1、Standard Method of Test for Determining the Fatigue Life of Compacted Asphalt Mixtures Subjected to Repeated Flexural Bending AASHTO Designation: T 321-17 Technical Section: 2d, Proportioning of AsphaltAggregate Mixtures Release: Group 3 (August 2017) American Association of State Highway and Transp
2、ortation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d T 321-1 AASHTO Standard Method of Test for Determining the Fatigue Life of Compacted Asphalt Mixtures Subjected to Repeated Flexural Bending AASHTO Designation: T 321-17 Technical Section: 2d, Proportioning of A
3、sphaltAggregate Mixtures Release: Group 3 (August 2017) 1. SCOPE 1.1. This standard provides procedures for determining the fatigue life and fatigue energy of 380 mm long by 50 mm thick by 63 mm wide asphalt mixture beam specimens sawed from laboratory- or field-compacted asphalt mixtures and subjec
4、ted to repeated flexural bending until failure. 1.2. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this procedure to establish appropriate
5、 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 Compactor1 R 66, Sampling Asphalt Materials T 2, Sampling of Aggregates
6、 T 168, Sampling Bituminous Paving Mixtures T 247, Preparation of Test Specimens of Hot Mix Asphalt (HMA) by Means of California Kneading Compactor T 269, Percent Air Voids in Compacted Dense and Open Asphalt Mixtures 2.2. ASTM Standards: D3549/D3549M, Standard Test Method for Thickness or Height of
7、 Compacted Bituminous Paving Mixture Specimens D5361/D5361M, Standard Practice for Sampling Compacted Bituminous Mixtures for Laboratory Testing E29, Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications 2017 by the American Association of State Hig
8、hway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T 321-2 AASHTO 3. TERMINOLOGY 3.1. Definition: 3.1.1. failure pointthe load cycle at which a peak occurs in the plot of stiffness multiplied by load cycles versus load cycles, which is indicati
9、ve of the formation of a crack in the specimen. 4. SIGNIFICANCE AND USE 4.1. The fatigue life and failure energy determined by this standard can be used to estimate the fatigue life of asphalt mixture pavement layers under repeated traffic loading. The performance of asphalt mixtures can be more acc
10、urately predicted when these properties are known. 5. APPARATUS 5.1. Test SystemThe test system shall consist of a loading device, an environmental chamber (optional), and a control and data acquisition system. The test system shall meet the minimum requirements specified in Table 1. Table 1Test Sys
11、tem Minimum Requirements Load measurement and control Range: 0 to 5 kN Resolution: 2 N Accuracy: 5 N Displacement measurement and control Range: 0 to 5 mm Resolution: 2 m Accuracy: 5 m Frequency measurement and control Range: 5 to 10 Hz Resolution: 0.005 Hz Accuracy: 0.01 Hz Temperature measurement
12、and control Range: 10 to 25C Resolution: 0.25C Accuracy: 0.5C 5.1.1. Loading DeviceThe test system shall include a closed-loop, computer-controlled loading component that, during each load cycle in response to commands from the data processing and control component, adjusts and applies a load such t
13、hat the specimen experiences a constant level of strain during each load cycle. The loading device shall be capable of (1) providing repeated sinusoidal loading at a frequency range of 5 to 10 Hz; (2) subjecting specimens to four-point bending with free rotation and horizontal translation at all loa
14、d and reaction points; and (3) forcing the specimen back to its original position (i.e., zero deflection) at the end of each load pulse. (Figure 1 illustrates the loading conditions.) 5.1.2. Environmental Chamber (Optional)The environmental chamber shall enclose the entire specimen and maintain the
15、specimen at the test temperature 0.5C during testing. An environmental chamber is not required if the temperature of the surrounding environment can be maintained within the specified limits. 5.1.3. Control and Data Acquisition SystemDuring each load cycle, the control and data acquisition system sh
16、all be capable of measuring the deflection of the beam specimen, computing the strain in the specimen, and adjusting the load applied by the loading device such that the specimen experiences a constant level of strain on each load cycle. In addition, it shall be capable of recording load cycles, app
17、lied loads, and beam deflections and computing and recording the 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T 321-3 AASHTO maximum tensile stress, maximum tensile strain, phase angle, stiffne
