Can the gravel used under my pool be used patio stone?
In my honest opinion if the idea of it turning into a soft concrete is what gave your fear, do not let it. That is the point of having a gravel base and the sand is simply there to easily level the pavers. Save money and recycle. :)

The gravel is used as saving money if you will from not having to pour a slab. Which also allows for a homeowner to do these types of projects. Many times in on jobs where there is concrete we just add sand and pave right over it, if it is uneven. If smooth you can add pavers and fill with sand.