hot cement

[goldmember81]

after having quite a few bags of cement delivered i started to move them from where they had been (lovingly) dumped on the drive. As i was moving them i noticed that the bags were quite warm, the further down the stack of bags i got the hotter they were. Apparently this is quite common when bags of cement are stacked on top of each other but why?

[himupnorth]

much of cement is Calcium Oxide, when this reacts with the moisture in the air it forms Calcium Hydroxide and gives out lots of heat.

Try heating a small (pea sized) lump of marble or limestone in a strong flame for 15 mins, let it cool and then put a drop or two of water onto it and see it boil.

N.B. Wear gloves to touch it and eye protection when adding water - you have been warned.

I believe that this reaction has been used in the past for self heating food tins but this may be untrue.

[Catso]

As h says, setting concrete (IE the reaction with water) generates heat. This is one of the limiting factors in making huge concrete castings. Because they were working so fast, the Hoover dam had to have water cooling built into it as they went, to stop it getting so hot it would have cracked the concrete.

[yassa]

Him up north,,, have to have a go at that,, i'll try to tell you the results..

[himupnorth]

Be careful Yassa, both the calcium oxide (quicklime) and the hydroxide (slaked lime) are very alkaline and therefore corrosive etc.

If you've had a go already I hope it lived up to your expectations.