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New Concrete May Extend Bridge Life

Wednesday, February 6, 2013

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A new concrete material that uses lightweight aggregates to absorb internal moisture that inevitably seeps in over time is fast finding a home in the decks of Indiana's newest bridges.

Developed by researchers at Purdue University, the new material is called "internally cured" high-performance concrete, and transportation officials have already begun specifying it.

Photos and video: Purdue University

Purdue University graduate students (from left) Paul Imbrock, Kambiz Raoufi and John Schlitter pour concrete for a test specimen in research to improve Indiana's bridges.

Monroe County, IN, has already decided to specify the new mix on all future bridges, officials say. The Indiana Department of Transportation (INDOT) has specified it for four bridge projects that are being built this year, starting with the State Road 933 Bridge in St. Joseph County.

Extending Bridge Life

"This material will reduce maintenance costs and allow bridge decks to last longer," said project leader W. Jason Weiss Ph.D., a professor of civil engineering and director of Purdue's Pankow Materials Laboratory.

"Our testing indicates that internally cured high-performance concrete experiences substantially less cracking and concrete damage caused by deicing salt and, when properly designed, the service life of bridge decks can be greatly extended."

The Joint Transportation Research Program, a partnership between INDOT and Purdue, worked with Weiss to create specifications for implementing the internally cured high-performance concrete.

Dr. W. Jason Weiss State Road 933 Bridge

The project led by Dr. Jason Weiss (left) at Purdue University may dramatically extend bridge life. INDOT has already specified the material for use on restoration of the State Road 933 Bridge in northern Indiana (right).

"We anticipate these relatively minor changes to our concrete specifications [will] substantially extend the life of our bridges," said Troy Woodruff, INDOT's chief of staff. "That means fewer traffic delays due to bridge maintenance and repair, and much lower expense."

How it Works

The project uses lightweight aggregates—typically made from expanding clay, shale, slate or slag—that pull water out of the material as it hydrates, according to a university video on the project.

Concrete is normally made by mixing Portland cement with water, sand and stone. As it cures, water helps the concrete mixture gain strength by reacting with the cement, the university notes. Traditionally, curing is promoted by adding water on top of the bridge deck surface.

The new internal curing technology, however, "provides additional water pockets inside the concrete, enhancing the reaction between the cement and water, which adds to strength and durability," the university says. The water pockets are formed by using lightweight fine aggregate to replace some of the sand in the mixture.

"A key step in the process is to pre-wet the lightweight aggregate with water before mixing the concrete," Weiss said. "Nearly five years of research has been performed to fully understand how to proportion these mixtures and the level of performance that can be expected."

Specifying and Testing

The team worked with Monroe County in specifying the material for a bridge built in 2010 and has been studying how that bridge performs compared to an adjacent bridge built the same year using conventional concrete.

Purdue University video

Aggregates like clay and slag replace some of the sand in the concrete and are able to absorb moisture from within, Purdue University researchers explain in this video.

"The control bridge has developed three cracks, but no cracks have developed in the internally cured bridge," Weiss said. "Tests also show the internally cured concrete is approximately 30 percent more resistant to salt ingress."

Purdue says Weiss has been working with other states outside Indiana to accelerate their use of the material. The composition of the material varies from state to state, depending on which materials are locally available and the design of bridge deck components.

Performance and an Environmental Plus

Supplementing the concrete mixture with materials like silica fume, fly ash and limestone also keeps them out of the waste stream and reduces the use of raw materials.

"We just finished a project for the Federal Highway Administration where we showed that we can take 60 percent of the cement out of a typical bridge deck concrete and obtain similar, if not better, performance for bridges by taking advantage of the benefits internal curing provides," Weiss said.

In additional to INDOT and the JTRP, sponsors and contributors to the work include the Indiana Local Technical Assistance Program, the National Institute of Standards and Technology, Lafarge North America, and the Expanded Shale Clay and Slate Institute.

The Purdue-INDOT collaboration "not only benefits Indiana taxpayers, but also provides valuable full-scale living laboratories for study by Purdue students and faculty," said Jay Wasson, INDOT deputy commissioner for engineering and asset management

"As further field data are collected by Professor Weiss, we anticipate even broader deployment of this concrete specification."

   

Tagged categories: Beneficial reuse; Bridges; Cement; Coal slag; Concrete; Concrete repair; Durability; Renewable raw materials

Comment from chris atkins, (2/6/2013, 4:43 AM)

Isn't expanding aggregate bad? eg alkali aggregate reaction chris


Comment from Rogers Karr, (2/6/2013, 8:07 AM)

Chris, this is not an expanding aggregate issue. Expanded aggregates are stable after they are made by heating raw clays or shale in a kiln where they expand. They are more porous than natural aggregates, hence the lower unit weights. Evidently, the free water in the pores is available for hydration of the cement. This idea of internal curing certainly differs from everything I've ever been told about making durable concrete.


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