Q&A: Are Composites Really the Best for Bridgework? AASHTO Weighs In.

Paul Liles is the state bridge engineer for Georgia DOT and chairman of AASHTO’s T6 committee, a technical committee focused on FRP. The group is responsible for design specifications on structures including bridges and walls. Liles says that while the composites industry hoped to take off in all facets of bridgework, only some areas have seen success.

How does the T6 Committee work?

The T6 is a technical committee for FRP. It consists of nine to 10 people, generally state employees and members of state DOTs. The committee is responsible for design specifications (specs) in regards to structures. That includes not only bridges, but also other structures such as walls. We meet once a year and discuss specifications and use of composites, current research and successful/unsuccessful projects. We’ll move those specs forward if we feel there’s a lot of activity in the area it relates to.

What help does the T6 Committee get from industry?

We receive institutional knowledge from composite industry researchers, schools and some companies who present studies they’ve completed. Researchers will come and make a presentation. We tell them to write a spec, which mainly details what formulas and safety factors to include in the design. Or industry comes in and says it’ll write a spec, and we’ll vote on bringing it forward. It goes to the overall bridge committee and it gets voted on. If it passes, AASHTO prints it out as a specification for design.

How did composites enter the bridge market?

When composites first came out, everyone said it was the greatest thing. We had people say composites would solve a lot of problems. The federal government pushed products, which resulted in program-sponsored innovative materials. But those people weren’t engineers, and were caught up in the enthusiasm of those possibilities rather than the reality of what the material could accomplish.

What ideas did states have for composites?

Decks, complete bridges, rebar, repairs with carbon wraps, earthquake mitigation and a whole gamut of things. As it turned out, a lot of these ideas were expensive. As a result, interested companies would come and go, but the ones that took off were those involved in wraps and repairs. It filled a huge need for deterioration, and took off because it was cost-effective. When a contractor damages a beam, repairing with carbon fiber is the cheapest thing for them to do. However, there are some questions about how long the repair will last. The industry tells us different amounts, from 15 to 25 years for exposed conditions, and we don’t know. It’s been out for 10 to 15 years, but we’ve seen no reports of taking it down.

What about composite in other products?

The other products have had some use but not a whole lot. Those uses have been niche markets, such as bridge construction on islands. For instance, California constructed an extended sidewalk for pedestrians and bikes on a lift bridge. They removed the old concrete sidewalk and put in a new, wider composite sidewalk, while maintaining the same weight, which is critical on lift bridges.

For complete bridges, a few have been built in low traffic areas. But there is potential for pedestrian bridges. The rebar has potential use in corrosion reinforcement for conventional steel. We have also looked at the use of glass fiber rebar, which has been used a little bit but is still expensive. There have also been a number of composite decks installed, and they work in low traffic volume conditions, but there are issues about the overlay and attachment of the railing.

What are some of the issues with composite decks?

They get pounded by trucks. Heavy truck traffic is very tough on structures. With most building products, you analyze it and it may look fine, but trucks seem to pound it apart. Composite decks suffer from such maladies as splitting along layers of fibers and delaminated overlays. It’s one of those things where you go through the equations and everything looks fine, but there are other factors to consider. However, steel and concrete have those issues too.

How is the performance of composite bridges monitored?

Every state is required to inspect bridges in a 2-year cycle. Maintenance workers will tell the state people if the bridges are not performing adequately. If the states are unhappy with something, they’ll discard it. Measuring the overall performance of the ones that have been installed, including some where they didn’t work, just comes from discussion between state officials.

Which ones don’t work?

The one that comes to mind was a bridge in Ohio. They tried four different decks on one bridge and ended up tearing them out. I think a large part of the issue had to do with some of the construction techniques. I don’t know if those companies are in existence now, but I know the Ohio DOT was not happy with it.

What is the future like for composites?

The future still looks good for wraps. They are cost-effective, simple to use and people use them a lot. However, time will tell on rebar. Prices are not down to steel level, which is an issue. And decks will continue to be used in niche applications. But if a state puts out a successful design, others will pick up on those procedures.

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