Repair and Rehabilitation of Bridge Components Containing Epoxy - Coated Reinforcement


INTRODUCTION AND RESEARCH APPROACH


NTRODUCTION

Early research by the National Bureau of Science (now National Institute of Standards and

Technology) and the Federal Highway Administration indicated that reinforcing bars that were

cleaned and then coated with select powdered epoxies using an electrostatic spray process

performed well in salt contaminated concrete (1). Such coated rebars were determined to be

resistant to corrosion, such that premature deterioration of concrete due to the pressures

generated by expansive corrosion products was minimized.





Epoxy resins are thermosetting poly-addition polymers and have, for the most part, been reported

to have good long-term durability in concrete and to be resistant to solvents, chemicals and water

(2). In addition, epoxy resins generally possess the necessary mechanical properties for such

service including good ductility, small shrinkage upon polymerization and good heat resistance

(3). Further, test results have indicated that the oxygen and chloride ion permeabilities of epoxy

coatings are relatively low, even in worst case exposures (1, 2, 4). Epoxy coatings are, on the

other hand, permeable to moisture (water); and it has been known for years, although not

highlighted within the highway community, that the adhesion of epoxy based coatings to steel is

reduced upon exposure to moisture (5). Thus, the fundamental attribute by which an epoxy

coating affords corrosion protection to substrate steel arises from its barrier nature which retards

ingress of chloride ions and oxygen. Also, by increasing the electrical resistance between

neighboring coated steel locations, these coatings reduce the magnitude of macroscopic


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