Cement – Questions and Answers

By
Last updated:

1.What are the raw materials for cement?

Ans: Calcarious materials – limestone,chalk etc.
Argllacious materials – clay, shale etc.
Powedered coal
Gypsum.

Cement - Questions and Answers


2. What is the highest temperature maintained in the rotary kiln during the cement manufacture.

Ans: 1500 – 1700°C.


3. What are the basic chemicals present in the cement produced by Dry process?

Ans:
i) Lime ( CaO )
ii) Silica (SiO2 )
iii) Alumina (Al2 O3 )
iv) Iron oxide (Fe2O3 )
v) Magnesium oxide (MgO)
vi) Gypsym (CaSO4)


4. What are the steps involved in the manufacture of cement?

Ans:

(a) Crushing and mixing of raw materials
(b) Burning
(c)Grinding of clinker
(d) Storage and packing


5. What is the difference between wet and dry process?

Ans:

S. No Wet process Dry process
1. It is an old method. It is new method.
2. Cost is high. Cost is low.
3. Wet process is preferred, if the lime stone and clay are soft. Dry process is preferred, if the lime stone and clay are hard.

6. What are the various zones in kiln?

Ans: Various zones in the kiln are,

    1. Drying zone
    2. Calcining zone
    3. Clinkering zone

7. What are the chemical reactions taking place in the rotary kiln during the manufacture of cement.

Ans.

2CaO + SiO2              →             2CaO. SiO2 or  C2S                                                                                                       (dicalcium silicate )

3CaO +SiO2           →             3CaO. SiO2 or  C3S                                                                                                         (Tricalcium silicate )

3CaO +Al2O3         →             3CaO. Al2O3 or  C3A                                                                                                     (Tricalcium aluminate )

3CaO +Al2O+ F2O3      →     4CaO. Al2O3. F2O3 or  C3AF                                                                                        (Tetracalcium alumino ferrite )


8. What is the chemical responsible for slow rate of setting of cement and why?

Ans:
Tri calcium aluminate (C3A) combines with water with the evolution of heat.

C3A + 6H2O —–> C3A 6H2O + Heat

The added gypsum retards the dissolution of  C3A.6H2O by forming insoluble calcium sulfoaluminate

3CaO. Al2O3 x CaSO7H2O


9. Give the equations of initial setting of cement

Ans. 3CaO. Al2O3 +6H2O → 3CaO. Al2O3 .6H2O

Or

C3A + 6H2O → C3A. 6H2O


10. What is the temperature maintained in the rotary kiln during the manufacture of cement?

Ans: 1500 to 1700°C


11. What is the function of adding gypsum to cement?

Ans: Gypsum retard the initial setting of the cement.


12. Give the sequence of changes during setting and hardening

Ans.
Cement       1day     Hydration of         7days          Gelation   28 day    Gelation of
   +                  C3A and C4AF           of C3S        →          C2S
Water paste

13. What is water proof cement?

Ans. These cements are prepared by mixing with ordinary or rapid hardening cements, a small percentage of some metal stearate ( Ca, Al etc.) at the time of grinding.

This type of cement decreases the wetting ability of cement.


14. What is white cement?

Ans. It is prepared from such raw materials which are practically free from colouring oxides of iron, manganese or chromium.

It is white in colour.


15. Mention some of the special cements and its uses.

Ans: a) White Portland cement used in joining marbles, white tiles etc.,                      Also used in the manufactured of monaic tiles.

b) Water proof cement is used in moisture or water contaminated                        area to protect it.

Read More Topics
Abrasives – Questions and answers
Protective coatings – Questions and answers
Electrochemistry – Questions and answers
For Feedback - techactive6@gmail.com

Leave a Comment