A Meaner, Greener Recipe for Concrete

Concrete in a Minneapolis bridge replacing that which collapsed in 2007 is made of a concoction that boasts less environmental impact and durability. And it's self-cleaning.
March 31, 2009, 2pm PDT | Judy Chang
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"The project, built for more than $230 million and finished in September, three months ahead of schedule, 'might have been the most demanding concrete job in the United States in 2008,' said Richard D. Stehly, principal of American Engineering Testing, a Minneapolis firm that was involved in the project. It is a prime example of major changes in concrete production and use - changes that make use of basic research and are grounded, in part, in the need to reduce concrete's carbon footprint.

Concrete may seem an unlikely material for scientific advances. At its most basic, a block of concrete is something like a fruitcake, but even more leaden and often just as unloved. The fruit in the mix is coarse aggregate, usually crushed rock. Fine aggregate, usually sand, is a major component as well. Add water and something to help bind it all together - eggs in a fruitcake, Portland cement in concrete - mix well, pour into a form and let sit for decades."

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Published on Monday, March 30, 2009 in The New York Times
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