Wind tunnel tests under constant temperature conditions indicated that bitumen crude source and processing can have a significant effect on the rate of evaporation of a volatile diluent from a bitumen film. The hydrocarbon nature of the diluent is of lesser importance. The photo oxidation skin formed where a film is exposed to sunlight has an important retarding effect and a seal cover aggregate also retards the process. In a sprayed seal, transfer of diluent from the bitumen to the atmosphere is controlled by its rate of diffusion within the binder film and its rate of diffusion as vapour through the stagnant air between the cover aggregate particles. Traffic compaction retards the process by forming a mosaic of the cover aggregate particles and increasing the thickness of the binder films between them. A model based on the two diffusion processes was developed and fitted to the wind tunnel test data. This model and its application to the estimation of evaporation rates in sprayed seals during the first few days after laydown are described. Long term evaporation was not considered as this will be very dependent on both the rate of traffic compaction and the frequency with which the photo oxidation skin is formed and subsequently disrupted by water and mechanical action. For some road trial seals laid under warm conditions on a medium trafficked road near Melbourne, only about one fifth of the cutter originally present (6 per cent of the cutback bitumen) was estimated to have been lost three days after laydown. For two seals laid under cooler conditions with 11 per cent of cutter in the binder, the loss was much less (4 and 10 per cent). This work, which indicates cutter is lost more slowly than was generally believed, has important implications for practice. Too high a cutter content in seals subject to traffic under warm conditions can lead to flushing and loss of surface texture. A particularly serious situation is where sealing is carried out at the end of the warm season and high cutter contents are used. Much of this cutter will remain at the start of the next warm season and the surfacing will be susceptible to flushing of the binder or loss of cover aggregates. The ISBN of the microfiche version is 0-86910-380-6. (Author/TRRL)

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    Melbourne, Victoria  Australia 
  • Authors:
    • Dickinson, E J
  • Publication Date: 1989-5

Media Info

  • Features: References;
  • Pagination: 27 p.
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00499030
  • Record Type: Publication
  • Source Agency: ARRB
  • ISBN: 0-86910-379-2
  • Report/Paper Numbers: ARR 157
  • Files: ITRD, TRIS, ATRI
  • Created Date: Sep 30 1990 12:00AM