Rebar is often coated to combat the expansive pressures created by oxidation when steel begins to rust while incased in concrete. Because ferric oxide (rust) has seven times the volume of the original steel, rusting will create tremendous pressures in surrounding concrete. This can result in cracking of the concrete, disbonding between the bar and concrete and may eventually lead to spalling of large chunks of concrete. Left unchecked, rusting reinforcing bar can quickly render a structure unsafe.

A secondary concern addressed by coating is cosmetic appeal. The appearance of rust stains weeping through the cracks in the concrete can be particularly objectionable in visible applications and may require replacement of architectural facades or details even if there is no structural damage.

It is estimated that as much as 30% of the reinforcing bar used in the United States has some form of coating. Typical applications for coated bar are in areas where moisture and high chloride levels are expected, such as bridges subject to salt water spray or de-icing salts, in sea walls, in structures on or near salt water and projects in industrial environments such as waste water treatment and chemical plants.

The most widely used system to combat these problems to date has been epoxy paint. Developed in the late 1960’s largely in response to the needs of the Eisenhower Interstate building program, it became the coating of choice for most State highway departments and from there spread into commercial use. However, this product has proved problematic and since the mid 1980’s there have been questions about epoxy’s long term performance. While the paint itself is impervious to water and chlorides, the coating’s susceptibility to damage during transport and installation has called into question its overall effectiveness. Research shows that a nick or ‘holiday’ in the coating can create an oxidation cell, and that once such a cell begins, the presence of the epoxy coating can accelerate rusting by trapping moisture between itself and the bar. These findings have resulted in a high level of scrutiny for epoxy, and the problem of ‘holidays’ and handling damage of the coating has become a major headache for fabricators and installers.

As a result of these problems, architects and engineers are casting about for a suitable, reliable alternative to epoxy. Proposed replacements or solutions have included:

• Solid stainless reinforcement (expensive)
• Stainless clad (never produced in volume)
• MMFX A-1035 steel (corrosion resistance claims challenged and tensile characteristics are outside of many design specifications)
• Low voltage anode systems connected to uncoated bar (unreliable)
• Zinc thermal sprayed bar with an epoxy coating (‘Z-Bar’ - being tested, but currently no cost data or performance data is available)
• Entrained (waterproof) concrete (micro-cracks in concrete will still allow water infiltration)
• RFP ‘synthetic’ bar (lacks the required strength characteristics for many applications)

Benefits of Galvanized Reinforcing

One of the most notable characteristic of galvanized reinforcing is its resistance to handling damage, especially when contrasted with the susceptibility of epoxy coatings to damage at the work site, a characteristic which has become a major issue for the concrete industry. Galvanized coatings offer the most cost effective solution to this problem, and inherent cathodic protection of galvanizing minimizes the probability that even severely damaged bars will create problems. Galvanizing also has higher bond strength than epoxy or black bar, which may reduce overall steel use in a given application. Add to this the excellent performance history on existing structures built using galvanized reinforcing bar and galvanized reinforcing bar becomes a clear winner.

Benefits of Air Wipe Coated Reinforcing Bar

With today’s high construction costs, the individual, company or agency who desires to have a structure built is looking for a design that is cost effective, durable and allows an aesthetic statement. In this competitive bidding environment, architects and engineers should look to the capabilities of concrete reinforced with galvanized bar to maximize their design opportunities and enhance their proposals. Specifying galvanized reinforcing can help them stand out from other firms in these important areas.

On the jobsite, contractors can reduce their costs by using Airwipe galvanized rebar whenever galvanizing is specified. Airwipe’s competitive price, in stock availability and elimination of field repairs can create real savings. With no delayed pours, no UV concerns, and no special handling equipment required, contractors can keep their jobs on time and on schedule.

For the bar fabricator using Airwipe galvanized bar the savings are even greater. Our proprietary process results in ASTM 767 compliant bars that can be cut and bent, having the workability of epoxy coated bars with none of the damage issues. By using Airwipe stock lengths of galvanized bar a fabricator can process material through his line, tag it and ship it the same day. There are no lost parts, no delays and no extra freight.

Technical information on galvanized reinforcing along with case studies and reports are available from the American Galvanizers Association and International Zinc Association. For information on Airwipe galvanized bar contact us directly.