Concrete inspires numerical superlatives when describing its ubiquity: Slightly more than a ton of concrete is produced every year for each human on the planet—over six billion—with Americans responsible for 2.5 tons per citizen. Produced at an estimated rate of five billion cubic yards per year, concrete is the second most widely consumed substance on earth after water. Concrete is the world’s oldest man-made building material. Yet, it’s the material’s dual personality that makes it both ubiquitous and appealing. Since the Industrial Revolution, concrete has been the robust, utilitarian workhorse for constructing bridges, tunnels, aqueducts, sidewalks, roadways, and barriers. Modern concrete is reinforced with steel and other materials, poured-in-place, precast, pre- and post-tensioned, tinted, molded, embossed, polished, and drilled. In its most modest state, it provides a building’s structure, which is then hidden behind a prettier skin. But it can also be a glamorous material, especially when it performs simultaneously as structure, form, and surface.
Earlier this month, Columbia University’s Graduate School of Architecture, Planning, and Preservation hosted a conference called Solid States: Changing Time for Concrete. A series of panel discussions explored the dual personality of the material with some stunning examples of form following innovation. French architect and engineer Marc Mimram presented his study of what he calls “living infrastructure,” a project underwritten by Lafarge, one of the world’s largest producers of cement, concrete, aggregates, and gypsum, and the conference’s sponsor. Mimram’s work focuses on reconciling a city’s infrastructure with the inhabitants. He is currently investigating that uneasy relationship by designing four hypothetical bridges for four cities, using Lafarge’s high-performance, fiber-reinforced Ductal concrete.
Ductal is indeed glamorous, which makes it a high-profile achievement in the realm of concrete innovation. French architect Rudy Ricciotti designed the Footbridge of Peace entirely out of Ductal in 2002. The pedestrian bridge crosses the Han River in Seoul, South Korea, with a 400-foot arch, no middle supports, and a deck only a breathtaking 1 1⁄4-inches thick.
The “world’s first” anything always captures the public’s imagination. Although many exquisite feats of engineering and design were presented at the conference, much attention was given to how much priorities have shifted with regard to building materials and construction. Global environmental imperatives are now at odds with concrete’s numerical superlatives. Not all large numbers are desirable. For example, the production of concrete uses approximately one trillion gallons of water each year—a devastating impact on many societies, especially if water becomes a diminishing resource, as scientific research suggests.
The environmental impact of manufacturing concrete is not lost on the industry. In 2000, the U.S. concrete industry’s Strategic Development Council (SDC) conducted a workshop to discuss the past, present, and future of concrete. A year later it published Vision 2030: A Vision of the U.S. Concrete Industry, a guide to the future presenting ambitious goals. First of all, it establishes the concrete industry’s commitment to sound energy use and environmental protection. Secondly, it commits the industry to improving efficiency and productivity in all concrete manufacturing processes. Research in new materials, processing technologies, delivery mechanisms, and applications of information technology is being developed to ensure that concrete remains the construction material of choice based on life-cycle cost and performance.
Vision 2030 is particularly focused on finding ways to unify a diverse and localized industry, which will have a positive environmental impact. The guide admits that because the industry is fragmented, it has been “slow to investigate new technology options, reluctant to invest in research, and hesitant to adopt new technology as it becomes available.” Risk aversion slows innovation, but there are external obstacles in play as well. For instance, transportation accounts for 20 to 50 percent of the cost of ready-mixed concrete. And yet, many communities have adopted a “not-in-my-backyard” attitude toward heavy industry, so concrete and cement plants and aggregate sources are forced to move farther away from delivery points.
According to the industry, manufacturing operates in a prescriptive rather than performance-based environment. Thus, the full potential of concrete often is unrealized. And yet, as long as concrete procurement favors the lowest bidder, manufacturers will have to keep costs low to be competitive. As a result, they have little incentive to spend money on the research and development of improved performance.
Extenuating circumstances such as these are not always apparent when discussing how all industries must reduce their impact on the environment. While the challenges are great, they are not insurmountable. A year after Vision 2030 was published the Concrete Research and Education Foundation produced Roadmap 2030, an initiative to assist implementation of the SDC’s goals. Roadmap 2030 is frank, detailed, and includes a myriad of alternative constituent materials, delivery systems, and manufacturing processes. It appears that the concrete industry would like to realize its goals in its own way before environmental compliance regulations do it for them, potentially reducing market share. Progress since 2001 is hard to quantify, but the SDC’s Accelerating Implementation Team has several promising initiatives underway, including the long overdue adoption of performance-based specifications.
