Corrosion Inhibition Mechanisms at the Steel/Concrete Interface - UTC

To investigate the corrosion and corrosion inhibition mechanisms at the steel/concrete interface as a result of chloride attack, in the absence and presence of corrosion inhibitors.

Concrete normally provides both chemical and physical protection for the steel reinforcement embedded in concrete. Cement hydration leads to the highly alkaline (pH ˜ 13–14) pore solution of concrete, which promotes the formation of an oxide/hydroxide film at the steel surface, a passive film of about 10 nanometers thick. For bridge structures exposed to deicer applications or marine environments, chloride ingress into concrete is of primary concern in terms of concrete durability. Therefore, the focus of this research is placed upon this cause of corrosion alone. Extensive research has been conducted to investigate the mechanisms of steel corrosion in concrete in the presence of aggressive chloride ion (CI ), and numerous corrosion inhibitors to mitigate the corrosion of steel in concrete have been studied. However, the corrosion inhibition mechanisms at the steel/concrete interface still elude direct explanation. This can be attributed to two major reasons. First, the existing research pertinent to steel corrosion in concrete has been conducted with the steel sample either immersed in a “simulated pore solution”, or embedded in the concrete specimen. In the former case the research findings are of little value to field applications as such experiments ignore the uniqueness of concrete environment compared with typical aqueous solution environments. In the latter case measurements of corrosion characteristics of steel are indirect and may not accurately reflect the real behavior of steel. Even if the concrete is broken open and the steel sample is then taken for analysis the exposure of the steel surface to mechanical damage or contamination renders the findings questionable. Second, corrosion inhibitors work through various mechanisms. The corrosion of steel in concrete consists of electrochemical reactions, anodic reactions and cathodic reactions which progress simultaneously. Corrosion inhibitors thus can be classified into anodic type, cathodic type, or mixed type. A combination of various corrosion inhibitors sometimes has significant synergetic corrosion inhibition effect, which adds to the complexity of the research problem. With the combined use of electrochemical and physical techniques, it is possible to further the understanding of the localized corrosion of carbon steel in concrete and to unravel the corrosion inhibition mechanisms of various types of corrosion inhibitors. Such knowledge would contribute greatly to the effort of searching for effective measures to mitigate steel corrosion in concrete and protect concrete structures in a chloride-containing environment.