The winter of 2013-2014 is making records for unleashing some of its coldest temperatures in more than 30 years. But before you grump about having to roll out of your warm bed to face another day of air that hurts your face, consider those whose calling is construction.
We recently checked in at some northern Minnesota jobsites to see how they’re dealing with the challenges of construction in extreme cold.
While working in an enclosed, temperature-controlled space is still the gold standard for winter construction conditions, with modern equipment, resourcefulness and careful collaboration, “We can perform just about any construction activity in cold weather,” said Gary Francisco, project superintendent in Bemidji.
Here are some of the considerations that come into play during various stages of extreme cold weather construction.
Excavation and Concrete Work
It’s easier to dig soft ground than frozen ground. Covering ground with insulated blankets or straw is a proactive approach to help keep frost out of the ground before excavation. Up to a point.
“It’s 17 below today,” says Steve Bergerson, KA superintendent at the Duluth Airport site, where crews lately have been excavating and setting up footings for a four-level parking ramp. On that site, “We’re using a concrete breaker to break through the frost in order to excavate.”
Frost and concrete do not mix. Concrete requires about 48 hours at moderate temperatures to cure properly, and frost cannot be allowed to get under the concrete footings. Ground thaw heaters may also be employed along with insulated blankets for winter excavation and foundation work, but that’s not the only way. At the Duluth airport site, KA collaborated with the owner, subs and third party inspector Braun Intertec to come up with a more cost-effective process: excavating just enough to stay ahead of the concrete and rebar installation, and covering the excavated area with double layers of insulated blankets. Braun inspects each section before the pour to assure that it is frost-free, and if frost is detected, the area is tented and heated for 24 hours until the frost is gone. As each section is poured and rebar installed, the concrete crew covers it back up again to keep it warm. A temporary shelter of frame work and reinforced poly with an additional heating source may also be used around the work area in extreme cold.
As foundation walls go up, they are also covered and heated until the wall is at 75% design strength. Then waterproofing is applied under the shelter, the shelter is removed and both sides of the wall are backfilled to protect from frost penetration. Any excavated earth to be used as backfill also needs to be kept under wraps with insulated blankets to keep out the frost.
Slab On Grade
Some project designs require the installation of underground mechanical systems prior to erecting and enclosing the building and pouring the slab. Again, insulated blankets and ground thaw heaters help get the job done, with the slab usually poured a section at a time. At the Itasca Biological Field Station project now under way on the University of Minnesota campus, Gary Francisco is using temporary heat boilers on the facility’s new in-floor heat tubing system to keep the frost at bay during the slab pour.
Steel Erection and Equipment
Unlike concrete, steel isn’t sensitive to freezing cold. But the erection equipment can be. Hydraulic cylinders on cranes and fork lifts tend to leak and diesel equipment is hard to start.
“On the really cold days it’s a challenge just to get the equipment running,” said Francisco. “We always make sure we plug in the engine heaters on the equipment over night, and sometimes put trickle chargers on the batteries and a magnetic heater on the hydraulic tanks.
“We build shelters for the stationary equipment like air compressors and heat the shelter with a milk house heater,” Francisco said. Tools, especially battery-powered tools, need to be stored in a heated area so they will work.
Also, “You need to use cold weather cords so they won’t break when you unroll them and are also much easier to work with. We have snapped many cords on power tools just trying to use them,” Francisco added.
If you’re lucky enough to have an erected building to work in, you still need to close off openings such as windows and doors with poly panels; bring in a licensed plumber to hook up temp heaters and check gas lines for leaks; and monitor for CO2 levels in work areas.
The Human Factor
Staying productive is a challenge when you’re both dressing in layers and dressing to move. Winter gloves can cut production by 30% to 50%, experts say.
“The largest hurdle is keeping our hands warm,” says Francisco, who keeps glove and boot warmers in his office trailer for the guys to put their gloves on so they can switch gloves periodically.
“We try to keep the guys in warm gloves and choose work activities where we can be the most productive depending on the temperature. On the really cold mornings I schedule an activity like shoveling snow, or something that needs to get done to clear the way for our construction activities,” Francisco said.
Safety is always the number one priority. “We all look out for each other by watching for frost bite on exposed areas of skin that you can’t see yourself. I tell the guys not to be heroes. We all have different thresholds for cold and if you need to warm up than go inside,” Francisco said.
In addition, subcontractor safety guidelines are strictly enforced. At -10 air temperature, or -20 windchill, the concrete team doesn’t work.
“This has been the ultimate cold weather challenge,” says Francisco. “I am proud of my KA crew. They have endured these cold temps and kept moving.”