Role of Concrete and Steel Surface on Performance of Structures

Abstract

Out of various types of applications of steels, their use in concrete reinforcement is perhaps in the largest proportion. The steels in contact of concrete is expected to be quite protected from corrosive attack. This is owing to the alkalinity provided by cement. The slurry of cement around the steel provides a pH of 10.5-11.0 which is cons-idered to be very favourable condition for the formation of protective oxide layer on the steel surface. The prot- ective condition, however, is disturbed once chloride, sulphate, metal cations, moisture and oxygen reach near the steel surface. Chloride is a well known activator of uniform and localized corrosion. Similarly sulphate, although not directly involved in the corrosion process but helps in destabilizing of concrete structures and allows the penetration of oxygen and moisture near the reinforcement steel rebars surfaces. The above mentioned impurities in concrete structures are encountered either through the contaminated water used to prepare the cement slurry or due to the diffision of the ions from the surroundings through the pores of the concrete. In many instances, chlorides are intentionally added in cements to enhance their curing rate. Due to corrosive attack of the above ingredients, catastrophic failures of buildings, bridges and other structures have been reported. To combat the problems-of corrosion, different types of techniques such as addition of corrosion inhibitors in concrete mixtures, application of galvanized coatings on steels surface, use of non-metallic coatings, applications of paints / coatings to provide outer protective layer on the reinforcement concrete structures and use of corrosion resistant steels are being employed.