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Concrete Facts
Tue Mar 25, 2003
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.
The Weather Notebook is a production of the Mount Washington Observatory. Our series on Global
Climate Change is supported by the New England Science Center Collaborative and the Roy A.
Hunt Foundation.
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