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Posted: Tue Dec 20, 2011 6:07 pm
by Hawk
Hi Guy`s, we have some concrete slabs to pour over the Christmas holidays while the factory is closed, what would be the minimum recommended thickness of the concrete ?
I would have thought 150mm reinforced C40 air entrained concrete would be enough, but one of the lads thinks it may not be, whats the concensus of opinion on here ?
Posted: Tue Dec 20, 2011 6:37 pm
by lutonlagerlout
depends how big the areas are
when we did our skip blokes yard all the concrete was 300 mm double reinforced
but obviously high usage and weight
we did a turning circle for artics 2 years ago at a factory and the spec there was 225mm of c25 with 2 sheets of mesh 1@75mm and 1@150mm
that is still there now but looks a little old and tired
LLL
Posted: Tue Dec 20, 2011 9:57 pm
by London Stone Paving
snap hawk, got to do a bit of concreting myself in the first week of January for our new yard. I was planning on putting about 200mm down and not bother with the steel, but I am no expert by any stretch
Posted: Tue Dec 20, 2011 10:01 pm
by ilovesettsonmondays
did you set up near all the garden centres in the end lsp
Posted: Tue Dec 20, 2011 10:05 pm
by Pablo
Steve a 150mm pad with steel would be stronger and cheaper than a 200mm pad without. Your trucks fully loaded weigh 33-35 tons and a container acrtic is 44+ if this is in a high usage area you should maybe think about upgrading your spec it could be cheaper long term. If it's an out of the way area then you'll be grand.
Posted: Tue Dec 20, 2011 10:07 pm
by London Stone Paving
It fell through Chris. the geezer we were supposed to be renting off turned out to be full of sand and grit (getting the hang of this cockney slang now 
). We'd chucked a bit of money at getting the design done so we were not very happy.
Anyway, its all turned out ok because we have decided to re-locate our depot first because we have completely outgrown our current site in Pikewell. Were starting the move on 16th January. we've got a maxmimum of 5 weeks to get it done so I'm going to hire a couple of temporary drivers and work it on 24/7 for 2 weeks to try and break its back.
I'm going to post some photos of the move on the site after christmas
Posted: Tue Dec 20, 2011 10:09 pm
by London Stone Paving
That makes sense Paul, will definately take your advice on that one as I dont know much about concrete
Posted: Tue Dec 20, 2011 10:11 pm
by ilovesettsonmondays
are you staying close by steve ie heathrow way
Posted: Tue Dec 20, 2011 10:15 pm
by London Stone Paving
Were moving about 5 minutes away to Langley. were only moving the operation, showrooms staying put
Posted: Tue Dec 20, 2011 10:28 pm
by local patios and driveway
Langley desh?
Posted: Tue Dec 20, 2011 11:32 pm
by lutonlagerlout
its not the artics or 6 wheelers that do the damage
it the fork trucks
big point loads on small wheels
good time to think of drainage as well steve
every builders yard i know has shagged drains
know wa'ai mean geezah? :;):
for a yard i would definitely use mesh and defo 225 thick
LLL
Posted: Wed Dec 21, 2011 8:02 am
by Dave_L
180mm with mesh and dowel bars will be fine.
Posted: Wed Dec 21, 2011 8:05 am
by London Stone Paving
At the moment the yard is part concreted and part block paved. There is a forklift which currently runs over the area but we are going to have 6 forklifts running over it. The site is garden centre and we need to remove some old watering pits and then fill the gaps with concrete. We've also got to dig a massive pit for our machine slurry and also modify a big green house to house our saws, finally we've got a little job to do which is to move about 5000 crates of stone, at least that job doesn't require too much thought
Posted: Wed Dec 21, 2011 8:06 am
by London Stone Paving
What are dowel bars Dave?
Posted: Wed Dec 21, 2011 11:48 am
by Brucieboy
Hawk - you're spot on with the grade of concrete, C40 air entrained. All external slab concrete subject to heavy goods vehicles should be air entrained. The current PAV2 (C35 air entrained) is most likley going to be upgraded to a C40 air entrained with associated increases in minimum cement content and minimum air content and a reduction in water/cement ratio - all linked to long term durability. The draft amendment to BS 8500 is currently out for public comment. As mentioned by LLL, this grade of concrete will also provide reasonable resistance to forklift traffic. For very aggressive site conditions such as scrap yards, more specialist types of concrete may be required - very high specification probably including steel fibres and possibly microsilica.
You can obviously use less than recommended, but the risk of failure increases. I have been involved in many disputes where the incorrect grade of of concrete has resulted in slabs being removed and replaced at the contractors (or specifiers) expense. When an independent expert is called in to mediate, they will always refer to the relevant British Standard (BS 8500) to determine the concrete specification requirements. Obviously other factors can come into the equation such as slab thickness, quantity/positioning of reinforcement, type of sub-base etc etc - hence your request for guidance on this site.
When ordering the concrete, ask the supplier for CEMI (100% Portland cement) in preference to mixes containing proportions of ggbs or pfa. Use of the latter, whilst permitted, will generally take longer to "go off" when concreting slabs in the winter. Make sure you've got the right amount of labour for the job (it's surprising how many people under-estimate this when dealing with ready mixed concrete - assuming that's what you're going to use?). Finally, order the correct slump (workability). Better the concrete arrives at the correct workability than the guys on site p*ssing the loads up by asking the driver to add doshes of water - the latter will, without doubt, reduce the durability of the concrete.
Sorry to go on, but after spending 45 years in the ready mixed concrete industry, I've seen many disasters, some costing millions of pounds to resolve, all because someone specified the concrete incorrectly or abused it.