The penetration grading system was developed in the early 1900s to characterize the consistency of semi-solid asphalts. Penetration grading quantifies the following asphalt concrete characteristics:

Pentration Grade Bitumen is Bitumen classified using the penetration property. Penetration grading’s basic assumption is that the less viscous the asphalt, the deeper the needle will penetrate. Bitumen which is produced during the process of oxidation of vacuum bottom (the Bitumen production feedstock that derives from distillation tower residue in vacuum oil refineries) at bitumen production unit in a manner that its penetration point (kind of test to indicate the hardness of bitumen) in specified group is classified in different grade of Bitumen.

Penetration Grade Bitumen is commonly used in road surfacing, and some industrial applications. Additional processing yields other grades of bitumen products and their application.

Penetration grading key advantages and disadvantages are listed as below

Advantages Disadvantages
The test is done at 25° C (77° F), which is reasonably close to a typical pavement average temperature. The test is empirical and does not measure any fundamental engineering parameter such as viscosity.
May also provide a better correlation with low-temperature asphalt binder properties than the viscosity test, which is performed at 60° C (140° F). Shear rate is variable and high during the test. Since asphalt binders typically behave as a non-Newtonian fluid at 25° C (77° F), this will affect test results.
Temperature susceptibility (the change in asphalt binder rheology with temperature) can be determined by conducting the test at temperatures other than 25° C (77° F). Temperature susceptibility (the change in asphalt binder rheology with temperature) cannot be determined by a single test at 25° C (77° F).
The test is quick and inexpensive. Therefore, it can easily be used in the field. The test does not provide information with which to establish mixing and compaction temperatures.

Penetration grades are listed as a range of penetration units (one penetration unit = 0.1 mm) such as 120 – 150. Penetration grades specified in AASHTO M 20 and ASTM D 946 are listed in below table

Penetration Grade Comments
40 – 50 Hardest grade.
60 – 70 Typical grades used in the U.S.
85 – 100
120 – 150
200 – 300 Softest grade. Used for cold climates such as northern Canada

Penetration Grade Bitumen Specification (AASHTO M 20 and ASTM D 946)

Units 40/50 60/70 80/100 100/120 Test Methods
Specific Gravity @25°C - 1.01-1.06 1.01-1.06 1.01-1.05 1.01-1.04 ASTM D-70
Penetration @25°C, 100gm, 5sec 0.1MM 40-50 60-70 80-100 100-120 ASTM D-5
Softening Point, Ring & Ball °C 52-60 49-56 45-52 42-49 ASTM D-36
Ductility @25°C, after TFOT, Min CM 100 100 100 100 ASTM D-113
Loss on Heating, Max %Wt 0.2 0.2 0.5 0.5 ASTM D-6
Drop in Penetration after Heating, Max % 20.0 20.0 20.0 20.0 ASTM D-6 & D-5
Flash Point Cleveland open cup, Min °C 250.0 250.0 232.0 250.0 ASTM D-92
Solubility in CS2, Min %Wt 99.5 99.5 99.5 99.5 ASTM D-4
Organic Matter Insoluble in CS2, Max %Wt 0.5 0.5 0.5 0.5 ASTM D-4
Sport Test - Negative Negative Negative Negative *A.A.S.H.O.T.102
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*American association of state highway officials

Bitumen Specification European Standard (BS EN 12591)

Units 35-50 40-60 50-70 70-100 100-150 Test Methods
Penetration @25°C, 100gm, 5sec 0.1MM 35-50 40-60 50-70 70-100 100-150 EN 1426
Softening Point, Ring & Ball °C 50-58 48-56 46-54 43-51 39-47 EN 1427
Resistace to Hardening@163°C
  - Change in mass, Max %Wt 0.5 0.5 0.5 0.8 0.8 EN 12607-1
  - Retained Penetration, Min 0.1MM 53 50 50 46 43
  - Softening point after hardinging, Min °C 52 49 48 45 41
Other Properties
Flash Point Cleveland open cup, Min °C 240 230 230 230 230 EN ISO 2592
Solubility in CS2, Min %Wt 99.0 99.0 99.0 99.0 99.0 EN 12592
Kinematic Viscocity @135°C, Min mm2/S 370 325 295 230 175 EN 12595
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