..homework...

[ermintrude35]

...my daughter needs some help with her homework, science is not my strong point, eventhough I have kind of answered her question, she doesn't believe me... (sweet child )

When laying concrete slabs why should you leave a space between them?

...Is it because of water expanding into ice in cold weather ..? or does concrete/water in the concrete expand too?..

she won't be copying your answers word for word as she then has to translate it into Welsh...

[Clanad]

If you look closely at, say a sidewalk made of concrete, you'll find that at about every 4 feet or so, there is a 'crease" in the sidewalk, then at about every 10 feet or so there is an actual divide in the sidewalk. The first relieves surface tension of the concrete and keeps it from cracking and only goes about a quarter of the way through the 4 inch thick concrete, while the second is usually filled with a piece of rubbery material or sometimes a bituminous material made for this purpose. This joint, by the way, goes all the way through the structure. The first mentioned control joints are sometimes cut into the finished sidewalk rather than when the cement is still workable...

[Clanad]

As an aside, by the way, concrete expands and contracts with the changes in temperature. Some road beds have actually expanded so much on hot days that they have caused car accidents when one hits the upthrust joint. This is because the engineers didn't allow enough of an expansion joint.

[ermintrude35]

..awww many thanks...though the first bit of your answer went completley over our heads...thankyou...

[stevie21]

Concrete definitely expands in the heat, as does metal etc.
A second reason for leaving gaps is that it probably makes it easier to replace individual slabs that become cracked or damaged by sheep. (You said it had to be translated...)