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Re: Unusual precast wall panels

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With a wall with H/t of 24, I'd have concern too.

Reinforcing steel corrosion can be present with no evidence of its presence
other than a crack that roughly parallels the reinforcing.  If little or no
liquid water is reaching the steel, visible red evidence of corrosion may
not be transported away from the reinforcing to the surface where it can be
seen.  Oxygen along with airborne water vapor that migrates into the
concrete and condenses act on the steel to do their dirty work, unseen.
However, the rust occupies a volume many times the volume of the source
steel and builds up great pressure.  The pressure can force the concrete or
masonry to crack, revealing the corrosion process, but the corroded steel
may not even be visible in the irregular crack.  There is generally no
deterioration of the concrete or mortar to give away that corrosion is

In the case of the damaged foundation stem wall near a swimming pool that I
posted about a day or so ago, there were only a couple of places that
provided the confirming view of rusted rebar.  Along most of the lengths of
nearly 1/4" wide cracks, the crack surfaces were so irregular that rebar
with 2" to 3" cover remained hidden from my flashlight-aided view.

Nels Roselund
Structural Engineer
South San Gabriel, CA

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