DEVELOPMENT OF CRITERIA FOR USING THE SUPERPAVE GYRATORY COMPACTOR TO DESIGN AIRPORT HMA PAVEMENT MIXTURES

1. DEVELOPMENT OF CRITERIA FOR USING THE SUPERPAVE GYRATORY COMPACTOR TO DESIGN AIRPORT HMA PAVEMENT MIXTURES 2010 FAA Worldwide Airport Technology Transfer Conference John F. Rushing MarielyMejias Ray Brown

2. Acknowledgements • This work was sponsored by the Federal Aviation Authority (FAA)

3. Problem Statement • A need exists in the HMA airport paving community for criteria using the Superpave gyratory compactor.

4. Objective • To establish number of gyrations (NDesign) for Superpave gyratory compactor to design HMA mixtures for airport pavements

5. Superpave Gyratory Compactor • Product of the Strategic Highway Research Program • Selected to represent field compaction • Criteria based on data from in-service pavements • Currently used by most states for roadways • Interim guidance developed by Federal Aviation Administration for airport asphalt pavement mixtures in EB 59-A

6. Superpave Gyratory Compactor Types

7. What Makes a Compactor a Superpave Gyratory Compactor? ram pressure 600 kPa 150 mm diameter mold 30 gyrations per minute 1.25 degrees ?

8. Comparison of Number of Gyrations to Match Field Density for Two Compactors Brand 1 angle = 1.24 Brand 2 angle = 1.15

9. External vs Internal Angle

10. Dynamic Angle Verification Kit • Fits inside mold with mixture, thus can be used with any SGC • Dynamically measures the angle of gyration during compaction of sample • Can be performed with mix or without mix

11. Research Plan Flow Chart Aggregate Property Testing Perform Marshall Mix Design Design Aggregate Blends Determine Design Binder Content Compact Samples in Superpave Gyratory Compactor Determine Ndesign Values

12. Asphalt Mixture Test Factors • Maximum Aggregate Size • 1-inch max • ¾-inch max • ½-inch max • Aggregate Gradation • Coarse side of P-401 limits for each max aggregate size • Fine side of P-401 limits for each maximum aggregate size • Aggregate Type • Alabama Limestone • Arkansas Granite • Mississippi Chert Gravel • Aggregate Shape • 100% crushed aggregate • Aggregate containing 10% mortar sand

13. Project Summary • Determined design binder content for 52 HMA mixtures using 75-blow Marshall • If FAA requirements not met then the mix was not included in the study • Determined equivalent compaction levels for equal air void content in Superpave gyratory compactor

14. FAA HMA Mix Criteria • Stability, lbs 2150 minimum • Flow, 0.01 ins 10-14 • Air Voids, % 2.8-4.2 • VMA : 1 inch max mix 14 minimum ¾ inch max mix 15 minimum ½ inch max mix 16 minimum

15. Marshall Compaction • Marshall hand hammer • 75 blows • 4-in. mold • Stability and flow measurements • Design binder content selected at 3.5% air voids • If mix did not meet FAA criteria it was not used

16. Observations • Design binder content increased with: • Smaller maximum aggregate size • Higher percentage of crushed aggregate • Finer gradations

17. Superpave Gyratory Compaction • Pine AFGC125X Superpave Gyratory Compactor • 6 Inch Molds • Target Specimen Height – 115 mm • Ram Pressure – 600 kPa • Internal Angle of Gyration – 1.16o • Compacted to 125 Gyrations • Volumetric Measurements

18. Superpave Gyratory Compaction Mean = 69 Standard Deviation = 25

19. Implications of NDesign • If too LOW • Excess binder • Potential for rutting, flushing • If too HIGH • Insufficient binder • Difficult field compaction • Potential durability problems

20. Recommendations • Use Ndesign value of 70 gyrations in place of 75-blow Marshall compaction. UFGS spec actually specifies 75. • Use same gradation as presently specified in P-401 • Do not use Ninitialor Nmax requirements recommended by Superpave

21. Questions?