STEVE ALLEN / SCIENCE PHOTO LIBRARY STEVE ALLEN / SCIENCE PHOTO LIBRARY
Cement production. Mechanical digger transporting powder components of cement in a warehouse. Cement is a finely-powdered building substance that hardens and adheres after being mixed with water. Cement can be made by mixing clay and lime, then burning the mixture in a kiln. Gravel or sand can then be added to make concrete.
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