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Frequently Asked Questions

1. What is the raw material used for manufacture of cement? Calicareous (Limestone Obtained from mines), argillaceous materials (Clay, Bauxite) and Iron are the commonly used raw materials in the manufacture of cement.
2. How is cement manufactured?
Step 1 Extraction of lime stone from mines.
Step 2 Blending of ground limestone,Clay or Bauxite and iron ore or Laterite in right proportion and cintering in rotary kilns at a high temperature of 1400oC to1500oC form Clinker.
Step 3 Grinding of clinker with Gypsum to form cement.
Step 4 Storing in silos, testing and despatch form the final process of manufacture.
3. What is the chemical composition of cement and the contribution of each chemical compound?
Chemical Compounds Range in *OPC% Reaction Rat Strength Attained Liberation of Heat
Tri-Calcium-silicate (C3S); 40-55 Fast High Very High
Di-Calcium silicate(C2S 25-40 Slow Lowfirst high later Low
Tri-calcium Aluminate(C3A) 8-11 Fast Low Very High
Tetracalcium Alumino ferite 13-17 Moderate Low Moderate
4. Why should cement be 'fine'? The rate of hydration of cement depends on the fineness of cement and for a rapid development of strength high fineness is necessary.
5. What does, 53 grade, 43 grade and 33 grade cement indicate? Grades 53 , 43 and 33 indicate the compressive strength of cements in Newtons for one mm2 area. i.e. 53 grade means a compressive strength of 53 N.per mm2 attained after a curing period of 28 days. Similarly 43 and 33 grades may be defined.
6. Does the colour of the cement affect it's strength? The colour of the cement depends on the raw mateirals used. If the raw materials contain more iron resulting cements will be darker. Colour has no significance on any properties of cement. The strength of the cement is dependent on the correct proportion of raw material mix.
7. How to store cement? Proper storage of cement shall permit easy access for inspection and identification.Cement shall be stored in suitable weather tight structures, to protect the cement from dampness.It shall not be piled more thah ten bags in a stack and shall be arranged in header and stretcher fashion as far as possible.while removing the bags for use,"FIRST IN FIRST OUT" rule shall be applied.
8. Why is concrete the most widely used construction material? Concrete is the most versatile mouldable construction material ever known to mankind.It bears excellent fire and weather resistant properties. Most intricate shapes can be achieved with concrete . It is very good in compression though weak in tension.It is supplimented by steel to achieve tensile strength. Centuries old monuments bear testimony for its life.
9. What is an admixture? An admixture is a chemical formulation generally added to concrete while mixing to induce certain desirable properties to it like better workability with water reducing admixture, delayed setting the retarders, improve the rate of hardening with accelerating admixtures, and air entertainment for better flow and lubrication.
10. Why is a 'crack' developed? A crack is developed whenever stresses in the structural component exceeds its strength .This may be due to external forces, foundation settlement, thermal changes, chemical action etc.
11. Why do 'plastering cracks' occur? Plastering cracks appear because of evaporation of water, increased thickness, very fine sand, low quality bricks, non uniform plastering, improper seasoning of walls, use of different mix proportion , improper filling of joints, insufficient curing, more free lime/MgO.
12. What are the common mistakes which affect the quality of concrete? Use of too much or too little water for mixing. Incomplete mixing of aggregate with cement. Improper grading of aggregates resulting in seggregation or blending of concrete. Inadequate compaction of concrete. Using concrete which has already begun to set. Placing of concrete on a dry foundation without properly wetting it with water. Use of aggregate containing foreign materials such as earthy matters, clay or lime. Use of water containing solids, chemicals etc Too much trowelling of the concrete surface. Leaving the finished concrete surface exposed to sun and wind during the first ten days after placing without curing.

 
 
 
 
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