How to calculate materials for concrete slab?

[mitc69]

Hi team

complete newbie at concrete but first time a charm right lol

So I'm looking at a diy concrete slab.. bearing loading of about 3-5T for a carport out in the farms 

5mx4mx100mm

i have the mesh and all, just need the maths for the mix and how to do smooth finish lol 

how many cubic meters of premix 10mm and how many cement bag? In addition how many liter of water per 80L as that the volume of the mixer ? 

thanks 

[MitchellMc]

Welcome to the Bunnings Workshop community @mitc69. It's terrific to have you join us, and many thanks for your question about creating a concrete slab.

A slab of that size would be a push to pour by hand. By the time you'd have mixed the bags and got them down, the area that you began with would be beginning to set. You'd need at least three friends: two on mixing and another to assist you with spreading. You're really at the point of something that's just not possible by hand. You could do it with an expansion gap down the middle. Mix and pour one half one day and the other the next.

On the maths, that is two cubic metres of concrete or 231 x 20kg bags of concrete. If you're following a typical concrete mix ratio of 1:2:4 (cement:sand:aggregate) then you'd need approximately 35 x bags of cement, 69 x bags of sand and 138 x bags of aggregate. It's going to require around 350L of water.

I strongly encourage you to consider having a slab of this size pumped or divided into manageable sections.

Here's a helpful guide: How to pour a concrete slab.

Please let me know if you have any questions.

Mitchell
 

[mitc69]

Hi Mitchell 

thanks for the maths, save me time to test and trail... I did get a quote but it was rather too high in that regard 😕 

Unlike brissy I can't seem to find any concrete truck that ready to pump or is willing to come out to the farms hence the diy 

And I'm planing to do section by section at this rate and again much appreciated  

[mitc69]

Just some updates, not perfect but with some self level will be able to tile it later

massive 13x10x14mm slab once completed,  then another 20x10 for the machines 

first slab took about 13hrs solo, with good ozitio mixer ! 

and again thanks  

[JacobZ]

Hi @mitc69,

A 20 square metre slab for your first foray into concreting is pretty brave and I have to say you've done a great job considering.

I bet your body was feeling it the morning after a 13-hour day of concreting.

Thank you for sharing.

Jacob