The manufacture of coated roadstone demands the combination of a number of aggregates, sand and a filler (such as stone dust), in the correct proportions, heated, and finally coated with a binder, usually bitumen based or, in some cases tar, although tar was removed from BS4987 in 2001 and is not referred to in BSEN 13108/1.
The temperature of the finished product must be sufficient to be workable after transport to the final destination.
Countries have individual specifications stipulating how much of the raw material can be allowed from recycled asphalt.
The asphalt plant is mainly composed of cold aggregate supply system, drum dryer, coal burner, coal feeder, dust collector, hot aggregate elevator, vibrating screen, filler supply system, weighing and mixing system, Pollution Control Unit , asphalt storage, bitumen supply system.
All these components have characteristics that impact not only the overall quality of the asphalt but also the effect on the environment.