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:


High alumina cement
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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