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Viscosity Grade Bitumen

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Viscosity Grade Bitumen (Asphalt) is a standard grade Bitumen usually used as a Paving Grade Bitumen suitable for road construction and for the production of asphalt pavements with superior properties. This grade of Bitumen is mainly used in the manufacture of hot mix asphalt for bases and wearing courses, and possesses characteristics and qualities unique sand quite different from other agents. They achieve very flexible and tenacious connections with other materials due mainly to viscoelastic response of bitumen, which behaviour depends on how fast charges are applied.
The main market for using mention Grade are India and far east countries

bitumen viscosity Grades

Viscosity grading can be done on original (as-supplied) asphalt binder samples (called AC grading) or aged residue samples (called AR grading). The AR viscosity test is based on the viscosity of aged residue from the rolling thin film oven test. With AC grading, the asphalt binder is characterized by the properties it possesses before it undergoes the HMA manufacturing process. The AR grading system is an attempt to simulate asphalt binder properties after it undergoes a typical HMA manufacturing process and thus, it should be more representative of how asphalt binder behaves in HMA pavements. Table 1 lists key advantages and disadvantages of the viscosity grading system.

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.

 

Advantages Disadvantages
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 temp.
  • 60°C (140°F) – high pavement temp.
  • 135°C (275°F) – HMA mixing temp.
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.  

 

 

Advantages and Disadvantages of Viscosity Grading as stated belowThe new method of grading the product has now rested on the viscosity of the Bitumen (at 60°C and 135°C). The new grades have thus evolved with nomenclature:

Viscosity grade over penetration grade several key issues are addressed, like:

  • Performance at high temperatures by 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)
  • Issues relating to compaction, which the tender asphalt mixtures create as push and shove under the roller wheels, have also addressed by having a requirement of minimum viscosity at 135°C, it will be helpful in minimizing the tender mix problems in the field.
  • Adoption of viscosity-graded paving bitumen specifications will also reduce the number of total tests to 7 Without compromising the quality of bitumen and no new tests are required in implementing this specification.

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

 


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