Research On Chemical Stability Of Magnetite In Concrete

The accumulation of tailings has always been a major problem both at home and abroad.The accumulation of a large amount of tailings not only wastes land,but also pollutes the ecological environment.Therefore,the utilization of tailings has become a research hotspot at home and abroad.Among them,the use of tailings as aggregates instead of natural sand and gravel can not only solve the problem of tailings accumulation,but also reduce the over-exploitation of natural sand and gravel.The pure Fe₃O₄ reagent and magnetite were selected as the research objects,immersed them in simulated concrete pore solution,5 wt%Na Cl solution and 5 wt%Na₂SO₄ solution at 20?and 80?respectively,using X-ray diffraction(XRD)and scanning electron microscope(SEM/EDS))analyze phase changes;prepare cement paste test blocks,use optical microscope and SEM/EDS to observe and analyze the interface reaction between magnetite and cement paste;use magnetite to replace part of the crushed stone to prepare concrete,soak them at 20?and In 80?water,5 wt%Na Cl solution and 5 wt%Na₂SO₄ solution,the effect on concrete strength was studied.The results show:1)In the simulated concrete pore solution with and without 5 wt%Na Cl,whether the temperatur of solution is at 20°C or 80°C,Fe₃O₄ transformes into Fe₂O₃ and gelatinous iron oxyhydroxide.2)In 5 wt%Na Cl and 5 wt%Na₂SO₄ solutions,the conversion of Fe₃O₄ is not affected by Cl^-and SO₄^2-,Fe₂O₃ and gelatinous iron oxyhydroxide also form.3)In the cement paste,the diffusion of elements at the interface between the magnetite and the hardened cement paste has been found,indicating that there is a reaction between the magnetite and the cement paste.4)Using 5 wt%magnetite instead of coarse aggregate to prepare concrete,whether the concrete is cured in water at 20°C and 80°C,or cured in 5 wt%Na Cl solution and 5 wt%Na₂SO₄ solution,the strength of all the concrete is improved to a certain extent.Figure 51;Table 5;Reference 50.