Bitumen is a dense, highly viscous, sticky, black hydrocarbon residue derived from refining crude oil after the lighter, more volatile fractions have been removed. In North America, this substance is commonly referred to as asphalt cement, which acts as the binder in the paving material known as asphalt. Bitumen possesses strong adhesive and hydrophobic properties, making it a useful compound in construction and industrial applications.
Separation Through Distillation
The manufacturing process begins by separating crude oil components in a controlled, two-stage distillation sequence. Crude oil is first heated to approximately 350°C before entering the atmospheric distillation column. Within this tower, lighter compounds like gasoline, kerosene, and diesel vaporize, rise, and condense at different levels for collection.
The heaviest portion of the crude oil, which does not vaporize at atmospheric pressure, remains as a thick liquid residue at the bottom of the column (atmospheric residuum). This residue still contains components that can be refined out. To avoid thermal degradation or cracking of the large hydrocarbon molecules, this residue is then transferred to a vacuum distillation unit.
In the vacuum tower, pressure is drastically reduced, creating a near-vacuum environment. This lowers the boiling points of the remaining heavy compounds, allowing them to be separated below 400°C. Lighter components, such as lubricating oils, are recovered, leaving the heaviest, most refractory material at the bottom. This final, extremely dense residue is the raw bitumen, also known as vacuum residue, ready for further modification.
Adjusting Characteristics for Grade
Once the raw bitumen is isolated, its characteristics must often be modified to meet specific performance standards. One common technique is oxidation, or air blowing, where hot air is injected into the bitumen, typically between 240°C and 320°C. This process initiates chemical reactions like polymerization and oxidation, which increase the material’s molecular weight.
The result is an oxidized bitumen with a higher softening point and increased hardness. This altered material exhibits reduced susceptibility to changes in temperature, making it suitable for industrial uses like roofing membranes where thermal stability is necessary. For high-performance paving applications, the bitumen’s properties are enhanced through polymer modification.
This involves blending the bitumen with synthetic polymers, such as Styrene-Butadiene-Styrene (SBS), to create Polymer Modified Bitumen (PMB). The addition of these elastomeric polymers improves the binder’s elasticity and recovery, allowing it to resist deformation under heavy traffic loads and extreme temperatures. Lighter oils are also blended in a process called fluxing to adjust the binder’s viscosity for easier handling and mixing with aggregates.
Key Uses of the Final Product
Roughly 85% to 90% of all refined bitumen is used as the binding agent in asphalt concrete for highways, airport runways, and parking lots. The material’s cohesive nature holds crushed rock and aggregate together, forming a durable, flexible, and weather-resistant pavement structure.
The remaining portion is utilized for its excellent waterproofing and sealing capabilities. Bitumen is a primary component in the manufacturing of roofing materials, including shingles and modified bitumen membranes for flat roofs. Its hydrophobic quality makes it valuable for joint sealants, pipe coatings, and protective coatings against moisture and corrosion in civil engineering projects.