If I didn't already own a small jackhammer, a industrial combination hammer would be what I rent.

Yeah, you could do it with an ordinary hammerdrill and masonary bits, but a combo-drill will do it a lot faster.

A hammer drill spins like a normal drill, and when it finds resistance, a "Hammer" strikes the bit, causing the rock to crack a bit and allow the bit to continue on.

A combination hammer drill accepts jackhammer style chisels as well as masonary drill bits. This allows it to work like a normal jackhammer aswell as a drill.

Or you could just rent a small electric jackhammer.

If you decide to go normal hammer drill, get a contractor or industrial grade one, rather than one you could buy at a hardware store. They aren't really made for rock.

There are four levels of tool for this job, the first 3 being inadequate:

1. Hammer drill or carbide bit in regular drill
2. Rotary hammer - even the largest will be slow
3. Chipping electric jackhammer (35#) - AKA small electric jackhammer - used from a standing position. Not heavy enough to do the job.
4. Pavement breaker (60#) suitable for concrete slab or rock penetration. Rental is about $40 for 4 hours which is longer than you will need it or want to use it anyway. Also used from the standing position.

While you are at it, buy a rock bar ($20) to pry out the pieces or break small pieces away where the jackhammer won't fit. I have 2 of these and they get used frequently.

I wouldn't mess around with a hammer drill. On my basement floor I used one the way you suggest, drilling holes an inch apart and then breaking the webs between them with a hammer and chisel. It worked great, but I only used the drill because I wanted to control the shape of the hole and not risk cracking the rest of the floor. If you just want to break up some concrete an electric jackhammer will get the job done a lot faster. I've taken out two long sidewalks and a couple of sets of concrete steps with an electric jackhammer. I tried the sledge first. The jackhammer was WAY easier.

I also urge you to have a pickup or trailer backed up to your work site so you can load the concrete as you go and haul it straight to the dump. Otherwise it will come back and haunt you.