Re: confused about concrete in knoxville Tennessee?
Being a Caliman myself, I can't say exactly what should be done in your new location. What I can tell you is this.
Concrete, in and of itself will expand and contract with temperature, which is why expansion joints are installed in slabs over about 10x10. The joint allows movement between slab sections in the case of a full separation, or a place for the slab to crack where it won't be seen as is the case with a surface seam. At any rate, one good freeze/heat cycle will have that slab cracked, which is going to allow moisture between and under the slab. So the guy telling you to replace the whole thing IMHO is only looking to get more money out of you.
Because of your climate, I would recommend pinning the new slab to the old and also pin it to the house. Pinning will allow movement without lifting, a hinge point if you will. Just so it's clear, pinning would be lengths of rebar that are drilled into the existing slab and house foundation that extend into the new slab.
The only place I've used reinforced concrete or reinforcing mesh is driveways and commercial patios where vehicles and/or heavy pedestrian loads are present. In the case of driveways, you want a thicker slab and the reinforcement to withstand the weight of vehicles. The reinforced concrete that I've used had fiberglass fiber mixed into it. I didn't like this because the fibers were left visible, sticking out of the surface which was unsightly and sharp which means bare feet were not allowed. I recently heard of horse hair being used as a reinforcing fiber, but I can't really see how that would work very well, quite frankly, though any exposed hair would wear away and not be a safety hazard.
If the bids have different levels of work or materials involved, then you don't have bids that you can compare based on price. Verify that each bid is for the exact same work, if it is, then choose the company you feel the most comfortable with as well as do the job you are looking for rather than the lowest price.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!