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Modes and Mechanisms of Degradation of Epoxy-Coated Reinforcing Steel in a Marine Environment.


pdf icon Modes and Mechanisms of Degradation of Epoxy-Coated Reinforcing Steel in a Marine Environment. (544 K)
Nguyen, T.; Martin, J. W.

Durability of Building Materials and Components 7th. Volume 1. Chapter 51. 1996, E&FN Spon, London, England, Sjostrom, C., Editor(s), 491-502 pp, 1996.

Keywords:

coatings; concrete solution; corrosion; degradation; marine; rebars; steels

Abstract:

Blasted-steel panels were coated with two commercial powder epoxy coatings at two thicknessess. half of the coated panels were scribed; the other half remained free of defects. The panels were immersed in a saturated calcium hydroxide aqueous solution containing 3.5% sodium chloride maintained at either 35 or 50DGC. Degradation was quantified by infrared thermography, wet adhesion test, and microscopic and analytical techniques. Unscribed panels exhibited only water-induced adhesion loss, but scribed specimens degraded by anodic blistering and cathodic disbondment, in addition to water-induced adhesion loss. Anodic blistering was attributed to localized crevice corrosion under coating followed by blistering via an osmotic pressure mechanism. Cathodic disbondment was caused by the alkalinity of the corrosion products at the cathodic sites. Water-induced adhesion loss was due to the presence of multiple layers of water at the coating/steel interface.