Bituminous mixes are most commonly used all over the world in pavement construction. They were being used as a mortar and water proofing agent; as early as 3800 B.C. Early bitumen was of natural origin, found in pools and lakes. Many of these pools and lakes exist even today. The bitumen lake on the Trinidad island and the Bermudez deposit in Venezuela, are the largest known sources of bitumen supply. Most of the roads are constructed in Bangladesh by bituminous materials.
In different parts of the world, bitumen is also found in porous rocks such as sandstone and limestone. These bitumen-impregnated rocks have been of limited commercial value, because of the range of bitumen content. Gilsonite is another form of natural bitumen rock and is related to rock asphalt. It is a form of asphalt or bitumen occurring in rock crevices or veins.
Many theories have been put forward to explain the formation of petroleum and bitumen. But it has now been accepted that these materials were produced by decomposition of Dead Sea organisms such as Alge, molluscs, radiolaria, and probaly fish also. The organic matter changed chemically to, hydrocarbons, which constitute crude petroleum. Due to distortion in earth's crust, crude petroleum deposits got exposed to evaporation. On exposure, lighter oils and gases were driven off, leaving behind a residue called natural asphalt which may be in the form of lake asphalt or rock asphalt. Crude petroleum is obtained by tapping the under ground reservoir by drilling.
There has been some confusion in regard to the terms `Asphalt' and `Bitumen’. In U.S.A. the term `asphalt' is used to refer to both the products manufactured from crude petroleum in the refinery and also to the natural or artificial mixture in which it is associated with inert mineral matter. But else-where in the world including India, the refinery product is termed bitumen and the mixture of bitumen and inert mineral matter as `asphalt'.
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