1、Standard Method of Test for Determining the Damage Characteristic Curve of Asphalt Mixtures from Direct Tension Cyclic Fatigue Tests AASHTO Designation: TP 107-141American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d
2、TP 107-1 AASHTO Standard Method of Test for Determining the Damage Characteristic Curve of Asphalt Mixtures from Direct Tension Cyclic Fatigue Tests AASHTO Designation: TP 107-1411. SCOPE 1.1. This test method covers procedures for preparing and testing asphalt concrete mixtures to determine the dam
3、age characteristic curve via direct tension cyclic fatigue tests. 1.2. This standard is applicable to laboratory prepared specimens of mixtures with nominal maximum size aggregate less than or equal to 37.5 mm (1.48 in.). 1.3. This standard may involve hazardous material, operations, and equipment.
4、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. A
5、ASHTO Standards: PP 60, Preparation of Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC) PP 61, Developing Dynamic Modulus Master Curves for Asphalt Mixtures Using the Asphalt Mixture Performance Tester (AMPT) R 30, Mixture Conditioning of Hot Mix Asphalt (HMA) R 62
6、, Developing Dynamic Modulus Master Curves for Asphalt Mixtures T 342, Determining Dynamic Modulus of Hot Mix Asphalt (HMA) TP 79, Determining the Dynamic Modulus and Flow Number for Asphalt Mixtures Using the Asphalt Mixture Performance Tester (AMPT) 2.2. Other Document: NCHRP Report 629, Equipment
7、 Specifications for the Simple Performance Test System, Appendix E, October 16, 2007. 3. TERMINOLOGY 3.1. Definitions: 3.1.1. complex modulus (E*)a complex number that defines the relationship between stress and strain for a linear viscoelastic material. 2015 by the American Association of State Hig
8、hway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 107-2 AASHTO 3.1.2. cyclic pseudo secant modulus (C*)the secant modulus in stresspseudo strain space for a single cycle. This pseudo modulus differs from C because it is computed using a stea
9、dy-state assumption and is used only with cycle-based data. 3.1.3. damage (S)the internal state variable that quantifies microstructural changes in asphalt concrete. 3.1.4. damage characteristic curve (C versus S curve)the curve formed when plotting the damage on the x-axis and the pseudo secant mod
10、ulus on the y-axis. It defines the unique relationship between the structural integrity and amount of damage in a given mixture. 3.1.5. dynamic modulus (|E*|)the norm of the E*, which is calculated by dividing the peak-to-peak stress by the peak-to-peak axial strain measured during the steady-state
11、period. 3.1.6. failure cycle (Nf)the cycle in which the measured phase angle drops sharply after a stable increase during cyclic loading. 3.1.7. phase angle ()the angle, expressed in degrees, between an applied sinusoidal stress and the resulting sinusoidal strain measured during the steady-state pe
12、riod. 3.1.8. pseudo strain (R)a quantity that is similar to strain but does not include time effects. Pseudo strain is calculated by solving the convolution integral of the strain and E(t). 3.1.9. pseudo secant modulus (C)the secant modulus in stresspseudo strain space. 3.1.10. relaxation modulus (E
13、(t)the quotient of the stress response of a material with time to a constant step amplitude of strain. 4. SUMMARY OF METHOD 4.1. A controlled and repeated cyclic loading is applied to a cylindrical asphalt concrete specimen until failure. The applied stress and on-specimen axial strain response are
14、measured and used to calculate the necessary quantities. The relationship between the damage (S) and the pseudo secant modulus (C) is determined and expressed as the damage characteristic curve. 5. SIGNIFICANCE AND USE 5.1. The damage characteristic curve represents the fundamental relationship betw
15、een damage and material integrity for asphalt concrete mixtures. This property is independent of temperature, frequency, and mode of loading. Combined with the linear viscoelastic properties of asphalt concrete, the damage characteristic curve can be used to analyze the fatigue characteristics of as
16、phalt concrete mixtures. 5.2. Damage characteristic curves can also be combined with additional pavement response models to predict the fatigue behavior of in-service asphalt concrete mixtures. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplic
17、ation is a violation of applicable law.TS-2d TP 107-3 AASHTO Figure 1General Schematic of Direct Tension Test Setup 6. APPARATUS 6.1. Direct Tension Test SystemConsists of a testing machine, environmental chamber, and measurement system. Figure 1 presents a schematic of the test setup for the fatigu
