1、Standard Method of Test for Determining the Fracture Potential of Asphalt Mixtures Using the Flexibility Index Test (FIT) AASHTO Designation: TP 124-181Technical Section: 2d, Bituminous Materials Release: Group 3 (August) American Association of State Highway and Transportation Officials 444 North C
2、apitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d TP 124-1 AASHTO Standard Method of Test for Determining the Fracture Potential of Asphalt Mixtures Using the Flexibility Index Test (FIT) AASHTO Designation: TP 124-181Technical Section: 2d, Bituminous Materials Release: Group 3 (August) 1.
3、SCOPE 1.1. This test method covers the determination of Mode I (tensile opening mode during crack propagation) cracking resistance properties of asphalt mixtures at intermediate test temperatures. Specimens are tested in the semicircular bend geometry, which is a half disc with a notch parallel to t
4、he direction of load application. The data analysis procedure associated with this test determines the fracture energy (Gf) and post peak slope (m) of the loadload line displacement (LLD) curve. These parameters are used to develop a Flexibility Index (FI) to predict the fracture resistance of an as
5、phalt mixture at intermediate temperatures. The FI can be used as part of the asphalt mixture approval process. 1.2. These procedures apply to test specimens having a nominal maximum aggregate size (NMAS) of 19 mm or less. Lab compacted and pavement core specimens can be tested according to this tes
6、t procedure. A thickness correction factor will need to be developed and applied for pavement cores tested at a thickness less than 45 mm. 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
7、 to establish and follow appropriate health and safety practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 67, Sampling Asphalt Mixtures after Compaction (Obtaining Cores) T 166, Bulk Specic Gravity (Gmb) of Compacted Hot
8、 Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 269, Percent Air Voids in Compacted Dense and Open Asphalt Mixtures T 283, Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage T 312, Prep
9、aring and Determining the Density of Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor TP 105, Determining the Fracture Energy of Asphalt Mixtures using Semicircular Bend Geometry (SCB) 2.2. ASTM Standards: D8, Standard Terminology Relating to Materials for Roads and Pavements 2
10、018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-2 AASHTO D3549/D3549M, Standard Test Method for Thickness or Height of Compacted Bituminous Paving Mixture Specimens 2.3. Other Publications:
11、Al-Qadi, I. L., H. Ozer, J. Lambros, A. El Khatib, P. Singhvi, T. Khan, and B. Doll. 2015. Testing Protocols to Ensure Performance of High Asphalt Binder Replacement Mixes Using RAP and RAS, FHWA ICT-15-07. Illinois Center for Transportation, Rantoul, IL. Doll. B., H. Ozer, J. Rivera-Perez, J. Lambr
12、os, and I. L. Al-Qadi. 2016. Investigation of Viscoelastic Fracture Fields in Asphalt Mixtures using Digital Image Correlation. International Journal of Fracture, Vol. 205, No. 1, pp. 3756. Ozer, H., I. L. Al-Qadi, J. Lambros, A. El-Khatib, P. Singhvi, and B. Doll. 2016a. Development of the Fracture
13、-Based Flexibility Index for Asphalt Concrete Cracking Potential Using Modified Semi-Circle Bending Test Parameters. Construction and Building Materials, Vol. 115, pp. 390401. Ozer, H., and P. Singhvi, T. Khan, J. Rivera, I. L. Al-Qadi. 2016b. Fracture Characterization of Asphalt Mixtures with RAP a
14、nd RAS Using the Illinois Semi-Circular Bending Test Method and Flexibility Index. Transportation Research Record, Transportation Research Board, National Research Council, Washington, DC, Vol. 2575, pp. 130137. Ozer, H., I. L. Al-Qadi, P. Singhvi, J. Bausano, R. Carvalho, X. Li, and N. Gibson. 2017
15、. Assessment of Asphalt Mixture Performance Tests to Predict Fatigue Cracking in an Accelerated Pavement Testing Trial. International Journal of Pavement Engineering, Special Issue for Cracking in Flexible Pavements and Asphalt Mixtures: Theories to Modeling, and Testing to Mitigation. RILEM Technic
16、al Committee 50-FMC. 1985. “Determination of the Fracture Energy of Mortar and Concrete by Means of Three-Point Bend Tests on Notched Beams.” Materials and Structures, Springer Netherlands for International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM),
17、Dordrecht, The Netherlands, No. 106, JulyAugust 1985, pp. 285290. 3. TERMINOLOGY 3.1. Definitions: 3.1.1. critical displacement, u1displacement at the intersection of the post-peak slope with t he displacement-axis. 3.1.2. displacement at peak load, u0recorded displacement at peak load. 3.1.3. final
