1、Standard Method of Test for Determining the Permanent Shear Strain and Stiffness of Asphalt Mixtures Using the Superpave Shear Tester (SST) AASHTO Designation: T 320-07 (2011) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C.
2、 20001 TS-2d T 320-1 AASHTO Standard Method of Test for Determining the Permanent Shear Strain and Stiffness of Asphalt Mixtures Using the Superpave Shear Tester (SST) AASHTO Designation: T 320-07 (2011) 1. SCOPE 1.1. This standard provides performance-related test procedures for the determination o
3、f stiffness and permanent shear strain of asphalt mixtures using the Superpave Shear Tester (SST). Modified and unmodified asphalt mixtures can be tested and analyzed using this standard. 1.2. This standard is applicable to specimens prepared in a laboratory or cored from a pavement for postconstruc
4、tion analysis. It is intended for use with specimens having the following minimum dimensions: Nominal Maximum Aggregate Size in Asphalt Mixture, mm Specimen Diameter Specimen Height 19 150 50 12.5, 9.5, 4.75 150 38 Note 1Nominal maximum aggregate size is defined in R 35 as the sieve greater than the
5、 first sieve to retain more than 10 percent of the total aggregate. Asphalt mixtures with a nominal maximum aggregate size greater than 19 mm can be tested using this procedure, but it is not recommended. The larger aggregate sizes may significantly interfere with the material response, thereby affe
6、cting the repeatability of the test. Note 2The SST is only capable of testing specimens with a maximum diameter of 150 mm. The specimen height of 50 mm is preferred, but may not be available in roadway cores where layer thickness may only be 38 mm. Specimen heights less than 38 mm usually cannot be
7、tested because of equipment constraints. Note 3The diameter-to-height ratio for shear test specimens should be 3:1 or greater. This effectively eliminates the use of 100-mm diameter specimens (because of minimum height requirement for testing discussed in Note 2). 1.3. This practice may involve haza
8、rdous materials, operations, and equipment. It does not purport to address all the safety concerns associated with its use. It is the responsibility of the user of this practice to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations
9、 prior to its use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 30, Mixture Conditioning of Hot Mix Asphalt (HMA) R 35, Superpave Volumetric Design for Asphalt Mixtures R 66, Sampling Asphalt Materials 2015 by the American Association of State Highway and Transportation Officials.All rights rese
10、rved. Duplication is a violation of applicable law.TS-2d T 320-2 AASHTO T 2, Sampling of Aggregates T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 168, Sampling Bituminous Paving Mixtures T 209, Theoretical Maximum Specific Gravity (Gmm)
11、 and Density of Hot Mix Asphalt (HMA) 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 2.2. ASTM Standards: D3549/D3549M, Standard Test Method for Thickness or
12、Height of Compacted Bituminous Paving Mixture Specimens D5361/D5361M, Standard Practice for Sampling Compacted Bituminous Mixtures for Laboratory Testing 3. SIGNIFICANCE AND USE 3.1. The test procedures and associated analysis techniques described in this method can be used to determine shear stiffn
13、ess and permanent shear strain of asphalt mixtures. The shear frequency sweep test at constant height can be used to determine mixture stiffness. The simple shear test at constant height can be used to determine shear deformation from the application of a static shear load. The repeated shear test a
14、t constant height can be used with corresponding analysis procedures to estimate the rutting susceptibility of an asphalt mixture. 4. EQUIPMENT AND MATERIALS 4.1. Shear Test SystemThe shear test system shall consist of a loading device, specimen deformation measurement equipment, an environmental ch
15、amber, and a control and data acquisition system. It shall accommodate test specimens 150 mm in diameter and 50 mm in height. 4.1.1. Loading DeviceThe loading device shall be capable of simultaneously applying both vertical and horizontal loads to a specimen. It shall also be capable of applying sta
16、tic, ramped (increasing or decreasing), and repetitive loads of various waveforms. As a minimum, the loading device shall be capable of applying horizontal shear load pulses in a haversine waveform with a load duration of 0.1 s with 0.6 s between load pulses. Loading shall be provided by two hydraul
17、ic actuators (one each horizontal and vertical) and shall be controlled by closed-loop feedback using either stress or strain control throughout the entire range of frequencies and temperatures. The loading device shall be capable of meeting the minimum requirements specified in Table 1. Table 1Mini
