Use of Epoxy coated bars in Bridges

[Hariharan]

How prevalent is the use of Epoxy coated Rebars in Bridges
in USA, apart from deck slabs? Are there any DOT
requirements in this regard in any state? My interest is in
girders, substructures including piers and other components
such as abutments, foundations. Any references, links would be
appreciated.
Thanks

 

[Qshake]

The use of "green" steel is as different as the many states we have to pick from.

Generally, and I emphasis generally, only the concrete bridge deck contains epoxy coated steel. However, many states also require that any steel which is embedded into the deck also be epoxy steel. This covers the steel which for composite reasons joins the prestressed I-girders and the concrete deck.

In the midwest where seasonal changes play havoc on the concrete bridge decks, I am aware of only one state which requires all steel in the bridge to be epoxy coated.

 

[Hariharan]

Thanks, Qshake. Could you elaborate a bit more?
Which is that state? And by 'all steel in the bridge', do you mean
only superstructure or substructure as well? My study of the
FHWA report on Corrosion of reinforcement seemed to indicate
that the deck slab alone was required to be provided with 'green bars'.

The recent field tests showed that the performance of the ECR bars
was not as good as originally envisaged. The potential for disbondment
(lack of adhesion between steel and epoxy) was very high although
corrosion rate was low. Has this resulted in any change of policy in
the USA?

What is the extent of Quality assurance inspections performed by the
owner on account of ECR bars, which require a number of special
precautions?

Related question, how about bridges/piers in coastal/marine zones?
Are ECR bars used there as well?

Hariharan

 

[Qshake]

Hariharan, Good to hear from you. The state I was referring to is Illinois which is located in the Central U.S. so it is away from the harsh coastal environments that you have inquired about. However, I have data for bridges located all over the world and, given some time, can located the information you are interested in for coastal applications.

Illinois is an interesting state in that the northern part of the state is located in a rough freeze/thaw environment (i.e. many cycles) while the southern section is in a more temperate environment. Bridges from the southern part experience less corrosion problems as a result of this. Those bridges are not salted up during winter ice and snow removal operations. Thier bridge counterparts in the northern half experience serious problems after only several years of use. It is a stark contrast.

Here in the US, green steel is about $0.5/pound more than black steel. Illinois obvisously thought this differnce to be insignificant (compared to the consequences and other factors) so they incorporate green steel in all bridge elements from the superstructure to the footings.

As for addressing additional concerns, the green steel is subject to stringent testing. In all states, additional rebar is set aside from that project to test the bar strength with emphasis on the performance of the epoxy coating. Also, the delivered lot of epoxy steel is tested for the appropriate coating thickness using resistivity principles. Often times the green steel is subject to 100% ties at the intersections whereas black is 50%. Tie criteria is also more stringent in the top layer of deck reinforcing than the bottom mat. Tie wire for green steel is also epoxy coated as is all resteel appendages like bar chairs etc.

As for the performance of the bond. I haven't heard of this being a significant problem. Of course, as you've stated, the overall effect is less corrosion problems so that maybe this overshadows the bond issue. I'm not sure about that but it is just a guess.

 

[Hariharan]

Thanks, Qshake. I shall wait for your feedback on use of ECR bars in
coastal applications.

I am evaluating the need for ECR bars in India, where there is practically
no snow or use of de-icing salts over bridges. (at least the applications
I have in mind). Also for marine structures, which are primarily in concrete.

 

[Qshake]

Hariharan,

I have looked into past designs, most notably, the second Cheaspeake Bay Bridge (Coastal application, east coast of USA) crossing and note that epoxy is used on in the deck. The bridge is a slab and girder bridge.

This issue has intrigued me and I will continue to report on the difference in applications by the various DOT's.

 

[mann]

Hariharan, I have worked with several DOT's on Bridge design. North Carolina only uses epoxy coated bars in the top of the deck while in Virginia epoxy coated bars are used in everything including the substructure. I did do some work with Florida, but can not remember their policy.

I have a friend who has done some research on epoxy coated bars in the decks. Some of the results were published in "Concrete International". It was in two parts in the February and March issues of this year. Check it out.

 

[Qshake]

I have recently found that Florida doesn't use epoxy coated at all.

 

[Hariharan]

Thanks for the responses. The Federal Highway Administration has compiled
the results of various studies conducted by DOT's on corrosion of rebars, field performance of ECR bars etc. The findings are available in their website
(Cant put my hands on the site address right now) and related files.
DOT Florida has not been using ECR for a long time, after the failure of the
piers of some of the bridges. Recent research in Virginia also stated that it is
not cost-effective, and there is no confirmed remedial procedure if an ECR
bar gets corroded.. The debate goes on... There is a search for alternates
to ECR bars. Research is not conclusive, yet.
I haven't been able to find evidence of large scale ECR application outside
of USA, say in Europe, Japan etc. Any info on the subject is welcome.

