Originally posted Monday, 10 October 2011
Written by Nick Dorman
Buildings alone are responsible for approximately forty percent of carbon emissions in the United States—a statistic widely cited by those advocating for more sustainable buildings. And although forty percent at first seems to be a tremendous portion of carbon emissions, the shock tends to wear off when one considers that we spend the vast majority of our time in buildings and that most of our carbon-emitting activities (driving being the notable exception) occur within buildings. The implications of this statistic, though, become alarming once more in light of a recent forecast estimating that humankind will construct roughly the same volume of buildings within the next generation as that which exists today. “If realized, not only will this volume require the use of massive amounts of material and energy resources, but the conventional strategy of tear-down and rebuild would result in an equally enormous level of waste,” writes Blaine Brownell, Assistant Professor at the University of Minnesota School of Architecture, editor of Transmaterial (now in its third edition), and creator of the blog Transstudio, which covers emergent materials, architecture, and design.
Aside from the embodied energy of buildings, there are significant concerns regarding the supply of many of the most prevalent materials in building construction today. A recent United States Geological Survey study suggests that we will exhaust known stores of several vital metals within the next two to three generations, based on a reasonable estimation of two percent growth in extraction. Stores of lead and tin will be exhausted within the next fifteen years, copper within twenty, and iron and bauxite within sixty and sixty-five years, respectively. While recycling efforts have accelerated, virgin materials are still being harvested at alarming rates. In light of the aforementioned projections for construction during the next generation, it can safely be said that we will need to completely re-engineer our handling of material resources.
All of this means that buildings of the future will not only need to be far more efficient, they will need to do so, in many cases, with very different materials. “It’s one of the greatest challenges that architecture and building construction has ever faced,” says Brownell. Fortunately, the past decade has witnessed an explosion of new materials and technologies for architectural applications, many of which offer novel and unusual properties. Environmental concerns, as well as laboratory-developed advances in high-performance materials, have driven recent transformations in the building products industry. The result is an increasingly complex set of choices. Owners will need to be informed about these new technologies, since many of them promise to alter the practice as well as the experience of building design and construction. As has been the case with LEED, Owners can play a central role in the adoption of these technologies. “In my experience as an architect, Owners are the individuals that architects meet with on an increasingly frequent basis,” says Brownell. “This group has already driven a lot of change in the construction industry with LEED. It used to be that architects would mention LEED to Owners, or anyone else from the client side, and they would say, ‘Hmm, interesting idea. Too expensive. Next.’ That’s all changed, based on the marketing power of LEED and some of the economic incentives based on LEED ratings, etc. So LEED is driven a lot now by this group.”
In the same way, Owners have the opportunity take a lead in adopting many of these new materials and design approaches. The benefits will not be strictly environmental. In many cases, the result is a more dynamic and interesting building, as well as an enhanced experience for those using the building.
The Age of Concrete
Concrete is the second most consumed substance in the world— water being first. The sheer quantity of concrete humanity produces—its pervasiveness in the built environment— makes it a natural starting place for the greening of our building materials. And, indeed, there is a great deal of research into reducing the embodied energy of concrete. Although, pound for pound, concrete’s contribution to carbon emissions isn’t as great as many other materials, because we use so much of it, concrete is responsible for between five and ten percent of CO2 emissions globally. The portion of concrete most responsible for those emissions is Portland cement. “The Portland cement is the real problem,” says Brownell. “It constitutes, depending on the concrete, roughly 12 percent of the mix. But in terms of embodied energy and CO2, it constitutes the majority of that, because the processing of the cement requires so much heat.”
Many of the approaches to developing a greener concrete involve minimizing (or eliminating) Portland cement, whether by offsetting it with things like fly ash—or other materials— or replacing it altogether with other types of cement that don’t require as much heat to produce.
