Report Urges Tests on Plastics in Bridges

Caltrans’ chief of new technology said Wednesday that far more testing must be done and some serious problems resolved before Space Age reinforced plastics--known as “advanced composites”--can commonly replace steel and reinforced concrete in building and strengthening the state’s bridges.

In a talk to the final session of a conference on bridge and highway seismic retrofitting here, Mohsen Sultan had a clear message to the 60 firms enthusiastically trying to market such products: Cooperate with Caltrans’ testing efforts and be patient until positive results are in.

“Caltrans is more than open to the contractors,” he said. “We will give a fair opportunity to everyone to demonstrate and test their products as fast as possible. But we must verify all these products for public safety. We don’t want major structural failures.”

Composite materials first developed by the aerospace industry have often, particularly since the 1989 Loma Prieta earthquake, been extolled as lighter weight, less expensive and more earthquake resistant substitutes for steel and reinforced concrete in major structures.

Sometimes, in the wake of the 1994 Northridge quake, the California Department of Transportation has been criticized as being resistant to using and testing them.

But Sultan warned Wednesday that on-site fabrication and application--two possible uses that make the materials cost-effective--may produce dangerously uneven quality.

He also cited evidence that some composites may degrade over time, causing structures to gradually lose strength.

“In the space effort, these materials have to last just two minutes before a satellite is in orbit,” he said. “In California’s bridges, they must last many years, and we have found the environment can adversely affect them.”

Sultan’s talk was accompanied by a paper he prepared with Gary Hawkins of the Aerospace Corp. of El Segundo, and Li-Hong Sheng of Caltrans’ Engineering Services Center.

“Recent experimental studies have shown that composite materials can strengthen structural elements, such as columns or beams, and may possess economic potential in retrofitting deficient structures,” they wrote. “Unfortunately, the physical properties of composites . . . may change from batch to batch and from contractor to contractor.”

Early Caltrans testing of the composites did not “thoroughly address strength degradation issues related to environmental, physical and chemical concerns,” the engineers report.

“Some fibers are very sensitive to moisture. . . . If the resin were to crack, even at a small rate, the question is not whether the composite will deteriorate, but rather how fast the speed of this degradation can be, as fast as a few days.

In some cases, Sultan, Hawkins and Sheng write, within just 10 to 15 years, “the remaining strength is on the order of 40% for hand laid-up fiberglass and 55% for filament wound composites.” And under “dynamic loading, such as the case in light poles subjected to wind load, 78% of the strength is lost over an extended period of time.”