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Re: Corroded Reinforcement

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ACI 318-05 (should be same or similar for older versions) Section 7.4.2.

In fact, it usually desirable to have a little rust/mill scale on bars.
Brand-spanking new bars with absolutely no rust or mill scale might have
some oils, etc still on them.  At minimum, a little (and I mean a little)
surface rust actually helps with the bond of the bars.

As to the original question, at a minimum, I agree with Bob.  If the bars
have lost enough cross-section such that the sections design capacity no
longer meets the expected (design) demand, then likely something should be
done.  In theory, there is still some significant "reserve" if one is
"just" below capacity.  But at that point, it becomes the engineer's
judgement as to how much risk s/he was to take on if they want to
contemplate "cutting" into that reserve.  I would personally hesitate to
do that, but it is largely a function of the specific of the situation
(i.e. how sure of the loads are you, where is the compressive strength of
the concrete in "real" finished construction terms relative to the design
strength, how accurate is the bar placement/location, what is the actual
strength of the rebars relative to the assumed design yield strength).

The bigger issue is potentially the spalling concrete.  Has enough
concrete spalled such that the required development length of the rebars
is no longer present?  It don't matter how much rebar you got left if it
can't be developed and the tension stresses be transferred into the
concrete.

Regards,

Scott
Adrian, MI


On Sat, 7 Jan 2006, Robert Kazanjy wrote:

> When the amount of material lost reduces the section design capacity below
> the design demand?
>
> In new construction lightly rusted (no loose material) can be used w/o
> reduction but
>
>  if the  rust is loose then the rebar must be cleaned up & evavluated for
> lost section plus if the rust is significant, the interlock of the rebar can
> be compromised.
>
> don't know the ACI section offhand that covers this
>
> are we talking about a little rust or are the deformations nearly gone as to
> render the rebsr smooth?  column? beam?  exterior exposure?
>
> cheers
> Bob
>
> On 1/7/06, Johnenader(--nospam--at)aol.com <Johnenader(--nospam--at)aol.com> wrote:
> >
> >  I am working on an old building remodeling, spalled concrete along with
> > corroded reinforcement were found.  At what percentage of loss in the bar
> > diameter would the bar need to be replaced.  Any help or direction were to
> > look is greatly appreciated.
> >
> > John
> >
>

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