The technology behind building systems of double-wall precast panel design has been around for decades. In fact, more than 300 plants specializing in the method are currently operating in several countries across Europe. But it wasn't until recently that Naperville, Ill.-based Dukane Precast, Inc., decided it was time to bring the method to North America, branding it Double-Wall. To that end, the company has built a plant geared for low-cost production of roof and wall panels that create what is arguably the safest, most durable and most energy-efficient building system available for low-rise residential and non-residential construction.

Double-wall building technology means that both sides of the wall and floor components are form finished. Interior surfaces of the walls are drywall smooth, and only a coat of paint is required to achieve the look and feel of a drywall finish. Exterior surfaces of walls can be produced with a variety of finishes and surface treatments. Brick, stucco, acid-etched stone, simulated limestone and wood-grained plank siding are among the exterior surfaces that can be produced using reusable form liners. Floor panels have the same smooth form finish on both sides — ceiling and floor — and no additional toppings are needed for the floors or ceilings.

Nearing full automation, Dukane's Double-Wall facility adjacent to the company's headquarters office is the first of its type in North America. Robotics operate directly from computer-aided design (CAD) drawings to lay out panels to the exact building dimensions and specifications for each project. Panel dimensions and door and window openings are marked on each casting table directly off CAD drawings. Magnets and edge forms are positioned on a casting table by robot, and electrical, cable, computer and phone conduits are placed in the wall panels. Reinforcing steel is placed on the casting tables, and steel truss girders are used to connect the two wythes of concrete. In the production of floor panels, radiant floor tubing is tied to the trusses.

Panels are moved throughout the plant using a series of floor-mounted rollers. The prepared wall panel form is then fed through to the concrete placement station, where quality control procedures are followed to ensure proper design strength. The panel advances to the next station for consolidation of the concrete within the wall section. The panel continues into a rack kiln at optimum curing conditions for about eight hours, after which the concrete panel will reach 3,000-psi compressive strength. Thus, Side A is completed.

Side B goes through the same stations as the first side until it gets to the consolidation station. At this point, Side A is brought out of the kiln and placed on the vacuum device, which flips the panel upside-down and lowers it onto its Side B mate. Consolidation of the joined panel completes the process, and the finished panel is sent back to the kiln. After removal from the kiln, insulating foam with a high R-value is placed between the two wythes for each wall section at the plant to produce the insulated sandwich panel, which is stored at the operation until trucked to the job site. Panels do not exceed 12 ft. in height and, by using special trailers, can clear most underpasses and do not require special permits.

Floor and wall panels are dispatched to the project site on a schedule to minimize clutter and crane time. After panels are braced, they are grouted together to form a monolithic structure. Once floors and walls are up and grouted, work can immediately begin on the next level. After the shell is completed, the rest of the home can be finished normally. In many cases the shell construction for a single-family home can be finished in three days.

Dukane's Director of Marketing-Residential, Brian Bock believes that while the Double-Wall process will prove itself initially in suburban Chicago's single-family home market, it is in the construction of schools and dormitories that his company sees a greater potential volume of work in the near future. Since this process offers the same benefits as many concrete structures — fire safety, quieter environment, energy efficiency, narrowed construction windows — applications for the system extend to multi-family dwellings; townhouses, condominiums, and three-story walk-ups; apartments; and hotels and motels.
— Steven Prokopy

DOUBLE-WALL ENERGY RATING BLOWS AWAY COMPETITION

That concrete building methods offer significant energy conservation due to thermal mass properties has been widely recognized. Now, as the first of its kind in North America, the Double-Wall panel design implemented by Dukane Precast takes energy efficiency through the use of concrete to a new level. Panels are cast in an automated CAD process incorporating robotic form assembly on steel tables that yield smooth surfaces requiring minimal treatment for walls and floors. Internally, the cavity construction of the double-wythe panel augments its insulating potential. Externally, the panels present finished surfaces that require minimal treatment — paint alone is sufficient — or the possibility of introducing a variety of finishes including faux brick or weathered limestone.

The Double-Wall panel design is a winning choice for homebuyers looking primarily for cost, comfort and health benefits in their selection of a home, according to energy rater James Cavallo, who heads Kouba-Cavallo Associates in Downers Grove, Ill. The advantages of such construction cut across all systems within the home to provide significant cost savings while maintaining a comfortable and healthy indoor environment. The high degree of insulation provided by the panels permits the use of smaller heating and air conditioning units, thus savings upfront, as well as lower monthly operating costs. Also key to energy conservation, comfort, and cost considerations are radiant floor heating lines embedded in the upper wythes of Double-Wall floor panels.

