5Background SHRP A-001 Contract Development of Superpave Mix Design ProcedureGyratory Compactor ExperimentsConducted at Asphalt InstituteIncluded rotational speed, Ndesign, sensitivity experimentsComparison between prototype and production SGCLed to discovery of angle sensitivityTolerance of ±0.02 degrees
7Differences in SGCs – NATC Mixtures 8.07.06.05.0Air Voids, %4.03.02.01.00.0Prototype123Compactor
8Measurement of the Internal Angle of Gyration Significant Differences in Air VoidsDifference in Design AC Could be as Much as 0.8% Asphalt ContentAngle of GyrationAll Compactors set to 1.25° ExternallyWhat is the Internal Angle of Gyration?Frame compliance?
94. APPARATUSSuperpave Gyratory Compactor – … The compactor shall tilt the specimen molds at an external angle of 1.25°+0.02° or an average internal angle of 1.16°+ 0.02° in accordance with AASHTO T312. The compactor shall gyrate the specimens mold at a rate of gyrations per minute…4.1
10Internal Angle of Gyration Development of the Dynamic Angle Validator (DAV) or Angle Validation Kit (AVK)Wireless UnitDrop into mold either before or after adding mix
11Dynamic Angle Validator Dr. Kevin Hall, “Evaluating the Superpave Gyratory Compactor Internal Angle of Gyration Using Simulated Loading”, submitted to AAPT2005
13Internal Angle of Gyration DAVValidate Differences in SGCsDemonstrated that internal angle of gyration could be different even though external angle was the same.CalibrationPotentially time-intensiveUp to 1 day for a calibrationAffected by mixture stiffness?Requiring recalibration for different mix types
14IssueThe DAV procedure, although effective, is labor intensive and time consuming requiring up to a day for the required angle measurements and compactor calibration
15Forces Acting in a Mold During Gyratory Compaction
16Mechanical Simulation of an Asphalt Mixture – RAM RAM – Rapid Angle Measurement Device (Pine)
17RAM OperationsIncreasing Ring Diameter =Increasing Mix Eccentricity
18Mechanical Simulation of an Asphalt Mixture – HMS HMS – Hot-Mix Simulator (TestQuip)
19Purpose of Research Objectives Improve the determination and calibration of the dynamic internal angle of gyration for the Superpave gyratory compactor using mechanical mixture simulation devicesReduce time for calibrationImprove reproducibility between different labsRecommend revisions to AASHTO T312
20Research Plan – Task 1Determine the Effect of Mix Eccentricity on Internal Angle of GyrationSGC-ASGC-BMix eInternalAngleAcceptable Rangeof Internal Angle
21Research Plan – Task 2 Using a Wide Variety of Mixtures… What is the relationship between mixture eccentricity and stiffness?What is an “average” or representative mixture eccentricity?Is there a standard mixture eccentricity that can be used to minimize variation in the percentage of air voids in specimens produced by different SGCs?
22Research Plan – Task 3Using Mechanical Simulation Devices in the Calibration ProcessIssuesNecessity of heated molds?
23Frame Stiffness (Deg / N-m) Superpave Gyratory Compactor (SGC) Model Frame Stiffness Measures – RAM onlyTesting AgencyFrame Stiffness (Deg / N-m)Superpave Gyratory Compactor (SGC) ModelPine AFG125xPine AFG1Pine AFGB1 (Brovold)Troxler 4140Troxler 4141ServoPacUniv. of Arkansas (Stiffness Study)Univ. of Arkansas (RAM ILS)Univ. of Arkansas (RAM-DAV/HMS Study)Florida DOT (used by permission)InstroTek (used by permission)Mean ValueStandard DeviationN/ACoefficient of Variation (%)19.019.530.317.157.5