19 June 2001
Reinforcing Steel. Reinforcing steel for concrete in waterfront facilities
is the same as for conventional concrete structures and should conform to ASTM
A 615,Specification for Deformed and Plain Billet-Steel Bars for Concrete
Reinforcement; ASTM A 616, Specification for Rail-Steel Deformed and Plain
Bars for Concrete Reinforcement; or ASTM A 617, Specification for Axle-Steel
Deformed and Plain Bars for Concrete Reinforcement. Place 8-cm (3.15 inch)
concrete cover, which is critical for durability, over the plain steel. If an 8-cm
(3.15 inch) concrete cover is not possible, then a barrier coating on the rebar
should be considered to isolate the steel from these corrosive agents. ASTM A
934, Specification for Epoxy-Coated Reinforcing Steel Bars should be specified
for new reinforcement.
Special Types of Concrete Mixtures. Special concrete mixtures
include polymer concrete and polymer-Portland cement concrete. Concrete
mixtures containing polymers are useful for repairing concrete and may provide
improvements over conventional concrete mixtures when used and applied
3-3.4.1 Polymer . Polymer concrete does not contain Portland cement. Epoxy
concrete is one common type of polymer concrete that is readily available and
possesses excellent bond and tensile strength qualities. Use extreme caution
when using polymer concretes for structures subject to thermal resistance due to
a high coefficient of thermal expansion that often results in repair failure.
3-3.4.2 Fiber Reinforced. Fiber reinforcements may improve the tensile
strength, toughness, and ductility of concrete. In general, steel fibers should not
be used in the marine environment. Polypropylene fibers avoid the corrosion
problem of steel fibers and improve impact resistance. Fiber should not be
considered as a replacement for the reinforcement.
are the results of chemical attack and rebar corrosion.
3-3.5.1 Chemical Attack. The most common chemical attack is from sulfates
in seawater that cause a softening of cement paste. Other causes of chemical
attack are poor quality aggregates reacting with alkali in the cement (alkali-
aggregate reaction). The alkali-aggregate reaction expands the aggregate and
results in cracking throughout the concrete in the presence of moisture. Use of
25% Class F fly ash is extremely effective in reducing chemical attack.
3-3.5.2 Corrosion of Reinforcing Steel. The high alkalinity of cement paste
protects steel from corrosion. With improper mix designs, chloride contamination
and carbonation eventually reduce the alkali film around the steel. Corrosion will
then occur if sufficient moisture and oxygen are present. In the splash zone, the
wet and dry cycles provide conditions for the chloride and oxygen to corrode the
steel. Accordingly, steel corrosion in concrete is most severe directly above the
mean low water (MLW).