cement(redirected from dental, Kirkland cement dressing)
Also found in: Dictionary, Thesaurus, Medical, Legal, Wikipedia.
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 concreteconcrete,
structural masonry material made by mixing broken stone or gravel with sand, cement, and water and allowing the mixture to harden into a solid mass. The cement is the chemically active element, or matrix; the sand and stone are the inert elements, or aggregate.
..... Click the link for more information. .
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.
the generic term for a group of artificial, inorganic, powdered, primarily hydraulic binding materials; upon interaction with water, aqueous solutions of salts, or other liquids, they form a plastic mass that hardens with time and becomes a solid, rocklike body. Cement is one of the most important building materials. It is used to make concrete and mortar, to secure individual structural elements, and for waterproofing and other purposes.
Cement in the general sense of the term has been known since ancient times. The first artificial binding materials were gypsum and lime, which the ancient Egyptians and Greeks used in building monuments, parts of which have survived to the present day. Later binders included lime solutions with admixtures of crushed volcanic rock (ancient Rome) or slightly roasted brick pieces (Kievan Rus’); the admixtures gave the binders the ability to harden on hydration.
In 1796, J. Parker received a patent for a hydraulic binder called Roman cement; it was a powdered product made by burning natural marls. J. Aspdin in England in 1824 and E. G. Cheliev in Russia in 1825 independently developed portland cement, obtained by burning an artificial mixture of limestone and clay in definite proportions until sintered.
The works of A. R. Shuliachenko, N. A. Beleliubskii, I. G. Maliuga, N. N. Liamin, and V. I. Charnomskii were extremely important in developing the theory and practice of cement production in Russia. High-quality domestic cement created as the result of their work has almost completely supplanted foreign-produced cement in construction. In prerevolutionary Russia, however, the number of cement plants and their capacities and levels of technology were inadequate. The only scientific center that studied cement was the mechanics laboratory of the St. Petersburg Institute of Railroad Engineers.
The October Revolution of 1917 opened up broad opportunities for the development of the cement industry and cement science. Such Soviet scientists as A. A. Baikov, V. A. Kind, V. N. lung, P. P. Budnikov, P. A. Rebinder, N. Ia. Toropov, Iu. M. Butt, and A. V. Volzhenskii provided the modern basis for the physical chemistry of cement, elaborated the theory of cement hardening, refined the technology of cement production, and devised new, highly efficient types of cement with special properties to meet the needs of different sectors of the national economy. In the USSR, scientific research and experimental design work related to the development of the cement industry and the raising of its level of technology is carried on by several specialized institutes, such as the All-Union Scientific Research Institute of the Cement Industry (NIITsement), the State All-Union Design and Research Institute for the Cement Industry (Giprotsement), and the All-Union Scientific Research Institute for Cement Machine-building Plants (NIITSemmash), as well as special departments at certain higher educational institutions.
The modern process of cement production includes several steps: extracting natural raw materials or securing certain industrial waste products, such as blast-furnace slag, ash from steam power plants, and mining overburden, used as raw material; crushing and grinding the material; preparing a uniform mix of
|Table 1. Primary types of cement produced in the USSR|
|Type||Mineral composition of cement (% by weight)||Compound composition of clinker (% by weight)||Grade||Special features||Primary areas of use|
|Portland cement||Portland cement clinker (85);|
gypsum (1.5–3.5) by SO3
content; active mineral
admixtures (up to 15)
|300, 400, 500, 600||–||Cast-in-place concrete for public|
and industrial buildings and
road building, exterior sections
of hydraulic engineering structures,
|Portland cement clinker (90);|
gypsum (1.5–3.5) by SO3
content; active mineral
admixtures (up to 10)
|3CaO·SiO2 + 3CaO|
·Al2O3 (up to 65);
2CaO·SiO2 + 4CaO
·Al2O3 Fe2O3 (33)
|Not less than 400; after|
three days, minimum
flexural strength 4
meganewtons per m2,
strength 25 meganewtons
|Hardens more quickly|
and is ground
finer than standard
structures, projects with
shortened construction periods
|Sulfate-resistant Portland cement||Portland cement clinker (100);|
gypsum (up to 3.5) by SO3
|3CaO·SiO2 (up to 50);|
3CaO·Al2O3 (up to 5);
(up to 22)
|400||Higher resistance to|
|For structures subject to sulfate|
action, cyclic freezing and
thawing, and cyclic wetting
|Plastic portland cement||Portland cement with plasticizing|
|Same as portland cement||300, 400, 500||Improved workability|
and higher resistance
|Same as portland cement; to|
conseve cement or concrete mix;
to increase concrete’s resistance
|Portland cement with hydrophobic|
|Same as portland|
|300, 400||Withstands prolonged|
|Same as common and plastic|
Portland cement; used when
prolonged storage of the cement
|Oil-well or gaswell|
cement: (a) for
wells with temperatures
up to 100°C;
(b) for wells with
|Portland cement clinker; permitted|
additives: (a) active (up to 15) or
inert (up to 10) mineral admixtures;
(b) slag (up to 15) or sand
(up to 10)
|Same as portland|
and slow setting
|Plugging oil and gas wells|
(white and colored)
|White portland cement clinker|
(80–84); diatomite (6); inert
mineral admixture (10) or mineral
(up to 2)
|300, 400, 500||White cement is|
divided into three
on degrees of
cements produced in
|Finishing of building and structure|
exteriors; sculptures and
|Portland cement clinker (60);|
volcanic (25–40) or sedimentary
(20–30) admixtures; gypsum
(up to 3.5) by SO3 content
|3CaO·Al2O3 (up to 8)||200, 300, 400||Higher resistance|
to sulfate action
|Underwater and subterranean|
structures subject to constant
action of sulfate waters
|Portland cement clinker (40–70);|
pellets of blast-furnace slag
