On 2010-07-11, David Nebenzahl wrote:

At this point, the only thing that gives me pause is the possibility
of weakening the existing slab by drilling into it for rebar dowels.

I'm pretty sure that if you drill an oversize hole (e.g. 9/16" for
1/2" rebar) and fill it with a structural epoxy adhesive, you won't be
weaking the existing slab and it may end up stronger than previously.
However, this is a definitely a job that calls for an engineer, so
stop beating around the bush and hire one.

Cheers, Wayne