Pachapapa wrote: ↑Fri Oct 15, 2021 2:38 pm
@exile
Puzzling me on cement.
The CO2 element involved is CaCO3.
Heat reduces it to lime CaO.
As a constituent of concrete the CaO element combines with CO2 to reform a solid rock "in situ".
Seems to me a convenient and efficient way of transporting solid rock around the world!
Two points both important:
1. Cement does not recombine with CO2 to make concrete. The reaction is a hydration reaction - which is why we add water. Cement left in store will slowly combine with atmospheric CO2 and become inert regarding concrete making. So cement as a material generates CO2 in large quantities.
2. In order to get that Calcium Oxide (CaO) you need a lot of energy which today is almost exclusively generated through burning gas, coal or petroleum products - more CO2.
This from Wiki:
Cement starts to set when mixed with water, which causes a series of hydration chemical reactions. The constituents slowly hydrate and the mineral hydrates solidify and harden. The interlocking of the hydrates gives cement its strength. Contrary to popular belief, hydraulic cement does not set by drying out — proper curing requires maintaining the appropriate moisture content necessary for the hydration reactions during the setting and the hardening processes. If hydraulic cements dry out during the curing phase, the resulting product can be insufficiently hydrated and significantly weakened.
and this:
If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8 billion tonnes, surpassed only by China and the United States.[6] The initial calcination reaction in the production of cement is responsible for about 4% of global CO
2 emissions.[7] The overall process is responsible for about 8% of global CO
2 emissions, as the cement kiln in which the reaction occurs is typically fired by coal or petroleum coke due to the luminous flame required to heat the kiln by radiant heat transfer.[8] As a result, the production of cement is a major contributor to climate change.
I fear Steve has misunderstood one part of the government announcement where it said that
"CF Fertilisers produces around 60 per cent of UK’s CO2, used primarily by the food sector."
The 60% relates to CO2 produced for sale. It is most certainly not 60% of CO2 emissions.
I have to say that if you are not in the know, it is a very easy misunderstanding to make.