Life Cycle
Assessment
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How Does Concrete Fit In the Big Picture?
by Jennifer G. Prokopy
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| Deaf Northwest’s Chestnut Lane is an assisted
living facility located in suburban Portland, Ore., built mostly with
concrete. Notable features include Arxx insulating concrete form walls
concrete mixes with fly ash, pervious concrete pavement, and an impervious/
waterproof concrete green roof. Photo courtesy of Glacier North
West. |
Life cycle assessment (LCA) is today’s sustainability buzzword.
The USGBC is preparing to integrate LCA into its LEED rating system, and
the industry is filled with lively debate about its impact. As LEED matures
and other rating systems find their place in the movement, increasing
emphasis is placed on the importance of examining all aspects of a structure:
not just the building itself, but the embodied energy of materials, the
long-term affects of manufacturing processes, the stages of construction,
building performance and operations, durability and maintenance of existing
structures, and—in the end—demolition, materials recycling,
and future land use ramifications. Although LEED considers some of these,
USGBC is considering more, and whether the points are weighted correctly.
LCI, LCA: Definitions
The International Organization for Standardization (ISO) defines LCA as
the “compilation and evaluation of the inputs, outputs and the potential
environmental impacts of a product system throughout its life cycle.”
Life cycle inventory analysis (LCI), often confused with LCA, is actually
the phase of life cycle assessment involving the compilation and quantification
of specific inputs and outputs—materials, energy and emissions—for
a given product system throughout its life cycle. The difference is key:
LCA is big picture; LCI trains a microscope on individual components.
Rita Schenck, executive director for the Institute for Environmental Research
and Education (which helped to form the American Center for Life Cycle
Assessment in 2001), says LCAs are valuable because they are fact-based.
“It’s a measuring tool, pulling all the information into one
place,” she says. “An LCA shows you where you can really get
better. What has happened historically is that we move pollution from
one type
to another, and an LCA can help make sure you’re not doing that.”
(Her book, LCA for Mere Mortals, is a valuable tool for beginners—available
for download at www.iere.org.)
From Dust to Demolition: Concrete in the Mix
Concrete has something of a bad rap in certain circles. Some argue that
cement production releases CO2, that the embodied energy of
the material is too high. But “the flip side to that is aggregate
can be attained locally, for lower transportation costs and pollution
generated,” says Schenck. And while cement does have a high embodied
energy, it is only a fraction of concrete, and its embodied energy is
a fraction of the energy used to heat and cool buildings. Concrete can
also contain recycled aggregates (derived locally), recycled steel (derived
locally), and supplementary cementitious mixtures (often industrial byproducts
that would otherwise be landfilled).
Concrete also brings numerous lasting benefits that many believe far outweigh
the front-end labor and energy. As Schenck mentioned, locally available
materials mean less transportation and pollution. Concrete also offers
high thermal mass, contributing to energy efficiency and comfort. Many
concrete structures are designed for a 100-year life span. The material’s
light color can provide reflectivity that reduces air conditioning loads
and helps reduce the urban heat island effect. And when a project is demolished,
much of the material can be recycled.
Recycled, Revitalized |
End of the runway is not end of the life cycle for Stapleton
Airport
In 1995, Stapleton International Airport was replaced with the ultramodern
Denver International Airport. Although Stapleton had reached the end
of its service life, a massive materials recycling project is in<
progress that will revive the area as a family-friendly residential
and commercial community.
On completion, 975 acres of concrete and asphalt will be recycled,
yielding enough material to construct a two-lane roadway roughly
10,000 miles in length. |
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At Denver’s now-closed Stapleton International
Airport, 975 acres of concrete and asphalt are being recycled.
Recycled concrete aggregates can be used for road building or
as aggregate in new concrete construction.
Photo courtesy of Recycled Materials Co., Inc. |
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Basics of recycled concrete aggregates
Old concrete can be crushed and recycled into many applications. In
the U.S., the most popular is road building. A survey recently conducted
by the Federal Highway Administration shows that 38 states recycle
concrete to create an aggregate base material; 11 recycle it into
new portland cement concrete.
