The fiber-reinforced pavement research being done by the National Road Research Alliance (NRRA) is not limited to test cells at MnROAD. Summer 2018, the Minnesota Department of Transportation (MnDOT) installed a unique roundabout in Sleepy Eye, MN that incorporated fiber-reinforced concrete.
Two things made this project a first of its kind project in MN.
- First, fiber has not been used in the mix for a roundabout before
- Second, and most importantly, there were no joints cut in the isolated circle or “donut” of the roundabout
Charlie Kremer, Materials Engineer-District 7, has seen many roundabouts built in the Mankato District. His concerns with the numerous odd-shaped-sawed panels and multiple cracking in the roundabouts led him to search out an alternative to a traditional jointed roundabout.
After attending a National Concrete Consortium (NCC) meeting presentation, the MnDOT Concrete Engineering Unit proposed a fiber-reinforced concrete roundabout with NO JOINTS.
The problem with cutting joints in a round shape, rather than square panels, makes the cracking more difficult to predict, said Rob Golish, Assistant Concrete Engineer-MnDOT’s Office of Road Research. MnDOT is aware that the roundabout pavement will crack, so the inclusion of fiber reinforcement should hold the cracks tighter together, keeping them from growing too large. Even though joints were not sawed into the concrete, MnDOT decided to try to influence the location of the cracks by creating 15-inch-long notches every 4 feet on the outside edges of the roundabout.
The early results show some of the cracking initiated at the ends of the notches, while other cracks occurred within a foot or two of the notch. After the first couple of weeks, the roundabout had cracked into four pieces.
This kind of project has never been tried before, so MnDOT will be watching it carefully to see:
- Where it cracks
- How it cracks
- Whether the fibers factor into the life of the roundabout
For the full article in the NRRA Newsletter, please go to: http://www.dot.state.mn.us/mnroad/nrra/newsletter/currentissue.html?utm_content=&utm_medium=email&utm_name=&utm_source=govdelivery&utm_term=#ict or http://www.dot.state.mn.us/mnroad/nrra/newsletter/currentissue.html
Home Page Photo: MnDOT “Roundabout Myths” Video: https://www.youtube.com/watch?list=PL8D3XXieDs8nM47JJOqwCqCJqgnSUs0eE&time_continue=54&v=HLDdWJzDFyI