Civil Engineering Reference
In-Depth Information
The picture is not made easier by the fact that the plastics are often full of addi-
tives. PVC is considered a plastic with very good durability, but it has been
known to undergo very rapid breakdown. In Sweden, 10-year-old plastic skirt-
ings crumbled, not because of the PVC but because of an added acrylonitrile
butadiene styrene (ABS)-plastic which should have increased the strength and
durability. All plastics oxidize easily.
Polyethylene sheeting, which was in use as a moisture barrier until 1975, had
an effective lifespan of 10 years. This is far too low considering that the sheeting
is usually inaccessible within the fabric of a building, and often supposed to pre-
vent condensation within the walls. Polyethylene has recently included additives
which should make it more stable.
Sealing strips of ethylene propylene rubber (EPDM) are often used between
the elements in prefabricated buildings of timber and concrete. Research has
shown that certain makes have lost elasticity after only one year, which means
that the joint is open and the material no longer functions.
Recycling
Even if plastics have a relatively short functional lifespan, it takes a long time for
them to decompose in the natural environment. On tips, plastic waste is a problem
in terms of volume as well as pollution because of the additives which seep into
the soil and ground water, these problems can be reduced by recycling plastic.
Recycling through re-use is not really practicable. Recycling through melting down
is possible. Thermoplastics, and even a few thermosetting plastics, can be recycled in
this way. Amongst them are polyvinyl chloride, polyethylene and polypropylene.
Recycling is also possible, in theory, for purified polyurethane products, but is not
happening very much at present. Synthetic rubbers can be crumbled for use as a filler.
The maximum potential of future plastic recycling is estimated at 20-30 per cent
in the form of down-cycling only. Almost all plastics are impure because of their
additives, which makes reclamation of the original materials technically difficult.
The uses for recycled plastic vary from park benches, sound barriers and flowerpots
to huge timber-like prefabricated building-units for construction. The latter are now
in production in Great Britain, Sweden and the USA, based on melted polystyrene
waste with 4 per cent talcum powder and 11 per cent other additives. Polystyrene
can also be ground and added to concrete to increase its insulation value.
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