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RE: Carbonation Induced Corrosion

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Nick,

Move on this one with caution.  I worked on a project several years ago that
had been reviewed by 3 teams of engineers.  I had some gyp panels removed
and found that the walls had moved out to such a degree that all of the
precast floor to wall connections were broken.  The cause was perceived to
be foundation settlement.  Foundation settlement was not the cause.  It was
the closest I had ever seen a structure come to a collapse condition without
actually collapsing.  Your 1/2" cracking is very large and may suggest
severe structural distress.

Getting the cores is a prudent first step to see what is going on in the
concrete matrix.  Get petrographic testing done by a competent lab.  There
are many that claim to be able to do petrographics, but few know how to get
it right.  (CTL and WJE / Erlin Hime Labs know how to do it right, there are
others)

Any form of concrete deterioration can be mitigated (including carbonation).
But it isn't like turning off the corrosion switch.  After any structural
repairs, (and depending on the petrographic analysis) consider using an
elastomeric coating that will serve as a barrier and bridge active cracks.
Assuming a heated 30 year building, you should also calculate where the dew
point is in the wall section and if there is a means to control water that
penetrates the cladding.  In other words, you may need to have a perm rating
on the coating.  You may have to provide weeps.

Applying a coating will eventually mitigate corrosion, but until the
concrete matrix looses whatever is pushing the rebar to a threshold of
corrosion, the corrosion process will continue.  You may have to patch again
in the future until the corrosion process slows down significantly.

You may find some help at the International Concrete Repair Institute at:
http://www.icri.org/

The US Army Corps of Engineers has some good information on concrete repair.
http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-2002/toc.htm

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	npitera(--nospam--at)mmm.com [SMTP:npitera(--nospam--at)mmm.com]
> Sent:	Wednesday, September 11, 2002 12:19 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Carbonation Induced Corrosion
> 
> I haven't seen any responses on this topic, so I'm resending this memo.
> 
> Regards,
> 
> Nick
> ----- Forwarded by Nick Pitera/EG-Engrg/3M/US on 09/11/02 12:17 PM -----
> |--------+------------------------->
> |        |          Nick Pitera    |
> |        |                         |
> |        |          09/10/02 10:08 |
> |        |          AM             |
> |        |                         |
> |--------+------------------------->
>   >----------------------------------------------------------|
>   |                                                          |
>   |     To:     seaint(--nospam--at)seaint.org                            |
>   |     cc:                                                  |
>   |     Subject:     Carbonation Induced Corrosion           |
>   >----------------------------------------------------------|
> 
> 
> 
> I'm presently looking at a 30 year old office building that has load
> bearing
> precast concrete exterior wall panels. The exterior precast wall panels
> are
> exposed aggregate ( you know that Soviet concrete look that was big
> architectural hit  in the early 70s) . Bad choice of wall system.....
>  Over 90% of the panels show cracking and rust bleed of from the rebar.
> Cracks
> range in .005" up to 1/2" in width with the typical crack width being
> about .03"
> .Previous epoxy injection efforts from years on by have had pour results.
> 
> I think that carbonation could be one of the culprits here along with the
> freeze
> thaw, and water penetration. I'm having some core samples taken for lab
> work.
> 
>  Has anybody had success stopping carbonation induced corrosion and with
> what
> coating systems. Do coatings really prevent further corrosion?
> Any comments on this issue will be greatly appreciated.
> 
> Regards,
> 
> Nick

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