Investigation On The Phase Transformation Of Iron Ores In Concrete

The subject selected pyrite,magnetite,hematite,limonite,ilmenite as research objects,from simulated concrete pore solution system,cement paste or mortar system,at20°C and 80°C,XRD,SEM-EDS and other testing methods were used to study the phase transformation of iron ores in concrete.Research indicates:In the simulated concrete pore solution,FeOOH and KFe（SO₄）₂·H₂O were formed at20°C;at 80°C,CaSO₄ was formed.In cement paste samples,corrosion spots appeared on the surface of the pyrite,and cement gradually loosed.In the simulated concrete pore solution,Fe₃O₄ was oxidized to Fe₂O₃,but at 80°C,dolomite is formed.The chemical composition of the solution showed that part of the iron component and the siliceous component were dissolved in the liquid phase.There is no obvious phase change of hematite in simulated concrete pore solution at20°C;at 80°C,when the age is 180 d,some minerals,such as diopside,actinolite and so on,are formed.When the age is 270 d,diopside is converted into magnesium chlorite.In low strength cement mortar samples,a Fe-rich and Ca-rich transition zone appeared near the interface.There was no obvious phase change of limonite in simulated concrete pore solution,but kaolinite dissolved in limonite.In the cement paste sample,red rust is enriched at the interface between the limonite ore and the hardened cement slurry at 80°C.In simulated concrete pore solution,hongquiite,Ti₄O₇ or FeTiO₃ is oxidized to TiO₂and K₂Ti₂O₅.In the cement paste sample,a Fe-rich and Ca-rich transition zone appeared near the interface,and no element enrichment was found in both cement mortar samples with different strength.