Anybody know the correct mix for no fines concrete ?

I am back-filling behind on-edge timbers against which sprags are run
to top walers of shuttering, intend using no-fines concrete (plenty of
40mm clean stone on site)

After concrete raft is poured when I strike the shuttering the no fines
concrete can stay there as it is below ground level.

Googling around gives wide variety of mixes
6:1 8:1 or 10:1

Osprey wrote:
Anybody know the correct mix for no fines concrete ?

I am back-filling behind on-edge timbers against which sprags are run
to top walers of shuttering, intend using no-fines concrete (plenty of
40mm clean stone on site)

After concrete raft is poured when I strike the shuttering the no fines
concrete can stay there as it is below ground level.

Googling around gives wide variety of mixes
6:1 8:1 or 10:1

Basically.
You take the cement paste - which is maybe yoghurt thickness, and add
enough of it to the stone to fill up all the gaps.
The cement paste is a constant amount per volume of water.
Take a 5 gallon bucket of dry sand.
Add water to it till it's brimming.
The amount of water you added is the amount of cement paste you need to
fill the gaps.
Take a bucket of rocks, and do the same.
The amount of water you need to add to make it brim over is now the
volume of sand+cement you need to add.

So if the rock absorbs 1/4 its volume of rocks, and the sand absorbs 1/4
its volume, then you need 1/16th the volume of cement paste that you
have of rock in order to fill all the gaps.

Ian Stirling wrote:
Osprey wrote:
Anybody know the correct mix for no fines concrete ?

I am back-filling behind on-edge timbers against which sprags are run
to top walers of shuttering, intend using no-fines concrete (plenty of
40mm clean stone on site)

After concrete raft is poured when I strike the shuttering the no fines
concrete can stay there as it is below ground level.

Googling around gives wide variety of mixes
6:1 8:1 or 10:1

Basically.
You take the cement paste - which is maybe yoghurt thickness, and add
enough of it to the stone to fill up all the gaps.
The cement paste is a constant amount per volume of water.
Take a 5 gallon bucket of dry sand.
Add water to it till it's brimming.
The amount of water you added is the amount of cement paste you need to
fill the gaps.
Take a bucket of rocks, and do the same.
The amount of water you need to add to make it brim over is now the
volume of sand+cement you need to add.

So if the rock absorbs 1/4 its volume of rocks, and the sand absorbs 1/4
its volume, then you need 1/16th the volume of cement paste that you
have of rock in order to fill all the gaps.

We are at crossed purposes here ... no-fine mix has no sand ... it is
stone & cement only, the main reason for this type of mix is that the
lack of fines means a honeycomb texture, and thus it is free draining
.... any fines (i.e. sand) fill the voids.

I am not after free draining there is another reason, but it certainly
would have no sand.

AJH wrote:
On 30 Jun 2006 04:37:26 -0700, "Osprey"
wrote:

I am not after free draining there is another reason,

Is it insulation? There is only point contact between the stones so it
transmits less heat by conduction. It was used as a sub floor in pig
houses for this reason. To set against that the point loading on the
stones is high, the smaller particles, like sand, in the interstitial
spaces distribute the load better. Hence no fines concrete is not very
strong.

AJH

No it's just bulk fill behind shuttering, no-fines doesn't shrink back
and is recc for this job.