MIL-HDBK-1011/1
corrosion-prone areas such as the tropics is the improvement in resistance to
chloride ion penetration for concrete containing high-range water reducers.
3.4
Corrosion
3.4.1
Pre-construction Corrosion Control. Do not use salt-contaminated
aggregate. The use of coral concrete devoid of salt is beneficial in
retarding the rate of oxygen and chloride ion transport to the ferrous metal
surface.
In a few instances, cathodic protection has been used to protect
reinforcing steel. The results of laboratory and field tests reveal that
fusion-bonded epoxy coatings on reinforcing steel also provide adequate long-
term corrosion protection; however, availability and costs must be considered.
Consider an increase in the concrete cover over the reinforcing steel to
reduce the risk of corrosion of the steel. Significant corrosion of steel
embedded in concrete is a major problem in tropical environments. Steel
corrosion occurs within concrete, regardless of the type of aggregate, as an
electrochemical and oxidation-reduction reaction. Control the corrosion rate
by reducing the rate of oxygen transport through the free water within the
concrete to the ferrous metal surface or to the reinforcement.
3.4.2
Corrosion Treatment. After corrosion of steel reinforcement begins
in an existing structure, there is no satisfactory attenuation technique.
Concrete surface coatings such as coal tars, cut-back asphalts, and asphalt
emulsions have been tested, but most are ineffective in preventing moisture
migration in concrete over time. Properly formulated epoxy resin coatings are
superior in preventing moisture migration. Completely expose and remove all
rust from corroded reinforcing steel in repair operations. If corrosion is
too advanced, replace reinforcing before concrete repair.
3.5
Hot-Weather Concreting. Ensure that specifications include
provisions for hot-weather concreting procedures in conformance with American
Concrete Institute (ACI) Recommended Practice 305, Hot-Weather Concreting.
3.6
Concrete Reinforcement
3.6.1
Precaution When Using Galvanized Reinforcement. Galvanic action
occurs when freshly mixed concrete is placed in contact with galvanized and
ungalvanized steel which are tied together. These metals in the presence of
portland cement paste acting as an electrolyte, create an electrochemical
cell. Galvanic action within hardened and fully-cured concrete may not
necessarily pose a problem because of the very low currents generated. A much
more severe problem exists, however, when the concrete is fresh. Until the
concrete sets, very large currents may flow from zinc anodes to the iron
cathodes, where hydrogen ions acquire electrons and form molecular hydrogen
which is liberated along the cathodic surface. This gas generation can cause
expansive pressure on the concrete encasing the steel reinforcement creating a
gas-filled void along the entire surface area of the reinforcement.
15
Previous Page
