Ensuring the Sustainability of Prestressed Concrete Bridges

Trey Hamilton, Ph.D., is a professor in the Structural Engineering group in the Department of Civil Engineering at UF. He is an affiliate faculty with the UFTI and a member of its Internal Steering Committee. Hamilton specializes in sustainable structure design, specifically in the durability of reinforced and prestressed concrete.

“I look at existing structures and work on how to make them safe, usable and serviceable, so that they don’t have big cracks or things falling off of them,” Hamilton said.

What is prestressed concrete? It is a combination of high strength concrete and steel strands or rods, which are pushed into tubes or pipes built into the concrete for support. This prestressed method is used in the building of bridges, for example, which creates a very strong material, resistant to heavy loads. A typical tendon would be composed of 19 steel strands, and each can carry nearly 60,000 lbs. These tendons can sustain roughly 1 million lbs., and there are a lot of these tendons used in bridges. In Florida, prestressed concrete is a very popular method for constructing bridges, and due to the shortage of steel resulting from World War II, prestressing became the method of choice for constructing bridges in Europe.

However, prestressing has it challenges. The steel strands or “tendons” that are inserted into the concrete may corrode quickly if not adequately protected, thus creating structural and safety issues. Protecting the steel tendons used in bridges, and making sure the concrete will last for the intended life of the structure is what Hamilton and his team are working on.

To study this issue, Hamilton, along with representatives from the Florida Department of Transportation (FDOT), the State Materials Office, and a U.S.-based engineering consulting firm, met with French bridge officials in Paris who were experiencing similar problems with their bridges and exploring ways to prevent corrosion. The U.S. team brought back ideas for alternative corrosion technologies such as waxy substances, for example. The working title of the project Hamilton and his colleagues are working on is called “Unbonded, Replaceable Prestressing Tendons for Prestressed Concrete Bridges”.

“We are looking at heating and injecting a wax-like material to fill the ducts and cover the tendons to protect them and keep them from corroding,” Hamilton said. “This is a different material and procedure than what is currently used. We have been testing multiple types of filler materials from various companies.”

Hamilton said the FDOT has issued a “design bulletin” that provides bridge designers with information on this new bridge construction procedure. This directive is based on the work currently being conducted by Hamilton and his team, along with the M. H. Ansley Structures Research Center and the FDOT State Materials Office. FDOT is ready to implement this new corrosion technology to not only make bridges safe, but sustainable and durable.

“We are now talking about designing bridges to have a service life of 100 years or more,” Hamilton said. “The idea is that we want to make bridges last longer. We have about 600,000 to 650,000 bridges in the U.S., and we continue to build more, but there are bridges that need to be taken care of.”

For more information, contact:

Dr. Trey Hamilton
Structural Engineering Group
Office: 475-K Weil Hall
Tel: (352) 392-9537 ext. 1509
Fax: (352) 392-3394
E-mail: hrh@ce.ufl.edu