CRREL concrete tests heat up

By Bruce Lyndes, CRREL PAO

It is a typical New England winter morning and a clear blue sky and bright sunshine have a dozen New Hampshire Department of Transportation workers squinting and shuffling around to stay warm, surrounded by steam from their own breath. The thermometer reads 5 degrees Fahrenheit as a concrete truck rumbles down the hill, stops, and the men set up the chute. A few minutes later, a high-slump mix is being poured into the curbing forms on a secondary road bridge. Researchers from CRREL watch over the work and occasionally dip sample cups into the mixture. This is their experiment, and as the concrete starts to set-up, everything looks good.

Normally, concrete is not poured when the temperature is below 40 degrees Farenheit, but a CRREL-designed concrete admixture is changing that long-held rule. After two years of laboratory and in-field testing, researchers say the concrete admixture is just as strong and durable as material poured in normal temperatures. It is also one-third the cost of conventional concrete construction mix poured in cold temperatures. Ten states, including Vermont and New Hampshire, are underwriting extensive testing of the cold-weather concrete mix, which could extend the transportation construction season by up to 60 days in the northern United States, and 120 days in moderate climates.

Two readily available ingredients are the differences between conventional concrete and the cold weather prototype, according to CRREL principal investigator Charles Korhonen. "The admixture accomplishes two things. We're lowering the freezing point of the concrete, similar to anti-freeze in a car's radiator, and we're forcing the concrete to gain strength faster than normal," he said.

Motorists in particular should welcome the new technology. "Work normally done in the summer creates construction zones and slow moving traffic, leading to frustration and lost time. But if some projects can be moved to low-traffic winter months, there'd be far less problems and roadway hazards for both drivers and workers," Korhonen said. In addition, the process could improve transportation infrastructure in cold weather regions by extending the construction season, while allowing longer seasonal employment and greater use of construction equipment.

"We're rewriting how cold weather transportation concreting can be applied,"said CRREL researcher Lynette Barna, who hopes to see the admixture process accepted by the concrete industry and commercial users. Prior to the cold weather admixture, concrete could only be poured and cured in temperatures below 40 degrees Farenheit by using heated tents or thermal blankets to enclose the construction area.

"We're very pleased with the project right now. We've saved a lot of money and man hours by not having to use a heated enclosure," said Leland Atwood, an engineer for the New Hampshire Department of Transportation.

The biggest hurdle in widespread use and availability of the cold weather admixture is the lack of an industry standard. Currently, the American Society for Testing and Materials (ASTM) doesn't recognize the process, but that may change soon. "We've proven this works, so ASTM will hopefully develop standards, and then commercial producers will start to manufacture it, and my hope is that it's going to change many rules about concrete construction," Korhonen said.

The admixture has been field tested in North Woodstock, Littleton and West Lebanon, N.H., and Rhinelander, Wis.