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93 APPENDIX D Proposed Standard Practice for Measuring Properties of Warm Mix Asphalt (WMA) for Performance Analysis Using the Mechanistic-Empirical Pavement Design Guide Software

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94 Proposed Standard Practice for Measuring Properties of Warm Mix Asphalt (WMA) for Performance Analysis Using the Mechanistic-Empirical Pavement Design Guide (MEPDG) AASHTO Designation: PP XX-XX 1. SCOPE 1.1. This standard presents procedures measuring engineering properties of warm mix asphalt (WMA) for performance analysis using the Mechanistic-Empirical Pavement Design Guide (MEPDG). The Level 1 inputs to the MEPDG that can be measured with this standard are: (1) dynamic modulus master curve, and (2) low temperature creep compliance and (3) low temperature tensile strength. Specimen fabrication procedures that replicate various WMA processes are also included. 1.2. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to its use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 35, Superpave Volumetric Mixture Design T 166, Bulk Specific Gravity of Compacted Asphalt Mixtures Using Saturated Surface-Dry Specimens T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures T 269, Percent Air Voids in Compacted Dense and Open Asphalt Mixtures T 312, Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor T 322, Determining the Creep Compliance and Strength of Hot-Mix Asphalt (HMA) Using the Indirect Tensile Test Device TP 60, Preparing Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC)

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95 TP 61, Developing Dynamic Modulus Master Curves for Hot Mix Asphalt Using the Asphalt Mixture Performance Tester (AMPT) TP 79, Determining the Dynamic Modulus and Flow Number for Hot Mix Asphalt (HMA) Using the Asphalt Mixture Performance Tester (AMPT). 2.2. Other Documents: ASTM D 3549, Thickness of Height of Compacted Bituminous Paving Mixture Specimens Equipment Specification for the Simple Performance Test System, Version 3.0, Prepared for National Cooperative Highway Research Program (NCHRP), October 16, 2007 Mechanistic-Empirical Pavement Design Guide, Interim Edition: A Manual of Practice, AASHTO, Washington DC, 2008 3. TERMINOLOGY 3.1. Warm Mix Asphalt (WMA) Warm mix asphalt refers to asphalt concrete mixtures that are produced at temperatures approximately 50 F (28 C) or more cooler than typically used in the production of hot mix asphalt. The goal with warm mix asphalt is to produce mixtures with similar strength, durability, and performance characteristics as hot mix asphalt using substantially reduced production temperatures. 3.2. Air voids (Va) The total volume of the small pockets of air between the coated aggregate particles throughout a compacted paving mixture, expressed as a percent of the bulk volume of the compacted paving mixture. 3.3. Creep The time-dependent part of strain resulting from stress. 3.4. Creep compliance The time-dependent strain divided by the applied stress. 3.5. Dynamic Modulus |E*|, the absolute value of the complex modulus calculated by dividing the peak-to-peak stress by the peak-to-peak strain for a material subjected to a sinusoidal loading. 3.6. Dynamic Modulus Master Curve A composite curve constructed at a reference temperature by shifting dynamic modulus data from various temperatures along the log frequency axis. 3.7. Tensile strength The strength shown by a specimen subjected to tension. 3.8. Voids in the mineral aggregate (VMA) The volume of the intergranular void space between the aggregate particles of a compacted paving mixture that include the air voids and the effective binder content, expressed as a percent of the total volume of the specimen.

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96 3.9. Voids filled with asphalt (VFA) The percentage of the VMA filled with binder (the effective binder volume divided by the VMA). 4. SUMMARY OF THE PRACTICE 4.1. This practice describes methods for preparing WMA test specimens and testing methods to measure the dynamic modulus, low temperature creep compliance, and low temperature strength of WMA mixtures. 5. SIGNIFICANCE AND USE 5.1. The engineering properties of WMA measured using this practice are Level 1 inputs for WMA layers for pavement performance analysis using the MEPDG. 5.2. With the measured engineering properties and the MEPDG, project specific estimates of the performance of pavements incorporating WMA layers can be made. 5.3. The dynamic modulus is used in the MEPDG stress-strain analysis, rutting model, and fatigue cracking model. 5.4. The low temperature creep compliance and strength are used in the MEPDG thermal cracking model. 6. APPARATUS 6.1. Specimen Fabrication Equipment Equipment for fabricating dynamic modulus test specimens as described in AASHTO TP 60. 6.2. Dynamic Modulus Test System A dynamic test system meeting the requirements of Equipment Specification for the Simple Performance Test System, Version 3.0. 6.3. Indirect Tensile Test System A low temperature indirect tensile test system meeting the requirements of AASHTO T 322. 7. DYNAMIC MODULUS 7.1. Specimen Preparation 7.1.1. Prepare two 100 mm diameter by 150 mm high test specimen.

