How to fix leak in ABS pipe going into cement
The correct way to fix this is to cut some of the pipe out coming from the Y, and replace it with glued-in fixtures.  I don't think silicone would hold and it is certainly not up to code -- epoxy I would have no problem with myself but is also probably not code.  Sand the plastic and make sure it is really clean if you go this route!

If you are inclined to re-glue, you can cut a section out of the pipe -- one cut right at the Y's hub, and another about a foot away.  Then you need to remove the 3/4" that is in the hub, being careful not to damage the hub itself.  This is a huge pain as you can imagine, and I usually use a rotary tool with an aggressive grinding bit to simply carve it out.

Your third option is to replace the Y which might not be as hard as you imagine, depending on the access you have -- just chisel out the concrete surrounding it enough to get a coupling on the pipe.