Carbon dioxide mineralization is a process in which CO₂ reacts with alkaline metal to form solid carbonate minerals.
Demolished concrete aggregate contains hydrated cement phases. These hydrated cement phases are in contact with water, e.g. pore water – and thus in a solid-liquid equilibrium. Part of the hydrated cement is dissolved in the water and therefore present as ions. As CO₂ is also dissolved in this water, new mineral that exhibit lower solubility than the hydrated cement phases precipitate. And voilà, calcium carbonate (CACO3) is formed.
Thus, the CO₂ and the hydrated cement undergo a chemical transformation to form rock. This so-called carbonation reaction of 1 kg CO₂ releases heat such that the temperature of 1,000 kg of concrete increases by about 2.5°C.
CACO3 is considered to be amongst the most permanent ways to sequester carbon. Only temperatures above 600°C or very strong acids could trigger the release of CO₂. This ensures that the CO₂ remains stored in the concrete, even if it is demolished again after being reused.