epoxy coated rebar 4

[jfortune7]

There has been discussion on this subject for bridges and buildings, but I haven't seen anything for potable water retaining structures.

Are the advantages worth the extra cost?
What is the industry trend?

 

[dlew]

I do not have personal experience with epoxy-coated reinforcing bars. Although we have considered their use in some cases where corrosion was an important consideration, as in wastewater plants or waterfront structures.

We heard many arguments in pro and con of the use of epoxy-coating. Some say that if a crack develops in the coat the chances of corrosion would be greater than on an uncoated bar. I think the Florida DOT for many years did not allow the use of epoxy-coated bars in bridges. I do not know what is their policy now.

You could also consider galvanized reinforcing bars or increasing the concrete cover of the reinforcing if you want to provide additional corrosion protection.

AEF

 

[LPPE]

For a portion of the Big Dig in Boston, the contractor was using #11's at 6" o.c. epoxy coated for the roof of one of the tunnels. (6ft thick with #11's @ 6" o.c. T&B E.W.). At every end cut, they had to paint epoxy on the exposed steel. So I think if you are going to use epoxy bars, you need a little extra in labor costs to seal up all exposed parts. But I think with proper care during construction you will have a long lasting structure.
As for your water tank, it would only seem prudent to use some sort of corrosion protection for your rebar.

 

[RiBeneke]

I did not find the detail of your structure in your posting, so perhaps I am on the wrong track ?
In my experience here in South Africa we would not normally use coated rebar (epoxy or galvanised) for concrete potable water reservoirs.
Control of concrete mix quality (strength and grading), compaction density, construction joint preparation, concrete cover to rebar, and proper curing have proved sufficient to produce concrete reservoirs that have worked well for 50 or more years, using only normal steel rebar.
If you are prestressing your reservoir, or if conditions are particularly corrosive, then it would make sense to consider special corrosion protection.

 

[BarryMartin]

I believe epoxy coated rebar came into use as a response to the problem of corrosion of reinforcing steel in bridge decks. The initiator was the increased use of deicing salts, penetrating the concrete and breaking down the passivating film that forms on steel in concrete due to alkalinity. In Europe where the buildings are very old, there has been another initiator of corrosion. Carbonation of the surface layer on concrete can penetrate to rebar over time and initiate corrosion.

Without the chlorides or carbon dioxide to initiate corrosion, I would not expect any problems in service. The suggestion to increase the cover of concrete is good. Another alternative is to cathodically protect the reinforcing steel. A system analogous to a well coated steel tank could be installed in the potable water to throw current for added protection. This would be a relatively cheap fix.

 

[jheidt2543]

How about contacting the Concrete Reinforcing Steel Institute (CRSI) and find out the pros and cons from their research? They could also fill you in on relative cost differences between plain, galvanized and epoxy coated.

In Illinois and Wisconsin the state DOT's are using tons (just a little pun intended <G>) of epoxy coated rebar not only in bridges but highways too.

 

[boo1]

In FLorida test results see

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

 

[kenvlach]

The Florida test results (link posted by boo1) basically shoot down any extra value imparted by epoxy coating when good quality concrete is used.
It mentioned reduced epoxy-steel adhesion and &quot;The laboratory tests confirmed that the chemical makeup of the concrete pore solution and the electrochemical service conditions of the rebar in the service environment are conducive to extensive loss of adhesion&quot; which reminded me of some past experiences:
I have had an epoxy concrete sealer damaged (I believe) by the high alkalinity of the less-than-fully-cured concrete (boss was in a rush). I also know of a case where fresh concrete was poured over an epoxy sealed concrete floor (for a temporary structure). The fresh concrete seemed to damage the epoxy.
Can anyone point me to test results for reaction of concrete & epoxy?

Re rebar. Why not use SS rebar? see

http://www.stainless-rebar.org/

 

[Rjeffery]

Also check with ICRI (International Concrete Repair Institute) I think, headquartered in Dulles, Virginia.

Also, If the concrete is of higher strength (6,000+ vs 3,000 PSI) the matrix is relativly impermiable, Isn't it?

That should prevent ion exchange.

 

[pug]

Have used epoxy bars for 20 years in bridge decks. Results are disappointing. Hot spots eat through the bar while normal corrosion is scaling variety over a longer area and not as deep. I would sugest putting your money in a waterproof deck system for bridge decks.

 

[boo1]

I have seen adds selling low carbon , chromium bearing steels that form a chromium oxide barrier on the steels surface - the same mechanism which protects stainless steel. Never used it so can't say how good it is!

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

 

[jheidt2543]

Just a couple of questions based on Pug's and Boo1's responses:

Pug: Are you saying that epoxy coated rebar is actually worse than uncoated? What type of time frames are you talking about, a few years or over the life of the structure? Is there an actual study that documents this?

