Refinement of the Hot-Mix Asphalt Ignition Method for High-Loss Aggregates

This study evaluated four methodologies for determining the asphalt content of mixtures containing high loss aggregates in the ignition furnace. The methodologies tested were the standard method using the Thermolyne furnace (control), the Troxler NTO Infrared furnace, the Ontario Method using the Thermolyne furnace and a Tempyrox glass cleaning oven. Six aggregate sources with high ignition furnace aggregate correction factors were obtained from around the country: four dolomites, a basalt, and a serpentinite/chlorite. Calibration factors were determined for each method at optimum asphalt content. Additional samples were then tested at optimum plus 0.5 percent asphalt content and the measured asphalt content calculated using the correction factor determined for that method/aggregate source. The Tempyrox Pyro-Clean oven, commonly used for cleaning laboratory glassware, produced the lowest aggregate correction factors. The correction factors are consistent with results from thermogravimetric analysis. The standard method and the Ontario method, both using the Thermolyne ignition furnace produced the smallest bias or error in measured asphalt content. The standard deviation of the corrected asphalt contents for these high loss sources was higher than the within-lab standard deviation reported for AASHTO T308. The only exception was the Alabama source using the standard method. The Ontario Method and Tempyrox Oven generally reduced the variability of asphalt content measurements for high loss aggregates. None of the methods evaluated statistically reduced aggregate breakdown on the NMAS and 4.75 mm sieves. The Ontario method significantly reduced, but did not eliminate aggregate breakdown on the 0.075 mm sieve. A gradation correction factor, developed from the same samples used to determine the correction factor for asphalt content, greatly reduced the measured biases, in most cases to less than 1 percent. The Ontario method is recommended for immediate implementation for determining the asphalt content by the ignition method for high loss aggregates. The method consists of using an altered end point of less than 1 gram change over three consecutive minutes and using the highest test temperature of 538, 480 or 450°C (1,100, 896, or 842°F) that produces a correction factor less than 1 percent. The current AASHTO procedure specifies a 0.01 percent change over three consecutive minutes at either 538 or 482° (1100 or 900 °F).

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Appendices; CD-ROM; Figures; References; Tables;
  • Pagination: 34p

Subject/Index Terms

Filing Info

  • Accession Number: 01006342
  • Record Type: Publication
  • Report/Paper Numbers: NCAT Report 05-05, ALDOT Research Project 930-491
  • Files: NTL, TRIS, STATEDOT
  • Created Date: Oct 19 2005 3:48PM