How is concrete made?

The basic recipe for concrete is simple and what you need for it is provided by nature:

•    Cement made from limestone and clay
•    Stone, sand, gravel
•    Water

The mixing ratio is 1 part cement, 4 parts rock and water.
The recipe changes and different additives such as iron, fly ash, rock flour, trass, silica dust, colour pigments, liquefiers, retarders...  could be added - depending on the use.