18、 displacement, ufinalrecorded displacement at t he 0.1 kN cut-off load. 3.1.4. flexibility index, FIindex intended to characteri ze the cracking resistance of asphalt mixture, calculated by multiplying the ratio of fracture energy to post-peak slope by a constant multiplier. 3.1.5. fracture energy,
19、Gfenergy required to create a unit surface area of a crack. 3.1.6. ligament area, Arealigcross-sectional area of specimen through which the crack propa gates, calculated by multiplying ligament width (test specimen thickness) and ligament length. 3.1.7. linear variable displacement transducer (LVDT)
20、sensor device for measuring linear displacement. 3.1.8. load line displacement (LLD)displacement measured in the direction of the load applicatio n. 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d
21、 TP 124-3 AASHTO 3.1.9. post-peak slope, mslope at the first inflection po int of the loadLLD curve after the peak. 3.1.10. semicircular bend (SCB) geometrya half disc with a notch para llel to the direction of load application. 3.1.11. work of fracture (Wf)calculated as the area under the loadLLD c
22、urve. 4. SUMMARY OF METHOD 4.1. A Superpave Gyratory Compactor (SGC) compacted asphalt mixture specimen or an asphalt pavement core is trimmed and cut in half to create a semicircular test specimen. A notch is sawn in the flat side of the semicircular specimen opposite the curved edge. The specimen
23、is conditioned and maintained through testing at 25 0.5C. The specimen is positioned in the fixture with the notched side down centered on two rollers. A load is applied along the vertical radius of the specimen and the load and load line displacement (LLD) are measured during the entire duration of
24、 the test. The load is applied such that a constant LLD rate of 50 mm/min is obtained and maintained for the duration of the test. The FIT fixture and FIT specimen geometry for an SGC laboratory compacted specimen are shown in Figure 1. 4.2. Fracture energy (Gf), post-peak slope (m), displacement at
25、 peak load (u0), critical displacement (u1), and a flexibility index (FI) are calculated from the load and LLD results. Figure 1FIT SGC Laboratory Compacted Sp ecimen Configuration (dimensions in millimeters) 5. SIGNIFICANCE AND USE 5.1. The FIT is used to determine fracture resistance parameters of
26、 an asphalt mixture at an intermediate temperature (Al-Qadi et al. (2015), Ozer et al. (2016a), Ozer et al. (2016b). From the fracture parameters of Gfand m obtained, the FI of an asphalt mixture is calculated. The FI provides a means to identify brittle mixtures that may be prone to premature crack
27、ing. The range for an acceptable FI will vary according to local environmental conditions, application of mixture, 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-4 AASHTO nominal maximum a
28、ggregate size (NMAS), asphalt binder content, asphalt binder performance grade (PG), air voids, and expectation of service life, etc. (Al-Qadi et al. (2015), Ozer et al. (2016a), Ozer et al. (2016b), Ozer et al. (2017). 5.2. The calculated FI indicates an asphalt mixtures overall capacity to resist
29、cracking related damage (Al-Qadi et al. (2015). Generally, a mixture with higher FI can resist crack propagation for longer time duration under tensile stress. The FI should not be directly used in structural design and analysis of pavements. FI values, obtained using this procedure, are used in ran
30、king the cracking resistance of alternative mixtures for a given layer in a structural design. The Gf parameter is dependent on specimen size, loading time, and is temperature dependent. Fracture mechanisms for viscoelastic materials are influenced by crack front viscoelasticity and bulk material (f
31、ar from the crack front) viscoelasticity. Total calculated Gffrom this test includes the amount of energy dissipated by crack propagation, viscoelastic mechanisms away from the crack front, and other inelastic irreversible processes (frictional and damage processes at the loading support points) (Do
32、ll et al., 2016). 5.3. Gf is one of the parameters used to calculate the FI, which is further used to predict AC mixture fracture potential. It also represents the main parameter input in more complex analyses based on a theoretical crack (cohesive zone) model. In order to be used as part of a cohes
33、ive zone model, fracture energy as calculated from the experiment shall be corrected to determine energy associated with crack propagation only. A correction factor may be used to eliminate other sources of inelastic energy contributing to the total fracture energy calculated directly from the exper
