Civil Engineering Reference
In-Depth Information
chance that very poisonous pollutants such as dioxin and heavy metals will be
released.
The basic materials
Bitumen and tar
Bitumen is obtained by distilling oil at 200-300°C. It is a strong waterproofing
substance used to impregnate materials such as paper, sheets and jointing mas-
tics, or applied directly to a surface. The products usually have organic solvents,
or are in a suspension of water and finely ground clay. By adding powdered
stone, sand or gravel different varieties of asphalt are produced which can be
used for road surfaces, damp-proofing on foundations or independent roof cov-
ering on a flat roof. Asphalt also occurs naturally, for example in Trinidad, where
it is called Trinidad asphalt.
Coal tar can be extracted from coal by condensation. This substance was once
used widely in the building industry, but is now almost completely replaced by
bitumen.
The chemical composition of tar and bitumen differ greatly. Tar is composed of
almost 50 per cent polycyclical aromatic hydrocarbon (PAH) compounds which
are almost non-existent in bitumen. Both materials can include early stages of
dioxin and are a potentially dangerous source of organic compound seepage.
Materials that contain tar or bitumen, need to be safely disposed of (Strunge,
1990).
Solvents and other chemicals
Light distillates can be used directly as solvents or as a chemical base for other
products. The monomers, which constitute essential components of plastics, are
important. Solvents are substances that break down other materials without
changing them chemically, and usually evaporate from a finished product (as in
paint that has dried).
The following substances are products directly and indirectly used in the
building industry.
Aliphatic and aromatic hydrocarbons
Amongst the aliphatic hydrocarbons are paraffins, naphthenes and n-hexane,
while the aromatics include substances such as xylene, toluene, trimethyl-
benzene, ethyl benzene and styrene. These substances can be used directly as
