A technical overview about what-is-bitumen-grade-types-properties for highway engineers & lab technicians.
Bitumen is a viscous, black, sticky hydrocarbon binder refined from crude oil (or naturally occurring). It is widely used as the binder in asphalt mixes, waterproofing, and roofing. This article explains grading systems, common types, and key laboratory properties used in QA/QC of roads.
Definition — What is Bitumen?
Bitumen, also known as asphalt cement in some regions, is a highly viscous, black or dark brown hydrocarbon product obtained from petroleum refining (residuum) or natural sources. It acts as a binder in asphalt concrete and provides waterproofing and adhesive properties.
Grades of Paving Bitumen (IS 73:2013)
Bitumen is classified based on viscosity for performance under expected traffic and climatic conditions.
Key Concept: Higher VG number = stiffer bitumen → better rutting resistance in hot climates or heavy traffic.
Viscosity Grades (VG) — IS 73:2013
Grade
Absolute Viscosity at 60°C (Poise)
Penetration at 25°C (min, 0.1 mm)
Suitable Max 7-Day Air Temp
VG-10
800–1200
80
<30°C (Cold)
VG-20
1600–2400
60
30–38°C (Moderate)
VG-30
2400–3600
45
38–45°C (Hot/Heavy Traffic)
VG-40
3200–4800
35
>45°C (Very Hot)
Major Types of Bitumen
Paving Grade Bitumen: Standard refined binder for hot mix asphalt.
Cutback Bitumen: Bitumen mixed with volatile solvent for low-temp application (RC, MC, SC).
Bitumen Emulsion: Bitumen dispersed in water for ambient temperature application.
Polymer-Modified Bitumen (PMB): Blended with polymers for improved elasticity, rutting & fatigue resistance.
Oxidized / Blown Bitumen: Air-blown for higher softening point; used in roofing and damp-proof membranes.
Essential Properties and Tests
Absolute Viscosity (60°C): Resistance to flow; controls rutting.
Kinematic Viscosity (135°C): Workability during mixing and coating aggregates.
Penetration (25°C): Hardness; lower = stiffer.
Softening Point: Resistance to high-temp deformation.
Flash Point: Safety during heating (min 220°C for VG grades).
Ductility: Stretch before breaking; indicates flexibility.
Solubility: Purity check; min 99% ensures effective binder.
How to Select the Right Grade
Match binder grade to climate (softer for cold, stiffer for hot/heavy traffic).
Consider PMB or PG grades for heavy traffic or extreme temperatures.
Ensure compatibility with plant/mixing temperatures.
Follow MoRTH/IRC/project specifications.
Frequently Asked Questions
Difference between Penetration and Viscosity grades?
Penetration grade = consistency at 25°C; Viscosity grade = flow resistance at 60°C/135°C.
