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Bitumen is an adhesive, water-proofing substance that is formed by distilling crude oil. The deposits of bitumen can be found at the bottom of several water bodies and typically in nature. This happened when extinct animals decayed and were exposed to pressure and heat. Most of the bitumen resources are found in places like Venezuela, Oman, Canada, and West of Iran. The substance is used as an additive for road construction, mud drilling, and water-proofing coating.
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Key Terms: Bitumen, Penetration Grade Bitumen, Cutback Bitumen, Viscosity Test
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What is Bitumen?
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Bitumen is a hydrocarbon substance and it consists of oxygen, sulfur, iron, and calcium. It is used in the construction industry. To be precise, at least 85% of global bitumen production is being used in road construction. Other constructions use 10% and the remaining 5% is used by other industries including insulation. The substance can be found naturally or through the crude oil refining process. Bitumen has a blackish-brown color and it exists in liquid to semi-solid phase.
Bitumen
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Types and Applications of Bitumen
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Grading bitumen could be critical as there are different types of bitumen as a result of different crude oils. To grade bitumen on the basis of properties, refineries run some tests to measure the penetration value, viscosity level, performance and consistency.
Penetration Grade Bitumen
It is the most widely used bitumen for the construction of roads. Once the refinery production is done, it is categorized by penetration test with the help of a penetrometer apparatus. The needle should be penetrated deeper into the bitumen surface so that it will be much softer and becomes efficient for colder weather. The most commonly used substance for the construction of roads is penetration bitumen of 60/ 70 grade and grade of 80/ 100. Similarly, 60/ 70 is commonly used water-proofing materials.
Natural Bitumen or Gilsonite
It is a natural bitumen with a solid, smooth, and shiny appearance. Gilsonite types are classified on the basis of their solubility in organic solvents and their ash contents. Gilsonite is mainly used in powder form because of its brittle and hard nature. A combination of refined bitumen and gilsonite are being used for some of the road constructions. Some of the applications of gilsonite are as follows:
- Chemical products
- Printing industries
- Painting industries
- Casting sand additive
- Improving the quality of bitumen
- Drilling mud and cement
- Asphalt and road construction
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Viscosity Grade Bitumen
The classification of viscosity grade bitumen is made on the basis of its viscosity after its production in the refinery. This classification is considered to be newer than the penetration classification. India has the highest consumption of this bitumen. The different grades of viscosity bitumen are VG10, VG20, VG30, and VG40. Viscosity grading is being used instead of using penetration because of the change in viscosity of bitumen during high temperatures. Some of the advantages of using viscosity grading bitumen are as follows:
- The VG system is designed to elevate the accuracy of bitumen in hot temperatures.
- A certain grade of penetration bitumen may show different results at a certain temperature, but viscosity grading behaves the same.
- Viscosity grading is better to predict bitumen behavior in the hottest time and properties in normal conditions.
- Viscosity testing is made on the basis of experimenting with bitumen’s properties at 3 different temperatures like 25° C and 60° C. Every VG bitumen grade comes with an easier application.
Cutback Bitumen
Cutback Bitumen is used in industries that demand low viscosity bitumen. They are also used in cases when bitumen cannot be preheated to make asphalt. In order to make cutback bitumen, penetration bitumen can be used by mixing it with organic solvents in a specific amount. The organic solvents consist of furnace oil, diesel oil, naphtha, and gasoline. It is used usually in cold climates. It is also suitable for sprayed sealing and primer sealing. When the bitumen is used, the solvents tend to evaporate. One drawback of cutback bitumen is that the volatile solvents are hazardous to nature, environment, and humans.
Emulsion Bitumen
The name emulsion bitumen has come from the way it is being produced. It is a chemical combination of water and bitumen. Emulsion bitumen came to the scene due to the threat caused by cutback bitumen. This is essential for spraying, water-proofing, and tack coats between the layers of asphalt pavement. Bitumen emulsions are classified based on its breaking or setting time and particles' electrostatic charge.
Bitumen emulsions can be cationic with a positive charge and anionic with a negative charge. Different grades of bitumen emulsions possess different properties, hence each type is used for a specific type of application. They are less viscous than other grades of bitumen. This is because they are mixed with emulsifiers and water, hence this is being used for spraying applications. Other major applications of bitumen emulsions are slurry seals, chip seals, tack coats, and micro surfacing.
