Bitumen is a dense, highly viscous, petroleum-based hydrocarbon that is mainly used in moisture insulation and asphalt manufacturing industries. Generally, bitumen is a black and paste-shaped material that is in found in deposits such as oil sands and pitch lakes (natural bitumen) or is obtained as a residue of the distillation of crude oil (refined bitumen). Bitumen has a variety of types, each of which has a special application. Bitumen is a derivative of oil.
The beginning of modern bitumen industry can be attributed to 1712 AD when The bituminous stones were discovered in France. At that time, the material was poured over the surface of the local road; this technique was quite successful and shortly thereafter, improvements in the work were achieved by powdering and heating the materials before use. With the advancement of science and technology bituminous applications became very diverse and widely used in various industries and for various uses including road construction, coating, flooring, roofing, underground metal protective coatings, sealing of reservoirs, canals, bridges, stabilization of sand, staining and etc. Today, more than 250 different applications for bitumen in agriculture, construction industry, road construction and many other industries are considered. In the United States and some areas bitumen is often called asphalt. Bitumen is also frequently called tar or pitch—though, properly speaking, tar is a byproduct of the carbonization of coal and pitch is actually obtained from the distillation of coal tar. Bitumen is defined by the U.S. Geological Survey as an extra-heavy oil with an API gravity less than 10° and a viscosity greater than 10,000 centipoise.
Bitumen is solid at ambient temperature but as the temperature rises, it becomes paste-like and then it becomes fluid. Important application of bitumen is due to the two important properties of this substance:
1- Impermeability against water
The major bitumen produced in Iran and the world is used in road construction sector. In road construction bitumen is used as a bonding agent in asphalt and in the construction industry, it is ranked second with insulation (waterproofing). Estimations show that the annual amount of bitumen in the world is about 102 million tons. About 85% of this bitumen is used in the road construction industry and the 60/70 bitumen is used the most. More than 10% of the bitumen produced in the world is used in the building industry and as waterproofing and the rest is used in sealing, insulating, pipes and etc.
Bitumen is usually obtained from distillation of crude oil. Such bitumen is called naphtha bitumen or distillation bitumen. Petroleum bitumen is a product of two stages of distillation of crude oil in distillation column. In the first stage of distillation, light materials such as gasoline and propane are separated from crude oil. This process is carried out at a pressure close to the unit atmospheric pressure. In the second stage, heavy compounds such as diesel oil and kerosene are also extracted. This process takes place at a pressure close to the vacuum. Ultimately, a mixture of very fine solid particles, called Asphaltene remains, is immersed in the gravel-like fluid called Maltene. But some types of bitumen are derived in nature, and due to the gradual conversion of crude oil and evaporation of its volatile matters over many years, such bitumen is called natural bitumen and its durability is more than oil bitumen. Such bitumen may exist in nature in pure form (bitumen lake), such as Behbahan Lake in Iran, and the Bitumen Lake of Thirinidad in America, or may be extracted from mines.
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