Hariharan

 

[Qshake]

One of our engineers recently returned from an ACI committee meeting with information on the efforts to improve deck performance using different rebar. Stainless steel and composite rebar were amoung the topics. I would take a look at ACI website and see if they have any information there regarding the committees their purpose, their progress and if any reports have be forthcoming.

Thanks for the information regarding the FHWA and use of epoxy coated rebar.

 

[Qshake]

I should note that galvanized rebar was also discussed but, if memory serves me, it didn't perform well.

 

[Hariharan]

As per FHWA summary, the best performance was from
stainless steel bars, and bars with Stainless steel cladding.
Others were not as good. This was however for
application as deck reinforcement in bridges subject to
snow and de-icing salts. These bars would not be cost
effective if applied over the entire structure. And for marine
applications (tidal and spray zone) the ECR bars were not
found appropriate. Florida DOT stopped the usage on this
score.
No code, however, mandates any protection of rebars in
any environment. The emphasis has always been on good
quality, dense concrete. ECR and other types of coated
bars have been used in USA, India and possibly in
other countries as well. This has been puzzling me. Are the
codes considered inadequate?

Hariharan

 

[RichardC]

Interested in your discussion as I live in the Middle East which is subject to heavy rebar corrosion problems. So far the best solution is epoxy coated rebars as they have a proven track record in many environments and structures. Few results are poor (small compared to the number of structures using ECR rebars)but research has shown that this is primarily due to poor application, installation (concrete cover thickness etc) and handling, rather than the powder epoxy coating itself. Alternatives such as concrete additives, membranes, non ferrous rebars, CP, galvanising etc have all problems be it performance, application difficulties or cost. We find that ECR is easy to test for quality and coating integrity which is useful for QC on site (we cannot determine the quality of the cement / concrete etc and are subject to trusting information and data sheets). Improved and more severe specifications (ASTM A775) for ECR has resulted in seriously improved coatings and performance. For me I still go with ECR as I have reservations with other solutions.

 

[Qshake]

Thanks for the input RichardC. I agree with your summary on the performance of ECR, mainly that there are many other factors involved and that there are only few incidents of poor performance in light of the total number of applications.

 

[Hariharan]

Thanks for the feedback, RichardC. I am aware that Epoxy coated bars
are quite popular in the middle east. What is the basic corrosion mechanism
there, salt laden humid atmosphere, or aggregate quality or something else?
Has it been used in Marine environs, (coastal structures, jetties etc)?
Functionally these are similar to bridge structures, but Chloride ingress
is more severe. I also understand that in many places in the middle east,
the bars are coated after cutting and bending, which reduces the potential
for damage due to transportation, handling and bending/forming.
And how much is the additional cost in the middle east
for ECR bars compared to ordinary bars? (My primary interest is the
application for Marine / coastal structures. I haven't been able to get
sufficient feedback on marine applications)

Hariharan

 

[RichardC]

Hariharan, glad that the information was interesting. To try and answer your questions - In the Middle East we are subject to a combination of heat, hummidity and Saline environments which combine to form an ideal mix for generating corrosion on the rebar. In addition, the quality of concrete components have also been found to aid the corrosion process, for instance high chloride levels, poor and incorrect mix of the concrete components (to cut costs). My view is that the ECR will act as a balance or safety net to counteract these problems as the ECR is easily quality controled.

ECR has been used in many structures subject to marine environments where corrosion will be an issue.

Most bars are cut and bent after coating. A liquid epoxy is used to touch up the cut ends and any damaged during the handling.

The added cost for coating steel bars is approximately US$ 90 - 100 per ton of steel. However, this will depend upon who supplies material, bar diameters etc. In any case the cost of the ECR is minimal compared to the project costs and it does provide a necessary safety net.

 

[Hariharan]

Thanks, gentlemen. Could you get time to check on the marine
applications of ECR bars? The discussions have not touched
my main application area!

Hariharan

 

[RichardC]

Hariharan,

The CRSI (Concrete REinforcing Steel Institute) in the US has writen a report on the 'performance of epoxy coated rebar, galvanized rebar, and plain rebar with calcium nitrite in a marine environment'.

They probably will have more information so I suggest you contact them. The numbers are:

Tel: +1 847 517 4758
Fax: +1 847 517 1206
Website:

http://www.crsi.org

 

[Hariharan]

Thanks, I am already in contact with CRSI. I want to know where
it has been used and what is the feedback. Lab. investigations
are many. I am interested in field applications, anywhere in the
world, (preferably as a standard practice in marine structures, not stray
incidences!)

Thanks

Hariharan

 

[rubedog]

My experience in California is all the deck reinf, and any reinf. going into the deck such girder shear reinf. and reinf. in concrete barrier rails.