Epoxy Coated Rebar 1

[71corvette]

I've heard that epoxy coated rebar needs to be protected from exposure to sunlight in order to prevent "chalking" of the coating. Could someone please describe to me the issues associated with rebar damaged by exposure to sunlight. To what extent does this affect bonding of the rebar? How about the effectiveness of the epoxy coating?

Thanks.

 

[dbuzz]

Check out

http://www.crsi.org/ECR/.

 

[Ron]

tinytim22....the reason for protection from excessive exposure of the epoxy coated rebar is that the epoxy formulation likely does not have adequate UV protective components for long term exposure to sunlight. If left too long in sunlight, epoxy and other polymeric materials will "chalk" or develop a light, dusty residue on their surfaces due to degradation of the polymer caused by UV exposure. This chalkiness can prevent proper bond of the rebar to the concrete (at least in theory), so it is a quality control/quality assurance measure to prevent long-term UV exposure of the ECR. Another change that takes place under UV exposure is a "hardening" of the epoxy. It becomes more brittle and more likely to suffer damage during placement and handling. Damaged ECR can be worse than having no coating since corrosion is often concentrated at the damage, rather than occurring in a general sense over the entire rebar.

 

[boo1]

Fot the most comprehensive study & compilation of materials & methods on protecting rebar from corrosion I have ever seen Check this site:
<

http://www.tfhrc.gov/structur/corros/results.htm>

FLorida test results see
<

http://www11.myflorida.com/research-center/Completed_Proj/Summary_SMO/FDOT_0510603.pdf>

I have seen ads selling low carbon , chromium bearing steels that form a chromium oxide barrier on the steels surface - the same mechanism which protects stainless steel.
<

http://www.mmfx.com/main.asp>

 

[LeoSC]

Consider the use of stainless steel rebar in areas of high corrosion protection.

 

[boo1]

The MMFX bars claim simular protection to stainless steel at a lower cost.

 

[LeoSC]

boo1:
My apologies. I missed the last part of your first post my first time around. The MMFX site has very interesting information, well worth examining. Thanks for the information.

 

[structuresguy]

FYI, I just had a contractor price out epoxy coated and MMFX rebar in Palm Beach FL. Regular Gr 60 rebar is going for about $800/ton, the epoxy coated @ $1200/ton, and the MMFX at $1400/ton. Sorry, I have no price for either stainless or galvanized rebar.

The epoxy coat is less expensive, but has many construction limitations and precautions which must be followed. Also, epoxy coat rebar had a dubious track record, and is hated by many engineers, including myself.

I spec'd MMFX in the last two beach side condo projects I have designed. THe advantage is inherent corrosion resistance (ie not a coating) and no construction limitations. THe MMFX can be field bent, and does not require coating repairs like the epoxy coat bar.

I figure that by the time you figure in handing difficulties, coating repairs, wasted bars (shop bent to wrong size and can't be field bent to fit), delays getting new bars bent and coated, etc that the MMFX is really the way to go.

 

[structuresguy]

Another cost note of interest, which many of you probably already know. Regular rebar was running around $500-550 / ton fabricated here in Central FL about 18 months ago. So the price has gone up by 45-60%. The prices I listed in previous post were for fabricated bars.