E3000s Ground Heaters Enlisted for Cold Weather Concrete Bridge Deck Curing

Cardi Corporation was charged with cold weather concrete curing on the $160 million Sakonnet River Bridge from Tiverton to Portsmouth, RI. Time was of the essence, necessitating multiple bridge deck pours throughout the winter months.

“The contract used calendar days, so it did not matter if winter delayed us,” says Keith Catanzaro, superintendent for Cardi Corporation. If crews missed the target completion date, the company would receive a $16,500 per day disincentive until it was completed.

Cardi needed an external heating solution to ensure the concrete didn’t freeze in the cold temperatures. “The Rhode Island Department of Transportation (RI-DOT) requires concrete to hold to a temperature range of 50° to 85° F during the winter,” Catanzaro says.

The bridge deck spanned the Sakonnet River more than 130 ft. above the water’s surface. Its steel box girder construction left 12-ft.-wide sections of the underside virtually exposed to frigid winter winds reaching 50 mph.

Constructing tents below the deck for propane heaters would be impractical and expensive. Catanzaro put the required monthly barge rental at $13,000, and the winds would wreak havoc on the poly enclosures.

Cardi considered using electric blankets on top of the bridge deck to maintain consistent concrete curing temperatures. However, the sheer size of the pours made this option unrealistic. “We were pouring nearly an acre of concrete at a time, so blankets were too expensive,” says Catanzaro.

A Cost-efficient solution

By far the most economical and practical heating solution was the Wacker Neuson E3000 hydronic heater. “Using our hydronic heaters to cure concrete typically costs 50% less than traditional heat protection methods,” states Ed Jaroszewicz, director of Wacker Neuson Climate Technology.

Cardi’s crews had previous experience using hydronic heaters to cure concrete. In that cold weather concreting application, the owner of a $270 million building project had Cardi on an extremely tight completion timeline that could not be missed. Cardi successfully poured footings, foundation and slab-on-grade concrete during the winter months using two E3000s.

The E3000 comes standard with 3,000 ft. of hose, allowing it to effectively cure up to 6,000 sq. ft. of concrete, or up to 18,000 sq. ft. with accessories. Providing a gross heater output of 385,000 BTU per hour and 83% heating efficiency, the heater delivers a normal temperature operating range of 100° to 180° F. Its large, 230-gal. fuel tank provides up to 140 hours of continuous run time between refueling.

Even with Cardi’s prior experience using the heaters — and the latest ACI 306R-10 specification for cold weather concreting including hydronic heaters as a viable solution — the RI-DOT required temperature monitoring and additional proof of its effectiveness. Catanzaro recommended using temperature loggers already approved for the job to ensure the concrete curing temperatures met spec. “We put the sensors wherever RI-DOT specified — on the deck, on girders and under the deck,” says Catanzaro.

Wacker Neuson assisted the effort by providing technical support and curing temperature models. “We supplied Cardi with curing temperature projection models based on 35° and 50° F ambient conditions,” Jaroszewicz says.

These models provided Cardi an effective heat protection strategy for the concrete placements to meet RI-DOT’s specifications.

Laying on the Heat

After adjusting mix design to allow crews to get on the concrete in a timely fashion, paving of a 200-ft.-long section of bridge deck commenced. The concrete mix included a slag retarder, which enabled crews to finish the pour prior to the deck setting up. It also enabled crews to apply heat within seven hours, so concrete temperatures would not dip below 50° F.

Crews set the hoses at 1-ft. spacing to optimize curing. Solution temperature returning to the heating unit was maintained at 160° F, which provided consistent concrete temperatures to within the 50° to 85° F spec range. “Ambient temperatures during the pour were in the low 40s, and the lowest ambient temperature reading was 25.2° F during the cure period,” Catanzaro says.

To direct heat onto the concrete surface, crews used Wacker Neuson IB 750 insulating blankets. Catanzaro mentions that the blankets worked well retaining the heat. Crews found it much easier to keep the blankets in position vs. trying to repair a damaged section of poly tent under the deck.

Post-curing analysis of temperatures found the concrete remained within spec temperature range, allowing the concrete to properly gain strength. “Wacker Neuson’s temperature model projections were very close to actual results on this job, and Ed adjusted the models using actual field conditions on this job to assist with future pours,” Catanzaro says. “The state is very happy with these results.” ET