Gaps between blocks

[PaulNi]

Hi thanks for a brilliant site!
We had a block paved driveway laid 2.5 years ago. The area is about 380 m2 and one section is sloped. As far as I can see the job was done well, but we now have some gaps appearing and a few rows of blocks have shifted slightly at the top of the sloped section. Looks like the blocks on the slope have compressed slightly over the period, leaving the gaps at the top. The driveway is still under guarantee and the contractor says the movement is due to heavy vehicles being driven on to the driveway - over the 2.5 years there's been a skip delivered a couple of times, plus the odd furniture van e.g. when neighbours moved in, and occasional other deliveries e.g. a tonne of firewood; two tonnes of topsoil. If it's our fault for having these vehicles on it, fair enough: my question is whether this movement is likely to have been caused by these vehicles or whether it's reasonable to expect the contractor to lift the loose blocks and replace to reduce the gaps under the guarantee.

All comments and advice appreciated.

[matt h]

heavy vehucles are going to move your blocks, and after this period i would suggest you negociate with your original installer to just deal with the affected area. It shouldnt cost that much, and as he did a decent job in the first place you Know it'll be put right without any hassle.

[lutonlagerlout]

what blocks are they?
i kinda disagree with the statement "heavy vehicles move your blocks"
not if they are 80-100 mm they dont
a photo would be handy
LLL

[matt h]

what blocks are they?
i kinda disagree with the statement "heavy vehicles move your blocks"
not if they are 80-100 mm they dont
a photo would be handy
LLL

standard 60mm ones would though! unless you were very lucky with those weights!

[James.Q]

soz but well laid 60mm bloks should be fine 80mm would be best 50mm only fit for patio or tbh a shed base

[colordrives]

50mm are perfectly fine for a residential driveway.

[James.Q]

50mm are perfectly fine for a residential driveway.

I'd hardly say that 380m2 driveway is a small domestic drive, and 50mm blocks will not hold up against removal lorries etc as they're only designed for light vehicular use.

[colordrives]

Well I have had no problems with any of the driveways I have done in 50mm pavers, in fact my own driveway is done in 50mm pavers and I often park a fully loaded 7.5 tonner on it and its still as sound as the day it was done, its more about whats under the pavers if you ask me, granted they wont take continued turning abuse from hgvs but residential driveways are not for constant hgv use. But to say 50mm pavers are only suitabable for patios is utter rubbish in my opinion and I have done many drives to back that fact up.

[Tony McC]

I'd be surprised if very occasional use by heavier-than-normal vehicles had caused the problem described.

There are two likely reasons for open joints: excessive localised settlement adjacent to the areas of open joints, or failure of restraining edges. Is there any sigh of either of these events?

The discussion regarding block thickness is largely missing the point. If blocks are too thin, they don't develop open joints: they crack. If the blocks are not cracked, then they are apparently adequate.

A typical residential driveway construction would utilise a minimum 100mm sub-base. Most sub-bases of this depth would cope with OCCASIONAL overrun by a heavy vehicle. Pavement design takes account of not solely the weight of the vehicles, but the number of movements they make. A skip wagon once or twice over a two year period is unlikely to do long term damage to the sub-base, but a skip wagon every day may well do so.

I'd investigate the edge courses as they are the most likely cause of open joints. If the edge courses have moved or failed, then the next question is why. If they've been run over by one of the heavier vehicles, you'd expect to see highly localised crush damage, but if it's sub-standard construction, this should be apparent throughout the project.

[colordrives]

Agree with tony. 90% of the gypo jobs i see tend to suffer from the same problem, restraining edge has gone bye bye and the blocks are following. As the gaps open up the blocks then start to move and you may well then see cracking and chiping, problem will only get worse as times passes.

[lutonlagerlout]

do you mean the soft sand mortar haunching the "lads" so carefully smear around the perimeter? straight on the top soil
re: 50s and 60's i was under the impression that the BS for drives required 60 mm concrete paviours??
then i could be wrong ???
can someone enlighten me
FTR may have laid a million bricks in the last 20 years or 2 million,but to be honest i wasn't counting
LLL

[James.Q]

as far as i know 50mm are not bs standard. thats why we only use on drives below 30 mtr anything more we use 60mm. :rock:

[Tony McC]

There is no BS for 'driveways'. There are three directly relevant BSs for concrete block paving: 7533/2 which considers design of *lightly trafficked* pavements; 7533/3, which relates to laying; and BS EN 1338, which covers manufacture. The standards provide guidance on manufacturing and laying block paving full stop. they do not go into detail of what should be used where and when: that is covered to some small extent, in the aforementioned BS 7533-2:2001 Pavements constructed with clay, natural stone or concrete pavers - guide for the structural design of lightly trafficked pavements, but again, there is no definitive guidance for 'driveways'.

It's debatable whether 50mm blocks should/could/would meet the requirements of 1338, but the best part of 20 years experience with 50mm pavers show that, in general they are fine for driveways and *occasional* overrun by heavier vehicles.

Many contractors find they can obtain 60mm blocks for the same sort of money (or even less) than the 50mm versions. There are 'tweaked' 50mm pavers that have been pimped for the residential market by having a richer colour or closer texture, but whether they are used is a decision taken by the contractor and/or the client. There is no right and wrong for lightly trafficked pavements.

[PaulNi]

Thanks everyone for all your thoughts - apologies for not answering some of the questions before now.
The blocks are Durapave Monksbridge Croft which are 50mm thick. The base spec. was 200mm of type 1 - I think it was pretty much done to spec.
There's no apparent movement of any of the edge courses or even the concrete haunch with drain across the bottom of the drive slope. The drive is L shaped and the section on the slope is approx. 35m long by 6 m wide.
At the top of the drive about 4m wide worth of blocks have gaps between them with the blocks towards the middle of this having shifted downhill slightly. As you walk down the slope the width of the blocks that have shifted downhill get progressively narrower - like a 'V', so that by the time you get to the bottom of the drive it's only a single block and the one above it that are visibly compressed compared to the ones next to it. But there's no visible crushing or movement in the concrete or the drain at the bottom. There's the odd block here and there that's cracked, but only a few out of the hundreds that must be down.
I'm thinking that it's gravity - the blocks have settled slightly downwards and inwards and tiny amounts of movement between each block over 30m or so equals a visible largish gap across a wider area at the top. (I think we need a photo here - the above kind of demonstrates that a picture equals a thousand words). But it's what to do about it (if anything - I've filled tha gaps with kiln dried sand and they don't move, but it's a bit less attractive since what was a nice straight line at the top now isn't).

All comments and advice gratefully received once again!

Cheers - what a great community of paving experts!

[Tony McC]

If I've understood this correctly, you have blocks laid in transverse stretcher or broken bond on an incline. Over time, gravity and the dynamic loads imposed by trafficking have caused the blocks to move, ever so slightly, down hill, resulting in courses that are no longer true.

You're right in thinking that, if you get 0.2mm of compression to a transverse joint, that's 2mm per metre or 20mm over a 10m run.

This is why I'm a big fan of intermediate restraining courses for this type of project. No matter how well laid are the blocks, the significant loads imposed by accelerating/decelerating vehicles on the pavement surface will cause loss of alignment over time. On steeper slopes, the argument for IRCs is even stronger.

I doubt that your pavement is likely to collapse, but if you ever do get to the point where remedial work is required, I'd definitely install an IRC or two (depending on the scale of the job and the degree of slope).