bitumen, dense, highly viscous, petroleum-based hydrocarbon that is 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). In some areas, particularly in the United States, bitumen is often called asphalt, though that name is almost universally used for the road-paving material made from a mixture of gravel, sand, and other fillers in a bituminous binder. 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. At the temperatures normally encountered in natural deposits, bitumen will not flow; in order to be moved through a pipe, it must be heated and, in some cases, diluted with a lighter oil. It owes its density and viscosity to its chemical composition—mainly large hydrocarbon molecules known as asphaltenes and resins, which are present in lighter oils but are highly concentrated in bitumen. In addition, bitumen frequently has a high content of metals, such as nickel and vanadium, and nonmetallic inorganic elements, such as nitrogen, oxygen, and sulfur. Depending on the use to which bitumen is put, these elements may be contaminants that have to be removed from the finished product. By far most refined bitumen is used in paving asphalt and roofing tiles, as is a large amount of natural bitumen. However, most of the bitumen extracted from Canada’s oil sands is upgraded into synthetic crude oil and sent to refineries for conversion into a full range of petroleum products, including gasoline

Understanding Bitumen

Bitumen is a by-product of crude oil. it is composed of complex hydrocarbons and contains elements like calcium, iron, sulfur, and oxygen. The quality of material and ease of production depends on the source and type of crude oil from which it is derived. It was first used for its natural adhesive and waterproofing characteristics, helping to bind building materials together, as well as to line ship bottoms. It has also been used as a medicine.

The product has several modern uses. It’s generally meant for industrial use and is commonly found in road paving. The majority of U.S. roads are made of either bitumen or a combination of bitumen and aggregates, such as concrete. Along with being waterproof and acting as an adhesive, engineers who replace asphalt roads can reuse the material for other road projects. Bitumen is also commonly used by companies that create and manufacture roofing products. 

Bitumen can deform permanently under heavy loads. Continued stress on the material can result in cracking. It oxidizes, which can leave the asphalt brittle. The way its shape is affected depends on a few things, including the composition of the asphalt mixture and the ambient temperature.

As noted above, bitumen isn’t just produced by distilling crude oil, it’s also a naturally-occurring product. The term is also used to refer to oil sands or partially consolidated sandstone containing a naturally occurring mixture of sand, clay, and water that is saturated with a dense and extremely viscous form of petroleum