The cost of carbon dioxide reduction
Emma Clarke, writing for ClimateChangeCorp.com, reports on the development of more environmentally friendly concrete in The truth about...cement. Don't ask me to explain the chemistry behind it - chemistry was my worst subject - but here are the basic facts. Cement accounts for some 5 percent of man-made carbon dioxide emissions. Traditional cements emits about .6 tonnes of carbon for every 1 tonne produced, and that's not counting emissions from the fuel burned to heat the kiln.
A new type of cement called geopolymer cement produces only about a third of the carbon of traditional cement. A company called Zeobond based in Australia has managed to produce it in small quantities at a price of only 10-15 percent more than traditional concrete. Assuming there are some economies of scale involved, I would guess that this price could be brought even lower. So it looks like the tradeoff in increased price vs. reduced pollution could be attractive. But there are naysayers.
First, the stuff is untested in terms of its longevity and durability. But that is just a matter of time and testing - although it could be a while. The more difficult problem may be getting to one of the input materials for this new kind of concrete, something called aluminosilicates. According to the article, this "would require an overhaul of infrastructure for transporting and handling concrete." Perhaps this is one place where some rapidly growing developing countries could leapfrog past outdated infrastructure?
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Not really all that amazing.
The CO2 emissions from cement production (from calcination, ie, not from the fuel used) are all reabsorbed by the cement over the decades that it stands there as a building.
Posted by: Tim Worstall | Sep 7, 2008 6:22:09 AM
Tim Worstall is wrong for at least three reasons.
1) Yes, it is known that Portland cement concrete reabsorbs CO2, but this phenomena occurs only on the surface of the concrete blocks (maximum 1-2 centimers deep).
2) This CO2 absorption happens very slowly and it would take centuries to recarbonate concrete blocks. There are historical remains of lime-based concrete that still contain uncarbonated lime after more than 1000 years. This means that the cinetic of CO2 emission during Portland manufacture is 1000 times faster than its reabsorption.
3) Concrete specialists avoid CO2 absorption because it is deleterious to Portland cement concrete. Indeed, Carbonation lowers the pH of the concrete and by so doing weakens the steel bars that become suceptible to rost (main cause of concrete degradation).
Posted by: Joseph Davidovits | Dec 15, 2008 10:51:39 AM