Evaluation of the Direct Tension Test and Critical Cracking Temperatures for Asphalt Binders in Kentucky (With Discussion)

In 2002, the Kentucky Transportation Cabinet (KTC) began evaluations of asphalt binders supplied in Kentucky to determine the efficacy of using the AASHTO MP-1a specification as an alternate means of specifying the low temperature grade of the asphalt binder. In the AASHTO MP-1a specification, the critical cracking temperature (CCT) is determined and compared to the required climatic grade. The KTC asked suppliers to provide monthly samples for testing for each grade supplied to Kentucky. Suppliers were asked to determine the CCT of their binders so that a direct comparison could be made between the KTC lab and the supplier’s lab. Four asphalt binder grades were provided for this study by five different producers. The four asphalt binder grades were: PG 58-22, PG 64-22, PG 70-22, and PG 76-22. Thirty-eight asphalt binder samples were evaluated in the study. In approximately 25% of the cases for each lab, the data indicated that the low temperature grade will change when using the CCT instead of the M320 grading. Considering the data from both labs, approximately 10% of all comparisons indicate a warmer grade than expected (i.e., -16 instead of -22) and approximately 10% of all comparisons indicate a colder grade than expected (i.e., -28 instead of -22). The data also indicated that the average CCT of the PG 76- 22 asphalt binders was lower than the average of the PG 58-22 asphalt binders, and considerably lower than the average of the PG 64-22 and PG 70-22 asphalt binders. Before implementing the AASHTO MP-1a specification, users should consider testing issues with the bending beam rheometer (BBR) and direct tension tester (DTT). Quality data checks are important to achieving an accurate, repeatable CCT value for an asphalt binder.

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  • English

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  • Accession Number: 01041386
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 30 2007 1:29PM