18、e test. 6.2. Asphalt Mixture Performance TesterAn Asphalt Mixture Performance Tester or system meeting or exceeding the requirements of Equipment Specifications for the Simple Performance Test System, NCHRP Report 629, Appendix E. 6.3. External Conditioning Chamber (optional)An environmental chamber
19、 for conditioning the test specimens to the desired testing temperature. The chamber shall be capable of controlling the temperature of the specimen over a temperature range of 5 to 25C (41 To 77F) to within 0.5C (1F). The chamber shall be large enough to accommodate at least a single test specimen
20、and a monitoring specimen with thermocouples mounted at the center and on the surface for temperature verification. 6.4. Measurement SystemShall be fully computer-controlled and capable of measuring and recording the time history of the applied load and axial deformations. A system that uses the cha
21、racteristics shown in Table 1 has been found to be sufficient: Table 1Accuracy and Resolution of Equipment Measurement System Measurement Range Accuracy Resolution Load 0.12 to 13.5 kN Error 1.0% 0.0012 kN Machine deformation At least 12 mm Error 0.03 mm 0.0025 mm On-specimen deformation Not specifi
22、edaError 1.0% Not specifiedbaA range of about 7000 is recommended. bA resolution less than 7.5 is recommended. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 107-4 AASHTO 6.5. Axial Deformation
23、 MeasurementsAxial deformations shall be measured using sensors mounted between gauge points that are glued to the specimen, an example of which is shown in Figure 2. The deformations shall be measured at two locations 180 degrees apart, three locations 120 degrees apart, or four locations 90 degree
24、s apart. Note 1It is recommended, but not specified, that these sensors be the loose-core LVDTs (linear variable differential transformers) type. If the gauge-head type (spring-loaded LVDTs) is chosen, care should be taken to ensure that the spring force is not so strong as to force the gauge points
25、 apart. This effect can be measured by monitoring the deformation of a sample that is lying on its side and is conditioned to the appropriate temperature measured using a spring-loaded LVDT that has been attached to the sample. As long as the spring force is confirmed to be not strong enough to caus
26、e deformation on the sample, gauge-head type (spring-loaded) LVDTs can be advantageous and convenient. They can also be used for performing the dynamic modulus test according to TP 79. Note 2Using four sensors set at 90 degrees apart has an advantage over using fewer sensors, because if one sensor d
27、oes not function properly, that sensor and the sensor 180 degrees opposed to it can be discarded, and the remaining two sensors can be used to determine the average deformation. Note 3The reliability of sensors should be verified with the supplier or manufacturer. Figure 2General Schematic of Gauge
28、Points (not to scale) 6.6. Loading PlatensAre required above and below the specimen to transfer the load from the testing machine to the specimen. The diameter of the loading platens should be within 0.5 mm (0.02 in.) from the target specimen diameter of 100 mm. Generally, these platens should be ma
29、de of hardened or plated steel, or anodized high strength aluminum. Softer materials will require more frequent replacement. Materials that have linear elastic modulus properties and hardness properties lower than that of 6061-T6 aluminum shall not be used. The face of each load platen shall be groo
30、ved to provide better adhesion between the glue and plate. The top loading platen shall be designed so that it can be mated to the test machine without inducing loading eccentricity. A locking ball joint that will lock when tightened into the machine as shown in Figure 3 is one potential design. If
31、the end plate gluing apparatus is sufficiently stiff, it may be possible to install the test specimen without the need for such a locking ball joint. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d
32、 TP 107-5 AASHTO Note 4Grooves in the end plates can improve the overall adhesion between the glue and the end plates. It is recommended that if grooved, the grooves be approximately 0.6 mm deep and spaced laterally by a distance of approximately 1.9 mm. The grooving pattern can be either concentric
33、 circles or a spiral pattern. A V-shaped groove or a cross-hatched groove is suggested. The 60-degree point threading bit has been used successfully for making the grooves. 6.7. End Plate Gluing ApparatusShould be available for gluing the end plates to the asphalt concrete specimen. The device shoul
