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28 LC DBM (Continued on page 30) the system temperature as it's pumped through the nearly five miles of tubing under the concrete." To construct the system, four-foot by eight-foot sheets of two- inch-thick extruded polystyrene were laid down end to end, followed by a layer of woven wire mesh. "This was designed so if the polystyrene separated from the con- crete during curing, the wire would keep the tubing tight to the bot - tom of the slabs," Hartberg relates. The radiant heat tubing was then positioned over the wire mesh and fastened to it with foamboard staples. Next, a #4 rebar grid was built, suspended over the tubing so as to end up centered in the five- inch-thick slab. In addition, the two 50-foot-long trench drains to intercept runoff were installed. "(They) were worked into the design to become an amenity, rather than utilitarian," reports Hartberg. "These heavy-duty drains are unique, as the tubing runs under the drains, keeping them flowing in sub-zero temperatures." Throughout the installation, the tubing was pressurized to endure foot traffic during the multiple concrete pours, and to alert construction crews to leaks, even pinhole sized ones, which could be heard before the concrete was poured, and then seen after the pour. Before that happened, concrete formwork was set up around the rebar and tubing. The colored bands of concrete were put down first, followed by the sidewalk infill after the outer bands had set. The form-liner seat walls, amphitheater, lighting and landscaping were then installed. As a final touch, a local artist was commissioned to sandblast a relief of the geographical boundary of Dakota County into the plaza, which was then painted with black epoxy, mirroring a mural above the door. The overall project timeline was five months from start to finish and the transformation of the space is nothing less than dramatic according to many Dakota County staff. When the snow makes an arrival, the heating system is triggered by moisture sensors in the plaza area. Hartberg sums up, "The introduction of the many colors, vertical elements, pedestrian access and safety, and reduced maintenance hit all of the project goals, and the space is set to welcome users for many years to come." (Continued from page 26) Top, Left: Concrete formwork was set up around the tubing and the #4 rebar grid, which was installed at 18" intervals in each direction and suspended over the tubing and mesh so as to be centered in the 5"-thick integral concrete pour. Top, Right: Concrete finish crews from Morcon Construction Company first installed the outer bands of colored concrete and let them set before moving on to the sidewalk in-fill. Above, Left: Overall it took 5 months to give the plaza a new surface, form-liner seat walls, amphitheater, lighting and landscaping. A map outline of Dakota County was sandblasted into the concrete by a local artist and then painted with black epoxy. Above, Right: Moisture sensors installed throughout the plaza trigger the heating system. Return water from the center's central heating plant preheats the glycol tank. A heat exchanger then boosts the fluid temperature that is pumped through the tubing.