Cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and Portland cement. Concrete is a hard, strong construction material consisting of sand, conglomerate gravel, pebbles, broken stone, or slag in a mortar or cement matrix. Concrete gets stronger as it gets older. Portland cement is the generic for the type of cement used in virtually all concrete. Cement compromises from 10 to 15 percent of the concrete mix, by volume. In the process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years that it brings the idea that concrete gets stronger and tougher as it gets older.