Cold Weather Concrete Curing with Hydronic Heat |
Project |
Cure 2,500 m2 (26,910 ft2) of concrete in subzero ambient temperatures |
| Contractor |
Eigner Fertigbau GmbH & Co. KG, Nördlingen, Germany |
Challenges |
With subzero ambient temperatures, maintain freshly poured concrete slabs at optimum curing temperatures to prevent freezing and facilitate rapid strength gain |
WNCC Equipment |
The E 700M Hydronic Heater |
Results |
Using the E 700M, Eigner Fertigbau was able to both thaw frozen ground and probably cure the concrete on two industrial building projects. In three days of being poured, the slab was strong enough to support up to 12 tons of prefabricated structural concrete. |
 Concrete is extremely sensitive to freezing temperatures, which makes cold-weather concrete curing during the winter months virtually impossible or extremely difficult at best. As the mercury drops, the length of time for initial strength gain of the concrete increases and the rate of strength gain reduces. Additionally, early freezing of the freshly mixed concrete can result in permanent damage.
Eigner Fertigbau GmbH & Co. KG from Nördlingen, Germany, solved these cold-weather concrete curing challenges with a high-quality E 700M portal hydronic heater from Wacker Neuson. During the harsh winter, Eigner Fertigbau was able to continue construction work on two industrial-scale buildings and cure the concrete quickly and efficiently with the E 700M. The company plans to also use the E 700M on future projects.
Concrete curing in winter
“Normally we have to abort our construction projects during the cold winter months and wait for the weather to improve before we can work and cure efficiently,” explains Reinhold Walter, project manager at Eigner Fertigbau. “Thanks to Wacker Neuson’s portable hydronic heater, we were able to work right through from December till March, thus saving time and costs.”
The higher the temperature, the faster the concrete sets. If the temperature of the concrete is 5° C (41° F), it takes between four and six weeks to harden, depending on the quality and thickness of the build. If the temperature rises to 20° C (68° F), however, this setting window is significantly shorter and the concrete is ready for use much earlier.
Building contractor Eigner Fertigbau, specialist in the construction of large-scale industrial and manufacturing buildings, used the E 700M from December 2008 to March 2009 for concrete curing on two different construction projects. To meet tight deadlines, the company needed to lay concrete floors at subzero temperatures on both of these projects.
One machine, two uses: thawing and curing
Eigner Fertigbau first used the E 700M at its warehouse site in Neuburg an der Donau in southern Germany, where it laid a concrete floor measuring around 2500 m2 (26,910 ft2) in January 2009. The foundation layer was made of recycled demolition material and was frozen to a depth of approximately 60 cm (24 in).
“In order to push ahead and stay on track given the tight timeline, we needed to divide the floor into sections, thaw each section individually and immediately lay the concrete on that footprint,” continues Walter. “We did this with a portable hydronic heater from Wacker Neuson and were so impressed with the results that we lost no time in deploying the heater on a second site we were working on.”
Work is underway to build a power plant powered by biomass at Mertingen near Augsburg. Here again, Eigner Fertigbau used the Wacker Neuson E 700M portable hydronic heater to lay the concrete floor of the plant between February and March. The E 700M first thawed the gravel foundation so the concrete could be poured.
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High quality results
The tight project timeline meant that Eigner Fertigbau had to move quickly. The concrete was poured as soon as the foundation was thawed. During the following two days, the E 700M then maintained the concrete at the optimum setting temperature of around 25° C (77° F).
On the third day after the concrete had been laid, the new floor was able to support up to 12 tons of prefabricated concrete structural elements. Around one week later, a false ceiling was installed on the prefabricated concrete dividing walls. Part of the power plant – a boiler weighing around 80 tons – was then installed on part of the new concrete floor a mere 10 days or so after the floor had been laid.
“The concrete floor proved extremely robust and strong," adds Walter. “Using an appropriate high-grade concrete, the E 700M enabled us to fully meet our high concrete strength and quality standards by heating the newly laid floor. In addition, the heater saved us several weeks and allowed us to stay on our tight schedule.”
“Standstill without the portable hydronic heater”
Even with extreme frost, the E 700M can heat large areas, so that construction work can continue as usual. To thaw the ground, the heater runs on diesel and heats a mixture of water and glycol up to 82° C (180° F). To cure the laid concrete, the solution is heated to a temperature of between 40° and 50° C (104° to 122° F), depending on the ambient conditions.
The heated liquid is pumped through a 700-meter (2,300-ft) hose that runs over a vapor barrier sheet that has been placed over the area that needs heating. An insulating blanket is then laid on top of the hose to prevent heat loss from the ground. The heat is transferred directly from the hose to the concrete surface. Up to 94 percent of the heat generated by the E 700M penetrates the surface area being treated.
Eigner Fertigbau is extremely happy with the results. “Because of this year’s strong winter we would never have made such good progress without the portable hydronic heater. The concrete would have taken several weeks to cure,” summarizes Walter. “We plan to use the E 700M from Wacker Neuson on any future projects where we are working under time pressure in sub-zero temperatures.”
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