I'm preparing to design a concrete sidewalk on existing pavement, (Asphalt and Concrete). The sidewalk will be an island for pickup and drop off of pedestrians from a bus. My approach is to consider the sidewalk as a concrete overlay which is unbonded. This approach will allow the existing pavement and new sidewalk to work independently. My only concern is water and upheave. We plan to place 1/2" premolded joint filler where the curb meets the sidewalk and at intervals of 8 ft. It is common that this premolded joint filler deteriotes to a point where water will seep if not maintained. Since our approach is to build on top of existing pavement there will be no drainage layer underneath to allow water to fill the voids. I believe over time frost heave will damage the sidewalk.

Is this the right approach? Or should we remove the existing pavement and place a drainage layer followed by your typical 4" concrete. The existing pavement is currently designed for aircraft. The existing concrete slabs has reinforcement. We are also installing 6" steel faced curbs as per the architect.

I wouldn't put concrete walk on top of asphalt.

Visa Versa, yes. But not this way. The asphalt is too soft. What if a UPS or Fed-Ex truck decides to jump the curb, and pull up on your sidewalk? Will it push/roll the asphalt out from under? I would think so.

Peel the asphalt, would be my opinion.

Concrete on top of asphalt doesn't work very well. They expand and contract differently, and yes, drainage (or lack of) will cause additional problems for your concrete. It actually doesn't matter what the existing pavement is rated for... strength isn't your problem. The fact that they are two very different materials is the problem.