To market the design for his Dymaxion prototype, Buckminster Fuller famously asked: “How much does your house weigh?” Composed of a lightweight sheet metal aluminum skin held in tension by a single, central mast, the Dymaxion weighed only about 1.5 tons—about 10 percent the weight of an average house.
Fuller's emphasis on weight is even more critical today, given the ever-increasing environmental impact of shipping raw and processed materials around the planet. The automotive and aerospace industries have made significant advances in the strategy known as "lightweighting" by employing new and lighter materials and reducing the weight of components. Such an approach enabled U.S. airlines to significantly increase fuel efficiency by 125 percent between 1978 and 2017.
Carbon fiber is increasingly employed in the fabrication of many ultralight structures, from Formula One car bodies to bicycle components. Made from carbon filaments that are typically woven together into a cloth, carbon fiber is often coated with resin or thermoplastics to create composites with a very high strength-to-weight ratio. The result is a material about five times stronger and five times lighter than steel—and twice as stiff—that can readily tolerate heat and corrosion, making it ideal for extreme environments.
Despite the relatively high cost of carbon fiber, architects and engineers have started using it to construct buildings and infrastructural projects. For example, researchers at the University of Stuttgart’s Institute for Computational Design and Construction (ICD) and the Institute for Building Structures and Structural Design (ITKE) utilized carbon fiber as a prominent construction material in their latest work: the 2019 BUGA Fiber Pavilion at Bundesgartenschau Heilbronn in Germany, a dome made of glass- and carbon-fiber ribs clad in a transparent ETFE membrane. The team programmed a robot to deliver more than 492,000 feet of fibrous filaments in a spatial arrangement whereby fiber type and density could be varied based on structural loads. Designed to mimic biological systems, the carbon fibers surround the transparent glass fibers to form bundled structure members resembling flexed muscle tissues. According to the team, a single fibrous component can support “around 25 tons or the weight of more than 15 cars.” The dome, which has a free span of around 75 feet and shelters a floor area of 4,305 square feet, is composed of 60 of these components, each of which weighs only 16.8 pounds per square meter.
Although the ICD/ITKE work assumes the form of bespoke demonstrations, another research team has been deploying carbon fiber broadly in public infrastructure. The University of Maine’s Advanced Structures and Composites Center has developed a composite arch bridge system made of carbon fiber–reinforced concrete. Designed for single-span bridges up to 65 feet, the system consists of a series of carbon fiber reinforced polymer (CFRP) tubes that are filled with concrete on-site and then topped with steel-reinforced concrete decking. Similar to inflatable rafts, the CFRP tubes are transported to the site in a compact, folded state—hence the nickname “Bridge-in-a-Backpack.” According to the center’s website, “The arches are easily transportable, rapidly deployable, and do not require the heavy equipment or large crews needed to handle the weight of traditional construction materials.” In addition to their lightness, the CFRP tubes serve as the concrete formwork, thus eliminating the need for additional materials. They also function as noncorrosive concrete reinforcing, a clear advantage over rust-prone steel. Based on these many benefits, the system has been used to build 23 bridges to date.
These examples demonstrate how lightness—among other material attributes—gives carbon fiber an advantage in construction. But how does this lightness perform when a project also calls for enhanced sustainability?
In a December 2019 Industry Week article, Ray Boeman, director of the Scale-Up Research Facility at the Institute for Advanced Composites Manufacturing Innovation in Knoxville, Tenn., explains, “Carbon fiber has the best potential for lightweighting, but takes a lot of energy.” According to a study conducted by the U.S. Department of Energy and Lawrence Berkeley National Laboratory, a typical CFRP composite requires 800 megajoules per kilogram (MJ/kg) of primary energy, on average, with the current typical energy intensity in U.S. production of 1,134 MJ/kg. By comparison, steel requires 50 MJ/kg, resulting in respective savings ratios of 1:16 and 1:22.
Furthermore, for every ton of carbon fiber produced, 20 tons of carbon dioxide are emitted. Carbon fiber is also closely tied to fossil fuels, as the most common feedstock is polyacrylonitrile, a precursor material produced by the petrochemical industry. The chemically activated resins or polymers typically used to make CFRP are also petroleum-derived. The 2017 article in The Guardian entitled “Carbon Fiber: the Wonder Material with a Dirty Secret” reveals the production impacts as well as recycling difficulties of carbon fiber.
For specific applications, however, carbon fiber shines in the trade-off between operational and embodied footprint. According to the Japanese manufacturer Toray Industries, the material can lead to significant reductions in the energy requirements of transportation: “When the body structure of a car is made 30 percent lighter using carbon fiber, 50 tons of carbon dioxide will be reduced per 1 ton of carbon fiber over a life cycle of 10 years; when the fuselage structure of aircraft is made 20 percent lighter using carbon fiber, on the other hand, 1,400 tons of carbon dioxide will be reduced under the same condition.”
So does the material make environmental sense for immobile buildings? Material weight and volume reductions can deliver positive impacts in most stages of a building’s life cycle because less fuel and heavy machinery are required for transportation, installation, and eventual disassembly. The operational case for carbon fiber is a more difficult argument to make for buildings regarding energy savings, however—although the material’s resistance to excessive heat and environmental degradation can extend building life spans and reduce maintenance.
To make an informed decision about whether to use carbon fiber in architecture, a design team must conduct a comprehensive assessment of the embodied and operational impacts over the anticipated lifetime of a building. Another critical consideration that I don't detail here is, of course, cost.
Environmentally speaking, the material’s performance should improve with the increased use of bio-based feedstocks, more efficient manufacturing processes, and growing recycling rates. As carbon fiber continues to become more ecologically advantageous, Fuller’s dream of replacing ponderous buildings with ultralight architecture may move closer to reality.
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website twice a month. His views and conclusions are not necessarily those of ARCHITECT magazine nor of The American Institute of Architects.
