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Cement and concrete

There are several problems with cement:

  • the huge amount of energy which goes into making it because of the high temperatures needed in the kilns. It is reckoned that cement manufacturing accounts for 7% of global CO2 emissions. (However it is worth noting that if you are designing high thermal mass into a house then concrete is considerably better than bricks or blockwork in terms of embodied energy. Concrete is about 1 MJ/Kg compared with bricks and blocks at about 3MJ/Kg)
  • the fact that most of this energy comes from fuels which release carbon dioxide
  • these fuels are often waste products which are being incinerated – with all the attendant risks of dioxin pollution well documented in this Green Building Press article
  • the quarrying associated with limestone production
  • on the demolition of a building –
    • concrete cannot be recycled, though it can be re-used as hardcore
    • cement based mortar is difficult to remove from brick and stone

The alternatives to cement-

Rather than using a normal concrete mix try to use GGBS (Ground Granulated Blast Furnace Slag) cement in a ratio of 50/50 or even 70/30 with OPC. This reduces the embodied energy very considerably. See the Hanson Regen web page for more details

For flooring there is an option to use limecrete. This is similar to concrete but uses lime (which cosumes less energy to manufacture and releases much less CO2)

Concrete lintels – consider not building with a masonry external wall. Rather, use a lightweight timber wall with a rain screen or use SIPS.

Foundations are almost always concrete but for lightweight construction such as timber frame, screw foundations may offer a better solution

Cenin ultra low carbon cement, made in South Wales, is worth considering


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