Bitumen Grading

Bitumen is a thermoplastic material, that is, its stiffness is dependent on its temperature. Its stiffness decreases as its temperature is increased. This temperature versus stiffness relationship is different for different bitumen based on the origin of the petroleum crude and/or method of refining.

Chewing in mouth was the first mode of testing to determine stiffness (hardness) of bitumen during the late 19th century. Experienced bitumen inspectors used the technique for testing and accepting bitumen for paving. Obviously, the test temperature was 98.6 F (37 C) equal to the average human body temperature.

Grading of bitumen by penetration test at 25 C was adopted in 1903, about 100 years ago. In penetration test a needle loaded with 100 grams is allowed to penetrate the bitumen maintained at temperature of 25 C in a water bath, for 5 seconds. The resulting penetration is measured in mm;1 penetration unit = 0.1 mm. The greater the penetration, the softer is the bitumen.

Viscosity grading at 60 C was introduced in the Unites States during 1970s. Viscosity Test is a more scientific measure of consistency than Penetration. Various tests are used to measure the resistance to flow of bitumen and to thereby define its consistency Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress.
In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).

Viscosity Grade Bitumen is widely used in spraying applications such as surface-dressing and paving in very cold climate. It is also used to manufacture Bitumen emulsion and Modified Bitumen products.



Sources: benzeneinternational.com, engineerstoday.blogspot.com, Singh, P. (2007). An overview of the viscosity grading system adopted in india for paving bitumen. Kandhal Indian Highways

P.S: Gildatar Bitumen is proud to make possible the supply of Middle East bitumen in multiple grades 60/70, 80/100, 85/100, 85/25, 40/50, and 30/40.