There is a very good article which includes the use of building rubble in
this months RHS journal "The Garden".
Years ago I had the same, and made a loose mound of it, then covered it with
a mixture of Peat (80%) and coarse sand (20%), this worked its way into the
gaps and I planted heathers on it and they were the best heathers I have
ever grown.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk