The form of pavement or road surface we now call "macadam" was invented about two hundred years ago by a Scot named John Loudon McAdam.
McAdam was born September 21, 1756 in Ayr, Ayrshire, Scotland. In 1770, at the age of fourteen, young John went to New York City, entering the countinghouse of a merchant uncle. He apparently applied himself, for he
returned to Scotland with a considerable fortune in 1783.
Back in his homeland, McAdam purchased an estate at Sauhrie in Ayrshire. After becoming a road trustee in his district, he noted that the local
highways were in poor condition. At his own expense, he undertook a series of experiments in road-making.
In 1798 McAdam moved to Falmouth, Cornwall, where he continued his
experiments under a government appointment. He recommended that roads should be raised above the adjacent ground for good drainage and covered, first with large rocks, and then with smaller stones, the whole mass to be
bound with fine gravel or slag. In 1815, having been appointed surveyor general of the Bristol roads, he put his theories into practice. To document his work, McAdam wrote Remarks on the Present System of Road-Making
(1816) and Practical Essay on the Scientific Repair and Preservation of Roads (1819).
As the result of a parliamentary inquiry in 1823 into the whole question of road-making, McAdam's
views were adopted by the public authorities, and in 1827 he was appointed Surveyor General of Metropolitan Roads in Great Britain. The accomplished Scot died November 26, 1836 in Moffat, Dumfriesshire.
Macadamization of roads did much to facilitate travel and communication. The process was quickly
adopted in other countries, notably the United States. In fact, the dignitaries who took part in the formal surrender ceremonies at the end of the Civil War traveled on a macadam road.
McAdam's original recipe called for a compacted subgrade of crushed granite or greenstone designed to support the load, covered by a surface of light stone to absorb wear and tear and shed water to
the drainage ditches. In modern macadam construction, crushed stone or gravel is placed on the compacted base course and bound together with asphalt cement or hot tar. A third layer to fill the interstices is then added and rolled.
Cement-sand slurry is sometimes used as the binder.
