Long-Term Field Performance of Warm Mix Asphalt Technologies (2017)

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69 Appendix D presents test methods in AASHTO stan- dard format for the fatigue/thermal monotonic testing of asphalt mixtures using the indirect tensile (IDT) test (Sec- tion D1) and the fatigue/thermal monotonic testing of asphalt binders using the dynamic shear rheometer (DSR) (Section D2). A P P E N D I X D Proposed Test Methods Section D1 Standard Method for Fatigue/Thermal Monotonic Testing of Hot Mix Asphalt Using Indirect Tensile Test Device AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method provides procedures for determining the fatigue and/or thermal cracking resistance of asphaltic mixtures under constant displacement rate loading using an indirect tensile (IDT) test device. The IDT strength, fracture energy, and fracture work density are obtained from the stress-strain curve or load-displacement curve. 1.2. These procedures may apply to test specimens that have a maximum aggregate size of 38 mm or less. The test method can be used with specimens fabricated following AASHTO T 312 or with field cores extracted from in-service asphalt pavements. 1.3. The values stated in SI units are to be regarded as standard. 1.4. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 225, Diamond Core Drilling for Site Investigation 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 Indirect Test Device

70 2.2. ASTM Standards: D5361, Standard Practice for Sampling Compacted Bituminous Mixtures for Laboratory Testing 2.3. Other Documents: Wen, H., and Y. R. Kim. Simple Performance Test for Fatigue Cracking and Validation with WesTrack Mixtures. Transportation Research Record, No. 1789, Transportation Research Board, National Research Council, Washington D.C., 2002, pp. 66-72. Wen, H. Use of fracture work density obtained from indirect tensile testing for the mix design and development of a fatigue model. International Journal of Pavement Engineering, 2012, DOI:10.1080/10298436.2012.729060. 3. TERMINOLOGY 3.1. Definitions: 3.1.1. IDT strength – The horizontal tensile strength shown by a specimen from an indirect tensile test, Pa. 3.1.2. Fracture energy – The area under the horizontal stress-horizontal strain curve up to the peak stress from an indirect tensile test, Pa. 3.1.3. Fracture work – The area under the vertical load-vertical displacement curve from an indirect tensile test, F·mm. 3.1.4. Fracture work density – Fracture work divided by the volume of the specimen, Pa. 4. APPARATUS 4.1. An IDT test system, loading device, deformation measurement devices, and environmental chamber shall be employed in accordance with AASHTO T 22. 5. SUMMARY OF TEST METHOD 5.1. This standard describes the procedures for determining the IDT strength, fracture energy, and fracture work density values for fatigue and/or thermal cracking analyses. 5.2. The IDT test is conducted by applying a constant rate of vertical displacement (or ram movement) to failure of the specimen. 5.3. The test specimens used in this test may be fabricated in accordance with AASHTO T 312 or may be obtained from field cores. The specimens shall be cored and cut to an appropriate size: 100 mm or 150 mm in diameter and approximately 38 mm in thickness. 6. SIGNIFICANCE AND USE 6.1. This test method is intended to evaluate the fatigue and/or thermal cracking resistance of asphalt mixtures in terms of IDT strength, fracture energy, and fracture work density. These parameters may be used to characterize the fatigue and/or thermal cracking performance of asphalt mixtures and may correlate with field performance as well. 7. SAMPLING 7.1. Laboratory-compacted specimens – Prepare a minimum of three replicate laboratory-compacted specimens with 4 percent air void content in accordance with AASHTO T 312. Use a suitable core drill and sawing machine to cut specimens into an appropriate shape 100 mm or 150 mm in diameter and approximately 38 mm in thickness.

