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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."
It's the composition of quite a few minerals, including asbestos, but also talc and soapstone. The issue with asbestos isn't the chemical composition per se, but rather its inclination to break into micron-sized fibers that can be deposited in the lungs. Compare fine silica, which is nearly chemically inert, but poses a serious danger if inhaled.
"FDA staff reviewers expressed concern about the number of patients who were left out of the study because they died."
One of my dorm friends, Jakob Husum, wrote his dissertation on ways of optimizing cement productions.
One of the rather impressive/scary things about that, is that it is responsible for about 2% of the world's energy consumption. That's an insane amount of energy for something that isn't even an end product.
The first paragraph of the paper actually grabs you by the balls and twists firmly:
Can't quite remember how much of the energy if spent on the last bit, but I think it was something like 25%. That's 0.5% of the world's energy usage spent on a 1% efficient process. Now imagine you could up the efficiency to 10% or even 5%. That'd be a reduction of the world's energy usage of 0.45 or 0.4% respectively, simply by improving a single process.
Now, there are a lot of arguments for saving energy. Saving the environment, less pollution etc., but it's hard to overlook the economic incentive of cutting back energy costs of a production, where a large part of the process is 1% efficient.
Fly ash is actually widely used as a supplementary cementitious material. It has all sorts of excellent properties, it reduces porosity, increases durability mitigates ASR. It is a so-called pouzzolane, which means it reacts with the carbon hydroxide produced by the reaction of the cement and transforms it into calcium-silicate hydrate which is the main responsible for the strength of cement (C-S-H is the main product of the reaction of cement with water)
In fact, we are running out of sources of fly ash to put in cement. So basically, no, there is no risk, or we would have known by now. Also, you have to realise that FA is essentially pure amorphous silica, and that heavy elements would only be there as traces and stay trapped as the FA reacts.
There is literally an entry that says "Cement Production" on that link.
Portland cement based concretes also absorb CO2 over their lifetime.
The difference here is that Portland cement emits a bunch of CO2 during production, but the new stuff does not.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!