Category Archives: Bitumen

Bitumen types for road Layers – Bitumen Emulsion types

Bitumen types for road layers are a vital topic to comprehend when it comes to road construction. Bitumen is preferred for flexible pavements in road construction because it has many advantages over other pavement construction materials. This article will demonstrate the importance of bitumen in road construction and the types of bitumen for road construction. Furthermore, bitumen emulsion types for road layers, different bituminous materials, cutback bitumen, bitumen grade, and bitumen attributes will be highlighted in this article.

  1. Bitumen types for Road layers /Flexible pavements 
    1. Tack Coat – Bitumen types for road layers
    2. Binder Course – Bitumen types for road layers
    3. Prime Coat – Bitumen types for road layers
    4. Base Course
    5. Sub Base Course
    6. Sub Grade
  2. Protective Asphalt
    1. Seal coat
    2. Slurry Seal
    3. Chip Seal
    4. Micro Surfacing
    5. Fog Seal

Bitumen types for Road layers /Flexible pavements 

The   flexible  pavement  structure   consists  of  the  following  layers: 

  • Tack   Coat  
  • Binder   Course 
  • Prime  Coat  
  • Base   Course  
  • Subbase Course
  • Subgrade Course
Bitumen types for road layers

Keep in mind that the primary component of the road is not protective asphalt. Protective asphalt is deployed to safeguard the road’s surface. Every layer mentioned above uses a different type of bitumen. We will illustrate what types of bitumen are used in each of these layers.

Tack Coat – Bitumen types for road layers

The application of coatings is a critical phase in the construction of asphalt roadways. Generally, a tack coat is a thin layer of asphalt emulsion or liquid bitumen used in between layers of hot mix asphalt to prevent slippage. Mostly, MC30 cutback bitumen, CRS-1, and CRS-2 emulsion bitumen are utilised in a tack coat layer of bitumen. The lower layer is sealed by the presence of a tack coat, which also increases the strength of both asphalt layers.

Bitumen types for road Layers

MC-30 is a medium-curing cutback bitumen that is ideal for cold climates. Basically, asphalt emulsions are the most often used tack coat materials. However, the most widely used slow-setting emulsions are SS-1, SS-1h, CSS-1, and CSS-1h (1). The usage of rapid-setting asphalt emulsions like RS-1, RS-2, CRS-1, and CRS-2 for tack coats is also on the rise.

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Binder Course – Bitumen types for road layers

The base course and the surface course are separated by the binder course. Generally, a binder course is used to keep the road surface from moving. Because the binder course is made out of coarse aggregates, less bitumen is utilised in the manufacture of this asphalt. In the hot asphalt of the binder course, various grades of pure bitumen can be utilised. The various grades of pure bitumen used in binder courses are listed in the table below.

Penetration Grade Viscosity Grade
30/40VG 10
40/50VG 20
60/70VG 30
80/100VG 40 
Bitumen types for road layers

Prime Coat – Bitumen types for road layers

A prime coat is a coating that is applied directly to the base layer. The primary objective of utilising the prime coat is to improve the bond between the base layer and the asphalt mix layer. It also fills in the voids. A priming coat might aid in sealing the base layer. The bitumen in prime coatings is either CSS or CMS.

Prime coats aid in reducing dust while protecting the granular base’s integrity throughout construction. In the event of a foundation that will be covered with a thin hot mix layer or a chip seal for a low-volume roadway, priming enables a good bond between the seal and the underlying surface, which might otherwise delaminate.

A primary coat is primarily responsible for safeguarding the substrate of a construction project before applying additional layers. They can also function as a binder with secondary and tertiary compounds in the preparation of asphalt, improving the adherence of the layers. Following the prime coat, a tack coat is applied to provide an adhesive bond between the tack coat and the subsequent layer of coating. For asphalt prime coat systems, the tack coat is one of the most vital parts of the process, as it connects the subsequent layers and forms the base of those layers’ strength.

Base Course

The base course is placed directly on top of the subbase course. This layer has a higher permeability than the sub-base layer because it is composed primarily of coarse aggregates. Basically, the base course, which is the first layer in direct contact with traffic, moves the weights from the upper layers to the sub-base course. Different base courses used in pavement include sand or stone base, macadam base, and bitumen base.


Sub Base Course

The first layer of flexible pavement constructed on the ground is the sub-base course. This layer is typically composed of river sand, an alluvial cone, and broken rock. Bitumen and cement can be used to stabilise the sub-base soil.

Sub Grade

It is the surface upon which further pavement layers such as the sub-base course, base course, and asphalt layers are placed. The subgrade absorbs any load tension or weight that is transferred from the top levels. A good subgrade should be able to support weights for a considerable amount of time without deforming.

Protective Asphalt

Generally, Protective asphalts are used to seal the road surface and improve the asphalt temporarily. However, It should be noted that asphalt sealing can cause the asphalt to become more slippery. Pure bitumen with low humidity and soluble bitumen are both utilised in protective asphalt. Because of its quickness and ease of installation, protective asphalt is more cost-effective than hot asphalt. There are various varieties of protective asphalts, some of which are listed below:

  • Seal coat
  • Slurry seal
  • Chip seal
  • Micro-surfacing
  • Fog seal

Seal coat

A seal coat is used to provide a long-lasting surface texture and to keep the surface waterproof. However, this kind of protective asphalt can be made using a variety of emulsion bitumen types, including CSS-1, SS-1h, SS-l, and CSS-1h.

Bitumen types for road layers

Slurry Seal

Generally, a slurry seal is used to lessen the harm done by bitumen oxidation. In the slurry seal, emulsion bitumens SS-1, SS-h1, CSS-1h, and CQS-1h are used. A slurry seal is appropriate for pavements with little to moderate damage, such as narrow cracks. However, it is not appropriate for severe damage such as holes.

Chip Seal

A chip seal is a thin protective surface that is applied to a pavement or subgrade. Water cannot easily seep through the base layer due to the chip seal. This layer also prevents freezing in areas where the temperature is below zero. Adding this layer improves the road’s reflectiveness for nighttime driving. A rapid-setting emulsion containing a CRS-2, RS-2, HFRS-2, and PMB is the best type of bitumen for chip sealing.

Micro Surfacing

Micro-surfacing aids in the sealing of cracks and the protection of existing bituminous layers against surface voids and minor ruts. Among the benefits of adopting this layer are environmental compatibility, cost-effectiveness, and fast construction time. PMB bitumens such as PMCQS-1h, PMQS-1h, and CQS-1P are suited for it.

Fog Seal

A fog seal is intended to neutralise the oxidation process that occurs over time. This layer protects the pavement surface by leaving a hard layer. This layer employs emulsion bitumen such as SS-1, SS-1h, CSS-1, or CSS-1h.

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.