ALTERNATE APPROACH FOR LIMITING CHLORIDES IN CONCRETE MIX

Abstract

Chloride is considered as an important parameter in concrete as it accelerates corrosion of reinforcement, which is one of the main causes of deterioration of reinforced concrete structures. Different Codes describe different limits for either one or more constituents of concrete. The Indian Standard 269 – 2013 “Ordinary Portland cement, 33 grade – fifth revision” prescribes a limit of total chloride content in cement used in prestressed concrete structures and long span reinforced concrete structures, while Indian Standard 456- 2000 ”Code of practice for plain & reinforced concrete – fourth revision” imposes a limit of total amount of chloride (as Cl) in the concrete at the time of placing, without any mention about the methodology of determining the total amount of chloride (acid soluble or water soluble). Further, Italian standard prescribes limit for aggregates. American Concrete Institute (ACI) publication has given a new direction to the study of chloride induced corrosion by taking limit of water soluble chloride in concrete mix as the criteria for evaluation of risk of corrosion. This novel & improved approach which avoids confusion in interpreting specifications and results, was applied to some concrete ingredients samples received from a Nuclear Power Project of coastal region of India. The alternate approach suggested in this Paper does away with te laborious process of casting cubes and and waiting for twenty eight days before test could be carried out. Where different quarries of coarse and fine aggregates have been identified, the alternate approach can at the initial stage itself rule out of the possibility of casting cubes of different grades of concrete mixes, resulting in time saving and economy.