The definitive guide to bitumen
Bitumen is a crucial part of our world, stitching together the infrastructure and buildings we constantly rely on. If you’ve ever wanted to know more about this important and adaptable material, in this definitive guide to bitumen we answer all your bitumen-related queries, including what is bitumen, its meaning, uses, and what bitumen grades mean.
What is bitumen?
Bitumen is a thick, black, viscous grade of petroleum found naturally in oil sands and seeps and produced during the fractional distillation of crude oil. Formed artificially at the deepest sections of crude oil fractional distillation columns at temperatures above 350°C, bitumen is often further refined in vacuum distillation columns, then mixed with a range of additive materials depending on the final use. Around 3% of a barrel of crude oil is made into bitumen.
Bitumen usually contains naphthene aromatics, polar aromatics, asphaltenes and saturated hydrocarbons. It is a particularly waterproof material and can be mixed easily and uniformly with other materials when heated, and while it does oxidise and degrade over time, it can be recycled.
What is the meaning of bitumen?
The term bitumen comes from the Sanskrit words jatu, which means ‘pitch’, and jatu-krit, ‘pitch creating/producing’. Later, this became the Latin gwitu-men, ‘pertaining to pitch’, from which the word became part of the French, then English languages. Pitch is a term for naturally occurring bitumen and asphalt.
Bitumen is used primarily in British English to refer to the raw material Americans commonly term asphalt. In the UK, asphalt also refers to the mix of concrete and bitumen known as tarmac in the UK (from tarmacadam).
What are the uses of bitumen?
There are all sorts of things bitumen is used for, with these primarily falling within the realm of industry, particularly construction:
Paving asphalt: Bitumen is most commonly used as a binder, mixed with crushed concrete and rock such as limestone. This asphalt has a huge variety of uses, from roads and playgrounds to runways and cycle lanes. Bitumen products destined for paving are usually mixed with polymers to improve their anti-wear properties.
Roofing: Bitumen can be used as a sealant and waterproof membrane. When used this way, it is often mixed with polymers to reduce the temperature it can be worked at, making installation easier for workers.
Construction: Used to insulate and seal buildings and construction materials.
Recycling: Bitumen can be recycled relatively easily, with recycling rates using current technology being around 70%.
As well as these, bitumen has its other, more unusual uses – learn more in our guide.
Bitumen grades explained
The grade of a bitumen denotes its stiffness. Grades equal the penetration of a 100g steel rod dropped onto a bitumen sample for 5 seconds at 25°C in tenths of a mm. These are known as ‘pen’ grades. For example, 160/220 pen is softer than 100/150 pen, 70/100 pen or 40/60 pen (the four most-commonly used pen grades in the UK).
In the UK, 100/150 pen bitumen is the most common grade, used in a wide range of tasks; 160/220 is often used when the bitumen must be laid by hand – such as roofing; while 40/60 is used for roadbuilding, given its greater resistance to malformation and wear.
Bitumen grades can also indicate the amount of volatile materials still present in the bitumen. The higher the quantity of volatiles present, the lower the grade. The term can also be used to denote different uses, such as penetration grade bitumen, which is used for asphalt but can incorporate a range of numbered grades.