Introduced is one thing. Introduced with success is another topic altogether. I would bank on 10-15%.
I agree with Dennis.. Depending on the size of your plant, 15% could be too much if your burner can not “super heat” the virgin aggregate to keep temp on the mix..
what i see is a greater amount of blue smoke from parellel flow drums when the rap percentage is increased and the mix temps are increased, I have had several customers running 20-25 % with out to much trouble, a major factor or problem is if the rap stops flowing during production, the temp spike has even caused a baghouse fire, ( plant safety system was ..BYPASSED) . I know of several PF designs running more than 15% , mostly southern states