(30–60); gypsum (up to 3.5)
by SO3 content
|Same as portland cement||300, 400, 500||Lower early strength;|
less heat evolved
low resistance to
freezing; increased resistance
to sulphate action
|Same as portland cement; suitable|
for precast reinforced concrete
prepared with steam curing
|Aluminous cement||Aluminous slag (100); addition of|
1% admixtures that do not lower
cement quality is permitted
|400, 500, 600|
(after three days’ hardening)
|Rapid hardening at|
normal and low
resistance to waters
with high mineral
content; loss of
strength (up to 60%)
after 15–20 years
|Emergency, reconstruction, and|
other work with shortened construction
subject to the action of sulfur
dioxide or waters with high
mineral content; heat-resistant
concrete and mortar; not suitable
for high-temperature or highmoisture
|Aluminous slag (70); dihydrate|
calcium sulfate (30)
|Same as aluminous|
|400, 500 (after three days’ hardening)||Expands on hydration|
(0.15% in 1 day,
0.3–1 % in 28 days);
rapid hardening; high
density; highly waterproof
|Waterproof concrete and mortar,|
caulking, repair work, plugging
oil and gas wells
|Quartz sand (90–96); sodium|
|SiO2; Na2SiF6||Tensile strength 2|
meganewtons per m2
(after 28 days’ hardening)
|Resistant to most|
mineral and organic
acids; not resistant
to action of HF, H2SiF6,
boiling water, or
|Acid-resistant concrete and|
mortar, coatings, and linings; not
suitable for equipment used in the
food-processing industry or for
use at temperatures lower
the required composition; burning the mix at a temperature of 1450°–1550°C until it sinters; and crushing the clinker obtained into a fine powder together with a small amount of gypsum and active mineral additives or other substances that give the cement the required properties. The three production methods used—wet process, dry process, and a combination process—differ in the manner in which the raw material mix is prepared. The method used is chosen primarily on the basis of technological and economic indicators: the possible degree of production concentration, fuel and electricity expenditures, and labor input.
In the dry process, the raw materials (limestone and clay) are crushed and ground in mills; during the process, the raw materials are dried and converted to a powder. The composition of the powder is corrected to match specifications, and the powder is then sent to kilns. Modern rotary kilns for burning clinker are usually equipped with external heat exchangers, in which the raw material is heated and partially decarbonized. The heat expended in burning the clinker amounts to 750–850 C per kilogram of clinker.
In the wet process, the raw material components are mixed with water and crushed in mills; the water acts as a softening agent, intensifies the grinding process, and reduces the specific energy expenditure for grinding. The pastelike mixture obtained, called a slurry, is corrected to meet specifications and sent to the kilns. The heat expended in burning is higher because of evaporation of the slurry water in the kiln and equals 5.45–6.7 mega-joules per kilogram of clinker (1,300–1,600 C/kg), depending on the size and design of the kiln.
In the combination process, the raw material mix is prepared by the wet process, and the material is then dehydrated in vacuum filters or vacuum presses, shaped (usually into pellets), and sent to the kilns. The heat expenditure with this process is approximately 4.19 megajoules per kg of clinker (1,000 C/kg).
The necessary cement properties are achieved by correctly planning the raw material mix and ensuring the specified composition during the production process with respect to chemical composition, the quality and quantity of minerals included in the clinker, and the quality and quantity of substances included in the finished cement. Correct planning of the raw material mix is crucial to ensuring the proper progression through the intermediate stages of clinker formation, completion of the burning process, and good economic indicators for production. The quality of the finished cement is monitored on the basis of the requirements of the appropriate All-Union State Standards. Physicomechanical testing methods used to determine cement properties have also been standardized.
Cement is graded according to strength. The grade is determined from the flexural strength of prismatic test samples 40 × 40 × 160 mm in size and from the compressive strength of half sections of such samples. The samples are prepared from a cement solution mixed at a ratio of 1:3 by weight with ordinary quartz sand; the test samples are allowed to harden on hydration for 28 days from the time they are made. For special cements, the composition and methods of making and storing test samples may differ.
Table 1 describes the composition, basic properties, and areas of use of the principal types of cement produced in the USSR. The types of cement produced abroad are approximately the same as those produced in the USSR. With respect to technical quality, Soviet cements are among the best in the world.
Current trends in Soviet cement production include the following: a steady increase in the volume of cement production, which will reach 143–156 million tons in the USSR by 1980; a widening of the assortment and an increase in the production volume of special cements, especially high-strength, quick-hardening, decorative, and expansive cements; and an increase in the average grade strength of cements produced, in particular, an increase in the production of grade 600 cement and introduction of the production of grade 700 cement. Other trends include intensification of the hardening process (reaching high strength after 4–6 hours of hardening); efficient location of cement plants in order to reduce shipping operations for raw materials and finished products; a decrease in the prime cost of cement production; achievement of a high level of mechanization and automation of cement production; and a further improvement in working conditions at enterprises of the cement industry.
REFERENCESTekhnologiia viazhushchikh veshchestv. Moscow, 1965.
Viazhushchie materialy, zapolniteli dlia betonov i nerudnye materialy. Moscow, 1973.
Kratkiispravochnik tekhnologa tsementnogo zavoda. Moscow, 1974.
I. V. KRAVCHENKO
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.