Concrete - where does the water go?

"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.

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

"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.

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.

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

Think on this: Concrete hardens when submerged.

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

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?

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

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

Otherwise it will just be

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

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