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[SEAOC] Re: [SEAOC] Epoxy Coated vs. Galvanized Rebars

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   If you are talking about the final in place condition of the wall
and your 
   flood wall is for a non-marine facility then neither epoxy coated
rebar or 
   galvanized rebar will be of much value.  The two main chemical
attacks on 
   concrete are sulphates and chlorides.  High concentrations of
sulphates 
   will attack the cement paste.  The solution for this is to use
either Type 
   II or Type V sulphate resistant cements.  The chlorides (salt)
have little 
   direct effect on the concrete paste/aggregate but will obviously
corrode 
   the rebar if allowed to come in direct contact.  The problem here
is that 
   the corrosion has a volume of 4 times the parent metal and hence
tends to 
   pop off the concrete cover due to this expansion. Theoretically
epoxy 
   coated rebar should prevent any corrosion regardless of concrete
cover or 
   quality on concrete.  However, epoxy coated rebar has come under a
lot of 
   scrutiny lately.  The Florida Dept. of Transportation conducted a
study 
   and found that even without signs of corrosion or physical damage
the 
   epoxy coating in some of their highway bridges was delaminating.
Epoxy 
   coated rebar is now band by several DOTs.  Galvanizing is a great
system 
   for preventing corrosion of metals in general but has not
performed well 
   against chlorides.  Galvanized rebar used to be popular for sewage

   treatment plants but resent studies in the 80's has shown that it
is not 
   as effective as was originally thought.  If you are worried about 
   corrosion there are additional steps you can take.  Among these
are a low 
   water cement ratio (0.40 or less), increase cover to 3 inches,
addition of 
   a mineral additive such as fly ash, blast slag, or silica fume
(silica 
   fume is the best but added curing precautions exist), use a
plasticizer 
   (or super plasticizer) for good consolidation, and finally you
could 
   consider a corrosion inhibitor such as Calcium Nitrite (by W.R.
Grace) or 
   Rheocrete 222+ (by Master Builders).  Moisture in the absents of
either 
   sulphates or chlorides should not effect the concrete paste or
initiate 
   corrosion of the rebar.
   
   Thomas Hunt


______________________________ Reply Separator
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Subject: [SEAOC] Epoxy Coated vs. Galvanized Rebars
Author:  seaoc::(SEAOCAB) at ~FABRIK
Date:    6/6/96 9:45 AM


From: seaoc(--nospam--at)power.net
Date: Thu, Jun 6, 1996 9:45 AM
Subject: [SEAOC] Epoxy Coated vs. Galvanized Rebars 
To: seaoc
We have a condition where a flood-wall is to be constructed.  The
construction 
is going to last for a very long time.  The foundation is exposed to
saturated 
conditions.  What are the advantages of epoxy coated vs galvanized
rebars.
Any information will be appreciated. 
thanks
ahmed nisar - Dames & Moore San Francisco, CA
        
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Subject: [SEAOC] Epoxy Coated vs. Galvanized Rebars 
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