18、ss, dissipated energy, and cumulative dissipated energy at load cycle intervals specified by the user. 5.2. Miscellaneous Apparatus and MaterialsA suitable saw for cutting the beams and a mechanism for setting proper clamp spacing. For loading devices that require a glued nut for deformation measure
19、ment, a screw, nut (suggested size M 8 by 1) and block assembly for referencing the linear variable differential transducer (LVDT) to the neutral axis of the specimen, and epoxy for attaching a target to the specimen at the neutral axis are also needed. Figure 1Load and Freedom Characteristics of Fa
20、tigue Test Apparatus 6. HAZARDS 6.1. Observe standard laboratory safety precautions when preparing and testing HMA specimens. SpecimenLoadLoadReaction ReactionDeflectionSpecimenClampReturn toOriginal PositionFree Translation and Rotation 2017 by the American Association of State Highway and Transpor
21、tation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T 321-4 AASHTO 7. SAMPLING AND SPECIMEN PREPARATION 7.1. Laboratory-Mixed and Compacted SpecimensSample asphalt binder in accordance with R 66 and sample aggregate in accordance with T 2. Prepare three replicat
22、e asphalt mixture beam specimens, from slab(s) or beam(s) compacted in accordance with PP 3 or T 247. Note 1The type of compaction device may influence the test results. It is recommended to cut beams from a large slab compacted by a vibratory roller. Note 2Normally, test specimens are compacted usi
23、ng a standard compactive effort. However, the standard compactive effort may not reproduce the air voids of roadway specimens measured according to T 269. If specimens are to be compacted to a target air void content, the compactive effort to be used should be determined experimentally. Note 3This s
24、tandard is suitable for testing asphalt mixtures with a nominal size of 19 mm or smaller. Care should be taken when interpreting results obtained from specimens that do not meet this requirement. 7.2. Plant-Mixed, Laboratory-Compacted SpecimensObtain asphalt mixture samples in accordance with T 168.
25、 Prepare three replicate asphalt mixture beam specimens, from slab(s) or beam(s) compacted in accordance with PP 3 or T 247. (See Notes 1 and 2.) 7.3. Roadway SpecimensObtain compacted asphalt mixture samples from the roadway in accordance with ASTM D5361/D5361M. 7.4. Saw at least 6 mm from both sid
26、es of each test specimen to provide parallel (saw-cut) surfaces to eliminate high air void sections on the specimen surface. For loading devices that require gluing a nut for deformation measurement, these cut surfaces provide smooth surfaces for mounting the measurement gauges. The final required d
27、imensions, after sawing, of the specimens are 380 6 mm in length, 50 6 mm in height, and 63 6 mm in width. 8. PROCEDURE 8.1. Specimen MeasurementMeasure the height and width of the specimen to the nearest 0.01 mm at three different points along the middle 100 mm of the specimen length in accordance
28、with applicable sections of ASTM D3549/D3549M. Determine the average of the three measurements for each dimension and record the averages to the nearest 0.1 mm. 8.2. Epoxying Target to Neutral Axis of SpecimenThe deformation of the beam shall be referenced to a target located at the neutral axis of
29、the specimen. One acceptable design has been to fix a nut located at the center of a specimen side. To fix the target, apply epoxy in a circle around this center point and place the nut on the epoxy such that the center of the nut is over the center point. Avoid applying epoxy such that it fills the
30、 center of the nut. Allow the epoxy to cure before moving the specimen. (Figure 2 illustrates a nut epoxied to the neutral axis of the specimen.) 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T
31、321-5 AASHTO Note: Not to scale Figure 2Nut Epoxied to the Neutral Axis Note 4Other forms of a fixed-target reference point at the center point of the neutral axis have been found to be acceptable and are allowable. The fixed target shall be at the position described and not at any other location on
32、 the beam. 8.3. Place the specimen in an environment that is at the test temperature 0.5C for 2 h to ensure the specimen is at the test temperature prior to beginning the test. Note 5A test temperature of 20.0oC has been found suitable. However, other test temperatures can be used within the measure
33、ment range of the equipment. 8.4. Open the clamps and slide the specimen into position (Figures 3, 4, and 5). Use the jig to ensure proper horizontal spacing of the clamps, 119 mm center-to-center. When the specimen and clamps are in the proper positions, close the outside clamps by applying suffici
