Adhesion Loss and Corrosion-induced Delamination of Fusion-Bonded Epoxy Coated Steel in Alkaline Electrolytes
Tinh Nguyen, Jonathan W. Martin
Fusion-bonded epoxy is used extensively for increasing the service life of steel-reinforced concrete structures. However, field observations have reported premature corrosion of fusion bonded epoxy-coated reinforcing bars used in marine concrete environments, leading to severe cracking and spalling of the reinforced concretes. This study was aimed to provide an understanding of the degradation of fusion bonded epoxy-coated steel exposed to salted concrete environment. Grit-blasted steel panels were coated with two commercial fusion-bonded powder epoxy coatings at two thicknesses. Half of the coated panels were scribed, the other half were non-scribed. The panels were immersed in a saturated calcium hydroxide aqueous solution (pH=12.5) containing 0.6 mole/liter NaCl maintained at either 35 °C or 50 °C. Degradation was characterized and followed by infrared thermography, wet adhesion, and microscopic and analytical chemical techniques. Unscribed panels exhibit only water-induced adhesion loss, most of which is recovered after drying. However, in addition to the water-induced adhesion loss, scribed panels show two modes of failure: anodic blistering near the scribe mark and cathodic delamination around the anodic blisters. Anodic blistering is attributed to localized crevice corrosion under the coating followed by blistering via an osmotic pressure mechanism. Cathodic delamination is probably induced by the alkaline cathodic reaction products, and water-induced adhesion loss is due to the presence of a water layer at the coating/steel interface. Thickness of the water layer at the fusion-bonded epoxy coating/substrate interface was also measured and will be discussed.
Adhesion Society Meeting
February 15-18, 2009
building technology, adhesion, coatings, corrosion, electrolyte, steel, concrete
and Martin, J.
Adhesion Loss and Corrosion-induced Delamination of Fusion-Bonded Epoxy Coated Steel in Alkaline Electrolytes, Adhesion Society Meeting, Savanah, GA
(Accessed December 10, 2023)