Maybe not the most desirable option but could you make up some stainless flat bar straps and set 2 anchor bolts on each side of the center joint? You can get anchor bolts that use screws instead of nuts that are relatively flat. They would run the length of the driveway and be located in the center.
I wondered About doing something like that but am concerned it may cause stress cracking around the bolts and result in a bigger mess
I doubt you will get enough of those to withstand the weight of two sections pulling apart like you describe. My thought is it will either bust or start big cracks on your otherwise smooth concrete surface.
I agree that something is moving under the surface. Seems odd that in this time you’ve not had a really bad movement though. Maybe you can ride this pony 15 more years? That would reach the lifespan of a concrete driveway. It lasting over 30 in good shape is a bonus.
