative silicon source,the hydration process of silicon source-substituted alkali-activated steel slag under the influence of activator parameters was explored by chemical deformation,hydration heat and transmission electron microscope-selected area electron diffraction（TEM-SEAD）.On the basis of mechanical properties and microstructure analysis（TG and FT-IR）,the optimal ratio of silica fume-substituted alkali-activated steel slag at room temperature was determined,and then the mechanism of silica fume substitution was obtained.（3）Drying shrinkage test,mercury intrusion porosimetry（MIP）and water absorption test were carried out on alkali-activated pure steel slag and silica fume substituted samples respectively.The drying shrinkage and pore distribution with modulus N,water/sodium ratioλand silica fume content were obtained by drying shrinkage test and mercury injection test.Based on the analysis of pore size distribution,mass recovery rate and length recovery rate,the drying shrinkage mechanism of silica fume-substituted alkali-activated steel slag was obtained,and the optimal proportion of silica fume-substituted alkali-activated steel slag in drying environment was put forward.（4）Mass growth rate and length growth rate of alkali-activated pure steel slag and silica fume-substituted samples after sulfate attack were compared and studied,and the microstructure of hydration products after corrosion by XRD,FT-IR and SEM-EDS mapping were characterized.Based on the compressive strength,strength loss index K and compressive corrosion resistance coefficient Ks,the influence of modulus n,water-sodium ratioλand sulfate cation(Na⁺and Mg²⁺)on sulfate erosion was obtained.On the basis of microstructure analysis,the different attack mechanisms of Na₂SO₄ and Mg SO₄on alkali-activated steel slag and the effect of silica fume substitution were obtained.Based on the inconsistent mass growth rate and length growth rate during Mg SO₄ attack,the indexes for evaluating the sulfate resistance of silica fume-substituted alkali-activated steel slag were selected.The optimal mixture ratio suitable for different sulfate environment was summarized.（5）The optimal ratio of silica fume-substituted alkali-activated steel slag in different environments is as follows:at room temperature without corrosion,n=0.75,λ=15,sodium silicate reduced by 20%,silica fume content is 10%;When Na₂SO₄ is corroding,n=1.25,λ=21,sodium silicate is reduced 20%,silica fume content is 10%;When Mg SO₄ corroded,n=0.5,λ=21,sodium silicate decreased 20%,silica fume content is 10%.Because the substitution effect of silica fume at low modulus is better,and even surpasses the high modulus non silica substituted samples at the optimal ratio.from this point of view,silica fume substitution can save 20%～64%of water glass in the noncorrosive environment at room temperature,20%～74.3%in Na₂SO₄ corrosion environment and 20%～63.1%in Mg SO₄ corrosion environment.