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Ive never worked with concrete before. I want to put some fence post concrete into a coffee can to hold a post for a softball base.

Does concrete expand or contract after curing?

TrailerParkJawa wrote:Ive never worked with concrete before. I want to put some fence post concrete into a coffee can to hold a post for a softball base.

Does concrete expand or contract after curing?

Contracts slightly, though not as much as Cement because it's got the hardcore in it. Basically it won't contract enough to make a difference in the volume of a Coffee can, it's only really apparent in large volumes. The more hardcore you add, the less the contraction, unfortunately it also lessens the strength of the concrete and makes it more prone to crumbling and cracking. If it's premixed, your fine, if your making it yourself, than follow any instructions you get, or ask at your local Hardware retailers.

Thank Rob, okay now I have to ask, what is hardcore?

TrailerParkJawa wrote:Thank Rob, okay now I have to ask, what is hardcore?

Also called Aggregate, it's the course sand and small ground up stone peices used in concrete to give it the extra strength under compression, that cement lacks. It makes it tougher, faster drying, and more resistant to weathering. However it lso makes it more susceptible to cracking and weakens it under stretching or torsion. You don't have to worry about ny of that, and you can get premixed concrete from most large hardware retailers or buy Concrete mix (Cement with containersof Various Aggregates and instructions for they're use and mixing). It may have a different name in the States.

Also called Aggregate,

Ah! I know what aggregate is! Is hardcore an English English word for Aggregate. I speak California English so you never know.

I bought a 50lb bag of fence post mix, and it has aggregate in it already. Ive got some curing out on the balcony in a can. Thanks for the tips.

TrailerParkJawa wrote:

Also called Aggregate,

Ah! I know what aggregate is! Is hardcore an English English word for Aggregate. I speak California English so you never know.

technically it's the description for the Packed rubble you lay down as the foundation for Concrete, when lying paths or patio's but I was taught how to use Concrete by a builder and the tend to use the two terms interchangably, and normally refer to the Packed rubble as 'Hardpack' and reserve 'Aggregate' for rough sand that is added to the Concrete as a balance to the normal hardcore. So it can be a bit confusing.

Just get a bag of "Quickcrete" it is fast and not a lot of mixing. It works great for posts..

one thing i should have said, you'r working in a closed container so ther maybe some air trapped at the bottom (it's not a huge problem and not something that happens a lot), so you can use a small nial to knock a couple of holes in the side, near the bottom. They will be too small for much concrete to get out, they will allow air to escape and because they have been punched through from the outside, they will give the set concrete something to grip.
Also fill the can completely right up to the top, then insert your pole, use a trowel or Plasterers Knife to remove the excess from the top and you can then be sure you have filled all the space in the Can completely and used the maximum you can. It shouldn't leave much wastage and you don't have to worry so much about any shrinkage.