34、d self-center the specimen within the end plates and ensure that no eccentricity exists between the specimen and end plates. It shall be possible to clamp or otherwise hold the gluing apparatus at a fixed height for a period of at least 4 h. Figure 4 shows a gluing jig that has been used successfull
35、y. If no jig is available, the specimen can be glued directly in the test machine. To do this, the gluing should be performed with the machine in load control. The applied compressive load should not be greater than 0.045 kN (10 lb). Figure 3Example Locking Ball Joint Design 2015 by the American Ass
36、ociation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 107-6 AASHTO Figure 4End Plate Gluing Apparatus 7. HAZARDS 7.1. Standard laboratory safety precautions must be observed when preparing and testing asphalt concrete specim
37、ens. 8. TESTING EQUIPMENT CALIBRATION 8.1. The guidelines provided in TP 79 shall be followed to ensure that the test equipment and on-specimen measurement devices are properly calibrated. 8.2. If any of the verifications yield data that do not comply with the accuracy specified, the problem shall b
38、e corrected prior to further testing. 9. TEST SPECIMENS 9.1. Direct tension testing shall be performed on test specimens cored and cut from larger Superpave gyratory compacted specimens. Test specimens with acceptable properties have been obtained from gyratory samples 150 mm (6 in.) in diameter and
39、 a minimum of 180 mm (7.1 in.) in height. The average diameter of test specimens shall be 100 to 104 mm (4 to 4.1 in.) in diameter with a standard deviation of less than 0.5 mm (0.02 in.). The average height of the test specimens shall be between 127.5 and 132.5 mm (5.0 and 5.2 in.), respectively. T
40、est specimens should be prepared in accordance with PP 60 with the exception of the allowance for 130-mm-height specimens. Note 5The specimen height that should be used and the cutting scheme will depend on the air void gradient produced by the specific compactor and the capabilities of the sawing e
41、quipment. For specimens compacted to a height of 180 mm, it has been found that 25 mm should first be cut from the bottom face of the specimen. The bottom face of the specimen is the one that was at the bottom of the gyratory compaction mold. Then, the remaining length should be cut so that the fina
42、l specimen height is between 127.5 and 132.5 mm. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d TP 107-7 AASHTO 9.2. AgingLaboratory-prepared mixtures shall be temperature-conditioned in accordanc
43、e with the 4-h, short-term oven-conditioning procedure outlined in R 30. Field mixtures need not be aged prior to testing. 9.3. Prepare three test specimens at the target air void content 0.5 percent. 9.4. ReplicatesOne replicate specimen should be tested at each input condition. Note 6Sample storag
44、eIf test specimens will not be tested within 2 days, it is recommended to wrap each specimen in polyethylene or seal it in a polyethylene bag and store in an unlit and environmentally protected storage area at temperatures between 5 and 25C (40 and 77F). Specimens shall not be stacked during storage
45、. To eliminate the effects of aging on the test results, it is recommended that specimens be stored no longer than 2 weeks prior to testing. 10. TEST SPECIMEN INSTRUMENTATION PROCEDURE 10.1. Thoroughly clean all end plates by first heavily brushing the face of each platen using either a hand operate
46、d wire brush or one attached to a standard electric drill. After cleaning the platen with the wire brush, wipe the surface clean of any dust by using a towel dipped in acetone or similar solvent. 10.2. Using the same towel, but with only a small amount of solvent, wipe the ends of the specimen clean
47、 of any residual dust. 10.3. Weigh out an appropriate amount of adhesive to adhere the end plates and specimen to one another. The gluing process will require approximately 1020 minutes, so prepare an adhesive that is appropriate for this length of working time. Note 7Steel putty, such as Devcon 101
48、10, has been found to be satisfactory for attaching the end plates. Devcon 10240 has also been found satisfactory, but the overall working time is less with the 10240 than it is with the 10110, so more careful attention will need to be paid to the gluing process. Note 8Approximately 120 g of the ste
49、el putty has been found sufficient for 100-mm-diameter samples. 10.4. Fill in any surface voids in the top and bottom surfaces of the specimen with the adhesive. 10.5. Divide the remaining adhesive into quarter measures and spread evenly between the end plates and specimen end faces (that is, 1/4to the top plate, 1/4to the bottom plate, 1/4to the bottom face, and 1/4to the top face). Insert and secure the end plates into the gluing jig and gently place the specimen on top of the bottom end plate, as close as
