Cement: Ballast by volume of weight?

[twm.bwen]

hi there,

When pouring my footings I ran out 2/3 of the way through. Something was up with my calcultations.

Footings 600x 200x3500 (3.5x0.6x0.2) which I worked out was 0.42 m3

I think my mistake came when I assumed a cubic metere bag was just that and thatit weighed a tonne. (I assumed wieght volume ratio is 1:1)

So I got 350kg of all in and 75kg of cement. (1:5 with 425kg in total)
I think in the end I ended up using 625kg of all in and 100 of cement. (weight volume 1.7:1)

This made and overly strong mix byu the look of it.

So, I assume I got it wrong because all in and cement are more dense that water (1m3 = 1000kg).


So my questions are these.
When you've worked out the volume you need to fill what factor do you multiply it by to get total weight needed/ (is it 1.7?

When trying for the correct mix is it done by volume as opposed to weight?
If so how are you ment to correctly judge the volume when using those poxy 25kg bags of cement?

And finally, if it is by volume how do you calculate the ratio of all in and cement by weight?


If any of that made any sense I'd be most gratefull for anyone shedding any light on this issue.

 

[noseall]

it takes about 2.2 tonnes of material to make 1 cubic metre of concrete.

1.9 tonnes of ballast and 13ish, 25kg bags of cement plus water.

people wrongly assume a tonne bag of ballast plus dust will make a cube.

wrong.

 

[twm.bwen]

I found a website with different densities on it and it says concrete made with gravel is 2400 kg/cu.m (which is pretty much the same as what you said.

It also say portland cement is 1506kg/cu.m, it does not however give the density of ballast.

so I still don't know if the mix ratio's are for volume or weight and how to measure volume when mixing (getting a constant "shovel full" of sand is easy enough but with these new little 25kg bags you end up getting a bit out at a time and having to add up estimated fractions!

For my footings I used half a bag of cement (tipped in by hand) to 3 25kg bags of all in ballast. So by weight that 1:6, but the mix came out looking alot stonger than that!

 

[noseall]

6 parts ballast (sand 'n' gravel) to 1 cement is the optimum mix for regular concrete.