ASBESTOS | TYPES OF ASBESTOS | PROPERTIES OF ASBESTOS | USES OF ASBESTOS | PRODUCTS OF ASBESTOS | CONSTRUCTION MATERIALS

ASBESTOS

Asbestos is a naturally occurring fibrous material. It is a silicate of calcium and magnesium and contains a small amount of iron oxide and alumina. The original source of asbestos was the mineral fibrous mineral actinolite.

 

TYPES OF ASBESTOS

The natural fibre of asbestos belongs to two groups, viz., those which are readily active with acid (i.e., non-acid-resistant) and others that are acid-resistant.

The first group primarily consists of chrysolite asbestos which is used for industrial purposes. The second group comprises ammonite and crocidolite asbestos. The second group is not recommended for commercial use as they are said to cause diseases related to the lungs. The Indian industry uses the first group asbestos. However, it is advisable to use asbestos cement products with caution and sufficient care. As a matter of fact, in some countries, the use of asbestos is not allowed in buildings.

Asbestos is mixed with cement and used mostly in the building industry as asbestos cement.

 

PROPERTIES OF ASBESTOS

Following are the properties of asbestos:

(i) It has high tensile strength along with fibre.

(ii) It is an excellent insulator for electricity (i.e., it is a non-conductor).

(iii) It is incombustible and hence acts as a good insulator for heat.

(iv) It is acid-proof.

(v) It is flexible, soft and non-porous.

(vi) It is fire-resistant and the melting point is 1200–1500°C.

(vii) It possesses good adhesion with cement and hence the fibre can be used as a fibre reinforcement.

(viii)  It is rust-free.

(ix) Its specific gravity is 3.10.

(x) It can be easily cut into pieces.

(xi) Its quality is critically affected by the length of fibres.

(xii) It is smooth like glass and silk.

 

USES OF ASBESTOS

Following are some of the uses of asbestos:

(i) Asbestos with cement as asbestos cement have plenty of uses as sheets and pipes. Sheets are used as roofing material and pipes are used for drain rainwater, seepage water, etc.

(ii) Asbestos being a good heat insulator, it is used for insulating furnaces, steam and exhaust pipes, boiler, etc.

(iii) Asbestos being high-temperature resistant, it is often used for making moulded shapes to resist high temperatures.

(iv) Fire fighting persons use fire-proof suits made of asbestos.

(v) Asbestos being a good sound insulator, it is used as small length fibres in different conditions.

(vi) In the form of fibres, asbestos is used for cable insulation and in sheet form, it is used in lining and partition in switches and fuse boxes.

(vii) In electric motors and coils exposed to high temperatures, asbestos paper is used as a cover for electric wires.

(viii) Asbestos felt is used as a damp proof layer in combination with bitumen.

(ix) Asbestos is used for internal combustion engine exhaust pipes and silencer gaskets and sparkling plug washers in combination with copper shell.

(x) Asbestos, when powdered or in the form of fibres, is sometimes kneaded into a dough form with water and used for blocking holes and cracks in metal objects.

(xi) In combination with magnesium carbonate, or wool felt, it is used for lagging steam pipes.

(xii) It is used to form asbestos paints.

 

PRODUCTS OF ASBESTOS

Some of the products of asbestos which are manufactured are discussed below.

1. Asbestos Boards

Asbestos fibres and Portland cement are mixed and moulded under hydraulic pressures. These are available in board and sheet forms. Some of the commercial forms are claddings, roofing and decking units.

Asbestos boards are available in natural mottled grey colour and pigmented boards are also marketed. Boards are dense and rigid but workable easily using carpenter’s tools. These boards can withstand temperatures up to 540°C.

Asbestos boards are marketed in two sizes, viz., Class A: thickness = 6.5 mm and width = 1.2 mm; Class B: thickness = 5.0 mm and width = 1.2 mm.

Asbestos boards are economical and completely incombustible. They can take up paints of any shade economically. These are easily workable and durable.

 

2. Asbestos Sheets

Asbestos sheets are flat and are classified as compressed and uncompressed. Compressed sheets are of minimum thickness unit which can withstand bending stress of 22 N/mm2 with a density of 1600 kg/m3, whereas uncompressed units can withstand bending stress of 16 N/mm2 with a density of 1200 kg/m3. Corrugated types of sheets are with thickness varying from 4.76 to 6.35 mm and the corrugation has a pitch of 10 cm and the weight being 145 N/m2.

Asbestos sheets are used for wall-lining, wall-panelling, partitions, side-cladding and false ceilings. Also used for wardrobes, cupboards and kitchen-pantry shelves. Blackboards, hoardings, signboards, window panes and door panels are also of asbestos sheets.

 

3. Asbestos Cement Pipes

These pipes are made using 15–20% of asbestos fibres, 80–85% of cement and water. Pipes of different sizes, bands, functions, taper pipes, shoes, etc., are also manufactured to the required shape and size. They can be easily cut and need no paint to maintain.

These pipes claim several advantages because of its adaptability, easy installation, and are light, strong and can withstand normal handling.

Asbestos cement pipes are used as rainwater pipes, valley gutters, soil waste and ventilating pipes, half-round gutters, etc.

 

4. Asbestos Paint

It is prepared by the addition of finely ground asbestos to oil paint or distemper. It is highly fire-resistant, heat and sound insulation. It is vermin-proof and prevents corrosion of metals.

 

5. Asbestos Fibres

Asbestos is also available in fibre form in the market. These fibres have adequate strength and flexibility and are used in making conveyor belts, boiler insulation, brake lining, etc.

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