It certainly can be used - the question is what frequency you want an
antenna for. The copper wire is rather heavy for self-supporting
designs below 2m, but will work for a dipole or loop with strong enough
supports. (The concern is purely mechanical - primarily supporting the
weight. Electrically it will work just fine.)
I've used #12 or #10 solid copper wire for yagi elements on 2m. Again
the thicker wire being heavier the elements may tend to droop a bit
if the antenna is subject to vibration. I tend to use #8 aluminum wire
instead because it is lighter and stiffer. But it would work very well in a
quad, for example, where there is a framework to hold the wire in shape.
Plastic water pipe is very good for this, especially on 2m, and I have
several quads built this way. For bands above 2m the wire should be
stiff enough to hold its own weight as a dipole and can be used for
yagis - the only thing to remember is to adjust the yagi design for the
wire diameter you are using. The "cheap yagi" designs from WA5VJB
(available as a download from www.clarc.org
if you look around) use
copper or aluminum wire or rod and are very easy to build and match.
I think they are designed for 1/8" elements, which is #8 wire, so you
shouldn't need to make any corrections for element diameter.
The galvanized rod is a bit harder to find a use for, for two reasons.
First, steel (and the galvanized coating) aren't as good of a conductor.
Second, and more importantly, the rod is a bit too short for a lot of
possible uses. But it could be used as a quarter wave vertical for 6m
with some wire radials. You could also use it as the top whip of a
loaded antenna, perhaps using the copper wire for a loading coil and
the lower portion of the radiator. Except for severely shortened
antennas, the conductor losses probably won't be a problem at HF.
You could bend it into an extended double zepp for 440 MHz, but
you'd need 10 feet of it to make one for 2m.