Degradation of Powder Epoxy Coated Panels Immersed in a Saturated Calcium Hydroxide Solution Containing Sodium Chloride. Final Report. August 1992-July 1994.
Degradation of Powder Epoxy Coated Panels Immersed in a
Saturated Calcium Hydroxide Solution Containing Sodium
Chloride. Final Report. August 1992-July 1994.
Martin, J. W.; Nguyen, T.; Alsheh, D.; Lechner, J. A.;
Embree, E. J.; Byrd, W. E.; Seiler, J. F., Jr.
FHWA-RD-94-174; 44 p. October 1995.
Sponsor:Federal Highway Administration, McLean, VA
Available from: National Technical Information Service
panels; degradation; anodic blisters; cathodic
disbondment; crevice corrosion; epoxy-coated rebars;
infrared thermography; peel; wet adhesion; exposure;
Blasted-steel panels were coated with two commercial
powder epoxy coatings. Approximately half (80) of the
coated panels were scribed; while the other half
remained defect-free. All of the panels were immersed
in a saturated calcium hydroxide solution containing 3.5
percent sodium chloride maintained at either 35 or 50
DGC. None of the unscribed panels degraded after 3074 h
or immersion at 35 DGC; whereas, all of the scribed
panels degraded within 25 h after immersion, regardless
of the immersion solution temperature. Scribed panels
degraded in three ways: (1) anodic corrosion, (2)
cathodic disbondmant, and (3) wet-adhesion loss. Anodic
corrosion was attributed to localized crevice corrosion.
The rate of anodic growth depended on the immersion
solution temperature, but it did not depend on the type
of coating or coating thickness. Liquid-filled blisters
formed above the anodic sites after approximately 1000 h
of immersion at 35 DGC. The chloride concentration of
the blister fluid was four times greater than that of
the bulk solution and its pH was around 5. The rate of
cathodic disbondment was not affected by the type of
coating or coating thickness, but it was greatly
affected by an increase in the temperature of the
immersion solution. Wet-adhesion loss was not affected
by coating thickness, but it does depend on the type of
coating and immersion temperature. Also, even though
the wet-adhesion strength of the two coatings differed
by a factor of five, the rate of corrosion for the two
coatings was not significantly different.