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Setting the bar for longer-lasting bridges

Illinois will receive $1.4 billion to repair its bridges through President Joe Biden’s five-year, $27 billion Bridge Formula Program, which is designed to replace, repair and rehabilitate bridges across the nation. The program will supplement Gov. JB Pritzker’s ongoing six-year, $33.2 billion Rebuild Illinois capital program.

Key to both programs is a focus on not only rebuilding transportation infrastructure, but also constructing it to last longer.

The Illinois Center for Transportation and IDOT focus on just that in the joint project, “R27-197: Bond Characteristics and Experimental Behavior of Textured Epoxy-coated Rebars Used in Concrete Bridge Decks.”

Bassem Andrawes, University of Illinois Civil and Enviornmental Engineering professor and Excellence Faculty Fellow, leads the effort to build longer-lasting bridges with Daniel Tobias, IDOT engineer of concrete, soils and metals, and Jayme Schiff, IDOT engineer of bridges and structures.

Their focus is on the coating of steel reinforcing bars, or rebar, which is placed in concrete to strengthen bridges. If unprotected, rebar can experience excessive corrosion due to the infiltration of water and deicing salts through cracks in bridge decks.

Adding a smooth epoxy coating to rebar, a popular technique since the 1970s, significantly increases its resistance to corrosive materials, but also may generally lead to increased crack width in bridge decks.

Here the researchers investigate adding a roughened texture to the smooth epoxy coating, which increases friction as well as the bond between the concrete and bars.

“One of the issues with bridge decks is that they crack,” Schiff said, “and the ex­pectation with this textured reinforcement is it will have less cracking and also hold the cracks tighter, so that’ll allow less chlorides to get into the bridge deck.”

Their goal? Find the optimal level of texture or roughness to add to the coated rebar.

“It’s like looking for just the right grit of sandpaper to sand your wood,” Tobias said. “We wanted to know if a smoother 220 grit or a rougher 40 grit was the best, or somewhere in between.”

To figure out the optimum texture, Andrawes isolated the conditions that bridge decks would experience in the field and recreated them in UIUC’s New­mark Structural Engineering Laboratory.

Andrawes started with taking microscop­ic images of various textured rebar and examining their surface profiles.

He and his team then embedded the rebar in concrete cylinders to test the bond between the bar and concrete.

Key to the research were several large-scale tests, where the researchers tested the cracking produced from shrinkage after the concrete was cast as well as thermal movement and flexural behavior. Andrawes’ methods showed that cracks in the bridge were not as wide as those when using nontextured, coated rebar and the bridge deck was stiffer and had smaller deflections.

Ultimately, Andrawes’ team verified the textured rebar improves bridge deck performance by about 33%.

“This is the first time that these bars are applied anywhere in the world,” Andrawes said, “so IDOT is pushing the envelope of the application of epoxy-coated rebar.”

The innovative technology is expected to have a nationwide impact, as many state agencies are searching for a way to reduce the number and severity of cracks in bridge decks.

“Several state DOTs are aware of Illinois’ research on this topic and are eagerly awaiting results for their potential implementation,” said Dan Brydl, Federal Highway Administration’s Illinois Division bridge engineer and a member of the project’s technical review panel.

“FHWA is very pleased with the results of this research,” Brydl said. “This marketable innovation could very possibly lead to a new standard in bridge deck reinforcing steel coatings both regionally and nationally.”

Drivers in Illinois can also expect to see an additional benefit: fewer traffic delays due to fewer closures for bridge maintenance and repair.

“Our goal here is to reduce future maintenance of bridge decks and hopefully reduce costs over the life of a bridge,” Schiff said. “That’s the long-term goal: to help save tax dollars.”