epoxy coated rebar
epoxy coated rebar
(OP)
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?
Are the advantages worth the extra cost?
What is the industry trend?






RE: epoxy coated rebar
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
RE: epoxy coated rebar
As for your water tank, it would only seem prudent to use some sort of corrosion protection for your rebar.
RE: epoxy coated rebar
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.
RE: epoxy coated rebar
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.
RE: epoxy coated rebar
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.
RE: epoxy coated rebar
http://www11.myflorida.com/research-center/Completed_Proj/Summary_SMO/FDOT_0510603.pdf
RE: epoxy coated rebar
It mentioned reduced epoxy-steel adhesion and "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" 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/
RE: epoxy coated rebar
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.
RE: epoxy coated rebar
RE: epoxy coated rebar
http://www.mmfx.com/main.asp
RE: epoxy coated rebar
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!
RE: epoxy coated rebar
See my earlier post on coated rebar reports from Florida.
Cheers
RE: epoxy coated rebar
http://www.tfhrc.gov/structur/corros/results.htm
RE: epoxy coated rebar
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: "Willing to Bend", Roads & Bridges, May 2002, p.34-37.
http://www.roadsbridges.com/rb/index.cfm?CFID=3662561&CFTOKEN=93601383&fuseaction=showArticleSearchForm
RE: epoxy coated rebar
There is lots of talk about how to make things last longer but that isn't the way to go.
RE: epoxy coated rebar
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
RE: epoxy coated rebar
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.
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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.
RE: epoxy coated rebar
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.
RE: epoxy coated rebar
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.