Discovery Guides Areas



Plastic Highway Bridges
(Released November 2000)

  by Jennifer R. Griffiths  


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Throughout the world, concrete infrastructure reinforced with steel is waging a losing battle against corrosion. Concrete is crumbling, leaving reinforcing steel exposed and subject to rusting. Steel-reinforced concrete bridges are deteriorating from the corrosive effects of de-icing, marine salts, and environmental pollutants. Other factors contributing to the problem are aging, increasing daily traffic, increasing truck weights, more frequent vehicle overloads, and insufficient maintenance and repairs. In the USA, almost 40% of bridges are structurally deficient or functionally obsolete, and the percentage is increasing, according to the Federal Highway Administration.

Plastic reinforced with fibers, a type of composite material, is seen as a possible solution for repair, strengthening, or replacement of an increasing number of substandard bridges. In the broadest sense, composite materials are combinations of materials that have their own distinctive properties. Fiber reinforced plastics (FRP) are composite materials that consist of high strength fibers immersed in a structural matrix such as epoxy or other durable resin. The most common fibers used are glass, carbon, and aramid (trade name Kevlar). Brittle materials such as glass and carbon can acquire enormous strength and stiffness when produced in the form of a fiber. The addition of these fibers to a weak, compliant matrix results in a material that demonstrates a dramatic improvement in performance, producing a material with much greater mechanical properties than its constituents.

Interest in FRP as a solution to the problem of upgrading and replacing these deteriorating bridges is increasing. Various research projects are underway and a number of companies are designing, manufacturing, and installing composite material components for bridges. The applications of FRP for bridge repair and replacement include new bridge decks, strengthening of concrete structures, and internal reinforcement of concrete.

The advantages of employing FRP in new bridge decks include its corrosion resistance, high strength-to-weight ratio, and ease of installation. The composite material can be customized to dimensions of traditional decks and allows the economic reuse of existing support structures.

The USA's first all-composite vehicular bridge deck on a public road was installed in November 1996 by composite manufacturer Kansas Structural Composites Inc (KSCI) of Russell , Kansas, employing a rapid, low-cost replacement system. Using lightweight cranes and factory-built sections, KSCI installed the bridge over No-Name Creek in Russell County, Kansas, in approximately 10 hours. Since then, the Kansas Department of Transportation has gone ahead with two new installations by the same company. KSCI uses a fiber-reinforced plastic honeycomb sandwich construction in fabricating its bridge decks.1

In another project, the New York State Department of Transportation decided to try a composite materials solution for replacement of a deteriorating 25 foot long concrete bridge built in 1926. NYSDOT selected the company Hardcore Composites of New Castle, Delaware, to fabricate the bridge deck. Hardcore employed glass-fiber fabric and vinyl ester plastics in forming the sandwich structure used in the deck, and installed the deck in one day.2

Hardcore Composites, which has manufactured and installed ten highway bridges and bridge decks so far, has been awarded a contract for the first phase of a project to provide composite bridge decks for Project 100 in Ohio.3 Initiated by the National Composite Center in Kettering, Ohio, the project aims to design, manufacture, and install 100 bridge decks throughout the state.4

FRPs benefits of light weight and high strength also make it attractive for strengthening existing concrete bridge structures. FRP can be wrapped like wallpaper around bridge columns and beams to provide additional reinforcement to increase earthquake resistance, durability, and corrosion resistance. The wet lay-up procedure is one technique. High strength fibers are matted or woven into a fabric and then immersed in an epoxy matrix, followed by adhesive bonding of the material to the column.

FRP composites have been used by Fibrwrap Construction Inc. of Los Angeles, California, for a seismic retrofit of the Arroyo Seco Bridge. The bridge, located in Pasadena, California, is a multiple arch structure that spans over 1300 feet of the Arroyo Seco Canyon. The bridges concrete columns were wrapped with glass- and aramid-fiber reinforced epoxy composite. The low-profile composite jackets had a final thickness of less than three-quarters of an inch, yet provided strength comparable to that of full-scale steel jacketing and had minimal impact on the appearance of the historic bridge.5

Composite materials have also been used in the rehabilitation of another historic bridge. This allowed the strengthening work to be done in keeping with the character and aesthetics of the structure. The Tickford Bridge in the UK, built in 1810, is the worlds oldest operational cast iron road bridge. Maunsell Ltd., a civil and structural engineering consulting firm in the UK, recommended that full highway loading could be achieved by strengthening the bridge with a wet lay-up carbon fiber sheet system.6

In another application of FRP, reinforcing bar (rebar) fabricated from either glass-fiber or carbon-fiber reinforced plastic composites is being used to replace steel as an interior structural reinforcement element in concrete. FRP can be used in new structures for reinforcing both cast-in-place and precast concrete. Besides rebar, it can take the shape of stirrups, grating, pavement joint dowels, tendons, and anchors.

The Canadian province of Quebec has built a bridge in Sherbrooke that is innovative in its application of carbon-fiber reinforced plastic (CFRP) reinforcements instead of steel. Part of the Joffre Bridge concrete deck slab is reinforced with CFRP, as well as a portion of the traffic barrier and the sidewalk. Fiber optic sensors were structurally integrated into the CFRP providing a smart structure. Over 180 instruments (fiber optic sensors, vibrating wire strain sensors and electrical strain gauges) were installed at critical locations in the concrete deck slab. These instruments will allow for the remote monitoring and continuous evaluation of the structural performance of the CFRP reinforcements under real-time conditions.7

As an increasing number of bridges require rehabilitation, strengthening, or replacement, interest has grown in fiber-reinforced plastic composites as a solution to the problem of an aging infrastructure. The range of composite materials manufactured for bridge construction and repair is expanding as more installations are undertaken. Soon, a bridge made of plastic may be coming to a highway near you!

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