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55.4 ENVIRONMENTAL IMPACT OF CEMENT

PRODUCTION

Although cement is very useful in buildings and construction work, yet the cement production has adverse effect on the environment in the following way. One of the major pollutants released from cement plants is cement dust. Its harmful effects are as under:

  • It increases the concentration of particulate matter in air.
  • The heavy metals present in the cement dust cause disturbance in various metabolic activities which further retards the growth process.
  • It also causes breathing problems and lungs infections.
  • Direct contact of cement dust with skin become the cause of many allergies and skin diseases.
  • Cement kiln-dust gets accumulated on the soil and researchers have reported that it changes the soil alkalinity which is harmful for the crops.

USES OF CEMENT

  1. Cement on a very large scale is used in building construction. For this purpose it is generally used in the form of a thick paste of cement, sand and water in appropriate proportion.
  2. In the form of concrete, it used for the construction of floors, and roads. Concrete is a mixture of cement, sand, gravel or small pieces of stone along with water. It sets into an exceedingly hard structure.
  3. In the form of reinforced concrete it is used in building roofs and bridges, etc. Reinforced concrete is the concrete which is made more stronger by embeding into it the steel frames or wire netting. The structures made of reinforced concrete are extremely strong because in these structures the compression strength of cement is coupled with tensile strength
    of steel.
  4. It is also used in making asbestos sheets.

SUMMARY

Cement is fine mixture of calcium aluminates and silicates of varying composition which’ sets into a rigid solid mass after treatment with water. The raw materials required for production of cement are lime and clay.

For production of cement, the raw materials are crushed and their mixture is subjected to calcination at 1400°-1600°C to get cement clinkers. The clinkers are mixed with gypsum and other additives and ground to get cement.

EVALUATE YOURSELF

I.  Objective Type Questions

Select the most appropriate choice from the options given as (a), (b), (c) and (d) after each question:

1.      Cement is

a)      Mixture of various elements

b)      Single compound of definite composition

c)      Mixture of aluminates and silicates of alkali metals

d)     Mixture of calcium aluminates and silicates.

2.      The credit of discovery of portland cement goes to

a)      Rutherford

b)      Joseph Aspdin

c)      Joseph Pristlay

d)     Linus Pauling.

3.      Which of the following is not a constituent of Portland cement?

a)      CaO

b)      Fe2O3

c)      Al2O3

d)     B2O3

4.      The colour of portland cement is

a)      Greyish white

b)      Greyish black

c)      Bluish white

d)     White.

5.      In the rotary kiln the product that we get is

a)      Clinkers

b)      Concrete

c)      Gypsum

d)     Powdered cement

6.      The formula of gypsum is

a)      CaSO4.1/2H2O

b)      CaSO4

c)      CaSO4.2H2O

d)     CaSiO3

II. Fill in the Blanks

7.      Complete the following sentences by supplying appropriate words:

I.            The most important silicate component of the cement is …..

II.            The charge introduced in the lime kiln consists …..

III.            The temperature in the rotary kiln ….. as we move down the kiln.

IV.            The formation .silicates/aluminates in the kiln occurs at the temperature range of …..

V.            Concrete is a name given to …..

III. Discussion Questions

8.      What is cement? Name its important raw materials.

9.      Describe briefly the production of clinkers from the raw materials.

10.  How is cement produced from clinkers? What is function of adding gypsum to it?

11.  Describe the chemical reactions involved in rotary kiln.

12.  What do you understand by setting of cement?

13.  Give important uses of cement.

14.  Explain the terms concrete’ and reinforced concrete.

Answers

I.  Objective Type Questions

1.      (d)

2.      (b)

3.      (b)

4.      (b)

5.      (a)

6.      (c)

 II.  Fill in the Blanks

7.      (i) 3CaO.SiO2

(ii) finely ground lime and clay.

(iii) increases

(iv) 1000 – 1500°C

(v) mixture of cement, sand and gravels.