The Brew Cabin

Posted: **Fri Jun 12, 2009 1:20 am**

Hi all.

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.

Posted: **Fri Jun 12, 2009 7:35 am**

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.

Posted: **Fri Jun 12, 2009 12:23 pm**

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 Â£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.

Posted: **Sun Jun 14, 2009 12:09 pm**

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.

The Brew Cabin

That sinking feeling