tarmac

thumb|right|alt=A smooth tarmac road with a roller engine in action Tarmacadam (a portmanteau of "tar" and "macadam") or tarmac is a concrete road surfacing material made by combining tar and macadam (crushed stone and sand), patented by Welsh inventor Edgar Purnell Hooley in 1902. It is a more durable and dust-free enhancement of simple compacted stone macadam surfaces invented by Scottish engineer John Loudon McAdam in the early 19th century. The terms "tarmacadam" and "tarmac" are also used for a variety of other materials, including tar-grouted macadam, bituminous surface treatments and modern asphalt concrete.

==Origins== thumb|Workers tarring a road in London during World War I Macadam roads pioneered by Scottish engineer John Loudon McAdam in the 1820s are prone to rutting and generating dust. Methods to stabilise macadam surfaces with tar date back to at least 1834 when John Henry Cassell, operating from ''Cassell's Patent Lava Stone Works'' in Millwall, England, patented "lava stone." This method involved spreading tar on the subgrade, placing a typical macadam layer, and finally sealing the macadam with a mixture of tar and sand. Tar-grouted macadam was in use well before 1900 and involved scarifying the surface of an existing macadam pavement, spreading tar and re-compacting. Although the use of tar in road construction was known in the 19th century, it was little used and was not introduced on a large scale until the motorcar arrived on the scene in the early 20th century. Ironically, although John Loudon McAdam himself had been a supplier of coke for Britain's first coal tar factory, he never in his own lifetime advocated for the use of tar as a binding agent for his road designs, preferring free-draining materials (see the page Macadam).