71 7.2. Roadway specimens – Sampling of roadway specimens should refer to ASTM D5361 or AASHTO T 225. The diameter of the specimens shall be 100 mm. The thickness shall be at least two times the nominal maximum aggregate size (NMAS). Note 1 – The thickness of the specimens used in this test shall be at least two times the NMAS in order to represent the mechanical properties of the overall asphalt mixture. A specimen that is too thin should be flagged and considered with caution. 8. SPECIMEN PREPARATION 8.1. Saw both sides of the test specimens to provide smooth, parallel surfaces for mounting the measurement gauges. The thickness of each specimen shall be approximately 38 mm. For roadway specimens, the thickness of the specimen should be at least two times the NMAS. 8.2. Determining Specimen Thickness and Diameter – Determine and record the thickness and diameter of each specimen using a measuring ruler or caliper to the nearest 0.1 mm. 8.3. Determining the Bulk Specific Gravity – Determine the bulk specific gravity of each specimen in accordance with AASHTO T 166. 8.4. Determining the Air Void Content – Determine the air void content of each specimen in accordance with AASHTO T 269. Note 2 – The maximum specific gravity value is required to calculate the air void content of a specimen. It shall be obtained from the mix design or from the specimens after conducting fracture tests. 8.5. Specimen Drying – Allow each specimen to dry at room temperature to a constant mass before testing. 8.6. Selecting the Specimens – Select three specimens that have air void contents at 4 percent ±0.5 percent. 8.7. Mounting Displacement Transducers – Attach four gauge points with epoxy to each flat face of the specimen. On each flat face of the specimen, two gauge points shall be placed along the vertical axis and two along the horizontal axis with center-to-center spacing of 50.8 mm. Mount the linear variable differential transducers (LVDTs) on the gauge points. Figure D1-3 shows the test set-up for a specimen. Note 3 – Mounting LVDTs onto the specimen is needed only if the fracture energy is to be determined. Skip Section 8.7 if only the IDT strength or fracture work is to be determined. 9. SELECTION OF PROCEDURE 9.1. Follow Procedure A in Section 10 if the fatigue property of a mixture is to be tested. Follow Procedure B in Section 11 if the thermal cracking property of a mixture is to be obtained. 10. TESTING PROCEDURE A (FATIGUE) 10.1. Specimen Installation – Place the specimen on the center of the pedestal and then connect and adjust the electronic measuring system until clear signals are presented. The sampling rate shall be at least 100 data points per second. Note 4 – The sampling rate may be adjusted up to 200 data points per second for more accurate data acquisition, if the device allows. 10.2. Condition the specimen at 20°C in the environmental chamber. A dummy specimen with a thermometer inserted may be used to monitor the specimen temperature. Once the specimen temperature of 20°C ±0.5°C is achieved, the test may be started.

72 10.3. Zero the electronic measuring system and apply a load to the specimen at a rate of 50.8 mm/min of ram movement. 10.4. Record the load, ram displacement, and vertical and horizontal LVDT readings for both sides of the specimen during the test. Do not stop the test until the load decreases to zero. Note 5 – The LVDTs shall be protected during the fracture test in such a manner that a rubber tube is used to wrap both ends of the LVDTs to avoid damage. Blocks may be placed at each side of the specimen without contact to prevent the broken specimen halves from falling against each other and stretching the LVDTs. 11. TESTING PROCEDURE B (THERMAL) 11.1. Determine the appropriate low temperature to be used for testing as follows: For mixtures made with binder grades PG XX-34 or softer: -20°C For mixtures made with binder grades PG XX-28 or PG XX-22, or mixtures for which the binder grade is unknown: -10°C For mixtures made with binder grades PG XX-16 or harder: 0°C For mixtures subjected to severe age hardening: increase the test temperature by 10°C 11.2. Specimen Set-up – Follow the same procedure as described for Procedure A in Section 10. 11.3. Condition the specimen at the test temperature in the environmental chamber. A dummy specimen with a thermometer inserted may be used to monitor the specimen temperature. Once the specimen temperature (±0.5°C) is achieved, the test may be started. 11.4. Zero the electronic measuring system and apply a load to the specimen at a rate of 2.54 mm/min of ram movement. 11.5. Record the load, ram displacement, and vertical and horizontal LVDT readings for both sides of the specimen during the test. Do not stop the test until the load decreases to zero. Note 6 – A specimen 100 mm in diameter is recommended for the thermal cracking test because a specimen 150 mm in diameter may not break easily at a low temperature due to the capacity of the testing machine. 12. CALCULATIONS 12.1. IDT Strength 12.1.1. Calculate the IDT strength value for each specimen as shown in Equation (D1.1): Eq. (D1.1) where SIDT = IDT strength, Pa; Pmax = maximum load observed for specimen, N; d = diameter of specimen, mm; and t = thickness of specimen, mm. 12.2. Fracture Work 12.2.1. Plot the load-vertical displacement curve as shown in Figure D1.1.

