Slashdot Mirror
Green Cement Absorbs Carbon
Peace Corps Online writes "Concrete accounts for more than 5 percent of human-caused carbon dioxide emissions annually, mostly because cement, the active ingredient in concrete, is made by baking limestone and clay powders under intense heat that is generally produced by the burning of fossil fuels. Now Scientific American reports that British start-up company Novacem has developed a 'carbon-negative' cement that absorbs more carbon dioxide than it emits over its life cycle. The trick is to make cement from magnesium silicates rather than calcium carbonate, or limestone, since this material does not emit CO2 in manufacture and absorbs the greenhouse gas as it ages. 'The building and construction industry knows it has got to do radical things to reduce its carbon footprint and cement companies understand there is not a lot they can do without a technology breakthrough,' says Novacem Chairman Stuart Evans. Novacem estimates that for every ton of Portland cement replaced by its product, around three-quarters of a ton of CO2 is saved, turning the cement industry from a big emitter to a big absorber of carbon. Major cement makers have been working hard to reduce CO2 emissions by investing in modern kilns and using as little carbon-heavy fuel as possible, but reductions to date have been limited. Novacem has raised $1.7M to start a pilot plant that should be up and running in northern England in 2011."
This sounds like a concrete nightmare:
If a material absorbs so much CO2 over it's lifespan, it significantly alters the chemical composition and therefore strength.
I doubt any builder will use this material unless it's been proven that the new material is sufficiently stable.
Example: as a geology student, I ran into an area in central spain with lots of Gypsum sediments (Ca|MG.SO4). Putting limestone and concrete buildings on this sediment wasn't done until the 20th century, but all the buildings built in that area are long gone, even though in nearby towns they still stand tall. Reason? The Gypsym in the soil chemically eats the mortar and limestone (CaCO3) out of the structure on top of it, making it crumble within a few decades. The Gypsum areas are largely a wasteland where only very few buildings remain.
Now, Mg.Ca-CO3 (dolomite limestone) is largely as stable or more stable than pure limestone, and certainly harder, but any new formula for the glue in concrete will have to pass the test of time before it will be widely adopted, especially in e.g. bridges and skyscrapers...
Perhaps we can start with the interstates, nobody would notice if they started to crumble early ;)
The summary doesn't explain things very well. Just to set things straight, most of the CO2 emissions from portland cement production is not from the fuel burned in the kilns but from the gas released by the limestone itself during the calcination process. The only real incentive for the use of energy efficient kilns is to reduce fuel costs and not to reduce emissions. The upside is that cement will reabsorb much of the released CO2 as it cures over the course of time.
I am becoming gerund, destroyer of verbs.
The house I live in is a mere 150 years old, but most of the street it is in was built between 1690 and 1695. In fact, our foundations go back to then. The composition and structure of Bath stone has been extensively studied, and I would imagine the results are just a small part of the data the technologists will take into account.
And your point was, again?
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."