Everything about Tarmac totally explained
Tarmac (short for
tarmacadam, a
portmanteau for
tar-penetration
macadam) is a type of
highway surface, pioneered by
John Loudon McAdam in around
1820. Strictly speaking, Tarmac refers to a material patented by
Edgar Purnell Hooley in
1901. The term is also used, with varying degrees of correctness, for a variety of other materials, including tar-
grouted macadam, Tarvia, bituminous surface treatments and even modern
asphalt concrete.
Origins
Macadamized roads were adequate for use by horses and carriages or coaches, but they were very dusty, subject to erosion with heavy rain and didn't hold up to higher speed motor vehicle use. Methods to stabilise macadam roads with tar date back to at least 1834, when Henry Cassell patented "Pitch Macadam". This method involved spreading tar on the
subgrade, then placing a typical macadam layer and then sealing the macadam with a mixture of tar and sand. Tar-grouted macadam was also in use well before 1900, and involved scarifying the surface of an existing macadam pavement, spreading tar and re-compacting. Hooley's patent for Tarmac involved mechanically mixing tar and aggregate prior to lay-down, and then compacting the mixture with a
steam roller. The tar was modified with the addition of small amounts of
Portland cement,
resin and
pitch.
Later developments
As
petroleum production increased, the by-product
asphalt became available in huge quantities and largely supplanted tar due to its reduced temperature sensitivity. The Macadam construction process also became quickly obsolete due to its high manual labour requirement; however, the somewhat similar tar and chip method, also known as
bituminous surface treatment (BST), remains popular.
While the specific Tarmac pavement isn't common in some countries today, many people use the word to refer to generic paved areas at
airports, especially the
airport ramp or "apron", near the
terminals despite the fact that many of these areas are in fact made of
concrete. This term seems to have been popularised when it became part of the news lexicon following live coverage of the
Entebbe hijacking in 1976, where "Tarmac" was frequently used by the on-scene
BBC reporter in describing the hijack scene. The
Wick Airport at
Wick in
Caithness,
Scotland is one of the few airports that still has a real Tarmac runway.
Patents
- Hooley, E. Purnell,, "Apparatus for the preparation of tar macadam", July 26, 1904.
Further Information
Get more info on 'Tarmac'.
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