Carbonation & Protection

Carbonation?in concrete is a natural process where calcium hydroxide Ca (OH)2 in the hydrated Portland cement paste combines with?carbon?dioxide (CO2) in the presence of moisture and produces calcium carbonate in subsequent reactions that produce Carbonic Acid and water.

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After the breakdown of the passivating layer around the steel due to the presence of the corrosive Carbonic Acid, sufficient moisture presence serves as a low-resistance electrolyte and sufficient oxygen to support the cathodic corrosion reaction. The rate of?carbonation?is strongly influenced by the concrete strength, permeability, relative humidity, depth of concrete cover, the curing period and exposure conditions.

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A good impermeable concrete having more concrete cover protects against the ingress of CO2. Alternatively, it is possible to formulate coatings which can prevent the diffusion of?Carbon?dioxide and thereby?protect?concrete structures from the detrimental effects of?carbonation?called “Anti?Carbonation?coatings”. Such 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.