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NACE International Standard TM0208 defines volatile corrosion inhibitor (VCI) as a chemical substance that acts to reduce corrosion by a combination of volatilization from a VCI material, vapor transport in the atmosphere of an enclosed environment, and condensation onto surface in the space, including absorption, dissolution, and hydrophobic ...
A fairly well-defined reaction front can often be observed in thin sections; ahead of the front the concrete is normal, or near normal. Behind the reaction front, the composition and the microstructure of concrete are modified. These changes may vary in type or severity but commonly include: Extensive cracking; Expansion
The effectiveness of a corrosion inhibitor depends on fluid composition and dynamics. Corrosion inhibitors are common in industry, and also found in over-the-counter products, typically in spray form in combination with a lubricant and sometimes a penetrating oil. They may be added to water to prevent leaching of lead or copper from pipes. [2]
Example of flat piece of concrete having dislodged with corroded rebar underneath, Welland River bridge across Queen Elizabeth Way in Niagara Falls, Ontario. The expansion of the corrosion products (iron oxides) of carbon steel reinforcement structures may induce internal mechanical stress (tensile stress) that cause the formation of cracks and disrupt the concrete structure.
The chemical reaction results in mineral hydrates that are not very water-soluble. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement was found by ancient Romans who used volcanic ash with added lime (calcium oxide).
Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
In sewerage areas where biogenic sulfide corrosion is expected, acid-resistant materials like calcium aluminate cements, PVC or vitrified clay pipe may be substituted to ordinary concrete or steel sewers. Existing structures that have extensive exposure to biogenic corrosion such as sewer manholes and pump station wet wells can be rehabilitated.
The increased chemical resistance to the ingress and harmful action of aggressive solutions constitutes one of the main advantages of pozzolan blended cements. The improved durability of the pozzolan-blended binders lengthen the service life of structures and reduces the costly and inconvenient need to replace damaged construction.
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