Epoxy coated rebar - "To coat or not to coat?"

Robert Caputo

Region Manager - New York and Washington DC Metro Areas at Western Specialty Contractors

Published Oct 10, 2021

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This particular subject appears to be a little bit of a controversial one. There are many opinions regarding the the longevity and corrosion protection of epoxy coated rebar (ECR), but the purpose of this article is to simply discuss some findings and allow for people to just talk and have dialogue about it. Over the years (whether in the repair or new construction), I've seen quite a bit of ECR installed (within core and shell jobs as well as infrastructure repair work) in the hopes that it will prevent salts, moisture & carbon to hit the surfaces of the rebar and start the corrosion process. And in most cases, that appears to be the case. Here are a couple abstract links from ACI (American Concrete Institute) showing their long term findings and prove that:

* 35-Year Field Performance of Epoxy-Coated Reinforcing Bars (concrete.org) Snapshot - "The corrosion state of bar samples removed in cores was examined as well as bond between the epoxy coating and steel and coating thickness. Chloride profiles from concrete cores were also obtained. Overall, the epoxy-coated reinforcing bars were in excellent condition, with very little active corrosion after up to 35 years of service."

* Assessment of Epoxy Coating on Bridge Deck Reinforcement (concrete.org) Snapshot - "Although the percentage of specimens exhibiting corrosion and cracking of the concrete cover was significantly lower for specimens containing epoxy-coated reinforcement, the results indicated that there was significant variability in the corrosion protection provided by the epoxy coating. Factors influencing the time to cracking of specimens containing epoxy-coated bars are discussed."

There is some research being done by a few DOT departments in the US and Canada that continue to challenge and explore the protection characteristics that ECR will provide over long periods of time. Here's an interesting investigation article:

* Field investigation of the corrosion protection performance of bridge decks and piles constructed with epoxy-coated reinforcing steel in Virginia. (bts.gov) Snapshot - "Abstract Virginia Department of Transportation 1401 E. Broad Street Richmond, VA 23219 The corrosion protection performance of epoxy-coated reinforcing steel (ECR) was assessed in three bridge decks and the piles in three marine structures in Virginia in 1996. The decks were 17 years old, two of the marine structures were 8 years old, and the other marine structure was 7 years old at the time of the investigation. The deck investigations included visually surveying surface cracks in the right traffic lane and drilling 12 cores randomly located in the lowest 12th percentile cover depth. The pile investigations included removing 1 core at an elevation between high and low tides from each of 30 piles. The evaluation of the concrete in each core included visually inspecting and measuring moisture content, absorption, percent saturation, carbonation depth, and effective chloride diffusion constant. The evaluation of the ECR from each core included visually inspecting and measuring physical damage, coating thickness, adhesion loss and corrosion at damaged sites, and undercoating corrosion at adhesion test sites. The chloride content of the concrete and the carbonation of the ECR trace were also determined for each core. In the majority of bars examined, the epoxy coating has debonded or is debonding from the reinforcing bar. This occurs without the presence of chloride, and its rate is related to concrete moisture conditions, temperature, coating defects, and other bar and coating properties. Based on the results of this field study, epoxy coatings can be expected to debond from reinforcing steel in Virginia's marine environments in about 6 years and from bridge decks in about 15 years. The authors recommend that additional bridge decks be evaluated to confirm these results"

I believe that there are a few variables at play here.....such as the thickness and quality of the epoxy applied to the surface of the bar and the imperfections (holidays) on the surface of the rebar caused during fabrication, delivery, storage, handling, installation, age, etc.

What type of rebar you use is ultimately up to your Engineer and how they feel about their design criteria and anticipated performance. I personally have always been a fan of black or galvanized rebar due to cost, availability, bond to concrete, etc. And I feel that there are so many technologies out there that can enhance the performance of your reinforcement starting with good quality concrete, proper coverage, coating systems, etc. It's not to say that epoxy coated rebar is a bad option but there are options. Epoxy coated rebar is a viable option and I think overall, it will provide you with significant protection from corrosion based on much history and testing. But knowing that the quality of the protection is based on the condition/quality of the epoxy coating on the bar itself is very important.

