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LCruiser (Civil/Environmental) (OP)
18 Dec 08 10:40
Purchase price of epoxy coated rebar is only about 10¢ per pound more than black rebar.  Why is it not used more?
cvg (Civil/Environmental)
18 Dec 08 11:13
purchase price is only part of the equation.  there are additional costs for installation due to the requirements to field repair any defects caused during construction.  this requires additional contractor and inspector time and consequently costs considerably more.  If you don't do the inspection and repairs, then you arguably may lose much of the benefits of the epoxy coated rebar in the first place. See CRSI summary of recommended field handling procedures:

http://www.crsi.org/corrosion/handling.html


Double coating such as Zbar might be a better option.


http://www.zbarusa.com/index.html
swivel63 (Structural)
18 Dec 08 13:25
it also has to be longer on splices.  the paint can get stripped off.  i personally don't like green bars.  

i'd rather just have some corrision inhibitor in the concrete and be done with it.   
hokie66 (Structural)
18 Dec 08 18:15
Galvanized reinforcing is a much better choice.  Little nicks in the zinc don't affect the corrosion protection.  Instead of epoxy coating, best to concentrate on better concrete.
civilperson (Structural)
18 Dec 08 21:16
It is used a lot in decks of bridges, parking structures and corrosive environments.  It is not needed in buildings or pavements.
frv (Structural)
18 Dec 08 21:50
I had a materials professor rail against those things.

He was a pretty smart guy and has done lots of research in that area. If the epoxy coating gets any kind of a ding, not only will it not help, it actually drives the corrosion at a more rapid rate.
kelowna (Structural)
19 Dec 08 3:15
I have to agree with the general sentiment. No matter how careful you are on site and how much you try to touch up every damage to the coating, it is just impossible to install the bars without damaging the eopxy at some point.
LCruiser (Civil/Environmental) (OP)
19 Dec 08 4:59
So what is the answer?
civilperson (Structural)
19 Dec 08 14:08
I agree with the DOTs that epoxy coated rebar is suitable for use in bridge decks.  The iron workers of my experience successfully tied thousands of tons of green steel with no damage in the finish product.  The execution is in the details using coated chairs and wire, close inspection and concrete placement by quality conscious workers.  The life of these decks were extended by double when compared to decks built with black reinforcement in the same construction season, even with cathodic protection and high strength/ high density concrete coupled with the bare steel.
LCruiser (Civil/Environmental) (OP)
19 Dec 08 14:37
So why not the whole bridge then?  The incremental cost to use epoxy coated bars in the substructure is way less than 1% of the bridge cost...
hokie66 (Structural)
20 Dec 08 0:33
Only about 1/3 of DOT in the US have used epoxy coated reinforcing in the last 10 years.  Several who used it earlier have stopped allowing its use due to concerns about corrosion, particularly in coastal areas.   
LCruiser (Civil/Environmental) (OP)
20 Dec 08 10:18
Have their been any actual studies on this, or are they just "concerns"?
hokie66 (Structural)
20 Dec 08 16:02
Yes, there have been a lot of studies.  Just google and you will find them.  The ones I have read are from Florida, which resulted in that state ceasing to use epoxy coated steel, and from Virginia, which I think still does.  There is still disagreement as to the benefit or otherwise of using epoxy bars.  Most of the states which use them are across the south and west, while most of the northern tier states do not.
dik (Structural)
22 Dec 08 9:36
Many jurisdictions are moving away from epoxy coating due to anodic corrosion issues.

Dik
 
chicopee (Mechanical)
28 Dec 08 9:14
Isn't there also an issue of weak bonding between epoxy coated rebar and concrete?
Qshake (Structural)
28 Dec 08 11:20
Some state DOT's use green bars in all parts of the structure.  Other DOTs use green bars only in the deck.  As is mentioned above, most DOT's have full time inspectors so that isn't a huge issue to them.  I think a bigger issue is the effectiveness of the application.  

No doubt there is a much improved performance in the use of green bars from when we used black steel only in bridge decks.  But then too our overall construction practice has also improved.  Concrete cover is more strictly held to and has a tremendous effect on protecting rebar.  We're also using sealers and other membranes to protect concrete especially in splash zones where deicing chemicals are inadvertently sprayed onto substructures from the snowplowing etc.

One application that holds a great deal of promise is non-ferrous reinforcing such as Glass Fiber Reinforced Polymers.  GFRP is relatively cheap compared to Carbon FRP and will not rust in any situation.  At present a handful of states have experimental applications and more research work may be necessary to assure owners that it will work but it's a start.

 

Regards,
Qshake
pipe
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