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."
You mean turning the cement industry from a big emitter to a small emitter...
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.
amorphous silica is fine to inhale even if it is really fine dust particles. crystalline silica is what will give you silicosis..
A similar product was presented on Australian TV) in 2005.
It's not a bug, it's a lepidopter!
It is good at load distribution not in actual strength.
More precisely, concrete is good in compression, but poor in tension. That's why you fill it with steel bars if it has to take any bending forces that would put part of it in tension.
âoeAny society that would give up a little liberty to gain a little security will deserve neither and lose both.
A *lot* more than hundreds of years. The Romans used concrete all over the place. Even the Pantheon's dome is concrete.
we would not breath (our rate of breaths is determined by amounts of CO2, not O2)
Not quite. It's determined by CO2, yes, but it's the CO2 in the blood that determines it, not atmospheric CO2.
Basically the intake is kept equal to the exhaust.
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.
It's not impossible but remember that (IIRC) theoretical optimum thermal efficiency is (THigh-Tlow)/THigh.
In practice that means that waste heat is generally too cold for this process. If it were hot enough to make cement it would be hot enough to extract power from.
Waste heat from Combustion Turbines (CTs) is already being used to generate steam in cogen plants.
'Pure' CTs are typically super-peaker plants. Lousy efficiency but they start and ramp fast. Which in practice means their heat is too unpredictable to run that kind of process in any case.
Typical applications of CoLo heating are greenhouses, malls and other large buildings. Market forces are making this (space heating) happen quite nicely where ever economically practical.
My university was/is entirely heated by the waste heat of the coal fired plant on campus (50+ year old setup). Good fun in the steam tunnels. Access to boiler rooms.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
All concrete absorbs CO2 as it cures. They don't bother to tell you that. It only gives off CO2 in its manufacture. Basically what I they're talking about is breaking down calcium sulfates instead of calcium carbonates to make one of the primary ingreedient. They're probably also using more calcium overall...making it a little more like masonry mortar. Were we to make the bulk of our concrete with this process we would quickly surpass our need for sulfuric acid and other sulfates and the resulting pollution would make CO2 look like the elixir of life. Hmmm, come to think of it CO2 just about is the elixir of life anyway. We really need to concern ourselves more with actual pollution and less with CO2.
As for structural integrity...it will increase over time, just like normal concrete. While concrete may be considered to be fully cured within a few days it takes decades before it reaches full strength (sometimes as much as twice as hard as when it's first considered "fully cured")
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!
Actually, all models take clouds into account. Which journal article led you to this conclusion? I've discussed this issue in the comments and linked to a new paper describing recent improvements to models of clouds.
Because, as I state in a popup on the words "very slightly" in the third paragraph of the article, there are so many changes to the Earth over such long periods of geological time (you have to go back tens of millions of years to see higher CO2 concentrations) that the dynamical models wouldn't be expected to apply. Plus, proxy data are unreliable at such timescales, so we're stuck with "recent" data like the last 650,000 years from EPICA.
Huh? You're not under the impression that climate models are empirical models, are you?
That's because those other effects have been shown to be very small. See 7 (b) in the index: "Cosmic rays are responsible for global warming." If you've found evidence contradicting these papers, please let us know.
I've explicitly addressed this point. The point is that feedback effects act on different time scales, and our forcing is geologically very rapid.
I didn't mean that man-made CO2 has a greater effect, just that feedback CO2 appears after the temperature rises, not before. Therefore the recent CO2 rise is anthropogenic, and we should expect the natural feedback CO2 (observed in Vostok) to add to it.
For instance? (I've got my own research distracting me, so I don't always have time to answer each and every question, but I've tried really hard to answer all the scientific questions that people have posed. I'd l
Could the waste heat from a coal or nuclear power plant be used to 'bake' the cement?
Far, far too cold.
Typical Rankine cycle plant tops out around 500-600C at the hot end. Higher would be nicer, but the problem is you need a material with immense tensile strength to contain the pressure, pleasant failure modes (not brittle), and good heat conductivity. Sorry but 600C is about as good as our technology gets. The cold end is of course much colder.
http://en.wikipedia.org/wiki/Rankine_cycle
On the other hand, cement kilns really need about 1500C. Kilns don't operate at much pressure, and insulating material is preferable. Seems our current technology is much better at weak insulators than strong conductors.
http://en.wikipedia.org/wiki/Cement_kiln
The hot side of the plant is way too cold for a kiln. The cold side of the plant at around 50C or so at the power plant is waaaaaaaay too cold for a cement kiln, barely good enough to preheat the materials.
If you built a rankine cycle plant that had the same temperature at the hot and cold side, by definition it wouldn't make any power, so it would just be a waste. Or if you minimized the temperature at the cold end, the plant would be efficient, but the cold end would barely be useful for household heating in the winter, much less cement production...
If only the hot side of the plant could survive kiln operating temperatures... then during non-peak times, keep firing the furnace full blast, but make cement instead of electricity. But our technology is way to crude for that.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger