Concrete volumes, dry mix vs wet mix ?

[Craka]

Hi,

So I have some small footings dug, which is near 1m3 in volume in total needing to be filled. Does wet mixed concrete have less volume than when it was just a dry mix? ie if 1m3 of volume needs to be filled with concrete is it approximate 1.5m3 of dry mix material requied (grave, sand and cement combined)?

So if I were using 14 bags of cement (approximate 0.28m3) , I would need appoxt 1.22m3 of sand&gravel mix to fill a void of 1m3?

[rwbuild]

1 cu m dry (1m x 1m x 1m) when mixed will result in 1m x 1m x 0.985m>0.990m in height. It can depend on how wet the mix is and how well it is vibrated in situ when you pour it.
If too wet you will get segregation of material when placed and if too dry you will not get optimum strength or vibration which will result in excessive shrinkage as it cures. . It is a good idea to add 1 extra bag of cement per Cu m when mixing it yourself more than is required for the mix.
Before placing the mix in your holes, lightly wet the sides and bottom of the holes first, this minimizes the rapid drying of the mix which increases the shrinkage factor and leads to a lesser structural strength of the mix.
IT IS CRITICAL that there is NO LOOSE material in the bottom of the holes before pouring, if there is you will get compaction settlement once loads are applied to concrete.

[Wrongwayfirst]

Calculate how much your bags will cost in total, I mixed many many bags in a wheelbarrow until I worked out my local mini mix brings it already done for less money.
as long as you have good access, much easier.
cheers

[Craka]

1 cu m dry (1m x 1m x 1m) when mixed will result in 1m x 1m x 0.985m>0.990m in height. It can depend on how wet the mix is and how well it is vibrated in situ when you pour it.
If too wet you will get segregation of material when placed and if too dry you will not get optimum strength or vibration which will result in excessive shrinkage as it cures. . It is a good idea to add 1 extra bag of cement per Cu m when mixing it yourself more than is required for the mix.
Before placing the mix in your holes, lightly wet the sides and bottom of the holes first, this minimizes the rapid drying of the mix which increases the shrinkage factor and leads to a lesser structural strength of the mix.
IT IS CRITICAL that there is NO LOOSE material in the bottom of the holes before pouring, if there is you will get compaction settlement once loads are applied to concrete.

Argh awesome, thanks for that. I hadn't given a thought to tamping down so no loose material in the bottom of the holes.

[Craka]

Calculate how much your bags will cost in total, I mixed many many bags in a wheelbarrow until I worked out my local mini mix brings it already done for less money.
as long as you have good access, much easier.
cheers

I bought a cheap cement mixer, as I'll probably use it for small concrete jobs and other things down the track. Where I'm doing the concreting its in a rural setting and no mini mix trucks nearby. It would have to be a normal size agi, and I wouldn't require their minimum volume and would have to pay a substantial delivery cost, but thankyou.

[rambunctious]

I bought a cheap cement mixer, as I'll probably use it for small concrete jobs and other things down the track. Where I'm doing the concreting its in a rural setting and no mini mix trucks nearby. It would have to be a normal size agi, and I wouldn't require their minimum volume and would have to pay a substantial delivery cost, but thankyou.

Not sure how you are getting the materials to site but it's always best to have more than you need at least for this initial job, and as you say, you will be using more later.
Store any excess concrete blend on black plastic or old corro sheets and store the bags of neat cement in a dry place or wrap and duct tape them as well.
The trailer I use these days is .75 cu metre (1800x1200x350) and when I buy 1/4 metre of concrete blend from the landscape supplies, I end up with usually 1/2 metre

1/4 metre of blend and 3 bags builders cement here cost $61 a couple of weeks ago