1、Standard Method of Test for Determining the Creep Compliance and Strength of Hot Mix Asphalt (HMA) Using the Indirect Tensile Test Device AASHTO Designation: T 322-07 (2011) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 2
2、0001 TS-2d T 322-1 AASHTO Standard Method of Test for Determining the Creep Compliance and Strength of Hot Mix Asphalt (HMA) Using the Indirect Tensile Test Device AASHTO Designation: T 322-07 (2011) 1. SCOPE 1.1. This standard provides procedures for determining the tensile creep compliance at diff
3、erent loading times, tensile strength, and Poissons ratio of hot mix asphalt (HMA) using indirect loading techniques. 1.2. The procedures described in this standard provide the data required to conduct the thermal cracking analysis. These procedures apply to test specimens having a maximum aggregate
4、 size of 38 mm or less. Specimens shall be 38 to 50 mm high and 150 9 mm in diameter. 1.3. This test 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
5、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: PP 3, Hot Mix Asphalt (HMA) Specimens by Means of the Rolling Wheel Compactor1 T 166, Bulk Specific Gravity (Gmb) of Co
6、mpacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 269, Percent Air Voids in Compacted Dense and Open Asphalt Mixtures T 312, Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor T 320, Determining the Permanent Shear Stra
7、in and Stiffness of Asphalt Mixtures Using the Superpave Shear Tester (SST) 2.2. ASTM Standards: D3549/D3549M, Standard Test Method for Thickness or Height of Compacted Bituminous Paving Mixture Specimens D4123, Standard Test Method for Indirect Tension Test for Resilient Modulus of Bituminous Mixtu
8、res (Withdrawn 2003) D5361/D5361M, Standard Practice for Sampling Compacted Bituminous Mixtures for Laboratory Testing 2.3. SHRP Document: The Superpave Mix Design Manual for New Construction and Overlays 2015 by the American Association of State Highway and Transportation Officials.All rights reser
9、ved. Duplication is a violation of applicable law.TS-2d T 322-2 AASHTO 3. TERMINOLOGY 3.1. Definitions: 3.2. creepthe time-dependent part of strain resulting from stress. 3.3. creep compliancethe time-dependent strain divided by the applied stress. 3.4. tensile strengththe strength shown by a specim
10、en subjected to tension, as distinct from torsion, compression, or shear. 3.5. Poissons ratio ()the absolute value of the ratio of transverse strain to the corresponding axial strain resulting from uniformly distributed axial stress below the proportional limit of the material. 4. SUMMARY OF METHOD
11、4.1. This standard describes the procedure for determining the tensile creep and tensile strength to be determined on the same specimen for thermal cracking analyses. 4.2. The tensile creep is determined by applying a static load of fixed magnitude along the diametral axis of a specimen. The horizon
12、tal and vertical deformations measured near the center of the specimen are used to calculate a tensile creep compliance as a function of time. Loads are selected to keep horizontal strains in the linear viscoelastic range (typically below a horizontal strain of 500 106mm/mm) during the creep test. B
13、y measuring both horizontal and vertical deformations in regions where the stresses are relatively constant and away from the localized nonlinear effects induced by the steel loading strips, Poissons ratio can be more accurately determined. Creep compliance is sensitive to Poissons ratio measurement
14、s. 4.3. The tensile strength is determined immediately after determining the tensile creep or separately by applying a constant rate of vertical deformation (or ram movement) to failure. 5. SIGNIFICANCE AND USE 5.1. Tensile creep and tensile strength test data are required for Superpave mixtures to
15、determine the master relaxation modulus curve and fracture parameters. This information is used to calculate the thermal cracking of HMA. The master relaxation modulus curve controls thermal crack development, while the fracture parameter defines a mixtures resistance to fracture. 5.2. The values of
16、 creep compliance, tensile strength, and Poissons ratio determined with this method can be used in linear viscoelastic analysis to calculate the low temperature thermal cracking potential of asphalt concrete. 5.3. Tensile creep data may be used to evaluate the relative quality of materials. 5.4. Thi
17、s procedure is applicable to newly prepared mixtures, reheated, and recompacted mixtures. Reheated and recompacted mixtures will have lower creep compliance values than newly prepared mixtures when measured under these specific loading conditions and temperatures. 5.5. This procedure is applicable f