At MIT’s Concrete Sustainability Hub, researchers have made significant headway in developing more environmentally benign concrete, as well as in engineering concrete for specific properties. “Almost every civil engineering department in the world, almost without exception, has a group of people who work on [the development of] concrete in one form or another,” says Hamlin Jennings, executive director of the Concrete Sustainability Hub (CSH). While most research has tinkered with formulations on the macro level, researchers at the CSH have re-engineered concrete on the molecular level, allowing the CSH to produce stronger, more durable, and greener concrete. “We try to understand the materials from a first-principles perspective,” says Jennings—meaning at the atomic level. This had not been achieved previously with concrete, and it will make possible the engineering of concrete for highly specific attributes and purposes, as is currently possible with materials like steel and glass. “The steel you get in a high-quality kitchen knife is a very different steel than is used in a bridge. Those materials are designed from first principles. There’s enough of a molecular understanding—that is, how the molecules and atoms bond together and develop into the engineering properties— that one can sit down in front of a computer and say, ‘I want to improve the landing gear on a plane that’s going to land on an aircraft carrier.’ That’s a highly complex problem. It’s a very corrosive environment, so a very special steel needs to be designed for that purpose.” Until recently, concrete has not been understood with anywhere near this degree of sophistication. “As we begin to finally understand concrete from first principles, the ability to design and use the material with greater efficiency will evolve, as it has with any other material where first principles have been applied.”
MIT’s “proof of concept” must now be taken up by the private sector and regulators, and, optimistically, the first structures to use the new concrete are still five years away from construction, but the implications are clearly considerable.
Recent advances in concrete aside, incremental developments over the decades have resulted in a material with three times the compressive strength of its 1970 counterpart, allowing concrete structures to be thinner, lighter, and far taller. The consummate example of how far concrete has come is Dubai’s Burj Khalifa, now the tallest building in the world. At more than half a mile high (twice the height of the Empire State Building), its structural frame is reinforced concrete. “From a technological standpoint, it’s profoundly impressive that a reinforced concrete frame has outperformed the steel of Taipei 101—the previous record holder for height—by 1,050 feet,” say Brownell. “This achievement suggests a new era in structural engineering.”
In fact, the strength of the concrete itself often isn’t the deciding factor in, for instance, the size of a column. “When you design a concrete column, it is much more about the reinforcing than it is about the volume of concrete,” says Larry Speck, principal in the architectural firm of PageSoutherlandPage and a professor, as well as the former dean, in the School of Architecture at the University of Texas at Austin. “For instance, you have to sheath all reinforcing with about three inches of concrete, or you jeopardize the security of the reinforcing. Water will penetrate to it, it will rust, etc. You’re actually deciding the size of that column not because of the strength of the concrete, but because the concrete is acting as protection for the reinforcement.”
One technology that would go a long way in addressing this limitation and allowing for thinner, lighter, and more corrosion-resistant concrete structures has been developed by AtlusGroup, a national organization comprised of 13 precast companies, and Chromarat, a producer of carbon fiber grids. Their solution to the problem of corrosion in precast concrete is surprisingly simple: replace the steel rebar with a carbon fiber grid. Steel is a corrodible material, and locking it into wet concrete that takes a very long time to cure (that, in fact, never completely cures) predisposes it to corrosion. The carbon fiber grid is lighter and thinner than steel, and since it is not corrodible, less concrete is needed to cover it. This new precast concrete is already in use in architectural and insulated sandwich wall panels. “From an engineering standpoint, a structural standpoint,” says Brownell, “the fact that you can use less material makes it part of the trajectory of doing more with less, which has an environmental aspect to it, as well as a trend of hybridization—of using different types of materials to make a sum that’s greater than the parts.”
