What is Bitumen? Definition, Uses, and Types

Bitumen is a dark liquid or semi-solid material which can be found in nature or derived from petroleum. It is used mainly in road construction but has over 250 applications. Read this article to learn more about bitumen.

1. What is Bitumen?

Bitumen is a mixture of hydrocarbons and can be obtained naturally or produced from crude oil. It is a dark brown to black color viscous liquid or semi-solid. The primary use of bitumen is in road pavement.

2. History of Bitumen

Bitumen has been a known material since ancient times. The Sumerians extracted the natural bitumen from rock to seal their boats. 

Bitumen also has a long history in road construction. The first record of use in road construction is around 615 BC. In the 19th century, people started to widely use bitumen in road construction. The first modern road using bitumen was built in Paris in 1837.

Since then, petroleum bitumen production technology has improved, and engineers have modified the bitumen to be a suitable material for different conditions.

3. Bitumen Sources

Bitumen comes from two main sources:

• Nature (Natural bitumen)
• Oil refineries (petroleum bitumen or refined bitumen)

Below is more detail on these sources.

3.1 Natural bitumen

Before 1907, the source of bitumen was nature. The volume of natural bitumen sources is about 1,856,853 billion barrels.

Natural bitumen sources are available in different locations around the world. Natural sources of bitumen are:

• Lake Bitumen
• Rock Bitumen
• Gilsonite
• Oil sand

3.1.1 Lake bitumen

Lake bitumen is a natural source found in locations such as Trinidad, North-Eastern Venezuela, and Nigeria.

In the lake bitumen, bitumen is a semi-solid and viscous material. Lake bitumen is a mixture of rock and bitumen. For example, Bermudez Lake bitumen is a mixture of limestone or sandstone and 5-30% bitumen.

3.1.2 Rock bitumen

Rock bitumen is another natural source of bitumen. Rock bitumen is formed when bitumen is trapped in an impermeable rock. This natural bitumen is extracted from mines.

3.1.3 Gilsonite

Gilsonite, also known as Asphaltite, Uintaite, or Asphaltum, is a solid hydrocarbon mainly made of asphaltenes.

Gilsonite forms when crude oil separates from its reservoir and moves through fractures and layers. Therefore, Gilsonite is usually found in cracks.

It is a soft and brittle material and can be easily crushed into dark powder.

3.1.4 Oil sand

Natural bitumen can also be naturally found in tar sand or oil sand.

Tar sand is a bituminous sand mixture. It means that tar sand is a mixture of sand and bitumen. This natural source of bitumen is located in various locations, such as Canada, Nigeria, and Iraq.

3.2 Petroleum Bitumen

Petroleum bitumen, or refined bitumen, is the greatest source of bitumen used in industry.

Petroleum bitumen is a byproduct of crude oil and is the residue of crude oil distillation. Crude oil has different components with different molecular weights. These components are separated in crude oil distillation at various temperatures. The residue of this process is a mixture of high molecular weight compounds and is used to produce bitumen.

In general, heavier crude oil contains more bitumen.

4. Bitumen Composition

Bitumen is a complex mixture with different compositions. In general, bitumen mainly contains these elements:

• Carbon 82-88%
• Hydrogen 8-11%
• Sulfur 0-6%
• Oxygen 0-1.5%
• Nitrogen 0-1%
• And a little vanadium, nickel, iron, magnesium and calcium.

Bitumen composition depends on the composition of the source crude oil bitumen derived.

Bitumen’s chemical composition is divided into two groups:

• Asphaltenes
• Maltenes (saturates, aromatics, and resins)

5. Bitumen Structure

Bitumen is a colloidal system. In a colloidal system, the tiny particles are spread throughout another substance. Here, the small particles are asphaltene molecules that are dispersed in maltenes.

Bitumen structure has two main parts:

• An oily liquid part, non-polar, containing low molecular weight compounds like saturates and aromatics.
• Asphaltene particles are polar and dispersed in the liquid part.

Resins (which are polar) act as a stabilizing agent to keep the asphaltenes dispersed in the oily phase.

6. Bitumen Properties

Bitumen is a complex mixture, and its properties differ depending on the composition. Also, the properties depend on the grade of bitumen. Below, you can see the range of physical properties of bitumen.

