Styrofoam is commonly used as a packaging material because it’s a lightweight solution to providing added protection against damage during shipping. But a new form of Styrofoam — called Geofoam — is being used increasingly as a construction material.
In Oregon, geofoam was recently used as a road foundation material in an area where the underlying ground was unstable and seismic events such as earthquakes are a common danger.
Lightweight Yet Heavy-Duty
Geofoam is comprised of expanded polystyrene, the same material used to make packing peanuts and packaging foam, but is made to be stronger, denser and more uniform in its composition, said Andrew Fiske, geotechnical engineer with the Washington State Department of Transportation. Sheets of the material are being used as part of a $133 million freeway interchange project because its light weight and stability make it perfect for the unique geological conditions.
“They’re not hugely different than what you would find wrapped around your TV when you open the box,” Fiske said. “However, we can dictate the strength requirements.”
Soil around the worksite was notoriously unstable and the area sits atop a seismic fault with is prone to earthquakes and shifting, said area engineer Leon Winger. While heavy crushed rock or earthen fill could be used to stabilize the site, an alternative was to lighten the load itself.
While gravel weighs about 130 pounds/foot, geofoam weighs only 1.5 pounds/foot. About 8,000 3’X9′ blocks of geofoam — or about 31,000 cubic yards — were used to fill the foundation for the highway supports. The foam will then be cut to match the slope and shape of the road and the whole thing will be finished with sand and a rubber liner.
The road will then sit on top of that and concrete walls will enclose the entire foundation, said Winger.
“You’ll never know that foam was ever part of the fill,” he said.
Geofoam Used to Build Chicago’s Millennium Park
Closer to home, geofoam was used in the construction of Chicago’s Millennium Park. Engineers were struggling to figure out how to build the 24.5 acre park on top of an existing 2,186-vehicle underground parking garage.
The solution they came up with was to use the lightweight geofoam — rather than the much heavier soil — to allow the additional weight of the park structures and facilities to be loaded on top of the existing facility.
Geofoam also was used to sculpt some of the showcase park’s landscape features in order to achieve the proper water drainage for the overall site plan.
One of the biggest benefits of geofoam is that it can be used in any weather conditions, unlike concrete which cannot be poured easily during freezing or rainy conditions. This was a key factor during the Millennium Park construction during Chicago’s harsh winters.
Besides building world-class parks and highway embankments, geofoam also has been used for stadium seating, floor elevation, pool and pool decks, for vibration and soundproofing, and to resolve frost issues, according to EPS Geofoam, a manufacturer of the material.