Determination of Optimum Gradation for Resistance to Permeability, Rutting and Fatigue Cracking

Permeability has become a major concern in recent years with the implementation of Superpave mixtures. It is important to have pavements that possess characteristics of low permeability which would minimize the effects due to moisture damage and increase the service life of pavements. The permeability of mixtures mainly depends on percent air voids, nominal maximum size of aggregate and the type of gradation. At any given air void content or nominal size, the permeability depends on the size and continuity of air voids. The nature of gradation influences the size and continuity of voids. So the aggregate gradation was optimized for lower permeability without compromising the fatigue and rutting performance of mixtures. The application of the Bailey method of gradation analysis showed that the permeability is greatly influenced by the aggregates of #4, #8 and #16 sizes. Guidelines were proposed for the mix designers to arrive at aggregate blends with low or high permeability. The guidelines recommend a low proportion of #4 size aggregates and high proportion of #8 and #16 size aggregates for low permeable mixtures. The higher proportions of 1/2 in. and 3/8 in. aggregates can be used to ensure the discontinuity of smaller voids. These guidelines were validated by permeability tests on a separate set of newly developed gradations. The gradation and the binder content of the field cores were used to compact a reference mixture using the Superpave Gyratory compactor in the laboratory. This reference mixture, the "unmodified gradation", is used for permeability tests and performance analysis. Four new mixtures were designed for both 12.5 mm and 9.5 mm mixtures in such a way that two mixtures had lower permeability and the other two mixtures had higher permeability than the coefficient of the unmodified gradation. Performance evaluation tests were conducted on field cores, the unmodified gradations, low permeable mixtures and high permeable mixtures before and after moisture damage. The performance evaluation tests included the Frequency Sweep Test at Constant Height, the Repeated Shear Test at Constant Height and the Asphalt Pavement Analyzer Test. The performance analysis indicated that the permeability of the mixtures directly influences their performance in terms of fatigue life, rutting life and moisture susceptibility. The low permeable mixtures have higher fatigue life and rutting life than the high permeable mixtures. The low permeable mixtures have lower percent of reduction in service life due to moisture damage than the high permeable mixtures.

• Record URL:
  • https://connect.ncdot.gov/projects/research/pages/ProjDetails.aspx?ProjectID=2003-10
• Corporate Authors:

  North Carolina State University, Raleigh

  Department of Civil Engineering
  Raleigh, NC  United States  27695-7908

  North Carolina Department of Transportation

  Research and Analysis Group, 1 South Wilmington Street
  Raleigh, NC  United States  27601

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Khosla, N Paul
  • Sadasivam, S
• Publication Date: 2005-2-28

Language

• English

Media Info

• Media Type: Web
• Edition: Final Report
• Features: Figures; Photos; References; Tables;
• Pagination: 141p

Subject/Index Terms

• TRT Terms: Aggregate gradation; Air voids; Binder content; Core samples; Guidelines; Laboratory tests; Mechanical fatigue; Mix design; Moisture damage; Pavement cracking; Performance tests; Permeability; Rutting; Service life; Superpave
• Uncontrolled Terms: Gyratory compaction; Moisture susceptibility; Nominal maximum aggregate size
• Subject Areas: Design; Geotechnology; Highways; Materials; I31: Bituminous Binders and Materials; I36: Aggregates;

Filing Info

• Accession Number: 01003750
• Record Type: Publication
• Report/Paper Numbers: FHWA/NC/2004-12
• Files: TRIS, USDOT, STATEDOT
• Created Date: Sep 2 2005 4:10PM