There’s another way to think about concrete. It has been in existence for thousands of years, because it is so flexible. It has accommodated every era’s technological progress. Its recipe allows for all sorts of material substitutions, including industrial waste. For example, typical production of one ton of Portland cement releases one ton of CO2 into the atmosphere, which accounts for about seven percent of all greenhouse gases. Increasingly, however, cement is being made of waste, such as fly ash (a byproduct of coal burning), slag cement (a byproduct of metal smelting), and silica fume (a byproduct of silicon metal production). Christian Meyer, chair of the Department of Civil Engineering and Engineering Mechanics at Columbia, and one of the organizers of Solid States has been researching how to make all kinds of waste valuable for concrete production—glass, carpet fibers, and even the highly contaminated dreck at the bottom of New York Harbor. The simple theory being, one industry’s detritus is another industry’s valuable resource. Waste—the new renewable resource.
Sara Hart is a writer in New York City who contributes regularly to Architectural Record, Architect, and other publications.
To survey the latest advances in concrete applications, AN presents ten projects that explore its structural and expressive potential. Whether for high-performance uses or elegant finish effects, these works show that the oldest construction material is still the most fluid.
With contributions from Alan G. Brake, Jeff Byles, Matt Chaban, Anne Guiney, Julie V. Iovine, and Aaron Seward.
Villa Navarra / Le Muy, France
Two projects from French architect Rudy Ricciotti are among the first to explore the structural potential of Lafarge’s high-performance Ductal concrete. With its visor-like roof jutting from the Provencal landscape, the Villa Navarra marks a boldly framed villa and gallery space for collector Enrico Navarra. Featuring a stunning, 25-foot cantilever, the roof is composed of 17 fiber-reinforced Ductal panels, each engineered to take into account thermal expansion, wind resistance, and size restrictions due to transportation of the units, which were precast by Montpellier-based Bonna Sabla using metal molds fabricated by an aviation-industry supplier. Each 7.7-foot-wide panel is edged by two lateral inertia ribs, which taper toward the cantilever and are joined together with a resin-injected socket. A silicon joint keeps the upper portion of the ribs waterproof, while perforations along the structure’s edge—which measures just over 1 inch thick at its tip—allow light to penetrate the porch-like gallery below.
Ductal’s compressive strength is taken more dramatically to task in Ricciotti’s Pont du Diable, a footbridge spanning 236 feet across a gorge in the Hérault district of southwestern France. Composed of 15 sections weighing 10.5 tons each (also precast by Bonna Sabla), the sleek structure, completed in August, makes a low impact upon this world heritage site along the route of Saint-Jacques de Compostelle. JB
Ultra-High Performance Concrete Pi-Girder Bridge
In building infrastructure, and especially bridges, the Federal Highway Administration does not choose a preferred material; it makes choices based on site-specific performance issues such as safety, construction speed and ease, and rate of deterioration. The new ultra-high performance concrete (UHPC)—in the U.S., Lafarge’s Ductal is the only one currently available, although Densit in Denmark and Bouyges in France have also developed UHPCs—makes the most sense for locations where weather conditions are subject to random freezes and sudden thaws. In late October, a UHPC was used for the first time in the U.S. for a bridge in Buchanan County, Iowa. The Aurora bridge differs from conventional concrete usage in that both beams and deck were fabricated off-site. Once cast, the bridge was assembled on-site in less than a week. “The advanced concretes are inherently more durable, quicker, and safer to use,” said Benjamin Graybeal, a research engineer for the Federal Highway Administration (FHA). Additionally, UHPC lends itself to a new girder shape developed by the FHA in collaboration with MIT, known as the Pi-Girder, where pier and deck plate are of a single piece, an added efficiency. “It’s a shape that optimizes the properties of this particular concrete and its abilities to address structural demands,” said Graybeal, noting that Ductal is still too expensive to be considered for widespread FHA use. JVI
