Viscosity Grade (VG) Bitumen is classified based on its absolute viscosity at 60°C and kinematic viscosity at 135°C, providing a realistic assessment of bitumen behavior under actual pavement temperatures and traffic loads.
Unlike penetration grading, VG grading is temperature-sensitive, predicts rutting resistance, and ensures consistent quality control. The system is standardized under IS 73 (India) and aligned with ASTM / AASHTO guidelines.
VG Grade Classification Logic
| VG Grade | Viscosity Level | Relative Hardness | Traffic Suitability |
|---|---|---|---|
| VG-10 | Low | Soft | Light to Medium |
| VG-20 | Medium | Medium-Hard | Medium |
| VG-30 | High | Hard | Heavy |
| VG-40 | Very High | Very Hard | Very Heavy / Industrial |
Higher VG number = higher viscosity = higher resistance to rutting and deformation.
VG-10 Bitumen
Performance: Lowest viscosity, high flexibility, excellent workability at low temperatures.
Applications: Cold climates, spray works, surface dressing, low-traffic roads.
Advantages: Reduced thermal cracking, low mixing temperature.
Limitations: Not suitable for heavy traffic or high temperatures.
VG-20 Bitumen
Performance: Balanced viscosity and flexibility for moderate climates.
Applications: Urban roads, semi-dense mixes, medium-traffic highways.
Advantages: Good fatigue resistance, easier handling than VG-30.
Limitations: Limited rut resistance under very heavy axle loads.
VG-30 Bitumen (Industry Standard)
Performance: High viscosity with excellent deformation resistance.
Applications: National highways, DBM, heavy-traffic urban roads.
Advantages: Superior rut resistance, strong aggregate bonding, long pavement life.
Industry Note: Replaced 60/70 penetration grade under IS 73 for hot climates.
VG-40 Bitumen
Performance: Very high viscosity and maximum load-bearing capability.
Applications: Expressways, industrial roads, airports, ports, mining routes.
Advantages: Exceptional stability under extreme loads and temperatures.
Limitations: Higher mixing temperature, reduced flexibility in cold regions.
Typical Mechanical & Rheological Properties (IS 73)
| Property | VG-10 | VG-20 | VG-30 | VG-40 |
|---|---|---|---|---|
| Viscosity @60°C (Poise) | 800–1200 | 1600–2400 | 2400–3600 | 3200–4800 |
| Kinematic Viscosity @135°C (cSt) | ≥250 | ≥300 | ≥350 | ≥400 |
| Penetration @25°C (dmm) | 80–100 | 60–80 | 50–70 | 40–60 |
| Softening Point (°C) | 40–47 | 45–52 | 47–55 | 50–60 |
| Ductility @27°C (cm) | ≥75 | ≥75 | ≥40 | ≥25 |
| Flash Point (°C) | ≥220 | |||
| Solubility in TCE (%) | ≥99 | |||
Climate & Traffic Suitability
| Condition | Recommended VG |
|---|---|
| Cold / Hilly Regions | VG-10 |
| Moderate Climate | VG-20 |
| Hot Climate | VG-30 |
| Extremely Hot + Heavy Traffic | VG-40 |
VG Bitumen vs Penetration Grade
| Aspect | VG Grade | Penetration Grade |
|---|---|---|
| Classification Basis | Viscosity | Needle Penetration |
| Temperature Sensitivity | Accurate | Limited |
| Field Performance Prediction | High | Moderate |
| Quality Control | Better | Less Precise |
| Current Usage | Modern Projects | Traditional |
Storage, Handling & Safety
Storage temperature: 150–180°C
Avoid prolonged overheating to prevent oxidation
Use insulated tanks and prevent moisture contamination
Standards & Compliance
IS 73:2013 (India)
ASTM D4402 – Absolute viscosity
ASTM D2170 – Kinematic viscosity
AASHTO references
Quick Selection Guide
| Project Type | Recommended VG |
|---|---|
| Rural roads | VG-10 / VG-20 |
| City roads | VG-20 / VG-30 |
| National highways | VG-30 |
| Expressways / Ports | VG-40 |