Application Research Of Iron Ore Tailings In Autoclaved Aerated Concrete

In the 14th Five-Year Plan period,China has posed a more serious challenge to the resource utilization of solid waste.Hydrothermal synthesis of porous materials under high temperature and high pressure conditions offers an effective solution for dealing with the large accumulation of solid waste,as the selection of raw materials for such synthesis has relatively low requirements.In this study,the effects of incorporating two different sizes of iron ore tailings(IOT)on the slurry and mechanical properties of autoclaved aerated concrete(AAC)were investigated,with steel slag used as a calcium source and deactivated Zeolite Socony Mobil-5(ZSM-5)as a silicon source and auxiliary foaming material.The AAC hydration products and pore structure were further characterized by X-ray diffraction(XRD),Fourier-transform infrared spectroscopy(FTIR),thermogravimetry-differential thermal analysis(TG/DTG),scanning electron microscopy-energy dispersive spectroscopy(SEM/EDS),and mercury intrusion porosimetry(MIP).The main conclusions of this study are as follows:(1)By designing different Ca/Si ratios,a benchmark ratio for the preparation of autoclaved aerated concrete with steel slag as a full replacement of lime was established.As the Ca/Si ratio increased from 0.71 to 0.92,the compressive strength and bulk density of the products showed a decreasing trend followed by an increasing trend,with the compressive strength ranging from 2.1 MPa to 3.1 MPa and the bulk density ranging from480 kg/m~3 to 535 kg/m~3.A Ca/Si ratio of 0.92 was established as the base ratio,with the following proportions:58%steel slag,24%deactivated ZSM-5,15%cement,3%gypsum and 0.14%aluminium powder.(2)By incorporating different levels of crude IOT into the base mix,it was found that the p H of the slurry decreased from 12.65 to 12.47,the flow of the slurry increased by 22%compared to the slurry without IOT,the expansion of the slurry ranged from 90%to 92%and the termination time of gas generation ranged from 69 to 90 min.The incorporation of IOT significantly improved the mechanical properties of the product,with a 32.2%increase in compressive strength and a 19.6%increase in bulk density.The microstructure shows that the unreacted IOT during the autoclaving process not only act as a filler aggregate,but also act as a carrier for the growth of tobermorite interconnecting with the surrounding tobermorite to form a dense network structure,which is much stronger than out pure tobermorite phase.(3)Partial replacement of steel slag by internal blending of fine IOT into the base mix,it was found that the p H of the slurry decreased from 12.58 to 12.42 with increasing admixture,the flow of the slurry increased from 195 mm to 220 mm,the gassing time of the slurry increased by 25%and the final expansion rate ranged from 120.1%to 124.8%.The compressive strength of the samples increased from 2.1 MPa to 2.8 MPa with a bulk density between 496.5 kg/m~3 and 527.3 kg/m~3 when the fine IOT were blended at 8%to24%.Compared to the coarse IOT,the fine IOT were more soluble and relatively more hydrated during the autoclaving process,and the diffraction peak intensity of quartz,the main mineral phase in the IOT,was significantly lower after autoclaving compared to the pre-autoclaving samples.In addition to this,the morphology of the reaction product,tobermorite,changes from grass-like to plate-like with increasing admixture of fine IOT and is more crystalline.