makadam

Makadam refers to a method of road construction and the resulting road surface named after the Scottish engineer John Loudon McAdam. Introduced in the early 19th century, the technique relied on layers of crushed, angular stone that were carefully graded and compacted to form a hard, well-drained surface. McAdam rejected binding material in the base and instead achieved stability through the interlock of the stones and thorough compaction. A typical macadam pavement consisted of a substantial base course of large stones, one or more intermediate courses of smaller stones, and a wearing course of fines or screenings that was rolled to a smooth finish. The porous surface allowed water to drain rapidly, reducing frost damage and ruts compared with dirt roads.

In the late 19th and early 20th centuries, tar was introduced as a binder, producing tar-macadam or tarmacadam, a pivotal development that paved the way for modern asphalt paving. The term tarmac is still used in some contexts, while "macadam" in many languages has come to denote paved surfaces in general. In contemporary practice, the original macadam method influenced various forms of base preparation for asphalt or concrete pavements, though modern roads frequently rely on asphalt or concrete as binding materials rather than dry stone layers.