Slow-curing concrete

Is there any way to retard the curing of concrete so that it will stay liquid for at least a few weeks? I am trying to prepare an exhibit about the properties of concrete, and I would like to be able to show some samples in both liqiud and solid form. It’s not reasonable to be able to mix up a new batch every few hours, however. Are there special formulations, or special conditions, under which the curing process can be slowed way down?

I’ve never tried it, but you could try increasing the water-to-cement ratio. Maybe even try to find an ingredient to <i>replace</i> the cement; something that would give the appearance of cement, but without the actual curing properties. My first thought is something like volcanic ash, but I’m not sure how easy that would be to get ahold of, barring Yellowstone erupting in the near future.

Are you going to keep it in a closed container? Because otherwise, evaporation might cause premature curing/drying on the exposed surface unless you stir it every so often.

Well, in order to prevent making an unholy mess, I had imagined a sealed container with some kind of gloves you could stick your hands into to feel the mixture.

Concrete cures underwater, so I doubt a sealed sealed container will do it. It’s a chemical process, not just a ‘drying’ one.

There are chemicals that can be added to slow down the curing process. Perhaps you could replace the water with that chemical.

I think I would try to make fake concrete. Sand, agraget, and perhaps some crusher fines (the dust made when a rock crusher, well crushes rock).

Some outfits sell crushed concrete for road base. It’s old concrete that has been torn up and run through a crusher. It may act and look like just mixed concrete when wet. If you add some agraget.

What about the old sugar method? Supposedly (this may be an UL or other fanciful nonesense) if a cement truck broke down or got unavoidably delayed, the driver would run out and grab a bag(s) of sugar and pour it in the batch of wet concrete. It would keep the stuff from turning solid inside the hopper (or whatever the big tank on a cement truck is called).

How about just omitting a key ingredient of the portland cement, like the gypsum or the lime, or whatever it is that causes the concrete to set?

The reaction is not caused by exposure to air, but rather by mixing with water. It also releases a fair amount of heat, so you definitely don’t want people sticking their hands in to setting concrete. If you omit an ingredient that is essential to the cement reaction, then it will stay the same consistency, barring evaporation and settling of the larger aggregate pieces.

[doing a bit of googling]

This powerpoint presentation gives a good overview of how concrete is made, poured and formed.

As stuyguy said, sugar will slow down the setting of concrete, but I don’t know how long the effect lasts. You definitely don’t want to take the gypsum out, because that would make it set much faster.

How about using some kind of mineral oil instead of water? It won’t set up that way, and it’ll look wet.

There are retarders available that will keep concrete/mortar usable for a couple of days. I don’t know of anything that will work beyond that.

I was thinking along the same lines as bump. If sugar helps and water is key, how about if you replaced the H20 with corn syrup or some other sweet liquid?