Minerals, Metals, and Other Materials

Man-Made Products

How were early macadam roads different from modern paved roads?

Macadam roads developed originally in England and France and are named after the Scottish road builder and engineer John Louden MacAdam (1756–1836). The term “macadam” originally designated road surface or base in which clean, broken, or crushed ledge stone was mechanically locked together by rolling with a heavy weight and bonded together by stone dust screenings that were worked into the spaces and then “set” with water. With the beginning of the use of bituminous material (tar or asphalt), the terms “plain macadam,” “ordinary macadam,” or “waterbound macadam” were used to distinguish the original type from the newer bituminous macadam. Waterbound macadam surfaces are almost never built now in the United States, mainly because they are expensive and the vacuum effect of vehicles loosens them. Many miles of bituminous macadam roads are still in service, but their principal disadvantages are their high crowns and narrowness. Today’s roads that carry very heavy traffic are usually surfaced with very durable portland cement.


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