Common misunderstandings that people seem to have is that petroleum bitumen and tar are the same thing. Although coal tar and petroleum bitumen looked similar with both are black in color and very sticky in nature, both of them are a really different in terms of chemical composition and their physical properties. The production of coal tar involves in heating coal to an extremely high temperatures and it is a by-product of gas and coke production. They are typically used as the binding agent in road asphalt during the industrial revolution on early 19th century but has been replaced now by refined bitumen as they are more suitable in terms of accessibility and price.
Bitumen is also sometimes confused with petroleum pitch which, although also derived from crude oil, is a substance produced by a different process from that used for refined bitumen. Petroleum pitches are the residues from the extreme heat treatment or “cracking” of petroleum fractions. Their properties and chemical composition are therefore quite different from those of bitumen.
Naturally-occurring bitumen, sometimes also called natural asphalt, rock asphalt, lake asphalt or oil sand, has been used as an adhesive, sealant and waterproofing agent for over 8,000 years. But it occurs only in small quantities and its properties are quite different from refined bitumen.
Bitumen is a sticky, black, and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used. The word is derived from the Ancient Greek ἄσφαλτος ásphaltos. The Pitch Lake is the largest natural deposit of asphalt in the world, estimated to contain 10 million tons. It is located in La Brea in southwest Trinidad, within the Siparia Regional Corporation.
The primary use (70%) of bitumen is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.
In material sciences and engineering, the terms “asphalt” and “bitumen” are often used interchangeably to mean both natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term “bitumen” for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, “bitumen” is the prevalent term in much of the world; however, in American English, “asphalt” is more commonly used. To help avoid confusion, the phrase “liquid asphalt”, “asphalt binder”, or “asphalt cement” is used in the U.S. Colloquially, various forms of asphalt are sometimes referred to as “tar”, as in the name of the La Brea Tar Pits, although tar is a different material.
Naturally occurring asphalt is sometimes specified by the term “crude bitumen“. Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at 525 °C (977 °F) is sometimes referred to as “refined bitumen”. The Canadian province of Alberta has most of the world’s reserves of natural asphalt in the Athabasca oil sands, which cover 142,000 square kilometres (55,000 sq mi), an area larger than England.
Asphalt properties change with temperature, which means that there is a specific range where viscosity permits adequate compaction by providing lubrication between particles during the compaction process. Low temperature prevents aggregate particles from moving, and the required density is not possible to achieve.