is formed by heating limestone
. Powdered clay and limestone are roasted in a kiln
to produce a complex mixture of calcium
silicates. This is cement.
When cement is mixed with water, a slow chemical reaction takes place that causes the cement to slowly set hard. It is used to bond bricks together in building. It is also often mixed with sand and chippings to make concrete, which is a very quick and cheap building material. Many consider it unattractive, however.