June 2015

Use And Handling Of Epoxy-Coated Reinforcing Steel

David Mcdonald, Managing Director, Epoxy Interest Group Of CRSI

Reinforcing steel in concrete is protected against corrosion (rusting) by the high pH of concrete as this alkalinity results in a very thin protective film being formed on the steel surface. Salts may penetrate the concrete and disrupt this protective layer, resulting in corrosion. As the steel corrodes, it expands, cracking the concrete.

In the 1960s, there was a sudden increase in the use of de-icing salts and bridge decks were exhibiting significant distress within 10 years of construction. In response, the National Bureau of Science undertook work for the Federal Highway Administration (FHWA), evaluating various coatings to protect reinforcing steel against corrosion. The first bridge constructed using epoxy-coated reinforcing was built in 1973 in Pennsylvania. Since then, over 80,000 bridges and many other structures have been constructed using this material and approximately 10 percent of all reinforcing steel is epoxy-coated. Epoxy-coated reinforcing steel is used in marine environments to protect against seawater and in inland environments to protect against de-icing salts.

Based upon a review of the past 40 years of use, bridges built with epoxy-coated reinforcing bars in areas exposed to de-icing or marine salts are predicted to last from 75 to 100 years without major costly repairs.

The manufacture of epoxy-coated reinforcing steel is covered by several ASTM standards including ASTM A775, A934, and A1055 for reinforcing bars and A884 for welded wire fabric (mesh). Bars manufactured to ASTM A775 are recognized by their green color, while bars manufactured according to ASTM A934 are either purple or grey. Bars manufactured according to ASTM A1055 are generally yellow. Welded wire fabric, covered by ASTM A884, may be green or purple, based upon the purchase specification. 

All standards require that manufacturers of epoxy-coated steel take steps to properly prepare the bars prior to coating, ensure that contaminants are not present, and confirm that the coatings are fully cross-linked and bonded to the bar. Most of the manufacturing operations are certified by the Concrete Reinforcing Steel Institute (CRSI).

Just like any material used on a jobsite, appropriate handling of epoxy-coated reinforcing steel is required. Handling and storage requirements for epoxy-coated reinforcing steel may be included in contract documents by referencing ACI 301 or ASTM D3963 or within individual agency specifications. Coating damage will affect the long-term performance of the coated reinforcing bar; however, even steel with damaged coatings provide better protection than uncoated bars. During coated bar manufacture, the holes that cannot be seen with the eye, termed holidays, are monitored and must be less than one per foot, and all visible damage must be repaired. General handling and storage requirements are outlined below. 

• Bars should be lifted using a spreader bar or strong-back with multiple pick-up points to minimize sag. During sagging, steel bars may rub on each other, causing coating damage. Nylon or padded slings should be used, and at no time should bare chains or cables be permitted. Steel should be unloaded as close as possible to the point of concrete placement to minimize rehandling, and at no time should coated steel bars be dragged, as this may result in coating damage on bar ribs.

• Bundles of coated steel should be stored on suitable material, such as timber cribbing, and should not be stored directly on the ground. Coated and uncoated steel should be stored separately. If the steel bars are to be exposed outdoors for more than 30 days, they should be covered with a suitable opaque material that minimizes condensation.

• Reinforcement should be placed on supports coated with non-conductive material, such as epoxy or plastic bar supports, and these should meet Class 1A, as defined in the CRSI Manual of Standard Practice. The coated steel should be tied using a coated tie wire. This wire is typically 16.5 gauge or heavier and black annealed. When used with epoxy-coated reinforcing bars it is typically coated with PVC.

• Coated bars may be cut using power shears or chop saws and cut ends should be repaired using a two-part epoxy. Bars must not be flame cut. Bars may only be bent at the jobsite with the permission of the engineer responsible for the particular project, and this should be documented. If bending is to be conducted, it must be conducted at ambient temperatures. 

• Bars should only be welded with the permission of the engineer responsible for the particular project. Stands or rails used for concrete placement machines should not be welded to the epoxy-coated steel. After welding, all exposed steel should be repaired using a two-part epoxy.

• Prior to concrete placement, all coating damage should be repaired using a two-part epoxy approved by the coating manufacturer. The epoxy-coated reinforcing industry does not recommend single component spray can systems, as these do not provide adequate coating thickness unless many coats are provided. Repair materials should be obtained from the reinforcing steel fabricator.

• Damaged coating should be prepared using a small wire brush that removes rust and other contaminants. Repairs should be strictly conducted according to the written instructions furnished by the patching material manufacturer. Repair materials should be mixed according to the manufacturer’s directions and should be used within the specified pot life.

Summary
Epoxy-coated reinforcing steel will provide long-term protection against corrosion and its life is maximized by reducing coating damage. It should be installed with care to minimize coating damage using common-sense practices, outlined above. If damage to the coating is observed, it should be repaired using a two-part epoxy. By following proper handling and storage, maximum life expectancy can be achieved.