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97 7.1.2. Prepare test specimens in accordance with AASHTO TP 60, except mixture preparation shall be as specified in the WMA Appendix to AASHTO R 35, and short-term oven aging shall be 2 hours at the proposed compaction temperature. 7.1.3. The target air void content for the dynamic modulus specimens should be representative of the in-place air void content required by the agency specifications. 7.2. Dynamic Modulus Testing 7.2.1. Test each dynamic modulus specimen at the temperatures and frequencies specified in AASHTO TP 61. 7.2.2. Conduct dynamic modulus tests in accordance with AASHTO TP 79. 7.3. Data Analysis 7.3.1. Analyze the resulting data and prepare a dynamic modulus master curve in accordance with AASHTO TP 61. Note 1 A Microsoft Excel workbook "MASTERSOLVER2.1.xls" was developed in NCHRP Project 09-29 to perform this analysis. 7.3.2. From the fitted dynamic modulus master curve, compute the dynamic modulus at the following temperatures and frequencies for use in the MEPDG software. A total of 30 dynamic modulus values should be calculated. Temperatures Frequencies -10, 4.4, 21.1, 37.8, and 54.4 C 25, 10, 5, 1, 0.5, and 0.1 Hz (14, 40, 70, 100, 130, F) 7.4. Report the following: 7.4.1. Mixture identification. 7.4.2. Target air voids and the actual air voids for the specimens tested. 7.4.3. VMA and VFA of each specimen tested. 7.4.4. Average VMA and VFA for the specimens tested. 7.4.5. Measured dynamic modulus and phase angle data for each specimen at each temperature/frequency combination. 7.4.6. Average measured dynamic modulus and phase angle at each temperature/frequency combination.

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98 7.4.7. Coefficient of variation of the measured dynamic modulus data at each temperature/frequency combination. 7.4.8. Standard deviation of the measured phase angle data at each temperature/frequency combination. 7.4.9. Reference temperature. 7.4.10. Parameters of the fitted master curve (Max, , , , and Ea). 7.4.11. Goodness of fit statistics for the fitted master curve (Se, Sy, Se/Sy, R2). 7.4.12. Plot of the fitted dynamic modulus master curve as a function of reduced frequency showing average measured dynamic modulus data. 7.4.13. Plot of shift factors as a function of temperature. 7.4.14. Plot of average phase angle as a function of reduced frequency. 7.4.15. Tabulated temperature, frequency, and dynamic modulus for input into MEPDG. 8. LOW TEMPERATURE COMPLIANCE AND STRENGTH 8.1. Specimen Preparation 8.1.1. Compact three 150 mm diameter by 115 mm high gyratory specimens in accordance with AASHTO T 312 to a void content that is 1 percent higher than the target test specimen air void content. The target test specimen air void content should be representative of the in-place air void content required by the agency specifications. 8.1.2. Prepare a companion sample of loose mix meeting the sample size requirements of AASHTO T 209. 8.1.3. Mixture preparation shall be as specified in the WMA Appendix to AASHTO R 35, and short-term oven aging shall be 2 hours at the proposed compaction temperature. 8.1.4. To simulate long-term aging, condition the gyratory specimens and the companion loose mix sample in accordance with Sections 7.3.4 through 7.3.6 of AASHTO R 30. 8.1.5. Saw one 50 mm thick IDT specimen from the middle of each gyratory specimen. 8.1.6. Determine the maximum specific gravity of the companion long-term oven aged loose mix sample in accordance with AASHTO T 209. Record the maximum specific gravity of the mixture.

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99 8.1.7. For dense- and gap-graded mixtures, determine the bulk specific gravity of the test specimen in accordance with AASHTO T 166. Record the bulk specific gravity of the test specimen. Note 2 When wet sawing methods are used, measure the immersed mass followed by the surface dry mass followed by the dry mass to minimize drying time and expedite the specimen fabrication process. 8.1.8. For open-graded mixtures, determine the bulk specific gravity of the test specimen in accordance with Section 6.2 of AASHTO T 269. Record the bulk specific gravity of the test specimen. 8.1.9. Compute the air void content of the test specimen in accordance with AASHTO T 269. Record the air void content of the test specimen. 8.1.10. Using calipers, measure the diameter of each test specimen along axes that are 90 apart. Record the average diameter to the nearest 1 mm. 8.1.11. Measure the height of each test specimen in accordance with Section 6.1.2 of ASTM D 3549. Record the average height to the nearest 1 mm. 8.2. Creep and Strength Testing 8.2.1. Instrument each test specimen and perform creep tests on each test specimen at temperatures of 20, -10, and 0 C in accordance with AASHTO T 322. A total of 9 creep tests will be performed. 8.2.2. Record the load, horizontal deformation on each face, and vertical deformation on each face at 0.1 sec intervals for the first 10 sec, then at 1 sec intervals from 10 to 100 sec. 8.2.3. Remove the specimen mounted instrumentation and perform a strength test at 10 C in accordance with AASHTO T 322. A total of 3 strength tests will be performed. 8.2.4. Determine the corrected tensile strength of each specimen using the following relationship: S corrected = 0.78 S uncorrected + 38 where: Scorrected = corrected tensile strength for thermal cracking analysis, psi 2 Pmax S uncorrected = hd Pmax = peak load during the strength test, lb h = thickness of the test specimen, in d = diameter of the test specimen, in

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100 Note 3 The corrected strength provides a good estimate of the AASHTO T 322 first failure tensile strength of the specimen without the risk of damage to the specimen mounted instrumentation. 8.2.5. Reduce the creep test data for each temperature in accordance with Section 13 of AASHTO T 322 and compute the average creep compliance as a function of loading time. 8.3. Report the following: 8.3.1. Mixture identification. 8.3.2. Target air voids and the actual air voids for the specimens tested. 8.3.3. VMA and VFA of each specimen tested. 8.3.4. Average VMA and VFA for the specimens tested. 8.3.5. Tabulated values of the average compliance versus time for 20, -10, and 0 C. 8.3.6. Corrected tensile strength at 10 C. 9. KEYWORDS 9.1. Warm Mix Asphalt (WMA), MEPDG, Dynamic modulus, creep compliance, tensile strength