Reuse of stale concrete sack mix

[Wayne Whitney]

Hello,

I have some concrete sack mix that has gone stale from being exposed to exterior humidity for too long. I discovered this when the small step I tried casting was very crumbly 24 hours later. So a few questions:

I'm wondering if the unused bags of sack mix are still useful as an aggregate mixture. Can they be combined with fresh portland cement to make a good concrete mix? Or will the presence of the hydrated portland cement interfere somehow?

Also, what about the crumbly non-concrete? It easily breaks up into a mixture resembling aggregate and wet sand, so I was wondering if it too could be combined with fresh portland cement and reused. Of course, it is easy to imagine that it would be too wet, or the mix of particle sizes is wrong, or whatever. Note that I'm just casting a concrete bottom step, so I'd be happy with 2000 psi concrete.

Thanks, Wayne

[Don Young]

I think the labor in making the step justifies using known good material, which isn't very expensive. I would not use the old mix for anything but fill.

Don Young

[Richard J Kinch]

No. Aggregate must be hard material in a certain mathematical population distribution of relatively large particle sizes from sand to gravel. You have weak material in very small sizes.

Your sack contains negative value. That is, garbage.