Viscosity testing to determine the strength of the asphalt is done by grading original
(as-supplied) asphalt binder samples (called AC grading) or by grading aged residue samples
(called AR grading). Based on the results of a rolling thin film oven test, the AR viscosity
test evaluates the viscosity of aged residue. A binder is graded according to the properties
it possesses before going through the HMA production process. This grading system was
developed in order to model the asphalt binder behaviour in HMA pavements after the asphalt
binder had undergone a typical HMA manufacturing process.
Advantages and Disadvantages of Viscosity Grades are stated below:
| Unlike penetration depth, viscosity is a fundamental engineering parameter. |
The principal grading (done at 25°C (77°F)) may not accurately reflect
low-temperature asphalt binder rheology.
|
Test temperatures correlate well with:
- 25°C (77°F) – average pavement temperature
- 60°C (140°F) – high pavement temperature
- 135°C (275°F) – HMA mixing temperature
|
When using the AC grading system, thin-film oven test residue viscosities can
vary greatly with the same AC grade. Therefore, although asphalt binders are of
the same AC grade they may behave differently after construction.
|
| Temperature susceptibility (the change in asphalt binder rheology with
temperature) can be somewhat determined because viscosity is measured at three
different temperatures (penetration only is measured at 25°C (77°F)).
|
The testing is more expensive and takes longer than the penetration test. |
| Testing equipment and standards are widely available. |
|
We have two methods of grading:
- Standard Bitumen Viscosity Grade (AC-Grades), in which the Viscosity of the standard
bitumen (asphalt) is measured at 60 ºC (140 ºF).
- RTFOT Bitumen Viscosity Grade (AR-Grades), in which the Viscosity of bitumen (asphalt)
is measured at 60 °C (140 °F) after the roll of thin-film oven test.
| AASHTO M 226 |
AC-2.5 |
AC-5 |
AC-10 |
AC-20 |
AC-30 |
AC-40 |
AR-10 |
AR-20 |
AR-40 |
AR-80 |
AR-160 |
| ASTM D 3381 |
AC-2.5 |
AC-5 |
AC-10 |
AC-20 |
AC-30 |
AC-40 |
AR-1000 |
AR-2000 |
AR-4000 |
AR-8000 |
AR-16000 |
| IS73:2013 |
VG 10 |
800 |
80-100 |
| VG 20 |
1600 |
- |
| VG 30 |
2400 |
60-70 |
| VG 40 |
3200 |
30-40/40-50 |
Viscocity grade over penetration grade, several key issues are addressed like:
- Adopting a viscosity-graded bitumen specification (based on viscosity at 60 °C) in place
of the current penetration-graded specification (based on penetration at 25 °C) will
improve performance at high temperatures.
- With a requirement for minimum viscosity at 135°C, the compaction of tender asphalt
mixtures created by push and shove under the roller wheels have also been addressed.
This will minimize the tender mix problems in the field.
- With the adoption of viscosity-graded paving bitumen specifications, the number of total tests will also decrease to seven without compromising bitumen quality, and there will also be no new tests required for implementing this specification. To know more about this, contact best bitumen suppliers in the UAE.
Viscosity Grade Bitumen Specification (ASTM D3381-09)
| Viscosity, 140°F (60°C) |
P |
1000±200 |
2000±400 |
3000±600 |
4000±800 |
ASTM D-2171 |
| Viscosity, 275°F (135°C), Min |
cSt |
150 |
210 |
250 |
300 |
ASTM D-2171 |
| Penetration, 77°F (25°C), 100g, 5sec, Min |
0.1MM |
70 |
40 |
30 |
20 |
ASTM D-5 |
| Flash point, Cleveland open cup, Min |
°C |
219 |
232 |
232 |
232 |
ASTM D-92 |
| Solubility in trichloroethylene, Min |
%Wt |
99 |
99 |
99 |
99 |
ASTM D-2042 |
| Tests on residue from thin-film oven
test:
|
| Viscosity, 140°F (60°C), Max |
P |
5,000 |
10,000 |
15,000 |
20,000 |
ASTM D-2171 |
| Ductility, 77°F (25°C), 5cm/min, Min |
CM |
50 |
20 |
15 |
10 |
ASTM D-113 |
Viscosity Grade Bitumen Specification (IS 73:2013)
| Penetration at 25°C, 100g, 5sec, Min |
0.1MM |
80 |
60 |
45 |
35 |
IS 1203 |
| Absolute viscosity at 60°C |
P |
800-1200 |
1600-2400 |
2400-3600 |
3200-4800 |
IS 1206 (Part 2) |
| Kinematic viscosity at 135°C, Min |
cSt |
250 |
300 |
350 |
400 |
IS 1206 (Part 3) |
| Flash point (Cleveland open cup), Min |
°C |
220 |
220 |
220 |
220 |
IS 1448 [P : 69] |
| Solubility in trichloroethylene, Min |
%Wt |
99 |
99 |
99 |
99 |
IS 1216 |
| Softening point (R&B), Min |
°C |
40 |
45 |
47 |
50 |
IS 1205 |
| Tests on residue from thin film oven
test:
|
| Viscosity ratio at 60°C, Max |
|
4 |
4 |
4 |
4 |
IS 1206 (Part 2) |
| Ductility at 25°C, Min |
CM |
75 |
50 |
40 |
25 |
IS 1208 |
Uses of Viscosity Grade Asphalt
- Bitumen with high viscosity is widely used in cold climates for surface-dressing,
paving, and a variety of other spraying applications. Also, it is used to make modified
bitumen products and bitumen emulsions.
- A very cold climate prefers the use of VG-10 instead of 80/100 penetration bitumen grade for spraying applications like surface dressing and paving. Also, it is used to produce modified bitumen as well as bitumen emulsion.
- In cold climates and high altitudes, VG-20 is used for paving.
- VG-30 is recommended for constructing extra heavy-duty Bitumen pavements that have to
withstand significant traffic loads. As an alternative to 60/70 penetration bitumen
grade.
- When high-stress areas are present such as intersections, toll booths, and truck
parking lots, VG-40 is used instead of 30/40 penetration grade. Because bitumen mixes
have a higher viscosity, they can be produced in stiffer forms to better withstand
shoving caused by higher temperatures and heavy traffic.
