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Re: Corrosion damage / Earthquakes

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Gail,
 
Thanks for the review of pH -- it's good to have that quantitative information as a reference.
 
My experience is that, long before loss of steel area becomes a problem, significant damage is done to the concrete by spalling and cracking.  Rust has a volume many times that of the steel that produced it and when corroded rebar, found because of cracks or loss of concrete cover, is exposed and cleaned, there is often little or no apparent loss of steel [but I have also seen significant loss of area].  My rule of thumb is has a serviceability period of 100 years + or - a few decades -- modern High-performance concrete will probably last somewhat longer.  The worst I've seen has been in a 100-year old + or - public sidewalk over a basement extension into a street right-of-way.  Two approximately 100 year old houses in a So. CA neighborhood, one of reinforced concrete, one of unreinforced concrete: the exterior walls of the reinforced house were rust-stained, cracked and spalled, the unreinforced house looked as if it could have been built 10 or 20 years ago.
 
International Concrete Repair Institute  [Sterling Virginia] publishes Concrete Repair Bulletin.  Aberdeen Group [Addison Illinois] publishes Concrete Repair Digest.  I've found both helpful in the past -- I'm not a current subscriber to either.
 
Nels
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net