Things are changing in the way that concrete is placed in northern climates. It includes a new mind-set and modified technique that extends the concrete construction season in some areas by as much as 2 months. This newly formed concrete mixture — referred to as antifreeze concrete, cold-weather admixture systems (CWAS), or “arcticrete” — has been in the making for approximately 15 years. It is being demonstrated in various areas by researchers with the U.S. Army Engineer Research and Development Center’s (ERDC’s) Cold Regions Research and Engineering Laboratory (CRREL).

The Process
Off-the-shelf, cold-weather admixtures, such as nitrates and nitrites, are combined with water in the concrete mix of gravel, sand, and cement. These chemicals depress the freezing point of the mix’s water and accelerate the curing time without the loss of strength. Water freezing in normal concrete mixtures decreases strength, and ice formation in fresh concrete causes irreparable damage. Several formulations have been developed and used in the field that protect fresh concrete down to an internal concrete temperature of 23 F, and laboratory tests show that this is not the lowest temperature limit. The air temperature at the time of placement may be much colder.

“In regions with a short summer construction season, such as Alaska,” said Lynette Barna, a CRREL civil engineer and the program’s principal investigator, “CWAS opens the door to continue concrete operations later into the fall when colder temperatures might otherwise discontinue construction projects.”

“CWAS provides a low-temperature alternative to conventional concrete,” she said. “The same construction practices are used and the only difference is that the temperature limitation of the concrete has been lowered. Working with antifreeze concrete is no different.”

Demonstrations
The second of two yearly field demonstrations (initial placement took place in Juneau, AK, in 2007) was held in March at Fort Wainwright, AK, proving that cold-weather concreting can be successfully placed and cured in cold temperatures without the usual or standard methods of building an enclosure and bringing in heat to safeguard the concrete from the cold.

The objective of this most recent concrete placement was to introduce the U.S. Army to the use of concrete admixture combinations that act as an antifreeze, allowing extension of the concrete construction and repair seasons to save time and money. Based on figures from the 1990s, it is estimated that $800 million is spent annually on safeguarding freshly placed concrete.

“We know this antifreeze concrete technology works. This year, we wanted to show the Army and others that cold-weather concrete is a suitable alternative to other cold-weather methods that consume considerable time, energy, and money,” said Dr. Charles Korhonen, a retired CRREL engineer who has been working on this technology for years. Korhonen now works for SpringBoard, an Alaskan state program that helped fund one of the demonstrations.

“We don’t need to preheat the ground, nor do we need to build enclosures and pipe in heat for days or weeks,” said Korhonen. “We place this mix on frozen ground. We don’t need to heat the water that goes in the cement truck. This concrete is a significant step forward for military and commercial uses.”

At Fort Wainwright, contractors and subcontractors placed five 25-by-15 foot sections with the overall slab dimensions of 25-by-75 feet, each with a different mixture of the admixture chemicals. The slabs created will be used as parking for communications and Stryker vehicles. “Monitoring of slab temperatures and breaking of cylinder specimens or samples provides scientific data needed to prove this,” said Korhonen.

This was a joint effort, with federal agencies and the U.S. Army working hand-in-hand with academia, private industry, and nonprofit organizations. Alaska Department of Transportation officials and University of Alaska engineering professors also attended the placements, test runs, and debriefing meetings.

Previously, cold-weather concrete was placed for two slabs at the Cold Climate Housing Research Center in Fairbanks, AK, in March 2007. An even earlier placement occurred in Juneau.

The 2007 demonstration was funded in part by SpringBoard, a statewide program of the Juneau Economic Development Council and a partnership intermediary with DOD. The recent demonstration in Fairbanks was funded by the U.S. Army’s Assistant Chief of Staff for Installation Management’s Installation Technology Transition Program (ITTP). The ITTP transfers innovative technologies that improve infrastructure design, operation, and maintenance on Army installations.

Editor’s note: Rollo Pool of the Juneau Economic Development Council provided information for this story.