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Affiliated with the Local History Network of the State Historical Society of Iowa, and the Iowa Museum Association.
MACADAM. Macadam was once a popular road-surfacing material made of crushed rock and oil. The surface was used first on Iowa Street in the late 1800s.
The invention of the construction method belonged to John Loudon McAdam (Ayr, Ayrshire, Scotland, Sept. 21, 1756--Moffat, Dumfriesshire, Scotland). McAdam had been appointed surveyor to the Bristol Turnpike Trust in 1816, where he decided to remake the roads under his supervision with crushed stone bound with gravel on a firm base of large stones. A camber, making the road slightly convex, caused rainwater to rapidly drain off the road rather than penetrate and damage the road's foundations. This construction method, the greatest advance in road construction since Roman times, became known as "macadamisation", or, more simply, "macadam".
The macadam method spread quickly. In the 1830s the first macadam road in North America, the National Road, was completed and most of the main roads in Europe were macadamized by the end of the nineteenth century.
McAdam's road building technology was applied to roads by other engineers. One of these engineers was Richard Edgeworth, who filled the gaps between the surface stones with a mixture of stone dust and water, providing a smoother surface for the increased traffic using the roads. 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. Roads constructed in this manner were described as "macadamized."
With the advent of motor vehicles, dust became a serious problem on macadam roads. The area of low air pressure created under fast-moving vehicles sucked dust from the road surface, creating dust clouds and a gradual unraveling of the road material. This problem was approached by spraying tar on the surface to create tar-bound macadam.
Macadam roads were the forerunners of the bitumen-based binding that was to become tarmacadam. The word tarmacadam was shortened to the now familiar tarmac. The first tarmac road to be laid was in Paris in 1854.
"Macadam," Wikipedia, Online: https://en.wikipedia.org/wiki/Macadam