Since the implementation of Superpave asphalt mixtures in South Carolina, there have been concerns about the use of 4-in.-diameter Marshall specimens used in SC-T-70, Laboratory Determination of Moisture Susceptibility. These concerns are due to the increased coarse aggregate content in Superpave mixtures. This research project evaluated the use of 6-in.-diameter gyratory made specimens to observe whether they would yield similar and more repeatable Tensile Strength Ratio (TSR) results than the 4-in.-diameter specimens. The objective of this research was to compare the test results from the smaller diameter Marshall specimens with the larger diameter gyratory specimens for the TSR. The Marshall specimens (4 in.) and the gyratory specimens (6 in.) of the same mixes were used to determine if the test results reasonably compared. The results of this research were used to determine whether to revise SC-T-70 to include the use of 6-in. gyratory specimens for determining the wet conditioned strengths and TSR. The data obtained from the moisture susceptibility testing were evaluated by comparing the wet conditioned strength to the dry conditioned strength to determine a TSR value of the different size specimens. In addition to the wet conditioned strengths and TSR values, the samples were rated for visual stripping for fine and coarse aggregate within the specimens. Several specimens were tested to failure (without an anti-stripping agent) to determine if the different size specimens gave comparable results. A line of equality showed that the larger gyratory samples (without an anti-stripping agent) yielded higher TSR values probably due to the orientation of the material within the gyratory mold being less susceptible to moisture damage. For the samples with hydrated lime as an anti-stripping agent, the TSR results compared favorably. The results of this research will benefit the South Carolina Department of Transportation as well as the Asphalt Contractors in verifying and designing asphalt mixtures using a more accurate method of testing. Based on the research findings, it is recommended that all mixtures designed with the gyratory compactor have the TSR results determined using 95-mm-high, 6-in.-diameter gyratory specimens. It is also recommended that after one season of further mix design verification, if everything remains consistent with this research's findings, the minimum wet tensile strength requirement be increased from 65 psi to 70 psi and the minimum TSR requirement be increased from 85% to 90%. Additionally, SC-T-70 should be revised immediately to reflect these recommendations.

  • Corporate Authors:

    South Carolina Department of Transportation

    Silas N. Pearman Building, 955 Park Street
    Columbia, SC  United States  29202

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Hawkins, C W
  • Publication Date: 2004-12


  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 46 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00989199
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-SC-04-09,, Final Report
  • Contract Numbers: SPR-637
  • Created Date: Apr 12 2005 12:00AM