As part of a new wellness center for the 100-year-old College of New Rochelle, Princeton-based Ikon.5 Architects used concrete to create a modern-day grotto, sandblasting the material in order to emphasize the rough texture of its aggregate content. A double shell vault spans 80 feet without structural interruption, with the exterior casing operating as both waterproof barrier and green roof container. Mechanical ductwork, fire suppression material, and lighting are contained within the poche, allowing the grotto space to maintain its raw simplicity. The concrete mix contains recyclable blast furnace slag, reducing the admixture of less sustainable Portland cement by 50 percent. There was a challenge when it came time for the concrete pour. Due to the natatorium’s irregular elliptical curve it was difficult to make a concrete without air pockets at the bottom. “Based on a site mock-up, the problem was solved,” said Joe Tattoni of Ikon.5, “by widening the back of the form—which was invisible—to a shape somewhat like an elephant’s foot, it allowed for a more generous flow. And that worked perfectly.” JVI
One Madison Park
For its first highrise condominium in Manhattan, the Office of Metropolitan Architecture put high-strength reinforced concrete to the test with a 30-foot cantilever graduated in steps extending over ten stories. The structural system, according to project architect Jason Long and developed with WSP Cantor Seinuk, is a shear tube or “3-D reinforced box system with concrete column sections like Vierendeel trusses” that thicken depending on the changing load (from a thickness of 4 feet 8 inches to 10 inches at the top). Rem Koolhaas described it as a “structural corset” squeezing the building’s midsection, from the 6th floor, where forces are transferred to the sidewalls, to the 15th floor at the maximum point of the cantilever. Openings in the sheer tube expand and contract the maximum amount allowed in relation to stresses, forming apertures for windows. The use of a structural tube system also meant column-free interiors, always a plus in residential work. While the architects wanted the condo to possess a certain urban toughness and hoped to reveal the structural concrete on the facade, the client balked (“If we were in Portugal the quality of concrete work might have made it possible,” said Long). Now the facade is to be finished in fiber reinforced concrete held in place with a polished stainless steel grid. JVI
Courtesy Reiser + Umemoto
With its concrete structure pulled to the exterior as a latticelike shell, Reiser + Umemoto’s 22-story Dubai office tower dispenses with conventional interior columns and walls. While freeing the core from the burden of lateral forces, the efficient, load-bearing shell also offers an appealing shading solution for exposed glass towers in the region’s blazing sun. Working with New York structural engineer Ysrael Seinuk, the architects modulated the tower’s circular openings to manage both structural requirements and sun exposure, cutting down on direct light while still permitting strategically placed views. A one-meter-deep cavity between the shell and building enclosure also creates a chimney effect, drawing hot air away from the building and cooling the tower’s inner glass surface. The perforated shell is created by pouring super-liquid concrete around a mesh of woven steel reinforcement, resulting in a structure that is roughly 60 percent solid and 40 percent void. The 1,326 apertures in the shell are achieved by introducing computer-numerically-cut polystyrene void forms into the rebar matrix, then siding the voids with modular steel slip forms prior to the concrete pour. The shell’s thickness tapers from 1.9 feet at the tower’s base to 1.3 feet at the parapet, offering a ruggedly refined addition to the Dubai skyline. JB
Courtesy Steven Holl Architects
The 1.3-million-square-foot mixed-use office, hotel, and condominium is depicted by its architect Steven Holl as a recumbent Empire State Building. Supported on eight legs, this floating skyscraper is unusual in that it takes a concrete structural frame and transforms it into a suspension bridge-type structure with elevator and mechanical shafts serving as piers. Now under construction and due to be completed in late 2009, the building hovers on 50-meter spans from core to core. Steel cables in stiffening tubes support the bottom deck suspended above a tropical garden, with a high-strength composite concrete structure rising five stories above. The bamboo formwork used on parts of the exterior adds a modest decorative effect. Before construction began, a full-scale mock-up was created and subjected to maximum simulated shaking to make sure this novel concrete megastructure would be tsunami-proof. JVI
Courtesy Allied Works Architecture
Clyfford Still Museum