18、mum Test System Requirements Measurement and Control Parameters Range Resolution Accuracy Load, N 0 to 31,000 2 5 Axial LVDT, mm 0 to 5 0.0025 0.005 Shear LVDT, nmm 0 to 0.05 0.001 0.002 Temperature, C 0 to 80 0.25 0.5 4.1.2. Environmental ChamberThe environmental chamber shall be capable of maintai
19、ning the temperature of the test specimen as specified in Table 1 during the testing sequence. 4.1.3. Data Acquisition and Control SystemThe data acquisition and control system shall automatically control user-selected measurement parameters, within the accuracy specified in 2015 by the American Ass
20、ociation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 320-3 AASHTO Table 1, during the testing sequence. The system shall record load cycles, applied horizontal and vertical loads, specimen deformation in two directions (vert
21、ical and horizontal), environmental conditions, and the required frequency of data sampling. At the conclusion of the test, the data acquisition and control system shall provide all applicable test data. 4.2. Conditioning ChamberThe conditioning chamber shall be capable of maintaining the specimen c
22、onditioning temperatures as specified in Table 1. 4.3. Platen-Specimen Assembly Device (optional)The platen-specimen assembly device is used to facilitate bonding the specimen to the loading platens with adhesive. The device shall maintain the platens in a parallel position (relative to each other)
23、during the gluing operation. The platens must remain parallel so that stresses do not develop in the specimen when the specimen-platen assembly is clamped in the test system. The device shall be capable of testing specimens with a maximum diameter of 150 mm and maximum height of 50 mm. 4.4. Aluminum
24、 Loading PlatensTop and bottom aluminum loading platens at least 6.35 mm greater in diameter than the diameter of the specimen to be tested and at least 20 mm thick. The bearing face of each platen shall be plane to 0.025 mm. 4.5. AdhesiveQuickset adhesive with a minimum hardened stiffness modulus o
25、f 2000 MPa for bonding the platens to the specimen ends. Note 4Devcon 5-Minute Plastic Steel Epoxy Cement is one possible material that is satisfactory for tests conducted at 20C or higher. 4.6. SolventAcetone, kerosene, or other equivalent solvent for cleaning the platens after testing. Note 5Most
26、of the epoxy and samples can be removed by heating and scraping the platens. The solvent is used only for a final cleaning. 5. STANDARDIZATION 5.1. The testing system shall be standardized prior to initial use and at least once every 12 months thereafter. 5.1.1. Verify the capability of the environm
27、ental control chamber to maintain the required temperature within the accuracy specified in Table 1. 5.1.2. Verify the calibration of all measurement components such as load cells and linear variable differential transducers (LVDTs) of the testing system. 5.1.3. If any of the verifications yield dat
28、a that do not comply with the accuracy requirements specified in Table 1, correct the problem prior to proceeding with testing. Appropriate action may involve correction of menu entries, maintenance of system components, calibration of system components (using an independent calibration service, man
29、ufacturer service, or in-house resources), or replacement of system components. 6. SAMPLING AND SPECIMEN PREPARATION 6.1. Five test specimens are preferred, and a minimum of three specimens are required, for performing the repeated shear test at constant height. Three test specimens are preferred fo
30、r performing the shear frequency sweep test at constant height and the simple shear test at constant height. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 320-4 AASHTO 6.2. Laboratory-Mixed, La
31、boratory-Compacted (LMLC) SpecimensSample asphalt binder and aggregates in accordance with R 66 and T 2, respectively. Use the appropriate proportions of asphalt binder and aggregates according to the final asphalt mix design. 6.2.1. Prepare aggregate batches of the appropriate size to produce a com
32、pacted specimen that will be 150 mm in diameter and 75 mm in height. Heat the aggregate batches to the appropriate mixing temperature. Note 6The Appendix contains information on the calculation of the appropriate aggregate batch weight to achieve the correct specimen dimension at the proper percenta
33、ge of air voids. 6.2.2. Heat the asphalt binder to the appropriate mixing temperature. Mix the correct proportions of asphalt binder and combined aggregates to match the asphalt mix design. 6.2.3. After mixing, condition the asphalt mixture for 4.0 0.1 h at 135 5C in accordance with “Short-Term Cond
34、itioning for Mixture Mechanical Property Testing,” R 30. 6.2.4. Compact the HMA mixture in accordance with T 312 to obtain a specimen with the appropriate percentage of air voids as follows: Test Air Voids, % Repeated shear test 3.0 0.5 Simple shear test 7.0 0.5 Shear frequency sweep test 7.0 0.5 No