73 Figure D1.1. Load-vertical displacement curve obtained from IDT fatigue test. 12.2.2. The fracture work is calculated as the area beneath the load-vertical displacement curve. The total area is calculated approximately as the sum of the trapezoidal areas between each data point until the load decreases to zero. Thus, the fracture work value is calculated as shown in Equation (D1.2). Eq. (D1.2) where W f = fracture work, N . mm; Pi = load observed at each point, N; and δi = ram (vertical) displacement corresponding to Pi, mm., 12.3. Fracture work density 12.3.1. Calculate the fracture work density value for each specimen as shown in Equations (D1.3) and (D1.4). Eq. (D1.3) Eq. (D1.4) where W d = fracture work density, Pa; V = volume of the specimen, mm3; and 12.4. Fracture Energy 12.4.1. Calculate the horizontal strain εh as shown in Equations (D1.5) and (D1.6). 0 2000 4000 6000 8000 10000 12000 0.00 5.00 10.00 15.00 20.00 Lo ad , N Vertical Displacement, mm Fracture Work

74 Eq. (D1.5) Eq. (D1.6) where εh = horizontal strain; ν = Poisson’s ratio; U(t) = averaged horizontal deformation of both sides of specimen, mm; V(t) = averaged vertical deformation of both sides of specimen, mm; and α1, α2, α3, γ1, γ2, γ3, γ4 = coefficients presented in Table D1.1. Table D1.1. Coefficients in Equations (D1.5) to (D1.6) Specimen α1 α2 α3 γ1 γ2 γ3 γ4 100 mm 4.580 1.316 3.341 12.4 37.7 0.471 1.57 150 mm 3.673 1.154 3.192 8.48 25.6 0.373 1.18 12.4.2. Calculate the horizontal stress σh as shown in Equation (D1.7). Eq. (D1.7) where h = horizontal stress, Pa; and P(t) = vertical load, N. 12.4.3. Plot the stress-strain curve as shown in Figure D1.2. Figure D1.2. Stress-strain curve obtained from IDT fatigue test. 12.4.4. The fracture energy is calculated as the area beneath the horizontal stress-horizontal strain curve up to the maximum horizontal stress. For the subsequent data points, the area under the curve is calculated as the sum of the trapezoidal 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 1800000 0 0.02 0.04 0.06 0.08 0.1 0.12 H or iz on ta l s tre ss , P a Horizontal strain Fracture Energy areas between each data point until the maximum shear stress ( max, εf) is reached, so that the total area is the fracture energy, which is calculated as shown in Equation (D1.8).

75 Eq. (D1.8) where Ef = fracture energy, Pa; σi = horizontal stress at point i, Pa; σi+1 = horizontal stress at point i + 1, Pa; εi = horizontal strain at point i, and εi+1 = horizontal strain at point i + 1. 13. REPORT 13.1. Report the following, if known: 13.1.1. Sample identification. 13.1.2. Air void or bulk specific gravity. 13.1.3. IDT strength to the nearest 0.1 kPa. 13.1.4. Fracture work density to the nearest 0.1 kPa. 13.1.5. Fracture energy to the nearest 0.1 kPa. 14. PRECISION AND BIAS 14.1. Precision – The research required to develop precision estimates has not been conducted. 14.2. Bias – The research required to establish the bias of this method has not been conducted. 15. KEYWORDS 15.1. Asphalt mixture, fatigue cracking, thermal cracking, fracture work density, fracture energy, indirect tensile strength 16. APPENDICES 16.1. Sample and IDT device set-up. 16.1.1. The IDT device and test set-up are shown in Figure D1.3.

76 Figure D1.3. Indirect tensile test set-up.

77 Section D2 Standard Method for Fatigue/Thermal Monotonic Testing of Asphalt Binders Using Dynamic Shear Rheometer AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method covers the determination of an asphalt binder’s resistance to fatigue cracking and/or thermal cracking under a constant shear rate of loading using a dynamic shear rheometer (DSR). 1.2. The values stated in SI units are to be regarded as standard. 1.3. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 315, Standard Test Method for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) M 320, Performance-Graded Asphalt Binder R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) R 29, Grading or Verifying the Performance Grade (PG) of an Asphalt Binder T 40, Sampling Bituminous Materials T 315, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) T 240, Effect of Heat and Air on Rolling Film of Asphalt (Rolling Thin-Film Oven Test) T 164, Standard Method of Test for Quantitative Extraction of Asphalt Binder from Hot-Mix Asphalt (HMA) T 170, Standard Method of Test for Recovery of Asphalt Binder from Solution by Abson Method T 319, Quantitative Extraction and Recovery of Asphalt Binder from Asphalt Mixtures T 315, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) 2.2. ASTM Standards: D8, Standard Terminology Relating to Materials for Roads and Pavements D1856, Standard Test Method for Recovery of Asphalt from Solution by Abson Method D5404/D5404M-12, Standard Practice for Recovery of Asphalt from Solution Using the Rotary Evaporator 2.3. Other Documents: Wen, H., and S. Bhusal. 2013. Toward Development of a New Thermal Cracking Test Using the Dynamic Shear Rheometer. Journal of Testing and Evaluation, Vol. 41, No. 3, pp. 425–432. 3. TERMINOLOGY 3.1. Definitions

