January 7, 2025

Which Is Better for My Project? Galvanized Vs Epoxy-Coated Rebar

Steel rebar is vital to enhance the strength of concrete in construction, and the success and longevity of your project may hinge on choosing the right type of rebar. In harsh environments corrosive agents can make their way through the concrete and start corroding the steel, causing serious problems. Rusting steel will expand up to seven times its original volume, cracking the concrete like a tree root under a sidewalk, incurring serious repair costs or even shortening the useful life of your structure.

While some concretes in use today are specially formulated to resist infiltration of corrosive agents, there is still the problem of cracking which creates a direct pathway to the rebar. For projects on or near salt water, or those exposed to chemical snow removal or other industrial atmospheres the use of a corrosion resistant rebar may be an important consideration.

There are several options on corrosion resistant rebar available to designers, but the two most affordable choices are fusion bonded epoxy and hot dip galvanized coatings. There is an ongoing debate about the value of galvanized vs. epoxy-coated rebar which we will discuss here.

We’ve explored this comparison in our earlier article, “Which is Better? Our Scoop on Hot-dipped Galvanizing vs Epoxy Coating,” Now, we want to focus specifically on how it relates to rebar and explain why galvanized rebar is the more logical choice. We’ll also explore some frequently asked questions about galvanized vs. epoxy-coated rebar.

Galvanized vs. Epoxy-Coated Rebar: Understanding the Different Coatings

Epoxy-coated rebar is applied as a powder sprayed on the surface and bonded to the bar using heat. Although it creates an adhered protective layer, it doesn’t form a metallurgical bond like hot dip galvanizing does and any areas where the epoxy is not properly bonded can be difficult to detect. This epoxy surface also doesn’t have the same ‘grip’ as the crystalline surface of the galvanized bar or even regular black rebar so extra epoxy bar is required by code to meet design loads

Epoxy coatings effectively stop corrosion…as long as the epoxy coating is not damaged. Unfortunately, epoxy is highly susceptible to handling damage. Loading, transporting and installing of epoxy all require the use of special equipment, and if cuts, dings, scrapes or the cut ends are unrepaired, the exposed material can corrode, and rust can even progress underneath the epoxy coating. along the bar.

Also, epoxy coatings can be damaged by UV rays, limiting the amount of time the bar can be exposed at a job site before concrete is poured.

In contrast, galvanized rebar protects the steel surface of the bar with a layer of metallurgically bonded zinc alloy. This alloy is actually harder than the steel it protects and is virtually impervious to handling damage and job site abuse.

The alloy coating protects the steel in a variety of ways. First, is a protective layer of calcium hydroxy-zincate crystals that is formed by the reaction between chemicals in the wet cement and the zinc surface during pouring of the concrete. This hard crystalline layer acts as a barrier between the bar and any corrosive agents that reach it. Secondly, if this barrier layer were to be penetrated by corrosive agents the remaining zinc under the barrier would continue to protect the steel beneath it by slowly dissolving and sending non-reactive byproducts back into the concrete clogging the pathways being used by the agents. These byproducts are extremely small and move into the concrete without creating any expansive pressure, unlike corroding steel. A third layer of protection is the well-known sacrificial behavior of Zinc, which will corrode more easily than steel. Before any significant steel corrosion can take place, all of the surrounding zinc must be consumed meaning the destructive corrosion of steel will be restrained and isolated to the point of attack.

The differences between epoxy barrier protection and the galvanized zinc sacrificial coating is clearly outlined by the International Zinc Association.

Which Type of Rebar is Best for Projects Exposed to Salt Water?

Galvanized rebar has a significant track record world-wide of protecting projects in salt water over many decades, which is why many DOTs and other high-profile ventures are giving hot dip galvanized a second look for these type projects. The long-term viability of bridges is of particular concern, and a study highlighting galvanized well-known durability on the Longbird Bridge in Bermuda. After 42 years, structural damage from a hurricane prompted the need for the bridge’s replacement. Examination of material from the demolished bridge showed that the galvanized steel still maintained its original thickness and in many cases was still tightly adhered to adjacent concrete. Had it not been destroyed by the hurricane this saltwater bridge would have remained in trouble free service for at least another 50 years if not longer.

What Are the Disadvantages of Epoxy-Coated Rebar?