34、ent pressure to hold the specimen in place. Next, close the inside clamps by applying sufficient pressure to hold the specimen in place. 380mm50 mm63 mmNut - M8 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicab
35、le law.TS-2d T 321-6 AASHTO Figure 3Specimen Clamping Procedure Clamp A Clamp B Clamp B Clamp AClamp A Clamp B Clamp B Clamp AStep 1Step 2Clamp A Clamp B Clamp B Clamp AStep 3 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violat
36、ion of applicable law.TS-2d T 321-7 AASHTO Figure 4Schematic of Flexural Beam Fatigue Test Apparatus, Side View Air PlenumEnvironmentalSystem 2017 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T 321-
37、8 AASHTO Figure 5Schematic of Flexural Beam Fatigue Test Apparatus, Top View 8.5. Attach the LVDT block to the specimen by screwing the screw into the nut epoxied on the specimen (see Figure 4). Clamp the LVDT into position such that the LVDT probe rests on top of the block and the LVDT is reading c
38、lose to zero. 8.6. Select the desired initial peak-to-peak strain (generally in the 250 to 750 microstrain for conventional asphalt mixtures) and loading frequency, and the load cycle intervals at which test results are recorded and computed, and enter them into the recording and control components
39、test program. In some instances, with highly modified materials for specialized applications, testing has been conducted with initial peak-to-peak strains as high as 2000 microstrain. Set the loading frequency within a range of 5 to 10 Hz. Note 6The data collection sequence should ensure that at lea
40、st 200 data points are captured within each log decade of loading and that these should enable a smooth curve of flexural stiffness versus load cycles to be obtained. The collection sequence shall include data capture at cycle 50. 8.7. Select a deflection level (peak-to-peak strain level) such that
41、the specimen will undergo a minimum of 10,000 load cycles before its stiffness is reduced to a condition that represents specimen failure. A minimum of 10,000 load cycles ensures that the specimen does not decrease in stiffness too rapidly. Note 7A test of 10,000 load cycles at 10 Hz will take 17 mi
42、n to conduct once the test is started. A practical upper limit on the test time would correspond to around 1 day, during which approximately 1 million load applications can be achieved (around 28 h). Data in this range can be Air OutAir InAirInPlenumAirOutPlenum 2017 by the American Association of S
43、tate Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d T 321-9 AASHTO used to produce a relationship between strain and life to failure. Some trial and error may be required to estimate the strain levels to achieve these testing times. If a
44、n estimation of endurance limit is required, then additional testing beyond 1 million cycles is needed. Some methods suggest that tests as long as 10 million cycles may be required. 8.8. After selecting the appropriate test parameters, begin the test. Activate the recording and control components so
45、 that the test results at the selected load cycle intervals are monitored and recorded, ensuring that the test system is operating properly. Records shall be stored by the software at the load cycles as defined by the minimum requirements specified in Table 2. Additional records may be stored in add
46、ition to the minimum points specified. Table 2Minimum Load Cycles for Result Storage during Test Repetitions Intervals (space equally within each range) Cycles at Each Collection Point Included in Average Reported 0 to 100 110, then every 10 to 100 5 (except for 110, report individual cycle) 100 to
47、1000 10 5 1000 to 10,000 40 equally spaced data points 5 10,000 to 100,000 At least one every 1,000 repetitions 5 100,000 to End of Test At least one every 10,000 repetitions 5 8.9. Determine at all load cycles the flexural stiffness and phase lag at each load cycle throughout the test while the tes
48、t is being performed as follows: 8.9.1. Maximum Peak-to-Peak Stress (Pa): ( ) ( )20.357 /tP bh= (1) where: P = peak-to-peak load applied by actuator, N; b = average specimen width, m; and h = average specimen height, m. 8.9.2. Maximum Peak-to-Peak Strain (m/m): ( ) ( )2212 / 3 4th La= (2) where: = m
49、aximum peak-to-peak deflection at center of beam, m; a = space between inside clamps, 0.357/3 m, (0.119 m); and L = length of beam between outside clamps, 0.357 m. 8.9.3. Flexural Stiffness (Pa): /ttS = (3) 8.9.4. Phase Angle (deg): 360 fs= (4) where: f = load frequency, Hz; and s = time lag between Pmaxand max, s. Note 8When automated testing software is used in the recording and control component of the test system, is approximated by an algorithm contained in the automated testing software. 2017 b
