Tarmac Asphalt vs Bitumen
Three extremely popular construction materials used worldwide, asphalt, bitumen and tarmac are indeed quite hard to differentiate from one another to the untrained eye. However, the nature of these three materials vary drastically, thereby making it very necessary to discern them from one another.
What is Asphalt?
Asphalt or asphalt concrete, a composite material that is used for construction purposes, is mainly used for the paving of road surfaces. Asphalt is also now increasingly being used as the core of embankment dams. Asphalt concrete, consisting of bitumen, a liquid or a semi solid form of black, sticky and viscous material, which acts as a binder for mineral aggregates such as sand and rocks, is sometimes also referred to as blacktop, or pavement.
There are various ways of mixing asphalt and aggregate, thereby creating different kinds of mixtures. Hot mix asphalt concrete, cut-back asphalt concrete , warm mix asphalt concrete, mastic asphalt concrete or sheet asphalt and natural asphalt concrete are some of them. Different types of asphalt concrete have different characteristics thereby responding to durability, tire wear, braking efficiency and roadway noise and other factors in ways unique to each mixture. The Hot Mix asphalt concrete is made by heating the asphalt binder to decrease its viscosity. The Warm Mix asphalt concrete uses waxes, emulations or even water to the asphalt binding which allows more rapid availability of the surface for use and is often used for construction sites with tight time schedules. The Cold Mix asphalt concrete is produced by emulsifying the asphalt with water and soap, thus reducing the viscosity of the mixture before adding it to the aggregate. This is essentially used on less trafficked roads or as patching up material. The Cut-back asphalt concrete is produced by dissolving the binder in kerosene or another lighter fraction of petroleum while Sheet asphalt or Mastic asphalt concrete is made by heating hard grade blown in a green cooker till it becomes a liquid and then adding it to the aggregates. Asphalt concrete is also known to be 100% recyclable and thereby, 100% environmental friendly.
What is Bitumen?
Bitumen, also sometimes referred to as asphalt, is a semi solid or a liquid form of petroleum that is sticky black and highly viscous in nature. Found in natural deposits, bitumen is used as a glue that binds the aggregate particles together to create a solid base. While the main use of asphalt is in road construction, it is also used for bituminous waterproofing products, production of roofing felt and for sealing flat roofs.
Naturally occurring asphalt/bitumen is more of less specified as “crude bitumen” and most of the commercially used bitumen is obtained from petroleum. However, deposits of bitumen also occur in the remains of ancient, microscopic algae and places which had once contained life, usually deposited in the mud at the bottom of lakes or the ocean where the organisms had once lived. Under the pressure of deep burial and a temperature above 50 °C, the remains are usually transformed into bitumen, petroleum or kerogene. One good example of this is La Brea Tar Pits.
The largest use for bitumen in modern times is in asphalt concrete which in turn is used for paving road surfaces. Bitumen is also used to produce Japan black, a lacquer that is known especially for its use on iron and steel.
What is Tarmac?
Short for tarmacadam, tarmac is a road surface paving material that was patented in 1901 by Edgar Purnell Hooley. The history of tarmac dates back to 8th century AD when it has been found that the streets of Baghdad had been paved with tarmac. However, it was more than 1000 years later that a road construction method called macadamisation was introduced by John Loudon McAdam which allowed horses and carriages or coaches to travel on the roads quite conveniently. Yet these roads were seen to be quite dusty and were easily subjected to erosion with heavy rain and later on, did not support the transportation of heavy motor vehicles. It was in 1834 that John Henry Cassell patented a method to stabilise macadam roads with tar which was named “Pitch Macadam, In this method one is required to spread tar upon the surface, placing a typical macadam layer on top followed by the sealing of the macadam with a mixture of sand and tar. However the 1901 patent for tarmac which came afterwards required the tar, modified with small amounts of Portland cement, pitch and resin and the aggregate to be mixed mechanically before laying it down and then compacting the mixture with a steamroller.
What is the difference between Asphalt and Bitumen and Tarmac?
• Asphalt and bitumen both refer to the same black, sticky semi solid or a liquid substance derived from crude oil.
• However, in regular use, asphalt can also be used as a shortened term for asphalt concrete which is a popular construction composite made up of bitumen and mineral aggregates.
• Although in UK, tarmac is a word commonly used for asphalt concrete, tarmac is a separate method in itself which involved stabilise macadam roads with tar.