Bitumen performance grade
The bitumen performance grade (PG) asphalt composition is effective across a wide range of temperatures. An ideal PG modifier would be one which lowers the low end of this temperature range while raising the upper end of the temperature range. It has been found that the addition of a high viscosity base oil or finished lubricant to the asphalt will decrease the lower and upper ends of the temperature range by about a one to one (1:1) ratio.
These modifiers, although not ideal, eliminate or significantly reduce the need to add polymers to the asphalt composition. This is due primarily to the fact that lubricants already contain polymeric compounds. However, these high viscosity base oils and finished lubricants are typically hydrotreated during their manufacture in order to purify them for use as lubricants. As a result, the hydrotreating process is extremely costly and requires a great deal of specialized equipment. What is needed are more cost-effective ways to modify the asphalt with alternative PG modifiers which would be able to lower the low end of the temperature range while raising the upper end of the temperature range.The working temperature range determines whether a given grade of bitumen requires special manufacture or addition of a modifier. For example, a PG 64-28 has a working range of 92° (64 + 28 =92). Usually, binders with a temperature difference of 92° or more would generally require some sort of modification (Table 5).
Table 5: PG grades for different bitumen blends