Macadam
387880
224713472
2008-07-10T02:19:00Z
LorenzoB
2054613
/* Tar-bound macadam */
{{For|the regions of imperceptible colour differences|MacAdam ellipse}}
{{Wiktionary}}
'''Macadam''' is a type of [[road construction]] pioneered by the [[Scotland|Scotsman]] [[John Loudon McAdam]] in around [[1820]]. It 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 (composite)|aggregate]], maximum size 3 [[inch]]es (75 [[millimeter|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 [[Road roller|roller]], causing the angular stones to lock together.
==Water-bound macadam==
This basic method of construction is sometimes known as "water-bound macadam". Although this method required a great deal of manual labour, it resulted in a strong and free-draining pavement. Roads constructed in this manner were described as "macadamised".
==Tar-bound macadam==
With the advent of [[motor vehicle]]s, dust became a serious problem on macadam roads. The [[vacuum]] created under fast-moving vehicles sucks dust from the road surface, creating dust clouds and a gradual raveling (pulling apart) of the road material. This problem was later rectified by spraying [[tar]] on the surface to create "tar-bound macadam" ([[tarmac]]). <!--Non-sequitur?: This may have led to the common misuse of the word macadam to refer to a road made with [[asphalt concrete]].--> While macadam roads have now been resurfaced in most [[Developed country|developed countries]], some are preserved along stretches of roads such as the [[United States]]' [[National Road]]. Due to uses of macadam as a road surface in former times, roads in some parts of the United States (as parts of [[Pennsylvania]]) are often referred to as macadam, even though they might be made of [[asphalt]] or [[concrete]]. <!--Parochial: The misidentified relative - [[tarmac]] - can still be sometimes found in New England.-->
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{{Road types}}
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[[Category:Pavements]]
[[Category:Scottish inventions]]
[[Category:Industrial Revolution]]
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