How much concrete do I need?

[Astrokev]

Hi

I'm just about ready to order ballast and cement for my concrete pier and base, but I'm not sure how many bags of ballast I need.

The volume of my pier block and pier tube is approx. 0.512 m3

I'm buying Wickes materials. The website says a "major" bag of ballast covers: 1.0x0.35x0.05 (WxLxD) = 0.0175 m3

Assuming the 0.0175 to be roughly correct, the simple maths suggests I will need ~29 bags.

But, I'm not sure if I should allow for the cement. With a 3:1 mix, will I need less ballast than calculated above?

I obviously don't want to order loads more than I need.

Can anyone please advise based on your own experience?

Thanks

Kev

[bottletopburly]

Thats 750kg @29 bags x25kg you will be cheaper buying a 850kg bulk bag  8 bags of cement 4:1 or 10 3:1

my base was 600x600 x 850 i used half a  bulk bag of 20 mm all in ballast and about 7 bags of cement if memory serves me right 

[DRT]

The cement will not add much to the volume of the ballast because it is much finer grained and will simply fill the space between the coarser grains of ballast.

 

[MarsG76]

That sounds about right.. when I was pouring my concrete slab which was only 1.8m x 2.2m x 0.2m I ended up using 400kg or aggregate, 400kg of sand and 40 x 20kg bags of cement... and it all went in... looking at the size of what you want to concrete it doesn't look like much but it is deceiving.... 

 

[DRT]

This might help: http://source4me.co.uk/calculate_concrete_mix.php

Enter 1, 1 and 512 in the top three fields and hit calculate  

[Astrokev]

Thanks everyone!

[Adam J]

A 1 to 4 mix really is all that is required. Going with 1 to 3 will not leave you with a significantly stronger pier in the end. Given the size you are going and the reinforcement bar its just not required.

[MikeSE19]

Try this link http://www.everything-about-concrete.com/concrete-mixing-ratios.html

As Adams says 1:4 is fine. 1:3 is for things like garage forecourts.