Another option to consider can be FRP bars (carbon fiber). FRP bars are expensive and their structural characteristics differ from a standard ductile iron bar. The major benefit is the elimination of corrosion all together by removing the iron component. But again, the unique performance characteristics of FRP bar and price are things to consider. Here's a good video by Tyler Ley (TylerLey.com - About Me) regarding this very topic :

https://youtu.be/thUZImUTZn0

I find this topic to be very interesting and no one seems to have the silver bullet answer to it but talk to your Professional Engineers, specialty contractors and ask tons of questions. Educate yourself and make the best possible decision for your building. Most of the time, the need, cost, design criteria, environment and availability will dictate what you use.

This habit alone will allow you to add many years to the life of your building & structure. Share and educate. Restore and protect.

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Kyle Hopwood

Robert Caputo I came back to your article Robert because it had me thinking about DOT work I see in my area. My territory is mainly the midwest, but I also cover a few "Rocky Mountain States". I see a lot more epoxy coated rebar than any other type of rebar being used on DOT jobs in my area. I do see uncoated bar and galvanized rebar as well. However, it seems like the east coast is big on galvanized rebar and stainless steel rebar. I believe stainless steel as caught a lot of engineers attention and its being used more and more - on big scale DOT jobs too. Also, FRP has made its way into the market on multiple DOT jobs in a few midwest states and down the coast to Florida. A major concern that engineers should be thinking about is with FRP rebar and Stainless Steel rebar, how or what type of mechanical couplers are they going to use to splice these types of bars together when they need to do a highway patch or repair job? There is no stainless steel type of coupler other than a formsaver (threaded) option for stainless and there's no FRP style mechanical coupler that has been brought to the market, yet. What are they going to do when a issue like this arises? Just a thought, but again, great article. It made me think :) Robert Caputo

11mo

In my experience, I see more black and galvanized bar in the North East. The stainless is very expensive so when it's used, it's for smaller jobs. The coupler question is a valid one for sure when you are talking different materials. I would think lap splices would need to be calculated and used instead if possible. Good stuff Kyle!

Shannon Price

Hi Rob, What are your thoughts regarding basalt rebar?

Stress Strain Diagram

Hey Shannon! Great question. When you look at the stress strain diagram for basalt, the structural characteristics are much different than steel. Although it’s “stronger than steel” the stiffness of the basalt is less than steel which results in larger cracks to occur in the concrete member. Also (and this goes for carbon fiber) the ductility of the reinforcement is much less. The lack of ductility doesn’t allow for any time while a member is in a state of failure. FRP rapidly fails. In my personal opinion, the use of both steel and FRP should be more prevalent and allow for Engineers to design using the best of both worlds. Lastly, when demand increases, costs will drop. Attached is a diagram showing a few products.

Chris Pisani

good article. It leaves me with even more questions than before. In Massachusetts we use epoxy but in Rhode Island I see that similar bridge has galvanized rebar on its decks. One has to be better than the other.

I would think in the North East corner of the US, you are faced with very high levels of de-icing and ocean salts so corrosion is a huge issue. Have yo done some post installation testing to see how effective each has been over the years?

Very interesting and insightful article 👍🏾 Robert Caputo Peter Fosnough 👆

Patrick J. Morrissey

Don't COAT or NOT COAT, eliminate altogether and use nonmetallic rebar.

I think cost hinders this from happening in most cases but nothing says you cannot combine the two and use both. I think it's a "best of both worlds" approach....but not sure how much that is happening. Something to think about.

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Epoxy coated rebar - "To coat or not to coat?"

Robert Caputo

Region Manager - New York and Washington DC Metro Areas at Western Specialty Contractors

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