Penetration grade bitumen is unique for road construction in various environmental conditions. These grades of bitumen are named due to their level of hardness and consistency of bituminous materials, which leads to the classification of bitumen in a range of grades from 30 to 120.
The main goal for grading bitumen based on penetration is to determine their suitability for use in various construction methods and under different climatic conditions. Known also as paving grade bitumen, PEN grades are classified based on the depth into which a certain laboratory needle penetrates them. A penetration test is performed to indicate the hardness of bitumen. If the achieved figures were high, the tested bitumen is soft. It means that the needle has penetrated in more depth. On the contrary, lower figures show that the tested bitumen is hard and the penetration depth is shallow. For instance,
when we say bitumen 60/70, the first number stands for minimum penetration, and the second one stands for maximum penetration.