Corrosion inhibitors

Abstract

Over recent years there has been a considerable amount of interest in the use of corrosion inhibitors in the repair of concrete.There are two types of inhibitor: those mixed into a fresh concrete or repair at the time of placing, or those that penetrate by diffusion and/or capillary action through a hardened concrete from the surface. With the former type and careful mixing, a uniform concentration of inhibitor at the rebar can easily be achieved. With the latter, penetrating corrosion inhibitors, getting sufficient inhibitor to the surface of the rebars in sufficient quantity is the main difficulty, with only limited penetration likely with reasonably good-quality concrete that might nevertheless be contaminated with chloride salts. Penetration into low-quality concrete can usually be achieved, however, although this then leaves the question whether it can exit just as easily! In practice, therefore, application of coatings is usually recommended following a repair with a penetrating corrosion inhibitor.Inhibitors can be classified into three main types: • Inorganic, including nitrites, phosphates etc.• Organic amines and some other organic compounds that include the presence of oxygen, nitrogen or sulfur atoms as well as the presence of double bonds. The lone-pair electrons of the mentioned atoms facilitate the adsorption process. These are adsorbed onto the metal surface and effectively block both the cathodic and anodic reactions.• Volatile inhibitors such as amino-alcohols that have a high vapour pressure and penetrate into concrete in the vapour phase. Again, concrete with a low permeability which is chloride contaminated can be difficult to treat with such materials, unless the cover to the reinforcement is very low.