78 3.1.1. Definitions of the terms used in this practice may be found in ASTM D8 or as determined from common English usage, or combinations of both. 3.2. Definitions of terms specific to this standard include those for fracture energy and fracture strain. 3.2.1. Fracture energy – The area underneath the shear stress versus shear strain curve up to the peak stress, kPa. 3.2.2. Failure strain – The strain at the maximum stress in the stress-strain curve, mm/mm. 4. APPARATUS 4.1. The DSR test system consists of parallel metal plates, an environmental chamber, a loading device, and a control and data acquisition system. This test system shall meet the requirements of AASHTO T 315. 4.1.1. Test Plate: Stainless steel or aluminum plate with smooth ground surfaces. A 4-mm test plate is used in this test. Figure D2.1 presents details regarding the 4-mm test plate. Location A B C Dimension 4 ± 0.02 mm ≥ 4.0 mm ≥ 3.5 mm Figure D2.1. Plate dimensions (4-mm test plate) . Note 1 – The 4-mm test plate is used in this test because some asphalt binders may be too stiff to generate an obvious stress-strain curve. Due to the low capacity of the DSR and the use of highly aged asphalt binder, a 4-mm test plate is recommended for testing. 4.1.2. Specimen Mold – The overall dimensions of the silicon rubber mold that is used to form asphalt binder test specimens may vary, but the thickness shall be greater than 5 mm. For a 4-mm test plate with a 1.75-mm gap, a mold cavity that is approximately 4 mm in diameter and 2 mm deep shall be used. 4.1.3. Epoxy – General-purpose epoxy may be sufficient with five minutes of curing time and a temperature range from −51°C to 82°C.

79 5. HAZARDS 5.1. Standard laboratory precautions should be used in handling the hot asphalt binder when preparing the test specimens. 6. SUMMARY OF TEST METHOD 6.1. A sample is prepared using a 4-mm parallel plate geometry with a 1.75-mm gap setting. The sample is tested in monotonic shear mode using a constant shear rate to load the sample continuously until peak shear stress is achieved and the sample has yielded. 7. SIGNIFICANCE AND USE 7.1. This test method is intended to evaluate the fatigue cracking resistance of asphalt binder in terms of fracture energy or the thermal cracking resistance in terms of failure strain. Fracture energy may be used to characterize the fatigue properties of different asphalt binders at the intermediate temperature in the stress-strain curve. Failure strain may be used to indicate the ability of the asphalt binder to stretch at a low temperature and to indicate field thermal cracking. 8. SELECTION OF PROCEDURE 8.1. Procedure A presented in Section 9 shall be used if the fatigue property of an asphalt binder is to be tested. Procedure B in Section 10 shall be used if the thermal cracking resistance of an asphalt binder is to be obtained. 9. PROCEDURE A (FATIGUE) 9.1. Sample preparation – The sample is prepared by pouring hot liquid asphalt into silicone rubber molds that are approximately 4 mm in diameter by 2 mm deep. 9.2. DSR preparation – A 1.7-mm gap is used in the test. The test is conducted at 20°C. Precondition the spindle that is 4 mm in diameter and the plate at 20°C for 10 minutes before zeroing the gap. Lift up the spindle and zero the gap. Then, condition the spindle and plate at 30°C for 10 minutes by adjusting the water bath temperature. 9.3. Sample installation – Lift up the spindle and immediately remove any water on the spindle and plate using a clean dry paper towel. Paste a drop of epoxy to both the protuberant end of the spindle and to the plate and then zero the gap as soon as possible. Lift up the spindle again and put the binder sample on the protuberant end of the plate. Use a heated spatula to trim the sample before starting the test. The Appendix shows the test set-up. Note 2 – The use of epoxy is to ensure the adequate adhesion between the asphalt binder and the plate and the spindle. The epoxy is a general-purpose type (Section 4.1.3). 9.4. Test protocol – The test is performed at the temperature of 20°C with a constant shear strain rate that should be determined beforehand. The selection of an appropriate shear strain rate is crucial to ensuring a stress-strain curve with an obvious peak stress. The shear strain rate should be chosen to fall within the range shown in Table D2-1 in terms of an asphalt binder with a high performance grade (PG). Both stress (τ, Pa) and strain (γ, mm/mm) are recorded at a sampling rate of two data points per second. The test is stopped after the peak stress is achieved. Check whether the asphalt binder has debonded from the plate or spindle after the completion of the test. If debonding has occurred, then this result shall not be used. Three replicates are recommended.

