Tech Brief 12
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Building Green with Gray Concrete
The buildings in which we live and work have a tremendous impact on our
global environment. Sustainability or "green building" seeks
to balance resource efficiency, health, and social concerns throughout the life cycle of a structure. Concrete has a variety
of benefits to offer in achieving this goal.
What is concrete?
Concrete and cement are often confused. Cement is a gray powder that,
when mixed with water, binds sand and aggregates together to create
concrete. Concrete is the world’s most prolific building material. This "liquid stone" can be shaped to make roads, bridges, dams,
hospitals, and homes. It is extremely
strong and durable. The longevity of concrete means less maintenance
and replacement when compared to other building products. This
contributes to the environmental value of this versatile material.
Although making cement requires a great deal of
energy, cement is only a minor portion (10%–12%) of concrete.
The other ingredients, aggregates and water, are locally sourced
and require very low energy to obtain.
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Progress from Research
The high temperatures needed for cement manufacturing make it a very energy intensive
process. Both the fuel for heating and the chemical reaction from processing
the raw materials generate carbon dioxide (CO2). Worldwide global concerns about
climate changes have led industry researchers to find ways to minimize CO2 production.
The result is a 33% decrease in carbon dioxide output since 1975.
Research has also led to the use of industrial by-products in the manufacturing
process. Let’s look at several examples. Pound for pound, used tires
contain about 33% more energy than coal, and the U. S. generates millions
of them. In 2005, about 58 million tires were consumed as fuel in cement
kilns, reducing
fossil fuel consumption and removing them from the waste stream. Concrete can
also utilize fly-ash, slag cement, and silica fume. These are by-products from
power plants, steel mills, and silicon manufacturing facilities. In reasonable
proportions, these by-products confer beneficial properties to concrete. In
2005,
the concrete industry was able to divert about 20.5 million tons of fly ash and other coal combustion by-products of electric utilities from
landfills and use them in concrete.
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A Cradle-to-Grave Perspective
Concrete is an extremely durable material. Life spans for concrete building products
are frequently double or triple those of other common building materials. Concrete
is virtually unaffected by heat and cold, UV rays, and moisture. This reduces
the waste created by the removal and replacement of weathered or moisture damaged
materials.
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Raw Material Production
The predominant raw material for cement is limestone, the most abundant
mineral on earth and readily available throughout North America.
An environmental study
conducted in Canada(1) analyzed the site impact of logging, ore mining, and
aggregate extraction. It concluded that aggregate quarries take
a lesser environmental
toll than the other construction materials. Quarries, the primary source of
raw materials, can be readily reclaimed for recreational, residential,
or commercial
use, or they can be restored to their natural state.
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Construction Phase
Ever seen the piles of scrap lumber and sheathing filling dumpsters at a construction
site? Concrete is ordered and mixed for each individual job. On-site scrap
and waste are minimized and any leftovers can be recycled.
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Operational Phase
Recently developed methods for home-building with concrete actually generate
less CO than some traditional home-building methods. Research
revealed that houses built with insulated concrete walls actually
contribute less CO2 to our environment over the life span
of a home than typical wood frame construction(2). Although the
initial manufacture of cement is energy intensive, these high
performance wall systems need less energy for daily heating and
cooling. In about 5 to 7 years, the total CO2 produced by a typical wood frame
home begins to exceed that of an insulated concrete home. This
environmental benefit continues for as long as the home is utilized.
Concrete contributes to indoor air quality as new concrete does
not have the off-gassing that is prevalent in many other new construction materials.
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Demolition Phase
Although concrete has one of the longest useful life-spans for construction
materials, its usefulness does not end after its original purpose.
In most urban areas, almost all concrete is crushed and recycled
for use in road base and backfill. In some cases, it is recycled
for aggregate in new concrete. Research continues to find new applications for recycled concrete.
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Versatility
The applications for concrete and cement-based materials is growing rapidly.
Stucco, fiber–cement siding, and concrete roof tiles need
minimal maintenance and provide long lasting protection from the elements. These products are also useful in fire prone areas where stray
sparks can lead to devastating results.
Decorative concrete slabs and concrete pavers for patios eliminate
the need for costly annual maintenance, associated cleaners,
and solvent-based coatings for wood decks. Even with good care, exterior
wood structures require replacement long before their concrete counterparts.
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For More Information
All of the sustainability advantages of concrete construction are
too numerous to address in this publication.
Learn more about using concrete for environmental benefits at www.concretethinker.org.
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1. "Assessing the Relative Ecological Carrying Impacts of Resource
Extraction," by Wayne B. Trusty and Associates Ltd. in association
with Environmental Policy Research, submitted to Forintek Canada Corp.
for its Sustainable Materials Project, August 1994
"
Ecological Carrying
Impacts of Building Materials Extraction," by
Dr. Robert Paehlke, Natural Resources Canada, submitted to Forintek Canada Corp for its Sustainable Materials Project, September 1993
2. "Partial Environmental Life Cycle Inventory of an Insulating Concrete
Form House Compared to Wood Frame House" by Construction Technology
Laboratories, for Portland Cement Association, 2003, Serial No. 2464
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