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For a basic definition of cement, we consulted the nifty online version of Webster's Dictionary: "a powder of alumina, silica, lime, iron oxide, and magnesium oxide burned together in a kiln and finely pulverized and used as an ingredient of mortar and concrete." That's fine for starters. Now it's time to get serious. From Yahoo!'s commercial Concrete > Organizations category, we found a link to the Portland Cement Association, a general educational resource about the cement industry. There we learned that lime and silica make
up about 85% of the mass of cement. Portland cement, the world's most popular building material, was invented by a British stonemason in 1824, and was named for its resemblance to a type of limestone found in Dorset's Isle of Portland. And how do you make the stuff? "The exacting nature of portland cement manufacture requires some 80 separate and continuous operations, the use of a great deal of heavy machinery and equipment, and large amounts of heat and energy." This entails heating the raw material to about 2,700 degrees Fahrenheit! You can read all about it at the PCA Concrete Basics section. Needless to say, you shouldn't try this at home.
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