THE USE OF GYRATORY COMPACTION FOR ASPHALT MIX DESIGN IN AUSTRALIA

This paper describes how gyratory compaction was adopted for asphalt mix design in Australia at about the same time as it was in the United States, and two Australian based gyratory compaction devices were also developed. Testing indicated that the aggregate packing of gyratory specimens more closely simulated field compaction than the previously used Marshall method. To more fully understand the compaction process, tests were carried using out oil/aggregate mixtures instead of bitumen/aggregate mixtures. This permitted variables associated with compaction temperature and cooling of the specimens to be eliminated. This was done by choosing an oil of such a viscosity that the compaction curves of aggregate/oil mixtures compacted at room temperature were identical to those for the corresponding aggregate/bitumen mixtures compacted at 150C. Use of oil/aggregate mixtures allowed measurement of the amount of aggregate degradation, which occurred during the compaction process. An important feature of gyratory compactors is that a plot of air voids or density against compaction cycles can be produced. Such curves contain important information concerning the internal friction of the aggregate particles and thus their resistance to deformation (rutting). Tests using oil/aggregate mixtures showed a relationship between 1-cycle voids content and resistance to rutting, as measured using a wheel tracker, for a very wide range of mixes. This suggests that 1-cycle, or possibly 10-cycle, voids may be a useful indicator of rutting resistance in the design of conventional, bitumen-bound asphalt mixes. The refusal density test has been proposed as the basis of an alternative mix design procedure. Testing using a mix consisting of smooth, rounded particles showed that, while it met refusal density requirements, it was extremely prone to rutting. The results of the study suggested that refusal density by itself is inadequate for ensuring rutting resistance in a mix.

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  • English

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  • Accession Number: 00964280
  • Record Type: Publication
  • ISBN: 087659229X
  • Files: TRIS, ATRI
  • Created Date: Oct 3 2003 12:00AM