Mechanism of Corrosion Promotion in RC (Reinforced Concrete) Structures

basic information

■The thickness of the concrete surrounding the rebar (known as cover) acts as a diffusion barrier against corrosion factors such as oxygen, water, and salt. ■Concrete has a strong alkaline nature with a pH of about 12, which allows for the formation of a passive film on the surface of the rebar. ■When using sea sand containing a large amount of salt, in environments where de-icing agents are spread in cold regions, or in coastal areas where salt is abundantly carried by the wind, the salt that permeates the concrete can destroy the passive film on the surface of the rebar, making it more susceptible to corrosion. ■Carbon dioxide in the atmosphere diffuses into the concrete and reacts with calcium hydroxide, which forms a high alkaline environment, resulting in carbonation (see the following equation). This carbonation reaction progresses from the surface of the concrete inward, and when it reaches the rebar, the passive film that was maintained under high alkalinity is destroyed, leading to rusting of the rebar. ■For corrosion of piping supports, Mitsui Sumitomo Metal Mining's copper alloy corrosion prevention materials are recommended. For details, please contact us.

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Applications/Examples of results

Reinforced concrete structures use steel bars to compensate for the disadvantage of having high compressive strength but low tensile strength in concrete. However, the steel bars are exposed to corrosive environments such as the use of sea sand, seawater, and salt from de-icing agents, as well as carbonation of the concrete. When the steel bars corrode, the corrosion products expand by about 2.5 times, leading to cracking and spalling of the concrete. As a result, the strength of the structure may decrease, potentially leading to dangerous conditions. Therefore, corrosion prevention measures for steel bars are essential for the long-term safe use of reinforced concrete structures (RC structures), which are part of social infrastructure.