Glass, plastics, bitumen, asbestos, paints, distemper and varnishes are some of the miscellaneous materials used in building constructions. Their properties and uses are briefly presented in this article.
Glass
Silica is the main constituent of glass. But it is to be added with sodium potassium carbonate to bring down melting point. To make it durable lime or lead oxide is also added. Manganese oxide is added to nullify the adverse effects of unwanted iron present in the impure silica. The raw materials are ground and sieved. They are mixed in specific proportion and melted in furnace. Then glass items are manufactured by blowing, flat drawing, rolling and pressing.
Important Properties of Glass
- It absorbs, refracts or transmits light. It can be made transparent or translucent.
- It can take excellent polish.
- It is an excellent electrical insulator.
- It is strong and brittle.
- It can be blown, drawn or pressed.
- It is not affected by atmosphere.
- It has excellent resistance to chemicals.
- It is available in various beautiful colours.
- With the advancement in technology, it is possible to make glass lighter than cork or stronger than steel.
- Glass panes can be cleaned easily.
Types of Glass
The glass may be broadly classified as:
1. Soda Lime Glass: It is mainly a mixture of sodium silicate and calcium silicate. It is fusible at low temperature. In the fusion condition it can be blown or welded easily. It is colourless. It is used as window panes and for the laboratory tubes and apparatus.
2. Potash Lime Glass: It is mainly a mixture of potassium silicate and calcium silicate. It is also known as hard glass. It fuses at high temperature. It is used in the manufacture of glass articles which have to with stand high temperatures.
3. Potash Lead Glass: It is mainly a mixture of potassium silicate and lead silicate. It possesses bright lustre and great refractive power. It is used in the manufacture of artificial gems, electric bulbs, lenses, prisms etc.
4. Common Glass: It is mainly a mixture of sodium silicate, calcium silicate and iron silicate. It is brown, green or yellow in colour. It is mainly used in the manufacture of medicine bottles.
5. Special Glasses: Properties of glasses can be suitably altered by changing basic ingradients and adding few more ingradients. It has now emerged as versatile material to meet many special requirement in engineering. The following is the list of some of the special glasses:
(a) Fibre glass (b) Foam glass (c) Bullet proof glass (d) Structural glass (e) Glass black (f) Wired glass (g) Ultraviolet ray glass (h) Perforated glass.
Plastics
Plastic is an organic material prepared out of resin. It may or may not contain fillers, plasticisers and solvents. Plastic may be defined as a natural or synthetic organic material which are having the property of being plastic at some stage of their manufacture when they can be moulded to required size and shape. Shellac and bitumen are the natural resins used as plastic for a long time.
In 1907, Blackland produced synthetic resin from the reaction of phenol and formaldehyde. The resin was hardened under pressure and heat to produce useful plastic articles.
Types of Plastics
Primarily there are two types of plastics:
1. Thermosetting Plastics: It needs momentary heated condition and great pressure during shaping. When heated cross linkage is established between the molecules and chemical reaction takes place. During this stage shape can be changed with pressure. This change is not reversible. The scrap of such plastic is not reusable. Bakelite is an example of such plastic.
2. Thermoplastic: In this variety, the linkage between the molecules is very loose. They can be softened by heating repeatedly. This property helps for reuse of waste plastic. These plastic need time to cool down and harden. These plastics are to be kept in moulds till cooling takes place completely. Bitumen, cellulose and shellac are the examples of this variety of plastics.
Properties of Plastics
1. Colour: Some plastics are completely transparent. Using pigments plastics of any attractive colour can be produced.
2. Dimensional Stability: It is dimensionally stable to a great extent.
3. Durability: Plastic offers great resistance to moisture and chemicals and hence more durable.
4. Electrical Insulation: The plastics possess excellent electrical insulating property.
5. Fire Resistance: The phenol-formaldehyde and urea-formaldehyde plastics resist fire to a great extent and hence they are used as fire proofing materials.
6. Strength: The plastics are reasonably strong. Their strength may be increased by reinforcing with various fibrous materials. Attempts are being made to produce structurally sound plastics.
7. Specific Gravity: The specific gravity of plastics is very low and hence convenient to handle.
8. Ductility: The plastics are not ductile and hence they fail without giving warning.
9. Fixing: Plastics can be bolted, drilled, glued, clamped or simply push fitted in position.
10. Maintenance: There is no maintenance cost for plastic articles i.e., they do not need painting and polishing.
Uses of Plastics
There are variety of plastics made to suit different uses. The typical uses of plastics in buildings is listed below:
- Corrugated and plain sheets for roofing.
- For making jointless flooring.
- Flooring tiles.
- Overhead water tanks.
- Bath and sink units.
- Cistern hall floats.
- Decorative laminates and mouldings.
- Window and door frames and shutters for bathroom doors.
- Lighting fixtures.
- Electrical conduits.
- Electrical insulators.
- Pipes to carry cold waters.
Bitumen
Ashalt, bitumen and tar are referred as bituminous materials, which are essentially hydrocarbon materials. The asphalt is a mixture of inert mineral matter lime alumina, lime, silica etc. and a hydrocarbon known as asphaltic bitumen. In some places like Trinidad and Bermudez, asphalt is available in nature at a depth of 3 to 60 metres. It is known as natural asphalt. Common variety used all over the world is residual asphalt, which is obtained by fractional distillation of crude petroleum oil.
Bitumen is the binding material which is present in asphalt. It is a hydrocarbon. It is obtained by partial distillation of crude oil. It contains 87 per cent carbon, 11 per cent hydrogen and 2 per cent oxygen.
