Study On Preparation And Excitation Mechanism Of High Activity Steel Slag

The cement industry emits a large amount of the greenhouse gas CO₂ in the process of processing and producing mineral raw materials,which is a major source of pollution in the world.Therefore,alternative methods that can effectively reduce such large-scale pollution should be studied.Steel slag is a solid waste generated by the steelmaking process,which not only occupies land,pollutes soil and water sources,but also brings serious harm to the environment.Steel slag contains similar minerals C₃S,C₂S and ferroaluminate as cement clinker,but its content is generally less than that in clinker,and the crystals are larger,more complete and less active.In addition,the steel slag also contains a large amount of free Ca O and Mg O after reacting with water,which will expand and crack the hardened slurry,causing potential safety hazards.In order to improve the activity of steel slag,this study proposes a new type of ammonium bicarbonate initiator to improve the activity of steel slag,convert steel slag into an environmentally friendly concrete cementitious material instead of part of cement used in the construction industry,which can not only turn steel slag into waste into treasure,but also alleviate the damage caused by the cement industry to the environment.In this paper,the effect of ammonium bicarbonate on the mechanism and microstructure evolution of steel slag hydration process was deeply studied.The results are as follows:Firstly,according to GB/T17671-2020 test standard,30wt%cement was replaced by highly active steel slag excited by ammonium bicarbonate.After 28 days of constant temperature curing,the activity index was calculated to be 92%.According to the GB/T1346-2011 test standard,the stability value of the test reached 1mm.From the performance test results,it is clear that the ammonium bicarbonate-excited high-activity steel slag is sufficient to meet 80%of the requirements of the GB/T 20491-2017 standard for the activity index of primary steel slag powder used in cement and concrete.Secondly,the micro-test results of the hydration products of highly active steel slag excited by ammonium bicarbonate were analyzed.In the XRD test results,the peak of C-S-H with high strength was detected.The TG test results also show the mass loss of hydrate,and importantly,there is an obvious mass loss of Ca CO₃.O-H,Si-O and CO₃^2-were detected in the results of FTIR and Raman tests,indicating that the hydration products were mainly C-S-H.At the same time,SEM more directly observed honeycomb,petal,and wheat tubular C-S-H.The microstructure of hydration products is also very dense from the physical point of view.Finally,through the analysis of the microscopic test results,it can be inferred that ammonium bicarbonate promotes the hydration of steel slag,resulting in a large number of vitreous depolymerization,RO phase decomposition,Si-O bond and Al-O bond fracture,recombination in the hydration process,resulting in a good deal of hydration products C-S-H,and improving the hardening strength of steel slag.In addition,the alkaline substance in steel slag is conducive to the carbonization of f-Ca O.Since ammonium bicarbonate is easy to decompose into CO₂,a large amount of f-Ca O in steel slag is carbonized to produce Ca CO₃,which improves the volume stability of steel slag.At the same time,C₂S and C₃S also carbonize in the process of hydration,which promotes the formation of C-S-H at the same time.