34、iment. 5.4. This test method and FI can be used to rank the cracking resistance of asphalt mixtures containing various asphalt binders, modifiers of asphalt binders, aggregate blends, fibers, and recycled materials. 5.5. The specimens can be readily obtained from SGC compacted cylinders or from pave
35、ment cores with a diameter of 150 mm. 6. APPARATUS 6.1. Testing MachineA FIT system consists of a clos ed-loop axial loading device, a load measuring device, a bend test xture, specimen deformation measurement devices, and a control and data acquisition system. A constant displacement-rate device, s
36、uch as a closed loop, feedback-controlled servo-hydraulic load frame, shall be used. Note 1An electromechanical, screw-drive n machine may be used if results are comparable to a closed loop, feedback-controlled servo-hydraulic load frame. 6.1.1. Axial Loading DeviceThe loading device shall be capabl
37、e of delivering loads in compression with a maximum resolution of 10 N and a capacity of at least 10 kN. 6.1.2. Bend Test FixtureThe xture is composed of a loading head, a steel base plate, and two steel rollers with a nominal diameter (D) of 25 mm. The tip of the loading head has a contact curvatur
38、e with a radius of 12.5 0.05 mm. The horizontal loading head shall pivot relative to the vertical loading axis to conform to slight specimen variations. The length of the two roller supports in Figure 2 and Figure 3 shall be a minimum of 65 mm. Illustrations of the loading and supports are shown in
39、Figures 2 and 3. 6.1.2.1. Method ATypically two steel rollers with a nominal diameter of 25 mm are mounted on bearings through their axis of rotation and attached to the steel base plate with brackets. One of the steel rollers may pivot on an axis perpendicular to the axis of loading to conform to s
40、light 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-5 AASHTO specimen variations. A distance of 120 0.1 mm between the two steel rollers is maintained throughout the test. 6.1.2.2. Method
41、 BAn alternate fixture design use s two steel rollers with a nominal diameter of 25 mm that each rotate in a U-shaped roller support steel block. The initial roller position is fixed by springs and backstops that establish the initial test span dimension of 120 0.1 mm. The support rollers are allowe
42、d to rotate away from the backstops during the test; but remain in contact with the sample. 6.1.3. Internal Displacement Measuring DeviceThe displacement measur ement can be performed using the machines stroke (position) transducer if the resolution of the stroke is sufficient (0.01 mm or lower). Th
43、e fracture test displacement data may be corrected for system compliance, loading-pin penetration and specimen compression by performing a calibration of the testing system. 6.1.4. External Displacement Measuring DeviceIf an internal displacement measuring device does not exist or has insufficient p
44、recision, an externally applied displacement measurement device such as a linear variable differential transducer (LVDT) accurate to 0.01 mm can be used (Figure 2 and Figure 3). 6.1.5. Control and Data Acquisition SystemTime and load, and LLD (using external and/or internal displacement measurement
45、device) are recorded. The control data acquisition system is required to apply a constant LLD rate at a precision of 50 1 mm/min and collect data at a minimum sampling frequency of 20 Hz in order to obtain a smooth loadLLD curve. Note 2The use of two LLD transducers 180 degrees from one another and
46、on each side of a test specimen may be used. In this approach, an average LLD value is computed to control the test. Controlling the test using an average LLD value may reduce test variability. 6.1.6. SawLaboratory saw capable of cutti ng asphalt specimens; must be capable of cutting the notch descr
47、ibed in Figure 1. 6.1.7. Conditioning ChamberWater bath or environmental cha mber capable of maintaining specimen temperature as described in Section 10.1. 6.1.8. Measuring DeviceCaliper or ruler accur ate to 0.1 mm for specimen thickness and area measurement. 2018 by the American Association of Sta
48、te Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-6 AASHTO Figure 2Method A Isometric, Cross-Section, and Elevation of the FIT Fixture (dimension in millimeters) 2018 by the American Association of State Highway and Transportation
49、 Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-7 AASHTO Figure 3Method B Isometric, Cross-Section, and E levation of the FIT Fixture (dimension in millimeters) 2018 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2d TP 124-8 AASHTO 7. HAZARDS 7.1. Standard laboratory caution should be used in handling, compacting, and fabricating asphalt mixtures test spec
