Talk:Un-sprung cart

Road metal
What is road metal ???

Peter Horn 20:04, 13 May 2006 (UTC)


 * Road metal or just 'metal', is broken stone used in forming the artificial, hard surface of a road. The word used to be almost interchangeable with 'ballast' but the two have become separated so that 'metal' has come to be associated with the macadam surface. Macadam was invented by the road engineer, John Loudon McAdam and consists of 'metal' bound together with a matrix of some sort. Nowadays, bitumen is used as the matrix. Once it used to be tar and before that, in McAdam's own time, a mixture of sand and clay. This last was very dusty in summer and without a good foundation of stone, was not very durable. The tar matrix was introduced initially to solve the dust problem.
 * For S.C.Brees, (Illustrated Glossary of Practical Architecture and Civil Engineering, (1852)), 'Ballast' was the predominant term with 'metal' as an alternative but now 'ballast' is the "metal" used in making concrete or, without a matrix, in forming the road bed of a railway. (RJP 10:07, 16 May 2006 (UTC))