Slabs for roadway - Paving slabs for roadway

[Roads]

An architect has proposed precast concete paving slabs for an access road into a hotel project I'm working on. The sizes vary but are up to 750x600mm. There'll be a nice bit of traffic on it with the occasional van and bus.
Its fairly hard to find guidance on this, most suppliers deal with occasional overrun and spec a sand bed.
I think a rigid bed will be needed ontop of a concrete slab but could do with a bit of advice/reassurance, will I need to put contraction and expansion joints in the concrete slab as if it was a concrete road? If so will these need joints need to be in the paving aswell? ???
Any help would be great.....

[Tony McC]

Another dimwit architect - 750x600mm flagstones will just fall apart under regular traffic. Wrong product in the wrong place.

[msh paving]

As usual, another straight to the point reply from our host

looks like your architect need to re-thinck the plan MSH

[Pablo]

Just checked your profile you shouldn't have any bother sourcing sand where you're from. Surely any work done to a hotel would have a proper set of engineer drawings and specs so that it can be scutinised by the authorities especially access roads. I would be more than happy to come out there and work for free for a while just pay my expenses and bar tab I could do with some sun on my back.

[Roads]

Thanks Gents,
I thought the slabs would be OK if using rigid construction in line with BS7533 pt 12, maybe I'm wrong in which case I've got a whole lot of trouble on my hands, so might have to clear out the spare room Pablo.
???
I see Charcon are calling up a modified mortar laying method for their flags with heavy traffic, anyone any experience with them?

[Tony McC]

You could put together a spec based on Part 12, but it would definitely not include sand as a laying course. But then, when you've spent all that money on bases, laying courses and jointing, why would the architect want to skimp by usiung the cheapest possible surface layer?

I see Charcon are calling up a modified mortar laying method for their flags with heavy traffic, anyone any experience with them?

Experience with Charcon or with modified mortars?

[Roads]

In fairness I have not made it very clear, a good 60% of the paved area is ontop of a podium slab (basement below) so for a good chunk of it the concrete base is there already, just a matter of pouring a screed to falls, placing mortar and wham bam...
The rest of it is a shortish road into the site, and is to be the same finish, so I was thinking I'd spec it to part 12.
What I can't figure out, is if the C40 concrete roadbase (called for in Pt 12) is just poured & paved over as if it were an aggregate roadbase or if it needs to be built like a concrete road with contraction & Expansion Joints, dowel bars and rebar.... Joints if needed would surely have to be carried up through the surface layer, would be a pain in the ass to build and would look bad.
I think block pavers on sand would be a better job both on and off the slab, with a Wet Mix or DBM base for the road section but I think I'm stuck with the precast pavers now.

[TheVictorianCobbleCo]

Question - how thick are these slabs?

[Roads]

60mm thick,
Seems thin but sized to pt 12...

[TheVictorianCobbleCo]

About 12 years ago I made 400 x 400 x 80 thk 48mPa strength sandstone coloured pavers for a street in Cape Town, about 1km x 4m wide, these seeing any kind of tyred vehicle. These were laid on a soundly compacted (300mm?) base and then in 10 - 20mm sharp sand, compacted, but adjusted for slight variations in slab thickness. They were packed touching, and dry grouted. (I didn't do the laying). I would say about 20% have cracked - mainly due to movement beneath the slab/being improperly laid. And there has been some movement in spite of sound kerbing. On this basis I would say you are looking for trouble - for the size slab you specify the thickness (guesstimate) would be a min of 120 to 150mm and even then, I would be loathe to lay them - weight, uncertain support. Its in the size! Having said that I did a place in Crowborough with 450 sq,450/225, and 225/225 slabs, all 50mm thick fully supported on 75mm average wet mix 5:1 which regularly sees tractors, digger loaders, and a 7 ton horse carrier, with no ill effects. Your Architect needs to redo his sums!!!

[Tony McC]

Roof decks and podiums are normally paved, as you say, with block pavers or small-element flagstones on a flexible laying course.

Following Pt 12 and using a rigid construction over a podium deck, you'd have to regard the existing base as individual slabs and carry through any movement joints. If you pave over existing joints, the paving will crack when (not if, but when) the underlying slabs shift and move as part of there day-to-day existence.

If you have control over construction of that base, then you have to follow the guidance given in SHW, which would probably lead to the inclusion of movement joints if there is any scale at all to the project.

[Roads]

Thanks a million for the help gents, I'll be trying to get the flags replaced with blocks or 300x300 slabs but I've a feeling I'm fighting a losing battle.
I can bring movement joints up through the paving because I can put them at 25m c/c but contraction joints are a different matter (4.5m c/c), I'm thinking they won't need to be brought up through the paving as a few cracks in the concrete base won't matter?!?
Is the mortar bed likely to require joints?
450x450 flags in Cowborough sound interesting, were they on a concrete roadbase?

[TheVictorianCobbleCo]

Re Crowboro flags - No, just on seriously compacted base that was originally concreted. I was always nervous of the owner putting heavy stuff on the pavers but he was quite confident - I would be very uneasy guaranteeing it - going the 300 x 300 x 60 route sounds a far better proposition, but please do your sums first.