As we mentioned earlier, when the epoxy coating is damaged or scratched, corrosion can creep in, leading to pitting and significant corrosion failures. This means you have to be extremely careful when you bend, transport or install epoxy-coated rebar. It is not at all uncommon for job site inspectors to require extensive touch-up of the installed epoxy rebar before allowing concrete to be poured.

Other disadvantages are:

UV light exposure: When storing epoxy-coated rebar outdoors you must use a specialized tarp to protect it from UV rays and ensure that it remains covered at all times.
Even with proper storage, the epoxy coating adhesion to the bar may also deteriorate over time making long term storage unadvisable.

What Are the Advantages of Using Galvanized Rebar?

The zinc alloy coating on Hot-Dip Galvanized rebar is actually harder than the underlying steel, and is virtually impervious to handling damage, as well as being unaffected by UV, precipitation and other exposures. HDG can be stored outside and uncovered for extended periods of time, so job site delays are not a problem,

We’ve already mentioned the crystalline layer that forms on the surface of the HDG bar when the concrete is poured and how it improves the bond strength of the bar. This allows HDG bar to use the same design properties as normal black rebar, avoiding the 15% extra bar required for development lengths using epoxy. These savings coupled with the job site toughness and real-world data showing the extraordinary longevity of HDG reinforced structures make galvanized rebar the clear choice successful DOT projects.

Minimal maintenance requirements result in lower cost over the life of the structure.
It minimizes the risk of concrete cracking and breaking apart. (spalling)
The hot-dip galvanizing process is “green”: It produces less waste and its materials are highly recyclable.

Why Is Epoxy-Coated Rebar Being Banned in Some State Projects?

Epoxy-coated rebar has long dominated the corrosion resistant rebar market, seen as a viable cost-effective method of protection, but in recent years focus has shifted to the difficulty of installing this product in a manner free from any defects. Quebec, Canada, Virginia, and Florida were among the first agencies to stop using epoxy in their structures, and other states and provinces are taking a closer look at epoxy coatings and their reliability. New York and New Jersey now specify HDG bar in all their bridge projects and numerous other states allow HDG bar as an option. In structures directly exposed to salt water there are serious concerns with possible damage to the epoxy coating during installation. According to the Federal Highway Administration:

“Laboratory tests and field inspections indicate that epoxy-coated rebar in a marine substructure application is more susceptible to corrosion than bare bar. The underlying clean bright metal, which does not passivate, as does bare steel when in contact with cement, is highly susceptible to corrosion.”

Are There Different Types of Hot-Dip Galvanized and Epoxy Coatings?

Both HDG and epoxy coated rebar may be ordered in different types of coating. Hot Dip Galvanized rebar is produced under ASTM A767 with a type 1, a heavier than normal coating generally applied to already fabricated shapes, or type 2 coating which is applied to bars that are going to be fabricated after galvanizing. The two types of epoxy coatings are the pre-coated bar (ASTM A775) common green epoxy applied to straight bar lengths for fabrication after coating and the less common purple bar (ASTM A-934) rebar which is applied to individual bar shapes after they have been fabricated.

Both A934 epoxy and Type I galvanizing tend to be more expensive, primarily due to labor costs in staging and the hand racking and un-racking of the varied shapes, along with poorer process control during the coating process coating which can increase material costs. There are also costs resulting from the inefficiencies inherent in processing mixed material in a job shop environment.

Both A775 epoxy and Class II HDG are able to leverage the efficiencies of uniform, standard shapes coated on a dedicated manufacturing line to minimize labor and excess material usage to produce coated bars at a significantly lower cost. Pre-coating of bar also eliminates extra trucking and gives the fabricator complete control over his material

What Is the Difference in Cost Between HDG and Epoxy Rebar?

Precoated Type 2 HDG and precoated epoxy are similar in cost, with epoxy usually holding a slight edge. However, when the costs of special handling and required touch up labor are considered HDG can be a money saver. Purple epoxy and Class 1 HDG are virtually the same in cost, which can vary tremendously based on the nature and configuration of the work being coated.

When You Want Reliable, Consistent Rebar That Stands the Test of Time, Galvanized Rebar Is the Obvious Choice

We have Type 2 galvanized rebar in stock, and with reliable, fast, nationwide delivery, you can rest assured we have you covered. If you need your rebar coated please contact your nearest South Atlantic Facility for a quote on Type 1 coating.