Thangavel , K. (2004) The threshold limit for chloride corrosion of reinforced concrete. Corrosion Reviews , 22 (1). pp. 55-70. ISSN 0334-6005

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Of the annual production of steel rebars, a substantial portion of 2 million tons of steel rods are used as reinforcements in RCC structures. Due to rebar corrosion, often more than the cost of construction is being spent on the repair of bridge structures in ports and industrial areas. Especially some RCC structures have to be repaired within 2 or 3 years of construction. In the years to come, if rebar corrosion problems continue, nearly 10 to 15% of the cost of annual construction will be spent on repairs and renovations. In India, the cost due to rebar corrosion problems was estimated at Rs. 100 crores being spent annually by the building and construction industry and the likely potential saving by application of proper corrosion control methods may be estimated at Rs.20 crores. Chloride-induced corrosion of reinforcing steel is recognized as a primary factor contributing to the deterioration of concrete structural elements. Moisture, oxygen dissolved in moisture and aggressive ions (particularly chlorides) are the three important factors necessary to induce corrosion of rebars. If oxygen and water are eliminated completely then corrosion will be arrested completely. However, it is normally impossible to eliminate oxygen or moisture from the structural elements because these species are inherently present in the structure. But it is possible to remove the aggressive ions (particularly chlorides) from the existing structures by a desalination process or by adding suitable chloride scavengers. In National Highway Bridges and Concrete Structures, if the chloride content exceeds the threshold value, suitable preventive measures may be implemented to enhance the service life of bridges and structures. The objective of this review article is to analyze the critical chloride content in concrete structures exposed to various environmental conditions and to correlate with corrosion conditions of embedded steel. From the correlatio~l an attempt has been made to predict a universal threshold limit of chloride to initiate rebar corrosion. From this critical analysis of the threshold limit of chloride, it is concluded that the CI-/OH- ratio is not the appropriate index to predict rebar corrosion under all conditions. Other environmental parameters like alkalinity, oxygen availability and impermeability do play a significant role besides the CI-/OH- ratio. Hence it is impossible to predict a universal threshold limit of chloride to initiate rebar corrosion in National Highway Bridges and Concrete Structures. Depending upon the environment the threshold limit will vary.

Item Type: Article
Subjects: Corrosion Science and Engineering
Depositing User: ttbdu cecri
Date Deposited: 29 Feb 2012 11:29
Last Modified: 29 Feb 2012 11:29

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