Concrete never truly sets. The chemical reactions continue for centuries.
Concrete structures put up 2000 years ago by the Romans are still perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been possible
without concrete. Some of the techniques developed then are still in use in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee that
the metalwork will remain in contact with moisture and conductive salts for
as long as the structure holds together. The constant exposure to moisture
and corrosive salts is the main reason for failure of modern ferro-concrete
structures. Concrete will suck up whatever moisture is around, either from
the air or the soil and is always damp inside, hence the steel rusting out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded in
concrete should give a DC or low frequency AC resistance/impedance of less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI

Then there is the matter of whether to extend the rebar into the soil
or totally encapsulate in a concrete base for a tower...

And the matter of applying a protective coating of paint to the rebar
to minimize corrosion...

I have a couple of clothes line poles that are in pretty good
condition above and below the ground line but rusted completely
through at the ground line!

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"