Copper and concrete are not a good mix. Many of the Levittown homes in
the NE have had to change from the original copper slab heat to
baseboard because of this.

From:
http://www.oldhousejournal.com/magaz...iantheat.shtml

"As time went by, some of the copper tubing began to leak, and water
would soak into the ground rather than rise up through the floor.
Consequently, homeowners didn't know when a minor leak occurred, which
eventually led to major problems. Both Levitt's and Wright's homes had
early copper piping that pushed the envelope right to its limits in
this way. If workmen operating on a tight schedule installed the piping
with too much play, the pipes could easily break. In fact, the very
nature of copper's interaction with concrete made corrosion of the
pipes likely to happen eventually, unless a protective barrier was
installed-a process that was perfected much later. Once leaks began
they were nearly impossible to fix, leading many homeowners with this
problem to abandon the systems and install baseboard convectors
instead."

You could always trust the guys at copper.org or the thousands of
people that had their system fail. I would at least wrap the pipe in a
thin layer of foam to keep the concrete from touching the copper.