Although a typical drum is as it is

Although a typical drum is as it is described earlier, numerous variations, as a result of continuous
development processes, have resulted over the years, specifically to improve the efficiency of
the heating process, and often to accommodate the use of recycled asphalt pavement (RAP) materials
(Figure 16.8). Two such developments are the concepts of the double-barrel drum and the
triple-barrel drum, which have outer “shells” that improve the heating process of aggregates and at
the same time cut down the potential of excessive oxidation of the asphalt binder–RAP materials.