Efflorescence on concrete paving when using recycled concrete aggregate

Hello everyone.

We are currently wondering whether it is sufficient to use RC gravel, or if it really has to be the mineral mixture, which is more than twice as expensive.

We are getting anthracite concrete paving stones. The surfaces will be completely "watered," meaning they will be exposed to the weather.

What are your experiences with this?

RC gravel is completely sufficient. If you are unsure, put another layer of geotextile in between. Why should anything effloresce?

Because I have already heard from several sources that crushed rubble releases substances that can cause efflorescence.

I cannot confirm that. Depending on the load, 25-30cm RC gravel, 4 cm crushed sand-gravel mixture (I prefer to use only gravel), and then the paving on top.

I can't imagine that. I have especially heard about anthracite-colored paving that it effloresces, but why should that have anything to do with the substructure? I rather suspect the paving itself. Probably the only help is not to take the cheapest stuff to keep the likelihood as low as possible.

One would say that sounds like an excuse... how is something supposed to come up against gravity, against the flow of water, through the split?