Jameson Simpson

In early 2010, the New York City chapter of the American Institute of Architects put out an open call for submissions for an upcoming exhibition showcasing innovative curtainwall design. When architect Peter Arbour, Assoc. AIA, heard about the request, he began brainstorming an idea for a new type of building enclosure that would combine durability with design flexibility. Arbour put together a group of architects, engineers, and façade developers at Paris-based RFR Consulting Engineers, where he was a project manager at the time, and they began working together to determine the ideal material for such an application. The solution they settled on was ultra-high-performance concrete.

The team believed that the material had several desirable features, Arbour explains. It is fluid and lightweight, and can be used to create a high-performance unitized building envelope that integrates various building systems while eliminating the need for aluminum extrusions and minimizing the need for metal extrusions.

The longevity of the material translates into extremely low life-cycle costs and provides ecological benefits derived from not having to replace or repair the material as frequently as typical curtainwall elements. Testing has shown that ultra-high-performance concrete has the capacity to last up to 1,000 years—exponentially longer than the typical 50- to 80-year life cycle of normal concrete. It is also extremely strong. Ductal, the ultra-high-performance concrete from Lafarge North America, whose Ductal division is based in Calgary, Alberta, Canada, has a denser and less porous matrix than conventional concrete and has been tested at 30,000 psi in compression strength. In comparison, the strength for concrete typically used for sidewalks clocks in at about 5,000 psi. Ductal’s “compressive strength and flexural strength allow us to create longer spans, thinner profiles and curvatures,” says Kelly Henry, architectural project manager at Lafarge North America. “You don’t have to use as much rebar or passive reinforcing, if any.” With Ductal, architects and designers are able to create a very thin and lightweight curtainwall system.

From a design perspective, unlike the rigid lines characteristic of metal and glass exterior walls, the fluidity of concrete lends itself to curving or undulating patterns and intricate detailing. “This system represents more of a design-driven technology,” says Arbour, who is now based in New York and works for Seele, a façade contractor headquartered in Gersthofen, Germany, that specializes in complex geometric façades and glass structures. “It’s a three-dimensional visual opportunity. With emerging computer design technology, that’s something architects want. … Using technologies on the market, it’s an enormous struggle to find out how to achieve what architects are trying to do [using typical curtainwall materials].” Arbour and his team dubbed their concept the Liquid Wall. In order to develop a prototype for AIA New York’s exhibition, the team enlisted the help of Lafarge North America, who supplied the Ductal material for the project; Ontario, Canada–based Coreslab Structures, manufacturers of precast concrete, whose Connecticut office helped built molds for the system and did the casting; and the Digital Fabrication Laboratory of the Georgia Institute of Technology, who milled the positive forms for building the molds.

“Getting to work with Peter [Arbour] was a great opportunity for us to gain exposure into the architectural market and show off Ductal in a highly architectural product,” Henry says. Despite the benefits of ultra-high-performance concrete, there were a few stumbling blocks in developing the Liquid Wall prototype. With no building codes in place for the material, as there are with typical façade materials such as aluminum and steel, developing the structural model proved to be a challenge. “It required primary research and analysis in ways that hadn’t been done before,” Arbour says.

The team used the 3D digital models to build full-scale positive polystyrene forms, which were then used to case flexible rubber molds. From these, the team created the concrete components of the Liquid Wall by first casting the front half of what would become the wall’s frame. This component was pierced through with 3/16 inch-diameter, 3-inch-long glass-fiber pins set into the concrete, while a back half was cast in a second mold and set on top of the first half’s pins. Placed together, with a thermal break in between, the pieces resist shear stress. “As wind hits the panel as a vertical force, the front and back pieces want to slide up and down, so the pins keep the two elements from moving relative to each other,” Arbour explains.

Stainless steel anchors, infill panels, and triple-glazed vision panels—which deliver high thermal performance while allowing ample natural light to penetrate the building—were then installed directly into the frame.

A key aspect of the Liquid Wall is the passive solar panel, a metal cassette in the spandrel area that contains flowing liquid, a nonfreezing mixture of glycol and water. As the liquid absorbs solar energy, it travels back into the building and is used for everything from domestic hot-water heating to underfloor radiant heat to dehumidification of forced air. “In the prototype we designed a radiator within the façade on the back face on the façade panel, so you get this kind of baseboard heater that’s built into the panel that uses solar-heated water,” Arbour says. Using solar energy within the façade system helps the building’s mechanical systems work more efficiently and greatly reduces the overall energy load of the building.

In addition, the elements within the concrete framework can be replaced over time as technologies develop and improve, without the need to dismantle or raze the building, as the elements are held in with a metal angle. The angle can be unscrewed to remove and replace the parts. As a whole, the system is meant to be 100 percent recyclable. The Liquid Wall won AIA New York’s competition and went on display at the Center for Architecture in New York from October 2010 to January 2011 as part of the exhibition “Innovate: Integrate,” and it also was shown in May at the AIA’s national convention in New Orleans. While the prototype was dismantled after the exhibitions, Arbour retains the patent for the system and he anticipates physical testing and digital modeling of the wall to continue over the next several months. He hopes to bring it to market and make it available to architects in about a year. “It’s a good fit for the problems architects are facing now,” Arbour says. “It’s an industry coping with an increase in sustainable demands.”

Heidi Moore writes about architecture and design from Chicago.