U.S. Army Corps of Engineers researchers are experimenting with concrete admixtures that allow for subzero pours in the open air–as low as 5°F. Underwritten by 10 state transportation departments, the three-year, $750,000-program is paving the way for reduced labor in winter months and a longer construction season.

"We're looking for a direct chemical substitute for heat," says Charles Korhonen, principal investigator at Corp's Cold Regions Research and Engineering Laboratory in Hanover, N.H. Korhonen, involved in such tests for years, says no American Society of Testing and Materials standard yet exists for antifreeze concrete admixtures (ENR 1/22/01 p. 15). In response, Korhonen and the lab team are working with combinations of off-the-shelf products in order to lower the freezing temperature of concrete. These substances, which are commonly available to contractors, include concrete accelerators, corrosion inhibitors and plasticizers already governed by their own set of standards.

Chuck Corliss, design engineer with the New Hampshire DOT's bridge maintenance bureau, says his crews "spend a lot of time building heated enclosures" for cold-weather pours, as the typical temperature of concrete cannot fall roughly below 40°F for a proper cure. He says that new admixture guidelines from the lab would "no doubt provide cost and labor savings for doing jobs." Other state DOTs involved in the project are Vermont, New York, Pennsylvania, Michigan, Wisconsin, Montana, Wyoming, Utah and Idaho.

One study performed this winter involved a 104-ft-long bridge curb in Lebanon, N.H. NHDOT crews say they saved 132 labor hours for building an enclosure and $50 in liquid propane by using the lab's experimental concrete. The total cost was $700 in contrast to $750 plus labor for traditional methods.

"The admixtures certainly will extend the construction season from two to three more months," says Korhonen.

With testing out of the way, Corliss believes the next step is for the group to develop a "recipe guide" for admixture chemicals, which is expected to be developed well into the summer. Lab officials hope to have guidelines available to state DOTs by next winter for subzero concrete admixtures.