Civil Engineering Reference
In-Depth Information
structure, etc. The first known building use of bitumen can be traced back about
5000 years to the Indus valley, where it was used to make a temple pool water-
tight. This fatty material often forms part of other building materials that are
exposed to moisture, such as perlite, wood fibre wind-proof sheeting and differ-
ent building papers, such as wind-proofing and roof covering. Coal tar was once
used instead of bitumen. Such products are no longer in use.
It is usual practice to oxidize the bitumen mass by blowing air into it. The
material is then warmed up and applied directly onto the surface, e.g. a founda-
tion wall. Solvents can be added to give a more workable consistence. Mixing
bitumen with crushed stone produces asphalt. Damp-proofing for foundation
walls can be carried out with a strong building paper membrane impregnated
with bitumen, or by applying 3-4 mm of asphalt reinforced with fibreglass. This
can also be used underneath a bathroom floor or a timber structure. The joints
are welded to make them watertight.
Bituminous mastic for making joints watertight consists of a solution or emul-
sion of bitumen with fine stone powder or synthetic rubber. The mixture contains
high levels of solvents. Bituminous sheeting is often built up on a fibreglass or
polyester base.
Bituminous products do not have a long life span if they are exposed to a com-
bination of sunlight, wide variations in temperature and a lot of damp. They can
also be attacked by acids found in soil. When protected from these conditions,
they can be very durable.
Today, bitumen is based solely on oil, which is an extremely limited resource
with a high pollution factor in its extraction and a potential for accidents. The
production of bitumen-based materials is intensive in its use of energy and also
has a high rate of pollution, but on a somewhat lesser scale than that of oil-based
plastic products.
The heating of bitumen on a building site emits dangerous fumes - polycycli-
cal aromatic hydrocarbons (PAH) amongst others, though the amount of PAH in
bitumen is considerably lower than that in coal tar. Some of the products contain
solvents. If bitumen products are exposed to heat or sunlight, fumes can be
released into a building. Bitumen products cannot usually be re-used or recycled.
Both bitumen and coal tar contain substances that are the initial stages of dioxin,
which can seep out; waste products should therefore be carefully disposed of
(Strunge, 1990).
Plastic materials
Many plastics have good water- and vapour-proofing properties and high ther-
mal insulation properties when produced as a foam. As a sealant, plastic can take
on many guises: paint, sheeting, paper, sealing strips and mastics.