An August 1 test on a Bolingbrook, Ill., home confirmed the prolific energy conservation potential of Dukane Precast's panel system. The ranch-style home, with 2,300 sq. ft. plus a full walk-out basement, was tested using a device called a blower door. The test examines and quantifies the structure's air infiltration — or how tightly it keeps out cold, winter air and hot, humid summer weather — by creating a 50 Pascal pressure difference between the inside of the house and the outside while measuring how much air is pulled in through the building's envelope. The structure was given a Home Energy Rating of 91.6 out of a possible 100, qualifying it for the U.S. EPA Energy Star Home label. Reporting these results, Cavallo affirmed, “I have never tested a house that tight before. It will be a very energy-efficient home for the buyer and — with the heat recovery ventilator — a very healthy house.”

Designed to promote residential energy efficiency, HERS or the “Home Energy Rating System” awards a number rating to a house based on a scale from 0 to 100. Energy-efficient structures built to the energy code begin with a score of “80.” Each point above 80 indicates that the house uses 5 percent less energy for the same level of comfort; accordingly, a home scoring 81 is 5 percent more efficient, 82 is 10 percent more efficient, and so on.

The rating system also assigns a “star” score. A house rating an 80 in the point system receives a Four Star Rating and qualifies for mortgage benefits. Very efficient houses rating at least 86 percent and 30 percent more efficient receive the top Five Star Rating.
— Martha Blastow

Double-Wall panels and plant-installed Andersen Window units afford air-tight construction. A heat recovery ventilator is used to draw fresh air into the home while trapping heat from the outgoing airstream to save energy and provide heat for water and indoor air.

Radiant tubing placement at plant. The ability to cast radiant heating lines into the Double-Wall floor panels is pivotal in Dukane Precast's building system for the single-family market. Field-labor savings in floor tubing placement join key Double-Wall enclosure advantages — thermal mass, insulating foam or board-filled cavities plus paint-ready interior and exterior surfaces — the producer is bringing to the single-family residential market.

FABRICATION

Dukane Precast designed the Double-Wall product operation around a carousel footprint, with 56 tables, 42 ft. × 12 ft. 4 in., traveling on floor-mounted rollers from preparation and mix placement and vibration points, to rack curing and vacuum-clamp or crane lifting stations. The company has commissioned North America's first Shuttering Robot System, developed by Weckenmann GmbH, Germany, and represented domestically by Columbus, Ohio-based Spillman Co. Early panel production follows a sequence with 1) transfer of tables from a cleaning and oiling station to the shuttering area; 2) painting of panel, opening and blockout areas using data points from a CAD-driven computer plotter (working in tandem with the Shuttering Robot); 3) robotic placement of magnets and end rails along plotted areas; and 3) table transfer to stations for reinforcement setting, prestressing or other preparation. The robot collects magnets and rails from magazines placed along the perimeter of the table area footprint. Pallet cleaning and oiling equipment and the CAD-driven plotter were part of the Weckenmann automation package.

A nine-gate concrete spreader, engineered for transverse or longitudinal movement, is charged by a 3.5-yd. twin-shaft mixer. PCE Elematic supplied the spreader and EA 710 3000 model mixer with companion skip hoist, while Dukane staff retained a local fabricator for aggregate and cement storage and handling components. Here, plant staff prepare to place a self-compacting mix for the interior wythe of a Double-Wall panel. The extremely smooth, uniform finish achievable with the SCC mix goes hand in hand with Dukane's promotion of a paint-ready interior wall — sans drywall — direct from the plant.

Along with the Shuttering Robot, Dukane Precast harbors a lifting and turning device (above) unique to this side of the Atlantic Ocean. Supplied through Spillman by Germany's Vollert GmbH, the unit is equipped with vacuum clamps and especially suited to Double-Wall fabrication. Here, a cured exterior wythe section, with embedded horizontal rebar and vertical truss reinforcement, is lowered onto the form bearing the freshly placed, self-compacting mix. The flipping device hovers above shaking and vibrating equipment earmarked for tables shifted from the mix placement station.