The combined effect of salt and temperature on the corrosion behavior of X80 steel in silty soil was studied by microscopic and spectroscopic characterization techniques and electrochemical measurements.

The mathematical model of impedance response and the equivalent circuit model is determined based on electrochemical kinetics theory, and a method for calculating the kinetic parameters of the metal interface is presented.

The corrosion differences of X80 steel are exhibited by electrochemical impedance spectroscopy, polarization curves, and scanning electron microscopy in saturated sandy soil containing different concentrations of NaCl and Na2SO4 under indoor simulation conditions. The corrosion rate of X80 steel is minimal with NaCl and Na2SO4 concentrations of 0.5% and 0.3%, respectively. Additionally, the corrosion morphologies are mainly shallow and small pits. However, the corrosion rates are hindered due to the accumulation of oxide films on the surface of X80 steel. The increase in sodium salt content accelerates the overall corrosion rate until 1.0%. Meantime, the oxide films are eroded by Cland SO4 2and re-accelerate the electrochemical corrosion process, so the pits evidently deepen and expand.

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In this study, the effects of high-sulphur fly ash on the properties of lightweight cement-treated materials (LCMs) immersed in sodium sulphate solutions were studied. The unconfined compressive strength of LCMs corroded by sulphate was tested. The microscopic properties were characterised by X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that high-sulphur fly ash has an adverse effect on the structural strength of LCMs after corrosion, but when the content of fly ash is less than 75%, the effect of fly ash on the strength is small. A small amount of high-sulphur fly ash can improve the density of the material structure; the internal pore structure of LCMs provides space for the growth of ettringite and other corrosive substances and relieves the expansion pressure. LCMs mixed with high-sulphur fly ash have a certain resistance to sodium sulphate corrosion.