Concrete ratio, how much cement is too much?

[SamTheMole]

Hi i've got a cellar underpinning job going on, and i just need to know one thing..is it advisable to mix a concrete ratio of 1:2:2? It's for the floor and a backfilled retaining wall, so it needs to be strong but how much can i get away with before there's too much cement in the mix? Cheers for any help

 

[PrenticeBoyofDerry]

1 part cement
3 part ballast/aggregate
and 1 part water.
Will give you a decent mix for concrete slab.

 

[studips]

trick is to not over mix it, not make to too wet and tamp or vibrate to settle it properly - that way you make the most of the potential strength of the mix

 

[RonnyRaygun]

What mix was specified? If the slab is structural then you should at least have a designated mix in the engineer's specification.

1:2:2 is going to be a pretty strong mix, probably somewhere in the region of C35 - C40 I would think...

Anyway, you can't really add too much cement, within reason. The more cement you add, the stronger the concrete will be, as long as the water/cement ratio is kept to acceptable levels for strength and workability.