• Bitumen density: Typically ranges from 1.01 to 1.04 g/cm³ at 15°C
• Bitumen viscosity: ranges from 100 to 10,000 poise at 60°C
• Bitumen penetration: Ranges from 20 to 300 dmm (deci-millimeters)
• Bitumen softening point: Typically ranges from 30°C to 120°C
• Bitumen ductility: Usually ranges from 5 to 100 cm
• Bitumen flash point: Usually between  230°C to 350°C

7. Types of Bitumen

Bitumen has several types and grades, each suited for different applications. The main types of bitumen include:

7.1 Penetration Grade Bitumen

Penetration grade bitumen is commonly used in road construction and is specified by its penetration depth and softening point.

Penetration grade bitumen is shown using two numbers: X-Y

It means that bitumen penetration value is in the range of X to Y.

Harder bitumen has a smaller penetration value.

Common bitumen penetration grades include 20/30, 30/45, 35/50.

7.2 Viscosity Grade Bitumen (VG)

Viscosity grade bitumen is graded based on its viscosity at 60°C and 135°C.

Viscosity grade bitumen is indicated by VG-X.

X is a number of 10,20,30,40, so the grades are VG-10, VG-20, VG-30, and VG-40.

A higher X number indicates harder bitumen in the viscosity grading system.

7.3 Performance Grade Bitumen (PG)

Performance grade bitumen, or PG, is graded based on its performance in different temperatures.

It is shown as PG and has two numbers: PG X-Y.

X is the maximum temperature of the pavement area.

Y is the minimum temperature of the pavement area.

For example, PG 52-22 indicates the bitumen is suitable for environments with maximum 7-day temperatures of 52°C and minimum pavement design temperatures of -22°C.

Some of the PG bitumen grades are PG 46-34, PG 46-40, PG 52-16, and PG 58-28.

7.4 Oxidized Bitumen (Blown Bitumen)

Oxidized bitumen, or blown bitumen, is obtained by blowing hot air (200-270 °C) into bitumen.

This type has lower penetration and higher softening points, which makes it suitable for roofing.  

Oxidized bitumen is indicated using two numbers: the first number is the softening point at °C, and the second number is penetration depth at 25°C.

For example, 75/30 is an oxidized bitumen with 75°C softening point and 30 deci-millimeter (0.1 mm) penetration depth.

Some oxidized bitumen are 75/30, 85/25, 85/40, 95/25.

7.5 Bitumen Emulsion

Bitumen emulsion is a combination of bitumen, water, and an emulsifying agent.

Bitumen emulsion has lower viscosity than pure bitumen and is suitable for cold pavement mixtures.

It can be anionic, cationic, or nonionic, and further classified as slow-setting, medium-setting, or rapid-setting.

SS-1, SS-1h, CSS-1, MS-2, and CRS-1 are some examples of bitumen emulsions.

7.6 Cutback Bitumen

Cutback bitumen is a penetration grade bitumen mixed with a petroleum solvent. It has lower viscosity than pure bitumen.

It is classified as slow-curing (SC), medium-curing (MC), or rapid-curing (RC) based on the volatility of the solvent.

SC 30, MC 30, MC 70, MC 250, and RC 30 are some grades of cutback bitumen.

7.7 Polymer-Modified Bitumen (PMB)

Bitumen is modified with polymers like polybutadiene, polyethylene, or epoxy resin to improve its durability and resistance to deformation and high temperatures.

8. Bitumen Uses

Bitumen is widely known for its use in road construction and pavement. In fact, bitumen is often known as asphalt binder in asphalt concrete. Although most commonly used in pavements, bitumen has over 250 uses, including:

• Road construction
• Waterproofing
• Flooring
• Roofing
• Coating
• Soundproofing
• Hydraulics and erosion control

It also has applications in agriculture, railways, sports fields, paints, automotive, and electrical industries.

For more information on how bitumen is used in pavement, see our comprehensive article on bitumen used in road construction.

9. Tests on Bitumen

Several tests can be used to measure bitumen’s properties. The usual tests are:

• Penetration test: measures consistency (hardness or softness) of bitumen
• Softening point test: determines the temperature at which bitumen starts to soften
• Viscosity test: measures the bitumen’s resistance to flow (viscosity) at different temperature
• Ductility test: assesses the cohesive strength of bitumen
• Specific gravity test: measures the ratio of bitumen mass to water mass
• Solubility: measure the purity of bitumen
• Flash and fire point test: determines the temperature at which bitumen produces flammable vapors
• Loss on heating test: obtains the amount of volatile part of bitumen