Raw Materials
For its raw material, cement draws upon minerals containing the four essential elements for its creation: calcium, silicon, aluminum, and iron. The most common combination of ingredients is limestone (for calcium), coupled with much smaller quantities of clay, iron ore, and sand (as sources of alumina, iron, and silica respectively).
So common are these elements that a wide variety of raw materials are suitable. Cement is made with everything from sea shells and shale to industrial byproducts such as blast-furnace slag from steel plants and fly ash from the electric power industry.
From 115 operating plants reporting
in the PCA publication: 2004 U.S. and Canadian
Portland Cement Industry:Plant Information Summary,
45 plants used blast furnace or iron slag as a
raw material and over 40 plants used fly ash or
bottom ash from electric power plants.
Other alternative materials used by portland cement plants in 2003 included:
- Bottom ash
- Copper slag
- Foundry sand
- Mill scale
- Sandblast grit
- Synthetic gypsum
- Waste glass
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