Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results (2021)

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171   A T T A C H M E N T Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing

172 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing • AASHTO Designation: TP xxx-xx • American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001

Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 173   Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing AASHTO Designation: TP xxx-xx 1. SCOPE 1.1. This standard practice describes a procedure for the long-term conditioning of uncompacted hot mix asphalt (HMA) for performance testing to simulate the aging that occurs over the service life of a pavement. The procedure for long-term conditioning in performance testing is preceded by a procedure for short-term conditioning in mixture mechanical property testing in AASHTO R 30. 1.2. This standard may involve hazardous material, operations, and equipment. This standard does not purport to address all 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 use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards:  PP 3, Preparing Hot Mix Asphalt (HMA) Specimens by Means of the Rolling Wheel Compactor  PP 60, Preparation of Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC)  R 30, Mixture Conditioning of Hot Mix Asphalt (HMA)  T 312, Preparing and Determining the Density of Hot Mix Asphalt Specimens by Means of the Superpave Gyratory Compactor  T 316, Viscosity Determination of Asphalt Binder using Rotational Viscometer 2.2. Other Documents:  NCHRP Research Report 871: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction, 2018.  Draft Final Report for NCHRP Project 09-54, Extension: Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction, 2020.

174 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results 3.1. Definitions: 3.2. Enhanced Integrated Climatic Model (EICM) – A one-dimensional coupled heat and moisture flow model that can be used to determine pavement temperature at any depth of interest. 4. SUMMARY OF PRACTICE 4.1. A mixture of binder and aggregate is conditioned in a forced-draft oven at 95°C after prior short-term conditioning for mixture mechanical property testing according to R 30. The duration of conditioning at 95°C is selected to reflect the time, climate, and pavement depth for a given pavement location in the United States using the climatic aging index (CAI). The long-term conditioned loose mixture samples are prepared for maximum specific gravity (Gmm) testing and then compacted for subsequent performance testing. 5. SIGNIFICANCE AND USE 5.1. The long-term performance of HMA can be predicted more accurately by using conditioned test samples rather than unconditioned samples. The long-term mixture conditioning in the performance testing procedure is designed to simulate the aging that the mixture will undergo in service. 6. APPARATUS 6.1. Oven: A forced-draft oven, thermostatically-controlled with horizontal air flow and capable of maintaining any desired temperature setting from room temperature to 176°C within ± 3°C. 6.2. Thermometers: Thermometers having a range from 50°C to 260°C and readable to 1°C. 6.3. Miscellaneous: A metal pan for heating aggregate, a shallow metal pan for the short-term conditioning of uncompacted HMA, a 1-inch tall metal pan for the long-term conditioning of uncompacted HMA, a metal spatula or spoon, timer, and gloves for handling hot equipment. 7. HAZARDS 7.1. This standard involves the handling of HMA that can cause severe burns if it contacts skin. Follow safety precautions to avoid burns. 3. TERMINOLOGY

Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 175   8.1. The long-term conditioning for performance testing applies to laboratory-prepared loose mixtures that have been subjected to short-term conditioning as part of the mixture mechanical property testing procedure described in R 30. 8.2. Determine the required long-term conditioning duration that reflects the desired field aging in terms of age, climate, and depth using Equation (1). 1601.167 0.426 1 0.0437 i N T oven i t CAI d e (1) where toven = required oven aging duration at 95°C to reflect field aging (days); CAI = climatic aging index; d = depth below pavement surface greater than 0.6 cm (cm); Ti = pavement temperature obtained from the EICM at the depth of interest at the hour of interest, i (kelvin); 8.2.1. Break down any large chunks of asphalt mixtures in the short-term aged loose mixture sample, taking care to avoid fracturing the aggregate, so that the clusters of the fine aggregate portion are not larger than the nominal maximum aggregate size (NMAS). This step needs to be performed shortly after short-term aging to ensure that the asphalt mixture is sufficiently soft to be separated into pans for oven aging. If an HMA sample is not sufficiently soft to be separated manually, then place it in a pan and warm it in an oven until it can be separated as described. 8.2.2. Apportion the short-term aged loose mixture into several pans such that each pan has a relatively thin layer of loose mix, approximately equal to the mixture NMAS. 8.2.3. Place the pans that contain mixture in a forced-draft oven at 95°C ± 3°C for the duration determined by Equation (1). Place the pans on different shelves so that the pans are arranged vertically within the oven as much as possible. Ensure that adjacent pans do not overlap. 8.2.4. Rotate the pans to different shelves at four evenly-spaced time intervals during the long-term conditioning period so that each pan has similar exposure to heat and air flow at different locations within the oven. 8.2.5. After long-term conditioning, remove the conditioned mixtures from the oven and mix all of the mixtures together in order to obtain a uniform mixture. 8.2.6. Allow the mixture to cool to room temperature. The long-term conditioned loose mixture sample is now ready for compaction or subsequent testing as required. 8.3. Preparing Specimens from Loose HMA 8.3.1. Specimens Compacted Using the Superpave Gyratory Compactor 8. LONG-TERM MIXTURE CONDITIONING PROCEDURE

