Bitumen is a typical binder consist of different types of materials like carbon and hydrogen. It is used mostly in road construction, and it is usually obtained as a residual product in petroleum refineries after higher fractions like gas, petrol, kerosene, and diesel, etc. are removed.

Also, you can define it as a black or dark brown non-crystalline soil or viscous material having adhesive properties derived from petroleum crude either by natural or by refinery processes. 

Bitumen has three types:

1– Natural bitumen or native asphalt is a type of bitumen which is found in nature, due to climate conditions with time, without the need for any other manufacturing process. This type of bitumen appears to be highly various regarding their composition and properties.

2– Coal tar Pitches: the thick black liquid that remains after the distillation of coal tar is coal tar pitch. It is used as a base for coatings and paint, in roofing and paving. It's also used as a binder in asphalt products. Both coal tar and coal-tar pitch contain many chemical compounds, including carcinogens such as benzene.

3– Petroleum Asphalts are the bitumen which is taken from petroleum. These are solid and semi-solid bitumen which is directly produced through distillation from oil or by additional operations such as air blowing. Compared with the other types, they are more commonly used and are in demand more than different types.

Petroleum distillation is the most common way of producing bitumen. This type is also known as petroleum asphalt or distillery bitumen. Petroleum bitumen is the product of two phases of petroleum distillation in a distillation tower.

On the first phase of distillation, light materials such as gasoline and propane are separated from the crude oil. This process is done at a pressure close to atmospheric pressure. On the second stage, heavy compounds like diesel oil and kerosene are extracted.

This process is done at a pressure close to vacuum pressure. Finally, a mixture of solid bits called asphaltene remains which float in a grease-like fluid called Malton.

One other way that natural bitumen forms are a gradual changing of petroleum and the evaporation of parts of its materials over time. These kinds of bitumen are called natural bitumen, and it is more lasting than petroleum asphalts. Such bitumen may be found in nature in pure form (lake bitumen) or extracted from mines (mineral bitumen).

Bitumen is required for different purposes, but they fall into these major categories: road construction or thin bitumen, and building bitumen and (roof insulator) or hard bitumen. About 90% of the produced bitumen is used in road construction activities, and 10 % of it is used for insulation applications.

The classification of road construction bitumen is usually according to its reaction to penetration. Analyzers leave a piece of a metal needle on the surface of a bitumen sample for a specific time and weight and temperature. They then measure the depth of penetration of the needle into the sample of bitumen.

This penetration rate indicates how robust and hard the rated bitumen is. It has been defined as the number of penetration unit (one-tenth millimeter) of one vertical standard needle in one bitumen sample.

The standard condition for this measurement is 25-degree centigrade with 100-gram weight and in 5 seconds.

Bitumen is a hydrocarbon substance which is black to dark brown and quite dissolvable in carbon-sulfur. In average environment temperature, it has a solid form, but in increased temperature, it first turns into a paste and ends up liquid. It has two essential properties, being waterproof and adhesiveness, which makes it a necessary element for the application.