Driveway renovation - Renovation of 30 year old driveway

[billc47]

My driveway is 25m with a fall of 1m. I intend replacing 30 year old concrete slabs (D50) currently laid as twin tracks, separated by 600mm, bedded on whin sand. The slabs are layed long edge across the run of the driveway. The existing slabs are hard butt jointed and over the years have shown some spalling at the edges.

I intend to essentially replicate the existing design.

Questions:
(a) is whin sand acceptable as the screed base?
(b) given the fall, what alternative to hard butt jointing would be better?

Any advice will be appreciated.

[lutonlagerlout]

we normally recommend laying on to at least 4 inches of concrete for driveway usage,but i see you live in texas
it may be different there but the normal practise here Bill is 100MM of type 1 compacted then 100mm of concrete with the slabs on top
cheers LLL

[billc47]

I've had some mail routed via Texas but the wee village of Houston in Renfrewshire is but a few minutes drive from Glasgow Airport.

The existing driveway hasn't suffered from subsidence, it seems to have approx 100mm of whin sand / crushed aggregate on top of compacted rubble/bricks. My intention was to remove the existing slabs and dress the surface with a further 20mm of screed and lay the new slabs on that.

[lutonlagerlout]

ahhh you are only 10 miles from my townies in greenock :;):
the original houston i guess
sadly once you disturb it it will be difficult to put it back on 20mm of dust
the first advice i gave still stands
cheers LLL

[billc47]

I'll go with your advice regarding the 100mm, a wee bit more work now but should provide a better result both short & long term.

Any thoughts on hard butting the slabs, or would I be better with a gap between the slabs? - I'm not sure which sealant between the slabs would would be suited to the fall of the driveway and stand the test of time.

[Tony McC]

Butt jointing? Not a good idea

[billc47]

OK hard butt jointing is not a good idea.

Is a close joint (2 - 5 mm) with a suitable jointing sand likely to work or do I need to go with a larger mortar filled joint.?

My concern is that a larger mortar joint is likely to crack and crumble in short order and wash out given the gradient of the driveway.