80 Table D2.1. Determination of shear strain rate (fatigue) High PG range (76, 82) (70, 76) (64, 70) (52, 64) Shear strain rate range, s-1 0.025 – 0.75 0.05 – 2.5 0.075 – 3 1 – 3 Note 3 – A stiff asphalt binder (such as polymer-modified or highly aged binder) may require a comparatively low shear strain rate to ensure that the stress-strain curve has an obvious peak stress. For comparing different asphalt binders, it is recommended to select the same shear strain rate to conduct the test. 10. PROCEDURE B (THERMAL) 10.1. Condition the asphalt binder in the same manner as described in Section 9.1. 10.2. Sample preparation – The sample is prepared in the same manner as described in Section 9.2. 10.3. DSR set-up – A 1.75-mm gap is used in the test. The test is conducted at 5°C or lower. Precondition the spindle that is 4 mm in diameter and the plate at 5°C for 10 minutes before zeroing the gap. Lift up the spindle and zero the gap. Then, condition the spindle and plate at 25°C by adjusting the water bath temperature. Note 4 – Immersing the plates in a water bath at 5°C at the beginning of the test is to minimize the thermal contraction effect on the spindle. 10.4. Sample set-up – Lift up the spindle and immediately remove any water on the spindle and plate using a clean dry paper towel. Paste a drop of epoxy to both the protuberant end of the spindle and the plate, and then zero the gap as soon as possible. Lift up the spindle again and put the binder sample on the protuberant end of the plate. Use a heated spatula to trim the sample before starting the test. 10.5. Test protocol – The test is performed at the temperature of 5°C or lower with a constant shear strain rate that should be determined beforehand. The selection of an appropriate shear strain rate is crucial to ensure that the stress-strain curve has an obvious peak stress. The shear strain rate should be chosen within the range shown in Table D2.2 based on the high PG of the asphalt binder. Both shear stress (τ, Pa) and shear strain (γ, mm/mm) are recorded at a sampling rate of two data points per second. The test is concluded after the peak stress is achieved. Check whether the asphalt binder has debonded from the plate or spindle when aborting the test. If debonding has occurred, then this result shall not be used. Three replicates are recommended. Table D2.2. Determination of shear rate (thermal cracking) Note 5 – A stiff asphalt binder (such as polymer-modified binder or highly aged binder) may require a relatively low shear rate to ensure that the stress-strain curve has an obvious peak stress. The shear strain rate may be lower than 0.025 s-1 for highly aged binder. For comparing different asphalt binders, the same shear strain rate should be selected to conduct the test. 11. CALCULATIONS AND INTERPRETATION OF RESULTS 11.1. In order to obtain results for the binder fracture energy and failure strain tests, the data should be analyzed as follows: High PG range (76, 82) (70, 76) (64, 70) (52, 64) Shear strain rate range, 0.025 – 0.05 0.03 – 0.2 0.05 – 0.4 0.075 – 0.6 s-1

81 11.1.1. Calculate the strain at each time point as shown in Equation (D2.1). Eq. (D2.1) where γi = shear strain at the time of interest; = shear . rate recorded by DSR; and ti = time. 11.1.2. Plot the stress-strain curve as shown in Figure D2.2. The maximum shear stress can easily be obtained as τmax, and the corresponding strain at the maximum stress is regarded as the failure strain γf. Figure D2.2. Stress-strain curve obtained from monotonic testing. 11.1.3. The fracture energy is calculated as the area beneath the stress-strain curve up to the maximum shear stress. The area under the curve is calculated as the sum of the trapezoidal areas between each data point until the maximum shear stress (τmax, γf) is reached. So, the total area is the fracture energy, calculated as shown in Equation (D2.2). Eq. (D2.2) where FE = fracture energy, Pa; τ = shear stress, Pa; and γ = shear strain. 12. REPORT 12.1. Report the following, if known: 12.1.1. Sample identification and PG, 12.1.2. Fracture energy to the nearest 0.1 Pa, and 12.1.3. Failure strain to the nearest 0.001 mm/mm. γ i

82 13. PRECISION AND BIAS 13.1. Precision – The research required to develop precision estimates has not been conducted. 13.2. Bias – The research required to establish the bias of this method has not been conducted. 14. KEYWORDS 14.1. Asphalt binder, fatigue cracking resistance, thermal cracking resistance, fracture energy, failure strain, dynamic shear rheometer (DSR) 15. APPENDIX 15.1. Sample and DSR set-up. 15.1.1. The DSR test set-up is shown in Figure D2.3. Figure D2.3. Monotonic test set-up of asphalt binder.