Boo1: I should think that the chromium oxide barrier (film) might inhibit or reduce the bond between the rebar and the concrete. I have never heard of this type of rebar. Do you know of any references or studies that might be available?

Just wondering on a cold winter night!

 

[boo1]

Jheidt, I dont have the experience too answer, but I posted links so you can check it out your self. The chrome rebar litature looked good, but...

See my earlier post on coated rebar reports from Florida.

Cheers

 

[boo1]

Check this site:

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

 

[kenvlach]

Boo1,
That's an even better link -- the most comprehensive study & compilation of materials & methods on protecting rebar from corrosion I have ever seen. Worth a star.
jheidt,
It appears that concrete bonds as well to Ni-coated, SS-clad & SS rebar as to plain steel. A little oxide (as long as thermochemically stable) on the surface enhances the bonding.
pug,
It appears that some epoxies are vulnerable to the long term high alkalinity of concrete, so tests are being done to determine which are the most stable. Also, as you noted, epoxy coated rebar doesn't last in highly loaded bridge decks where flexing may occur. For this situation, the Oregon DOT chose Alloy 2205, a duplex stainless steel, for rebar in a bridge projected to last 120 years: &quot;Willing to Bend&quot;, Roads & Bridges, May 2002, p.34-37.

http://www.roadsbridges.com/rb/inde...KEN=93601383&fuseaction=showArticleSearchForm

 

[pug]

I had a chuckle over the 120 year life. First, bridges might be in museums by then. Furthermore, sufficiency criteria will be vastly different in 50 years let alone 120. Never heard of loads getting smaller or speeds becoming slower for example but always in reverse. Initial cost being kept as low as possible is the most cost effective in almost all life analysis situtations.

There is lots of talk about how to make things last longer but that isn't the way to go.

 

[MetalMan14]

For those of you who might still care...
Yes there is a new alternative to epoxy coated rebar. It's a new steel created by MMFX Steel Corp. Boo1, I believe you were the first to inquire about it. Yes it does have Cr in it which does for a Cr oxide layer when scratched, thus one of the advantages over epoxy coated...you don't have to be as careful during installation. Also, they have developed a different microstructure that nearly eliminates the galvanic reactions. For more information visit:

http://www.mmfxsteel.com

Hope this helps

 

[LittleWheels]

Pug said:
I had a chuckle over the 120 year life. First, bridges might be in museums by then. Furthermore, sufficiency criteria will be vastly different in 50 years let alone 120.
------------

Things may be different on the other side of the pond but in Britain, I have some 100 year old bridges supporting major trunk roads. A significant number of motorway bridges are 40 years old with minimal chance of them being replaced within my lifetime.

In a similar vein, a temporary grandstand erected in Brisbane for a three week sporting event is still being used 20 years later (with minor strengthening). Be careful of assuming reduced design life.

 

[pug]

Hey Dave

You also have some bridges that are new and closed like the 20 million dollar millineum bridge no? There are old bridges here as well for the same reasons as you have old bridges. The engineering community didn't have the knowledge that we have today so they were cautious resulting in over designing. Don't forget they were designing for horse drawn loads and such back then. I agree a stone arch will outlive a steel girder bridge on the condition that the functionality doesn't change appreciably.

I seem to have more faith in mankinds ability to solve global problems with transportation being one of them. In 120 years, I suspect nanotechnology will be playing a much larger role as well as other emerging technologies. Go ahead and spend twice as much for a bridge to last 120 years. My guess is it will be outdated 60 years from now. Cannot say what will make it obsolete but am sure our lifestyle and resources at that time will dictate what the bridges will look like rather than the other way around. Perhaps we can put some blackdirt on it and use it for a garden for the last 60 years.

You mention a temporary structure being used 20 years later. Doesn't surprise me a bit. It is the functionality of the original design that drives the useage. Technology will likely change more quickly in transportation than social activities such as gathering to watch an event.

Perhaps I am a lot older than you and have seen much more. I have witnessed the cleverness of engineers designing for future expansion etc and watched them being torn down without taking advantage of what they hoped for. I have also watched as the truck loads have increased in weight and size. I see no reason to believe transportation is at a standstill at this point. Take my advice and don't try to think like you know what life will be like in 2125 because no one does.

Be careful of assuming reduced design life is what you ended with. I will end with be careful of assuming the intended useage will stay the same for an unforeseeable future.

 

[LittleWheels]

Hello pug, the Millennium Bridge in London is open and working fine now. In fact, my employers were involved with the retro-fit to damp the movement.

http://www.arup.com/MillenniumBridge/

is the designer's website.

I'm interested to see the technology that will make 'getting things to the other side of the river' obsolete. It is usually easier to build infrastructure that exceeds initial requirements (perhaps by over-conservative design through ignorance) than to come back later and try to upgrade capacity or to extend its lifespan.