Tag Archives: bitumen for road construction

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 
120/150
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.

road-layers-of-flexible-pavement
road-layers-of-flexible-pavement

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 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.

BitumenTar
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!