Concrete slab (large) - Doing it the right way?

[winco2]

I am in the process of putting a large concrete base down to errect a new garage.
The dimensions of the base are 11m Long X 3.6m Wide.

The land gradually falls away from the house where the garage will start, so the shuttering is approx 300 at the front going to 500 at the rear.

i have layed a sub base of 50mm to dust crusher which i have compacted down, this leaves me 200mm around the edges and 150mm across the span to fill with concrete.

The slab would sit on the base above ground level at the rear, this would have to be back filled to retain the sub base, but not to a level to cover the concrete.

Reading the pages from this site i have a few concerns.

1) Can i lay a single slab of concrete for this area?

2) What type of reinforcement should i use? (single A252)??

2) if i lay a fibre concrete do i need steel, is fibre more expensive and a better option.

I can send pictures of the area if required, not sure how to post.

Regards,

martin

[Tony McC]

It could be cast as asingle slab, but it will need a crack control joint in the centre, giving two slabs of 5.5m x 3m

Reinforcement depends on type of garage. Brick is heavier than sectional which is heavier than timber. I'd only use steel for brick-built garages. Fibres are adequate for sectional or timber structures and are a fraction of the cost of steel mesh.

[winco2]

Hi Thanks Tony,

Ive been advised to put a single layer of A252 steel down and pour a concrete C30 / 35 with an 80 Slurry, this is obviously wet and easy to move around,
without a joint??

Any advance on this info??

[Tony McC]

C30/35?? Is this a garage slab or a floor for a nuclear power station? C25 would be more than adequate - C30/35 is the sort of cement content we use for power-floated internal floors and high-load bays.

And A252 is a bit more than would normally be used. 252 uses a 8mm mesh, whereas most garage slabs would use A142 (6mm) or A193 (7mm). Is there some reason why such a heavy spec is being given?

I think you mean an 80mm slump, not slurry. That's pretty wet so it will be easy to work but will give you a lot of bleed water. How many men will you have with you?

[winco2]

Hi

Yes its an 80 Slump, i have been lead to believe it will find its own level, but 3 to 4 of us will paddle it along the 11 mtr.

Will 8.5m of concrete (80 Slump) travel 11m when dumped at the front of the shuttering??

A252 is the choice because the web page advises this one for 150mm concrete (mine is 150 across the centre and 200 arond the edge).

C35 concrete. not got a clue why, i know as much about the difference between C25 & C35 as you probably know about the operation of a Baracuda Fire vehicle.

There cant be much of a difference and i wouldnt think the price would decrease that much for opting for the C25.
I`m paying £649 for the 8.5M3.

I am playing on the side of caution its much cheaper than having to do it right next time.

Cheers

[Tony McC]

8.m³ of 80mm slump concrete will not flow 11 metres distance. It will flow relatively easily for 3 metres or a bit more, but beyond that, you'll need to work it.

A252 mesh - yes, I forgot you were using a 150 slab, so that's fine.

C25 and C35 is a measure of the 'strength' of a concrete when cured. In longhand, it means 25 (or 35) Newtons per square millimetre, and this strength is achieved primarily by using extra cement. For most slabs that are to carry medium-weight single storey building, C25 is usually strong enough. You're right about price - there might be 80 quid diff between that quantity of C25 and C35.

[winco2]

Thanks Tony

You have been a great help