WHAT IS BITUMEN ?
Bitumen is an oil based substance. It is a semi-solid hydrocarbon product produced by removing the lighter fractions (such as liquid petroleum gas, petrol and diesel) from heavy crude oil during the refining process. As such, it is correctly known as refined bitumen. In North America, bitumen is commonly known as “asphalt cement” or “asphalt”. While elsewhere, “asphalt” is the term used for a mixture of small stones, sand, filler and bitumen, which is used as a road paving material. The asphalt mixture contains approximately 5% bitumen. At ambient temperatures bitumen is a stable, semi-solid substance.
Petroleum bitumen is often confused with tar. Although bitumen and coal tar are similarly black and sticky, they are distinctly different substances in origin, chemical composition and in their properties. Coal tar is produced by heating coal to extremely high temperatures and is a by-product of gas and coke production. It was widely used as the binding agent in road asphalt in the early part of the last century, but has since been replaced by refined bitumen.
Bitumen is also sometimes confused with petroleum pitch which, although also derived from crude oil, is a substance produced by a different process from that used for refined bitumen. Petroleum pitches are the residues from the extreme heat treatment or “cracking” of petroleum fractions. Their properties and chemical composition are therefore quite different from those of bitumen.
Naturally-occurring bitumen, sometimes also called natural asphalt, rock asphalt, lake asphalt or oil sand, has been used as an adhesive, sealant and waterproofing agent for over 8,000 years. But it occurs only in small quantities and its properties are quite different from refined bitumen.
The vast majority of refined bitumen is used in construction: primarily as a constituent of products used in paving and roofing applications. According to the requirements of the end use bitumen is produced to specification. This is achieved either by refining process or blending.
It is estimated that the current world use of bitumen is approximately 102 million tonnes per year. Approximately 85% of all the bitumen produced is used as the binder in asphalt for roads. It is also used in other paved areas such as airport runways, car parks and footways.
Typically, the production of asphalt involves mixing sand, gravel and crushed rock with bitumen, which acts as the binding agent. Other materials, such as polymers, may be added to the bitumen to alter its properties according to the application for which the asphalt is ultimately intended.
A further 10% of global bitumen production is used in roofing applications, where its waterproofing qualities are invaluable.
The remaining 5% of bitumen is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint.
Bitumen is applied in construction and maintenance of:
· Airport runways
· Footways / Pedestrian Ways
· Car parks
· Tennis courts
· Damp proofing
· Reservoir and pool linings
· Pipe coatings
· Cable Coatings
· Building Water Proofing
· Tile underlying waterproofing
· Newspaper Ink Production
· And many other applications
How is bitumen Produced?
Petroleum Bitumen, normally called “Bitumen” or “Asphalt” is produced by refining crude oil. Used as a binder in road-building products, it is a very viscous, black or dark brown material.
The crude oil is pumped from storage tanks, where it is kept at about 60°C, through a heat exchanger system where its temperature is increased to typically 200°C by exchanging heat gained from the cooling of newly produced products in the refining process. The crude is then further heated in a furnace to typically 300° C where it is partly vaporized into an Atmospheric Distillation Column. Here the physical separation of the components occurs. The lighter components rise to the top and the heaviest components (the atmospheric residue) fall to the bottom of the column and pass through a second heat exchanger prior to treatment in a vacuum distillation column. Finally, Bitumen is obtained by vacuum distillation or vacuum flashing of atmospheric residue from the vacuum distillation column. This is "straight run bitumen”. This process is called bitumen production by straight run vacuum distillation.
An alternative method of bitumen production is by precipitation from residual fractions by propane or butane-solvent deasphalting. The bitumen thus obtained has properties which derive from the type of crude oil processed and from the mode of operation in the vacuum unit or in the solvent deasphalting unit. The grade of the bitumen depends on the amount of volatile material that remains in the product: the smaller the amount of volatiles, the harder the residual bitumen.
Specialists in bitumen view bitumen as an advanced and complex construction material, not as a mere by-product of the oil refining process.