Biosurfactant coatings as innovative inhibitors against corrosion of steel rebars

Reinforced concrete is the most widely used material in civil engineering. Nevertheless, the problem of corrosion of the rebar remains the main cause of degradation and consequently damage of the concrete structures. Protection of the steel rebars against the corrosion is ensured by the formation and the stability of the passive layer mainly composed of iron oxide based species in the high alkalinity media of concrete. The penetration of carbon dioxide and/or of chloride anions can damage the protective layer formed on the steel surface, leading to local corrosion of the steel rebars. Thus the corrosion phenomena will continue up to the complete deterioration of steel reinforced concrete.

Recently, a large number of preventive and curative methods are known to increase the service life of reinforced concrete. The use of chemical surfactants is one of these methods, due to their significant ability to influence the surface properties. Biosurfactants are surfactants synthesized by some microorganisms and they have interesting biocompatibility characteristics.

The objective of this study is to evaluate the biosurfactant properties against corrosion of rebar in a contaminated (chlorides) concrete media. A biosurfactant produced by Pseudomonas aeruginosa is investigated in simulated concrete pore solutions. A first step is to understand the formation of the biosurfactant layer on the steel surface using XPS and contact angle measurements. The composition of the layer is also investigated using FT-IR. Afterwards, the use of biosurfactant as corrosion protective coating for rebar is evaluated using corrosion tests (OCV, LP). Various parameters such as biosurfactant concentration, layer characteristics and corrosion behavior are discussed.