Portland Cement

portland cement

Binding agent of present-day concrete. It is a finely ground powder made by burning and grinding a limestone mixed with clay or shale. Its inventor, Joseph Aspdin (1799–1855), patented the process in 1824, naming the material for its resemblance to the limestone of the Isle of Portland, England. The cement combines chemically with the water it is mixed with, then hardens and strengthens.

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portland cement [′pȯrt·lənd si′ment]

(materials)

A hydraulic cement made of pulverized, calcined argillaceous and calcareous materials; the proper name for ordinary cement.

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portland cement

A cementitious binder used in most modern structural concrete; manufactured by grinding and burning a mixture of limestone with clay or shale with a small amount of gypsum. It is mixed with water and an aggregate (such as sand and/or gravel) to form a thick, heavy liquid that dries as a monolithic product. Although cement was developed by the ancient Romans, portland cement was first developed in England in 1824; since then, its tensile strength has greatly increased.

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Portland Cement 

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.

REFERENCES

Volzhenskii, A. V., Iu. S. Burov, and V. S. Kolokol’nikov. Mineral’nye viazhushchie veskchestva, 2nd ed. Moscow, 1973.

K. N. POPOV