I need some help with a problem I've created for myself.
The 40mm granite aggregate that I have chosen to use for my driveway, whilst very pretty in dark green, is not behaving like type 1 or rail ballast as I hoped it might. Rather it is mis-behaving like gravel only on a larger scale . Walking on it presents no major issue but powered wheels result in rapid progress downwards instead of forwards.
I am hoping that if I add some finer material to the mix, it might help tie the aggregate together and prevent movement. The question is what to add? I had thought 2-6mm grit would be a sensible option to try, but despite its use in modern eco-paving it seems the only way you can buy grit is by the 100T from a quarry or by the 10kg from garden centres. Neither of which is affordable or feasible.
If anybody has any economical suggestions that dont envolve "start again", I would be eternally grateful.
if it is a 40mm single size (nowadays called 20/40mm) then you'll have about 30% voids (gaps) in the material so of course the material will move under force. Type 1 is generally a 0/40mm pretty evenly graded material containing fines, 6mm, 10mm, 14mm, 20mm, 32mm, & 40mm+, and after compaction should provide a solid sound foundation.
if adding undersized aggregate to fill in the voids, you really should be re-mixing for the whole depth you've laid the 40mm material. if you want drainage, maybe add a 6/14mm or 4/10mm. if you want to bind it, then add 0/20mm.
i used to love using tarmac, but got fed up with getting my asphalt
Thanks for the response Phil. Yes it is 20/40. I will try a test area with some 4/10 added.
You say "of course the material will move..". A point I would make is that regardless of the voids if the pieces were adequately triangular (which unfortunately they are not), theoretically they would interlock and prevent movement.
I am not a groundworker by trade, (my trades are 90% inside the building). I'm just some eejit who thought "I know, I'll save myself £700 on the gravel stabilisation systems needed to make small gravel behave, by using a larger sized well drained stone." What I'm starting to realise is that it doesn't matter what you choose for a driveway, they all cost the same by the time the suppliers have had their pound of flesh.
Gravel drives should be predominantly type 1, with just enough stone on top to cover the sub-base. While triangles (or pyramids!) should interlock, there's nothing to bind them so any pressure will cause shear immediately.
. Walking on it presents no major issue but powered wheels result in rapid progress downwards instead of forwards.