Bituminous Macadam (BM) is a base course in which coarse aggregates are mixed with a bituminous binder. The mix is open-graded with 20-25 per cent voids. Two gradings are used :
Nominal size of aggregates 40 mm Thickness of layer 75-100 mm Binder content : 3.1-3.4 per cent
Nominal size of aggregates 19 mm Thickness of layer 50-75 mm Binder content : 3.3 to 3.5 per cent
The binder used is 60/70 penetration grade bitumen. The mixing is done in a hot-mix plant and the laying is done by a paver finisher. Rolling is done by a 80-100 kN vibratory roller.