used it will be appreciated that heating by microwave apparatus will result in consumption of a considerable quantity of electricity in the production of the asphalt however additional running costs incurred this way can to some measure be offset by the substantial decrease in electric power consumed by ancillary equipment normally used in an asphalt plant more particularly conventional plants making use of drum dryers for heating the aggregate will normally require a substantial electric motor to rotate the drum in which the aggregate is heated an additional motor to provide an air blast for operation of the oil burner used in the drum dryer as well as a substantial motor to operate cyclone and other separators and dust extractors needed to remove dust generated because of the necessary agitation of the aggregate during heating in a medium sized plant motors operating these apparatuses may have a total power consumption of the order of 350 kilowatts aside from this the conventional dryers together with dust extractors occupy a substantial area of plant which need not be provided by use of the invention these apparatuses are also costly and even with proper dust and combustion products extraction conventional plants still create very substantial environmental problems as well as the use of a microwave.