Construction materials: Plastic

Uses of polymers

pipes

surface coatings

membranes

adhesives

jointing compounds

roofing materials

claddings

thermal insulants

fibre- reinforced plastics

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Types of polymerisation

Addition polymerisation: thermoplastics

  • relative movement on heating- softens at 60-100 C and stiffens on cooling
  • range from hard and rigid to soft and pliable but all subject to creep and have a low elastic modulus 
  • generally unsuitable for load bearing
  • do not rot or corrode or absorb water

Condensation polymerisation: thermosetts

  • cannot be softened by heat
  • rigid and hard
  • insoluble in organic materials
  • do not rot or corrode or absorb water
  • sunlight may fade colour
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Modification of polymers

chemical 

  • replace H atoms to increase stiffness and strength

co-polymerisation

  • two or more monomers eg high impact polystyrene

additives

  • plasticisers- reduce brittleness
  • fillers- colouur, economy, lower brittleness, heat and chemical resistance
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Thermoplastics

polythene

  • water tanks, pipes, damp proof courses, waterproofing and seperating membranes

PVC

  • sewerage pipes, roofing sheets, cladding, wall and floor tiles, wire insulators

adhesives and binders

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Thermosetts

mouldings

  • decorative

adhesives

fibre- reinforced polymer materials

cellular products

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Cellular forms

  • full of holes that are either open or closed
  • open cells tend to be flexible but closed cells are best as they float on water and absorb very little
  • low to very low density: 16-640 kg/m3
  • high strength:weight ratio
  • modulus of elasticity 3-3.6 GPa
  • good thermal insulation

examples

  • expanded polystyrene
    • boards, sheets, packaging, insulation
  • polyurethane foam
    • open cell: upholstery
    • closed cell: rigid insulation panels
  • foamed glass reinforced plastics
    • polyester resin and glass used for timber replacement
  • lightweight embankments
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Glass fibre reinforced plastics

  • made of glass fibres and resins
  • used in facades, lightweight bridges, bridge repairs
  • good durability, lightweight, good strength:weight ratio
  • beware creep and thermal sensitivity
  • short fibres in concrete
    • polypropylene
    • high impact resistance
    • crack control
    • used as facade units, precast concrete products, industrial floor slabs
    • potential reation with alkalis in cement to produce expansive matrix
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Polymer fibre composites

  • rapid growing interest in composites in general
  • most has been focused on fibre reinforced polymers
  • fuelled by the need to improve durability, reduce labour costs, construction time and to improve safety
  • Uk government launched two initiatives:
  • innovative manufacturing initiative
  • materials for better construction programme
  • ACCIS at Bristol Uni has 4 (5) central themes
    • multifunctional composites
    • novel microstructures
    • design
    • analysis and failure
    • intelligent structures
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Polymer fibre composites 2

Building industry 

  • infill panels and cladding elements

Civil engineering industry

  • structures made completely of advanced polymer composite materials
  • frp-concrete beam construction
  • internal reinforcement to concrete members
  • external reinforcement for metallic and reinforced concrete structures
  • replacement or degraded concrete bridge decks
  • frp confinement of concrete columns
  • bridge enclosures
  • increase ductility for blast resistance
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Polymer fibre composites 3

  • reinforcement of a relatively low modulus polymer with a high modulus high strength fibre uses the platic flow of the polymer material under stress to transfer the load to the fibre
  • the product is a two phase material
    • the fibre is the primary phase and is well dispersed in and bonded by the weak secondary phase which is the polymer
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Polymeric materials

  • most polymer materials are carbon based, produced largely from gas, oil and raw materials
  • there are routes to polymers from wood and other natural materials
  • rarely used in pure form but usually are supplied in a variety of types and grades in which the base polymer is compunded with additives
  • commonly mixed with fillers
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