Materials and Manufacturing
Materials used in the FRP bridge
decks consist of highly engineered glass fiber reinforcements
with various resins including iso-polyester, vinyl ester and
epoxy. These materials are selected because of there strength
and inherit corrosion resistance. FRP bridge decks are designed
to be modular to allow flexibility for assembly, shipping and
installation. Several of the FRP deck panels are designed with
different sandwich cores providing stiffness. These cores are
characterized as fiber-reinforced foam, cellular core honeycomb,
or fiber-reinforced polymer honeycomb.
Manufacturing processes used to
fabricate FRP bridge decks include pultrusion, vacuum-assisted
resin transfer molding (VA-RTM), and hand layup/contact molding.
(For more information, see
Composites Manufacturing Processes)
Pultrusion
In the pultrusion process, rolls
of reinforcements are strategically aligned and pulled into the
tooling and folding process. The dry fabrics and fibers are
pulled through a shaping tooling that brings them together to
form a closer shape of the final product. The reinforcements are
wet-out by pulling them through a resin bath. The saturated
reinforcements enter a heated die where the composite is cured
to form a hard part. A translating saw is used to cut the
continuous structural profiles into the desired lengths.
Vacuum Assisted Resin Transfer
Molding (VARTM)
VARTM uses the negative pressure
of vacuum to infuse resin into dry reinforcement fibers and
fabrics that are placed in a mold and sealed in an airtight
chamber. A nominal vacuum of 28 in. of mercury is used to
evacuate the mold of air. After the air is removed, the assembly
is infused with resin and allowed to cure under vacuum. VARTM
has been used to fabricate yachts, aircraft components,
railcars, subway car body panels, marine piling and fenders
(bumpers), components for naval berthing, concrete formwork and
bridges. This manufacturing process allows structural components
of virtually any size or geometry to be fabricated.
Hand Layup/Contact Molding
Hand lay-up techniques are used to
fabricate the unique sandwich panels comprised of a core and
face skins for bridge decks. The face skins are produced by hand
layup on a flat surface where resin is manually applied to
chopped strand mat glass fiber reinforcement using common paint
rollers. Grooved metal rollers are used to remove air bubbles
from the laminate. The corrugated sheets that form the core are
produced in a similar fashion to the face skins but have a
defined shape called flutes. Assembly of the precured flat sheet
is then placed on top of the wet corrugated sheet to produce a
bond as sandwich panel cures. After cure, the combined
corrugation/flat assemblies are trimmed to the proper width.
This determines the core thickness of the sandwich panel.
Adhesive resin is applied to the fluted side of the strip before
it is mated to the flat of an adjacent strip.
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