Could Carbonated Concrete Offset Itself?
Concrete is the most important building material in the world, but as the world is more mindful of its carbon footprint, that leads to some very difficult questions being asked.
According to a study published in Nature, eight per cent of human-produced global emissions come just from the production of concrete, so any net-zero future needs to decarbonise concrete or use far less of it.
Whilst there has been research into alternative building materials, there is also a potentially promising development published by The RIBA Journal, which would develop a process that would allow bespoke concrete to effectively offset its own carbon dioxide emissions.
The process, known as concrete carbonation, uses calcium hydroxide and other similar hydrated salts mixed into the cement that, once cured, reacts with carbon dioxide in the atmosphere, creating crystals of calcium carbonate, a major part of limestone.
The advantage of this is that calcium hydroxide is relatively easy to get a hold of and can absorb a lot of carbon dioxide, with researchers theorising that if scaled up globally could absorb as much as 2 gigatonnes. This is 77 per cent of the annual global emissions caused by the production of cement.
The problem is that if left to its own devices, the carbonation process is slow, uneven and can potentially lead to structural damage. This is especially true if the carbonation method is used on reinforced concrete, as the process can cause the steel rebar to rust and potentially lead to cracked concrete.
However, these processes can be controlled in order to make the finished concrete structure more consistent.
The first involves using carbonation chambers in the concrete, where carbon dioxide gas is pumped into the concrete material in controlled conditions to force the production of calcium carbonate.
The other approach involves mixing in materials rich in carbon dioxide along with recycled concrete aggregate, which also helps to increase stability, improving the carbon dioxide that is absorbed.
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