I recently had to jack hammer out a small section of my basement floor (about 1 1/2 feet tall by about 5 feet wide) in order to install new sewage lines for a bathroom.

When I go to replace the concrete floor, should I add rebar in order to help hold the old concrete to the new concrete or should I just use a bonding agent? The concrete is about 4 inches thick and has a sand base followed by clay. Any ideas?

I don't think re-bar is necessary. Make sure the soil under the new concrete is compacted as tight as possible.

I recently had to jack hammer out a small section of my basement floor (about 1 1/2 feet tall by about 5 feet wide) in order to install new sewage lines for a bathroom.

When I go to replace the concrete floor, should I add rebar in order to help hold the old concrete to the new concrete or should I just use a bonding agent? The concrete is about 4 inches thick and has a sand base followed by clay. Any ideas?
Okay, now what if I wanted to lay tile over the new and old concrete? A friend told me that the new concrete may shift and cause the grouting to break. Should I lay some proboard or plywood down to help prevent this?

Look at the edges of your hole. Are they ragged or nice and smooth. If you imagine the floor suspended in the air and not supported underneath, would you be able to push your concrete patch out, or would the ragged edges tend to hold it in. Now imagine that the whole repair is sitting on a nice, solid, compacted foundation. The new patch fits the hole absolutely perfectly, because you poured it as a semi-liquid and, assuming you worked it well into the hole, and the mix was sufficiently strong there is no way it could move once it sets, unless, of course, it shrinks, which might happen if you use too much water in your concrete mix.

I assume you will be using pre-mix concrete. I always sweeten that stuff up some with a bit of extra portland cement.

I would probably wait a month or so before tiling.

Great, thanks for your help. The way you described it makes perfect sense.