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Posted: Sun Feb 22, 2009 9:36 pm
by cw76
I've got a design of a 600x400x63mm concrete flag being used in commerical pedestrian areas, where cherry pickers and the ocassional car (advertising for draw prizes) etc. I want to bed on a rigid bed (for ease of maintenance) but I've been told where vechicular overrun is expected, whether it be cherry pickers or not that I should bed on a flexible bed, regardless of the size of flag...is this right or wrong?
I'm new to Landscape Architecture, so I'm learning alot...all i have to go by are the BS 7533 standards, this site is bloody brillant for asking the questions that are not black and white!!!!
I know the rule of tumb is smaller than 450x450 on flex bed and bigger sizes on rigid bed.
Oh and one more question, why can't you use a dried sand joint when laying on a rigid concrete bed (the BS standards dont allow this)?
Greatfull for any help
Thanks
Posted: Sun Feb 22, 2009 10:34 pm
by Pablo
NO NO NO NO NO. Someone is feeding you rubbish. All flagsshould have some kind of cement bound bedding especially where vehicles will hit them. Imagine a solid flag over a flexible base put something heavy on it and it's going to snap. Everything you need to know is on the main site I don't know how to link you across but the flag menu will put you right. Are you from Greenmount College.
Posted: Mon Feb 23, 2009 3:25 pm
by Tony McC
No - you're wrong there, Pablo. These vehicle overrun flags are purpose designed for flexible bedding. that's why they have the chamfered arisses and the extra thickness. They are intended to be laid as 'large format block pavers'.
Although they *could* be laid on a rigid bed, that's not their intended purpose.
As for sand jointing with a rigid bed: why would you have flexible (unbound) jointing when you have a rigid (bound) bed? Like with like, so flexible jointing for flexible construction and rigid jointing for rigid construction.
Posted: Mon Feb 23, 2009 5:40 pm
by msh paving
im with you on that one Tony,lay them the same a block paving, screeded sand laid like blocks and vibrated plate over them with kiln dry sand 
MSH
Posted: Mon Feb 23, 2009 6:38 pm
by DNgroundworks
Can all flags take being passed over with a vibrating plate or just ones that are purposley manufactured to be bedded on sand?
Posted: Mon Feb 23, 2009 6:46 pm
by msh paving
Is only small element slabs that are 63-65mm thick are designed for final compaction with a plate and kiln dry sand,on a few occasions i have plated 600x600 50mm slabs buts its not the way forward as they could crack,and the edges chip away because of no arris on the edge, MSH
Posted: Mon Feb 23, 2009 8:14 pm
by DNgroundworks
Cheers!
Posted: Mon Feb 23, 2009 10:04 pm
by cw76
Thanks guys, but I should have also explainded that there will be a small area that has to be laid on a rigid bed (due to problems with drainage/levels and a combination of feck ups!)
So I have no choice in that area, thats why I was trying to have a rigid bed throughout, as I wanted to maintain the same joint widths. Again the standards state a 6-10mm for a rigid joints and 2-5mm for flexible.
1. Practically or is it allowed to have a 5mm rigid joint (how hard will it be to fill the narrow joints), the flags will have a slightly textured surface as well.
2. And is a 5mm joint for kiln dried sand too much? I've read in other posts that a joint/sand stabiliser can be used...again as I'm concerened with maintanence and having to re-fill sand joints, over the life-time of the project...
3. How much would I be going against the rules with having a rigid bed with the type of traffic that would be expected?
Again any advice would be great
Thanks a mill.
