Since the enactment of the 1970 Clean Air Act many asphalt plants have been forced to install baghouse dust collectors. Often this dust is added to asphalt concrete mixtures. The dust can stiffen mixes, thereby making them hard to compact, or it can act as an extender, thus causing bleeding and tenderness. There are no accepted specification tests for controlling the stiffening or the extending effects of baghouse dust. A variety of simple test procedures were evaluated for possible use for specification or quality control purposes to control stiffening. The customary physical properties of the dust, such as pH, shape, and gradation, do not predict stiffening. Two types of test procedures--fractional voids and consistency--were correlated with stiffening as measured by the increase in viscosity or softening point caused by the addition of dust to asphalt cement. Fractional voids in dust-asphalt mixtures were calculated from the bulk volume of dust compacted with impact and vibratory compaction and by consolidation in fluid media. Consistency tests included the kerosene, balling and crumbling, and bitumin number tests. The best correlation with stiffening ratio was obtained from the fractional voids as determined from the dry impact compaction. This test procedure is acceptable for process control and acceptance procedures; the other test procedures are not acceptable. The best means of determining the stiffening effect is to determine the stiffening directly with capillary viscometry. However, before either the fractional void test or the direct measure of stiffening is included as a specification criteria for stiffening, they must be determined through correlation with field performance.

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 31-37
  • Monograph Title: Asphalt mixtures and performance
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00394927
  • Record Type: Publication
  • ISBN: 0309037506
  • Files: TRIS, TRB
  • Created Date: Nov 30 1985 12:00AM