Small slab for water tanks

[BadtzBee]

Hi all. Wondered if any one can help with slab design to sit two 2,000 litre plastic water tanks. I haven't a clue about rebar sizes and slab thickness. Bit of a problem really - I've got the workers, but nobody knows what to do!

The slab will be 2.5 x 6 metres, and I'm guessing it should be 150mm thick, and probably have thickened edges (like a floating slab).

The ground is stable, level and compacted.

Any advice would be appreciated.

[Crossy]

It's not structural it just needs to transmit the load to the ground, so all you need to do is make sure it won't crack or sink, no need to over think the structure.

Take off the topsoil from below where you are slabbing and place a layer of sand 2" or so, tamp well.

Set up your wooden formwork, make sure it's level and isn't going to fall apart when you place the concrete.

100-150mm thick sounds about right, drop in some mesh reinforcement (it's about 4" squares), stand it on rocks or bricks to place about 1/2 way up the concrete thickness.

Mix and place the concrete.

Pummel and / or vibrate to get all the air out, finish to a nice smooth, level surface.

Use plastic / wet sacking to stop it drying out too quickly.

[ExPratt]

How are you getting your concrete delivered

[ExPratt]

What do you recon crossy , 100mm deep 1 and a half cube ?

[Crossy]

How are you getting your concrete delivered

Good point, you're going to need about 1.5-2m³ for that slab (100-130mm thick), readymix would be easiest (check my sums before ordering).

Absolutely everything must be ready before the delivery, it won't wait long in the truck.

Loads of manpower and spreading tools, barrows if the truck can't get up to the site. etc etc.

[BadtzBee]

How are you getting your concrete delivered

Thanks for the advice. I'm getting the concrete delivered; from experience my workers aren't really up to speed with mixing to a given ratio. I'm doing a bit of curbing as well, all up about 3 cubic metres. For the slab, would you put a layer of plastic down first?

Edited February 19, 2015 by BadtzBee

[ExPratt]

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How are you getting your concrete delivered

Good point, you're going to need about 1.5-2m³ for that slab (100-130mm thick), readymix would be easiest (check my sums before ordering).

Absolutely everything must be ready before the delivery, it won't wait long in the truck. Loads of manpower and spreading tools, barrows if the truck can't get up to the site. etc etc.

I dont know how it works here with ordering , I would imaging they'll just give you what you want like other countries in the region. UK they are usually more obnoxious , have to pay for 3 metre minimum because of the smallest lorry size

[Crossy]

I wouldn't bother with plastic unless it's going to have a shed built over it, just a layer of sand.

[ExPratt]

I wouldn't bother with plastic unless it's going to have a shed built over it, just a layer of sand.

Yes its only a base for a tank , good tip about the curing though , soon turn into a dogs breakfast in you put your trowel down and walk away

Edited February 19, 2015 by Crossy

[BadtzBee]

Apparently, if you ask, they have a chute extension, but probably a good idea to have a couple of wheelbarrows on hand " just in case".

By the way Crossy, some time ago you replied to my post about DIY genset. I finished up getting a Kipor from GenSet Solutions. (Did I just highjack my own thread? )

Cheers.

Edited February 19, 2015 by BadtzBee

[IMHO]

Remembering that each of these tanks will weigh > 2 tons, no way 10cm will do - even with heavy use of rebar, 10cm is at best rated to 500kg/sqm load. Use a min. depth of 15cm. If the slab is isolated from other slabs (i.e. has some room to expand and contract), 6mm rebar in a 20cm x 20cm grid, vertically in the middle of the slab will do.

After pouring, keep the slab hydrated for at least the first week, so it can achieve at least 80% of its strength under controlled conditions.

Edited February 19, 2015 by IMHO

[BadtzBee]

Remembering that each of these tanks will weigh > 2 tons, no way 10cm will do - even with heavy use of rebar, 10cm is at best rated to 500kg/sqm load. Use a min. depth of 15cm. If the slab is isolated from other slabs (i.e. has some room to expand and contract), 6mm rebar in a 20cm x 20cm grid, vertically in the middle of the slab will do.

After pouring, keep the slab hydrated for at least the first week, so it can achieve at least 80% of its strength under controlled conditions.

The good thing about TV is there is always a variety of helpful advice. Much appreciated.

[canuckamuck]

I have started putting plastic under all the concrete I pour here. Too many times I have seen the concrete's moisture get sucked through the ground before a nice finish can be made. it is so hot and dry usually.

[eyecatcher]

Remembering that each of these tanks will weigh > 2 tons, no way 10cm will do - even with heavy use of rebar, 10cm is at best rated to 500kg/sqm load. Use a min. depth of 15cm. If the slab is isolated from other slabs (i.e. has some room to expand and contract), 6mm rebar in a 20cm x 20cm grid, vertically in the middle of the slab will do.

After pouring, keep the slab hydrated for at least the first week, so it can achieve at least 80% of its strength under controlled conditions.

The good thing about TV is there is always a variety of helpful advice. Much appreciated.

But its still like trip advisor reviews; you have to pick out the posters who quite simply dont know anything about a particular topic and just guessing without experience.

Follow everyone's advice and you will get a dogs dinner, thats for sure!

[cooked]

I used a minimum of 12cm reinforced concrete for pedestrian pathways so in mind of the fact that concrete isn't expensive in Thailand, why save money here? Just bung in a lot of concrete and lots of iron bars. I have never tamped in sand under a concrete slab, nor have I put down plastic. Nobody hydrates concrete here, for goodness sake, you aren't going to build a 20 storey office block on it! I built a few houses in Switzerland (temperatures to be reckoned with -25°C to +40°C), one of which I lived in for 30 years.