MANKATO — The Minnesota Department of Transportation office in Mankato has started using a cutting-edge construction material: geofoam.
Geofoam is made of expanded polystyrene, a material similar to foam coffee cups, and is significantly lighter than regular construction material. Used in large blocks, the foam is stacked like Lego bricks to build a stable platform to effectively float the road over the mucky soil.
The District 7 MnDOT office utilized geofoam for the first time last month to build a support base for a one-eighth of mile stretch along Highway 60 between St. James and Butterfield, near where Wantonwan County Road 19 intersects with the highway.
Geofoam is most often used where patches of unstable soil are too large or too deep to fill in a cost-effective manner. The geofoam portion of Highway 60 costs $750,000 but is still cheaper than filling the 900 feet by 80 feet patch of swampy ground discovered around the highway, District 7 engineer Dan Franta.
Franta said geofoam first started being used in the U.S. in 1974 and MnDOT adopted the material in 1996 due its unique capabilities. He said MnDOT only performs one to three projects with geofoam per year in Minnesota. He said it is most commonly used in projects such as embankments for bridges or below-ground level parking lots where the expensive material can be more cost effective than traditional methods.
“(MnDOT) expects to keep using geofoam into the future. It’s very useful for what used to be very challenging problems,” Franta said. "It's useful because it can last the life of the road."
And sometimes beyond. The geofoam is sealed in a membrane before being buried to protect the material and ensure it remains effective for decades. In one extreme example, geofoam bricks used to support a highway in Norway were exhumed 20 years later and still usable for another highway project.
The Highway 60 project itself is a two-year project expected to cost $14 million to complete.