From the Privateers' newsletter, Mills, Wyoming
Tarmac
I have
always heard the word “Tarmac” and it was always in
reference to a runway. Most of the folks that used
the term tarmac generally had 10-15 years of more
life experiences. I also noticed these folks, at
some point in time, enlisted in one of our armed
forces and therefore thought it was a term that came
out of the armed forces. Boy was I wrong on that
assumption. Let us look into this a little deeper
and find out how this name actually came about and
what it really means.
First, tarmac is short for tarmacadam, a type of
highway surface. In 1901, E. Purnell Hooley patented
this type of material. John McAdam invented macadam,
which is a form of pavement. It consisted of crushed
granite or greenstone compacted as subgrade to
support the load. This was covered with a light
stone to take the abuse and repel water off the
road.
In
more recent time’s macadam construction, crushed
rock was then placed on the compacted course and hot
tar used to bind together the materials. A final
layer was then added and rolled to fill in the
spaces.
Originally, macadamized roads were sufficient for
horse-and-buggy day. However, these roads were quite
dusty and eroded with intense rain. Henry Cassell
patented “Pitch Macadam” back in 1834 that helped to
stabilize macadam roads with tar.
This process 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 then compacting the mixture with a
steamroller.
As
petroleum production increased, the byproduct
asphalt became available in huge quantities and
largely supplanted tar because of its reduced
temperature sensitivity. The macadam construction
process also became quickly obsolete because its
high manual labor requirement. However, the somewhat
similar tar-and-chip method, also known as
bituminous surface treatment, remains popular.
While the specific tarmac pavement is not common in
some countries today, many people use the word to
refer to generic paved areas at airports, especially
the airport apron, near the terminals despite the
fact that many of these areas are in fact made of
concrete.
The Wick Airport at Wick in Caithness, Scotland is
one of the few airports that still have a real
tarmac runway. Q
—From Wikipedia, the free encyclopedia
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