Tarmac is a type of "highway" surface particularly used in the construction of roads, but can refer to many types of concrete material including tar-grouted macadam, Tarvia, bituminous surface treatments and even modern asphalt concrete.
The Origins of Tarmac
Originally roads were 'Macadamised', which consisted of creating three layers of stones laid on a crowned subgrade with side ditches for drainage. The first two layers consisted of angular hand-broken aggregate, maximum size 3 inches (75 mm), to a total depth of about 8 inches (200 mm). The third layer was about 2 inches (50 mm) thick with a maximum aggregate size of 1 inch (25 mm). Each layer would be compacted with a heavy roller, causing the angular stones to lock together with their neighbours.
This type of surface was used by horses and carriages and became dusty and prone to erosion with heavy rain and could not hold firm with the introduction of faster paced motor vehicles. The introduction of tar to the macadam date back to 1834 and involved spreading tar on the subgrade, placing a typical macadam layer and finally sealing the macadam with a mixture of tar and sand. A later patent of tarmac involved mechanically mixing tar and aggregate prior to lay-down, and then compacting the mixture with a steam roller.
Later Developments with Tarmac
As petroleum production increased, the byproduct from the process used to create petrol, asphalt, became available in huge quantities and so largely took over the use of tar due to it's reduced temperature sensitivity and lower price tag.
The tarmac pavement that was once used to describe the result of this method has now become a very general term used to describe many different types of generic paved areas, such as those at airports, despite the fact that these are generally made using concrete and not tarmac. In actual fact there remains only a handful of airports in the world that still use the original tarmac in it's proper form.
Tarmac is not the most popularly used method of covering areas around the home because of the difficult and relative expensive of mixing and laying. If there is a large area to cover then contractors can be hire to lay tarmac where needed, but generally concrete is used to lay smaller areas that are likely to have little traffic as it can be mixed relatively easily and bought just as cheaply.