Bitumen in Flexible Pavement

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Road pavement is one of the most important operations in road construction. Altogether there exist two types of pavements: Flexible Pavement and Rigid Pavement. 

In flexible pavement, we have different types of layers and sublayers. 

The main layers are Surface Course, Base Course, and Sub base Course. The Sub layers are tack coat, prime coat, and binder course.

In this post, we read more about flexible pavement and the different grades of bitumen that can be used in these layers.

Main Layers

Surface Course

The Surface layer is a high-quality and relatively high-strength layer.  It is the top layer of the flexible pavement.

This layer is in direct contact with the wheels of vehicles. It is made of different grades of bitumen. Both hot asphalt and cold asphalt can be applied to the surface layer. Hot asphalt should be prepared in the factory and cold asphalt can be obtained in the project place.

The required grades of bitumen in hot asphalts are penetration grades and viscosity grades. Oxidized bitumen can also be used as an additive in asphalt to improve the hot asphalt quality.

For cold asphalt, different grades of liquid bitumen like cutback and emulsion can be used.

Base Course 

Base Course is the second important layer in flexible pavement. It consists of different materials including macadam, riverbed rocks, and mountain gravels.

It tolerates the stress from the above layers and distributes them to the below layers. This layer’s permeability is more than the Sub-base layer.

Sometimes, this layer also can consist of bitumen but it is not usual in road construction.

Sub Base Course

Sub-base course is a layer below the Base Course. It can distribute the entering stress from the base course to the sub-grade layer. It consists of crushed aggregates. It is necessary to mention that the Bitumen cannot be used in this layer.

Sub layers

The Flexible pavement has three sublayers. These sub-layers are as below:

  • Tack Coat
  • Binder Course 
  • Prime Coat

Tack Coat

When there exist 2 asphalt layers, we apply a tack coat. Tack coats can bond these asphalt layers to each other.

It is a thin layer of liquid bitumen. Different grades of Cut back and Bitumen Emulsion can be used in tack coats.

It is better to use bitumen emulsion instead of cutting back bitumen. Because bitumen emulsion consists of bitumen, anionic or cationic emulsifier, and water. While the cut back bitumen is a combination of bitumen and a petroleum solvent. 

Altogether, bitumen emulsion components are more compatible with the environment, as a matter of fact, bitumen emulsion is eco-friendly and more cost-effective than cut-back bitumen. Because petroleum solvent is expensive and it degrades the environment.

Binder Course 

As we mentioned above, we have different main layers like the surface course and base course. Between these two layers, there exists a binder course. 

This layer prevents shifting and moving the surface course and stabilizes it. Hot asphalt of this layer consists of bitumen and coarse aggregates.

Different grades of Viscosity bitumen and Penetration bitumen can be used in the binder course.

Prime Coat

The prime coat can be applied on the sandy surface of the base course. 24 hours before pouring the asphalt of the binder course, it is necessary to apply a prime coat.

 The minimum air temperature for the application of a prime coat must be more than 10 degrees Celsius, and it is not allowed to apply it in foggy, humid, or rainy weather.

Same as a tack coat, bitumen emulsion, and cut-back bitumen can be used in this layer but generally using the appropriate bitumen depends on the air temperature.

For example in cold weather, it is better to use cut-back bitumen RC-70. In warm weather, it is good to use MC-70 and SC-70 is a suitable type of cut back in hot weather.

Protective Asphalts 

Besides these layers and the bitumen that are used in them, there are different protective asphalts that can maintain the road surface and protect it from damage and cracks.

In all of these protective asphalts, several grades of liquid bitumen including cationic and anionic bitumen emulsion, slow, medium, and rapid curing cut-back bitumen can be used. These protective asphalts are as below:

  • Seal Coat
  • Slurry Seal
  • Chip Seal
  • Fog Seal 
  • Micro Surfacing

Infinity Galaxy has prepared an info-graphic related to the different types of bitumen that can be used in the flexible pavement. 

Bitumen in Flexible Pavement

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