Anti-carbonation coatings are used as surface treatments that have a high resistance to carbon dioxide. They shield the concrete from carbonation by acting as a barrier.
How does carbonation take place?
In the construction industry, carbonation is referred to as ‘the process of chemical weathering by which minerals containing soda, lime, potash and other basic oxides are changed to carbonates by the action of carbon dioxide and water’.
The process is represented by the reaction below,
Co2 + H2O—— > H2C03
H2C03 + Cao ——> CaC03 + Hp
As represented by the above chemical reaction, carbon dioxide with water forms carbonic acid. This carbonic acid subsequently reacts with alkaline material such as lime to form calcium carbonate. In addition to carbonation, chloride ions in the atmosphere (sea-side structures) will also substantially affect concrete durability.
The above factors indicate that the protection of concrete and reinforcement from the ingress of water, CO2, chloride and other harmful gases (if any) is imperative to prolong the life of the structure (especially the parking decks) utilizing flexible PU coatings (rather than rigid epoxy coatings).
While PU deck coatings take care of carbonation on the floor concrete, it is important to consider the other areas exposed to concrete such as beams, columns, soft slab and restraining RCC walls. A simple paint is not sufficient to protect these structures from carbonation or chloride attacks and it is imperative that these are to be coated with anti-carbonation coatings.
Checklist for anti-carbonation coatings
- The thickness of anti-carbonation coating shall be at least 200 microns (anti-carbonation properties at around thickness of above 200 micron DFT i.e Sd value obtained anything above 50 m is sufficient to give necessary anti-carbonation properties.)
- The anti-carbonation coating is extremely durable (The durability of the coatings depends upon its stability against the harsh environment)
- It is capable of allowing moisture inside the concrete to breath-out (Generally, water-based coatings are more permeable to gases and water vapour. These coatings are formulated by using polymer dispersions. Water vapour permeability is a desirable property to allow water vapour to escape from the substrate. But, if the permeability is too high, carbon dioxide can diffuse from the atmosphere into the substrate easily. Hence there is a need for coatings with moderate gas permeability which can prevent Carbon dioxide from diffusing into the substrate while allowing moisture to escape.)
- Anti-carbonation coatings are flexible enough to take care of minor cracks in concrete (Obviously, cracked areas will allow CO to permeate into the concrete 2 and cause the failure)
It should be noted that there are numerous ways to mitigate the effects of carbonation deterioration, including thicker concrete covers, lower w/c ratios, treated reinforcement bars, anti-carbonation coatings or a combination of all. These measures are especially pertinent to consider when designing concrete structures in dense urban areas, which are subject to high levels of atmospheric carbon dioxide, humidity, and temperatures. Carbonation will only become more of a concern in the future as carbon dioxide increases in conjunction with urbanization, and the number of structural failures related will escalate
Written by Mr.B.M.Nagarajan (Director) Neocrete Technologies Pvt. Ltd
For any queries on anti-carbonation coating you can visit- neocrete.co.in