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Re: Repair of reinforced concrete members.

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Dr. Sinha:

I have observed that in some repaired concrete, the closely spaced,
smaller surface cracks indicative of a subsurface corrosion problem may
very well not be present in the area that was patched.  In those cases,
however, the patch tended to delaminate from the parent concrete as a
unit.  Sounding with a hammer easily revealed the lack of a proper bond
between the patch and the parent concrete.

I would not perceive the problem as grounds to preclude the use of any
of the repair materials that you listed.  I would strongly advocate
periodic inspections to repaired structures to monitor performance.

In the process of assessing a particular damaged concrete structure for
repair, one should investigate statistically significant areas to
determine the alkalinity and chloride ingress at various depths to
determine the relative potential to develop the battery effect.  Often
it is not cost effective to replace all of the concrete that has lost
the ability to passivate and prevent rebar corrosion, but the tendency
of future corrosion can be determined in advance.

There are many techniques of concrete repair that can lessen the battery
effect problem also: membrane application, cathodic protection, and
topically applied migrating corrosion inhibitors have been used with
some degree of success.

Regards,
Harold Sprague
Black & Veatch
 ----------
From: Dr. Ravi Sinha
To: seaoc(--nospam--at)seaoc.org
Subject: Re: Repair of reinforced concrete members.
Date: Monday, October 06, 1997 1:55AM


On Sun, 5 Oct 1997, Lew Midlam wrote:
> 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'?

My mistake for improper wording of the query...

The most popular method that I have observed is to clean the rebars,
apply corrosion inhibitor on the surface of the bars, apply epoxy
on the concrete patch, and then replace the excavated concrete with
polymer concrete with similar strength as the original.

This engineer (who probably speaks from many years of experience
in this field) has expressed his apprehension that the presence of
epoxy would make the concrete amenable to some change in volume.
So, if the rebars corrode again in future, the tell-tale sign of
surface cracks parallel to the rebars may not apper.  This will imply
that the structure may deteriorate without any visual warning.
I have not seen any such apprehension in literature and was wondering
if there is any truth to this view.

 -----------------------------------------------------------------------
----  ---
Ravi Sinha, Ph.D.		email: rsinha(--nospam--at)gemini.civil.iitb.ernet.in
Assistant Professor		       rsinha(--nospam--at)civil.iitb.ernet.in
Department of Civil Engineering	       Phone: (91-22)-578-2545 Ext. 7336
IIT, Powai, Bombay - 400 076, India    Fax: (91-22)-578-3480, 578-3557