NY Times: Concrete Is Remixed With Environment in Mind

[OKIsItJustMe]

http://www.nytimes.com/2009/03/31/science/earth/31conc.html

Concrete Is Remixed With Environment in Mind

By HENRY FOUNTAIN
Published: March 30, 2009

Soaring above the Mississippi River just east of downtown Minneapolis is one remarkable concrete job.

There on Interstate 35W, the St. Anthony Falls Bridge carries 10 lanes of traffic on box girders borne by massive arching piers, which are supported, in turn, by footings and deep pilings.

The bridge, built to replace one that collapsed in 2007, killing 13 people, is constructed almost entirely of concrete embedded with steel reinforcing bars, or rebar. But it is hardly a monolithic structure: the components are made from different concrete mixes, the recipes tweaked, as a chef would, for specific strength and durability requirements and to reduce the impact on the environment. One mix, incorporated in wavy sculptures at both ends of the bridge, is designed to stay gleaming white by scrubbing stain-causing pollutants from the air.

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.

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[drm604]

1. Very interesting article.

It talks about the possibility of making concrete that actually sequesters CO2, making the concrete carbon negative. Currently it's a huge source of CO2.

[NYC_SKP]

2. Well, not negative, but much less harmful.

Calera's plan is to create aggregate for concrete using the seawater/CO2 capture process described.

But aggregate isn't the culprit, the production of cement (the powdery substance) is the big CO2 problem, aggregate can be gravel or glass or any solid chunks of filler.

And, yes, the worldwide production of cement (not concrete) is a huge contributor to the CO2 problem.

"Climate
Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is heated, producing lime and carbon dioxide<13>, and also indirectly through the use of energy, particularly if the energy is sourced from fossil fuels. The cement industry produces 5% of global man-made CO2 emissions, of which 50% is from the chemical process, and 40% from burning fuel.<14> The amount of CO2 emitted by the cement industry is nearly 900 kg of CO2 for every 1000 kg of cement produced. <15>
Newly developed cement types from Novacem<16> and Eco-cement can absorb CO2 from ambient air during hardening.<17>"

http://en.wikipedia.org/wiki/Cement#Climate

[drm604]

3. The article says that it may be possible.

According to the article it may be possible to make it carbon negative by ending the use of portland cement (which is a huge energy hog) plus making concrete which actually sequesters carbon instead of emitting it.