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Concrete
Tue Nov 29, 2005
Listen in RealAudio 
Many scientists believe that carbon dioxide, or CO2 emissions play a major role in
helping to change the earth's climate. That carbon comes from several sources,
including one that might not readily spring to mind. Hi, I'm Bryan Yeaton and this is The
Weather Notebook's weekly segment on Global Climate Change.
The majority of atmospheric CO2 comes from fossil fuel combustion and
deforestation, but a small amount comes from cement production. That's right --
cement production.
The type of cement that we typically use today is known as Portland cement, which is
60 percent calcium carbonate (CaCO3). Cement manufacturers cook substances high
in CaCO3, like limestone and chalk, to produce lime, in a process called calcination.
Calcination leaves us with Calcium Oxide (CaO) and Carbon Dioxide (C02). Concrete
is made by adding sand and gravel to the cement.
In 1991, the Inter-Governmental Panel on Climate Change or IPCC, attributed seven
percent of world-wide CO2 emissions to cement production. That equaled 1.56 billion
tons of CO2 annually.
Some organizations have been working toward a more environmentally-friendly
cement. The Eco-Smart Project, a joint effort by industry and government agencies in
Canada, is dedicated to reducing CO2 emissions by using "supplemental cementing
materials". These include industry by-products such as fly ash, blast furnace slag,
husk ash, and silica fume. By replacing 30 to 60 percent of the actual cement in the
concrete, not only are CO2 emissions reduced, but cost is lowered as well. LaFarge,
the world’s largest cement producer, has been working with the World Wildlife Fund, to
reduce its emissions by 20 percent by 2010, and is the first industrial group to become
a WWF Conservation Partner.
The Weather Notebook is a production of the Mount Washington Observatory. Regular
funding for our show comes from Subaru of America. Special support for our series on
Global Climate Change comes from Environmental Defense.
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