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Viscosity grades Bitumen is categorized according to Viscosity (degree of Fluidity) grading. The higher the quality, the stiffer the Bitumen. In Viscosity Grade, Viscosity tests are conducted at 60 deg. C and 135 deg. C, which represents the temperature of the road surface during summer and mixing temperature respectively. The penetration at 25 deg. C, which is the annual average pavement temperature, has also been retained in the Specifications.

Characteristic Test Method Value
Absolute Viscosity at 60°C , Poises IS 1206 Min 800
Kinematic Viscosity at 135°C , cSt IS 1206 Min 250
Flash point (Cleveland open Cup,) °C IS 1209 Min 220
Solubility in Trichloroethylene, % IS 1206 Min 99
Softening point. (R&B), °C IS 1205 Min 40
Penetration @ 25°C, 0.1 mm 100gm, 5 sec. IS 1203 80-100
Test on Residue from TFOT/RTFOT    
Viscosity ratio @ 60°C IS 1206 Max 4.0
Ductility @ 25°C (cm) IS 1208 Min 75
Specific Gravity @ 27°C IS 1202 Min 0.99

Characteristic Test Method Value
Absolute Viscosity at 60°C, Poises IS 1206 Min 2400
Kinematic Viscosity at 135°C, cSt IS 1206 Min 350
Flashpoint (Cleveland Open Cup,) °C IS 1448 Min 220
Solubility in Trichloroethylene, % IS 1216 Min 99.0
Softening point. (R&B), °C IS 1205 Min 47
Penetration @ 25°C, 0.1 mm 100gm, 5 sec. IS 1203 50-70
Test on Residue from TFOT/RTFOT    
Viscosity ratio @ 60°C IS 1206 Max 4.0
Ductility @ 25°C (cm) IS 1208 Min 40
Specific Gravity @ 27°C IS 1202 Min 0.99

Characteristic Test Method Value
Absolute Viscosity at 60°C, Poises IS 1206 Min 3200
Kinematic Viscosity at 135°C, cSt IS 1206 Min 400
Flashpoint (Cleveland Open Cup,) °C IS 1209 Min 220
Solubility in Trichloroethylene, % IS 1206 Min 99
Softening point. (R&B), °C IS 1205 Min 50
Penetration @ 25°C, 0.1 mm 100gm, 5 sec. IS 1203 40-60
Test on Residue from TFOT/RTFOT    
Viscosity ratio @ 60°C IS 1206 Max 4.0
Ductility @ 25°C (cm) IS 1208 Min 25
Specific Gravity @ 27°C IS 1202 Min 0.99