The manufacturing of cement produces about 5% of the world’s CO2 output. Analysis has concluded that producing a single pound of cement generates .73 – .99 pounds of CO2.[i]
The concrete that is so ubiquitous in our highways is 7% to 15% cement by total weight. All of this concrete is susceptible to the freeze and thaw cycle as well as general wear and tear. Anything that can be done to reduce the carbon footprint of concrete by increasing the times between repairs and replacement would be a major win for both the concrete industry and sustainability movement.
This is great news:
Northwestern [University] engineer Surendra Shahand and his team are adapting cutting-edge technology to improve a decidedly low-tech substance by infusing concrete with carbon nanotubes. Carbon nanotubes are strong, flexible pipe-like arrangements of carbon atoms too small to be seen by most microscopes.
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“We use 2 tons per capita per year of concrete, can you imagine that?” Shah said. Worldwide, that translates into nearly 12 billion tons of concrete per year. And, as countries such as China and India continue to develop, that amount will almost certainly go up.
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That’s where Shah’s work comes in. At the atomic scale, concrete looks like a bunch of tennis balls packed together. The chemical reactions that take place between cement and water create nanovoids, or spaces, between the balls. This means that chips, cracks and potholes actually start at the nanoscale.
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Using carbon nanotubes would make the concrete nearly impenetrable, greatly extending the lifespan of roads, bridges and buildings.
“If you can make concrete very impermeable, so that salt doesn’t go through, then you can extend the life to a hundred years rather than 20,” Shah said.
Not surprisingly, this new technology isn’t cheap. But when that higher price tag is spread out over a much longer lifespan, it could become cost-effective. And this doesn’t factor in the reduced cost to the environment.
“We have to include all of this, not only the material cost,” Shah said.
As stated, the technology is expensive, but sounds very promising. And frankly, we have grown accustomed to cheap materials only because they do not include the true, long term negative externalities, so some sort of Pigovian tax to cover these negative consequences doesn’t strike me as particularly bad. From this point of view, the extra cost of the nanotube concrete might be worth it but everyone knows that only the truly committed would be willing to pay the extra upfront costs. Luckily, prices should be expected to come down as the industry accepts the product, production figures rise, and marginal costs fall.
[i] http://www.concretethinker.com/Papers.aspx?DocId=312
