| About Us - Registration/Login - Contact Us - Message Board - Glossary - Features - B-School - Legal - Biz-End - Orange-GTM - WAP |
| STOCK MARKETS | COMPANIES | SECTORS | ECONOMY | MUTUAL FUNDS | ONLINE TRADING | INVESTOR POINTS |
| |
|
| 'This site is a must read for investors ..' Forbes magazine | |
| India Infoline Sector Reports | Wed, 14-Jan-2004 11:24:07 IST (GMT+5:30) | |
| Cement | ||
|
 |
Introduction
Cement is a mixture of limestone, clay, silica and gypsum. It is a fine powder which when mixed with water sets to a hard mass as a result of hydration of the constituent compounds. It is the most commonly used construction material.
There are different varieties of cement based on different compositions according to specific end uses namely Ordinary Portland Cement, Portland Pozolona Cement, Portland Blast Furnace Slag Cement, White Cement and Specialized Cement. The basic difference lies in the percentage of clinker used.
OPC, popularly known as grey cement, has 95% clinker and 5% of gypsum and other materials. It accounts for 70% of the total consumption. White cement is a variation of OPC and is used for decorative purposes like rendering of walls, flooring etc. It contains a very low proportion of iron oxide.
PPC has 80% clinker, 15% pozolona and 5% gypsum and accounts for 18% of the total cement consumption. Pozolona has siliceous and aluminous materials that do not possess cementing properties but develop these properties in the presence of water. It is cheaply manufactured because it uses flyash/burnt clay/coal waste as the main ingredient. It has a lower heat of hydration, which helps in preventing cracks where large volumes are being cast.
PBFSC consists of 45% clinker, 50% blast furnace slag and 5% gypsum and accounts for 10% of the total cement consumed. It has a heat of hydration even lower than PPC and is generally used in construction of dams and similar massive constructions.
Basically, it is OPC: clinker using fuel oil (instead of coal) and with iron oxide content below 0.4% to ensure whiteness. Special cooling technique is used. It is used to enhance aesthetic value, in tiles and for flooring. White cement is much more expensive than grey cement.
Oil Well Cement: is made from clinker with special additives to prevent any porosity. Rapid Hardening Portland Cement: It is similar to OPC, except that it is ground much finer, so that on casting, the compressible strength increases rapidly. Water Proof Cement: OPC, with small portion of calcium stearate or non-saponifibale oil to impart waterproofing properties.
The wet, semi-dry or dry processes can be used to produce cement. In the wet/semi-dry process, the raw material is produced by mixing limestone and water (called slurry) and blended with soft clay. The dry process and semi-dry processes are more fuel-efficient. The vertical shaft technology employed by mini cement units, use the wet process where as the rotary kiln technology uses the modern dry process. The Indian cement industry has been progressively using the wet process with the dry process, which now accounts for 91% of the installed capacity.
The manufacturing process of cement consists of mixing, drying and grinding of limestone, clay and silica into a composite mass. The mixture is then heated and burned in a pre-heater and kiln and then cooled in an air cooling system to form clinker, which is the semi-finished form. This clinker is cooled by air, subsequently ground with gypsum to form cement. Limestone is the key raw material and normally, 1.2-1.5 tons are needed for every ton of cement. The quality of the limestone significantly affects the operating efficiency of the units. Under normal conditions, to produce 1 ton of cement, 0.25 ton of coal, 120 kwh of power and 0.05 ton of gypsum is required.
|
|
|
| 5PAISA | PREMIUM CONTENT | ADVERTISE WITH US | FEEDBACK | DISCLAIMER | PRIVACY POLICY | JOBS | FAQS | SITE MAP | HELP |
