Epoxy Coated Rebar 2

[nicaeng]

Are there different types of epoxy coated rebars?. We are building a geothermal power plant in Nicaragua and a drawing specifies field applied fusion bonded epoxy coating on the rebar for a foundation, we will buy the rebar coated in the US since we can't find any on Central America, i just need to be sure that if i ask for epoxy coated rebar they won't reply back asking "what kind do you need?"

Thanks.

 

[Ron]

I would recommend against epoxy coated rebar. Most studies have shown it to be of limited value. I certainly would not recommend field coating any rebar.

 

[hokie66]

Agree with Ron. If you need corrosion protection on the steel, galvanize it. Protection by the zinc extends to damaged areas, while damage to epoxy coatings accentuates corrosion at that point.

 

[nicaeng]

We are also buying some spray coating to applied to any area we damage while we fabricate and install the rebar. We don´t really have a choice here, they want epoxy coated rebar, i´m just checking if there are different kinds of epoxy coated rebars?.

 

[JAE]

Ron and all:

I’m not trying to promote epoxy coated bars here. But I’ve noticed over the past several years that this issue isn’t all that clear cut. Most of the US state bridge departments use epoxy coating in their bridge decks. Here’s a few other article links. Again - I’m not cheerleading here - just curious as to how you compare the negative comments on epoxy coated bars above with articles such as these:

http://www.utexas.edu/research/ctr/pdf_reports/1265_3.pdf

http://www.lrrb.org/pdf/200847TS.pdf

An older paper from Australia:
paper link

An FHWA report (where they intentionally damaged the coating)

http://www.fhwa.dot.gov/publications/research/infrastructure/structures/04090/index.cfm#exec

http://www.ctre.iastate.edu/reports/corrosion_resistant_steel.pdf

 

[Ron]

JAE...I agree that State DOT's are again looking at epoxy coated rebar. The Florida DOT did extensive investigation into epoxy coated rebar and the conclusion was that it was good, but if you breached the coating in the field by damage of any sort, corrosion concentration was the result (as Hokie66 noted).

A German study back in the 80's showed that good, dense concrete with appropriate control on cover was more effective than either epoxy coating or galvanizing in marine applications.

 

[cvg]

bridge decks in cold climates are exposed to a lot of deicing salt which corrodes the steel. bridge decks in cold climates are not comparable to a foundation in central america. I fail to see a need for epoxy coating unless the soil is extremely aggressive.

Either way, if you must use it, then there are specifications for the rebar which are readily available on the internet. Look for reference to ASTM / AASHTO

fusion coating method (better)

http://www.astm.org/Standards/A934.htm

electrostatic spray method

http://www.astm.org/Standards/A775.htm

 

[nicaeng]

Thank you all for sharing your point of views.

cvg, so even if the rebar is bought with the coating from the factory, they can only be coated by these two methods?.

By the way, we are using this rebar for a Rock Muffler foundation, i can only guess that the designer is specifying these rebar because it is close to the cooling towers, so they expect to have some acid water not only inside of the muffler but also outside. We are building phase 2 of the project, for phase 1, the rock muffler was specified with common rebar, no coatings. I also believe that the water is not that acid since by the time it gets to the rock muffler it has gone through several filters to remove almost all the brine. I'm not a mechanical or chemical engineer but i'm pretty sure i'm right, i'll post some pictures of the phase 1 muffler (already built) and the phase 2 rock muffler when we build it.

 

[cvg]

I would recommend one of these two specifications. I have never specified anything else.

 

[Rebarguy]

There are two general types of epoxy-coated reinforcing, but the most common meets ASTM A775. Approximately 600,000 ton of this is produced each year in the USA and about 400,000 ton is produced in the middle east. Please visit

http://www.epoxyinterestgroup.org

for more information.

 

[nicaeng]

What products would you recommend for the touch up of this rebar? I have in mind Dayton's Epoxy Spray J-62, please comment.

 

[Rebarguy]

Single component or spray materials are not recommended. Two part epoxies are the best method for damage and end repair. They should be available from the bar supplier.

 

[nicaeng]

Excellent, thank you for your help.

 

[dik]

Rebarguy...
Do you have the relative costs for epoxy coating under ASTM A934 and ASTM A775?

I expect that A775 is less costly.

Dik

 

[Rebarguy]

ENR publishes prices of uncoated and coated bars. The 20-city average costs published in September 2011 for the USA were $0.45 and $0.66 for black and coated bars, respectively.

I would expect the A934 coating to cost in the range of $0.70 above the steel price, but there are so few coaters doing this that it is difficult to provide a reasonable cost.

Hope this helps.

 

[cvg]

installation cost for epoxy coated bars is also much higher due to the need for protection during delivery, storage and installation and repair of damaged coating.

 

[Rebarguy]

I disagree with the "much higher." Many iron workers I talk to actually prefer epoxy bars as they don't get as hot as black bars. In north america, costs for installation may be $0.05/lb more than black bars.

 

[dik]

Thanks Rebarguy and cvg...

Dik

 

[cvg]

regardless of the temperature, I believe the cost and schedule impacts can be greater than stated.

shipping requires special handling and storage procedures. Installation must be done without damaging the coating. Any field adjustments will require repairs. And then there is additional inspection verify coating thickness and to find and repair all the damaged areas and protect it until concrete is poured. Depending on the size of the project, this can be a major cost factor.

Epoxy-coated steel bars shall comply with the requirements of ASTM A 775/A 775M, including written certifications for coating material and coated bars, sample of coating material, and 0.5 pounds of patching material.]

DELIVERY, STORAGE, AND HANDLING

A. Handling of Epoxy Coated Rebar:
1. Use padded or nonmetallic slings and padded straps to protect coated reinforcement from damage.
2. Handle bundled bars to prevent sagging that could damage the coating.
3. Do not drop or drag rebars.
4. Store on wooden cribbing.
5. Coated rebars subject to rejection by Engineer if rebar coating has been damaged.

2.04 FABRICATION

C. Ship rebars to jobsite with attached plastic or metal tags.
3. For epoxy coated rebars, use only plastic tags secured to rebars by nylon or plastic ties.

3. Rebar support:
b. Coated rebar:
1) Support coated rebars and fasten together to prevent displacement.
2) Use plastic or nylon ties to hold rebars rigidly in place.
3) Support rebars by use of plastic or plastic coated chairs, runners, bolsters, spacers, hangers and rebar supports as required.

B. Inspection of Epoxy Coated Rebars:
1. Coated rebars will be inspected on the jobsite for handling defects, coating abrasion, coating thickness and continuity of coating.
2. Engineer may defer final inspection of rebar coating integrity and repairs until the rebars have been erected and all handling is completed.
3. Repair coated areas as directed by Engineer. Do not place concrete until all repairs to coatings have been completed.
C. Patching of Epoxy Coated Rebar:
1. Patching and repair to be performed in accordance with the instructions of patching material manufacturer.
2. Patching material to provide a minimum film thickness of 5 mils over the bare area. Thickness of area adjacent to patched area not to exceed 15 mils.
3. Areas to be patched to be clean and free of surface contaminants. Treat areas in accordance with patching material manufacturer's instructions before oxidation occurs.
4. Total surface area covered by patching material not to exceed 2 percent of total surface area of the rebar.
5. Rebar welds and adjacent bare rebar areas to also be patched after welding is completed.

 

[nicaeng]

The pictures i promised, this is the existing Rock Muffler.