BUILDING MATERIALS                


ASBESTOS

Asbestos is a naturally occurring fibrous mineral substance. It is composed of hydrous silicates of calcium and magnesium (CaSiO3, 3 MgSiO3). It also contains small amounts of iron oxide and alumina. Natural asbestos can be divided into groups, namely, acid resistant asbestos and non-acid resistant asbestos. The first group comprises actinolite asbestos, amosite asbestos, antophyllite asbestos, crocidolite asbestos and tremolite asbestos. The second group comprises only chrysolite asbestos, which is of great industrial importance.

Properties of Asbestos
1. Holes can be drilled and screws can be fitted on the surface.
2. It can be cut into pieces.
3. It is an excellent insulator for heat and electricity.
4. It is fireproof and acid-proof.
5. It is flexible, soft and nonporous.
6. It is smooth like glass and silk.
7. It possesses a good adsorption capacity. Hence, when it is mixed with cement and cured with water, it adsorbs i.e. retains firmly on its surface. Thus asbestos cement items can be considered as reinforcement in the form of asbestos fibres.
8. Its colour is brown, grey or white.
9. Its melting point is 1200 degree Celsius to 1550 degree Celsius.
10. Its molecules are strongly bound together only in one direction and that is why it possesses very high tensile strength along the fibres.
11. Its quality is critically affected by the length of fibres and hence, this characteristic of asbestos serves as a basis for classifying asbestos into different grades.
12. Its specific gravity is 3.10

Uses of Asbestos:
1. Asbestos cement products have become very popular at present. They are prepared by mixing asbestos fibres with cement. They include sheets and pipes, The sheet are used as roofing material and the pipes are used to convey rainwater, seepage water etc.
2. Asbestos felt can be prepared by coating asbestos fibres with bitumen and it is used as damp-proof layer.
3. It is used as covering material for magnetic coils.
4. It is used as lining material for fuse box and switch box.
5. It is used for insulating boilers, furnaces, etc.
6. It is used for preparing fireproof cloths, ropes, etc.
7. It is used to form asbestos paint.

Asbestos cement products:
The term asbestos cement is used to mean an artificial stone material, which is obtained by hardening a mix of cement, asbestos and water. Asbestos serves as reinforcement and it assists in providing high strength in tension and bending to asbestos cement items. The percentage of asbestos in asbestos cement items will depend on the type and quality of asbestos. But it generally varies from 10% to 20%.
The quality of asbestos cement products depends greatly on the quality of asbestos and fineness of cement. The moulding of these products requires longer time than that of concrete items. Hence it is necessary that the initial setting of cement products should begin somewhat later than for common portland cement and it should preferably be not less than 90 minutes from the time it is mixed with water.
The manufacture of asbestos cement products will require a great amount of water for preparing the asbestos cement mix and for washing the machines. Water to be used for this purpose should be free from clay impurities, organic substances and mineral salts.
The properties of asbestos cement include high mechanical strength in bending, frost resistance, low heat conductivity, high resistance to attack by mineralised aqueous solutions, high water tightness and small bulk density. However, asbestos cement is brittle and it wraps due to changes in humidity and its strength is lowered when saturated by water. Coloured asbestos cement products can also be prepared by the use of dyes and coloured enamels, resins and varnishes.
As per research, it has been found that asbestos dust produces a disease very similar to silicosis, which results in fibrosis of the lungs called asbestosis. It is also observed that about half the persons who get asbestosis also gets lung cancer. Some experts have also claimed that a five-minute inhalation of blue asbestos dust can produce cancer upto 20 years afterwards. Thus asbestos which finds a wide variety of uses in industry and in homes has emerged as a versatile killer in the eyes of some people. In a similar way, the exposure to asbestos dust can have harmful effects on the health of workers engaged in industries handling asbestos. It is therefore absolutely necessary to follow strict rules and standards laid down to prevent, control or minimize the risk of exposure in asbestos mines and factories producing asbestos based products.


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