Concrete expands and contracts from the temps. Hot days, it gets bigger, cold days, it gets smaller. This is why porches are poured separate from the house pad when building a house. The house stays constant, so there is minimal movement, while the porch changes.
On roads, their has to be some sort of expansion joint between each section of concrete. Not just cutting it, that just hides the cracks. It has to have space to get bigger in summer. The amount of movement is so small that it's almost impossible to measure it, but it is happening and if it's not planned for, you will have failure.
Asphalt also moves according to the outside temperatures, but it's elastic enough that you do not have to provide expansion joints to it.
Since they both move differently, it's extremely challenging to put one on top of the other. Where I live, about ten years ago, they redid Interstate 20 with concrete as a base and then paved over it. This was in the news and there was a lot of talk about how expensive this was, and if it was just TXDOT wasting money, or if it would save money in the long term. Since then, they have repaved the Interstate, so it was a failure in saving money. Overall, I never notice any issues when driving on it, so maybe it's just TXDOT spending money to get more in their budget every year? I don't really know.
For a driveway, home owner, I would be very cautious of mixing the two. You really need to do one or the other. I know a lot of people think concrete is better, but it really has to be done right in every regard or it will fail. Asphalt is used in almost every road all over the world for a reason. It's not just that it's cheaper, but that it's a very effective road surface. The problem home owners have is with installing it. Was the base properly compacted? Is it stable and does water run away from it? Then the biggest problem is in the mix. Most driveways are done with a cheap mix that is done at the plant. City, County and State projects all have a certain mix that must be done for their roads. This is more money. Next is in how thick it's applied. Most homeowners only get two inches, and if the guy doing it isn't honest, it might not even be two inches. I was told that you really have to have four inches for it to last. When done properly, with the better mix of materials, it will come closer to the cost of concrete, but will easily outlast concrete.
