Source:
U.S. News & World Report
By JASON KOEBLER
June 4, 2013

The secret to making sustainable, strong concrete may have been at the bottom the Mediterranean Sea for the past 2,000 years: Researchers believe that the ancient Romans created concrete that is more environmentally friendly and durable than modern cement.

Concrete is one of the most commonly used building materials in the modern world, but its role in creating carbon emissions is often overlooked. Worldwide, some 19 billion tons of concrete is used annually, and the high temperatures necessary to produce it are responsible for up to 7 percent of all human carbon dioxide emissions.

"It's a beautiful material, it's used all over the world, but the weakness is we use too much of it. We cannot continue with business as usual," says Paulo Monteiro, a researcher at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. His findings were published in the Journal of the American Ceramic Society. "We have to find alternative ways to make concrete."

Monteiro and his colleagues may have found an alternative: "sea" concrete used by Romans for harbor installations in the Mediterranean is made with a different concentration of materials than today's mix of limestone and clay, which allowed it to be baked at a much lower temperature (about 1,650 degrees, compared to 2,640 degrees for modern "Portland" concrete). The result is a strong concrete that is less harmful to the environment.

http://www.usnews.com/news/articles/2013/06/04/the-ancient-romans-were-better-at-making-sustainable-concrete-than-we-are