18、or mixtures with a maximum aggregate size of 38 mm or less. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 322-3 AASHTO 6. APPARATUS 6.1. Indirect Tensile Test SystemThe indirect tensile test sy
19、stem shall consist of an axial loading device, a load-measuring device, specimen deformation measurement devices, an environmental chamber, and a control and data acquisition system. 6.1.1. Axial Loading DeviceThe loading device shall be capable of providing a fixed or constant load of 100 kN with a
20、 resolution of at least 20 N and constant rate of ram displacement of at least 12 mm/min. 6.1.2. Load-Measuring DeviceThe load-measuring device shall consist of an electronic load cell, designed for placement between the loading platen and piston, with a sensitivity of 20 N and a minimum capacity of
21、 100 kN. 6.1.3. Specimen Deformation Measurement DevicesThe specimen deformation measurement devices shall consist of four displacement transducers with a range of at least 25 mm, reducible to 0.25 mm through software, and a minimum resolution throughout the range of 0.10 m. 6.1.4. Environmental Cha
22、mberThe environmental chamber shall be equipped with temperature conditioners and controls capable of generating test temperatures between 30 and +10C inside the chamber and maintaining the desired test temperature to within 0.5C. The internal dimensions of the environmental chamber shall be suffici
23、ent to hold a minimum of three test specimens for a period of 12 h prior to testing. 6.1.5. Control and Data Acquisition SystemSpecimen behavior in the creep compliance test is evaluated from time records of applied load and specimen deformation. These parameters shall be recorded on an analog to di
24、gital data acquisition device. 6.1.5.1. When determining the 100-s tensile creep for Superpave, digital data acquisition devices shall provide a sampling frequency of 10 Hz for the first 10 s and 1 Hz for the next 90 s. When determining the 1000-s tensile creep, digital data acquisition devices shal
25、l provide a sampling frequency of 10 Hz for the first 10 s, 1 Hz for the next 90 s, and 0.1 Hz for the rest of 900 s. When determining the tensile strength test, digital data acquisition devices shall provide a sampling frequency of 20 Hz through the entire test. A 16-bit A/D board is normally requi
26、red to obtain the resolution needed when determining the tensile creep and the range needed when determining the tensile strength. 6.1.6. Gauge PointsEight brass gauge points having a diameter of 8 mm and a height of 3.2 mm are required per specimen. 6.1.7. Mounting TemplateA mounting template that
27、has been used successfully for placing and mounting the brass gauge points to each side of the test specimen (four per side) is illustrated in Figure 1, which shows an example of a template for use with 150-mm diameter specimens. Other similar and comparable systems such as those used in T 320 can b
28、e used. 6.1.8. Test Specimen Loading FrameThe specimen load frame shall be as described in ASTM D4123 and capable of delivering test loads coincident with the vertical diametral plane of the test specimen and with less than 20 N frictional resistance in guides and/or bearings. Often a smaller guide
29、frame with special alignment capabilities is used in conjunction with the larger loading frame to accomplish this. The frame may be configured with two support columns or four support columns (Figure 2). 2015 by the American Association of State Highway and Transportation Officials.All rights reserv
30、ed. Duplication is a violation of applicable law.TS-2d T 322-4 AASHTO Notes: 1. All dimensions shown in millimeters unless otherwise noted. 2. Tolerances 0.2 mm unless otherwise noted. 3. Not to scale. Figure 1150-mm Gauge Point Template 128 SquareHole (Typ.)50 Rad.38 to C.8 x 8 x 1.5Backing Plate6
31、x 12 x 1.5Backing Plate ( Typ.)25 C. To C.(Typ.)3 x 6 Slot(Typ.)Top View150Varies(Minimum 25)Side View 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 322-5 AASHTO Figure 2Specimen Loading Frame
32、7. HAZARDS 7.1. Observe standard laboratory safety precautions when preparing and testing HMA specimens. 8. STANDARDIZATION 8.1. Calibrate the testing system prior to initial use and at least once a year thereafter. 8.1.1. Calibrate the environmental control component to maintain the required temper
33、ature within the accuracy specified. 8.1.2. Calibrate all measurement components (such as load cells and displacement transducers) of the testing system. 8.1.3. If any of the verifications yield data that do not comply with the accuracy specified, correct the problem prior to proceeding with testing
