In the past, the penetration index was defined based on the assumption that thermal sensitivity in the bitumen used in road construction was zero. Bitumen is a thermoplastic material, meaning that it becomes pliable or moldable above a specific temperature and returns to a solid state upon cooling.
Penetration-grade bitumen 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.
Pasargad Oil Company is capable of producing different grades of road surfacing bitumen in compliance with national and international standards in its six plants located at Tehran, Tabriz, Arak, Shiraz, Bandar Abbas, and Abadan refineries. Penetration rate bitumen is graded based on penetration and softening point tests. This table describes the physical properties of penetration-grade bitumen based on European standards. Penetration-grade bitumen is mainly used in road construction. During the last two decades of the 20th century, most road construction projects showed inclination for solid bitumen which results in more effective asphalt.

Penetration bitumen is the most widely used bitumen for road construction.
After production in the refinery, it is classified by bitumen penetration test using a penetrometer apparatus. The deeper the needle penetrates into the bitumen surface, the softer it will be and suitable for colder weather. The most widely used bitumen for road construction is penetration bitumen of 60/70 grade and then grade of 80/100. Furthermore, 60/70 grade is widely used as a waterproofing material in buildings.
To use this bitumen, you should pay attention to the average temperature of the area and the amount of traffic.
In the table below, you can see the different grades of this penetrating bitumen along with its application.