>I was a Chicago licensed masonry contractor.
>
>Even on the sides of concrete buildings, rebar, too close to the surface
>would adsorb enough moisture through the concrete to rust.
>Rust can cause rebar to increase it's size 11 fold.
>That would cause the concrete to spall off, exposing more rebar etc. etc.
>
>I don't know if that's empirical, actual, or just "been dere, made lots of
>money fixing it" evidence.
>
>Now how long before the bottom of the concrete base spalled off to cause
>problems certainly depends on many factors and I can't predict.
>
>But moisture contact with rebar will cause rust, and will cause concrete to
>deteriorate.
Reminds me of a show I saw on NOVA years ago, about the restoration of the
Parthenon in Athens. The structure had remained in almost perfect condition
for over 2000 years, until sometime in the 1700's the Greeks and Turks were
going at it, and one of the armies was using the building to store
gunpowder. During a battle, the powder was ignited and the Parthenon was
blown to bits.
It remained in almost complete ruins until sometime in the early 20th
century when a British engineer oversaw its "restoration." The pieces were
painstakingly gathered up and put back together like a jigsaw puzzle.
Unfortunately, they used steel pins to hold the pieces of stone together.
Over the decades, moisture crept in through the porous marble, and the steel
pins rusted and expanded, causing the stone blocks to further crack and
disintegrate.
They ended up having to use x-ray machines to locate each one of those steel
pins in the walls, and drill in and remove them, to avoid the final and
complete distruction of the building. It would have been better if that
restorer had simply left well enough alone.
The same thing will happen to rebars set in concrete if they get exposed
to the moist soil. Not from the moisture, but from galvanic reaction
between the exposed steel bar and minerals in the soil. It generates an
electrical potential on the rebar, causing further corrosion of the rebar
and cracking of the concrete throughout thestructure, not just near the
surface.
Don k4kyv
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