Historically, the penetration index of bitumen utilized in road construction has been defined under the assumption of negligible thermal sensitivity. 

Bitumen, as a thermoplastic material, becomes pliable or moldable when exposed to elevated temperatures and solidifies upon cooling. Penetration-grade bitumen is primarily employed in road surfacing applications. Generally, lower penetration grades are recommended for warmer climates, whereas higher penetration grades are advisable for colder regions.

The classification of penetration-grade bitumen is established through penetration and softening point tests. Below, we present the physical properties of penetration-grade bitumen in accordance with European standards. This type of bitumen is integral to road construction, and over the past two decades, there has been a significant preference for solid bitumen in road projects, leading to enhanced asphalt performance.