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Wet Lay-Up Composite Laminate
Wet lay-up, carbon/epoxy laminate was chosen to externally reinforce
the underside of Bravo 25. The contractor used Carbon Fiber Sheet
system. The Carbon Fiber Sheets system consists of uniaxial carbon
fiber tow sheets in an epoxy resin matrix (saturant). The epoxy
saturant was formulated to provide completely wetting of all carbon
fibers in each laminate ply. The saturant also provides a high interlaminar
shear strength and bond with the concrete to develop the concrete
shear and tensile strength.
The upgrade reinforcement for each structural element (center slab,
track slab, and curb slab) required 5-plys of carbon laminate with
an areal fiber weight of 0.06 lb/ft2 (300 g/m2) and a fiber strength
of 500,000 psi (3,40 mPa). The laminate has a measured tensile strength
of 18 kips/in.-width (5.8 kN/cm-width).
The design layout for the laminate included special consideration
for three future construction projects on the Bravo Wharves:
- Special Project R25-97 “Structural Repairs and Fender
Upgrade Bravo Dock B 25”
- MCON Project P-400 “Bilge and Oily Waste Collection and
Processing Facilities Pearl Harbor Naval Complex, Hawaii
- MCON Project P-504 “Alter Electrical System Bravo/Mike
Wharves”
These projects require hanging additional utilities and conduits,
replacing utility hangers, and removing utilities and conduits under
the Bravo Wharves. The upgrade design layout of laminate strips
allowed clear surface space under Bravo 25. The clear areas (6 inch
(15-cm) wide) were built in to bypass existing utility hangers as
well as allow additional areas for the electrical power upgrade
hangers and the oily waste recovery system.
The concrete surface was ground smooth (Figure 65)
and abraded with a copper slag blasting after repairs were made
and the ICCP system installed. Primer was applied to the entire
surface area (Figure 66). After primer was applied,
bugholes and other surface anomalies were filled with an epoxy paste
(Figure 67). The paste was also used to fill concave
areas on the surface. In most areas, the paste was applied to the
entire surface to be reinforced (Figure 68). The
first ply of the carbon tow was cut to length and applied after
coating the concrete surface with an epoxy saturant (Figures
69 through 71). The saturant was worked into the tow sheet
by hand, rolling and brushing to completely wet the carbon fibers.
Excess saturant and bubbles were worked out with a squeegee and
onion roller (Figure 72). The process of applying
saturant and tow sheet was repeated for successive plies to obtain
the required area of carbon for each structural element. The specifications
did not allow holes to be cut in the composite when obstructions
such as drains, pipe hangers, or other hardware were encountered.
Instead, tow sheets were split along uniaxial fibers to bypass the
obstruction (Figures 73 and 74). Although lap splices
(a minimum of 8 inches (20 cm) in length) were allowed, all tow
sheets were cut full –span-length. Five plies of finished
laminate were less than 0.2 inch (5 mm) thick. For those areas where
the required widths could not be obtained due to pipe hangers or
other obstructions, additional plies were added to meet the required
area of carbon reinforcement. The contractor also exercised the
option of lowering or removing existing large hangers and reinstalling
them after the laminate reinforcement was placed.
Strain gauges were encapsulated in the saturant between the laminate
layers during installation. The gauges were positioned at crucial
midspan points where outrigger load response would be greatest.
The strain gauges were 5-inch (13 cm), 120-ohm, single wire element
on paper backing. The gauges were placed in the uncured epoxy saturant
at the tow sheet edge of the second laminate ply. Bridge completion
units were externally added to the strain gauge circuits above the
deck during the proof-testing phase of the project.
Figure 65. Grinding concrete surface
in preparation for Carbon Fiber
Sheet installation. |
Figure 66. Applying Carbon Fiber
primer with roller. |
Figure 67. Applying epoxy putty to
fill bugholes and other
surface anomalies. |
Figure 68. Putty covering entire
surface of track slab. |
Figure 69. Cutting Carbon Fiber
tow sheet to length. |
Figure 70. Applying first layer of
saturant to bottom side of track slab. |
Figure 71. Applying first layer of
Carbon Fiber tow sheet to bottom
side of track slab. |
Figure 72. Working saturant into tow
sheet fibers with “onion” rollers
and removing air bubbles. |
Figure 73. Laminate placement in
strips to avoid large utility
hanger anchors. |
Figure 74. Finished reinforced track
slab with spaces for future
utility hangers. |
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