Methods to Evaluate Aggregate Coating for Asphalt Mixtures Produced at WMA Temperatures

In recent years, considerable progress has been made in implementing Warm Mix Asphalt (WMA) products to reduce production and compaction temperatures. One of the challenges in determining the allowable temperature reduction is quantifying effects of such reduction on the coating of aggregates. In current practice, a binder viscosity limit is used to select the proper mixing temperature. For WMA additives it is recognized that viscosity could be a misleading surrogate to measure coating and thus direct measure of coating at reduced mixing temperature is necessary. The current method for evaluating coating in HMA, AASHTO T195, involves visually identifying uncoated and partially coated particles. This method is not only time consuming, but is also found to introduce subjectivity in the results. This paper investigates two alternative methods to evaluate coating which are more objective and less time consuming: (a) an indirect water absorption method and, (b) a digital imaging analysis method. Asphalt mixtures compacted at four different temperatures were tested using the proposed coating evaluation methods, as well as the existing AASHTO method. It appears that the absorption technique can be used to quickly and reasonably evaluate coating in an objective manner. The results raise serious questions about the validity, objectivity, and repeatability of the AASHTO visual method. (A)


  • English

Media Info

  • Pagination: p. 225-38
  • Monograph Title: Proceedings of the Fifty-Seventh Annual Conference of the Canadian Technical Asphalt Association: Vancouver, British Columbia November 2012

Subject/Index Terms

Filing Info

  • Accession Number: 01494235
  • Record Type: Publication
  • Source Agency: Transportation Association of Canada (TAC)
  • Files: ITRD, TAC
  • Created Date: Sep 24 2013 12:57PM