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RE: Carbonation Induced Corrosion

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Nick,
By 1985 we evaluated a 50 years old concrete chimney which was permanently
exposed to CO2 effluents. It showed some signs of reinforcement corrosion.
We got some coredrills and test them for ion chloride content according to
ASTM.
In spite of the fact these ion chloride contents were very below the %,
codes (ACI, BS, and others) specify as threshold, we concluded that
carbonation induced by CO2 reduced the PH of the cement paste which protects
the bars from corrosion. In that condition, low contents of chlorides can
corrode reinforcing steel at very low rate.
Actually the chimney is still working.
There are some ACI's publications which can help you about this topic.
Regards
Marcos J Salom

-----Mensaje original-----
De: npitera(--nospam--at)mmm.com <npitera(--nospam--at)mmm.com>
Para: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Fecha: Miércoles, 11 de Septiembre de 2002 01:50 p.m.
Asunto: 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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