base for patio with concrete slabs
Surely you can but there a couple of things to consider. Concrete should not be less than 2 inches, so based on a 2x4 as your footing/frame I would not add more than 1.5inches of base loose pieces. The other thing is expansion as it cures. So you may want to add chicken wire overlay and use large enough pieces of concrete where you can tie the concrete pieces with wiring to the chicken wire. This will allow for the concrete to stick and stay regardless of expansion during the first 3 days of curing which is the most important.

If you are using crushed pieces then I would just make sure to tamper the rocks very well so the no sinkage occurs over time.