construction engineering materials Flashcards
What plastic materials were developed and made in 1945?
PVC, Perspex, Polystyrene
PVC stands for polyvinyl chloride; Perspex is polymethylmethacrylate.
What process involves heating pellets of plastic and feeding it under pressure through a shaped die?
Extrusion
This process is followed by cooling the product.
What is the alternative method to extrusion for forming plastics that uses pressurized air?
Blow moulding
Injection moulding is also a method used for forming plastics.
How are thermosetting plastics made into components?
Compression moulding
Powder of granules of the plastic is placed in the mould, which is then heated and pressed.
Define copolymerisation.
When more than one monomer is used to form an irregular chain structure
Example: propene-ethene-ethene-propene.
What characterizes a flexible polymer?
Chains able to slide past each other.
What is the difference between thermoplastics and thermosets?
Thermoplastics have no cross links and can change shape; thermosets have extensive crosslinks that prevent movement.
Thermoplastics can be re-shaped when warmed.
What are crystalline polymers?
Areas where chains are packed in a regular way
More crystalline polymers are stronger but less flexible.
What is cold drawing in relation to polymers?
A process where polymers are stretched to form a ‘neck’, increasing strength.
List three advantages of using plastics for soffits and fasciae over timber.
- Economic
- Waterproof
- Lighter
- Possible longer lifespan
What is the composition of PVC?
Consists of hydrogen and chlorine.
What are the properties of PVC?
- Resistant to acids
- Resistant to alkalis
- Resistant to water
- Decomposes when burnt
- Low specific gravity
- Good insulator
Chlorine gas is given off when PVC is burnt.
What are the applications of polyethene?
- Water pipes
- Tanks
- Flexible films
- Damp proof membranes
High-density and low-density variants are available.
What is the significance of using a 1000 Guage damp proof membrane?
It provides effective moisture protection.
What is polyester fiberglass known for?
High strength and resistance to impact
It behaves similarly to reinforced concrete.
What are miscellaneous expanded plastics primarily used for?
Pipes, cladding, roofs, and decorative work.
What considerations are important in building construction?
- Sustain imposed loads
- Prevent ingress of moisture
- Act as barrier to heat transfer
- Act as barrier to water vapour
- Have provisional passage for sunlight
- Fire resistance
- Economic