Tar is obtained in the distructive distillation of coal, wood or other organic materials. When coal or wood is heated to redness in an closed chamber, it yields volatile product and residue coke. After separating and cooling volatile product gives tar. Comparison between asphalt, bitumen and tar is presented in Table 1.
Asbestos
Asbestos is a general name for several varieties of fibrous minerals which are available in nature. But presently, most of the commercial asbestos produced is ‘chriotile’ [Mg6SiO11(OH)6.H2O].
Properties of Asbestos
- It is flexible, soft and non-porous.
- It is fire proof and acid proof material.
- It is a good insulator of heat and electricity.
- When it is mixed with cement and water, it retains shape firmly.
- Its colour is brown or grey.
- It can be cut into pieces or can be drilled.
- It possesses high tensile strength in the direction of its fibres.
- Its specific gravity is
Uses of Asbestos
- Asbestos cement sheets are the cheapest roofing materials.
- Asbestos cement pipes are used as down take pipes of rain water from the roof.
- With bitumen it forms good damp proof layer.
- It is used for preparing fire proof ropes and clothes.
- It is used as covering material for fuse and electric switch boxes.
- It is useful for insulating boilers, furnaces etc.
Solid and Hollow Concrete Blocks
Solid and hollow concrete blocks are manufactured in factories to meet the requirements of building blocks in cities and towns. These blocks may be called as artificial stones, since they replace the stones in the masonry construction. They are manufactured with lean mixes of cement, sand and aggregates of sizes less than 12 mm. Instead of sharp edged aggregates, round aggregates are professed in the manufacture of these blocks. The properties and uses of these blocks is given in this article.
(i) Solid Concrete Blocks: Solid concrete blocks of size 400 mm × 200 mm × 150 mm are commonly manufactured. To reduce the weight of the block no fine concretes are preferred. No fine concrete is the concrete in which fine aggregate is not used, but round aggregates of size less than 12 mm are used. IS:2185 (part I) 1983 covers the requirement, for such blocks.
The blocks should satisfy the strength requirement of 4N/mm2. Their density should be as low as possible, so that handling is not difficult. They should have sharp edges which are at right angles to each other. These blocks are used for load nearing wall construction also.
(ii) Hollow Concrete Blocks: To reduce the weight of concrete blocks, they may be made hollow as shown in Fig. 1. Hollow blocks of sizes 400 mm × 200 mm × 190 mm (nominal size 400 × 200 × 200 mm) and also of sizes 400 mm × 300 mm × 190 mm (nominal size 400 × 300 × 200 mm) are manufactured. IS:2185 (Part I) 1983 covers the specifications for these blocks. These block need richer mixes. Fine aggregates upto 60% and coarse aggregates upto 40% are used.
These blocks also should satisfy the strength requirement of 4 N/mm2. They should have truly right angled corners. Advantage of using concrete blocks is that the construction activity is fast. Mortar requirement for finishing the surface is less. Pointing alone is sufficient, in other words plastering is not necessary. Table 2 gives the differences between solid and hollow concrete blocks.
Both solid and hollow blocks can be used for the construction of load bearing as well as partition walls. They are ideally suited for the construction of compound walls.
Roofing and Flooring Tiles
These are also clay products like brick but are thin. Depending upon their use, building tiles may be further classified as:
1. Roofing Tiles: Roofing tiles are used to cover sloping roofs. They are supported on wooden reapers. Sometimes light gauge steel or steed rods are also used as reapers. After supporting on reapers these tiles should be strong enough to take load of a man safely. The tiles should he leak proof. Normally these tiles are having curved surface having ribbed sections, so that with thin section they are sufficiently strong to resist the load. However many times flat tiles are used under curved/ribbed tiles. These tiles are not subjected to load directly. They serve in reducing adverse thermal effects. Mangalore, Allahabad tiles, and corrugated tiles are popularly used roofing tiles [Ref. Fig. 2].
Allahabad tiles are generally laid side by side and the joints are covered with half round tiles. Mangalore tiles are red in colour and they are of interlocking type. These tiles are manufactured in Mangalore, Calicut, Cochin and Gujarat. Corrugated tiles satisfy the requirements of appearance and leak proof but they can be easily blown away by wind.
The desirable properties of the roofing tiles are:
- They should not absorb moisture more than 20 per cent by weight.
- They should give pleasing look.
- They should be capable of taking load of a man safely, after they are supported on reapers.
- They should be durable.
- They should be uniform in shape and size.
- Warpage should not exceed 2% along the edges and 1.5% along the diagonal.
2. Flooring Tiles and Wall Tiles: These tiles are manufactured by burning pressed green tiles twice. First they are burnt at 700°C. Then they are dipped in the glaze solution and again burnt at 1250°C to fuse them with glaze. The thickness of these tiles varies from 15 to 20 mm. These tiles are flat and they have pleasing appearance. There are two types of flooring tiles:
(a) Glazed Tiles: These tiles are used as finish surfaces for floors and walls in kitchen and bathrooms. These tiles are glazed and are provided with attractive colours and designs.
(b) Mosaic Tiles: These are precast concrete tiles with marble chips on the top surface. After fixing these tiles polishing is done. The desirable properties of flooring and roofing tiles are:
- Tolerance for length = ± 5 mm. 2. Tolerance for thickness = ± 2 mm.
- They should be uniform in shape and colour.
- They should be sound, hard and durable.
- They should have very low percentage of water absorption.
- They should give a clear ringing sound when struck with each other.
- They should show good resistance to abrasion.