Understanding the Corrosion and Remedial Measures to Control the Deterioration of Reinforcement Steel Bars by Modification in Their Chemistry and Application of Surface Coatings

Abstract

Corrosion of reinforcement bars embedded in structures near coastal areas is a serious problem and has been attributed to many premature distresses of structures. The passivity imparted by the alkalinity of the cement to reinforcement steel surface becomes ineffective when chloride concentration at the steel surface exceeds a critical threshold value. Under such a situation, the total loss of the steel thickness per unit area is negligibly small in comparison to penetration rate at certain susceptible part of the reinforcement bars. As a result of increase in stress intensity factor at the tip of localized pits formed on the surface of rebars, the tensile strength of the concrete structures which is mainly imparted by the steel reinforcement bars, is adversely affected and results in collapse of structures. Many techniques have been developed to control the corrosion problems associated with rebars. These include use of corrosion resistant alloys, corrosion inhibitors, cathodic protection and use of organic/metallic coatings on surface of steel bars. Amongst these techniques, the applications of surface coatings appear an effective and economical method to control corrosion of steel rebars. However, the efficacy and mechanism of their protective action are still matter of controversy and subject matter of studies all over the world. The present work is in continuation of our earlier studies published in different scientific journals where the above aspects had been addressed. This paper incorporates experimental results and literature review in understanding the corrosion and remedial measures to control the deterioration of reinforcement steel bars by modification in their chemistry and application of surface coatings. A brief historical background is given on development of reinforcement concrete structures. Various types of reinforcement bars used in construction industries and their merits and demerits are described. It has been established by the experimental proofs that the current scenario of protecting steel rebars used in chloride contaminated concrete, is not at all satisfactory. Amongst the protective coatings, metallic coated rebars appear to be more effective than organic based coatings. Causes and mechanism of deterioration of coated and bare steel rebars are discussed by providing experimental evidences.