Bitumen Refinery Processing, Road Rutting Causes, and Grades

Posted on Jan 30, 2025 in Civil Engineering, Transportation, and Urban Services

What is Refinery Processing of Bitumen?

The most common refining process used to produce bitumen is the straight reduction of crude oil, or a crude blend, using atmospheric then vacuum distillation. Bitumen produced in this manner is referred to as straight-run and is typically used in paving applications. The crude is heated by a furnace and is sent to a distillation tower, where it is separated by boiling point. Then the material is converted by heating, pressure, or a catalyst into finished products including fuels like gasoline and diesel, and specialty products like asphalt and solvents.

What are the Causes of Rutting in Roads?

There are three primary causes of rutting in flexible pavements:

• Asphalt layer problems
• Structural layer problems
• Weak subgrade problems

1. Asphalt Layer Problems

Unsuitable mix-design or inadequate compaction of the asphalt layers can result in unacceptable road surface rutting, whereas correct design mix should ensure traffic can be supported for the full design life. The asphalt layers must be sufficiently stiff as to prevent deformation and outward flow under the high tire loading, whilst remaining flexible enough to prevent fatigue cracking.

2. Structural Layer Problems

The structural layers of the pavement are the subbase and base layers. They perform the essential function of distributing traffic loading onto the pavement foundation. The thickness of these layers determines their structural strength. If the structural layers are too thin, the load on the subgrade may be excessive, resulting in subgrade failure and large pavement deformations, which show up as rutting at the surface. In some cases, particle movements within the unbound structural layers can occur under repeated traffic loading. The lateral movements away from the wheel path result in thinning of the base layer accompanied by rutting at the surface.

3. Weak Subgrade Layer Problems

The pavement design is highly dependent upon the strength of the subgrade. If the subgrade is weaker than assumed in the design, the pavement structural strength is compromised and rutting can result. The most likely cause of this is a rise in moisture content through a cracked pavement allowing surface ingress of rainwater through it or poor drainage – perhaps due to failed or inadequate side drains. Both issues can be solved with a maintenance regime, timely intervention, and resurfacing if required.

Grades of Bitumen

Penetration Test on Bitumen: Commonly used grades are 30/40, 60/70, and 80/100. For bituminous macadam and penetration macadam, IRC suggests bitumen grades 30/40, 60/70, 80/100.

Classification of Viscosity Grade Bitumen: Viscosity test on bitumen results the classification of bitumen in a range of grades, including VG10 Bitumen, VG20 Bitumen, VG30 Bitumen, and VG40 Bitumen. The higher the number, the harder the bitumen in the viscosity grading system.

Application of Viscosity Grade Bitumen