Correct mix for no fines concrete?

[Osprey]

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

[Ian Stirling]

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.

[Osprey]

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]

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

[Osprey]

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