Unprocessed recycled concrete aggregate (RCA) can be used as general
bulk fill material, in bank protection, base or fill for drainage
structures, road construction, noise barriers, and embankments. Processed
material can be used in new concrete for many transit applications,
as structural grade concrete, for soil-cement pavement bases, and
more. |
LEED points and other green benefits
Using recycled concrete aggregates (RCA) may help earn points toward
LEED credits, says Kerkhoff, both for incorporating recycled materials,
and for construction waste management. In addition, recycled aggregate
brings the same benefits of conventional concrete. For more on using
RCA, see ACI 555R-01: Removal and Reuse of Hardened Concrete.
PCA also has many resources on RCA. |
This is not to say that the cement industry is sitting on its laurels.
On the contrary, manufacturers are working harder than ever to make processes
cleaner and more efficient.
Danger of a Narrow Focus
CTLGroup is publishing a paper on the “Perils of Basing Sustainability
Decisions on Simple Metrics.” In response to many articles ranking
one product over another based on only a few metrics (embodied energy,
CO2 emissions, and the weight of raw materials), Authors Martha
G. VanGeem, principal engineer, and Medgar Marceau, building science engineer,
performed a full LCA of a house modeled with two types of exterior walls,
wood-framed and insulating concrete form (ICF).
Conducted according to ISO 14040 series guidelines, with energy modeling
based on Phoenix, Miami, Washington, Seattle, and Chicago, the study showed
that “the most significant environmental impacts are not from construction
products but from the production and household use of electricity and
natural gas.” The research shows that studies that examine only
a few components can make nearly any product look bad; when the full range
of effects is examined, it might be hard to argue with the comprehensive
results.
A Weighty Issue
David Shepherd, director of PCA’s sustainability program, says LCAs
are the next big battle ground for the green building movement. “LCA
is the tool that will allow people to evaluate and compare brand A to
brand B,” he says. The big question, he continues, is how boundaries
will be set for various impacts.
This is something with which VanGeem is becoming increasingly familiar.
VanGeem currently serves on an industry task group addressing weighting
issues related to USGBC’s LCA into LEED project. “Weighting
is a subjective method of giving relative importance to impacts such as
human health, climate change, energy, scarce resources, etc.,” she
explains.
Wayne Trusty, president of the Athena Sustainable Materials Institute,
says that individual impact indicator methods use different weighting
criteria: “For example, when the same LCI data was put through three
different impact indicator systems as part of a European LCA of highway
construction, the systems produced three very different answers.”
He prefers to conduct LCAs with what he calls the “food label approach,”
one in which all environmental ingredients and influences are listed—allowing
the organization (or owner, developer, etc.) to determine the weight of
each component according to their particular situation.
Multiple Systems
Meanwhile, a number of green building systems are currently available
in the marketplace with LEED, each with its own take on LCAs.
- BEES (Building for Environmental and Economic Sustainability) 3.0
is a product-to-product materials comparison tool developed by the National
Institute of Standards and Technology. (According to VanGeem, it addresses
only four possible concrete mixes out of thousands.)
- Green Globes is an online building and management environmental audit,
developed in Canada as a self-assessment tool.
- Athena Sustainable Materials Institute offers the Environmental Impact
Estimator, software that provides an LCA examination of conceptual building
designs and renovations of existing structures.
VanGeem says CTLGroup performs energy analyses and uses a few different
European developed models to create LCAs, but reports that American clients
sometimes prefer not to have a European-based approach. What the North
American industry needs, says VanGeem, is a standardized LCA approach
that can be universally adopted. Shepherd agrees: “A national organization
will establish standards eventually,” he says. But, the process
could take a while.
Meanwhile, members of the concrete industry are working together to be
better neighbors, cleaner and more efficient in production, better at
using recycled materials in the production of cement and concrete, and
innovative in divining new uses for the world’s oldest building
material. Building a sustainable future is the driving force. “I’m
really impressed with what the concrete industry is doing right now that
is environmentally positive,” says Schenck.
About the Author: As principal of Orange
Grove Media, an independent communications firm, Jennifer
G. Prokopy provides expert writing, editing and media relations services
to the construction industry. As president of the Construction Writers
Association (CWA), Jenni works with the nation’s top construction
journalists and publicists to improve the quality of construction communications.
She is a winner of the CWA Marketing Communications Award, recognizing
her writing on sustainable construction with concrete, and a graduate
of Northwestern University’s Medill School of Journalism.
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