The (re)carbonation of concrete: a natural process of CO₂ absorption

What is (re)carbonation?

By (re)carbonation we mean the process by which CO₂ present in the air (including CO₂ emitted during the firing of the clinker), is reabsorbed by the hardened concrete. Carbonation is a slow process which occurs when calcium hydroxide, Ca(OH)₂ produced by the reaction of cement and water, it binds to atmospheric carbon dioxide, thus forming calcium carbonate and water.

In practice, the decarbonation reaction which takes place inside the kiln for the production of clinker (transformation from calcium carbonate into calcium oxide, CaCO₃ → CaCO + CO₂), is repeated in the reverse direction in the concrete (transition from calcium hydroxide to calcium carbonate) and one share of CO₂ it is permanently bound into the concrete mass; for this reason this phenomenon is increasingly identified with the name of (re)carbonation. THE’IPCC (Intergovernmental Panel on Climate Change) of the UN has recognized the natural process of recarbonation as a active phenomenon in the removal of CO₂ from the air.

There quantification of CO₂ that participates in the recarbonation process is a complex exercise that depends on a series of factors such as, for example, the porosity of the concrete produced, the geometry of the concrete elements (surface/volume ratio), their exposure and the presence or absence of surface treatments. From a life cycle perspective, the demolition process of reinforced concrete structures, with a consequent increase in the exposed surface and therefore in the rate of (re)carbonation of the concrete itself.

For the quantification of CO₂ linked, you can refer to the evaluations of the Swedish institute IVL (Swedish Environmental Research Institute) which conservatively estimates recarbonation equal to 23% of CO emissions₂ by decarbonation during clinker production (20% during the service life and 3% during the subsequent end-of-life phase).

Heidelberg Materials’ commitment

Heidelberg Materials aims to reduce CO₂ emissions by 50% by 2030 and achieve carbon neutrality by 2050, in line with EU goals.

Net of the energy efficiency of cement production plants, the reduction of emissions can occur through the use of alternative fuels. Heidelberg Materials intends bring the percentage of alternative fuels to 45% of our mix by 2030.

In compliance with the cement standards (UNI EN 197-1, UNI EN 197-5 and UNI EN 197-6), Heidelberg Materials is committed to production of sustainable cements (green cements with reduced CO emissions₂), characterized by a low clinker contentthanks to the use of alternative constituents to clinker, both of natural origin, such as pozzolans, and deriving from other industrial processes, such as blast furnace slag. Heidelberg Materials offers its customers products that enhance sustainability and the circular economy. THEThe value of a work is also measured by the local availability of the materials used to create it, by a short supply chain rooted in the territory.

The company is at the forefront of capture and in CO storage₂ emitted by decarbonation and in the transformation of the sector. With evoZerothe first Net-zero carbon captured cement, offers the most far-sighted partners in the construction sector the opportunity to build a better tomorrow.

On the regulatory front, Heidelberg Materials is an active participant in standardization of new types of cements with improved characteristics in terms of circularity and sustainability, moreover, it raises the awareness of its customers and designers in the choice of solutions that minimize the environmental impact of the concrete work in its entire life cycle, in consideration of the fact that the greater the durability of the work over time, the lower its impact on the environment will be.