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 Mariely Mejias Ray Brown

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

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

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

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

Superpave Gyratory Compactor Types

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

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

External vs Internal Angle SGC Number Ext Angle Int Angle Brovold 11 1.27 1.15 Interlaken 1.24 0.95 Pine A 35 1.25 1.20 Pine B 10 1.23 Troxler A 1.05 Troxler B 5 1.06

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

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

Asphalt Mixture Test Factors Aggregate Type Alabama Limestone Arkansas Granite Mississippi Chert Gravel Aggregate Shape 100% crushed aggregate Aggregate containing 10% mortar sand 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

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

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

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

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

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

Superpave Gyratory Compaction Mean = 69 Standard Deviation = 25

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

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 Ninitial or Nmax requirements recommended by Superpave

Questions?