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UBC Theses and Dissertations

Non-destructive detection of corrosion of epoxy coated rebar Goffin, Brigitte


Deteriorating infrastructure is an acute and dangerous problem, which is often caused by the corrosion of concrete reinforcement. Marine structures and bridge decks, where sea water and de-icing salts lead to chloride ion diffusion into the concrete are particularly at risk. Epoxy coated rebar (ECR) is a popular choice for the latter structures. However, corrosion of ECR, which occurs due to coating damage, poses a challenge to non-destructive corrosion detection. This study investigated the corrosion behaviour, accelerated corrosion and non-destructive corrosion detection of ECR. The electrochemical corrosion behaviour of ECR in simulated concrete pore solutions was studied and compared to uncoated rebar (UCR). The polarized area of ECR was related but not proportional to the sodium ion concentration of the test solution. Furthermore, ECR was more susceptible to corrosion than UCR, particularly in the presence of NaCl and in NaHCO₃ solution. A test solution of Na2CO₃ and NaHCO₃ led to the formation of a very fragile passive layer, that grew slowly but continuously. However, the protective layer was sensitive to even small amounts of NaCl. Corrosion of ECR was accelerated in neutral and alkaline NaCl solutions as well as in concrete. Neutral and alkaline environments promoted coating holiday and undercoating corrosion, respectively. Part of the undercoating corrosion process was cathodic delamination, whose acceleration prior to corrosion acceleration slowed down the lateral corrosion expansion. Once corrosion had expanded across the entire surface, the subsequent corrosion rate was not affected by the initial cathodic disbondment. Successful ECR corrosion detection was limited with the linear polarization resistance and ground penetrating radar method. However, concrete properties such as maturity, moisture and chloride content had a significant effect on the measurements. Corroded bars affected the Hall effect (HE) voltage to a lesser extent than intact rebar. Furthermore, corrosion of ECR led to higher concrete surface and lower bar temperatures during active infrared thermography (IRT) tests. The thermal results of ECR opposed those of UCR. The HE and IRT tests showed that the effects of corrosion on the thermal and magnetic behaviour during induction thermography would complement and oppose each other for UCR and ECR respectively.

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