Concrete question.

[andrewpreece]

Yes, I have seen this written somewhere: the strongest mix is 3:1 sand to cement ( different for ballast of the 3/4" to dust variety ).

Andy

[Ian Stirling]

With a given mix of aggregate and sand, is the strongest mix when the cement paste fills the gaps between the touching aggregate, with no extra? Assuming that the mix does not have too much water?

[Ian Stirling]

Hmm, so mixed sized gravel needing 300ml of water to fill every l of gravel would reduce the amount of sand and cement by 3.

I used 8:3:1 of aggregate/sand/cement, mixed for a long time, it ended up so that it would not easily flow, but would tamp down to a beautiful firm surface. Just wanted a sanity check, as others were doubting mine.

[andrewpreece]

Given that the strongest mix is know to be 3:1 sand/cement, why don't you do your little experiment with dry sand: if your theory is true, then dry sand should absorb 1/3 of its own volume in water.

Andy

[Ian Stirling]

It does, about. (for the sand I've got)