Concrete is a building material made from a mixture of broken stone or gravel, sand, cement and water, which can be spread or poured into moulds and forms a mass resembling stone on hardening. In addition to its potential for immense strength and its initial ability to adapt to virtually any form, concrete has become one of the most common building materials in the world.

It is characterized by the type of aggregate or cement used and by the methods used to produce it. In ordinary structural concrete, the character of the concrete is largely determined by a water-to-cement ratio. The mixture must have just enough water to ensure that each aggregate particle is completely surrounded by the cement paste, that the spaces between the aggregate are filled, and that the concrete is liquid enough to be poured and spread effectively. Another durability factor is the amount of cement in relation to the aggregate.