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Harbor
Overview
The objective of rehabilitating the concrete was to provide sound
concrete, a uniform surface, and moisture protection for the installation
of the cathodic protection system and for the application of the
composite reinforcing. The scope was limited to the top and bottom
of the deck and the track slabs. Piles, transverse girders, curb,
and bollard/cleat platforms were not included. The NFESC-designed
concrete repair represented state-of-the-art methods and materials.
Some of the steps or procedures required in the specifications were
not typical of normal construction but were strictly imposed due
to the critical nature of preparing a sound surface for applying
external reinforcing.
NFESC identified areas that required repair based on earlier condition
assessment studies. Since Bravo 25 underwent extensive repairs in
1996, only minimal unsound concrete was expected to be encountered.
Bravo 25 exhibited rebar corrosion and carbonation typical of a
50-year-old waterfront structure subject to chloride contamination.
There is ongoing rebar corrosion, especially along the joints, cracks,
and rails.
Concrete rehabilitation on the deck top surface between Bents 177
and 189 and between Bents 216 and 225 included:
- Removing the outside crane rail
- Removing asphalt, paint, oil, and chemical spills
- Removing unsound concrete in the deck
- Adding longitudinal steel rebar along the rail slot
- Replacing unsound concrete with a polymer modified cementitious
concrete
- Repairing the rail slot with a polymer modified cementitious
concrete
- Slotting and sealing concrete cracks
The removal of the outside crane rail and the subsequent repair
of the rail slot and adjacent concrete was a significant portion
of the rehabilitation effort.
Concrete repair of the deck bottom surface between Bents 177 and
189 and between Bents 216 and 225 included:
- Removing paint and coatings
- Removing unsound concrete
- Knocking down formed, built up patches from previous repairs
- Replacing unsound concrete with a polymer modified cementitious
concrete
- Filling small voids, holes, and other “low” areas
with a polymer modified cementitious grout
Below deck scafolding consisted of a continuous 5/8-inch (15 mm)
plywood deck secured to a system of aluminum beams placed approximately
3 feet (1 m) apart. The beams rested on triangular knee braces that
were clamped to the wharf piles. The staging provided a safe and
convenient platform about 6 feet (2 m) below the deck to perform
the work and a “net” to prevent concrete debris from
falling into the harbor. Screening secured to the outer perimeter
provided a barrier to confine the fine particles of concrete from
being blown into the water.
Top Deck Concrete Removal. NFESC engineers defined
the limits of unsound concrete with the contractor at the site.
Limits were extended a few inches beyond suspected unsound concrete
areas to simplify geometry of the repair area and minimize shrinkage
stress concentrations. The contractor saw-cut a ½-inch (1.3
cm) deep perimeter around the unsound concrete. A 15-pound (7.3
kgm), pneumatic, hand-held chipping hammer was used to remove concrete
inside saw-cut perimeters. Impacts tools greater than 15 pounds
(7.3 kgm) can cause cracks in sound concrete and were strictly prohibited.
Concrete was removed until only sound concrete remained, which sometimes
required additional saw cuts to extend defined limits. The concrete
removal process produced a very rough surface texture (roughness
approximately ¼ inch (7 mm) in depth) without polishing the
aggregate. Rebar with visible corrosion was “chased”
to the point where no surface corrosion was visible beyond normal
mill scale. Concrete around all bars was removed to at least 1 inch
below the rebar.
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