Research On Chemical Stability Of Siderite In Concrete

The large demand of mineral resources for national economic development had led to a large number of tailings accumulation,resulting in many environmental problems.Using iron tailings instead of natural sand as the aggregate of concrete can not only reduce the over exploitation of natural sand,but also improve the comprehensive utilization of tailings.Taking siderite as the research object,firstly,the possibility of siderite reaction in the liquid environment of concrete was proved by thermodynamic calculations;then,in the simulated concrete pore solution system,cement slurry system,aggressive aqueous environments at 20 ? and 80 ?,research the phase transformation law of siderite in concrete by Mortar rod length measurement,concrete strength experiment and XRD,SEM/EDS,laser Raman and other testing methods.The results show that:1)It is proved that FeCO₃ can react in Ca?OH?₂ solution by thermodynamic calculation.The possible products are Fe₃O₄,Fe2O₃ and CaCO₃.The reaction that produces Fe₃O₄ is thermodynamically easier than produces Fe2O₃.2)The Pure pulp experiment shows that FeCO₃ reacts in the liquid phase of Portland cement,and the main products are Fe₃O₄ and CaCO₃.Besides,the increased temperature promotes reaction.3)The conversion of FeCO₃ to Fe₃O₄ in the liquid phase environment of Portland cement is not significantly affected at the presence of Na Cl and Na₂SO₄,which shows that the aggressive media Cland SO₄^2- have no obvious promoting effect on the transformation process of FeCO₃.4)Theoretical analysis and mortar bar test results show that the transformation of FeCO₃ into Fe₃O₄ in the liquid phase environment of Portland cement is a process of solid volume expansion.The expansion rate increases with the increase of FeCO₃ content.5)In the case of concrete formulated with 5% siderite ore instead of ordinary crushed stone,it has almost no effect on the strength of the concrete at 90 d,whether the concrete is cured at 20 ? or at80 ?.Besides,the strength at 90 d is also not affected at the presence of aggressive media Cl^- and SO₄^2-.Figure 74;Table 11;Reference 70.