35、te 7Other compaction procedures than the Superpave gyratory compactor (T 312) and other target air void percentages may be used. However, caution is needed to prevent comparisons between asphalt mixtures with different target air voids or compaction. The test procedures and analyses are sensitive to
36、 both the percentage of air voids and the compaction procedure. Note 8Specimens are often compacted to a target air void percentage that is higher than the anticipated percentage of air voids in the cut test specimen. This is done because cutting the top and bottom of a compacted specimen removes lo
37、wer density material, thereby raising the density (lowering the air voids) of the test specimen. The magnitude of the difference between the target percentage of air voids for the compacted specimen and the target percentage of air voids for the test specimen is dependent upon the nominal maximum ag
38、gregate size of the mixture and the mixture gradation. Coarse mixes, and/or mixes with a larger nominal maximum aggregate size, tend to have greater differences between the compacted specimen air voids and the test specimen air voids. In general, a 1.0 percent offset (compact to a target of 4.0 perc
39、ent air voids or 8.0 percent air voids) should be sufficient to achieve the appropriate percentage of air voids in the test specimen. 6.2.5. Cool the compacted specimen to room temperature. Cut the compacted specimen to a height of 50 mm with two parallel faces. Determine and record the height of th
40、e cut specimen at the least and greatest heights. If the difference in the least and the greatest height is more than 2 mm, then discard the specimen and prepare another. 6.2.6. Determine the percentage of air voids in the test specimens in accordance with T 269. Determine the height and diameter of
41、 the test specimens in accordance with ASTM D3549/D3549M. 6.3. Field-Mixed, Laboratory-Compacted (FMLC) SpecimensObtain HMA samples in accordance with T 168. Compact specimens in accordance with T 312 to the appropriate percentage of air voids. (See Section 6.2.4 and Notes 7 and 8.) 2015 by the Amer
42、ican Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d T 320-5 AASHTO 6.3.1. Cool the compacted specimen to room temperature. Cut the compacted specimen to a height of 50 mm with two parallel faces. Determine and record
43、the height of the cut specimen at the least and greatest heights. If the difference in the least and the greatest height is more than 2 mm, then discard the specimen and prepare another. 6.3.2. Determine the percentage of air voids in the test specimens in accordance with T 269. Determine the height
44、 and diameter of the test specimens in accordance with ASTM D3549/D3549M. 6.4. Field-Mixed, Field-Compacted (FMFC), or Pavement Core SpecimensObtain asphalt pavement specimens having a diameter of 150 mm and a minimum thickness of 38 mm in accordance with ASTM D5361/D5361M. 6.4.1. Cut the specimens
45、to the proper test dimensions. Cool the compacted specimen to room temperature. Cut the compacted specimen to a height of 50 mm with two parallel faces. Determine and record the height of the cut specimen at the least and greatest heights. If the difference in the least and the greatest height is mo
46、re than 2 mm, then discard the specimen and prepare another. 6.4.2. Determine the percentage of air voids in the test specimens in accordance with T 269. Determine the height and diameter of the test specimens in accordance with ASTM D3549/D3549M. 6.5. Preparing the Specimens for TestingThe followin
47、g steps discuss the bonding of the test specimen to the platens for testing in the shear tester. 6.5.1. Ensure that the platens are clean, aligned, and clamped in place in the platen-specimen assembly device (optional) or shear test device. 6.5.2. Prepare the adhesive. If using an epoxy, proportion
48、and mix the resin and hardener together in accordance with the manufacturers instructions (Note 4). 6.5.3. Apply a thin coating of the adhesive to the top of the test specimen and to the bottom platen. Center the test specimen on the bottom platen and lower the top platen onto the specimen. Rotate t
49、he specimen slightly to ensure good bonding. Note 9Approximately 135 g of epoxy cement has been found suitable to provide bonding without excess waste. Half of the epoxy cement should be used on the bottom platen and the other half on the top of the specimen. 6.5.4. Bond the specimen to the platens using a light pressure (approximately 35 kPa) for 5 min. Begin removing excess adhesive from the sides of the test specimen by trimming as soon as the light pressure is applied. 6.5.5. After the adhesive has stabilized, remove the
