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 abundant 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, as with the production of many building
materials. Both the fuel for heating and the chemical reaction
from processing the raw materials generate carbon dioxide (CO2).
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 from cement plants 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 25% 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 (out of 290 million produced), reducing fossil fuel consumption and
removing them from the waste stream. Concrete can also utilize
fly-ash, slag cement and silica fume as a partial replacement
for portland cement. 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 from electric utilities and use
it 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, sheathing and packaging materials
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 or made into large
blocks for erosion protection.
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Operational Phase
Recently developed methods for home-building with concrete use
less energy and generate lower greenhouse gas emissions than
traditional home-building methods. Research revealed that
homes built with insulated concrete
walls actually use less energy over the
life span
of a home than typical wood frame construction(2). Less
than 0.5% of the life cycle energy is due to the manufacture of
cement and production of concrete.
Household energy use for heating and cooling represent 85 to 95%
of the total life cycle energy use. In about 5 to 7 years, the
energy used to produce and operate a typical wood frame home
begins to exceed that of an insulated concrete home. The lower
thermal efficiency also means greater fossil fuel consumption and
a corresponding increase in the CO2 burden for wod frame construction.
These cumulative environmental benefits of concrete vs. wood frame
continue to grow the longer the home is utilized. (Figure 1)
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Figure 1. 100-Year Life Cycle Green House Gas
Emissions
Less Efficient Wood Frame Home vs. ICF Home in Chicago 3
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Concrete contributes to improved indoor air quality as new concrete does
not have off-gassing often 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.
3. "Comparison of the Life Cycle Assessment of an Insulating Concrete
Form House and a Wood Frame House" by CTL Group for Portland Cement
Association, 2008, Serial
No. 3041.
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