THE EFFECT OF AIR VOIDS ON THE TENSILE STRENGTH RATIO (WITH DISCUSSION)

Moisture damage of asphalt concrete pavements, often referred to as stripping, is a problem which has become very prevalent in recent years. Several different tests are used to determine the moisture sensitivity of an asphalt mix. Many states are using a test based on the Lottman procedure. Some states require a freeze-thaw conditioning (Lottman procedure) and other states require only the hot-water soak (Tunnicliff-Root procedure). These tests require that the specimens be compacted to a given level of air voids, +/-1%. The samples are grouped by air void content and then separated into two groups. One group is conditioned and the unconditioned group is used as the control. The tensile strength ratio (TSR) is the ratio of average tensile strength after conditioning to that before conditioning, expressed as a percent. Following this procedure requires a large number of samples. Also, significant variations can result between the TSRs determined for mixes having average air voids within the specified range. A study was conducted to determine how to minimize the number of samples required for testing and to reduce testing variation. Test results from over 200 Marshall samples were analyzed. Testing was conducted using eight different aggregate blends which included four limestones, a river sand and gravel, and a slag source. Three asphalt sources and five asphalt additives (from hydrated lime to polymers) were used. Samples were conditioned by either the Lottman freeze-thaw procedure or the hot-water soak. The boiling water test was used on selected material combinations. Data from an additional 186 granite mixes from Georgia were used in the calculations for precision. The results from the study indicate the following. The number of samples and TSR test variation can be reduced. The procedure involves making specimens at various air void contents and using statistical or graphical methods to interpret the tensile strength results. The TSR is a function of air voids. The Lottman procedure, with the freeze-thaw cycle, is more severe than the Tunnicliff-Root procedure that uses only a warm water soak. The precision of both methods is similar. The boiling water test results are biased against hydrated lime. A recommendation is made that moisture-damage specifications should be two-tiered. Along with the minimum TSR, a minimum conditioned tensile strength should be specified.

• Corporate Authors:

  Association of Asphalt Paving Technologists (AAPT)

  400 Selby Avenue, Suite I
  St Paul, MN  United States  55102
• Authors:
  • Dukatz Jr, E L
  • Phillips, R S
• Conference:
  • Association of Asphalt Paving Technologists Proc
• Publication Date: 1987

Language

• English

Media Info

• Features: Appendices; Figures; References; Tables;
• Pagination: p. 517-554
• Serial:
  • Volume: 56

Subject/Index Terms

• TRT Terms: Air voids; Asphalt mixtures; Graphics; Moisture content; Precision; Recommendations; Samples; Specifications; Statistical analysis; Test procedures; Variables
• Uncontrolled Terms: Graphical analysis; Moisture sensitivity; Tensile strength ratio
• Old TRIS Terms: Air voids content; Test results
• Subject Areas: Data and Information Technology; Highways; Materials; Research; I31: Bituminous Binders and Materials;

Filing Info

• Accession Number: 00739808
• Record Type: Publication
• Files: TRIS
• Created Date: Aug 29 1997 12:00AM