176 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results 8.3.1.1. Compact the specimens in accordance with PP 60. Cool the test specimens at room temperature for 16 ± 1 hour. Note 1. Extrude the specimen from the compaction mold after cooling for 2 to 3 hours. Note 2. Specimen cooling usually is scheduled as an overnight step. Cooling may be accelerated by placing the specimen in front of a fan. 8.3.2. Specimens Compacted Using the Rolling Wheel Compactor 8.3.2.1. Compact the specimens in accordance with PP 3. 8.3.2.2. Cool the test specimens at room temperature for 16 ± 1 hour. 8.3.2.3. Remove the slab from the mold and saw or core the required specimens from the slab. 9. REPORT 9.1. Report the binder grade, binder content (to nearest 0.1 percent), and the aggregate type and gradation, if applicable. 9.2. Report the following long-term conditioning information for the performance testing conditions, if applicable: 9.2.1. Long-term mixture conditioning temperature in laboratory (nearest 1°C); 9.2.2. Long-term mixture conditioning duration in laboratory (nearest 5 min); and 9.2.3. Laboratory compaction temperature (nearest 1°C). 10. KEYWORDS 10.1. Conditioning; hot mix asphalt; long-term conditioning. APPENDICES (Nonmandatory Information) X1. LABORATORY AGING DURATION MAPS X1.1. The CAI values for various locations in the United States were calculated, as described in Section 9, using hourly pavement temperature history data obtained from the EICM to provide an overview of the proposed laboratory aging durations for various climates, field aging durations, and depths. X1.2. The CAI values and measured durations that are needed to match field aging correlate linearly in a one-to-one relationship. Thus, the CAI values represent the

Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 177   required duration at 95°C that is needed to match the field aging for a given pavement temperature history and depth. X1.3. Laboratory aging durations were calculated for three field ages: 4 years, 8 years, and 16 years. For each field age, the laboratory aging durations were determined at three depths: 6 mm, 20 mm, and 30 mm, and rounded to the nearest day. X1.4. Figure X1.1 shows the CAI-determined loose mixture aging durations at 95°C that are required to match 4, 8, and 16 years of field aging at a depth of 6 mm. Figure X1.1 demonstrates that climate has a significant effect on laboratory aging duration that is required to match a given field age. (a) 6 mm Depth (a)

178 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results Figure X1.1-Required oven aging duration at 95°C to match level of field aging 6 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. (b) 6 mm Depth (c) 6 mm Depth

Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 179   X1.5. Figure X1.2 shows the CAI-determined loose mixture aging durations at 95°C that are required to match 4, 8, and 16 years of field aging at a depth of 20 mm. A comparison between the laboratory aging durations presented in Figure X1.1 and Figure X1.2 demonstrates that significantly shorter laboratory aging durations are required to match the field aging at a depth of 20 mm compared to 6 mm, indicating that the temperature gradient and diffusion in pavements significantly affect oxidation levels. X1.6. A depth of 20 mm represents a reasonable depth for the evaluation of surface layer asphalt mixtures because it better reflects bulk behavior within a pavement structure than nearer the surface and avoids the effect of ultraviolet oxidation. (b) 20 mm Depth (a)

180 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results Figure X1.2-Required oven aging duration at 95°C to match level of field aging 20 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. (b) 20 mm Depth (c) 20 mm Depth

Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 181   X1.7. Figure X1.3 shows the CAI-determined loose mixture aging durations at 95°C that are required to match 4, 8, and 16 years of field aging at a depth of 30 mm. The results demonstrate that considerably shorter aging durations are required to simulate aging at a depth of 30 mm compared to depths of 20 mm and 6 mm, thus indicating the presence of a significant oxidation gradient with depth near the surface of the pavements. In Figure X1.3, the required aging duration of zero days in a few cold northern states indicates that long-term aging at 30 mm below the pavement surface in these cold regions is not significant enough to require long- term oven conditioning to mimic field conditions. X1.8. Based on the results presented in the draft NCHRP Project 9-54 report, the researchers concluded that long-term aging does take place below a depth of 30 mm, but does not change appreciably below that depth. Consequently, the evaluation of asphalt mixtures that have been prepared to match field aging at a depth of 30 mm or greater could be useful for evaluating intermediate and base asphalt layers. (c) 30 mm Depth (a)

182 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction: Phase III Results Figure X1.3-Required oven aging duration at 95°C to match level of field aging 30 mm below pavement surface for (a) 4 years of field aging, (b) 8 years of field aging, and (c) 16 years of field aging. (b) 30 mm Depth (c) 30 mm Depth

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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