Types of Bitumen
Table of Contents :
Overview of Bitumen Types.
Bitumen Classification by Source.
Bitumen Classification by Application.
Physical and Chemical Properties.
Specialty Bitumen Types.
Other Bitumen Types.
Overview of Bitumen Types :
Bitumen is a highly versatile material with a wide range of applications, but its primary use—accounting for nearly 90% of global demand—is in road construction and maintenance, either in its pure form or as a component of asphalt mixtures. The most common types used for paving include penetration grade bitumen, cutback bitumen, and bitumen emulsions. Other variants such as oxidized (blown) bitumen, hard bitumen, and mastic asphalt are used in non-road applications like sealants, waterproofing membranes, paints, electrical products, flooring, pipe coatings, and adhesives. More recently, polymer-modified bitumen (PMB) has gained popularity due to its enhanced performance in both road and industrial uses.
Bitumen Classification by Source :
Bitumen can be categorized based on its origin into three main types:
Natural Bitumen (Native Asphalts) :
Formed naturally over time through geological processes, these bitumens require no distillation. Their composition and properties vary significantly. They can be found in lakes (lake bitumen) or extracted from mines (mineral bitumen).
Coal Tar Pitches:
Produced from the distillation of coal tar, these are hard, shiny black substances. When heated, they melt quickly as their viscosity drops. The melting point varies depending on the production method.
Petroleum Bitumen (Distilled Bitumen):
The most widely used type, petroleum bitumen is obtained through the distillation of crude oil. After removing light fractions (gasoline, diesel, kerosene), the residue—rich in asphaltenes and maltenes—is collected. Additional processes such as air blowing may be applied to alter its properties.
Bitumen Classification by Application :
Bitumen can also be divided into two main categories based on usage :
Road Construction Bitumen (Soft Grades) :
Typically defined by their penetration grade, which measures how deeply a standard needle penetrates the material under controlled conditions (25°C, 100g, 5 seconds). Common penetration grades include 60/70 and 85/100. These grades determine the hardness and elasticity of the bitumen, which affect road durability and temperature resistance.
Building and Industrial Bitumen (Hard Grades) :
Used in roofing, insulation, and waterproofing. These harder grades offer high resistance to deformation and water ingress.
Physical and Chemical Properties :
Bitumen is a black to dark brown hydrocarbon that is:
Solid or semi-solid at ambient temperature
Soluble in carbon disulfide
Water-resistant
Adhesive
Becomes pasty and then liquid when heated
These properties make bitumen ideal for binding materials, waterproofing, and structural uses.
Specialty Bitumen Types :
Blown Bitumen (Oxidized Bitumen) :
Produced by blowing hot air (200–300°C) through bitumen at the final stage of refining. This process increases the softening point and decreases the penetration rate, resulting in a more rigid material. It is used in roofing sheets, car batteries, and industrial coatings.
Cutback Bitumen (Solution Bitumen) :
A blend of bitumen and a volatile solvent such as gasoline, kerosene, or fuel oil. At room temperature, it behaves like a liquid or soft material. Based on evaporation speed, it is classified as :
RC (Rapid Curing) – mixed with gasoline
MC (Medium Curing) – mixed with kerosene
SC (Slow Curing) – mixed with gas oil or fuel oil
These are used in cold-mix asphalts and surface treatments.
Emulsion Bitumen :
Made by dispersing bitumen in water with the help of an emulsifier (typically an alkali salt or ammonium compound). The charged bitumen particles repel each other and remain suspended in water, reducing environmental pollution and fire risk during transportation. Emulsions are widely used in maintenance works, cold applications, and eco-friendly road construction.
Other Bitumen Types :
Beyond the common paving and industrial grades, several specialized types of bitumen exist to meet specific performance, environmental, and technical requirements. These include viscosity-graded, performance-graded, penetration-graded, oxidized, and polymer-modified bitumens.
1. Viscosity-Graded Bitumen :
Viscosity-graded bitumen is classified based on its dynamic viscosity at 60 °C or kinematic viscosity at 135 °C.
Dynamic viscosity is measured in Poise, while kinematic viscosity is expressed in centistokes (cSt).
Grades are typically denoted by the prefix “V”, followed by a number indicating the nominal viscosity (e.g., V10).
This method provides more accurate insights into bitumen’s flow behavior at service temperatures and is commonly used in regions with high traffic and temperature variations.
2. Performance-Graded Bitumen (PG Bitumen) :
Performance grading (PG) is the most advanced classification system, developed under the Strategic Highway Research Program (SHRP).
It evaluates the mechanical performance of bitumen over a range of temperatures, both high and low, ensuring suitability in diverse climate conditions.
A PG grade specifies the minimum and maximum pavement temperatures for which the bitumen is designed (e.g., PG 64-22).
This system is used for both pure and polymer-modified bitumen, providing better precision in product selection.
3. Penetration-Graded Bitumen :
Penetration grade classification is based on the depth a standard needle penetrates into a bitumen sample under controlled conditions.
The lower the penetration value, the harder the bitumen.
Grades are expressed as a range, for example: 50/70, 60/70, or 85/100.
This method also considers other properties such as softening point, solubility, and flash point for full specification.
Although it is one of the older grading methods, penetration testing remains widely used due to its simplicity and historical standardization.
4. Oxidized Bitumen (Blown Bitumen) :
Oxidized bitumen is produced by passing hot air through bitumen at elevated temperatures. This process alters the bitumen’s structure and physical behavior :
Air-rectified or semi-blown bitumen undergoes light oxidation to slightly adjust its properties.
Fully blown bitumen experiences a significant chemical transformation, resulting in a higher softening point and lower penetration, making it more rigid and water-resistant.
Grading is typically based on a combination of softening point (measured via the ring and ball test) and penetration value. The distinction between air-rectified and oxidized grades has been clarified in documentation by Eurobitume.
5. Polymer-Modified Bitumen (PMB) :
Polymer-Modified Bitumen (PMB) consists of bitumen blended with synthetic polymers to enhance its viscoelastic properties.
The most common polymer used is styrene–butadiene–styrene (SBS), which increases elasticity and improves performance under traffic loads and temperature extremes.
Other modifiers include styrene–butadiene rubber (SBR), ethylene-vinyl-acetate (EVA), and polyethylene (PE).
While PMBs are more expensive than conventional bitumen, they are more cost-effective in the long term due to extended pavement life and reduced maintenance needs. Their superior performance makes them ideal for heavy traffic roads, airport runways, and climate-sensitive applications.