Tag Archives: properties of bitumen

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.

  1. Bitumen for roads – Bituminous binder types
    1. Bitumen vs Tar – Comparison
    2. Tar manufacturing
  2. Desirable properties of bitumen- an important topic in bitumen for roads
  3. Bitumen for roads – Types of Bituminous materials
    1. Cutback bitumen
    2. Bituminous emulsion
  4. Grade of bitumen for roads – Types and Uses
  5. Bitumen road layers

Bitumen for roads – Bituminous binder types

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.

Petrolium productDistillation of coal or wood
Soluble in carbon disulphide and carbon tetrachlorideSoluble in toluene only
Temperature succeptibility is lowTemperature succeptibility is higher than bitumen
Free carbon content is lessFree carbon content is more
Comparison between tar and bitumen

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

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Tar manufacturing

Bitumen for roads - Construction in progress
Bitumen for roads – Construction in progress

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.

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

Bitumen for roads - Properties
Bitumen for roads – Properties

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

Bituminous emulsion

bitumen emulsion
Bitumen 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 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 grade of bitumen now.

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

VG- 20- Used in cold area

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.

 bitumen road layers
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.

Bitumen road layers
Bitumen road layers
  • 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

Happy learning!

Bitumen tests – 9 lab tests for flexible pavements.

Bitumen is a binding material extensively used in the construction of flexible pavements, damp-proofing of the basement, floors, waterproofing of roofs, corrosion protection of reinforcement structures, etc. The bitumen is viscous black or brown mixture of hydrocarbons obtained as a byproduct on refining crude petroleum.

Bitumen is responsible for imparting quality and durability for flexible pavements and is necessary to confirm its quality before applications. This article is about the various lab tests and procedures performed on bitumen for ensuring the quality.

Must Read : Components of a road pavement structure

Must Read : Classification of roads – 5 road types full details

Properties of bitumen

The properties of bitumen play a major role in determining its quality. They should possess the following desirable properties.

  • A good quality bitumen does not become soft in cold conditions and brittle in hot conditions.
  • Bitumen should possess the required viscosity for enabling perfect mixing and subsequent compaction. Viscosity adjustments are managed by adding emulsions or heating aggregate bitumen mix in a hot mix plant.
  • The binding properties of bitumen should be adequate to provide a good bonding with aggregates.
Bitumen for flexible pavements
Flexible pavements

Tests on bitumen

For ensuring the quality the following tests are performed.

  • Softening point test
  • Flash and fire point test
  • Solubility test
  • Viscosity test
  • Distillation test
  • Water content test
  • Ductility test
  • Penetration test
  • Specific gravity test

Must read : Grade and properties of bitumen

Softening Point Test

Softening point test indicates the point at which bitumen attains a particular degree of softening under standard test conditions. The test helps in determining the consistency of bitumen and done using ring and ball test apparatus.

Ring and ball test apparatus include a brass ring, steel ball, water bath, and thermometer as shown in the figure.

softening point test
softening point test

Test procedure

  • Firstly, heat the sample at a temperature of around 75 to 100-degree wherein the bitumen transforms to a liquid state.
  • The brass ring is heated before placing inside the mercury-coated metal plate. Glycerine is applied over the ring to prevent sticking.
  • Then fill the brass ring with molten bitumen and cool it for 30 minutes. Trim the excess material using a knife.
  • After filling assemble the apparatus and place the balls over the top of the specimen sample.
  • Then fill the apparatus with boiled distilled water. However, the height of filling should be 50mm above the topmost surface of the ring.
  • After that heat the water bath at a rate of 5-degree Celsius per minute.
  • On heating, the bitumen softens and the ball slowly sinks and touches the bottom plate.
  • Finally, note down the temperature at which the specimen touches the lower plate and this temperature is the softening point of the bitumen specimen.

Normally the softening temperature varies from 35 degrees to 70 degree Celsius. 

Flash and fire point test

Flash-point test refers to the temperature at which the specimen becomes volatile and catches fire under test conditions. The apparatus for the flash and fire point test is Pensky – Morten’s closed cup apparatus.

Flash and fire point test
Flash and fire point test


  • Initially , fill the bitumen sample up to the filling mark and close the apparatus.
  • Then, fix the thermometer in a proper position as shown in the figure.
  • Heat the specimen at a rate of 5-degree Celsius per minute.
  • Then, constantly keep stirring the specimen and apply the test flames at regular intervals.
  • The temperature at which the flame produces a light flash inside the cup is the flash point.
  • On further heating, the bitumen specimen inflames and catches fire and this temperature is the fire point.

Solubility Test

The solubility test determines the purity of bitumen. Lot of impurities like carbon, salts, etc gets entrapped in bitumen and hamper the quality . Hence this test is necessary for calculating the impurity percentage.

