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Carbonation of concrete is a type of chemical corrosion that affects concrete. The process by which CO2 in the air penetrates into concrete, reacts chemically with its alkaline substances to form carbonates and water, thereby reducing the alkalinity of the concrete, is known as concrete carbonation, or neutralization. The chemical reaction involved is: Ca(OH)2 + CO2 = CaCO3 + H2O. During the hydration process, cement produces a large amount of calcium hydroxide, which fills the pores in concrete with a saturated solution of calcium hydroxide. This alkaline environment provides good protection for the steel rebar, causing insoluble compounds such as Fe2O3 and Fe3O4 to form on the surface of the rebar; this layer is known as a purification film. Carbonation reduces the alkalinity of concrete; when carbonation penetrates beyond the concrete’s protective layer, in the presence of water and air, the concrete loses its ability to protect the rebar, causing the rebar to start rusting. It can be seen that concrete carbonation generally does not directly lead to a deterioration of its properties. In the case of plain concrete, carbonation even has the effect of enhancing its durability. However, for reinforced concrete, carbonation reduces the alkalinity of the concrete and increases the amount of hydrogen ions in the pore solution; as a result, the protective effect of the concrete on the steel reinforcement is weakened. By the sea, due to the high concentration of chloride ions in the air, the penetration of these ions greatly accelerates the corrosion of concrete structures. Its mechanism of action is as follows: ① Intrusion of chloride ions: As moisture penetrates, the neutralization of concrete occurs due to the penetration of carbon dioxide and chloride ions. ② Reinforcement corrosion: Reinforcements are corroded due to water, moisture, chloride ions, etc. that penetrate them. Even without neutralization, the phosphorus contained in the surface layer of steel bars can cause them to corrode. ③ Crack formation: Cracks appear in the concrete due to the corrosion of the rebar and its volume expansion (by 2.5 times). ④ Reduced strength: Corrosive substances penetrate further from the cracks, accelerating the corrosion of the rebar and causing volume expansion, thereby reducing the strength of the concrete. In short, corrosion reduces the strength of concrete structures, thereby significantly shortening their service life. The use of anti-corrosion coatings on concrete structures is an effective measure to prevent corrosion, and it can serve the following purposes: ① It forms a protective barrier layer on the surface of the concrete, preventing corrosive agents such as chloride ions and carbon dioxide from penetrating the concrete and causing corrosion. ② It enhances concrete surfaces that are carbonized, porous, and cracked. ③ Coating can give concrete structures a color that matches the surrounding landscape.