The trajectory of doing more with less also includes materials that do double duty—that allow the Owner to get more from them than their primary functions in the structure. Concrete, being a mixture, is an ideal candidate for such applications. Titanium oxide, added to the concrete mixture (or applied after the fact), reacts catalytically in the presence of sunlight and oxygen to convert nitrogen oxides into harmless nitrate, which is then washed away by rain. Nitrogen oxides are among the pollutants emitted by fossil-fuel-powered vehicles, and in the form of nitrogen dioxide are a major constituent of acid rain, as well contributing to the formation of ozone and smog. A number of respiratory and other diseases are also associated with high levels of nitrogen oxide. With testing revealing as much as a forty percent local decrease in nitrogen oxides where the air-purifying concrete has been used, the benefit to end-users is clear.
Titanium oxide also breaks down dirt, algae, and fungus, making it a self-cleaning material, which presents yet another benefit for end-users. This feature of titanium oxide has been utilized for centuries and can be seen in the impeccably white walls of many traditional Japanese castles, where it was a component of the plaster mixture. Its benefits can also be reaped in interior applications (as long as there is sufficient ultraviolet light), where it not only purifies air but also deodorizes it.
For all of these reasons, titanium dioxide has emerged as an extremely promising material from the perspectives of air quality and pollution reduction. It can be added not only to concrete, but also to open asphalt, glass, ceramic tiles, and paint, meaning that it can be applied after the fact to any number of materials, from metals to plastics. A ceramic tile utilizing a substance called OFFNOx and developed by the Institute of Chemical Technology in Valencia, Spain, is currently being tested in London in preparation for the 2012 Olympic Games, in hopes of avoiding a ban on cars in central London, which may otherwise be necessary due to air pollution. And the Japanese Suzuran Corporation has developed an environmentally remediating paint, called Reben, containing titanium dioxide and scallop-shell powder, which prevents mold and bacteria growth, as well as flame-spread.
Concrete’s role in carbon emissions is also being addressed through additives that allow it to absorb CO2 as it cures. Several additives are being researched and tested, and one product already on the market uses magnesium oxide. Because the cement must be semiporous to facilitate CO2 absorption, it’s not the highest-strength concrete available, but low-strength concrete is sufficient for a majority of projects. Since concrete never fully cures, these products would continue to absorb CO2 throughout their lifetimes, though, of course, that absorption capacity would taper off over time to a negligible level.
Building Integrated Photovoltaics
It is not only the materials of the future that will be expected to do double duty, though. Buildings themselves will increasingly be utilized for energy harvesting. Building Integrated Photovoltaics (BIPV) is one of the imminent developments in building construction and is, in fact, gaining traction already. A recent industry analysis predicts that BIPV products will surpass $11 billion in 2016, up from $2 billion this year. Installed capacity is expected to increase 10-fold during that same period, growing from 343 MW in 2011 to more than 3.6 GW in 2016. From windows to curtain walls to walkable pavements to roof shingles, photovoltaics products are being developed that enable far greater generation potential than roof-mounted arrays, with their obvious surface-area limitations.
Photovoltaic windows typically use two panes of clear or tinted glazing with the PV modules adhered to the front of the window’s inside pane (i.e., the third surface). PV glazing is semi-transparent, and in most cases the individual PV modules are discernible, but transparency and uniformity are improving, and glazings of the future may appear only as a slight tint. One benefit of PV glazings is that they can be integrated into daylighting strategies, offering two functions in one material. In those cases in which glass would be tinted or patterned to reduce glare or heat gain, or with any non-view glass, PV glazings may be an ideal solution.
A larger-scale integration of photovoltaics may come in the form of a curtain wall or rainscreen, which allows the entire exterior of the building to be utilized in energy harvesting. “For all kinds of durability issues, a rain screen is a very sophisticated, very good, building skin,” says Speck. “And the cool thing is that you’re actually saving some money in the skin of the building and applying it to the purchase of photovoltaics— you’re getting a twofer. It’s producing energy, and it’s fulfilling a building function.”
