Bitumen comes in many forms
Bitumen is a very versatile material that is produced in many forms and has many different applications – 80–85 % of bitumen produced today is used in paving applications, with the balance in roofing or industrial applications.
The common starting point for all bitumen is the distillation of a carefully selected type, or types, or selected blends of crude oil - as only approximately 10–15% of crude oils are suitable for producing bitumen that will meet precise engineering specifications.
The properties, and hence the applications, of these different types of bitumen vary according to a combination of factors, including: the blend of crude oils they are distilled from; which refining method is used; and what, if anything such as an additive, is blended into the bitumen within the production process. All circumstances, crude oils and production technologies are carefully investigated before, and checked during the production, as described in the site quality management plan.
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 process involves heating crude oil to between 300 and 350oC, which separates lighter fractions from the non-boiling component. To remove the last traces of the lighter fractions, the atmospheric residue is introduced into a vacuum distillation unit, where the pressure reduction lowers boiling temperatures and avoids unwanted thermal cracking of the molecules. The pressure and temperature conditions within the vacuum process determine the hardness of the residuum and, therefore, the grade of bitumen produced.
By controlling the variables in the vacuum distillation process, bitumen with varying degrees of hardness can be produced.
By carefully mixing various types of polymers into bitumen, homogeneous, ready-to-use polymer modified bitumen (PMB) is produced. PMBs are widely used to improve the durability and performance of bituminous products in road building, and also in industrial applications.
In order to alter the physical properties, the straight-run bitumen can be further processed by blowing air through it at elevated temperatures. Depending on the degree of oxidation, one of two different types of bitumen are produced in this way: air-rectified bitumen and oxidised bitumen.
- Air-rectified bitumen are mildly blown and similar to straight run bitumen.
- Oxidised bitumen are used in roofing applications: they have a distinctive consistency at room temperature and a rubbery nature that affects how they respond to stress – such as can be caused by large temperature changes as found on rooftops.
The process of oxidation increases the stiffness and raises the softening point, which considerably alters key physical properties. Varying the length of the oxidation or air blowing process varies the extent of the reaction and produces distinctive end products.
Blending higher and lower viscosity residues in the required proportions can take place at the refinery, at terminals or at a third party facility, from where finished products can be distributed. Each processing technique can result in different grades of bitumen products.
There are four main types of bitumen used in hot mix paving applications offering assorted benefits including durability, speed of application, tailor-made design, safety, noise reduction and recyclability. For more details click here.
Roofing & industrial bitumen
Approximately 10 to 15% of bitumen is used in construction applications, mainly roofing, with oxidised bitumen principally being used in roofing membranes. Increasingly, polymer modified membranes are now also used in roofing applications.
Hard industrial bitumen is typically a variety of oxidised bitumen and has numerous and wide-ranging niche applications: from sound-deadening panels in the automotive industry, battery sealants and seed pots, to pipe coatings, bituminous paints and printer ink. For more details about the industrial applications, click here.