Cathodic Protection for steel inside concrete: The corrosion of steel in concrete occurs as a result of chloride attacks or carbonation of a concrete surface and incursion into the concrete until it reaches steel, which reduces concrete alkalinity. The presence of moisture and oxygen brings about practical corrosion and will continue until a complete deterioration of concrete takes place.
Some materials are used to paint the surface of concrete to a saturation point. Then this material will spread through the concrete to reach steel at speeds of 2.5–20 mm per day (depending on the porosity of concrete) up to the surface of steel by capillary rise, such as water movement; by penetrating concrete with water in cases of chloride attack; or through propagation by gas such as carbon dioxide when exposed to surface carbonation.
Therefore, when these materials reach the surface of steel, they form an isolation layer around the steel bar’s surface which will reduce the oxygen in the cathode area to the surface on the cathode and reduce the melting of steel in the water in the anode area, thereby delaying the process of corrosion and reducing its rate.
Next figure presents the influence of this cathodic protective coating on the surface in protecting the steel bars. These new advanced materials are used for new construction or for existing structures in which corrosion has started in steel bars. They are also used when corrosion is clearly present and complete repair to the damaged concrete surface is required followed by painting of the surface
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