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Re: Repair of reinforced concrete members.

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Riva,
I'm not sure if you mean 'fill the patch area with epoxy' or 'apply a
coating of epoxy to the exposed and cleaned bar or 'apply a coating of
epoxy to the surface of the concrete patch'?

Filling the patch area with epoxy or coating the cleaned bar with epoxy
would both be ill-advised.  Both methods would result in a 'battery
effect' at the two ends of the epoxied area and these ends would then
corrode very rapidly.

Coating the patched surface with epoxy might have some effect in keeping
cardon-dioxide, oxygen, salt, chlorides, and moisture out of the
concrete, and therefore might be beneficial.

Our normal recommendation here in Florida is to excavate the bar, clean
it, coat it with a corrosion inhibiting agent and fill the patch with
concrete with similar properties of the surrounding area - in order to
minimize the 'battery effect', differential expansion, contraction,
shrinkage, cracking at the boundary of the patch.

Hope this helps,

Regards,

-- 
Lewis C. Midlam
http://www.lcm.com
============================

Dr. Ravi Sinha wrote:
> 
> This may be relevant to those who are faced with rehabilitation
> of degraded reinforced-concrete structures.  As you all know,
> major corrosion in rebars manifests on the surface of the member
> by cracks parallel to the rebar.  The most popular method for
> repair is by applying a coating of suitable epoxy after cleaning
> the rebar to remove any corroded material.
> 
> I was recently informed by an engineer that the this method is
> not very good as the presence of epoxy coating prevents future
> surface cracks even if the bars are subsequently badly corroded
> due to some problem.  As a result, the most important visual
> warning sign is eliminated making the entire process of epoxy
> coating repair a very dangerous one.
> 
> I have not come across any technical reports indicating such
> problems.  However, my specialisation is in earthquake engineering
> and my information in the intricacies of using epoxy coating may
> not be as exhaustive.  I will appreciate any information on this
> apprehension that has been raised.  If there is any genuine problem
> with the use of epoxy repair of rebars, I feel that the information
> should be very widely distributed since this is the most popular
> method of rehabilitation of degraded section.
> 
> I look forward to more light on this issue.
> 
> -Dr. Ravi Sinha
> 
>