19 June 2001
Use a water-reducing admixture (ASTM C 494) when concrete is
placed in area congested with reinforcing or in pours difficult to
consolidate. This will decrease chance of voids and temptation to
add water to the concrete.
Specific guidelines for underwater concrete include:
Water-cement ratio must not exceed 0.40 (19 L (5 gallons) per bag
Use a minimum of 445 kg (10.4 bags) to a maximum of 556 kg
(11.25 bags) of cement per cubic meter.
Use an air-entraining admixture to obtain 3 to 6 percent entrained
air for improved workability.
A water-reducing plasticizing admixture may be used to enhance
Special Types of Repair Concrete
Fiber-Reinforced Concrete. Concrete and mortar containing fibers of
steel, glass or polypropylene are sometimes used in repair work. Fiber
reinforcement provides improved tensile strength, toughness and ductility to
concrete. The fibers reinforce crack repair material by distributing tensile strains.
Fiber-reinforced shotcrete is good to use in marine repair work. In
some applications, the fibers can replace steel mesh. Although steel fibers
corrode near the surface, in the interior sections they are protected from
corrosion by the high alkali of the cement paste. Steel fibers are usually 0.3 mm
to 5 mm (1/100 to 1/5 inch) in diameter and 13 to 40 mm (1/2 to 1 3/5 inch) long.
The quantity of steel fibers used varies from 30 to 90 kg/m2 (6.2 to 18.5 psf.)
Glass fibers in concrete can lose strength over periods of time in a wet
environment and are not recommended. Synthetic fibers reduce crack size due
to plastic shrinkage, but should not be the primary reinforcement.
Latex Modified Portland Cement Concrete. Latex modified Portland
cement concrete should not be confused with epoxy or polymer concrete
discussed in Paragraph 184.108.40.206. Latex modifiers improve the bond and tensile
strength and reduce the permeability of Portland cement concrete. Latex
formulations of acrylics, styrene-butadiene, and polyvinyl acetates are available.
The first two latexes are suitable for wet environments. Polyvinyl acetates should
not be used in concrete for repairs exposed to water. Latex modified concrete is
recommended for overhead and vertical repairs when placed in lifts less than 4
cm (1 3/5 inch.)