Macadam is a type of road construction pioneered by John Loudon McAdam in the early 1800s. It consists of three layers of stones laid on a sloped subgrade, with side ditches for drainage. The first two layers consisted of angular aggregate hand-broken, maximum size 3 inches (75 mm) for 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). The layers would be compacted with a heavy roller. This caused the angular stones to lock to their neighbours. This basic method of construction is sometimes known as water-bound macadam. Although this method required a great deal of manual labor, it resulted in a strong and free-draining pavement. John Loudon McAdam (September 21, 1756 - November 26, 1836) was a Scottish engineer and road-builder. ... Events and Trends Beginning of the Napoleonic Wars (1803 - 1815). ... In highway engineering, subgrade is the native material underneath a constructed pavement. ...

Roads which were constructed in this manner were described as Macadamized.

With the advent of motor vehicles, dust became a serious problem on macadam roads. The vacuum created under fast moving vehicles sucked the dust out of the surface leading to a gradual raveling of the larger size materials, as well as an unpleasant dust cloud. This problem was later rectified by spraying tar on the surface thus creating tar-bound macadam, or tarmac. This may have led to the common misuse of the word macadam to refer to a road made with asphalt concrete. While macadam roads are extinct in modern America, the misidentified relative - tarmac - can still be sometimes found in New England. The article on the vacuum cleaner is located elsewhere. ... For the computer term, see tar file format. ... Tarmac, short for tar-penetration macadam, is a type of highway pavement no longer commonly used. ... Asphalt concrete is a construction material commonly used for paving roads, highways and parking lots. ... Tarmac, short for tar-penetration macadam, is a type of highway pavement no longer commonly used. ...