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.--> <br> <br> {{Road types}} <!--Categories--> [[Category:Pavements]] [[Category:Scottish inventions]] [[Category:Industrial Revolution]] <!--Other languages--> [[da:Makadam]] [[de:Makadam]] [[eo:Makadamo]] [[eu:Macadam (sistema)]] [[fi:Murske]] [[fr:Macadam (route)]] [[it:Macadam]] [[nl:Macadam]] [[no:Makadamisering]] [[pt:Macadame]] [[sv:Makadam]]