What is Macadam?
Macadam is a variety of road covering invented in the 19th century. The inventor, John Loudon McAdam, pioneered his technique as a replacement for dirt roads. Even though macadamized roads are rarely used in modern times, its influence is still seen in some forms of road construction. John McAdam was born in Scotland in 1756, and grew up to working in English road construction efforts around the city of Bristol. After several decades of work, McAdam published two treatises on the need for an improved road system using layered rocks. In 1816, as the surveyor on Bristol Turnpike, McAdam tested out his process for creating roads, called macadamizing. The original system used for macadam roads involved a triple layer of stone. The bottom two layers were comprised of hand-broken rocks laid to a depth of 8 in (20.3 cm) over a formation level called a subgrade. The top layer was much smaller rocks, made to be no more than 2 in (5 cm) thick. The entire road was then compacted and crushed toget
Macadam is a type of road construction pioneered by the Scotsman John Loudon McAdam in around 1820. It consisted of creating three layers of stones laid on a crowned subgrade with side ditches for drainage. The first two layers consisted of angular hand-broken aggregate, maximum size 3 inches (75 mm), to a total depth of about 8 inches (200 mm). The third layer was about 2 inches (50 mm) thick with a maximum aggregate size of 1 inch (25 mm). Each layer would be compacted with a heavy roller, causing the angular stones to lock together. http://en.wikipedia.
