Robert Frosch, associate professor of civil engineering at Purdue, displays various types of reinforcing bars used in bridge construction. At top left are two segments of conventional steel rebar. The remaining samples are corrosionresistant plastic bars reinforced with glass or carbon fibers. |
The concretestrengthening steel bars currently used in bridges are susceptible to corrosion, especially in the "deck," the uppermost portion of the bridge. Rebar embedded in bridgedeck concrete is exposed to deicing road salt that seeps through cracks in the pavement. Normally, bridge decks must be replaced every 20 or 30 years, but replacing rebar with bars made from fiber-reinforced polymers could extend the lifetime of a deck by as much as 50 to 100 years, says Robert Frosch, an associate professor of civil engineering.
As steel rebar corrodes, it makes the rebar expand, eventually causing chunks of concrete to break away from the bridge deck. This increases the exposure of underlying bridge components, which leads to more corrosion. The salty water also causes steel bars in both the upper and bottom portions of the deck to act as the negative and positive poles of a battery, increasing the rate of corrosion.
Replacing the steel rebar in the upper portion of the deck with fiber-reinforced polymer bars eliminates one of the poles and shuts down the battery effect, Frosch says.