Electrochemical Evaluation of Self-Healing Epoxy Coated Rebar in Simulated Concrete Pore Solution

Abstract

The use of epoxy-coated rebar (ECR) has become a major form of protection for reinforcing steel in concrete bridges in North America. ECR has been shown to increase the service life of reinforced structures but a few structures showed severe corrosion of the rebar when the coating had been previously damaged or in the presence of high chloride concentrations. The increase of protectiveness from the addition of microcapsules containing triethanolamine (TEA) in the presence of chlorides is studied. The microcapsules containing TEA were produced by free radical polymerization and involving a 4-step process. When the coating has been damaged the microcapsules can release TEA either due to mechanical rupturing or when there is a local pH difference due to the corrosion of the rebar. To test the corrosion inhibition effect of the admixed microcapsules the coating is damaged to accelerate the corrosion of the rebar. Electrochemical corrosion testing and visual inspection were performed to determine the effect of the addition of microcapsules on the damaged coatings protection. A carbonated simulate pore solution was chosen for electrochemical testing to simulate an aggressive environment to initiate the corrosion process to promote the release of the corrosion inhibitor. Electrochemical impedance spectroscopy, linear polarization resistance, open circuit potential, and scanning vibrating electrode technique were the electrochemical tests performed to characterize the interfacial reactions under corrosive environment. The addition of microcapsules to the epoxy coating showed a corrosion inhibition effect for the damaged coating. This can be seen by a delay in the time for the exposed area to become fully corroded for samples exposed to electrochemical testing and exposed in an accelerating fog chamber. Also, the samples with the addition of microcapsules showed larger values of the polarization resistance (Rp) for the duration of testing, but all samples showed a decrease in the Rp with exposure, which is due to corrosion occurring in the exposed area.