What is Anti Carbonation? Carbonation means chemical conversion to a carbonate. Carbonation is a term which is widely used in beverage industry. It refers to the impregnation of Carbon dioxide into a fluid. But in construction industry, carbonation is referred to as the process of chemical weathering by which minerals containing soda, lime, potash are other basic oxides are changed to carbonates by the action of Carbon dioxide and water.
Effects of Carbonation on concrete structure: The action of atmospheric carbon dioxide on lime mortars and cement concretes has been known for centuries. Roman plasters used air hardened lime, which gained strength due to the reaction of carbon dioxide with calcium hydroxide formed an interlocked mass of calcium carbonate. But, traditionally concrete is reinforced with steel to increase tensile strength. Concrete protects steel from corrosion by forming a “passive layer” because of very high alkalinity induced by cement and other minerals. But many concrete structures are exposed to atmospheric carbon dioxide emitted from various sources. In presence of moisture / water and as describe in the above reaction, atmospheric carbon dioxide diffuses slowly through the concrete and the process of carbonation is initiated. Due to the process, the pH of concrete slowly turns acidic and destroys the passive layer protecting the reinforcing steel bars. Once the passive layer is destroyed, rusting of steel bars begins. Carbonation is a slow process but is detrimental to concrete structures as life expectancy of concrete structures are between 50 - 100 years.
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| Speed and depth of carbonation on CC |
It is possible to formulate coatings which can prevent the diffusion of Carbon dioxide and thereby protect concrete structures from the detrimental effects carbonation. This article discusses the functionality of coatings which can be called “Anti Carbonation coatings”. Generally, water based coatings are more permeable to gases and water vapor. Typically, these coatings are based on polymer dispersions. Water vapor permeability is a desirable property to allow water vapor to escape form 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 surface treatments that have a high resistance to carbon dioxide. They protect concrete from carbonation by acting as a carbon dioxide barrier. The elastic properties of some manufactures products allow for an amount of movement and crack bridging.
Anti-carbonation coating helps to provide a protective barrier to the concrete structures not only for carbonation but also to prevent the ingress of chlorides and moistures. Acrylic, silicone enhanced, epoxy and polyurethane are most suitable for such coatings. Considering extreme environment all the RC structures should be protected with an aliphatic acrylic coating to increase their service lives.
Thanks to google, doc88, Mideng.in, from where the details were taken.
