cement (redirected from zinc oxide-eugenol dental cement)

cement, binding material used in construction and engineering, often called hydraulic cement, typically made by heating a mixture of limestone and clay until it almost fuses and then grinding it to a fine powder. When mixed with water, the silicates and aluminates in the cement undergo a chemical reaction; the resulting hardened mass is then impervious to water. It may also be mixed with water and aggregates (crushed stone, sand, and gravel) to form concrete.

A cement made by grinding together lime and a volcanic product found at Pozzuoli on the Bay of Naples (hence called pozzuolana) was used in ancient Roman construction works, notably the Pantheon. During the Middle Ages the secret of cement was lost. In the 18th cent. John Smeaton, an English engineer, rediscovered the correct proportions when he made up a batch of cement using clayey limestone while rebuilding the Eddystone lighthouse off the coast of Cornwall, England. In the United States, production of cement at first relied on processing cement rock from various deposits, such as those found in Rosendale, N.Y. In 1824, Joseph Aspdin, an English bricklayer, patented a process for making what he called portland cement, with properties superior to its predecessors; this is the cement used in most modern construction.

Modern portland cement is made by mixing substances containing lime, silica, alumina, and iron oxide and then heating the mixture until it almost fuses. During the heating process dicalcium and tricalcium silicate, tricalcium aluminate, and a solid solution containing iron are formed. Gypsum is later added to these products during a grinding process. Natural cement, although slower-setting and weaker than portland cement, is still employed to some extent and is occasionally blended with portland cement. Cement with a high aluminate content is used for fireproofing, because it is quick-setting and resistant to high temperatures; cement with a high sulfate content is used in complex castings, because it expands upon hardening, filling small spaces.

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cement

Agent that binds concrete and mortar. Cements are finely ground powders that, when mixed with water, set to a hard mass. The cement of 2,000 years ago was a mixture of ash and lime. Volcanic ash mined near the city of Puteoli (now Pozzuoli), near Naples, was particularly rich in essential aluminosilicate minerals, giving rise to the pozzolana cement of the Roman era. See also portland cement.

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cement

1. Dentistry any of various materials used in filling teeth

2. mineral matter, such as silica and calcite, that binds together particles of rock, bones, etc., to form a solid mass of sedimentary rock

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cement [si′ment]

(geology)

Any chemically precipitated material, such as carbonates, gypsum, and barite, occurring in the interstices of clastic rocks.

(histology)

Calcified tissue which fastens the roots of teeth to the alveolus. Also known as cementum.

(invertebrate zoology)

Any of the various adhesive secretions, produced by certain invertebrates, that harden on exposure to air or water and are used to bind objects.

(materials)

A dry powder made from silica, alumina, lime, iron oxide, and magnesia which hardens when mixed with water; used as an ingredient in concrete.

An adhesive for the assembling of surfaces which are not in close contact.

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Cement

A material, usually finely divided, that when mixed with water forms a paste, and when molded sets into a solid mass. The term cement is sometimes used to refer to organic compounds used for adhering or for fastening materials, but these are more correctly known as adhesives. See Adhesive, Adhesive bonding

In the fields of architecture, engineering, and construction, the term portland cement is applied to most of the hydraulic cements used for concrete, mortars, and grouts. Portland cement sets and hardens by reacting chemically with water. In concrete, it combines with water and aggregates (sand and gravel, crushed stone, or other granular material) to form a stonelike mass. In grouts and mortars, cement is mixed with water and fine aggregates (sand) or fine granular materials. See Concrete, Mortar

Adjustments in the physical and chemical compositions allow for tailoring portland cements and other hydraulic cements to special applications. Blended hydraulic cements are produced with portland cements and materials that by themselves might not possess binding characteristics. Special cements are produced for mortars and architectural or engineering applications: white portland cement, masonry cement, and oil-well cement, expansive cement, and plastic cement. In addition to acting as the key ingredient in concrete, mortars, and grouts, portland cements are specified for soil-cement and roller-compacted concrete, used in pavements and in dams, and other water resource structures, and as reagents for stabilization and solidification of organic and inorganic wastes.