by Mary Weaver

photos by William Weaver

When Mortenson Construction Company broke ground for the new $1 billion Vikings Stadium in downtown Minneapolis, they planned, as they often do, to work straight through the frigid Minnesota winter by enlisting the help of a company they had used in previous wintertime construction, Flex-Temp Systems. Flex-Temp is a company that has expertise in thawing deeply frozen ground and in curing concrete evenly despite extremely cold temperatures.

Jason Brown of Mortenson Construction stated, “It’s important for us to work with partners who are also experts in these types of conditions. They can deliver value and can keep the projects moving forward. We selected Flex-Temp for the new stadium project because of these reasons.”

Flex-Temp System’s President Charles Sanvik explained, “Our hydronic system is similar to an in-floor heating system, but is above the ground. We can thaw a foot of frozen ground per day using our zone network of flexible hoses covered by construction blankets, which circulate heated Propylene Glycol (food-grade antifreeze).” At the heart of the system is their top-of-the-line Fusion 3000, which reheats the circulating fluid to a preset temperature.

No temporary heated shelter needs to be constructed because only the surface is heated and covered by construction blankets. This keeps fuel costs to a minimum. Workers have uninterrupted winter employment, and concrete trucks and other construction equipment that would normally be idled by frozen ground between Thanksgiving and spring can be put to work.

“In addition to our ground thawing capabilities, we have the best technique of warming concrete to date,” continued Sanvik. “Our MAXCURE system originated with us. We designed it so that between the supply side of the heated antifreeze and the return side, there is a sensor to ‘read’ the temperature of the returning fluid.”

Because cement in concrete has its own chemical heat hydration process, if the concrete forms or the base and the rebar have been pre-heated, the amount of heat that needs to be added will vary over time. However, if you set the Fusion 3000 for the desired temperature of the return fluid and set it on automatic, you can walk away. The sensor will be paying attention. “MAXCURE is the only system that automatically responds to within a degree or two of change in the temperature of the fluid in the hoses.”

Heated antifreeze in the machine is maintained at the set temperature in a reservoir. As soon as the return fluid falls below the set point, a mix valve will automatically open to let in just enough of the heated fluid to bring the circulating mixture up to temperature. Then, it automatically closes. “This very close regulation of the temperature results in the best curing and bonding of the concrete throughout the slab,” he said.

It is particularly important in concrete mixes that qualify for LEED credits. These designs use less Portland cement and more fly ash, slag and silica fume powder, a mixture that produces less of its own heat, although it makes a superior concrete, according to Sanvik.

The efficiency of the Fusion 3000 in thawing deeply frozen ground and in giving optimum curing of concrete at cold temperatures is why Mortenson Construction rented five of the Fusion 3000 units for use at the new Vikings Stadium during the winter of 2014-2015. There were also other reasons for choosing Flex-Temp’s Fusion 3000. The system is used for above and below grade slabs, forms, concrete walls and columns. They called upon Flex-Temp System’s associated sales and rental partner, Winter Construction Specialties.

Other companies have somewhat similar technology, but Flex-Temp, whose rented and purchased units are widely distributed throughout northern US and Canada, (two of their distributors in Canada are the two largest CAT dealers in the world,) can truthfully make the claim that their units are the most dependable.

“We reverse-engineered our units to eliminate almost every conceivable problem,” stated Sanvik, whose company began manufacturing in 2009. “Flex-Temp has done everything possible to make their units fail-proof.”

For example, the Fusion 3000 has a REMOTE ALERT GPS that transmits sensor and data information. When the unit’s temperature drops, or the fuel is low, the remote alert makes multiple notifications at once, even to gas and oil companies for refueling.

“There’s nothing worse than arriving at the job site on a Monday morning, with workers and equipment ready and subcontractors scheduled, to find a cold machine,” commented Sanvik.

To make doubly sure that doesn’t happen, Flex-Temp is also equipped with FAILSAFE POWER that activates a backup generator as needed. “For example,” explained Sanvik, “suppose a workman ‘temporarily’ unplugs a unit so he can plug in a saw, and then forgets to plug in the unit when he is finished. The generator will automatically start to keep the unit running. Once power is restored, the Generator shuts down.

“They’ve been [using this technology] at hospitals for a long time,” he said. “It’s not rocket science. But now we’ve applied it to this technology to help to make it fail-safe. Instead of coming to the job site and the machine is ice cold, you hear the generator running.”

