The first diagram illustrates the process of cement manufacture, and the second diagram shows the materials that go into the production of concrete. To produce concrete, four different materials are mixed together. At the first stage in the production of cement, limestone and clay are crushed to form a powder. This powder then is mixed before it passes into a rotating heater. After heating, the resulting mixture is ground, and cement is produced. Finally, the cement is packaged in large bags. Cement is one of the four raw materials that are used in the production of concrete, along with gravel, sand, and water. To be exact, concrete consists of 50% gravel, 25% sand, 15% cement, and 10% water. All four materials are blended together in a rotating machine called a concrete mixer.