An Overview of the Asphalt Mixture Performance Tester

2 Overview of AMPT Overview What is the AMPT? What does the AMPT do? What kind of samples do I test in the AMPT? How do I prepare these samples? How do I know if the AMPT is running properly? How do I know if my Dynamic Modulus data is any good? What do I do with the Data?

3 Overview of AMPT What is the AMPT? AMPT = Asphalt Mixture Performance Tester Formerly “SPT” The AMPT is a machine specifically designed for testing asphalt concrete materials and measuring the engineering properties of those materials

4 Overview of AMPT Why is the AMPT Important? 3 ways to test your paving materials… 1. Build a Highway $$$$$ 2. Build a Test Section $$$ 3. Do a Lab Test $

5 Overview of AMPT Why is the AMPT Important? Lab test gives complete characterization of stiffness of asphalt pavements over wide range of conditions Frequency of Loading Testing Temperatures Primary Material input for Mechanistic-Empirical (M-E) Pavement Design Predict Pavement Performance! Better Data = Better Prediction

6 Overview of AMPT

7 Critical Components Computer (Data Acquisition System) Test Chamber Environmental Chamber (Constant Temp) Confining Chamber (Constant Pressure) Simulates Overburden Pressure Bubble Chamber Check for Leaks Hydraulic Load System Applies Load to the Test Sample Bottom-Up

8 Overview of AMPT

9 Critical Components Confining Pressure System Driven by Compressed Air Temperature Control System Controls Chamber Temperature Actuator and Actuator LVDT Loads sample and reads sample location On-Specimen LVDT Measures Deformations around Specimen Perimeter

10 Overview of AMPT What Does the AMPT Do? Measures Critical Engineering Responses of Asphalt Concrete Multiple Tests Can be Performed Dynamic Modulus Flow Number Uni-Axial Fatigue

11 Overview of AMPT M-E Design Framework Traffic Climate Material Properties Pavement Structure Mechanical Analysis ,  Transfer Functions Performance Criteria Layer Stiffness: HMA Base Subgrade

12 Overview of AMPT Dynamic Modulus Mixture Stiffness and Visco-Elastic Response Can be used to Predict Performance Rutting Cracking MEPDG (Mechanistic-Empirical Design) Input Develop “MasterCurve”

13 Overview of AMPT Flow Number Repeated Load Permanent Deformation Axial Compressive Load of 0.1 sec every 1.0 sec Correlation to Rutting Resistance Practically – The number of cycles at which the rate of rutting dramatically increases Commonly Modeled with a Francken Model

14 Overview of AMPT

15 Overview of AMPT Uni-Axial Fatigue Testing New Development in AMPT Steel Platens glued to each sample end Repeated Fatigue Loading Bottom-Up Cracking Resistance

16 Overview of AMPT What Samples Do I Test? Samples Compacted with the Superpave Gyratory Compactor (SGC) AASHTO PP 60-10

17 Overview of AMPT Sample Specifications Mix Compacted to a Target Height 170 mm – Minimum 150 mm Diameter Specimens Target Air Void Level 7 ± 0.5% on Cut Sample Typical – Not Specified AASHTO R30 Aging (Short-Term) Optional

18 Overview of AMPT Sample Specifications Samples must then be cored to testing diameter 100 to 104 mm Cut off sample ends to appropriate height 150 ± 2.5 mm Check End Flatness and Perpendicularity Feeler Gauges Flatness < or = 0.5 mm Perpendicularity < or = 1.0 mm

Sample Preparation

20 Overview of AMPT Sample Preparation Glue Studs to Side of Sample for Seating of LVDT Mounts

21 Overview of AMPT Sample Preparation Place Membrane Over Sample for Confined Testing

22 Overview of AMPT Sample Testing Dynamic Modulus and Flow Number Testing AASHTO TP79-10

23 Overview of AMPT Temperature Specimen Temp (°C) Time from Room Temp 25°C (hrs) Time from Previous Test Temp (hrs) -10Overnight 4 4 or Overnight Samples must be conditioned at appropriate temperature prior to testing Dummy Sample with Thermocouple (New)

24 Overview of AMPT Sample Testing Add LVDTs and Compensating Springs

25 Overview of AMPT Temperatures and Frequencies Properties of AC – Time/Temperature Dependent Fully Characterize Stiffness High Temperature depends on Binder PG 35 o C for PG 58-XX or softer 40 o C for PG 64-XX to PG 70-XX 45 o C for PG 76-XX or stiffer

26 Overview of AMPT

27 Overview of AMPT Is My AMPT Running Properly? Tuning Calibration Verification

28 Overview of AMPT Tuning Adjusts the performance properties of the servo- hydraulic system to minimize the error between load and response Closed-Loop System Minimizes the difference between command and feedback Why do you need tuning? THE SAMPLE IS PART OF THE SYSTEM!!! HMA stiffness changes by a factor of 100 over the range of temperatures tested in the AMPT

29 Overview of AMPT Tuning

30 Overview of AMPT Tuning Values to Adjust P.I.D. Proportional (P-Gain) Integral (I-Gain) Derivative (D-Gain) Factory Parameters on Newer Machines are Fairly Robust Only Tweak in the Event of Data Quality Errors or Highly Specialized Mixes

31 Overview of AMPT Calibration CALL A CERTIFIED PROFESSIONAL!! Items to Calibrate Load Cell Pressure Transducer (Sensor) Actuator Displacement System Specimen Mounted Deformation System (LVDT) Temperature Measuring System

32 Overview of AMPT Verification Check to make sure everything is working properly Proving Ring

33 Overview of AMPT The Proving Ring Run the proving ring for system verification A metal Ring of known modulus If running this sample gives you the correct modulus, all the system components are working properly

34 Overview of AMPT The Proving Ring When to Run the Proving Ring… Weekly for System Verification Keeps a Log Helps you track down any problems that occur When you think you are getting goofy data

35 Overview of AMPT Data QC List of Parameters in AASHTO TP Parameters ensure quality dynamic modulus test Important for Person operating machine

36 Overview of AMPT What Do I Do With the Data? Dynamic Modulus Make a Mastercurve AASHTO PP61-10 Relative Comparisons of Mixes Normalized for Temperature Enter Data for M-E Design Flow Number Relative Mix Comparisons

38 Overview of AMPT More Info… AASHTO Specs AMPT Website NHI Training Course 2 Day Short Course Held at NCAT Contact FHWA for more info Jeff Withee

39 Overview of AMPT Questions?