| Ground Heater's
Hydronic Heat Cures Tilt-Up Walls With more than nine
years experience in tilt-up concrete construction, Clayco Construction, based in St.
Louis, Mo., is considered the best in its field. As with any concrete construction job,
cold weather always presents a problem. In addition to dramatically reducing the concrete
curing rate, cold temperatures decrease both labor and equipment productivity, which slows
overall project progress. Because of these concerns, many companies choose not to place
concrete in the winter. Tilt-up concrete construction is no exception. In fact, the
problems caused by cold weather are the reason that tilt-up construction is mostly used in
warmer climate states, and has only recently gained attention in the North.
The Tilton, N.H. job involves the construction of a 550,000-square foot
office building and distribution warehouse for DM Management, a mail-order catalogue
company. Valued at more than $17 million, the job presented a problem that even Clayco had
not yet faced. According to Pete Woolley, project superintendent for Clayco Construction,
the weather conditions were difficult to overcome. "We’ve never done a job in
conditions like they have here in Tilton – I mean this is extreme," Woolley
said. "We had 24 inches of snow in November alone and winds up to 50 miles per
hour."
Though Clayco Construction had overcome extreme winter conditions in the
past, it was the high winds that made this tilt-up job extraordinarily difficult.
"Propane heaters and tents were totally out of the question. We didn’t even
think twice about it," Woolley said. "The cold weather is bad enough, but the
high winds make it ten times worse. The wind chill can freeze the face of the concrete,
causing integrity problems and requiring patchwork. We had to find a way to get this job
done, and because of scheduling demands, postponing was not an option."
While Woolley was searching for a way to keep the job on schedule, a
salesperson from Action Equipment, a Ground Heater dealer with four locations throughout
New England, provided a solution. "[Action Equipment] suggested we use the Ground
Heater to help facilitate the cure," Woolley said. "Though the Ground Heater was
designed for thawing frozen ground and curing concrete, it had never been used for a
tilt-up curing application, but we saw the potential." Clayco decided to rent five
E3000 Ground Heaters from Action Equipment for this large curing job.
"Normally, in a non-winter job, we would cast our panels on the
concrete floor of the building, but winter conditions require a different approach,"
Woolley said. "In winter, we construct a below-grade, temporary casting slab for
pouring the wall panels. We poured the casting slab over the Ground Heater’s hoses
and basically made a large radiant heating pad to keep the wall panels warm during the
curing process."
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Pete Woolley
Project Superintendent,
Clayco Construction Co. |
 The
preparations began by deciding where to create the casting slab and then laying out the
Ground Heater’s hoses accordingly. "Using all five Ground Heaters, we laid out
roughly 40,000 feet of hose for this slab – over seven miles of hose," Woolley
said. With the Ground Heaters running, the Clayco 30-person crew poured concrete over the
hoses to make the large radiant heating pad.
Once the casting slab was ready, the crew began positioning the wood
wall forms on the slab. A release agent was sprayed into the forms and on the casting slab
itself. Next, foam-strip rustications were placed into the forms to provide a decorative
appearance on the face of the finished concrete wall. Galvanized mesh was then placed into
each form, followed by a 2.5- to 5.5-inch concrete pour (depending on wall size) known as
a "skin." A 2-inch wall insulation was then laid on top of this
"skin," rebar was set, and the remainder of the concrete, known as
"backs," was poured and trowel finished.
"We ran the Ground Heaters full bore, pumping out 180° F into the casting slab and
heating more than 12,000 square feet of slab with each unit," Woolley said. "The
idea was that the heat going through the slab would conduct up through the wall panels,
facilitating the cure. For a proper cure, we wanted to keep the panels at 50° F or more." With average
temperatures below freezing and sometimes as low as 0° F, Clayco placed insulation blankets on
top of the panels to retain the heat and prevent the face of the concrete from freezing.
Checking the gauges on the Ground Heaters, Woolley found that the Heat Transfer Fluid
coming back into the boilers was between 70° to 80° F,
meaning the concrete walls were sufficiently warm to cure properly. "We did a
seven-day cure on the walls, running the Ground Heaters 24 hours a day. To ensure the
concrete achieved proper strength gain, we did five-day breaks on our test cylinders.
Everything worked great."
From November to January, Clayco poured and cured 167 wall panels,
ranging from 40’ to 44’ in height, 10’ to 18’ in width and 14" to
17" in thickness (roughly 15.3 million pounds of concrete overall). "Although
this technology was a gamble on [Clayco’s] part, this job could not have been done
without the Ground Heater," Woolley said. "Everyone up here can’t believe
we poured concrete in these weather conditions, but we did – using the Ground
Heater."
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"Everyone up here can't
believe we poured concrete in these weather conditions, but we did - using the Ground
Heater." Pete Woolley
Project Superintendent
Clayco Construction Co. |
