Civil Engineering Reference
In-Depth Information
Michael G. Grantham
10.1 Introduction
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.
