[Superman]

Though I've never worked as a cement mason, I have been dealing in the construction industry for a while and I can report there is some mythology in the posts above. Glossing past that, I'll offer just a couple of suggestions. Expansion joints - yes. reinforcing - yes. Go ahead and mess around with wire and fiberglas, but also take my advice and use some STEEL. Rebar sticks are very cheap. Use them. Use many.

Concrete does not dry. It cures. You can wet it until you're blue in the face and it will still cure. It will cure under water. I recommend you stay away from hot mixes, unless you are building a runway and the planes are getting ready to land. Slower curing is better.

The compression strength of the concrete will be determined by the aggregate used. Use good rock and you get good concrete.

And finally, go ahead and prepare the site yourself. Have a carpenter check it before pour-day (like the 30-year veteran above, I and the rest of the construction industry seems to be unaware that you don't 'pour' concrete....they all think that's what they're doing....even the engineers). When it comes time to pour, hire a crew that knows what they're doing. Or at least, hire a crew that contains at least one person who knows what they are doing and brings tools.

Oh, and thickness is often less important than people think. Be sure you create a good, dense, packed, non-organic (use rock or sand, not dirt) sub base. If you do this, two inches is enough. I mean, two inches is enough thickness for a concrete garage floor (two inches is not enough for certain other things). wink.