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Friday, April 27, 2012

How to grade bitumen



Bitumen used for paving grades are categorized according to viscosity (degree of fluidity) gradings. The higher the grade, the stiffer the bitumen gets.

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).


The test procedures used for paving grades of bitumen are as follows:

  • Penetration Test;  used to determine the consistency of bitumen by measuring the distance that a standard needle will penetrate vertically into a sample
  • Viscosity Test; is a more scientific measure of consistency than Penetration. Various tests are used to measure the resistance to flow of bitumen and to thereby define its consistency.
  • Flash Point: used to measure the temperature to which a sample of bitumen may be safely heated by establishing the temperature at which a small flame causes the vapour above the sample to ignite or flash.
  • Ductility: gives an indication of the extent to which a sample of the material can be stretched before breaking. A standard briquette of bitumen, placed in a mould in a water bath heated to 15°C, is pulled apart, usually at a speed of 5 cm per minute. The length of the thread of bitumen at the moment when it breaks, expressed in centimetres, is the ductility of the sample.
  • Solubility and the Presence of Insolubles: indicates the degree of contamination of the bitumen by other matter and therefore the presence of pure bitumen. The Australian test measures the percentage of matter that is insoluble in toluene.
  • Effect of Heat and Air: is determined to simulate the conditions obtained when the bitumen is used to manufacture hot-mix. In the Rolling Thin Film Oven Test a moving film of bitumen is heated in an oven at 163°C for 60 minutes. The viscosity is measured before and after treatment.
  • Softening Point: a measurement of the temperature at which a sample of bitumen held in a ring in a water bath allows a steel ball of specified weight to fall to a point at a specified distance below it.


The chart below shows typical applications for paving grade of BP bitumens:

Applications for Bp class
Bitumen class Sprayed Sealing Asphalt
Light Medium Heavy Extra Heavy
Class 170 ok ok      
Class 320   ok ok ok  
Class 600       ok ok




AASHTO M 226 and ASTM D 3381 Viscosity Grades
Standard
Grading based on Original Asphalt (AC)
Grading based on Aged Residue (AR)
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






Following table is the specification for performance grade bitumen


PROPERTY
GRADES
STANDARD

PG 76-10
PG 82-10


Min
Max
Min
Max

Flash Point, COC, °C
230
-
230
-
T48
Viscosity @ 135°C, Pa·s
135°C
3.0
135°C
-
ASTM D4402
Dynamic Shear @ 70°C, G*/sin d, kPa
1.00
-
-
-
-
After RTFO
-
-
-
-
-
Dynamic Shear @ 70°C, G*/sin d, kPa
2.20
-
-
-
-
Mass Loss, %
-
1%
-
1%
-
After PAV @ 100°C
-
-
-
-
-
Dynamic Shear @ 28°C, G*·sin d, kPa
-
5000
-
-
-
Creep Stiffness @ -12°C, S, MPa
-
300
-
-
-
Creep Stiffness @ -12°C, M-value
0.300
-
-
-
-









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