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Superpave Gyratory Compaction Requirements for FAA’s Hot Mix Asphalt Specification

Superpave Gyratory Compaction Requirements for FAA’s Hot Mix Asphalt Specification. D. Christensen, T. Bennert, R. McQueen, and H. Brar FAA Airport Technology Transfer Conference, April 2010. Introduction.

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Superpave Gyratory Compaction Requirements for FAA’s Hot Mix Asphalt Specification

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  1. Superpave Gyratory Compaction Requirements for FAA’s Hot Mix Asphalt Specification D. Christensen, T. Bennert, R. McQueen, and H. Brar FAA Airport Technology Transfer Conference, April 2010

  2. Introduction • Ongoing research on relationship between 75-blow Marshall and Superpave gyratory compaction • Develop recommendations for N-design • Help establish specifications using gyratory compaction • Verification testing

  3. Mixes

  4. Mixes

  5. General Approach • Verify Marshall design • Prepare gyratory specimens at three compaction levels • 50, 75, 100 • 75, 100, 125 • Plot air voids as a function of gyrations • Determine N-equivalent

  6. General Approach • Two independent laboratories • Advanced Asphalt Technologies, LLC • Soiltek • Three binders • PG 64-22 • PG 76-22, SBS modified • PG 76-22, Novaphalt (PE modified) • Full replication

  7. Determination of N-equivalent

  8. Results: N-equivalent, part 1

  9. Results: N-equivalent, part 2

  10. Results: Statistics • Average N-equivalent 62 gyrations, but high degree of variability • Two significant effects • Laboratory (p = 0.001) • Mix type (p < 0.001) • Insignificant effects • Binder type/grade (p = 0.51) • Binder content (p = 0.62) • Air voids marginal (p = 0.16)

  11. Variability in N-equivalent • Variability between mixes not surprising • Marshall and gyratory compaction effected differently by aggregate size, shape, texture • Significant variability between laboratories due to differences in verified Marshall designs • In repeating verifications, found more uniform results

  12. Comparison with Other Studies • Cooley et al., AAPTP Project 04-03 on Superpave Design • Average N-equivalent of 49 • Recommended values of 50, 65 and 80 depending on tire pressure • Rushing, Army ERDC Study • Average N-equivalent of 69 • Rounded to 70 • We recommend using 70 gyrations

  13. AC Contents:JMF vs. 70 Gyrations, Part 1

  14. AC Contents:JMF vs. 70 Gyrations, Part 2

  15. Asphalt Binder Contents • AAT average asphalt content for 70-gryation mixes: 5.43 • Soiltek average asphalt content for 70 gyration mixes: 5.55 • JMF (Marshall) average asphalt content: 5.15 • Results fairly consistent

  16. How Will Change to 70-Gyration Design Effect Performance? • Rutting, fatigue resistance • Overall or average effect • Slight change in overall binder content? • Slight change in typical gradation? • Changes in variability of performance • Variability in binder content • Variability in gradation

  17. Performance Testing • Rut resistance • Flow number • Asphalt pavement analyzer (APA) modified for high pressure • Fatigue test using uniaxial (push-pull) fatigue test and continuum damage analysis

  18. Preliminary Results of Performance Testing: Flow Number Test, PG 64

  19. Preliminary Results of Performance Testing: Rut Resistance • Similar level of rut resistance for Marshall and gyratory designs • Variability similar • Most mixes made with PG 64-22 showing performance consistent with highway traffic levels of 3 to 10 million ESALs

  20. Example of Fatigue Test

  21. Conclusions • Average N-equivalent for HMA mixes with good performance record was found to be 62 • Rounded up to 70 for consistency with ERDC recommendations • Significant variability in N-equivalent among mixes • Currently evaluating performance in laboratory tests

  22. Acknowledgments • FAA • Co-authors • Lab personnel at AAT and Soiltek

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