Corrosion Investigation of Reinforcing Bars in Pavements and Bridge Decks Part II: Chloride Penetration/Rebar Corrosion Mechanisms

Abstract

The main factors that influence the initiation and propagation of rebar corrosion in concrete are concrete properties, aggressive corrosive elements from the environment and concrete, and defects of the reinforcing material. The presence of chloride ion appears to be the dominant cause for rebar corrosion in concrete. Rebar corrosion is complex and the basic mechanisms of individual factors are not well understood because of the complex nature of physical and electrochemical factors and because of their interdependence. A visualization technique was developed for use in our laboratory for the determination of chloride ion distribution and concentration near the reinforcements in concrete. A galvanic current measurement technique was developed for estimating the corrosion rates of rebars in simulated concrete solutions and for investigating the effects of relevant parameters that may be responsible for macro-cell corrosion on rebars as a function of chloride ion concentration. The corrosion mechanism of rebars was explored by using the galvanic current measurement method as well as by using optical and scanning electron microscopy. The compounds that combine the properties of a corrosion inhibitor and a surfactant were explored for retardation of rebar corrosion. Organic compounds slowed the corrosion of rebars acting as an adsorption-type inhibitor. Organic compounds developed hydrophobic surfaces on concrete. Such an observation implies that salt solution may be prevented from penetrating the microcracks in concrete. Appendix I contains "Visualization of Chloride Distribution in Concrete," an abridgment submitted to the Transportation Research Board 70th Annual Meeting (1991). Appendix II contains "Rebar Corrosion under Simulated Concrete Conditions Using Galvanic Current Measurements," a paper submitted to the Transportation Research Board 70th Annual Meeting (1991).