34、. Appropriate action may include correction of menu entries, maintenance on system components, calibration of system components (using an independent calibration agency, or service by the manufacturer, or in-house resources), or replacement of system components. 2015 by the American Association of S
35、tate Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 322-6 AASHTO 9. SAMPLING 9.1. Laboratory Molded SpecimensPrepare a minimum of three replicate laboratory molded specimens, in accordance with T 312 or PP 3. If PP 3 is used, use a suit
36、able core drill to cut specimens from the sample after compaction. 9.2. Roadway SpecimensObtain roadway specimens from the pavement in accordance with ASTM D5361/D5361M. Prepare cores with smooth and parallel surfaces that conform to the height and diameter requirements specified in Section 10.2. Pr
37、epare a minimum of three replicate cores. 10. SPECIMEN PREPARATION AND PRELIMINARY DETERMINATIONS 10.1. Saw at least 6 mm from both sides of each test specimen to provide smooth, parallel (saw-cut) surfaces for mounting the measurement gauges. Note 1Measurements taken on cut faces yield more consist
38、ent results, and gauge points can be attached with much greater bonding strength. 10.2. Specimen SizePrepare specimens with a height of 38 to 50 mm and a diameter of 150 9 mm. 10.3. Determining Specimen Height and DiameterDetermine and record the diameter and height (thickness) of each specimen in a
39、ccordance with ASTM D3549/D3549M, to the nearest 1 mm. 10.4. Determining the Bulk Specific GravityDetermine the specific gravity of each specimen in accordance with T 166, except that if the water absorbed by the specimen exceeds 2 percent, substitute a thin, adherent plastic wrap membrane that is w
40、ater-resistant instead of the paraffin coating. 10.5. Specimen DryingIf specimens were immersed directly into the water, after determining the bulk specific gravity, allow each specimen to dry at room temperature to a constant mass. 10.6. Mounting Displacement TransducersAttach four brass gauge poin
41、ts with epoxy to each flat face of the specimen (four per face). On each flat face of the specimen, two gauge points shall be placed along the vertical and two along the horizontal axes with a center to center spacing of 38.0 0.2 mm for a specimen diameter of 150 9 mm. The placement and location of
42、the gauge points on each face shall produce a mirror image of each other. Mount the displacement transducers on the gauge points such that the transducers center line is 6.4 mm above the specimens surface. Figure 3 shows a system for mounting linear variable transducers that has been successfully us
43、ed for IDT creep measurements at low temperature. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 322-7 AASHTO Notes: 1. All dimensions shown in millimeters unless otherwise noted. 2. Tolerances
44、0.2 mm unless otherwise noted. 3. Not to scale. Figure 3Cross Section of LVDT Mounting System for 150-mm Specimen 11. TENSILE CREEP/STRENGTH TESTING (THERMAL CRACKING ANALYSIS) 11.1. Determine the tensile creep compliance of each of the three specimens at three measurements at 10C intervals. The fol
45、lowing test temperatures are recommended: For mixtures made using binder grades PG XX-34 or softer: 30, 20, and 10C; Core Assembly2.4(Typ.)6.425.412.7(Typ.)0.81.6 O.D. Brass TubeCore AssemblyLVDT CoreClamp ScrewM 1.5 0.3 6 LVDTTo SignalConditionerGauge Point( 8.0 Dia 3.2 )5 Wire A.C.SubminiatureLVDT
46、SpecimenSurfaceCore Assembly (Undermount) Side ViewCore Assembly2.4(Typ.)6.40.814.3 LongCore AssemblyLVDT CoreClamp ScrewM 1.5 0.3 6 LVDTTo SignalConditionerGauge Point( 8.0 Dia. 3.2 )5 Wire A.C.SubminiatureLVDTSpecimenSurfaceCore Assembly (Overmount) Side View4.817.51.6 O.D. Brass Tube15.98.0 Circu
47、larBore (Typ.)8.0 Bore12.74.9 Dia.2.4Core Assembly Front View8.00.8 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 322-8 AASHTO For mixtures made using binder grades PG XX-28 and PG XX-22, or mi
48、xtures for which binder grade is unknown: 20, 10, and 0C; For mixtures made using binder grades PG XX-16 or harder: 10, 0, and +10C; and For mixtures subjected to severe age hardening, the test temperatures should be increased by 10C. Note 2The original Superpave mixture analysis procedures specifie
49、d test temperatures of 0, 10, and 20C. 11.2. Lower the temperature of the environmental chamber to the test temperature and, once the test temperature 0.5C is achieved, allow each specimen to remain at the test temperature from 3 1 h prior to testing. Under no circumstances shall the specimen be kept at 0C or less for more than 24 h. 11.3. Zero or rebalance the electronic measuring system and apply a static load of fixed magnitude (2 percent) without impact to the specimen f
