Na₂SiO₄-and Cement-Based Activation On Waste Steel Slag And Its Application On Soft Soil Stabilization

Large number of steel slag is produced annually in China but not utilized efficiently for the less cementimation.This study focused on the potential cementimation of steel slag,and the composition adjustment and activation of steel slag were carried out after the analysis of the composition.Based on the previous Ca(OH)2-based activation,the Na2SiO4-based and cement-based activation were attempted.Hereafter,the composite of activated steel slag was applied on the stabilization of the soft soils.Main works and results can be concluded as bellows:(1)After comparing the composition difference between steel slag and cement,component adjustment was firstly carried out by adding metakaolin in slag,hereafter,activity excitation was carried out by Na2SiO4 and cement.The strength evolution and relationship between that and components were investigated.The results show that the optimal mass porportion of Na2SiO4-based activity excitation is Na2SiO4:metakaolin:slag equal to 35:10:90,where the strength arrived at 19.8MPa.On this occasion,the cement ratio values(SM,IM,and KH)were 2.7,0.76 and 0.30 respectively.On the other hand,the optimal porportion of cement-based excitation is cement:metakaolin:slag equal to 50:15:85,where its strength arrived at 41.3 MPa and the cement ratio values(SM,IM,and KH)were 2.08,1.3 and 0.41 respectively.Note that its SM and IM are quite consistent with that stimulated by Ca(OH)2.(2)Microscopic test techniques were adopted to clarify the characteristics of the porosity,type and pattern of hydrated products,thereafter,the activativation mechanism was also explained with chemical reaction formula.The results show that different excitation almost have the same hydration products C-S-H,C-A-H and C-A-S-H,whilst the cement-based excitation can also generate ettringite.The hydration products of Na2SiO4-based excitation were mainly composed of C-S-H in the bulky pattern and C-S-H generated from slag particle.While those stimulated by cement-based excitation were mainly reticular C-S-H and slag-inner C-S-H,which fulfilled and connected the composite matrix,including the inside of the slag.This finding suggests that that the slag particle took part in the chemical reaction.The prolific the hydration product as well as the smaller capillary pore size led to the strength continuous generation.(3)Considering the strength,microstructure and formation of hydrate,the optimal mass ratio of Na2SiO4 solution(40%concentration)to metakaolin and ratio of cement to metakaolin both was 3:1.(4)The strength(after 28 days' curing)of the soft soil stabilized by slag composite activated by the cement at the optimal ratio,arrived at 1.2MPa with 20%incorporation,and its strength reduces with the moisture content increasing.Meanwhile the material cost is obviously lower than that of traditional modification materials.It shows that the developed composite of the slag,metakaolin and cement is effective and cheap.