Inhibition Mechanism in Concrete by Organic Substances: An Experimental and Theoretical Study

Corrosion inhibitors are one of the preventative techniques used to prevent chloride-induced corrosion in reinforced concrete structures. Several commercial inhibitors are available on market, but their efficiency as well as their inhibitive mechanism in not well understood. In this paper the inhibiting behaviour of five organic substances in delaying chloride-induced corrosion was evaluated in alkaline solution using electrochemical impedance spectroscopy and potentiodynamic tests. The studied substances were sodium tartrate, sodium benzoate, sodium glutamate, dimethylethanolamine and triethylenetetramine. The best results were obtained with tartrate and benzoate. To establish the interaction between inhibitors and passive film, theoretical calculations based on molecular mechanics and molecular dynamics were used, as well as Langmuir-Freundlich and Temkin adsorption isotherms were established from the experimental results. The theoretical results showed the presence of repulsive interactions between the substances and how the inhibitor scattered across the surface. The adsorption isotherms confirmed both the presence of a strong chemisorption between the inhibitors and the substrate and a repulsive interactions between the molecules of inhibitors, leading to a the formation of a non-homogeneus monolayer, i.e. a layer of inhibitor scattered across the surface of the substrate.