Epoxy-coated Rebars

Europe s first rebar coating facility was opened in Cardiff in 1987. 

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Coated reinforcement MacroceU formation may be important in the case of epoxy-coated rebars (Section 15.4) in chloride-contaminated concrete if there are defects in the coating and the coated bars are electricaUy connected with uncoated passive steel bars in deeper parts of the structure. Small anodic areas are created at the defect points of coated rebars in contact with chloride-contaminated concrete, while the uncoated passive rebars provide a cathodic surface of much greater size. In these situations the macroceU can result in considerable anodic current densities and can significantly accelerate the attack on corroding sites. This is why coated rebars should be electrically isolated from uncoated bars. 

K. C. Gear, Y. P. Virmani, Corrosion of non-specification epoxy coated rebars in salty concrete , Corrosion/83, NACE, Houston, Paper No. 114, 1983. 

At present, epoxy-coated rebar is the most common corrosion protection system and is used in 48 states. At present, there are nearly 20,000 bridge decks using fusion-bonded epoxy-coated rebar as the preferred protection system. This amounts to nearly 95% of new deck construction since the early 1980s. 

The data from the Concrete Reinforcing Steel Institute (CRSI) shows that more than 3.6 billion kg (4 million tons) of epoxy-coated rebar (150 million m reinforced concrete) were used as of 1998. A significant amount of the epoxy-coated rebar was used in bridge decks. Over time, the formulation of epoxy has been modified to achieve better performance of the epoxy coating. 

Multiple Protection Systems Corrosion inhibitors are used in multiple corrosion protection systems in conjunction with epoxy-coated rebars and low-permeability concrete, in particular, for marine applications. Epoxy-coated seven-wire strands are not commonly used for prestressed concrete bridge members. Corrosion inhibitors are used in place of coated seven-wire strands in the prestressed highway construction industry. 

With constant updates in the American Association of State Highway and Transportation Officials (AASHTO) and American Society for Testing and Materials (ASTM) specifications for epoxy-coated rebar, this corrosion protection system will continue to improve. The specifications involve all aspects of fabrication of epoxy-coated rebar. All these will result in improved performance of epoxy-coated rebar and more durable new concrete stmctures. 

Epoxy coated rebars present particular problems to determining the corrosion condition of the Steel. In the first place the bars are electrically isolated from the concrete except at areas of damage. The size and locations of the areas of damage are obviously unknown. Attempts to carry out reference electrode potential surveys and linear polarization measurements have therefore been unable to come up with definitive criteria for corroding and non-corroding areas. The other problem is that the bars are isolated from each other, therefore a connection must be made to each bar measured to be sure that there is electrical contact. 

The protection system of choice on highway bridges in North America for a ressive chloride conditions continues to be fusion bonded epoxy coated reinforcement (FBECR). It was first installed in a bridge deck in Philadelphia in 1973 (Manning, 1996). It was estimated by the EHWA that 100 million sqnare feet (10 million m ) of bridge deck on the US federal-aid highway system contains epoxy coated rebar up to 1889 (Virmani and Clemena, 1998). 

Epoxy coated rebars will corrode eventnally if the chloride level builds up to a high enough level at the rebar surface and there is moisture and oxygen to fuel the corrosion reaction. However, they should take longer to start corroding than nncoated reinforcing steel and then should corrode more slowly than nncoated rebars. 

Advantages and limitations of fusion bonded epoxy coated rebars... 

United States and Canada also apply them. Membranes come as two main types, a liquid that solidifies in place, and a sheet that is stuck to the concrete (see Section 5.3.3). The main problem with waterproof membranes is similar to that of epoxy coating rebars they must be applied without defects. Defects can occur as blow holes, penetrations or mechanical damage to the liquid applied types, or cuts, tears, bad joins or perforations in the sheets. Either type of membrane can be damaged by the overlay of asphalt, either by its heat or mechanical damage from the aggregate particles. 

The advantage of silane type penetrating sealers is that they are inexpensive compared with cathodic protection, epoxy coated rebars or other preventative or active treatment methods. If penetration is good then there is no maintenance... 

Epoxy coated rebars will corrode eventually if the chloride level... 

Figure 9,4 Schematic t>f corrosion between anodes and cathodes at defects on an epoxy coated rebar.

There are certain disadvantages to using epoxy coated rebars. Their insulating properties mean that they inhibit the use of electrical and electrochemical techniques. Taking half cell potential measurements on epoxy coated rebar is very difficult. Since only small areas of the steel are exposed they are not nece.ssarily in an alkaline environment as the... 

In the field one must locate the bar and drill or core to make an electrical connection. If there is good continuity between the bars, one connection can allow for testing at multiple sites. However, in the case of poor continuily, e.g., epoxy-coated rebars, multiple connections will be needed. 

Effectiveness of Epoxy-Coated Rebar Final Report to Pennsylvania Department of Transportation, Project No 94-05. 

Performeince of Epoxy-Coated Rebars in Bridge Deck FHWA-RD-96-092. 

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