Bitumen

The term asphalt is often used as an abbreviation for asphalt concrete.

Asphalt is a type of bitumen, a highly viscous liquid that occurs naturally in most crude petroleums. Asphalt can be separated from the other components in crude oil (such as naphtha, gasoline and diesel) by the process of fractional distillation, usually under vacuum conditions. A better separation can be achieved by further processing of the heavier fractions of the crude oil in a de-asphalting unit which uses either propane or butane in a supercritical phase to dissolve the lighter molecules which are then separated.

Further processing is possible by "blowing" the product: namely reacting it with oxygen. This makes the product harder and more viscous.

Among one of the most mis-pronounced words in the English language, it is properly pronounced "ASS-falt" as opposed to the common "ASH-falt". The erroneous "sh" the result of confusion over noting that the 'h' actually creates the "ph" sound.

Asphalt is sometimes confused with tar, which is an artificial material produced by the destructive distillation of organic matter. Both tars and asphalts are classified as bitumens, a classification that includes all materials entirely soluble in carbon disulfide.

Bitumen is commonly used in roofing shingles, and combined with mineral aggregate to make asphalt concrete for pavements. The binder used for asphalt concrete is called bitumen in many countries and is blended up from various components in an oil refinery to meet the desired hardness.

Asphalt is rather hard to transport in bulk (it hardens unless kept very hot) so it is sometimes mixed with diesel or kerosene before shipping. Upon delivery, these lighter materials are separated out of the mixture. This mixture is often called bitumen feedstock, or BFS.

Gilsonite is a natural form of asphalt.

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