Bitumen for roads – Bitumen Uses, Grades and Types

Bitumen for roads is an important topic to understand when it comes to modern road construction. It plays a crucial role in flexible pavements due to its superior performance, durability, and binding capabilities. Engineers widely use bitumen for roads because it offers excellent waterproofing, flexibility, and resistance to traffic loads and environmental factors. Compared to other pavement materials, bitumen provides a cost-effective and long-lasting solution, especially for high-traffic areas. This article will explain the significance of bitumen for roads and how it supports different structural layers in flexible pavement systems. Additionally, we will explore the types of bitumen road layers, various bituminous materials, cutback bitumen options, bitumen grades, and the essential properties that make bitumen for roads a preferred material in the construction industry.

Bitumen for roads – Bituminous binder types

Bitumen is a black, viscous liquid derived from petroleum processing. When combined with aggregates, it forms robust road surfaces used worldwide. Its waterproof and adhesive properties make it ideal for road construction. Regular maintenance ensures longevity of bitumen-based roads.

There are two types of bituminous binder for road construction.

• Bitumen (by distillation of crude oil)
• Tar (Produced from coal)

So, what are the difference between them?

Bitumen vs Tar – Comparison

The table below shows a comparison between tar and bitumen.

Bitumen	Tar
Petroleum product	Distillation of coal or wood
Soluble in carbon disulphide and carbon tetrachloride	Soluble in toluene only
Temperature susceptibility is low	Temperature succeptibility is higher than bitumen
Free carbon content is less	Free carbon content is more

Now, let’s sneak into the manufacturing of tar, being one of the important bituminous materials

Tar manufacturing

Manufacturers generally make tar by heating coal inside a chemical apparatus. Most producers obtain tar from coal as a byproduct of coke production, but they can also produce it from petroleum, peat, or wood.

The major steps in tar manufacturing are,

• Coal undergoes carbonation and produces crude tar
• Crude tar undergoes distillation/ refining and produces a residue
• The residue blends with distilled oil fraction and produces tar

I am going to tell more about the properties of bitumen now.

Properties of bitumen for road construction

The desirable properties of bitumen are,

1. Viscosity of bitumen during mixing and compaction is adequate
2. Bituminous material should not highly temperature and susceptible
3. In presence of water the bitumen should not strip off from aggregate
4. The adhesive property of bitumen binds together all the components without bringing about any positive or negative changes in their properties
5. Bitumen is insoluble in water and can serve as an effective sealant
6. Due to versatility property of Bitumen it is relatively easy to use it in many applications because of its thermoplastic property
7. Bitumen play a vital role in distributing the traffic loads on the pavement to the layers beneath

Bitumen for roads – Types of Bituminous materials

Okay. So, what are the types of bituminous materials that are used in flexible pavement construction? Below is the list for you.

1. Paving grade material
2. Modified bituminous binder
3. Cutback bitumen
4. Bitumen emulsion

Among the list, cutback bitumen is the major. Let me tell you more details about cutback bitumen.

Cutback bitumen

Cutback bitumen is the bitumen the viscosity of which is reduced by a volatile diluent. It is used in low-temperature mixing.

Three types of cutback bitumen are available

1. Rapid curing
2. Medium curing
3. Slow curing

The diluent while mixing varies with the type of cutback bitumen.

Type of cutback bitumen	Diluent
Rapid curing	Nafthal, gasoline
Medium curing	Carosine or diesel oil
Slow curing	High boiling point gas oil

Bituminous emulsion

A bitumen emulsion is a liquid product in which a substantial amount of bitumen suspended in a  finely divided condition in an aqueous medium and stabilized by means of one or more suitable material

Three types of bitumen emulsions are available

1. Rapid setting
2. Medium setting
3. Slow setting

Also read: Alignment of road: Factors affecting- obligatory points with figures

Grade of bitumen for roads – Types and Uses

To determine the grade of bitumen, penetration test is conducted. The results are expressed in 1/10 mm. When penetration value is represented as 80/1000, it is called grading of bitumen.

The old method of grading is viscosity test. Two viscosities kinematic and absolute and penetration value by penetration test results are collected. Based on this, bitumen is graded. The tables shows the grade of bitumen and values of viscosity in accordance with penetration.

Grade of bitumen	Absolute viscosity	Kinematic viscosity	Penetration
VG 10	800	250	80- 100
VG 20	1000	300	60- 80
VG 30	2400	350	50- 70
VG 40	3200	400	40- 60

Let me tell you the application of each of the grade of bitumen now.

VG- 10- Used in spray application since viscosity is very less

VG- 20- Used in cold area

Th most Commonly used grade in India is VG-30

VG- 40- High grade bitumen used in high traffic areas

Okay. So, lets’ learn about the bituminous layers.

Bitumen road layers

Let’s first look into the road layers to understand bitumen road layers.

The bitumen road layers come in the surface layer shown in the figure above. The figure below shows that. Bituminous mix consists of aggregate and binder. Aggregate consists of coarse aggregate, fine aggregate and filler less than 0.075mm.

• Bituminous concrete consists of aggregate and bitumen.
• Thickness of base course depends on grading of aggregate
• Dense graded aggregates are provided in base course. That is the permeability will be very less
• Number of voids should be very less
• Dense bituminous macadam should be given as a binder course

So, the trip is over. Hope the time you spend for reading about the bitumen for road was worth it.

MUST READ: Road margins- 6 types of road margin in highway

Key Takeaways

• Bitumen for roads is essential for flexible pavement construction.
• It offers water resistance, adhesion, durability, and temperature stability.
• Common uses include binder layers, surface sealing, and protective coatings.
• Bitumen types include penetration grade, viscosity grade, cutback bitumen, and bitumen emulsions.
• Penetration grades like 30/40, 60/70, and 80/100 are widely used.
• Emulsion types (CRS, CSS, SS) suit tack coats and low-temperature applications.
• Cutback bitumen (MC30, RC70) is used where quick curing is needed.
• Bitumen ensures strong bonding between road layers and improves lifespan.
• Engineers select bitumen grades based on climate and traffic needs.
• Proper bitumen selection enhances pavement performance and sustainability.

Conclusion

Bitumen for roads plays a critical role in the construction and performance of modern pavements. Its unique properties—such as waterproofing, adhesion, flexibility, and resistance to traffic loads—make it a preferred material for road engineers worldwide. Engineers employ various types and grades of bitumen for applications ranging from base layers to surface sealing, based on project requirements and environmental conditions. They use penetration and viscosity grades for high-traffic areas, while they choose emulsions and cutbacks for lower-volume roads and cooler climates. Each bitumen type serves a specific purpose in road layers like prime coats, binder courses, and tack coats. Ultimately, the correct selection and application of bitumen ensure a durable, cost-effective, and long-lasting road infrastructure.