Posted: Mon Feb 23, 2009 11:18 pm
by msh paving
Can you lay a lean mix concrete base compacted with a wacker plate to form a rigid base bringing it up to the same sub base leval as the flexable area,then carry on screeding and laying the slabs keeping the joints all the same it will look rough if you vary the joints ,that way you just kiln dry sand and wacker it,when you lay small element slabs they are just butted together that way they keep a consistent tight joint thay stays full of sand,its not so much as against the rules what you what to do but its making extra work ,and as tony says stick with one type of construction dont try to mix them,with a large joint street sweepers will suck the sand out very easy,im working on a repair job at the moment where they have mixed the laying methods in a town centre and the street sweeper has sucked al the sand out and the slabs rock hope this helps MSH
Posted: Mon Feb 23, 2009 11:24 pm
by Pablo
Tony McC wrote:No - you're wrong there, Pablo. These vehicle overrun flags are purpose designed for flexible bedding. that's why they have the chamfered arisses and the extra thickness. They are intended to be laid as 'large format block pavers'.
Although they *could* be laid on a rigid bed, that's not their intended purpose.
As for sand jointing with a rigid bed: why would you have flexible (unbound) jointing when you have a rigid (bound) bed? Like with like, so flexible jointing for flexible construction and rigid jointing for rigid construction.
I understand and am aware of what you are talking about but in my opinion that spec isn't good enough if you factor in what will usually happen to paving in a public setting over the course of it's lifetime. I admit I was perhaps overzealous when I said what I did but if you were to show me a well installed area that has stood the test of time I could show you 9 others that haven't. I understand that I am only talking from a regional perspective here but an area spec'd for occassional overrun is likely to get hit by some very large vehicles like utility grabs and delivery trucks. Flexible large or small element construction isn't capableof with standing these vehicles. That combined with the utilities digging it up for installation and repairs thennot reinstating itproperly can very quickly leave it looking awful. Sand joints quickly start to look filthy as they turn black and collect cigarette butts and all manner of debris that gets pressed into it by passing feet.You never see a spec like that over here anymore presumably because of all the factors above for both commercial and LA work. Footpaths that are unlikely to see vehicle traffic then yes but otherwise no. I'll probably incur your wrath here but a lot of paving here is butt jointed over a solid bed it really does give a much cleaner better looking finish and I have yet to see any spalling or other faults because of it. The utilities seem to be better at reinstating to this spec also.
Right I'm off to bed apologies for some of the typing but the overwrite mode seems to be stuck and I can't be ars#d retyping whole sentences.
Posted: Tue Feb 24, 2009 11:49 am
by Tony McC
I appreciate what you're saying Pablo, but if small element paving has failed, then it's either the wrong type of paving for that location or it's not been properly constructed, which may be the fault of the specifier or the installer. SEP is intended for *occasional* vehicle overrun and, done properly, it can cope with the *occasional* HGV. It can't handle everyday trafficking, and if that was the scenario, then SEP is not the answer, but we have used it very successfully on dozens of projects where it's lasted the course and done just what was required of it: providing a low-cost, fast-lay, serviceable surface.
Anyway, back to CW76's problem: if you want a rigid bed, then go for it. Always remember that the BS's are guides to best practice, not hard-and-fast, immutable rules, and they can never accommodate every eventuality. The longer you spend in this trade the more you'll realise that you need to be "creative" with some of the guidance.
A 5mm rigid joint will be a challenge mainly because 5mm of almost any mortar is not very strong. In this scenario, I'd be tempted to consider using one of the specially developed narrow jointing mortars, the best of which seem to be resin-based, rather than cement-based. Further, the cement-based options are invariably slurries that involve enormous amounts of cleaning effort.
You could use KDS with a stabiliser, but it would really need to be one of the better products otherwise it will break down relatively quickly, partly due to the joint width.
Rules are man's attempt to constrain an inherently chaotic world, and as such, are doomed to failure!
Posted: Tue Feb 24, 2009 9:08 pm
by lutonlagerlout
i wonder what the definition of occasional is?
if i was the installer i would say once a month,but i expect the client will think its whenever necessary.
future proof FTW!
LLL
Posted: Thu Feb 26, 2009 11:59 am
by Tony McC
The semi-official definition of "occasional" is 5 or fewer vehicles per day
Posted: Thu Feb 26, 2009 1:29 pm
by GB_Groundworks
i'm gonna tell the wife that occasional is 5 times a day hahaha 
:p 
:laugh: