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?
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.
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.
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.
Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can smile when things are going wrong, you've thought of someone
"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.
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