Raw Materials
For its raw material, cement utilizes four elements for its manufacture: 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 coal-fired electric power plants. Cement plants are increasingly turning to industrial byproducts that otherwise would be discarded. After completing detailed analyses to determine the effects on product chemistry and facility emissions, many cement plants can utilize byproducts in the manufacture of clinker.
From 115 operating plants reporting
in the PCA publication: 2006 U.S. and Canadian
Portland Cement Industry:Plant Information Summary,
55 plants used blast furnace or iron slag as a
raw material and over 50 plants used fly ash or
bottom ash from electric power plants.
Other alternative materials used by portland cement plants in 2006 included:
- Copper slag
- Foundry sand
- Mill scale
- Sandblasting grit
- Synthetic gypsum
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