Study On The Effect Of Carbonation On The Hydration Activity And Stability Of Steel Slag And Ro Phase In Steel Slag

Steel slag contains cementitious active materials such as tricalcium silicate(C3S)and dicalcium silicate(C2S),which have great application potential in cement and concrete production.The presence of f-CaO and f-MgO in steel slag will cause poor volume stability of steel slag.At the same time,the content of RO phase with less hydration activity in steel slag is higher,and the influence on the hydration activity and stability of steel slag is still uncertain.Low hydration activity and poor stability limit the application of steel slag in cementitious materials.In this study,by synthesizing different ratios of RO phase to simulate the composition of RO phase in steel slag,the hydration activity of RO phase and the influence on the volume stability of steel slag were explored,and the carbonation experiments on steel slag and RO phase were carried out to study the effect of carbonation.The influence and mechanism of the properties of steel slag and RO phase.Finally,carbonated steel slag is used to prepare cementitious materials,which significantly improves the stability and mechanical properties of cementitious materials,and the mechanism is studied.The main mineral phases of steel slag are C3S,C2S,calcium aluminate ferrite(Ca2(Al,Fe)2O5),RO phase,calcium ferrite(C2F)and calcium iron manganese phase.BSE shows that the microscopic morphology of RO phase in different steel slags is different.The increase of MnO content(or the decrease of FeO content)makes the surface morphology of RO phase more irregular.The hydration rate of MgO in the RO phase is about 20.10%,which is a hidden danger of the volume stability of steel slag.The carbonation of steel slag and RO phase was studied.The results show that with the increase of carbonation time,the storage of CO2 in steel slag and RO phase has increased;under autoclave conditions,the hydration rate of MgO in the RO phase is only 20.10%,and through carbonation,58.83%of the RO phase is MgO is converted to MgCO3,and shows the activation effect of carbonation on the RO phase.The carbonation reaction improves the mechanical properties and volume stability of steel slag,which proves that the carbonation reaction has a positive influence on the application of steel slag in cement cementitious materials.Carbonated steel slag was used to replace part of cement to prepare cementitious materials,and the mechanical properties and volume stability of cementitious materials were studied.From the aspect of hydration performance,the reasons for the influence of carbonated steel slag on the performance of cementitious materials are discussed.The results show that the carbonation reaction can reduce the content of f-CaO in the steel slag.The carbonated products are mainly calcite,and the microstructure presents the form of uneven particles and carbonated layers.Although the silicate phase in the steel slag can be carbonated,the CaCO3 produced by carbonation fills the microcracks or pores of the cementitious material,or becomes the core of the hydration product,which significantly improves the 28-day strength of the cementitious material.