Jack feel free to email me directly to ask questions if you like. Getting the contractor to replace the drive is a BIG step to fixing the problem. Now what you need to do is make sure that the new portion gets done so that it never has to be done agian!!! Make sure the base is consistent for 12" depth, then make sure the design mix is right, for this you may want to go directly to the supplier and talk to them. If they send the correct mix design then the only screw up could be with the placement, limit the possible problems. Keep me informed on what is happening and when, because I would be willing to talk to the supplier for you if you wish. Now what you are asking yourself is WHY IS THIS GUY DOING THIS? Concrete and ICF'S are my passion I want it done right or it reflects on me. You have a good experince with concrete now you will use it agian, but, if your experince with concrete is bad you'll never use it agian and you'll make sure all your friends know about it too. Now you know my reasons.