shotcrete

or gunite

Concrete applied by spraying. Shotcrete is a mixture of portland cement, aggregate, and water conveyed by compressed air to a spray gun. For structural uses, shotcrete is usually sprayed over a framework of reinforcing bars and steel mesh. Because it can take any shape, is easily coloured, and can be sculpted after application, it is used for a variety of specialized structures, including artificial rock walls, zoo enclosures, canopies, shell structures, pools, and dams. It is sometimes used to bind the walls of tunnels.

Find more information on shotcrete. Upgrade to Britannica Online for more on shotcrete.