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Posted: Sun Nov 07, 2010 1:04 am
by Blagard
I plan to use an alternative edge restraint so I thought I would post here in case I have missed something.
I will be laying a conventional concrete bed and haunch except the haunch will be 30mm higher than usual and preformed using simple formwork. Pretty much what you would do for a edge block laid on concrete and haunched except the block will not be placed at that time. The sub-base, restrained by this foundation will be placed so that finished, it is level with the top of the concrete bed. The finished compacted sand bed will be 30mm and is placed on the hardcore and top of the edge foundation. The preformed haunch will restrain the sand bed and the block placed on top. Finally compact the lot. The block is 80mm deep so the extra high haunch will still be below top of finished block level.
Is they any reason doing it like this could be a problem?
I could use a conventional edge detail in certain areas but not in others so I plan to adopt the same detail all round.
The block is 300 x 200 80mm thick.
For this type of block on a pre-compacted and screeded bed, what do you think I sould allow for in compaction. I was thinking of trying a precompacted 35mm bed to allow 5mm settlement after final compaction.
I'm looking for answers from people who are really familiar with block paving, I have over 35 years in construction and still learning.
Posted: Sun Nov 07, 2010 6:30 am
by msh paving
What is the reason you what to do it this way, seams like alot of extra work, 35mm compacted sand bed will be tight to acchive the type 1 will have to be perfect to allow screed rails to lay
MSH 
Posted: Sun Nov 07, 2010 9:04 am
by seanandruby
Your edge course needs to be bedded directly onto your concrete founds'. Doing it your way will result in differential settlement if using sand on the edge. If you go that route then i would bed the blocks on the kerb race with a good C B M, then the infill as normal. On new roads we used to place kerb race and place house concrete blocks stretcher course on top. The race kept 25ml low then, tarmac up against the blocks. Once the houses were built and most of the machine work done, the blocks are taken up and replaced with kerbs bedded on 25 ml of C B M. And then haunched as normal, this is because it saves on a lot of remedial work.
Posted: Sun Nov 07, 2010 10:14 am
by Blagard
msh paving wrote:35mm compacted sand bed will be tight to acchive the type 1 will have to be perfect to allow screed rails to lay
I agree the type 1 will need to be accurately laid. But this should be done on every job and in this instance it simply means paying a little more attention to it. One of the reasons you get bad block paving is sloppy sub-base work where the contractor uses the sand bed to make up for the lack of attention to proper sub-base preparation. Then with a substantially varying sand bed you will get differencial settlement and compaction.
The design of the paviours layout in this case does away with a "feature" edge that means around half the block edges will not be perpendicular to the edges.
Of course using a keyform edge restraint would do the job but I am not keen on them! I have been on projects where previous contractors used keyform type restraints and the edge has moved simply because the pins relied upon were not up to the job, either by what they were driven into or just skimped on quantity.
seanandruby wrote:Doing it your way will result in differential settlement if using sand on the edge.
I don't think you understood what I described. There is a probably a greater differencial settlement risk using mortar bedded edgings, because you introduce the skill/judgement in knowing what the main area will compact down to. I'm glad you used the term "used to" in the example. Adding a haunch to a kerb race later is never the best way, especially if the race is going to get dirty or flat where the haunch will be. You need to fit dowel bars to tie in a haunch to a kerb race if you are going to do it properly at a later time for road work.
Posted: Sun Nov 07, 2010 10:32 am
by Tony McC
Sean's point about differential settlement is valid and this construction would not be allowed on a commercial project because it doesn't match the requirements of the British Standard. You have some blocks laid on sand over a flexible sub-base and some blocks laid on sand over a rigid base: that's what we normally try to avoid.
However, the BS are a guide to best practice and if this is how you want to work, and you accept responsibility for the job, then you are free to work how you want, but it does seem to be an incredibly awkward way of working for no apparent benefit.
Posted: Sun Nov 07, 2010 11:08 am
by seanandruby
Blagard wrote:seanandruby wrote:Doing it your way will result in differential settlement if using sand on the edge.
I don't think you understood what I described. There is a probably a greater differencial settlement risk using mortar bedded edgings, because you introduce the skill/judgement in knowing what the main area will compact down to. I'm glad you used the term "used to" in the example. Adding a haunch to a kerb race later is never the best way, especially if the race is going to get dirty or flat where the haunch will be. You need to fit dowel bars to tie in a haunch to a kerb race if you are going to do it properly at a later time for road work.
