Effect of Magnetite on Compressive Strength of Concrete and Its Mechanism

The magnetite ore was taken as the partial aggregate to prepare two types of concrete specimens mixed with magnetite and without magnetite. Both were cured in water and 5 wt % Na₂SO₄ solution at 20 and 80°C, respectively, to study the influence on the strength of concrete. In addition, the magnetite ore was ground into powder, and cured in simulated concrete pore solution and 5 wt % Na₂SO₄ solution respectively, and the mineral and morphological change at different ages was tested by X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). The experimental results show that the strength of concrete with magnetite ore is a little higher than that of concrete without magnetite ore whether cured in water or in Na₂SO₄ solution, and the magnetite transforms into Fe₂O₃, ferrihydrite and other minerals in simulated concrete pore solution and in 5 wt % Na₂SO₄ solution. The experimental results also demonstrate that using some magnetite ore as aggregate for concrete is beneficial for improving the sulfate resistance of concrete.