Coal tar can be extracted from mineral coal by condensation. This substance was once used widely in the building industry, but is now almost completely replaced by bitumen. Bitumen is obtained by distilling crude oil at 200-300 °C. It is a strong waterproofing substance used to impregnate materials such as building paper, sheets and jointing mastics, or applied directly to a surface as moisture membrane. These products either contain added 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 that can be used for roads, damp proofing of foundations and roof coverings.
The chemical composition of coaltar and bitumen differ greatly. Tar is composed of almost 50% polycyclic aromatic hydrocarbons (PAH), which are very damaging in the environment; bitumen has almost none of these compounds. Both these materials can include precursors of dioxins and are a potentially dangerous source of organic compound seepage. Materials that contain tar or bitumen need to be very carefully disposed of (Strunge et al., 1990).
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