Bitumen is graded based on absolute viscosity at 60 ºC or kinematic viscosity at 135 ºC. The SI physical unit of dynamic viscosity is Poise and kinematic viscosity is expressed in Centi Stokes. Pure bitumen has been graded based on AASHTO-M226 and ASTM-D3381 standards.
Table 1-1: Technical Specifications of Pure Bitumen Based on Viscosity at 60 oC (AASHTO-M226)
PG is the latest standard of the day. This relatively new method classified bitumen is based on varying temperatures. It is a fully scientific method studying the mechanical specifications of bitumen. In this method, a temperature range is defined for bitumen and the consumer can easily choose the desired product. Having installed SHRP systems, Oil Company is capable of selling bitumen to its customers based on PG method. Today, a PG is defined for polymer modified bitumen and pure bitumen based on environmental conditions and temperature. A wider PG range means higher resistance and more favorable specifications. Oil Company has the capacity to produce all these grades.
Bitumen is ‘cutback’ by adding controlled amounts of petroleum distillates, such as kerosene. This is done to reduce the viscosity of the bitumen temporarily so it can penetrate pavements more effectively or to allow spraying at temperatures that are too cold for successful sprayed sealing with neat bitumen. The materials used to cutback bitumen will evaporate after application to leave the remaining material similar in hardness to the original bitumen. Cutback bitumen is used when there is limited access to heating equipment and bitumen may be cooled throughout working. This type of bitumen is used in road operations for surfacing and pavement. Medium-Curing (MC) bitumen is achieved from solving pure bitumen into kerosene. Cutback bitumen is classified based on viscosity grade. It is divided into three categories:
Rapid-Curing (RC) : The cutback bitumen is known as rapid-curing (RC) if the bitumen is solved in gasoline. The reason is that evaporation occurs quickly and the bitumen is deposited.
Medium-Curing (MC) : MC cutbacks are prepared by solving bitumen in kerosene which evaporates more slowly than gasoline.
Slow-Curing (SC) : Slow-curing cutback may be achieved from solving bitumen in gasoil or fuel oil or directly from distillation of crude oil.
... is mainly used in road surfacing. Bitumen with lower penetration grade is used in the regions with warm climate while higher penetration grade is used in colder weather. Oil Company is capable of producing different grades of road surfacing bitumen in compliance with international standards .
Oxidized bitumen is mainly used for industrial purposes, such as roof insulation, flooring, industrial mastics, pipe coating, and paints. Oxidized bitumen is categorized based on softening points and penetration rate. For example, oxidized bitumen 85/40 is a type of bitumen whose softening point is 85±5 degrees Centigrade and its penetration rate is 40±5 dmm. Oxidized bitumen is also expected to make up for weight loss under heat. The softening point in oxidized bitumen is much higher than in regular bitumen, causing lower thermal sensitivity. The penetration index (PI) in oxidized bitumen is higher than in road construction bitumen (8>PI>2) because the letter has a gel-like structure due to asphalt accumulation.
The following table shows different grades of oxidized bitumen:
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