The Fusion units are also designed to eliminate problems with oil change service, with SERVICEGUARD, an engine that is customized with a large capacity oil tank and fuel filter. “We used to send out plenty of oil so the oil could be changed on site several times during the season, but the rental units frequently came back with the oil unchanged.” This system neatly eliminates the need for any oil changes during the construction season. “We’ve reduced generator engine service time to once every 3,000 hours. For motor longevity, the Fusion uses a low 1800 RPM motor,” continued Sanvik’s technical partner, engineer Shawn Yurczyk. Sanvik and his partner Shawn Yurczyk had over a decade of experience working in the field with similar technology before starting their own company. “There are cheaper, faster motors, but they have a shorter working life and a greater chance of breakdown, so we chose to go with the more expensive- but also more dependable- package of a low RPM motor and generator.”

The machines are designed with FLEXGUARD, a containment reservoir built into the trailer to catch 150% of possible fluid spills, which is an important feature on environmentally sensitive sites.

“In designing the machine,” added Sanvik, “we didn’t care how much a component costs. Compared to the cost of downtime and a service call, the difference between a part that cost $50 and a more dependable version that cost $300 was irrelevant. For dependability and reliability, we would buy the more expensive, dependable part.”

“This is one of the reasons why we are Mortenson Construction Co.’s preferred vendor for this type of equipment. We have worked with them on a variety of projects, including government buildings and a large Data Center. We consult with them on time lines and equipment needs for a given project, and all our customers have 24 hour tech service backup,” said Yurczyk.

It’s also the reason Flex-Temp machines are prized by rental companies. “A lot of rental companies don’t know this technology is available,” commented Sanvik. “We give rental companies detailed instruction and training. We want to make it as simple as possible for them to get into this business.”

Because the Fusion units are used in extreme arctic conditions, they also have a fuel heater so the diesel fuel does not gel. “It’s the most efficient heater in the industry.”

This technology gives significant savings in a number of ways. “For example,” continued Yurczyk, “we recently worked on new construction for a nursing home in Minneapolis. The parent company was from Kansas, where they can dig through the frost, and they hadn’t anticipated the difficulties of Minnesota winters, with 2 feet of snow and -25 degree temperatures. Initially they were flabbergasted at the cost of ground thawing and concrete curing in winter.”

However, it all paid off handsomely. “They had not planned to open the new nursing home until fall, but by working through the winter with our equipment, they were able to open that spring. They paid off their construction loan early and made their money back on the Flex-Temp machine in the first month by beginning operations earlier than planned.”

“Utility Companies love these machines,” added Sanvik. “We sold 12 Fusion 3000’s to Excel Energy, an electric utility. Their area can get four feet of frost with wires frozen into the dirt. They also use the units to thaw a footing area, keeping the dug-out soil warm with a construction blanket while they cure the foundation, then back fill with the original, still-thawed soil, all in one operation.”

The unit is also used to thaw pipes and valves, and for other uses at fracking sites in North Dakota, PA, West VA and elsewhere. The smaller machines have a lot of potential for residential uses as well.

In spring and fall, the ground isn’t frozen, but Flex-Temp’s equipment is still needed by contractors, particularly for bridge decks and other cold weather concreting projects.

The individual components of the Fusion 3000 and 1400, and the similar but smaller machines Hydro 200 and 500, which are electric, as well as Indy Heat,eaH are subcontracted to experienced US companies, who use US materials. “That way, we can spend our time designing and innovating,” noted Sanvik. The units are assembled and tested by a crew of up to 12 at company headquarters in St. Cloud, Minnesota. A machine can be assembled and field ready in a very short timeframe.

Other major construction projects in the Minneapolis area that have used Flex-Temp units and the company’s expertise include the TCF Bank Stadium, the Minneapolis-Saint Paul Airport (Tram and Humphrey Terminal), and Target Field. There has also been a high demand for the machines on the East Coast and Canada

The Flex-Temp 3000 units are designed so they can be picked up with a forklift or lifted by a crane, and are lightweight enough to be pulled by a pickup truck. North American delivery is available, and the units are designed for turnkey use. Flex Temp’s machines can be rented through their rental arm, Winter Construction Specialties. For more information, contact them at 800-328-7094.