Viscosity Grade Bitumen
Viscosity is defined as the degree of fluidity or described as the inverse of fluidity. Thus, viscosity determines the fluidity of a substance and deals with resistance to flow. Viscosity-grade bitumen was introduced to analyze bitumen behaviors at different temperatures, particularly at higher temperatures. Hence, asphalt used in the hot mixture is produced with superior characteristics. Moreover, viscosity-grade bitumen is generally used in hot climate regions to get pothole-free roads that last for years.
Viscosity-grade bitumen softens at higher temperatures and is stiffer at lower temperatures due to its thermoplastic properties. The relation between temperature and viscosity plays a significant role when establishing the performance characteristics of rheology, durability, adhesion, and impermeability.
Using the vacuum bottom oxidation process all the different grades of viscosity bitumen have been produced. The quality of the raw material decides the performance of viscosity-grade bitumen, utilized in the construction of roads or any other applications.
History of Viscosity Grading Method:
It is important to analyse the physical and chemical properties to identify the best use of bitumen and its performance. Over a period, Bitumen grading practices have evolved from simple methods to complex test procedures to meet the requirements of specific applications. Initially, bitumen was graded using a chewing system at a temperature of 37°C, which is close to normal human body temperature. However, this method is flawed as it is based on empirical evidence and lacks control over temperature susceptibility. Following that, penetration grading was introduced and widely used to grade bitumen at a testing temperature of 25°C. For over 100 years, this grading system was widely accepted. However, it was insufficient because it did not include tests conducted at high and low temperatures. This method failed to analyse the performance of bitumen at higher and colder temperatures, making it unsuitable for identifying the appropriate bitumen to use in hot and cold regions. Ultimately, in the early 1960s, the Indian Standard viscosity grading system was introduced to grade the bitumen at 60°C and 135C which are the highest temperatures (hot region) of pavement during summer and the mixing temperature respectively. The Viscosity Grading System is accepted globally to grade the bitumen as it is based on rational scientific tests to analyse the performance of the bitumen, penetration, ductility, softening point and solubility.
Different Types:
Viscometer is a testing system to categorize different grades of viscosity grade bitumen which includes VG 10, VG 20, VG 30, and VG 40. As the number of viscosity grades increases, the hardness of bitumen increases. VG 10 is less hard than VG 20, and VG 20 is less hard than VG 30, likewise, it goes on. Compared with penetration grade bitumen, viscosity grade bitumen is widely used as it is easier to mix and compact with the hot mix asphalt. Additionally, its resistance to deformation and rutting is more efficient than the other bitumen grades.- Viscosity-grade bitumen provides excellent performance in hot climatic conditions and higher resistance to deformation and rutting.
- As a result, the minimum kinetic velocity of viscosity grade bitumen at 135°C helps effectively in reducing the possibility of tender mixes while applied to road construction.
- The minimum penetration capacity is at 25°C assists in making roads durable, long-lasting, and high-performance.
- The viscosity bitumen tested in two different temperatures would help the bitumen supplier to provide an accurate and suitable asphalt mixture and compaction.
VG 20:
Viscosity Grade (VG 20) bitumen is known for its ideal properties of resistance to deformation, rutting and cracking because of its fluidity and penetration capacity over the surface. Generally, VG 20 is utilized in cold regions and high-altitude areas with average temperatures ranging from 30°C to 37°C.Besides, the VG 20 grade is widely used in road construction in the hot mix asphalt as it is ideal to withstand higher traffic loads and adverse climate conditions.
VG 10:
Viscosity Grade Bitumen (VG10) is a low-viscosity bitumen which has a higher penetration value and fluidity. VG 10 is primarily used for road maintenance and surface dressing of roads due to its excellent fluidity properties.Moreover, VG 10 is used broadly in cold regions because of its lower viscosity capacity, resistance to adverse weather conditions and higher performance to maintain roads long and durable.
VG 30:
Viscosity grade (VG 30) bitumen is usually applied in hot and cold regions, unlike penetration grade bitumen because of its good thermal susceptibility for weather resistance. As the viscosity of the bitumen is higher, there are minimal chances of getting in touch with water and other atmospheric particles.VG 30 provides excellent waterproofing for roads and structures because of its increased impermeability characteristics. Also, it is an ideal choice for building roads in hot regions because of its high resistance to adverse weather conditions and deformation to rutting.
VG 40:
Viscosity grade bitumen (VG 40) is thicker and has increased resistance to flow which makes it a perfect choice for making resilient roads. When compared with penetration-grade bitumen, VG 40 is most suitable for constructing durable structures.Furthermore, its lower kinetic velocity to flow and higher resistance to deformation make it suitable for building pavements where heavy-duty traffic loads and adverse climatic conditions are expected.
