Concrete
Component
Cement
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What is cement and how it is working
Portland cements are hydraulic cements composed primarily of
hydraulic calcium silicates Hydraulic cements set and harden by reacting
chemically with water. During this reaction, called
hydration, cement combines with
water to form a stone like mass, called paste. When the paste (cement and
water) is added to aggregates (sand and gravel, crushed stone, or other
granular material) it acts as an adhesive and binds the aggregates together to
form concrete, the world’s most versatile and most widely used construction
material. Hydration begins as soon as cement comes in contact with water. Each
cement particle forms a fibrous growth on its surface that gradually spreads
until it links up with the growth from other cement particles or adheres to
adjacent substances. This fibrous build up results in progressive stiffening,
hardening, and strength development. The stiffening of concrete can be
recognized by a loss of workability that usually occurs within three hours of
mixing, but is dependent upon the composition and fineness of the cement, any
admixtures used, mixture proportions, and temperature conditions. Subsequently,
the concrete sets and becomes hard.Hydration continues as long as favorable
moisture and temperature conditions exist (curing) and space for hydration products
is available. As hydration continues, concrete becomes
harder and stronger. Most of the hydration and strength
development take place within the first month, but
then continues, though more slowly, for a long time with adequate moisture and temperature. Continuous strength increases exceeding 30 years have been recorded
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MANUFACTURE OF PORTLAND CEMENT
Portland cement is produced by pulverizing clinker which consists
primarily of hydraulic calcium silicates. Clinker also contains some calcium
aluminates and calcium aluminoferrites and one or more forms of calcium sulfate
(gypsum) is interground with the clinker to make the finished product.
Materials used in the manufacture of portland cement must
contain appropriate amounts of calcium, silica, alumina, and iron components.
During manufacture, chemical analyses of all materials are made frequently to ensure
a uniformly high quality cement.
Selected raw materials
are transported from the quarry ,crushed , milled, and proportioned so
that the resulting mixture has the desired chemical composition.
The raw materials are generally a mixture of calcareous
(calcium carbonate bearing) material, such as limestone, and an argillaceous
(silica and alumina) material such as clay, shale, fly ash, or blast-furnace
slag. Either a dry or a wet process is used. In the dry process, grinding and
blending are done with dry materials. In the wet process, the grinding and
blending operations are done with the materials mixed with water in a slurry
form.
For more information about Cement and its type
please check attached file