You are right i don't "....understand what you mean ". You were on about "an alternative edging." ??? then you go on about edge blocks, kerbs etc: which is convential edging. I have done a lot of roads with kerb race placed first and then kerbed and haunched when the houses built and not a dowel bar in sight. Getting it right comes with years of experience.
Posted: Sun Nov 07, 2010 11:51 am
by Blagard
Tony McC
Lets consider a conventional concrete restraint edge cast integral with edge blocks and the blocks on the main area. That is where you will always get differential settlement in top level of the blocks. The difference will usually be acceptable/in tolerance because of the skill of the operatives.
The problem here is there is no clean line breaking the area of the edge blocks and main area. So a keyform type restraint would get over this. But! - I don't like them.
It seems to me you are suggesting that because the sub-base is flexible I will get differencial settlement there compared to the concrete area. On this point I agree and is one reason I posted in the first instance. However my thoughts are that properly compacted type 1, will for all practical purposes, not settle further (Always providing the formation is up to the job as well). There will in all probability be the greatest differencial in the sand bed itself and one reason why the type 1 needs to be accurately laid anyway.
For your information, the proposed formwork will be laid almost the same way as, but instead of, an edging block. It will not be difficult at all.
Perhaps no-one has tried what I am proposing because it relies on a high standard of workmanship with regard to the sub-base. Ultimately the situation is pretty much the same as blocks that are laid to the edge of manhole frames. The "sub-base" varies and I'm sure most here will have seen what happens if you don't get the sub-base right.
Posted: Sun Nov 07, 2010 11:57 am
by Blagard
seanandruby wrote:You are right i don't "....understand what you mean ". You were on about "an alternative edging." ??? then you go on about edge blocks, kerbs etc: which is convential edging.
Sorry about using the words edge blocks. I did not mean purpose made edge blocks, just the normal blocks that are at the edge.
Posted: Sun Nov 07, 2010 1:22 pm
by lutonlagerlout
i have the same issues as yourself blagard about differential settlement,and if anyone believes that subbase dont settle drive around and look at recessed covers sticking up like a tanner on a sweep's bottom on many many driveways
i always do the kerbs first (i know its slow but i prefer it that way) but although the back is haunched the front edge (paving edge) I try to keep as vertical as possible so that when the stone goes in and gets compacted it is just stone the sand and blocks sit on not concrete
your system seems to me to be overcomplicating a relatively simple job,if you are doing what you suggest you may as well use 900 by 50 path edgings and keep them 30 mm down,they are only 4 quid each
as for 30 mm of sand that is what i aim for nowdays, much less settlement with less sand
last 50 M drive i did only used 3 tonne of sand
regards LLL
Posted: Sun Nov 07, 2010 1:58 pm
by Blagard
seanandruby wrote:I have done a lot of roads with kerb race placed first and then kerbed and haunched when the houses built and not a dowel bar in sight. Getting it right comes with years of experience.
On that comment which was a little off topic. I accept that you can do a kerb race and fit kerb and haunch later in housing type developments. I think I have worked on too many commercial projects where dowel bars are a requirement for setting the kerb and haunch after the kerb race.
It was interesting to air my own subject, but in the absence of anyone having tried it before, I will go ahead as planned.
Posted: Sun Nov 07, 2010 2:05 pm
by Blagard
lutonlagerlout wrote:your system seems to me to be overcomplicating a relatively simple job,if you are doing what you suggest you may as well use 900 by 50 path edgings and keep them 30 mm down,they are only 4 quid each
Ah!
I had overlooked using a path edging hidden like that. That is worthy of serious consideration.
Thanks
Posted: Sun Nov 07, 2010 5:07 pm
by seanandruby
This is to heavy for me....i'm out :laugh:
Posted: Sun Nov 07, 2010 7:31 pm
by msh paving
I'm with you sean,to much complications for a very simple edge job,unless you have time and money on your hands MSH
Posted: Sun Nov 07, 2010 9:34 pm
by mickg
i felt the same and thats why I have not posted a reply, the way the original poster is commenting makes the way I have operated for the last 30 years sound like I have done it wrong
the bottom line is this though, its a simple job laying 3 x 2 flags with a block paving border....not quite taxing on the brain stuff really is it....*sigh*
Posted: Sun Nov 07, 2010 10:31 pm
by pickwell paving
I can't see what the benefits are of doing it this way, as everyone has said your just over complicating what should be a relatively straight forward job. Surely the edgings would be a lot stronger bedded directly onto the concrete??