The Investigation of the Cause and Severity of Corrosion at the Port of Dover

This thesis is an investigation into the origins and severity of corrosion caused to the elevated road at the Port of Dover. The research in this thesis is comprised of collecting and analyzing samples, taken uniformly across the bridge as well as providing a recommendation of an adequate protection system based on the results.

The first stage of the project was a visual inspection of the bridge, completed in October 2017. Based on the observations it was concluded that the original (old) part of the bridge showed a higher degree of corrosion than the more recent (younger) part of the bridge. It was also concluded that the Port of Dover itself is affected by parameters of both industrial as well as marine environments, classifying the Port of Dover as a C5 corrosive environment.

There was two occasions of sample collecting, one on the 4th of December 2017 and the second sample collection on the 12th of June 2018. Collected from the old and new parts of the bridge respectively. The sample where stored in a controlled environment until characterized by visual inspection (Scanning Electron Microscopy; SEM), pH, conductivity, X-ray Diffraction (XRD), Electron Dispersive X-ray Fluorescence (EDX) and Raman spectroscopy. From these analyses, the severity, corrosion rates and products could be determined.

The results obtained from the samples characterize the corrosion products to have high levels of iron-based compounds from the steel of the structure. In addition, heavy metal compounds and carbon-based compounds forming black particulates originating from the fuel emissions of heavy traffic could be observed in a majority of the samples. The type and quantity of anions observed in the samples varied across the bridge, proposing that the samples collected in areas exposed to sea spray (elevated and open sites) demonstrated higher levels of chlorine. While sites under the bridge with poor circulation showed higher amounts of sulphates and nitrates from the diesel emission.

The severity of corrosion on the elevated road is not showing signs of structural failure at the present, however, there is corrosion occurring all over the bridge particularly around the bolts where the current paint system has worn off. The most common types if corrosion identified across the bridge are crevice and uniform corrosion.

Carbon-based particulates originating from the diesel emission in the area are a major cause to the observed corrosion types and rates. The particulates create a thin film across the bridge adsorbing other airborne compounds, which contribute to the chemical reaction rates of the corrosion products. Hence, reducing the formation of the carbon(soot) thin films will improve the lifetime of the corrosion protection system. Washing the bridge regularly, is advised to prevent the build-up of the particulates, and that the steel construction of the elevated road is carefully washed and prepared appropriately prior to the addition of the new coating system. The coating system proposed, based on the work in the thesis, is a zinc epoxy/polyurethane paint system.