Types of Bitumen

Bitumen used in road construction is generally classified into two main types: Natural or Mineral Bitumen, obtained directly from mines, Petroleum Bitumen, produced from the refining of crude oil.

Types of Bitumen

۱) Natural Bitumen

Natural bitumen forms when the volatile components of crude oil deep underground gradually evaporate due to atmospheric exposure, leaving behind a black, viscous material. Natural bitumen includes lake bitumen and rock bitumen.

a) Lake Bitumen

When crude oil naturally rises through fractured layers of the earth and volatile components evaporate, natural bitumen accumulates on the surface as bitumen lakes. The most famous lake bitumen sources worldwide include the Trinidad Lake, with an estimated volume of 10–15 million cubic meters, and the Bermuda Lake in Venezuela. In Iran, the Behbahan Bitumen Lake is a notable example.

b) Rock Bitumen

Rock bitumen occurs mainly in limestone and sandstone, where crude oil has penetrated and the volatile components have evaporated over time. The remaining bitumen content in these rocks ranges from 7% to 80%.

c) Gilsonite

Gilsonite is a natural hydrocarbon resin found in the Bonita River area in northeastern Utah. It resembles hardened natural asphalt and is also known as Asphaltum or Utahite. Gilsonite is soluble in aliphatic and aromatic organic solvents, like natural asphalt.
In its lump form, Gilsonite is shiny, black, and brittle, similar to obsidian. In micronized powder form, it appears dark brown. It is typically found in vertical underground layers.

۲) Petroleum Bitumen

In the early 20th century, petroleum bitumen, produced from refined crude oil, entered the market and gradually replaced natural and mineral bitumen in asphalt pavements and other industrial applications. This type of bitumen is obtained during the distillation of crude oil, remaining at the bottom of the distillation column at temperatures above 380°C.

Types of Petroleum Bitumen

a) Pure Bitumen

During crude oil distillation, lighter oils evaporate at lower temperatures, while heavier oils separate at higher temperatures. The residue at the bottom of the distillation column is pure bitumen. By adjusting the temperature and pressure in the column, bitumen of varying hardness grades can be obtained.

Specifications of Pure Bitumen

b) Blown Bitumen

Blown bitumen is produced by blowing hot air into pure bitumen during the final stage of refining. The liquid, high-temperature bitumen is placed in a special chamber, and air is injected from perforated pipes at the bottom. This process, typically performed at 200–300°C, modifies the bitumen properties to achieve the desired characteristics.

Specifications of Blown Bitumen

c) Bitumen Emulsions

Bitumen emulsions have several advantages, No heating is required during application, No intermediate solvents are needed to produce liquid bitumen, Safe for storage, handling, and transportation, Environmentally friendly. In road construction, emulsions are used for cold asphalt, surface asphalt, single coats, slurry seals, and more. Other applications include mulching for sand stabilization, protective coatings for tanks, and waterproofing roofs. Common emulsions are oil-in-water, where fine bitumen particles are dispersed in an aqueous phase. Emulsions are generally classified into anionic, cationic, and clay-based, with the first two types most commonly used in road construction.

d) Cutback Bitumen

Cutback bitumen is produced by dissolving pure bitumen in solvents or petroleum oils. The type and quality of cutback bitumen depend on the original bitumen quality, solvent type, and concentration.

Cutback bitumen is categorized based on setting speed and solvent type:

۱. Rapid-Setting (RS) Bitumen

Produced using gasoline as the solvent. Graded by viscosity in four types: RC-70, RC-250, RC-800, RC-3000 (suffix indicates viscosity in centistokes)

۲. Medium-Setting (MS) Bitumen

Produced by dissolving bitumen in kerosene. Viscosity at 60°C ranges from 60 to 6,000 centistokes, divided into five grades.

۳. Slow-Setting (SS) Bitumen

Produced using slow-evaporating solvents such as diesel or heavy oil, or directly from crude oil distillation. Also called road oils, retaining the motor oil fraction of crude oil.

e) Polymer-Modified Bitumen (PMB)

Since plain bitumen does not provide fully satisfactory physical properties, researchers have worked to modify and improve its characteristics. Polymer modification enhances bitumen quality, increases the service life of pavements or coatings, and significantly reduces maintenance and repair costs. Thermoplastic rubbers such as SBS (Styrene-Butadiene-Styrene) and SIS (Styrene-Isoprene-Styrene) 

Benefits of polymer addition: Increased resistance to deformation Reduced rutting and secondary compaction under traffic Improved resistance to cracking and agin.

Specifications of Polymer-Modified Bitumen