Concrete - where does the water go?

I have a question that's been bugging me for a wile now. When I mix cement, sand, gravel and some water I get concrete. I pour the concrete into a form and allow it to dry. I assume that letting it dry means the water is being removed. Why then, when the water is removed, does the concrete not shrink? Beats me! Anyone have an answer?

Reply to
D.W.
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"D.W." wrote in news:24Tuc.11153$ig5.6037@edtnps89:

Bad assumption. The water is chemically reacting with the cement to make concrete, not evaporating.

It does shrink, but not much -- about 1/16 inch for every 10 linear feet.

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will answer almost any question you care to ask.

Reply to
Murray Peterson

To add to it, cement is exothermic. As it hardens, it produces heat which must be removed if poured in large amounts.

Interesting fact: When the Hoover Dam was built, mechanical cooling was used to cool the cement forms. (I don't know if it was refrigeration or not.) It was also built in "blocks" for the sake of cooling. To this day, Hoover Dam is still curing, producing heat.

--Mike

Reply to
Mike Fritz

"Allow it to cure" is a better term than "allow it to dry". Concrete cures by a chemical reaction between the cement and the water. A small amount of water does evaporate, but most of it chemically combines with the cement and is permanently incorporated into the crystal structure of the concrete. It doesn't shrink significantly "when the water is removed" because the water is in fact *not* removed.

Reply to
Doug Miller

In fact, you have to prevent the concrete from drying out, either by covering it or keeping it wet. Otherwise it will just be dust.

Reply to
Toller

For how long? I just sent my wife out to wet down the concrete we poured a few years ago. Did I do the right thing? Can she come back in if it starts to rain? Ed

Reply to
Edwin Pawlowski

Think on this: Concrete hardens when submerged.

Reply to
JerryMouse

Hi, It takes 20 years or more to make the concrete mature. Just go to a hydro dam and see what they do on the concrete dam. Tony

Reply to
Tony Hwang

Hmm. I've seen guys using sprinkler hose on new concrete to keep it wet. Are they trying ot make sure it has enough water to set up properly?

Reply to
Stormin Mormon

Until the color of the concrete changes blue for 24 straight hours.

Reply to
Stormin Mormon

To keep it from drying out. Keeping it from drying out is the major reason. Concrete can be poured under water and will cure just fine as long as you don't get excess water mixed into the 'crete.

Harry K

Reply to
Harry K

Otherwise it will just be

Right. Think of your own body--your're upwards of 95% water, and you hold together very well. zemedelec

Reply to
Zemedelec

It may well still producing minute amounts of heat, but the cooling water was turned off 69 years ago! And yes, refrigeration was used during the forced cooling period.

See:

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Jeff

Reply to
Jeff Wisnia

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