Tag Archives: subbase course

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.

Road Pavement Layers – Components and Functions

Road pavement structure: Road is the most important structure that decides the economic growth of a country. The road structure is to be constructed based on the traffic requirements, climatic conditions of the area, terrain, etc. The road structure has to withstand abrasion loads and climatic and terrain conditions without failure. This article is about the components of a flexible pavement structure.

  1. Road pavement structure
    1. Road pavement – Subgrade
      1. Function of subgrade
    2. Sub base course
      1. Functions of subbase coarse
    3. Base course
      1. The function of base course
    4. Surface course or wearing course
      1. Function of Surface or Wearing Course

Road pavement structure

The road pavement structure layers are as follows.

  • Subgrade or road bed
  • Sub base course
  • Base Course
  • Surface coarse or wearing course

Also read: Components of Road pavement structure – Parts of a road and functions

Also read: 4 Types of Pavement |Flexible and Rigid Pavement Full Details

Also Watch : The flexible pavement vs Rigid Pavement Youtube video

Road pavement – Subgrade

The subgrade is the compacted natural soil below the pavement layers and it is the finished or compacted surface on which the pavement rests. They are also known as the formation and serve as the foundation of pavement layers.
Depending on the nature of the terrain the sub-grade can be an embankment or a cutting or it will be in line with the natural ground level. The load-bearing strength of the sub-grade structure is determined by the California bearing ratio test (CBR).
The material used for subgrade shall be locally available, strong, and cheap.


Function of subgrade

Serves as the foundation and acts as a uniform support to pavements.

Sub grades bear the  entire load of the payments along with the service load of traffic.

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Sub base course

The sub-base course comes between the base coarse and sub-grade. The material used for this layer shall satisfy the specifications in terms of gradation, strength, and plastic characteristics.
This layer is necessary if the sub grade is of poor quality. In that case, an additional layer of burnt clinkers, gravel, slag, etc is provided to strengthen the sub grade.

Functions of subbase coarse

  • The sub-base layer enhances the bearing capacity of the subgrade and improves the load distribution capacity of the base course and wearing course.
  • The sub-base course prevents the entry of finely graded sub-grade soil to the base course layer.
  • They prevent the capillary rise of water and enable free drainage of water entering the pavement. The sub-base material must be free draining for this application with suitable systems must be included in the pavement design for collecting and removing any accumulated water from the sub-base.
  • This layer provides insulation to sub-grades against frost
  • The sub-base course is used for raising the heights of pavements to be in line with the natural water table.
  • The Sub-base course provides a perfect hard stratum for remaining construction activities.

Base course

The base course is a layer or layers of specified or select material of designed thickness placed on a subbase or subgrade (if a subbase is not used) to provide a uniform and stable support for binder and surface courses.
The base course is the most important layer of a road structure which transfers the stresses developed due to traffic impacts through the wearing course. The base course layer provides the required foundation stiffness and structural strength.
Good quality crushed aggregates in line with technical specifications have to be used. If the crushed aggregate does no meet the required criteria it can be stabilised with Portland cement, lime, or asphalt. In the case of high-quality pavements, the crushed aggregates are treated with asphalt or Portland cement.


The function of base course

  • To act as the foundation of the road pavement and to transfer the traffic load safely to the sub-base and subgrade.
  • To withstand high shearing stresses due to the impact of traffic.
  • To prevent the undesirable entry of subgrade soil in the pavement when the base course is constructed directly over the subgrade.

Surface course or wearing course

The surface course is multiple layers of pavement structure where the top layer is directly exposed to traffic. The surface course is also called the wearing course. For flexible pavements, the bituminous surface is the wearing course whereas in rigid pavement the concrete surface act as the base course cum wearing course. The wearing course reduces the percolation of water and provides an anti-skid and abrasion-resistant riding surface.


Function of Surface or Wearing Course

The Function of surface or wearing course are as follows:

  • To provide a smooth and uniform rigid surface.
  • To resist the abrasive forces of traffic.
  • To prevent dust nuisance.
  • To act as a structural part of the pavement.