Concrete corrosion
Concrete corrosion is a process which consists in the destruction of the material and leads to the deterioration of its properties, even to the destruction of its structure. Three factors can contribute to this process:/p>
- physical (cavitation, erosion, frost corrosion)
- biological (algae, fungi, strains of bacteria)
- chemical (corrosion: acid, leaching, sulphate, magnesium, chloride).
One ingredient very susceptible to corrosion is calcium hydroxide. The durability of concrete is to some extent dependent on this ingredient, because the remaining ingredients of “bonded” concrete are durable only under alkaline conditions.
The reinforcement is protected because the high pH of concrete causes its passivation. This protection can be weakened by carbon dioxide penetrating into the material. The gas triggers the process of carbonisation, as a result of which the webbing pH decreases. If the decrease proceeds and the pH drops under 11, then the steel ceases to passivate and thus begins the corrosion of the reinforcement.
To maintain the mechanical properties and extend the longevity of concrete structures, it is necessary to use protective coatings. Such protection consists in creating a continuous insulation layer separating the concrete from the environment. Therefore, it is possible to entirely cut off the concrete structure from its exposure to water, aggressive gases (including CO2), chlorides and other substances. The condition to be fulfilled for successful protection is its proper adherence to the substrate and continuity. An agent which meets the requirements for protective coatings is the PUREX AM polyurea system.
