Could a sustainable building be built without concrete? Sure—but it’s easier with concrete. The durability alone that is one of concrete’s inherent qualities provides an advantage in creating a sustainable structure.

In a recent article in Residential Architect, LEED for Homes Chair Steven Winter, FAIA, wrote “virtually every green home standard we have encountered places far greater emphasis on durable construction techniques that are later hidden from view than on flashy finish products.”

But concrete’s greatest attributes — its durability and recyclability — yield fewer points under LEED than they might. A University of Minnesota study comparing LEED and Green Globes noted that “LEED does not refer explicitly to life cycle assessment (LCA), although collectively the LEED rating criteria cover practically the entire life cycle of buildings…what is lacking are insights over possible trade-offs between life cycle stages.” Green Globes, on the other hand, “collectively embrace(s) the major components of a building product system’s life cycle…(and) features a distinct rating criterion referring to LCA and covering the entire life cycle of building materials.” (This study is available at www.thegbi.org/gbi/Green_Building_Rating_UofM.pdf.)

Without consideration of LCA, especially when looking at the entire life of a project, concrete appears to be at a disadvantage, since it has a relatively high initial embodied energy and environmental impact through the manufacture of cement and the mining of aggregate. With concrete, you are investing up front, but reaping the payout over the entire lifetime of the structure. Insulated concrete wall systems dramatically reduce air leakage and its thermal mass moderates peak cooling and heating loads, helping to conserve energy and minimizing the lifetime energy cost. And not to consider concrete’s recyclability at the end of a structure’s life also underestimates its sustainable contribution.

On the LEED side, a working group has submitted a report to the USGBC board on how to incorporate LCA, which it has endorsed. Ultimately, the approach will most likely be to treat LCA like energy and require a whole-building analysis, although that will take some additional time. Some form of LCA, though, is likely to be a part of LEED 3.0 and options on how to proceed will presented at Greenbuild in fall 2007.

But even without consideration of its durability, concrete makes important contributions to points under LEED, and Green Globes, in several ways:

• Stormwater management (see “Concrete Pavement without the Runoff,” page s12)
• Minimizing and optimizing energy use
  Reducing construction wastes
• Utilizing recycled content in both the concrete and reinforcing steel
• Use of regionally produced materials
  Improving indoor air quality (see “Concrete in Disguise,” page s14)

Minimizing and Optimizing Energy Use

Reducing Construction Wastes

Concrete construction, performed using modern construction equipment—such as modular forms and bracing—generates very little waste. There is always, however, some excess concrete from clearing pump hoses, excess delivered concrete, or out-of-spec concrete. This waste concrete can be crushed and used as fill.

Recycled Content

LEED credit MR-C4 and Green Globes credit E.2.2 encourage the use of recycled material in a building’s construction. Using fly ash or slag as a replacement for portland cement, however, is not enough to reach the required amount. “In a recent example,” says PCA Director of Sustainable Development, David Shepherd, “I found that a fairly high 50 percent replacement of portland cement with fly ash resulted in a recycled content value of 0.85 percent for the total project. This is an 8.5 percent contribution to achieving one credit, but people shouldn’t think they’re going to get a full credit from just using supplementary cementitious materials such as fly ash.”

Significant use of concrete in a structure should easily qualify a project for the two points awarded by LEED for having 20 percent of the building’s materials originate regionally. While there are exceptions, typically all aggregate is regional, and there are very few instances when ready-mixed concrete would be transported more than 500 miles—it would be cost prohibitive to ship it that far even if one wanted to. While it is true that portland cement is a worldwide commodity, the best prices are typically on portland cement that is manufactured within 500 miles. In most of the United States, without too much difficulty, regionally manfuactured cement can be found.

Sidebar: Concrete Efficiency in Colorado

The CH2M Hill corporate headquarters in Englewood, Colo., achieves two separate building objectives that are not always compatible: Efficient, cost-effective construction and optimal energy performance. When engineering firm CH2M Hill set out to build a new three-building campus that reflected its conservationist tradition, it chose precast concrete wall systems to speed installation, limit construction budgets, and create an energy-efficient thermal envelope for each structure.

The use of precast also allowed CH2M Hill to leverage some additional benefits of concrete construction, including the use of recycled content and locally sourced materials. As a result of the campus’ clever design and the integration of concrete with other ecologically safe building applications, the CH2M Hill headquarters received LEED certification in 2004.

Precast wall panels, such as those used by CH2M Hill, arrive at the construction site fully formed, therefore, no concrete is poured onsite, limiting construction time, and significantly minimizing waste. “In Denver, precast is used extensively for two reasons: cost and schedule,” says Paul Todd, formerly of Barber Architecture, the design firm that conceived and executed the design.

In addition to avoiding construction delays, cost overruns and construction waste relative to other building systems, the precast concrete wall systems at CH2M Hill’s headquarters provide the same superior energy performance as other insulated concrete structures: high thermal mass and low infiltration. And like all concrete wall systems, the precast walls at CH2M Hill are durable and will help extend the life of the building, requiring little maintenance.

The precast wall system used a concrete mix that incorporates fly ash, a recovered byproduct of coal burning power plants.