Brad Cloepfil, like so many notable architects before him—Le Corbusier, the Smithsons, Tadao Ando—has been fascinated by the limitless possibilities of working in concrete. “I always think about concrete as witchcraft,” he said. “No one knows everything you can do with it.” Starting with his earliest work, the Maryhill Overlook on the Columbia River Gorge, the Portland architect has always pushed the boundaries of concrete. Now, with Allied Works’ designs for the Clyfford Still Museum in Denver, he is attempting to render it as the very earth from which it came. To evoke the prairies from which the museum rises, Cloepfil is developing a unique pouring process that will create geological bands of concrete within the walls. “The feeling is that it’s almost carved out of the earth,” he said. Using a monolithic pour, the design team has been experimenting with varying the types of aggregate, dryness of the mix, and time between pours so that each pouring, which takes place in 12- to 36-inch bands, takes on its own character. Cloepfil said he has never encountered such an application before, and he thinks he knows why—it is incredibly challenging to get right. After 30 4-foot-by-8-foot mock-ups, he’s still experimenting. “It’s like a choreography,” he said. “We’re doing a dance, and it’s got to be perfect, but that takes an unbelievable amount of work.” MC
Courtesy Toshiko Mori Architect
Darwin Martin Visitor Center
In the otherwise all-glass Darwin Martin Visitor Center, the designers at Toshiko Mori Architect inserted a solid concrete wall at the back of the space to conceal bathrooms, kitchens, and other non-public spaces. Rather than settle for a blank screen, they wanted the wall to respond to the Frank Lloyd Wright house which the facility serves, and so introduced horizontal banding across the surface to match the Roman brick and recessed mortar joints of Wright’s work. Achieving a materiality that the designers were satisfied with turned out to be more work than they expected. They experimented with nine different mixes of architectural concrete and conducted numerous studies to realize a smooth finish. The mix they wound up using employs a superplasticizer, which increases the material’s fluidity by softening the mix before it hardens and reducing the amount of water needed, thus increasing compressive strength. The method of installation also required extensive testing, as avoiding bubbles in the surface was made more difficult by the horizontal bands. In the end, the contractor injected the concrete into the base of the custom-made forms, filling them from the bottom to the top, and used an internal vibrating machine to shake out excess air. AS
Rien Van Rijthoven
Congregation Beth Sholom Synagogue
The ark-like form which is the distinguishing feature of Congregation Beth Sholom’s new synagogue in San Francisco presents a perfectly smooth and solid face to the street that belies the difficulty in creating a 24-foot-high, 24-inch-thick concrete double shell. According to Neil Kaye, project manager at Stanley Saitowitz | Natoma Architects, to achieve the incredibly fine finish that they wanted for both interior and exterior of the volume which holds the sanctuary, they built several full-scale mock-ups and tested everything from the form release to the way the sealant affected the concrete’s color. “It was a very plastic mix because we had to keep a certain level of liquidity during the lift in order to get fine cold joints,” said Kaye. The outer shell went up first in three separate lifts, and then the rebar was laid in; the inner shell came last. On the interior, Saitowitz made use of concrete’s plastic qualities and incorporated the acoustic baffles into the walls themselves. The acoustician, Charles Salter, had determined that a 15 degree offset would be optimal for the space, and so when the formwork for the inner shell was going in, they inserted pre-fab fiberglass liners. The resulting panel-like forms incorporated into the sanctuary’s walls serve a second and valuable function of decoration, as they shape sunlight as well as sound. AG
Steve Hall/Hedrich Blessing
SOS Children’s Village Lavezzorio Community Center
With material costs rising and a fixed budget of $3.5 million, the architects at Studio Gang had to rethink their design for this community center, stripping away the planned brick screen. That left the double-cantilevered concrete structure exposed. “We thought, ‘let’s investigate the fluidity of concrete,’” said managing architect Mark Schendel. To express this structurally, the architects used three different strengths of concrete in alternating bands for the 12-inch-thick walls. They used chemically stiffened concretes with very low slump, or viscosity, so that even after vibration, the bands kept their wavy appearance. Each of the seven bands was a separate pour, or lift, and each is reinforced according to the strength of the concrete (if the wall had been constructed conventionally, it would have been poured in two lifts). Working with general contractor Bovis Lend Lease and engineer Thornton Tomasetti, the architects choreographed the elaborate sequence of pours to keep costs low. “Bovis was working on Trump Tower at the time, so whenever they had a truck with the strength of concrete we were looking for, they would pull it out of the line and send it to our project,” he said. That allowed them to leverage the economy of scale from the massive skyscraper project. In addition, the architects economically tested their ideas by using the elevator core as a mockup. AGB