The Federal Highway Administration (FHWA) initiated an evaluation of the dryer drum mixing process in which cold aggregates are blended on belts according to formula, and fed into the dryer drum where penetration grade asphalt is introduced. The mixture is discharged onto a conveyor and elevated to a hot storage bin and then to the hauling equipment. The correct blending of aggregate is accomplished (at the cold feed source) by mechanical feeders and good stockpiling techniques. The evaluation process was directed primarily toward answering two questions concerning quality: (1) was the mixture being harmed by exposure to the direct flame in the dryer? and (2) would the equipment consistantly produce a uniform product? Answers to the first question were obtained by determining the degree of hardening of asphalt through the various stages of the process. The tests performed are detailed. The uniformity of asphalt and the uniformity of aggregate gradation is discussed. In some plants, the changes in the rate of flow of asphalt were controlled automatically by the aggregate belt scale system to match the variation in aggregate flow rates. The standard deviations of extracted asphalt content for the plants investigated in this study were compared with standard deviations of conventional batch plants. Aspects of compaction are discussed and the need is indicated for research on the effect of water as an aid to compaction. Advantages in the use of this process include a reduction of many pieces of operating equipment and a reduction of fuel consumption. Variations in plant design and operation can affect production and cost. The control of dust emissions from the exhaust stack is expected to be easier than with a conventional plant.

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  • Corporate Authors:

    Department of Transportation

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Granley, E C
    • Olsen, R E
  • Publication Date: 1973-9

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Filing Info

  • Accession Number: 00262076
  • Record Type: Publication
  • Files: TRIS, USDOT
  • Created Date: Oct 22 1974 12:00AM