Concrete Roadway Design: Help Needed!

nedzer2011

Hi All,


I've being scouring google for the last while looking for a design solution to this problem but to no avail.
My uncle plans to install a concrete roadway into his farmyard with the most severe loading envisaged to be an articulated milk lorry. At a point, this lorry will be turning a full 90 degrees so I'm assuming there will be HUGE tensile stresses.
The department of agriculture provide guidance (http://www.agriculture.gov.ie/media/migration/farmingschemesandpayments/farmbuildings/S129%20April%202007.pdf) on concrete roadway design but I've a feeling that it wouldn't be sufficient to handle this loading condition.

Further to this, I'm also curious about the best surface finish to specify in this case. A rougher surface can provide better skidding resistance but I assume this may lead to high stress and possible cracking near surface?

I'd be grateful if anyone with roadway or concrete experience could share their experiences in such a situation or recommend a solution.
I'm a civil engineer by training (currently working in geotech) but this seems a bit over my head!!

harry21

'The design should meet the requirements of specific loading. In the absence of specific design data A393 mesh to BS 4482 / BS 4483 [10mm @ 200mm centres: 6.16kg/m2] shall be placed 40mm below the finished paved surface.'

Had a quick flick through the document above. The above seems pretty sensible although it recommends a minimum of 125mm concrete depth.

I would go 150mm and I would place the mesh 40mm from the bottom, not the top.

Other than that, I can't imagine any problems.

annfield1978

anything on nra road construction details?

Prenderb

annfield1978 wrote: »

anything on nra road construction details?

You'd need to get into the Design Manual for Roads and Bridges (or the older LR1132), the RCDs are figurative when it comes to layer thicknesses IIRC. And if you look at the DMRB you'd be scratching your head wondering about how the design load relates to the units of million standard axles! It's going to be down to experience probably aswell...

Don't forget a sub-base design aswell (you could suggest a geomembrane :P) which will be more important than the concrete - if the concrete doesn't bear well on the base beneath it there will be cracking and that's not good.

Caveat concretor, but I would say 150mm concrete on a good 150-200mm of 804 stone will save the day. (Standard caveat applies - it's not my fault, I don't know what your ground is like, I only suggested it, I'm actually a cat sitting in front of this keyboard taking a break between piano lessons, your mileage may vary)

If it's a big job (and it sounds like it is), it might be worth throwing a few quid at the local civil engineer to specify it for you. He/she might be able to specify the thicknesses in materials and save you the extra 50mm you might have thrown in for good measure if you know what I mean.

annfield1978

you;d be cheaper ringing round a few concrete suppliers to see what they would put down, there are 1000s of farm yards around the country, so theres no point getting bogged down in first principles, rule of thumb for the win!!

annfield1978

http://www.farmersjournal.ie/site/farming-Concreting-the-farm-laneway-13129.html

nedzer2011

Many thanks for the replies guys, your help is much appreciated.

As regards the size of the job, its a c. 150 metre laneway but because of the 90 degree turn at the end of it I can only really see the need for a rigorous design for maybe a 30m2 (or less) area so in the scheme of things, I think cost for this section could be ignored to a certain extent.

So I'm thinking (including a good sub-base) the department specification may be sufficient (possibly increasing depth slightly) but for this turning area increasing depth to 150mm and possibly include 2 layers of mesh, top and bottom. The lads in the Farmers Journal article increased mesh size for conservatism but I think the 2-layer option could be a better reason to increase cost?? Let me know if you think this is a ridiculous suggestion...

Ideally I'd definitely like to err on the side of caution but not completely overdo it! Although to quote the uncle "this has to last a lifetime" so maybe a ridiculous over-design could be the way forward.:D:confused:

The idea of getting an experienced Civil Eng is a good option but realistically I could never justify it... The family believe that after 4 years of studying for a BEng I should be able to design... eh.. everything!!

Also, would anyone have opinions on surface finish??

nedzer2011

annfield1978 wrote: »

you;d be cheaper ringing round a few concrete suppliers to see what they would put down, there are 1000s of farm yards around the country, so theres no point getting bogged down in first principles, rule of thumb for the win!!

Also thinking after all the discussions, this could well be the best solution...

Although that would assume that the supplier is honest and not looking to sell an extra few m3's!!??

harry21

I would follow the guidlines... there normally there for a reason.

I can't see any point in the mesh at the top. You would be better off with a larger one placed near the bottom, but insure adequate cover for the maximum aggregate size.

Make sure you get the sub-base right.It is as important as the conrete. 804 as suggested would be perfect, but it must be compacted properly. Regards the surface finish, I always think the brushed finish is best. I wouldn't float it.

Regards concrete suppliers, pricing around is fine, but I wouldn't be asking them for advice. At the same time, I wouldn't be getting carried away with specifying slumps etc either. Just the grade, 35N as in the guidelines you linked. You could always see what the price difference between 35N and 40N concrete is. Might be best off to get the 40 if there price is similar??

nedzer2011

Yeah you're thinking along the same lines as myself... placing the mesh at the bottom to counteract the traditional beam type bending and associated tension under load.

But as you say, the regulations are there for a reason and they specify mesh at the top. I've a feeling that it may be something to do with more localised surface tensions which would be due to tyre-pavement friction but as always I'm open to correction...!