Cement and concrete are among the most important building materials. Cement is a fine gray powder. It is mixed with water and such materials as sand, gravel, and crushed stone to make concrete. Cement and water form a paste that binds the other materials together as the concrete hardens. People often misuse the words cement and concrete. A person may speak of "a cement sidewalk." But the sidewalk actually is made of concrete.
Concrete is highly fire-resistant, water-resistant, and comparatively cheap and easy to make. When first mixed, concrete can be molded into almost any shape. It quickly hardens into an extremely strong material that lasts a long time and requires little care.
Nearly all the cement used today is portland cement, which is a hydraulic cement, or one that hardens under water. This cement was named portland because it has the same color as stone quarried on the Isle of Portland, a peninsula on the south coast of England.
