When bridge decks crack, water and salt reach the steel reinforcing bars underneath, causing the bridge to deteriorate faster.
That’s what Illinois Center for Transportation and Illinois Department of Transportation are trying to prevent in their joint project, “R27-178: Bridge Decks: Mitigation of Cracking — Phase III” (vol. I and vol. II), the third phase of an 11-year series of projects on the topic (phases one and two).
James Krstulovich, IDOT’s engineer of concrete and soils, leads the projects with Paramita Mondal, a University of Delaware associate professor, and Riyadh Hindi, a Saint Louis University professor.
Here the team seeks to explore how adding new mixture components to concrete may help reduce cracking caused by concrete’s tendency to shrink.
“Concrete is like a piece of chalk. When you pull it, it snaps, it cracks,” Hindi said. “As the concrete shrinks with time, that shrinkage is going to make it shorter, so it’s going to build a lot of tension inside the deck and it’s going to crack.”
The project’s goal?
To reduce the amount or potential of cracking as well as reduce the tensile strain that builds in the deck without significantly changing construction practices.
“It’s an area that can save a lot of resources for IDOT in general,” Hindi said. “This will really help reduce spending in terms of maintenance costs and increase the lifespan of the bridge.”
Researchers took up a two-part approach, with Mondal’s team looking at how to enhance concrete mixes with different shrinkage-mitigation strategies and Hindi’s team exploring how to use those mixes with bridge deck models that simulate actual restraint conditions.
Mondal’s team began by exploring a cement material that counteracts shrinkage by producing an expansive reaction in the concrete before it sets, creating a prestressing effect that helps reduce cracking.
This material, however, requires extra water when pouring, which may make the concrete more absorptive of water and corrosive materials.
So Mondal and team sought to test several combinations of chemical admixtures with the material to reduce the concrete’s absorbency and increase its strength and durability.
Mondal found that adding the admixtures decreased the potential for water absorption and improved early-age expansion properties in Hindi’s bridge deck model.
Together, they were also able to verify the findings of Mondal’s small-scale testing with Hindi’s large-scale models, validating both methods’ effectiveness in understanding the success of shrinkage-mitigation strategies.
Other shrinkage-mitigation strategies investigated include shrinkage-reducing chemical admixtures and internal curing with prewetted lightweight fine aggregate.
“The research identified some very promising technologies to make better-performing bridge decks for the state of Illinois,” Krstulovich said. “All of the shrinkage-mitigation techniques we looked at outperform our control mix that we currently are using.”