Integrating photovoltaics into a building’s design ideally occurs during the initial design stages, but existing structures can also be retrofitted with BIPV technologies. Window shades or awnings may be added, architectural textiles with integrated thin-film PV modules can be incorporated into the building’s design, and in some cases windows themselves may even be replaced with PV glass. Other options include photovoltaic leaves, especially a new product called Solar Ivy. Designed to mimic the natural growth of ivy on buildings and in nature, it consists of a layer of thin-film material on top of polyethylene leaves with a piezoelectric generator attached to each leaf. When the sun shines on the leaves or the wind blows them, energy is generated. Solar Ivy can easily be integrated into existing structures and may be scaled to any size desired.
The possibilities of BIPV are not limited to new buildings, nor are they limited to buildings per se. Walkable photovoltaic pavers will allow the ground itself to be part of a facility’s energy harvesting profile. While the tiles are not suitable for vehicular traffic, they are designed for human traffic and furniture, meaning that they can be integrated into a wide variety of environments without sacrificing design or aesthetics. While the tiles (developed by Onyx and Butech) will not be released to market until the end of the year, technologies for photovoltaic curtain walls, rainscreens, windows, and many other materials are already in use around the world. “There’s research into just about any type of exterior material and how it can be combined with photovoltaics,” says Brownell. “What we’ll increasingly see, I predict, is photovoltaics integrated in a better way. Right now, you typically see these recognizable strips of black silicon that are added on top of things like windows and fabrics. Increasingly, these materials will take on different colors and will be woven, or stitched, or applied in ways that are more homogeneous.”
Though not a photovoltaic system, another promising technology that harvests daylight for use in buildings is known as active daylighting. It uses roof-mounted solar collectors and fiber optic cables to deliver light deep into building interiors. It is active (as opposed, for instance, to passive tubular skylights) because the collectors track the sun as it moves across the sky. That tracking capability and the concentrating power of the collectors, which use an array of lenses to focus the light and direct it into the fiber optic cables, enable active daylighting to deliver tremendous amounts of daylight to areas of buildings where daylight has been previously unavailable, even through the use of tubular skylights.
The fiber optic cables can be run through interior wall cavities, ceiling plenums, or wiring chases, and their bending radius can be as tight as two inches. Once the light reaches its destination, a variety of fixtures can be used to disperse the light, including spotlights, conventional-looking panel arrays, and hybrid systems that incorporate high-efficiency fluorescent lighting. Prices for these systems are still quite high but should come down with scaling and as they are adopted more widely. If they do, it will be a very appealing lighting strategy for many applications.
Another imminently practical building element is the green roof, or living roof. Essentially, a green roof is one that covers the impervious roof surface with a layer of soil in which vegetation is grown. While green roofs can be pitched, they are most often flat. For a relatively low-tech and low-cost measure, they offer a tremendous range of benefits, which is probably why they have been used in the traditional building of many cultures for centuries. They provide insulation, reduce the heat island effect, absorb CO2, improve local air quality, and mitigate storm water runoff—an increasingly significant threat to natural water supplies as impervious infrastructure continues to proliferate. “Increasingly, municipalities are charging more money for storm water runoff, and so buildings will have to deal with it on site,” says Brownell.
Green roofs also offer aesthetic benefits that many of the high-tech solutions discussed here simply don’t, allowing for better integration of buildings into their landscapes and offering an attractive method of hiding mechanical systems that are often located visibly on a building’s roof. Green roofs are gaining traction in building construction, largely because they have achieved significant value in LEED scoring systems. They are a very low-tech solution to concerns about carbon emissions and embodied energy. While additives to concrete can allow it to absorb CO2 as it cures, that absorption drops off precipitously after a certain point. A green roof, on the other hand, will continue to absorb CO2 for its entire life, in many cases to an increasing degree as its flora matures.
Green roofs are broadly categorized as either extensive or intensive. Extensive roof systems carry two to six inches of soil and are generally planted with moss, sedum, or grasses. They are designed to be self-sustaining, requiring no irrigation, and are the only roof system that can be used for a pitched roof. Intensive roofs carry six to sixty inches of soil and can handle a wide variety of plants, including trees, which may necessitate irrigation and maintenance. Their insulating properties are substantial, though they are suited only to flat roofs.
