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Harbor
Embedded Reinforcement
Embedding pultruded carbon/epoxy composites as negative reinforcing
is particularly attractive for the top surface of the deck where
exposed external reinforcement would be subject to mechanical and
environmental damage and would require protective cover. It also
precludes some of the surface preparation steps. The contractor
selected DFI pultruded carbon composite rods to meet the rod specifications.
These smooth rods contain 65 percent high strength carbon fibers
(700 ksi (4830 mPa) ultimate strength) in an epoxy matrix. The rods
were encapsulated in Sikadur 32?, a two-part amine epoxy, in slots
that were cut in the concrete surface. The manufacturer removed
the epoxy surface “sheen” on the rods to ensure better
bond to the epoxy encapsulant. The epoxy encapsulant was required
to have significant tensile and interlaminar shear strength. It
was also desirable to have a glass transition temperature well above
the highest temperature expected in the deck.
In preparation for rod installation, the contractor cleaned the
deck surface, removed all loose material, and applied a two-part,
penetrating epoxy primer/sealant (Sikadur 55©) over the areas
to be reinforced. The contractor laid out the reinforcing pattern
after the primer had set, and NFESC made adjustments to avoid drains,
rails, cleats, and other obstacles (Figure 51).
One of the key functions of the primer was to penetrate microcracks
and strengthen the concrete surface to minimize damage when cutting
slots. The contractor used a diamond blade and cut each slot with
a single pass (Figure 52). NFESC set the depth
and width of the slots to ensure that the carbon reinforcing would
be completely encased in epoxy with enough clearance to allow for
variances in the concrete finish (Figure 53). NFESC
required at least a 1/4-inch (6 mm) clear cover and 1/16-inch (1.5
mm) clearance between the reinforcing and the slot walls. The minimum
spacing of the slots was 4 inches (10 cm) on center. Existing reinforcing
steel was well below the bottom of the slots and was not encountered.
The slots were thoroughly cleaned and abrasive blasted using copper
slag under 200 psi (1.4 mPa) pressure (Figure 54).
Slot surfaces were primed with Sikadur 55? (Figures 55 and
56).
Slots were filled with Sikadur 32? epoxy up to ¼ inch (6
mm) of the surface and the bars were laid and pressed in place in
the slot (Figures 57 through 60). Sikadur 32? has
excellent wetting capabilities. Its tensile strength exceeds 5,500
psi (38 mPa) and its shear strength exceeds 5,000 psi (35 mPa).
Its Young’s modulus is 250,000 psi (1,770 mPa). Stainless
steel clips were used to hold the rods in place where the concrete
surface was not planar (Figures 61 and 62). After
placing the rods into partially filled slots, the slots were “topped-off”
with a sand/epoxy (Sikadur 22©) grout for ultra violet (UV)
protection (Figures 63 and 64). The UV protection
grout was specified as two parts 60 grit sand to one part epoxy.
The contractor varied the amount of sand from 1.25 to 2 parts to
1 part epoxy. More sand provides more UV protection but is more
difficult to place.
Strain gauges were attached to 12 rods prior to encapsulation for
post construction proof test monitoring. The gauges were positioned
at crucial points above the transverse and pile girders where outrigger
load response would be greatest. The strain gauges were 1/2-inch
(13 mm), 350-ohm foil gauges. Bridge completion units were externally
added to the strain gauge circuits during proof tests.
The contractor used copper slag to abrasive blast the rod slots.
It is the most effective abrasive NFESC has encountered. However,
the contractor did not have any means of recycling the abrasive
and it became an environmental pollutant.
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