Tag Archives: bituminous roads

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!

5 Types of road construction Complete Guide

Types of road construction are significant to understand the category of roads and their characteristics. In this blog, we will find out the details of 5 types in detail.

5 Types of road construction

In this section, the important types of road construction is broken down in detail.

Whitetopping roads

  • Whitetopping is the coating of a layer of Portland cement concrete on the existing asphalt pavement.
  • Depending on the thickness of the concrete sheet and if the layer is bonded to the asphalt substrate, whitetopping is divided into different types.
  • The main objective of an overlay is either to restore the existing pavement or to improve the load-carrying capacity, or both.
  • In achieving this goal, in addition to rectifying other defects such as loss of texture, overlays often restore the ride-ability of existing pavements that have experienced rutting and deformation.
  • Asphalt is considered to be much less robust and powerful than most other alternatives and is therefore not the best for the setting.

Polymer fiber reinforced concrete roads

Polymer Fiber Reinforced Concrete roads
Polymer Fiber Reinforced Concrete roads
  • Polymeric fibres are now used because they are cost-effective and have no chance of corrosion.
  • Polymeric fibres are either polyester or polypropylene that are normally used.
  • FRC material technology, including highways, local streets, intersections, parking lots, bus pads, sidewalks, driveways, bridge decks, pavement overlays, manufacturing floors, airfield pavement overlays, and patches, is used for a large number of pavement applications.
  • FRC may be used for new construction as well as for maintenance (patching), rehabilitation (overlays), and reconstruction.
  • The use of FRC for bonded concrete overlays on asphalt or composite pavements has seen substantial growth in the past few years for minor pavement rehabilitation.
  • The thickness of an asphalt bonded concrete overlay (BCOA) varies from 3 to 6 in., and the thinner installations were the majority of FRC overlays of this kind.

Bituminous roads

Bituminous roads
Bituminous roads
  • Bituminous surface treatment (BST) or chip seal is primarily used as a sealing coat to rejuvenate asphalt concrete pavement, but also on low-traffic highways.
  • It typically consists of aggregate spread over an asphalt emulsion sprayed-on or asphalt cement cut-back.
  • By rolling it, usually with a rubber-tired roller, the aggregate is then deposited in the asphalt.
  • “A broad range of regional words, like “chip seal,” “tar and chip,” “oil and stone,” “seal coat,” “sprayed seal,” or “surface dressing,” or simply “bitumen,” define this form of surface.
  • These are laid down using specialised and proprietary equipment.
  • In urban areas where the roughness and lack of stone associated with chip seals are deemed inappropriate.

Composite pavement road

concrete road
Concrete road
  •  In composite pavements, portland cement concrete sublayer is mixed with asphalt.  
  • Usually, they are used to rehabilitate existing roadways. To restore a smooth wearing surface, asphalt overlays are sometimes laid over distressed concrete.
  • For reflective crack management, geosynthetics can be used.
  • A heavyweight is dropped on the concrete with breakage and seat and crack and seat processes to cause cracking, then a heavy roller is used to seat the resulting parts into the subbase.
  • The machinery used to crack the concrete pavement and the scale of the resulting fragments is the key difference between the two methods.
  • The hypothesis is that regular small cracks disperse thermal stress over a wider area than uncommon large joints, minimising the strain on the asphalt pavement overlying it.
  • Rubblization is a more complete fracturing of the old, worn-out concrete that essentially turns the old pavement into a new asphalt road aggregate base.

Gravel road

  • Two distinct uses of road surfacing have been used to add gravel, or “metalling.”
  • Second, the highway path would have been dug down several feet and French drains may or may not have been installed, depending on local conditions.
  • Large stones were then positioned and compacted, accompanied by successive layers of smaller stones until the road surface consisted of small stones that had been compacted into a rough, durable surface.
  • “Road metal” later became the name of stone chippings combined with tar to form the tarmac material for the road surface.
  • The decision on whether or not to pave a gravel road also depends on the amount of traffic.
  • Maintenance costs for gravel roads have been found to sometimes exceed maintenance costs for paved or surface-treated roads if the traffic level reaches 200 vehicles a day.

I hope you found the article insightful. Let me know in comments if you have any doubts.

Happy learning!

Classification of roads- 6 types of roads

Classification of roads or Types of road is an important topic in transportation engineering. It varies with different parameters. Let’s go through the important types of roads every civil engineer should know. We will see important details about cement concrete roads and types of road surface through the course of journey.

    Classification of roads or Road types

    There are 6 basic types of roads depending on a mouthful of factors.

    • Types of roads based on type of road surface
    • Types of roads based on location and function
    • Types of roads based on number of lanes
    • Types of roads based on weather
    • Types of roads based on the type of road pavement  
    • Types of roads based on volume of traffic they handle  

    We are going to sneak peep into types of roads in detail.

    Classification based on type of road surface

    This category in the types of roads is based on the type of road surface used in the construction. These can be divided into 7 types.

    Classification or road types

    Now, let’s go deep into each of this.