Several high-profile buildings completed in recent years have included a living roof, perhaps most notably the California Academy of the Sciences, in San Francisco’s Golden Gate Park. Its undulating, grass-covered surface integrates the building perfectly into the surrounding hills of the Bay Area.
A Look Ahead
There are literally thousands of materials in various stages of research, development, and commercial availability, the applications of many of which are not yet entirely clear. The construction industry, historically, has been fairly risk-averse and, therefore, slow to change. That, combined with the tremendous quantities of a given material necessary for application in the built environment, means that many of the building materials of the future will make their first appearances in, for instance, consumer electronics or healthcare technologies. Still, certain materials seem destined for construction applications, and it is worth taking a look ahead at what may be coming.
One such category is self-repairing materials. From concrete to metals, self-repairing materials are being developed that could dramatically reduce maintenance costs and increase the lifespans of buildings. Since they last longer, they also reduce the embodied energy of buildings by reducing the quantity of a given material that needs to be produced. They even have the potential to save lives by keeping structures safer. Developments in nanotechnology have made these materials possible, allowing nanospheres containing bonding chemicals (or chemicals that react with components already present in the material to form a bonding agent) to be incorporated into a building product. When damage occurs, those spheres break, releasing their contents into the damaged area and repairing it. In the case of concrete, these nanospheres can be incorporated directly into the mixture. With metals, they have are so far only been used in the galvanizing layer, meaning that the repairs they are capable of will be more cosmetic than structural for the time being.
Another family of materials made possible through nanotechnological research is that of “glassy metals,” which have properties of both glass and metal. “The benefit is that you can have a material that is ductile and not brittle, but is also transparent, like a glass,” explains Brownell. The “bulk-to-shear” stiffness ratio of these glassy metals allows them to bend rather than crack, and in some cases their fracture toughness exceeds all but the strongest materials known. “Like a lot of materials, early commercial applications will usually start with biomedical technologies or portable electronic devices,” Brownell says. “We’ll see something like this, for example, in an iPhone before we see it in a building window. But still, as we’ve seen with technology, with enough time and development, and brining the cost down, we’ll begin to see things like this in buildings.”
An old material that has recently received a makeover is drywall. Until recently, the production process had not changed since its invention in 1917. Essentially, ground-up gypsum rock was heated in a kiln to 500 degrees, in order to allow it to congeal into a solid panel—in the process emitting about 25 billion pounds of greenhouse gases a year. Thankfully, a new drywall has been developed and is commercially available, including a product called EcoRock, produced by Serious Materials of Sunnyvale, California. It is produced without heat and even using recycled materials that don’t require mining. Fly ash, slag, kiln dust, and fillers—85 percent of which are industrial by-products— react chemically when mixed with water and bind together into a paste that is poured into sheets. This kiln-free process uses just one-fifth the energy of the traditional approach, and without the starch and cellulose that’s mixed into ordinary gypsum board, it is impervious to termites and mold.
The impact of kiln-free production methods on the embodied energy of buildings in the aggregate would be tremendous, given that 85 billion square feet of drywall are produced for the North American market alone each year. And at a cost comparable to high-end traditional drywall, it is likely to become prevalent in the industry in coming years.
It’s hard to know precisely what the materials of the future will be, but it is certain that they will be quite different from the materials of today. The convergence of a number of factors—from natural resource scarcity to legislative mandates—will require that the building construction industry, which has traditionally been slow to change, move swiftly into new paradigms of design and construction. Fortunately, the work has already begun. “It’s not any one product that is amazing to me, but instead the collective aspirations and positive endeavors behind so many new products and materials,” says Brownell. “It seems as if there are many, many people—designers, architects, engineers— struggling to proactively mitigate our circumstances.” The Owner’s role will be to support and encourage the use of these materials as they become available and accessible.