Oxidized Bitumen
It is being obtained in the refinery with the help of hot air blowing into the penetration bitumen. The substance formed from this process has high durability and is chemically stable. It is also suitable for insulation and impermeable to water. Oxidized bitumen has a higher softening point and a lower degree of penetration. Water-proofing of buildings, and dam construction is made using oxidized bitumen. It is also being used to cover pipelines to prevent corrosion.
Performance Grade Bitumen
This is a type of bitumen grading system because of its performance at different levels of temperatures. Performance grade bitumen is mainly used in sealing cracks in both and open grade Hot Mix Asphalt, sealing edges, construction and re-construction pavement.
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Bitumen Tests
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Bitumen Tests allow classification and quality of bitumen in the industrial sectors.
- Penetration test: Used to measure the softness and hardness of bitumen. The degree of penetration is related to the ductility of the substance. It also shows that asphalt has higher loading capability. This test is performed by penetrating a needle to the bitumen surface with a load of 100g for 5 seconds. The unit of measurement is 0.1 mm.
- Viscosity test: It is being used to evaluate the adhesion of bitumen to asphalt aggregates. The time needed to remove a specific amount of bitumen from the viscometer is measured and multiplied by the correction factor of the device.
- Some of the other known bitumen tests are softening point test, ductility test, specific gravity test, flash and fire point test, loss on heating test, etc.
Things to Remember
- Bitumen is the substance formed by distilling crude oil.
- The substance is known for its adhesive and water-proofing properties.
- Distillation of bitumen removes lighter crude oil substances including diesel and gasoline leaving only the heavier bitumen.
- Bitumen can be found in nature especially in the bottom of lakes and similar water bodies as deposits of the decayed animals. It happens due to the exposure of deposits to pressure and heat.
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Sample Questions
Ques. Give a brief definition of what bitumen is. (2 marks)
Ans: It is a viscous, dense substance which is drained from earth in an oil reservoir. It is a low grade crude oil made up of heavy, complex hydrocarbons. In the United States, bitumen is also known as asphalts.
Ques. List down the properties of bitumen. (2 marks)
Ans. The properties of bitumen are as follows:
- It is normally solid, but when heated it becomes liquid
- It is blackish-brown in color
- It is vulnerable to oxidation and makes cracks and blisters
- It is not water-soluble and has a high acid tolerance
- The substance becomes fuzzy at 30° C to 100° C
- The main components of bitumen are carbon (87%), hydrogen (11%), and oxygen (2%)
Ques: Describe the applications of bitumen? (2 marks)
Ans: They are commonly used in bituminous membrane products and asphalt road construction. It is also widely used in the construction of rail networks and highways. The substance has good water-proofing properties, hence it is commonly being used in the manufacturing of roofing materials.
Ques. What are some of the tests for bitumen? (1 mark)
Ans. There’re various tests to name, among which, ductility test, penetration test, viscosity test, softening point test, specific gravity test, flash and fire point test, water content test, are some of the few.
Ques. Why is bitumen emulsion used? (2 marks)
Ans. It is a liquefied type of bitumen with lesser viscosity. By adding an emulsifier and dispersing bitumen in water, the ordinary bitumen transforms into a low viscosity liquid which can be used in different applications, including spraying, water-proofing, repairing and maintaining roads, etc.
Ques. Explain specific gravity of bitumen? (2 marks)
Ans. It is the ratio of the mass of a particular volume of a material to the equal volume of water. The specific gravity of pure bitumen spans from 0.97 to 1.02.
Ques. Give the three types of bitumen? (2 marks)
Ans. The 3 varieties of bitumen emulsion are slow setting (SS), medium setting (MS), and rapid setting (RS) depending on the stability offered by the emulsifying agent. It is applied at ambient temperature, merely mixing with aggregate for road works.
Ques. Explain blown bitumen? (2 marks)
Ans. Oxidized bitumen or blown bitumen grades are made by passing air through the penetration grades. This procedure provides the bitumen with more rubbery properties than its original formula.
Ques. How is the bitumen grade calculated? (2 marks)
Ans. The penetration is measured in mm and that indicates the relative hardness of the bitumen substance. The more the penetration, the softer the bitumen. A penetration of 0.60 to 0.7mm states 60/70 penetration grade bitumen.
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