This is a difficult problem to solve. Sealers or barrier
coatings help, to some extent, to slow down the process but
do not stop it. Barrier coatings on the reinforcing steel, such
as epoxies, latex slurries, or zinc-rich coatings, can inhibit
the corrosion activity; however, there are field-application
problems that can significantly reduce their effectiveness.
Cathodic protection and chloride extraction are alternatives
that should be considered where economically feasible.
Recently, several highway departments have used galvanic
anodes to reduce corrosion in and around patches and in
concrete overlays (Section 4.7.4).
4.3.6 Cracks—All concrete repair programs and protection
systems should address the proper treatment or repair of
cracks. Intrusion of water into cracks can result in corrosion
and freezing-and-thawing problems in cold climates.
Only after determining the reason for the occurrence of a
crack can a proper repair technique be developed. Structural
cracks requiring repair should be able to reestablish load
transfer across the crack, usually coupled with epoxy
injection to ensure a positive repair.
Active cracks, especially those due to thermal changes on
exterior exposures, should be repaired to allow for future
movements. Techniques involving caulking, chemical
grouts, elastomeric coatings, and high elongation epoxies
have proven to be useful in addressing moving cracks.
The repair of active cracks on exterior exposures can be
difficult. Most of the materials used for crack repair are
temperature-sensitive and cannot be installed much below
4 °C (40 °F). It is most common to repair cracks at temperatures
above the manufacturer’s recommended minimum. Although
this facilitates the installation of the repair material, active
cracks due to temperature variations tend to close in warm
weather. Cracks that open in the winter are closed in the
summer. Both the contractor and the engineer should be
aware of this before commencing with the repair process. If
feasible, an inspection of the structure should be conducted
in cold weather to document the location of the cracks
requiring repair (ACI 224.1R). It is also desirable to conduct
repairs when the crack is near its maximum width, because
most flexible materials used in repair of active cracks
perform better in compression than in tension (Emmons
1994; ACI 504R).
4.3.7 Chloride/chemical attack—Penetration of chemical
or salt solutions through concrete contribute to the corrosion
of the embedded steel. In addition, chemical attack,
including acids, alkalis, and sulfates, may have a detrimental
effect on the concrete itself. Barrier protection systems are
commonly used to minimize the intrusion of chemicals into
concrete. This is thoroughly discussed in ACI 515.1R, and it
provides a summary of the effects of a variety of materials on
concrete. Refer also to Portland Cement Association’s
Publication IS001 (1997).
4.3.8 Surface erosion—Erosion of concrete at the surface
is a major concern on dams, spillways, and other waterfront
structures, as well as on bridge decks, ramps, parking decks,
industrial floors, and other traffic-bearing structures. Usually
to a lesser extent, it can also be a concern on buildings
exposed to acid rain and severe weather conditions. Concrete