As seen in ENR Magazine, March 9, 1998     Portable Radiant-Tube System Heats Up Concrete Construction Slab-curing approach melts cold-weather work stoppages By William J. Angelo     Some savvy contractors are taming winter conditions by warming up to a patented radiant heat system that thaws frozen ground, pre-heats forms and cures concrete in cold weather. The system has been used on buildings and bridges alike, and proponents claim demand is so hot that sales may more than double this year. To prove the year-round viability of tilt-up construction and capitalize on an incentive clause, managers at St. Louis-based Clayco Construction Co. Inc. used the system this winter on a $17-million, 550,000 sq. ft. concrete warehouse in Tilton, NH. They successfully thawed frozen ground, poured a 2,700 ft. x 46 ft. casting slab, and poured and cured 174 panels over a 10-week period between December and February during sub-zero temperatures. "In northern cities you don’t see tilt-up construction because the perception is that it’s strictly a summer product," says Robert G. Clark, president of Clayco. "This will change our industry." The $250-million firm, which pours 6 million sq. ft. of wall a year, is purchasing five units at $48,000 each. "The rental cost of the system was 75 cents per square foot," he adds. Workers for C-T Concrete Co. Inc., Allentown, Pa., are using the system to build a seven-story concrete flour mill in the state’s Pocono Mountains area. "We’re heating the floors as we go up, curing the concrete and also heating the place," says Angelo W. Sorrentino, C-T president. For the job’s 12 in. thick floors, the firm runs hoses 2 ft on center between two rebar mats. "We knocked off about six hours a day in overtime for finish work," he says. "If the structure was enclosed overtime would be minimal." The closed and portable system, manufactured by Ground Heaters, Inc., Spring Lake, MI., consists of a gravity flow expansion tank, pumps and rubber hoses. Two models, a 150,000 or 300,000 BTU heater, can cover up to 6,000 sq. ft. A thermostat controls heat, which ranges from 50° to 180° F. The burners use 2.5 gallons of fuel oil per hour to heat biodegradable antifreeze that is pumped through the system as low pressure. A compressor can blow the antifreeze out if hoses are left in the pour. When re-decking work on Chicago’s Green Street Bridge across the Kennedy Expressway was delayed until last December, managers for Kurtz Construction, Inc., Burr Ridge, IL., opted for the heaters. After scarifying 6,000 sq. ft of deck, the firm heated it for 24 hours at 180° F. While the ambient air temperature hovered about 30° F, the deck temperature remained at 55° F. "We poured concrete the next morning, covered it with burlap, re-laid the hoses, covered them with a vapor barrier and insulating blankets, and dialed the temp down to 50° F," says Douglas M. Nichele, ACCC project manager. "Layout took four guys 20 to 30 minutes." He adds that the bridge opened to traffic after a seven-day cure. Sales of the units started slow in 1995, totaling only $285,000 but reached $3.5 million last year. "Our ’98 pace is double last year" says Sue Meekhof, GHI Vice President. Contractors "can configure the hoses any way they want: around columns, protecting footings, or vertical poured walls," she adds. Printable PDF version available here.