Cement
Cement, one of the most important building materials, is a
binding agent that sets and hardens to adhere to building units such as stones,
bricks, tiles, etc. Cement generally refers to a very fine powdery substance
chiefly made up of limestone (calcium), sand or clay (silicon), bauxite
(aluminum) and iron ore, and may include shells, chalk, marl, shale, clay,
blast furnace slag, slate. The raw ingredients are processed in cement
manufacturing plants and heated to form a rock-hard substance, which is then
ground into a fine powder to be sold. Cement mixed with water causes a chemical
reaction and forms a paste that sets and hardens to bind individual structures
of building materials.
Cement is an integral part of the urban infrastructure. It is
used to make concrete as well as mortar, and to secure the infrastructure by
binding the building blocks. Concrete is made of cement, water, sand, and
gravel mixed in definite proportions, whereas mortar consists of cement, water,
and lime aggregate. These are both used to bind rocks, stones, bricks, and
other building units, fill or seal any gaps, and to make decorative patterns.
Cement mixed with water silicates and aluminates, making a water repellant
hardened mass that is used for water-proofing.
Cement is chiefly of two kinds based on the way it is set and
hardened: hydraulic cement, which hardens due to the addition of water, and
non-hydraulic cement, which is hardened by carbonation with the carbon present
in the air, so it cannot be used underwater.
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