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Innovations in HMA Performance Testing. John D’Angelo D’Angelo Consulting, LLC johndangelo@dangeloconsultingllc.com. Canadian User Producer Group for Asphalt Moncton 2009. Materials Testing. The HMA is tested in some fashion to simulate the real world.
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Innovations in HMA Performance Testing John D’Angelo D’Angelo Consulting, LLC johndangelo@dangeloconsultingllc.com Canadian User Producer Group for Asphalt Moncton 2009
Materials Testing • The HMA is tested in some fashion to simulate the real world. • The tests go from simple to sophisticated. • From Empirical to Fundamental.
What is a performance test? • It is a test that directly or indirectly relates to the performance characteristics of the material. • These tests can be Empirical or Fundamental or a combination of both. • Empirical tests relate results to past experience. • Fundamental tests relate stress, strain, and temperature to past performance.
APA Sample Small sample with loading very unlike the real world. Must be correlated over a narrow range of conditions and material to the real world.
Hamburg Tester Unrealistic loading. Again must be correlated over a narrow range of conditions and material to the real world.
Next Generation of Performance Testers • New tests have a closer relationship to fundamental properties of the mix. • Measured material properties tied to performance models to estimate distress.
SST Device Developed during SHRP to evaluate mix performance. Expensive, complicated, difficult to interpret results.
Simple Performance Tests (SPTs) Development 9-19 Identification of SPTs and Protocol Development (Complete) 9-29 Equipment Specification and Development for SPTs (Active) 9-33A Mix Design Manual for Hot Mix Asphalt (Active)
AC Mix Performance Tester The test can evaluate the rutting and fatigue response of the AC mix. The equipment is relatively inexpensive and easy to use. Test results are inputs for the Mechanistic Empirical Pavement Design Guide.
IPC ServoPac Sample Preparation • Superpave Gyratory Compactor • 180 – 190 mm Ht. Va = 9.5%
Sample Preparation Test Specimen Va = 8%
Performance Tests E* – Dynamic Modulus Fn – Flow Number (Repeated Load) Ft – Flow Time (Static Load)
s 0 = E s * = dynamic stress e 0 0 e = recoverable axial strain 0 Phase Angle 75 ~ 125 µε Load Displacement Loading Frequency Dynamic Modulus E*
b k b k 2 f æ ö 3 f 2 æ ö 1 1 3 ç ÷ = b N k ç ÷ ç ÷ f f 1 e 1 è ø E è ø t b b b ; ; Calibration Factors f f f 1 2 3 Fatigue Cracking Model
HMA Performance Tester • Dynamic Creep • Simulates Traffic Load • Loading on 0.1 sec • Load off for 0.9 sec • Repeat sequence • Cumulative axial strains recorded
Flow Number Test (Fn) Dynamic Creep Simulates Traffic Load Loading – 0.1 sec Rest – 0.9 sec
Repeated Load Test Results • Laboratory test run at 53.4°C
Repeated Load Axial Test • Actual test parameters are still being developed. • Parameters are based on stress conditions in the pavement.
Beam Fatigue Test Test provides loss of modulus with load repetitions. This is empirically compared to field performance. Test is time consuming to run and loading relation to the real world questionable.
Axial Fatigue Test New push pull test allows fatigue testing in the AMPT with inputs to the VEPCD model.
IDT Testing Indirect Tensile test- Used for low temperature properties of the mix Expensive, easy to setup and run. Use Creep Strain and Strength
Use of the BBR device to test mix Volume of material tested may not be representative Asphalt mixtures contain aggregate sizes larger than smallest dimension of beam Main obstacle: the use of smaller size specimens that may not capture overall behavior of pavement
Use of the BBR for Low Temperature Mix Testing Previous research at University of Minnesota suggested use of simpler test method based on creep tests of thin beams in three-point bending Thin beams (6.25 x 12.5 x 100mm) can be used to investigate effect of surface aging, microcracking, and compaction on mechanical properties of asphalt pavements
Predict Lowest Temperature Creep Stiffness Loading Procedure
Performance Testing • We have new tools that provide results closer to the real world. • New modeling procedures allow us to do a better job of interpreting the results. • We can do a better job of estimating performance.
