Analysis for Structure of Rust Layer Formed on Weathering Steel Bridge for Bare Use Exposed in Coastal Industrial Zone for 27 Years

The rust layer formed on the 27 years old weathering steel bridge exposed in coastal industrial zone was characterized. The rust layer indicated protective characteristics in terms of the color of rust, the corrosion loss of the steel and the anodic polarization curve. The rust layer consisted of the stacking layers which were dark and bright in the polarized light. The dark rust layer covered the steel surface continuously, while the bright one partly covered the dark rust layer. The outer bright rust layer was in rich of the constituents of γ-FeOOH and β-FeOOH according to the Raman spectroscopy. The inner dark rust layer consisted of α-FeOOH and amorphous substance. The α-FeOOH spread in the wide range of the inner dark rust layer. The elements of Cr, Ni and Cu were observed in the inner rust layer. Copper concentrated both at the crack of the inner rust layer and in pits of the steel. Sulfur concentrated simultaneously with Cu.