Epoxy-coated reinforcement , concrete steel

Virmani, Y.P., Clear, K.C. and Pasko, T.J. (1983). Time to Corrosion of Reinforced Steel in Concrete Slabs, Vol. 5, Calcium Nitrite Admixtures or Epoxy Coated Reinforced Bars as Corrosion Protective Systems, FHWA-RD-83-012, FHWA, US Department of Transportation, 71. 

K. C. Clear, Effectiveness of epoxy-coated reinforcing steel , Concrete International, 1992, 5, 58—62. 

Epoxy coatings cost approximately 4.7-5.3/l while antifoulants are more expensive at 11.8-21.1/1. Environmental regulations have led to decreased amount of chemicals released from industrial installations along waterways, especially corrosives such as chlorine. The materials of construction for some water structures have also changed. Piers and docks are no longer constructed with wood, but instead are constructed with steel-reinforced concrete. To improve the lifespan of the structure and prevent corrosion of reinforcing steel, fusion-bonded epoxy-coated reinforcement or corrosion-inhibiting admixtures are sometimes utilized in the concrete mix. 

Steel reinforcements in concrete, being passive, are noble in potential with respect to steel outside the concrete that is galvanically coupled to the reinforcements. The measured potential difference is in the order of 0.5 V [62]. The effect of large cathode area and small anode area has caused premature failures of buried steel pipe entering a concrete building [63]. In this situation, use of epoxy-coated reinforcements (to coat the cathode) or insulated couplings should prove beneficial. 

The corrosion of buildings and concrete structures is a major area of concern to engineers and builders. Repairs to concrete structures are essential to maintain their integrity. The design of the structure should have sufficient accessibility for repairs as shown in Fig. 8.47. During repair, spalled concrete is taken out ensuring that the salts have been sufficiently removed and the steel is cleaned. The concrete is replaced by a suitable mortar or concrete with proprietary additives. It has been observed in recent years that epoxy coated reinforcement provides an excellent protection against reinforced concrete corrosion. 

The MDB is a two-story, steel-framed building with thick, reinforced-concrete floors and most interior walls made of concrete and foam-core sandwich panels. Explosion containment rooms have 2-foot-thick reinforced concrete floors, walls, and ceilings. Because concrete is a porous material capable of absorbing agent, all concrete surfaces in the JACADS process areas were sealed with an epoxy coating. A total of 134,153 square feet of concrete will require decontamination (U.S. Army, 1999d). 

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. 

The cost of various techniques can only be given very roughly, and any estimate will be incomplete, since the actual cost will vary from one application to another. Furthermore, different types of prevention mechanisms are not directly comparable. Beyond this, it can be said that with respect to normal carbon-steel reinforcement, use of galvanized and epoxy-coated bars costs about twice as much, and the cost of stainless-steel reinforcement is about 5 to 10 times higher. The use of nitrite inhibitors in higher doses costs approximately 30 /m of concrete (volume). Coatings may vary from 7 to 50 /m of concrete surface, hydrophobic treatment costs about 10 /m. Cathodic prevention varies from 50 to 100 /m. ... 

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. 

Important areas of use of epoxy resin powders include the interior and exterior coating of pipes, fittings, fixtures, filter plates, and steel bars for reinforced concrete, as well as the electrical insulation and the encapsulation of electronic components. 

Since the maximum voltage that can be generated with zinc anodes is extremely unlikely to generate hydrogen embritdement, galvanic systems have been used to protect prestressed concrete members. They are also used on fusion bonded epoxy coated steel reinforced piles as the effects of electrical discontinuity between bars is unlikely to lead to significant stray current induced corrosion as the currents and potentials are low. 

There are several methods that can be used to control corrosion of steel reinforcements in concrete. First, the design of the structure should provide for drainage of salt-containing waters away from the reinforced concrete. Second, concrete of adequate thickness, high quality, and low permeability should be specified to protect the reinforcements from the environment. Third, chloride content of the concrete mix should be kept to a minimum. For further protection, the steel reinforcements can be epoxy-coated. In many parts of North America, steel reinforcements used in bridge decks are now epoxy-coated as a standard construction procedure. Cathodic protection is also being used, both with impressed current anodes and with sacrificial anodes [61]. (See Chapter 13.)... 

Concrete is extremely stiff and good in compression, but quite poor in tension. Steel rebar reinforcement is normally used to make a stronger structure, but because steel is subject to atmospheric corrosion, it has to be shielded with a relatively thick protective layer of concrete, which with time, is removed by weathering and erosion, eventually exposing the steel to attack. Carbon fiber has very good corrosion resistance and would not be affected by any alkalis in the cement. Hence it should be possible to utilize a carbon fiber composite such as carbon fiber/epoxy pultruded rods that would only require a relatively thin coating of concrete. Alternatively, carbon fiber can be incorporated directly into the concrete mix [9]. 

Concrete should not be relied upon as an electrical insulator. Reinforcing bars should be coated with, for example, epoxy resin. They should not be connected to building steel and should not be allowed to form a continuous path along the length or the width of the building. The joints between sections of precast reinforced concrete should be insulated. 

Walkways are fabricated with FRP grating. All concrete surfaces in the cell room are constructed with fusion-bonded epoxy coated steel reinforcing bars, and Type V... 

Yeomans, S. R. (1991). Investigations of galvanized and epoxy coated steel reinforcement in concrete. I6th Int. Galv. Conf., EGGA, London, GBl/1-5. 

Rebars are polymer fibre reinforced-concrete composites, and they are used as primary structures. It is estimated that replacement of steel reinforcing bars by non-corrosive polymer fibres, i.e., by Kevlar or carbon fibres (which gives rise to Kevlar or C-composite bars) for concrete structures produces structures with one-quarter the weight and twice the tensile strength of the steel bar. It is known that, corrosion of steel reinforcement from carbonation or chloride attack can lead to loss of the structural integrity of concrete structures, and such a danger is non-existent for rebars. Thermal expansion coefficient (TEC) values of these fibres are closer to concrete than that of steel, which provides an another advantage and they have the same surface deformation patterns as the steel bars. In addition, they can provide more economy than epoxy-coated steel bars. 

While ordinary carbon or alloy steel is used most commonly for reinforcement or prestressing of concrete, stainless steels have been used in construction of piers with special service requirements [/] or in critical areas on other structures [2]. Other materials such as reinforced pktstics and nickel-copper alloy 400 have been used also to a limited extent or have been proposed for use as reinforcement for concrete in piers and docks. Stainless steel clad carbon steel is a relatively new development and its use for reinforcement of marine structures currently is being evaluated. Epoxy-coated carbon steel reinforcement also has been used successfully in many marine applications, but some failures have occurred. 

Nuclear coatings are formulated to seal and protect concrete, concrete block and steel surfaces. The most commonly used coating types are the amine and polyamide cured epoxy systems. The solids, by volume, can vary from 50 to 100% with fillers or reinforcement fibers usually added so that the coating can perform a wide variety of functions. Reasons for their wide use are that they bond tenaciously to a variety of substrates they cure to a hard smooth finish which results in superior decontamination qualities and, most importantly, they perform satisfactorily in Ciass 1 and 2 service. 

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