Placing concrete in cold weather poses many challenges for contractors. As the average daily temperature dips below 5° C (41° F), these colder temperatures have adverse affects on pouring and curing concrete.

Concrete’s sensitivity to the cold presents several issues that can result in delays and additional costs for the contractor when placing and finishing concrete during the winter months. First, time for initial concrete set is extended, which requires the finishing crew to stay at the job longer. These longer hours can lead to overruns, which ultimately decreases bottom line profitability.

Second, early freezing permanently damages concrete. Freshly mixed concrete freezes at -2° C (29° F), and if allowed to freeze before curing to 3.5 MPa (500 psi) compressive strength, voids formed by ice make the concrete weaker, less durable and possibly unstable. This can lead to the need to replace freeze-damaged concrete, which is expensive.

Finally, lower temperatures slow the rate of strength gain. This delays removal of protection and the time for when the new concrete can be safely stripped or loaded, which can increase project costs.

Pfaffenhausen, Germany-based Xaver Lutzenberger Company recently encountered its own cold-weather concrete challenges while constructing a new hydroelectric power plant in Kempten, Germany. To remain on schedule, Xaver Lutzenberger need to work through the cold winter months, in which outdoor temperatures plummeted to -2° C (-29° F) during a scheduled concrete pour.

The project called for the crew to cast new concrete atop an existing concrete slab. The subfreezing temperatures necessitated warming the existing 100 m² (1,076 ft²) slab in order to keep the freshly poured concrete from freezing during the cure process. To deliver the heat, Xaver Lutzenberger chose the Wacker Neuson E 700M hydronic heater.

The versatile E 700M is the least expensive, most efficient means of performing a wide variety of cold-weather heating applications. In addition to concrete warming, similar to the need at the hydroelectric plant site, the portable hydronic heating system also helps to properly cure concrete, efficiently prevent frost and quickly thaw frozen ground. Compared to fuel-inefficient traditional methods of operating a gas or oil heater inside an enclosure that delivers merely 15% energy to the surface, the portable E 700M hydronic heating system boasts as much as 94% energy delivery to the surface.

With its standard 700 m (2,296 ft) length of hose, the E 700M offers heating/thaw capacities from 204 to 409 m²/h (2,195 to 4,402 ft²/h) and cure capacities reaching 409 m²/h (4,402 ft²/h). The hydronic heater delivers a 74 kW (252,723 BTU/hr) heat output at normal operating temperature ranges of 38 to 82° C (100 to 179° F). The bottom-line benefit of the E 700M is the unit efficiently heats large areas so that construction activities can continue, even in subfreezing temperatures.

In a typical application, the hoses of the E 700M would be placed directly on the existing slab to heat it to the optimal temperature for the new concrete cast. However, the work at the hydroelectric plant was not your typical application. “Extremely dense reinforcing steel was already in position for the new cast,” explains Robert Brauneis, product manager for utility at Wacker Neuson SE in Europe. “The crew was forced to lay the E 700M’s hydronic hoses on top of the steel, 120 cm (47.2 in) above the existing slab.”

Undaunted, the crew placed the hose with positioning to maximize the heating effects of the E 700M and set the output temperature to 82° C (179° F). Insulating mats were placed on the hoses to facilitate the heating process and subsequently were covered with tarps.

Within a short time period, an increase in the temperature below the insulating mats could be felt. The E 700M was successful in not only warming the concrete but also the frozen reinforcing steel for the new cast.

Wacker Neuson helped Xaver Lutzenberger complete the new cast successfully and on time. Additionally the crews noticed one more benefit to using the E 700M. “The heater is extremely quiet when running and was not a noise nuisance for the workers or local residents,” adds Brauneis.

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