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portland cement[′pȯrt·lənd si′ment]
a hydraulic binder composed chiefly of calcium silicates. The most widely used cement in modern construction, Portland cement is obtained by pulverizing clinker with gypsum (3–7 percent); active mineral additives (10–15 percent) may be added to the mixture. Clinker is produced upon calcination (to the point of complete sintering) of an artificial mixture of raw materials containing approximately 75 percent calcium carbonate, usually limestone, and 25 percent clay. The raw material is generally calcined in rotary kilns at 1450°-1500°C.
The properties of portland cement depend mainly on the clinker composition and on the degree to which the clinker is pulverized. The most important property of portland cement is its ability to harden upon interaction with water. This property is reflected in the grade of portland cement, which is determined by the compressive and bending (tensile) strengths of standard specimens made from a sand-cement solution after a 28-day setting period under humid conditions; grades of portland cement from 300 to 600 have been established in the USSR.
In addition to ordinary portland cement, other varieties are produced, which differ in composition, properties, and use. They include quick-setting, plastic, hydrophobic, sulfate-resistant and white portland cements, as well as a special type for use in the manufacture of asbestos-cement articles.
REFERENCESVolzhenskii, A. V., Iu. S. Burov, and V. S. Kolokol’nikov. Mineral’nye viazhushchie veskchestva, 2nd ed. Moscow, 1973.
K. N. POPOV