tegwin
|
| posted on 18/3/10 at 05:25 PM |
|
|
Casting upstands on a concrete slab
Ok... here is a problem I cant quite fathom..
If you need to cast a 6x6 meter concrete slab 17cm thick... in the middle of it you want to cast a rib type reinforced upstand..
I assume you need to cast the entire thing at once..
So how do you cast a slab and the narrow upstand in the middle of it without the concrete seeping out of the upstand mold into the surrounding slab
area?
Anyone ever done this sort of thing?
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
|
|
iank
|
| posted on 18/3/10 at 05:28 PM |
|
|
Would you not put a rebar tower in the middle, pour the slab, when cured/dried shutter the upstand and then pour that separately.
Not that I know what I'm talking about, but that's how I'd assume it was made.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
|
|
|
Peteff
|
| posted on 18/3/10 at 05:30 PM |
|
|
As long as the reinforcing for the upstand is cast into the base you can cast the base then shutter round the reinforcing and pour the upstand after.
If you get the right slump the concrete could all be cast at once though.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
Bluemoon
|
| posted on 18/3/10 at 05:36 PM |
|
|
quote:
Originally posted by Peteff
As long as the reinforcing for the upstand is cast into the base you can cast the base then shutter round the reinforcing and pour the upstand after.
If you get the right slump the concrete could all be cast at once though.
I guess it depends on how strong it needs to be. The set concrete will not bond to the new very well, but that probably does not matter..
Dan
|
|
|
designer
|
| posted on 18/3/10 at 06:06 PM |
|
|
Cast the upstand first, each side after.
|
|
|
smart51
|
| posted on 18/3/10 at 06:10 PM |
|
|
Could you wait until the slab is firm enough that it doesn't flow then cast the rib in shuttering before the slab is cured?
Can you make a fairly dry mix like wet beach sand so it doesn't flow?
|
|
|
MkII
|
| posted on 18/3/10 at 07:21 PM |
|
|
start with a sheet of reinforcing mesh under where you need the upstand, tie L shaped starter bars to the mesh and then pour the base. when the base
has set you can tie th reinforcing for the upstand to the starter bars and cast the upstand hth .m.
|
|
|
Puzzled
|
| posted on 18/3/10 at 07:23 PM |
|
|
how high is the upstand???
|
|
|
rachaeljf
|
| posted on 18/3/10 at 07:31 PM |
|
|
Hi there, this is a very common situation in civil engineering. What you need to do is cast a "kicker", which is in effect a starter, or
base, for your upstand.
Fix two strips of 4x2 on their sides, set the desired distance apart, to form a 50 mm high raised strip across your slab as you pour it. You will find
the concrete, if it is not too wet, will happily sit between the timbers without slumping. Bend up a U shaped reinforcing cage using mesh or
individual bars, and push the legs down onto the slab to give 100 to 120 mm embedment.
Once your slab and kicker has gone off, clean off any "laitence" (loose or soft concete) using a water jet played onto the top face of the
kicker.
Then make up formwork to the required height of the upstand, using the kicker as the guide. Finally, pour the upstand concrete straight onto the top
of the cleaned off kicker.
If you can give me some more details, e.g. dimensions and intended use, I can give you more detailed guidance.
Cheers R
PS yes I am a civil engineer!
|
|
|
tegwin
|
| posted on 18/3/10 at 08:16 PM |
|
|
The concrete slab will be 175mm thick.... the centre upstand will be 600mmx600mm x 6 meters long
There will also have to be a smaller upstand at the front..
We currently have a cast reinforced concrete roof on our partially underground garage... The idea is to use the existing thin roof as a former for a
new cast slab on top... the upstands are required to spread the load of the new slab out to the side walls to support the load..
The aim is to then use some foam blocks to build up the level and top with about a foot of soil for the lawn to be laid on top of...
Just trying to work out costings.... and work out which bits I can do myself, and whihc bits have to be done by a pro...
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
rachaeljf
|
| posted on 18/3/10 at 08:47 PM |
|
|
Ahh, a green roof, highly commendable!
I think your proposal needs a proper structural design. There are a few things to consider:
1) Will the existing roof be able to carry the wet concrete, or will you be using plenty of Acrow props?
2) Has the beam reinforcement been designed?
3) The new slab would be structurally far more efficient with downstand beams. To achieve this, use your polystyrene as formwork, placed directly onto
Visqueen laid on the existing roof. Leave two strips to form your beams, place your rebar and mesh, pour the new roof in one go. After a few days
curing, paint the new slab with "blackjack" to waterproof it, then cover it with your new lawn. The concrete will also protect the
polystyrene from animal/vegetation damage and weather.
|
|
|
Puzzled
|
| posted on 18/3/10 at 11:08 PM |
|
|
You got that one R
|
|
|
tegwin
|
| posted on 18/3/10 at 11:30 PM |
|
|
Hmm.... interesting idea..
The old slab is not in a wonderful condition... so I think the idea of laying the slab first directly on the old would be the best idea...
unfortunately..
We have had a preliminary engineers report.. he has done some drawings of the layout I described above.....
I am just now trying to work out how much that would actually cost to impliment...
The big issue is that, the old slab leaks water... It appears to percolate from the edges into the middle and then pee out all over my cars so
another good reason to put the new slab directly over the top and then put a membrane on it to seal up the crack in the old slab edge... this will
give us an oppertunity to add drainage around the retaining walls...
Is this going to need planning/building notification? I would assume so as its a major structural change..
Any idea how much it would cost to have a slab like the one above laid... with the foam and membranes etc?... Assuming minimal ground work required
from contractors.
[Edited on 18/3/10 by tegwin]
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
rachaeljf
|
| posted on 19/3/10 at 01:05 AM |
|
|
Well, its your roof, but....
The slab I described would be easier to waterproof, as it will be a simple flat topped structure. Waterproofing over and around upstands on building
roofs are always a source of trouble. Concrete on its own is not waterproof - you will need proper waterproofing details for what is in effect a
buried structure.
The slab I described will use less concrete. No engineer would design a reinforced concrete T beam upside down, unless there were very pressing
reasons to do so.
The slab I described will be cheaper to build as there is much less formwork, and there is only one pour required.
The slab I described will protect your polystyrene insulation.
It sounds like you may need to bring the new concrete down the sides, like a shoe box lid, to get a reliable waterproof structure.
However, I don't know your site, so I can't say much more.
For prices, you need to get some decent drawings showing the structure and the waterproofing and drainage details. You are moving into the realms of
the Highways Specification, e.g. MCHW Clause 513 and the 200 series, for drainage and waterproofing of buried structures:
http://www.standardsforhighways.co.uk/mchw/vol1/index.htm
I will try to work up a budget if I get time tomorrow!
|
|
|
tegwin
|
| posted on 19/3/10 at 09:15 AM |
|
|
Thanks for the response... serioiusly useful stuff 
We paid a local specialist quite a bit of money to come up with the upsideown T design.... he has encporated a membrane into the drawings etc..
One of my concerns with constructing the T the right way up would be issues with water getting trapped in the foam area... Because the thing is
almost toally burried on 3 sides, casting a shoe box lid might be exceedingly tricky..
If I am looking for a contractor to do this sort of thing.... what should I be searching for?... A normal buildier wouldnt have a clue I suspect..
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
|
|
|
