Failure mechanism on sulfate attack and dissolved corrosion of diseased tunnel lining structure

To study the corrosion failure mechanism of tunnel lining structure subjected to sulfate attack and dissolved corrosion, site investigation was carried out on a diseased tunnel in Chongqing. The corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the tunnel lining structure had been exposed to groundwater containing substantial concentrations of salts (SO42-, HCO3-, et al.) for many years, resulted that the concrete strength was lower than its design value. The formation of thaumasite made concrete lose its strength completely. Concrete structure would be destroyed when crystallization pressure exceeded the tensile strength of concrete. The tunnel also appeared dissolved corrosion which made the cement stone density and concrete strength reduce.