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RE: Rusted rebars

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The tradition has been that a little surface rust is not a problem, and
actually enhances bond to the concrete.  Flaking rust may or may not be a
problem, but generally reflects a loss of section.  How much of a problem
depends on the amount of stress in the bar compared with the loss of
section.  It takes a lot of flaking corrosion to result in a significant
loss of section.

Any flaking rust should be removed prior to placing the concrete.  This is
more to achieve proper bond than anything else.

Remove the corrosion, and measure the cross section area.  If there is only
about a 5% loss of bar section or less, I would not worry about it.  With
any greater cross section area loss, one should compare the measured cross
section area with the theoretically required cross section area.  

I generally don't get too concerned if I have about 90% of the section
required by design theory.  I figure that for that particular section I just
ate up my phi factor.

All this needs to be weighed against the type of possible failure mode and
the purpose of the structural element (if it is nuclear containment I break
out the jack hammer), and good old engineering judgement.

Harold Sprague

> -----Original Message-----
> From:	Julian Chu [SMTP:julian(--nospam--at)]
> Sent:	Monday, April 24, 2000 12:30 PM
> To:	seaint(--nospam--at)
> Subject:	Rusted rebars
> Is there any reference/standard regarding rusted rebars to be poured with
> new slab? We have an existing structure with some exposed rebars left
> unprotected for several years. Those bars were designed to be lapped for
> later phase of construction. Can someone use wire brush to brush off the
> rust and reuse them for the lapping?    
> Any suggestion or help will be appreciated.
> Regards,
> Julian Chu