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 |