the productive capacity of a drum heater and mixer for asphalt paving composition intended for processing recycled materials can be increased substantially by spraying a curtain of water vertically into the pathway of the raw material as it falls into the drum intake and before any substantial contacts with heated gases or flame and by spraying a curtain of water into the pathway of the heated gases and flame for controlling the temperature profile across the interior of the drum . the latter curtain of water is disposed at about thirty - five degrees to a plane perpendicular to the drum axis . additional sprays of water downstream from the angular curtain of water may be supplied if necessary .