Tarmac is the abbreviation for tarmacadam which in turn is also sometimes referred to as tar penetration macadam. Basically, it is just a kind of road surface and furthermore it refers to material that was patented by a person known as Edgar Purnell Hooley. He patented this material way back in the year 1901 and the term has since then been used differently for other materials as well including for Tarvia and tar grouted macadam as well as for bituminous surface treatment and even for the latest asphalt concrete.
Tarmac – first used in Baghdad
Baghdad, the capital of Iraq is credited as being the first city in the world to have created tarmac streets. This was done by the Iraqis in the eight century AD. Another thousand years would pass before John Ludon McAdam would come up with his discovery which was a special way of constructing roads with the help of something that was to be known as macadamisation. However, those roads were mainly fit for use by horses and by carriages and by coaches and the roads tended to be dusty and easily would erode during the wet season.
When motor transport was introduced new methods had to be formed in which the macadam roads needed to be stabilised with tar. This practice was actually being followed as early as in the year 1834 when a person called John Henry Cassell patented his method which was to be known as Pitch Macadam.
Spread tar on sub-grade
This method required that tar be spread on a sub-grade and over that a macadam layer would be laid and then the entire thing would be sealed with more tar that was mixed with sand. The year 1900 also saw the introduction of tar grouted macadam. Even though there were many companies that were making use of tar in the construction of roads in the year 1900 this was not so widespread a practice and large scale use only became common after the motor car was invented in the twentieth century.
In 1901, Hooley patented the Tarmac by mixing (through mechanical means) a quantity of tar with some aggregate and then the mixture was laid down and then compacted with the help of steam rollers. Later, the tar would undergo changes because Portland cement would also be mixed in small quantities that along with pitch and resin helped to create the perfect tarmac mix.
When petroleum began to be produced in large amounts there was an interesting development in the use of tarmac because a petroleum by-product called asphalt was found to be useful in constructing roads. In fact, asphalt began to slowly replace tar because of the fact that asphalt did not heat up quite as much as tar.
This led to Macadam construction processes becoming obsolete and the main reason for it was that tar was too sensitive to temperature changes while asphalt was not and also because tarmac construction required a lot of manual labour input. Even so, an alternative method that still made use of tar and which was known as bituminous surface treatment or BST became quite popular