Martin Eastburn wrote in news:s43Tw.145571
:

Macadam is a premix and is hot spread and rolled. Chip #1 and #2
is oil and spread of chip rock. Dry rock is spread on top or onto
the old surface with hot oil tar sprayed on top or on the pavement.

Technically, "macadam" is just a crushed rock surface. If
tar is added then it's "tarmac".

In modern usage, tho, "macadam" and "tarmac" have become
synonomous, since no-one uses plain crushed rock any more
(pneumatic tires tend to pull crushed rock apart, whereas
steel wheels and horseshoes compacted it further; hence the
replacement of macadam with tarmac following the advent of
the automobile).

John