Carbonation > The Phenomenon

Carbonation heavily damages reinforced concrete structures. The outside surfaces are exposed to physical and chemical interaction with their environment. Carbon dioxide in the atmosphere, when it gets into contact with the concrete, tends to react, starting from the most external layers and gradually passing inward, reducing the protective effect on the reinforcements. Carbonation is a primary condition for corrosion, which will take place when there is oxygen and water. Expansion due to corrosion reduces adhesion to the concrete, and is a risk for the safety on which the structural planning is based.

Some signs of corrosion taking place appear on the outside surface as rust spots, cracks or delamination, which at the most critical points can even lead to the ejection of the cover (spalling). However, these signs appear during the phase of Propagation thus limiting the possibility of intervention which could be carried out if one got to know the problem during the Initiation phase.
Once carbonation has affected the reinforcements, corrosion appears on the parts of the structure which get into touch with water or wetted by rain. The worst situation is that of dry-wet cycles, which favour the entry into the cement of both water and oxygen. Obviously the structures which are most vulnerable to this type of decay are balconies, eaves, façades and infrastructures, such as tunnels and viaducts. Carbonation therefore is a problem which affects residential buildings, but also infrastructures and public buildings.