a mill or coating facility usually by a fusion-banding process as a result 

 of an irreversible heat--catalyzed chemical reaction. The careful applica- 

 tion of a fusion-bonded or electrostatically applied epoxy coating has 

 produced virtually pinhole-free coating protection of the steel bars from 

 the moisture, chlorides and other contaminates that may be in or enter the 

 concrete. 



Fusion-bonded epoxy coatings have had a short but successful history of 

 protecting reinforcing steel against corrosion in a highly alkaline and 

 chloride contaminated environment. The fusion-bonding epoxy coating if 

 formed by combining an epoxy resin with appropriate curing agent, pigments, 

 catalysts, flow control agents, etc. to achieve the desired application and 

 performance characteristics. 



Fusion bonded means that the coating achieves adhesion as a result of 

 a heat-catalyzed chemical reaction. When a fusion-bonded coating is 

 exposed to heat, a chemical reaction occurs; and sufficient heat must be 

 supplied for a given amount of time to allow that chemical reaction to 

 reach completion. The reaction is irreversible. Unlike thermoplastic 

 coatings, if heated after the coating is cured, it will not soften. The 

 material is applied to rebars at a mill away from the job site and is 

 therefore not weather dependent as is coated under controlled conditions. 



The coating system is composed of four parts: surface preparation, 

 material selection, application, and cure. Surface preparation requires 

 sandblasting to white metal since the surface must be completely clean and 

 possess an anchor pattern. It is desirable that both physical and chemical 

 adhesion be obtained. Materials selection can be made from those commer- 

 cially available that are selected in accordance with ASTM Standard D3415. 

 Application is accomplished by heating the rebar with a noncontaminating 

 heat source to approximately 232° Celsius (450 Farenheit) but as recom- 

 mended by the manufacturer. The resin application should be by electro- 

 static deposition to obtain an even coating of 0.13 to 0.26 millimeter (5 

 to 10 mils) thick. Heat is continued until the gel time has been satisfied. 

 The bars are then cooled, followed by an electrical holiday inspection. 

 Following this type of coating application rebars can be transported to job 

 site and bent to necessary configurations with reasonable ease. 



(c) Prevention of Cracks . Cracks allow carbonation penetra- 

 tion and are also a route for oxygen to the surface of the steel. Cracks 

 may further play a part in electrolytic cell formation in the concrete. 



(d) Elimination of Voids at Steel Surface . Studies, indicate 

 that steel corrosion is associated with a void at the steel surface. This 

 can be diminished by mix design and thorough consolidation. In posttension- 

 ing, grouting procedures should be adopted which will prevent or minimize 

 these voids . 



(e) Proper Grouting of Ducts in Posttensioned Concrete . 

 Proper grouting is essential for corrosion protection and prevention of 

 bursting during freezing. 



(3) Abrasion Resistance . The abrasion resistance of concrete is 

 defined as the "ability of a surface to resist being worn away by rubbing 

 and friction." Research to develop meaningful laboratory tests on concrete 



107 



