Process of cement making
Process
of cement making
What is cement? It is a hydraulic binder that sets
under water and in open air once mixed with water or it is an adhesive material
which is capable of binding fragments into compact or it is a greenish-gray
powder made of lime (Calcium hydroxide) and alumina.
Cement is also referred to as Portland cement
because concrete that it is made from calcinations of orgillaceous rocks
resembled in color and quality the famous building stone obtained from the Isle
of Portland near England.
Raw
materials needed for cement making must be rich in:
calcium-source limestone, silicates-source orgillaceous rocks, clays (Kunkur),
gypsum (calcium sulphate) and iron ore.
There are two methods of cement making:
v Wet
process- which is costly to run and it is rarely used.
v Dry
process-this is less costly and is what is employed in modern cement factories.
How
it is done (process)
Raw materials are crushed and stored and which then
are mixed in predetermined ratio. The preferred mixture is heated at about 500ºC
in inclined kiln until fusion occurs. This is referred to as clinkering
manufacture while clinkering is the conversion of raw materials to cement like
materials. Grinding of the clinker to fine powder is the next step. Fine powder
is then heated to 1400-1600ºC for sintering to take place (semi fusion) while calcium
sulphate or gypsum is added. Cooling the lamps which are group to cement or
Portland is the last step.
Things
which are associated with this process (Dry process)
v Hot
gases from the kiln (1500ºC) are used to dry the crushed materials
v Dry
process conserves energy and therefore reduces production cost
v Carbon
(IV) dioxide and water of constitution which are given off during heating is
what causes the shrinkage of the final
product.
v From
1.7 tones charged in the process as raw materials one tone is of the product
that means approximately of 40% of loss in the process.
Reason
why concrete is wetted after it is made: This is to avoid
undesirable fast evaporation to retard hydration of cement to take place.
There are other two types of cement which differ
slightly from the one discussed above due to the things which are added during
the process. They include:
In this Bauxite is added during clinkering. Bauxite is composed of: Iron ore which has
Iron oxide, Silica magnesium and impurities. Its pros are that it is very fast
and strong and it resists saline water thus it is used at the coast.
Pozzolanic
cement
In this Pozzolanic materials/turf (volcanic ash rich
in silicaceous or silica and Alumina)
are added during grinding of the clinkers. Its pro is; it resists
corrosion due saline solution and sea water much more than ordinary cement
(Portland cement).
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