Bitumen for roads- Bitumen Uses, Grades and Types

Bitumen for roads is an important topic to understand when it comes to road construction. Bitumen is used in road construction because of the wide range of features and advantages it possesses over other pavement construction materials. The significance of bitumen in the construction of roads will be demonstrated in this article. In addition, we shall see bitumen road layers, various bituminous materials, cutback bitumen, bitumen grade, and bitumen properties.

Bitumen for roads – Bituminous binder types

There are two types of the bituminous binder for road construction.

  1. Bitumen (by distillation of crude oil)
  2. Tar (Produced from coal)

So, what are the differences between them?

Bitumen vs tar – A comparison

The table below shows a comparison between tar and bitumen.

BitumenTar
Petroleum productDistillation of coal or wood
Soluble in carbon disulphide and carbon tetrachlorideSoluble in toluene only
Temperature susceptibility is lowTemperature susceptibility is higher than bitumen
Free carbon content is lessFree carbon content is more
Bitumen vs tar – Comparison

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

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Tar manufacturing

Generally, tar is made by heating coal inside a chemical apparatus. Most tar is produced from coal as a byproduct of coke production, but it can also be produced from petroleum, peat or wood.

Figure shows the road construction using bitumen
Road construction using tar

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.

Also read: Classification of roads- 5 types of roads full details

Desirable properties of bitumen- an important topic in bitumen for roads

figure shows bitumen oozing out from pipe
Bitumen oozing out from the pipe

The desirable properties of bitumen are,

  1. The 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 the versatility property of Bitumen, it is relatively easy to use in many applications because of its thermoplastic property
  7. Bitumen plays 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 for roads

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 bitumenDiluent
Rapid curingNafthal, gasoline
Medium curingCarosine or diesel oil
Slow curingHigh boiling point gas oil
Type of cutback bitumen and a suitable diluent

Bituminous emulsion

figure shows Bituminous emulsion
Bituminous emulsion

A bitumen emulsion is a liquid product in which a substantial amount of bitumen is 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, a penetration test is conducted. The results are expressed in 1/10 mm. When the penetration value is represented as 80/1000, it is called the grading of bitumen.

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

Grade of bitumenAbsolute viscosityKinematic viscosityPenetration
VG 1080025080- 100
VG 20100030060- 80
VG 30240035050- 70
VG 40320040040- 60
Grade of bitumen and viscosity

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

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

VG- 20- Used in cold areas

VG- 30- Commonly used in India

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.

figure shows bitumen road layers
Road layers

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

figure shows bitumen mix
Bitumen road layers
  • Bituminous concrete consists of aggregate and bitumen.
  • The thickness of the base course depends on the grading of aggregate
  • Dense graded aggregates are provided in the base course. That is the permeability will be very less
  • The 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 reading about the bitumen for the roads was worth it.

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

Happy learning!

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