A special ground-thawing system is helping to keep construction moving on the Minnesota Vikings' new stadium.
A special ground-thawing system is helping to keep construction moving on the Minnesota Vikings' new stadium.

Even during brutally harsh winters, construction companies in northern parts of the U.S. don’t slow down. Exterior site work for companies like Minneapolis-based Mortenson Construction doesn’t stop for subfreezing temperatures and frozen, snow-packed jobsites.

“We build all year round and in all weather conditions,” says Mortenson senior superintendent Jason Brown.  “Here, in our home state of Minnesota, that can mean cold weather construction in winter, which can be challenging to project schedules and budgets.”

For example, Mortenson is working to build the $1 billion Minnesota Vikings Stadium in downtown Minneapolis. Construction has progressed steadily through winter thanks to a special system that literally thaws the ground using antifreeze and heated blankets. St. Cloud, Minn.-based FlexTemp Systems provides surface heating equipment used in winter construction for ground thawing and concrete curing. FlexTemp currently has five portable surface-heating units installed at the Vikings Stadium project to keep the ground thawed and ready to go. (Click here for video.)

A rendering of the new Minnesota Vikings stadium, to be open July 2016. 
A rendering of the new Minnesota Vikings stadium, to be open July 2016. 

FlexTemp’s technology is specifically engineered for thawing frozen ground as well as warming and curing concrete — even at 30 degrees below zero, says FlexTemp’s Chuck Sanvik. Workers lay a complex network of hoses on the ground, run them full and antifreeze, and cover them with insulating blankets. It's a technology that is mainly used in commercial construction but could one day be used by residential builders in cold climates.

“Generally, you’ll find six feet of frost on the ground in a Minnesota winter— eight feet if it’s brutally cold like it has been this month,” he explains. “FlexTemp Systems can thaw one foot of frozen ground per day with our machines, which are similar to home in-floor heating systems — just above ground.”

A similar system is used to cure concrete, allowing work to continue throughout the winter and resulting in more efficient scheduling of construction crews and equipment. The company’s cold weather concrete curing system handles pre-pour warming, thaws sub grades and cures concrete walls, forms, columns and slabs without the need for expensive and time-consuming heated enclosures.

FlexTemp has also been used to help winter construction run smoothly for other local projects, including at TCF Bank Stadium, and the Minneapolis-Saint Paul Airport. “The most difficult project we ever worked on was a SuperTarget in West St. Paul — we thawed 83,000 square feet of ground, through asphalt, using more than 10 miles of hose, so construction could continue through a very harsh winter,” says Sanvik.

FlexTemp operates in other cold-weather states of Pennsylvania, Montana, Wyoming, North Dakota, and in Canada, and plans international expansion in 2015.