Corrosion in bridges

Citation

(2001), "Corrosion in bridges", Anti-Corrosion Methods and Materials, Vol. 48 No. 4. https://doi.org/10.1108/acmm.2001.12848dab.002

Corrosion in bridges

Corrosion in bridgesKeywords: University of Illinois, Testing, Inspection, Corrosion

Pretensioned deck-beam bridges that are inexpensive and easy to design and build are used in more than 7,200 bridges on Illinois, USA highways. Two beams from such bridges have fallen apart, initiating a crash course in bridge inspection and repair.

"Two years ago, a beam in a state highway bridge collapsed in Kankakee, and then a beam in another bridge broke apart near Lawrenceville while being removed", says Neil Hawkins, a professor of civil and environmental engineering at the University of Illinois (Champaign, Illinois). "Intended to last for at least 50 years, several of the state's pretensioned deck-beam bridges have shown unacceptable levels of corrosion damage after only 20-30 years of service."

In a project funded by the Illinois Department of Transportation, Hawkins and colleagues at Illinois University are helping to ensure public safety by designing better standards to evaluate a bridge's condition. The researchers have developed visual inspection procedures to assess the corrosion damage in deck beams, the rate at which the damage is spreading, and the remaining service life of the bridge.

"Each pretensioned deck beam resembles a long, hollow box", explains Hawkins. "To create a beam high strength steel cables are first stretched tightly, an additional reinforcing bar is added, and then concrete is poured around the steel. After the concrete has cured, the cables are cut at the end of each beam, pulling the concrete into compression."

In the bridge-building business, the beams are laid side by side, bolted together, and the joints are grouted with cement. Over time, the joints can crack and allow water and salt to infiltrate. The salt corrodes the steel reinforcing cables within the concrete and weakens the bridge.

"By chipping away the concrete to expose rusted steel, and by testing beams in the laboratory, we came up with a reasonably reliable scenario for visually determining how many strands have been lost to corrosion", says Hawkins. "We can assess the hidden damage and evaluate the remaining capacity and life of the structure by inspecting the location and amount of rust on the surface."

Down the road, the ultimate solution lies in building better bridges. From the time these bridges were first built, technology has improved considerably.

Bridges in Illinois are inspected every two years.