Plastics and Glass
Building Material Civil Engineering
Properties of Plastics:
Sound Absorption:
By infusing fiberglass with phenolic resins, acoustic board are prepared, as they have a high absorption coefficient.
Chemical Resistance:
Plastic offer great resistance to chemical and corrosion.
Fire Resistance:
Phenol formaldehyde and urea formaldehyde resists fire and hence are used as fire-fighting materials.
Electrical Insulation:
Plastic are good insulator of electricity.
1. Glass
- It is manufactured by fusion of silica with varying proportions of oxides of sodium, calcium, potassium and magnesia.
- They are fabricated by blowing, drawing, pressing, rolling or casting.
- After annealing they are given treatment by tempering, opaque making, silvering,bonding or cutting.
- It can be made stronger than steel and lighter than cork.
Types of glass are many:
- (1) Common glass;
- (2) Soda lime glass;
- (3) Potash lime glass;
- (4) Potash lead glass;
- (5) Coloured glass;
- (6) Special glasses.
Special glasses are fibre glass, wired glass, safety glass, bullet proof glass, shielding glass,ultraviolet ray glass, structured glass, glass blocks, ribbed glass, perforated glass and glass wool, etc.
2. Plastics
Plastic is a natural synthetic material, which has a property of being plastic at some stage of its manufacture. Synthetic material nay be phenol, formaldehyde, cellulose vinyl, etc. At presentthere are more than 1000 varieties of plastic.
• Synthetic of plastics are polymers. Polymerization is the process in which relatively small molecules, called monomers combine chemically to produce a very large network molecules,called polymers.
• Classification of the plastics may be on various basis.
1. On the basis of structure: Homogeneous plastics and heterogeneous plastics.
2. On the basis of physical and mechanical properties. Rigid plastics, semi-rigid plastics, soft plastics and elastomers.
3. On the basis of thermal properties: Thermoplastics and thermosetting plastic. Thermoplastics soften on heating and harden on cooling. The process of softening and hardening can be repeated several times. Thermosetting plastic undergo chemical changes at 127 – 177° C and set into permanent shape under pressure. Reheating will not soften them.
Advantages of plastic are — they can be moulded easily, do not rust, resist chemical action, light in weight and possess high strength to weight ratio. Disadvantage is that they have low modulus of elasticity.
3. Glass fibre reinforced plastics (GFRP) v
In these glass fibres provide stiffness and strength while resin provides a matrix to transfer load to fibres. GFRP is used for door and window frames, partition walls, roofing sheets, skylights, water tanks, for making chairs and tables.
4. Asbestos v
Asbestos is a naturally available mineral substance. It is fire-proof, acid-proof. It is good insulator of heat and electricity. It is used with cement to produce asbestos cement sheets for roofing, wall panelling, to cover fuse and electric boxes, for making downtake pipes, etc.
5. Bitumen, asphalt and tar v
These are called bituminous materials and their main constituent is hydrocarbon.
- (a) Bitumen: It is obtained by fractional distillation of crude petroleum. It is specified by term penetration, say 80/100 means penetration of standard needle is 80 to 100 mm at a temperature of 25°C. It is used for damp proof course, roofing felt.
- (b) Asphalt: It is bitumen mixed with inert material like sand, gravel and crushed stone. It is found in natural form. It is artificially manufactured also. It is used for waterproofing floors and roofs, lining reservoirs and swimming pools, for grouting expansion joints.
- (c) Tar: It is obtained by destructive distillation of coal, wood or mineral tar. It is used for road work, anti-termite treatment and waterproofing.
6. Fly Ash v
It is a by-product in coal based thermal plants. Its particles can fly in ordinary air. At one time it was considered a nuisance but now it is used as a useful material in manufacturing bricks, for stabilizing soil and to improve workability of concrete.
7. Steel Putty v
It is a plaster filler which can be applied with knife to fill dents in steel plates. It hasgood adhesive property and dries hard.
8. Adhesive, sealants and joint fillersv
- An adhesive is a material used to join two or more surfaces. Asphalt, shellac and cresin are natural adhesives which are used to glue papers. Rubber is another natural adhesive used to join plastic,glass and rubber. There are many synthetic varieties of adhesives like melamine resin, phenoil resin, urea resin and polyvinyl resin. They are used for joining plywood and laminated products.Starch glue, animal glue, casein glue (glue from skimmed milk), sodium silicate glue are also available for joining various materials.
- Sealants: Sealants are the substances used to seal cracks or joints between wall and window frames, glazing and window frame or between roofing sheets. Elastomeric sealants are most efficient. They are based on silicon, acrylic or polysulphide.
- Joints fillers: To prevent seepage of water through construction joints, these materials are used.They should be compressible and resilient. The common joint fillers used are built in strips of metals, bitumen treated felt and cork bound rubber.
9. Heat, electrical and sound insulating materialsv
- Thermal comfort may be achieved by providing air spaces by using aerated concrete, hollow blocks, using blast furnace slag in mortar and concrete and providing insulators and reflectingpaints.
- Electric insulators are used to separate the conductors carrying electric current. Mica, asbestos, porcelain, rubber, leakalite are electrical insulators.
- Paraffin and chlorinated diphenyl are liqui dinsulators which are used in transformers. In refrigerators thermocol is used.In auditoriums and cinema halls, sound insulators are required.
- The commonly used sound insulators are cellular concrete, asbestos, gypsum plaster, pulp boards, perforated plywood, glass mineral wool, etc.
10. Waterproofing and damp-proofing materialsv
- Preventing passage of water from one side of a surface to other side under normal hydrostatic pressure is known as waterproofing while damp-proofing is to prevent transfer of water bycapillary action.
- Bituminous materials, integral compounds, epoxy based materials, slurry coat and elastomeric materials are various waterproofing materials.
11. Thermocol v
- It is a general-purpose crystal polysterene. It can be cut easily with knife or saw. It contains 3–6 million discrete cells/litre. It has insulating efficiency against heat, sound, humidity and shock. It is used as packing material and display board.
12. Epoxy v
- It is a thermosetting polymer. It possesses excellent mechanical and adhesive properties. It is used with paints also.
13. Polyurethene v
- It is a product produced by mixing polymeric diol or triol with a silicon surfactant and a catalyst. This has elasticity of rubber, combined with the toughness of metal. It is used for making gaskets, tiers, bushings, shoe soles, pipes, waterproofing chemicals, etc.
14. Geosyntheticsv
- These are synthetic materials made of nylon, PVC, polypropylene etc. They last long even when buried under soil. Geotextiles, geogrids, geomembranes and geocomposites are commonly used geosynthetics. These materials are used for soil stabilization.
15. Ferrocement v
- Wire meshes embedded with cement and baby jelly is known as ferrocement. Theyare used for making door/window frames and shutters, partition walls, signboards, furnitures and even boats.
16. Cladding materialsv
- Cladding materials are used to enhance aesthetic appeal of walls, kitchen slab, stairs, roofs, ceiling, etc. Slate, granite, marble, clay tiles, mosaic, glass, wall papers etc. are the commonly used cladding materials in buildings.
17. PVC building products v
- Polyvinyl chloride (PVC) is versatile plastic. Its properties can be easily modified by addition of other compounds. PVC pipes, door and window frames, partition walls, kitchen cabinets, tiles and false ceiling are very popular products.
