Concrete

[emmagleb]

Does anyone know how much carbon dioxide is produced in the manufacture of 1 cubic metre of concrete? I think its something like 1m^3 CO2 to 1 tonne of concrete, but I'm not sure if this is right. Thanks, Emma

[jake-the-peg]

It will vary depending on the mix of the concrete becasue it's the cement that's the major contributer.

Have a look at http://www.cembureau.be/ look at key facts Cement industry's attempts to reduce CO2 they say:

In 2003 the cement industry in the European Union produced about 194 million tonnes of cement and emitted about 0.75 tonne of CO2 per tonne of cement via direct emissions (fuel combustion and raw material de-carbonation) and 0.05 tonne of CO2 per tonne of cement via indirect emissions (use of electricity from fuel based power plants). Direct and indirect emissions of CO2 together amounted to about 0.8 tonne of CO2 per tonne of cement.

It's more accurate to talk about tonnes of CO2 produced rather than cubic meters because the volume will vary depending on atmospheric pressure

1m^3 at ground level is not the same as in the upper atmosphere

Does this help?

[brachiopod]

Here's an attempt to work something out from first principals, using a bit of schoolboy chemistry !

As jake says, the amount of cement in concrete varies according to the mix / purpose etc, so I'm also calculating for a tonne of cement;

Cement is approximately 67% calcium oxide (CaO), so that would be 670kg of CaO in every tonne.

CaO is obtained from the thermal decomposition of calcium carbonate (CaCO3) - usually in the form of limestone which is heated to produce solid calcium oxide and carbon dioxide gas;

CaCO3 ---> CaO (s) + CO2 (g)

Assuming a limestone consisting of pure CaCO3, then every tonne of limestone would produce 560kg and 440kg of CaO and CO2 respectively;

CaCO3 ----> CaO + CO2
1000 560 440

(Relative Atomic masses: Ca = 40, C = 12 & O = 16)

Since we need 670kg of CaO to make up our 67% in every tonne of cement, we need to multiply by 670 / 560 = 1.196, therefore;

Every tonne of cement requires;
1196kg of CaCO3 (limestone) which needs to be heated to 1450�C,
which produces
670kg of calcium oxide and
526kg of carbon dioxide.(That's over half a tonne of CO2 !!)

[brachiopod]

[cont.]

And that is just the CO2 that is produced in the reaction alone. This does not include the energy needed to heat the limestone to a high temperature - (which requires burning a fuel) - which in itself creates more CO2. It is also assuming the limestone is pure calcium carbonate - which it never is! And ignores totally the cost in CO2-terms of exploitation and transportation of raw materials, processing, delivering the finished produce etc. etc.

Phew! Having worked that out, jake-the-peg's figure of 800kg of CO2 for every 1000kg of cement sounds about right !!

[emmagleb]

You've both been extremely helpful, thanks very much!