UpDate - Vol. 14, No. 13, Page 3
December 1, 1994
Pilot project; Composites applied to DelDOT bridge repairs

     Some people might be surprised to see University researchers
involved in highway repair, but a group of faculty and students have
joined forces in an innovative project designed to correct structural
problems on area bridges.
     This bridge rehabilitation, undertaken by University researchers
from the Department of Civil Engineering in conjunction with the
Center for Composite Materials, is one of the first of its kind in the
United States.
     The project represents a cooperative effort between the research
team and the Delaware Department of Transportation (DelDOT) through
the Delaware Transportation Institute (DTI).
     "DelDOT came to us with a problem," Michael J. Chajes, assistant
professor of civil engineering, said. "We had to find out why bridge
damage was occurring and stop the cracks from spreading while
reinforcing the existing structures."
     An examination of the structures, referred to as box beam
bridges, led researchers to conclude that the problem centered in the
original design of the beams, which made them susceptible to water
damage.
     According to Chajes, water gets into hollow areas, or voids,
which run the entire length of the beam. Once inside, the water is
subject to periods of freezing and thawing, which can, over time,
cause concrete to crack.
     Water also can cause the steel reinforcing strands in the beams
to corrode. This corrosion causes the steel to expand, which also can
cause the beams to crack.
     Because of the way these beams are reinforced, there is nothing
to protect against the spreading of these cracks and the weakening of
the structure.
     "Serious strength loss in a single beam can cause a bridge to
need total replacement," Chajes said. "It's not just a matter of
replacing a single beam."
     The researchers have identified about 30 bridges of this type in
Delaware. During the last two years, two of these bridges had to be
replaced, at a cost of roughly $250,000 each.
     To solve the problem and avoid such costly replacements, the team
developed a rehabilitation procedure that involves the use of a carbon-
fiber reinforced plastic (CFRP) to externally reinforce the beams.
     A bridge on Foulk Road, just north of the Naamans Road
intersection in northern New Castle County, provided Chajes and his
team with the opportunity to conduct the first practical application
of this reinforcing process.
     Accompanying Chajes on the retrofit, which began in mid-October,
were Dennis R. Mertz, associate professor of civil engineering;
William W. Finch Jr., a research assistant; and five graduate and
undergraduate students.
     After grinding the damaged areas and injecting an epoxy-based
material into the cracks, the 54-foot-8-inch-long beams were
sandblasted, and a coat of primer was applied to help the composite
material bond to the concrete.
     When surface preparations were completed, the team rolled a coat
of resin adhesive onto the beams. After pressing the individual sheets
made of uni-directional carbon fibers into place, they used a squeegee
to remove any remaining air pockets. Finally, a final layer of resin
was applied.
     "This was the first, full-scale bridge application involving CFRP
in the United States," Chajes said. "The exciting thing about this is
that we will be able to see how the retrofit performs over time."
     The cost of this type of rehabilitation, which took a week to
complete, is estimated to be around $25,000, or about one-tenth the
cost of a complete bridge replacement.
     Other possible uses of these composite materials include
strengthening bridges columns and the repair of steel and wooden
structures.
     Researchers here and elsewhere are exploring new ways to
incorporate the use of composite materials in new structural systems.
     This bridge rehabilitation project has generated attention from
many quarters, including federal highway officials involved in
research at government laboratories.
     "Currently, research and application of composite materials to
civil structures is occurring throughout the world, particularly in
Europe and Japan," Chajes said. "I see this use of composite materials
for bridge rehabilitation being an area of real growth in the future."
                                                         -Jerry Rhodes