  • Firstly, dissolve the sample in carbon disulfide.
  • Then filter the solution using a porosity filter.
  • Finally, calculate the percentage of impurity from the residue left.

Penetration test on bitumen

The penetration test measures the hardness or softness of the bitumen. A penetrometer is an apparatus used for computing penetration tests which consist of a needle that weighs 100 gms. Similarly, penetration readings are measured in terms of mm/10.

Penetration test
Penetration test
Penetrometer- equipment for penetration test


  • Firstly, heat the specimen into pouring consistency and immerse the specimen in the water bath. However, make sure the temperature is around 25-degree Celsius.
  • After half an hour, take-out the specimen and place it below the apparatus.
  • Meanwhile, adjust and set the dial to zero reading and allow the needle to fall on the specimen.
  • Immediately, measure the penetration depth.
  • Then repeat this process a minimum of three times and note down the values. The average values

The penetration value ranges from 20 to 225. Low penetration values represent good quality bitumen.

Viscosity test on bitumen

The viscosity of bitumen is the measure of the resistance of the fluid to flow. The unit of viscosity is seconds. Too High or low viscosity impacts the compaction, penetration, lubrication, and coating capacity over aggregates. A viscometer apparatus is for finding the viscosity.


  • Prepare the specimen under standard temperature. 
  • Further, Level the cup with the help of the bubble level.
  • Then heat the water bath at a constant temperature.
  • Next, clean the receiver and pour the specimen up to 20ml.
  • Allow the bitumen to pass through the orifice. Open the valve.
  • Start the stopwatch and note down the time at which it reaches 25ml.
  • Then repeat the test three times and calculate the mean value of viscosity.

Distillation test or loss of heating test

The distillation test determines the quantity and nature of volatile elements in bitumen. Through this test, volatile and non-volatile components are separated.

  • Initially, take 200 grams of bitumen and Note down the weight of the sample.
  • Next, continuously heat the sample at 360-degree Celsius for 15 minutes.
  • After that, carefully distil the sample in a 500ml distillation flask.
  • Measure the residue left. This is the actual quantity of bitumen.

Water content test

In a good quality bitumen, the water content should be minimum. Because excess water content produces foam when heated above the melting point.

  • Initially,the bitumen sample is weighed using a weighing machine.
  • Next step is to immerse the sample in pure petroleum which is free from water.
  • After immersing, immediately start heating the specimen and distill the water.
  • Then condense the distillate and collect the condensed water at the bottom.
  • Record the weight of residue

The water content is the weight of condensed water to the weight of the sample. However, for good quality bitumen water content should not exceed 0.2 percent by weight.

Ductility test

The ductility is the ability to undergo deformation or elongation under load. Ductility is measured as the distance in centimeters to which a standard specimen of bitumen will elongate without breaking. The ductility value ranges from 5 to 100 cm. However, the minimum ductility value should be 73 mm as per BIS.

Ductility test on bitumen
Ductility test
  • Initially, heat the specimen into pouring consistency.
  • Then, allow them to cool for 30 minutes and remove the excess specimen using a knife.
  • After that, take the sample specimen in the form of a standard briquette.
  • Continue to keep the specimen assembly in a water bath for 90 minutes, however maintaining the temperature to 27- degrees Celsius.
  • After hooking the clips in the ductility machine, start applying the load and allow them to stretch.
  • Finally, record the reading on the scale at which the bitumen breaks.

Specific gravity test

Specific gravity is the ratio of the weight/mass of the bitumen specimen with equal mass of water at 27-degree Celsius. Normally the specific gravity of bitumen ranges between 0.97 to 1.02. The apparatus to determine specific gravity is a pycnometer.

The formula for specific gravity is 

Specific gravity = (W3-W1)/[(W3-W1)-(W4-W3)]

Where, W1 – Weight of empty pycnometer

W2 – Weight of pycnometer with distilled water

W3 – Weight of pycnometer with half-filled bitumen

W4 – Weight of pycnometer with half-filled bitumen and distilled water

The test procedure is as follows.

  • Firstly, clean and dry the pycnometer. Make sure it contains no water.
  • Then weigh the empty pycnometer and mark it as W1.
  • Then ,empty the apparatus and again fill it with fresh distilled water.
  • Similarly, weigh the pycnometer and record it as W2.
  • Again empty and fill half of the apparatus with melted bitumen. Avoid the inclusion of air in the sample.
  • Then allow the sample bottle to stand for 30 minutes. Similarly weigh the sample and mark it as W3.
  • Now fill the rest with distilled water. Again, weigh the specimen. This is W4.
  • Finally, determine the specific gravity using the formula.