    Natural earth roads – Main road types

    The figure shows natural earth roads

    These are the cheapest type of road and is used at the places where traffic is rare. The type of road surface used in these roads is soil. The pavement structure is totally made up of soil available at site. The performance of these roads mainly depend upon the effective maintenance and proper drainage.

    Gravel roads

    These are intermediate between earthen and metalled roads. The carriage way of these roads is made by compacting a mixture of gravel and earth. These type of road surface usually consists of 26 percent sand, 13 percent clay and 61 percent gravel.

    Kankar roads

    The type of road surface used in this classification of roads is Kankar. Kankar is impure form of limestone. Hard variety of kankar may be as strong as stones, but soft variety may be very weak. The road having pavement layer of kankar are termed as kankar roads. Traffic capacity of this type of road depends on the type of kankar used.

    Moorum roads

    In this type of roads, Moorum is the material used for building the road. Moorum is obtained due to disintegration of igneous rocks by weathering agencies. In this road, the surfacing of the traffic way is constructed from Moorum. These type of roads are low and is equivalent to gravel and Kankar road in performance.

    Water bound macadam roads (WBM roads)

    The broken stones of base and surface course, if any are bound by the stone dust in presence of moisture is called WBM rods. Total thickness may vary from 7.5 to 30cm depending upon the traffic.

    Bituminous roads

    Most of the roads around the world are constructed by using bitumen. It is also called flexible pavement because it changes according to nature of loads and sub base. This is an important member in the types of roads in India. For the road construction, the major concerns, as with concrete, are cost and durability.

    Applications of bituminous roads
    • Highways
    • Express ways
    • Runways

    Now, let’s meet cement concrete roads.

    Cement concrete roads types – Most durable classification of road

    Cement concrete roads are the roads whose wearing surface is constructed with cement concrete. They are otherwise called concrete roads. They can be constructed either reinforced or plane type. Cement concrete roads are compatible to all weather conditions. It comes under rigid pavements. These are best suitable to roads having higher traffic.

    Main applications of cement concrete roads
    • Parking aprons, taxiways and runway take off areas in airports
    • Parking grounds for vehicles of heavy weight
    • Heavy duty Industrial floors (vehicles on tracks and military tanks)
    • Floors for handling and storage of containers at ports
    • Industrial floors with high requirements in terms of flatness and durability to abrasion and surface exposure to aggressive attacks (use of toxic materials, welding etc)
    • Bridge decks
    • Road pavements in long tunnels for fire safety reasons, immediate reuse of the road following a fire and better energy consumption during service life (lower intensity lighting required)
    • Pavements at toll stations (resistance to braking and acceleration)

    Now, let’s move on to the next classification of roads.

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    Classification of roads according to location and function

    The figure shows roads in high altitude areas

    Roads can be classified according to the location and function as follows.

    • National highways
    • Highways
    • District roads
    • Village roads

    Going deep to each of them,

    National highways- top member in classification of roads according to location

    Main highway runs through the length and breadth of the country. Roads connecting the neighbouring country. are also called national highways. Roads connecting the neighbouring countries are also called national highways. It should have high class surface finishing together with adequate structural strength.


    These are the main roads within a state. These connect important towns and cities of the state. Highways should be two lane wide, but if it is one lane only, it must be provided with wide shoulder.

    District roads

    These roads should carry the traffic to the interior rural areas. These roads are considered as main branches from NH or SHs. District roads are of 2 types. Major district roads and other district roads.

    Village roads

    These roads are mainly meant for village roads use. These connect villages with each other and also with nearby towns. These roads can be stabilised each roads, but if metal surface is provided it can serve more useful purpose.

    Moving on to the third classification…

    Classification of roads based on number of lanes

    You might have observed this type of classification while you travelled. There are mainly 4 types as given below.

    • Single lane road- having only one lane for to and for mobility.
    • Double lane road- having two lanes for direction to opposite sides
    • Three lane road- having three lanes for movement in a road
    • Multi lane road- having more than three lanes for vehicle movement.

    The decision on which of the above lanes is to be chosen is based on the traffic.

    The next classification of roads is based on the geographic location of the roads.

    Types of roads depending on weather

    Classification of road based on weather

    These are of 2 types.

    1. All weather roads- Roads which are compatible to all weather conditions. Types of roads in India should mostly belong to this type. Because the weather conditions are extreme.

    2. Fair weather roads- Roads which are not compatible to worse weather conditions.

    Next is an interesting classification based on the geometry of roads.

    Types of roads based on Road pavement type

    • Parallel roads- These are local roads running parallel to a higher-speed, limited-access road
    • Unparallel roads- These are local roads that don’t run parallel to a higher speed and limited access road. The village roads that connect small geographical places best fit for this classification other than other types of roads in India.

    Cool. Let’s jump into the last classification of a road.

    Types of roads according to the volume of traffic they handle

    Roads can be classified depending on the traffic through it.

    • Light traffic road- Road carrying up to 400 veh/ day
    • Medium traffic road- 400- 1000 veh/day
    • Heavy traffic road- More than 1000 veh/day

    That’s it. Any doubts or comments? Drop it in the comments. Let’s dwell on more.

    MUST READ: Traffic signals in India- All types simplified