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Natural Cement: The first natural cement was made in small, pright, wood-burning kilns that were fired for bout a week, after which the clinker was ground etween millstones by waterpower. In 1899 early 10 million barrels (1.7 million metric )ns) of natural cement were produced in the rnited States, but because of the increased pro-uction of portland cement, production of natural sment had dropped by 1918 to less than half a lillion barrels (85,000 metric tons). Since then production has again increased and is now more than 3 million barrels (513,000 metric tons) annually.
The production of portland cement is a major industry in the United States, increasing from 8 million barrels (1.4 million metric tons) in 1900 —when it trailed natural cement slightly in output—to almost 400 million barrels (68.4 million metric tons) annually. (A 376-pound, or 171-kg, barrel is the standard unit of weight for hydraulic cement in the United States, even though no cement, except for export, is now shipped in barrels. The 94-pound, or 42.7-kg, bag now in general use contains one fourth of a barrel.) The leading cement-producing countries are the United States, the USSR, West Germany, Japan, and France.
Many other combinations of mineral oxides would qualify as hydraulic cements but cannot compete for use in jrdinary construction because of their cost. Most hydraulic cement is used in the form of concrete, ivhich consists of cement, water, sand, and gravel )r crushed stone. The cement is the bonding igent, and the other rock materials, which are :alled aggregates, act as filler.
Three classes of cements have been developed ;ommercially: natural cements (including hy-Iraulic limes), aluminous cements, and portland :ements. |
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