What Is Bitumen?
Bitumen (also called asphalt binder in North America) is a thick, black, sticky substance derived from the fractional distillation of crude oil. It is the primary binder used in road pavement construction, waterproofing, and roofing applications.
Bitumen at room temperature is a semi-solid viscoelastic material. When heated, it becomes fluid and can be mixed with aggregate to form Hot Mix Asphalt (HMA) — the most common road surfacing material worldwide.
How Is Bitumen Produced?
Bitumen is a by-product of petroleum refining. It is produced by:
- 1Atmospheric Distillation: Crude oil is heated to around 350°C. Lighter fractions (petrol, diesel, kerosene) evaporate first.
- 2Vacuum Distillation: The remaining heavy residue is further distilled under vacuum to extract more lighter oils, leaving behind bitumen.
- 3Oxidation (Air-blowing): For some grades, air is blown through the residue at high temperatures, making the bitumen harder and more temperature-resistant.
Key Properties of Bitumen
| Property | Typical Value |
|---|---|
| Density | 1,000–1,050 kg/m³ |
| Softening Point | 45–60°C (Penetration Grade) |
| Penetration (25°C) | 25–300 dmm |
| Ductility | ≥ 75 cm at 25°C |
| Flash Point | ≥ 220°C |
Types and Grades of Bitumen
Penetration Grade Bitumen
The most widely used type. Graded by how far a standard needle penetrates the bitumen under specific conditions (units: 0.1mm = 1 dmm).
- 30/40 – Very hard, used in hot climates
- 60/70 – Most common grade globally
- 80/100 – Softer, used in cold climates
- 120/150 – Very soft, specialized use
Viscosity Grade (VG) Bitumen
Classified by viscosity at 60°C. Used in India and some Asian countries.
- VG-10 (≈ 80/100 pen)
- VG-20 (≈ 60/70 pen)
- VG-30 (≈ 50/60 pen) — most common
- VG-40 (≈ 35/50 pen)
Performance Grade (PG) Bitumen
Used in North America (Superpave system). Graded by performance temperature range.
- Example: PG 64-22 performs well at high pavement temperature of 64°C and low temperature of -22°C.
Modified Bitumen
Standard bitumen modified with polymers to improve performance:
- Polymer Modified Bitumen (PMB) – SBS, SBR, EVA polymers added for better elasticity and temperature resistance
- Crumb Rubber Modified Bitumen (CRMB) – Recycled tyre rubber improves noise reduction and fatigue resistance
Bitumen vs. Tar
Bitumen is not the same as tar. Coal tar (a by-product of coal processing) was historically used in roads but is now largely phased out due to health concerns (carcinogenic PAHs). Modern road surfaces use petroleum-derived bitumen.
Applications of Bitumen
- Road pavement (the largest use): wearing course, binder course, base course
- Waterproofing: roofing felt, bridge decks, tunnels
- Hydraulic structures: canal lining, dam facings
- Industrial coatings: pipe protection, anti-corrosion
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