Specification for IFIT Equip Purchase 04-30-25 Clean.docx

April 04, 2025 Specification for I-FIT Testing Equipment Purchase Overview:

The equipment shall consist of a testing machine for the I-FIT testing, a load measuring device, a bend test fixture, specimen deformation measurement devices, and a control and data acquisition system. A closed loop feedback-controlled servo-hydraulic load frame shall be used to control the constant rate test from the dual load line displacement transducers. This entire assembly shall be on a cart with wheels to easily move for maintenance. Further, the testing results shall be consistent and comparable with the original TestQuip servo-hydraulic machines that Illinois Department of Transportation is currently using.

Axial Loading Device:

· A two-column loading device shall be provided.

· The loading device shall be capable of delivering loads with resolution of 5 N.

· The load capacity of the loading device shall be 5000 pounds force (25kN).

· The machine shall be capable of operating on a standard 110-volt AC, 50/60 Hz outlet under 20 Amps.

· The platen shall be capable of travel in the range of 2 to 4 inches (50 to 100 mm).

· The machine shall be capable of a loading speed range of 0 – 6.0 inch / minute (0 – 152.0 mm / min) and be able to maintain the displacement rate within 1% of set rate.

· The loading device shall have a rapid travel speed for moving the platen into place quickly.

· The equipment shall be capable of controlling the load rate, contact load and displacement rate from load line displacement transducers in true closed loop from separate transducers.

· The loading device shall have adjustable setup for test parameter selection with recording of the selected values in the test report.

· The loading device shall have a minimum data storage capacity of 4000 readings per test file.

· The loading device shall be capable of collecting data at a range of sampling frequencies from 1 to 50 Hz.

· The axial loading device and the data acquisition system should be capable of providing a smooth load-displacement curve.

· The device shall be calibrated according to the ASTM E4 requirements.

Bend Test Fixture:

The bend test fixture shall be according to Method A in Section 6 of Illinois modified AASHTO T 393 (attached below) and as follows:

· The bend test fixture shall be composed of two 25.4 mm (1 in.) diameter and 102 mm (4 in.) long stainless-steel rollers which are mounted on bearings through their axis of rotation and attached to the stainless-steel base plate with brackets. One of the stainless-steel rollers shall pivot on an axis perpendicular to the axis of loading to conform to slight specimen variations. A distance of 120 mm (center to center) between the two stainless steel rollers shall be maintained throughout the test.

· The tip of the loading head shall have a curvature with 25 mm diameter. The loading head shall be mounted in a pivot bearing that will allow it to contact the surface of the specimen uniformly.

· The steel used to fabricate the test fixture shall be stainless steel.

Displacement Measuring Device:

The loading displacement shall be measured using two externally applied displacement measurement devices positioned 180° from each other to each measure the load line displacement which is the distance between the loading head center contact and the contact line of the fixed lower roller. The average reading of the two referred to as “Average Load Line Displacement” is used as the control variable as well as the recorded displacement for calculation of the flexibility index.

Software for Data Collection and Data Transfer:

The system shall be capable of measuring, calculating, storing, outputting, and evaluating the following in a standard test report template:

· Fracture Energy. The fracture energy is calculated by dividing the work of fracture (the area under the load versus average load line displacement curve) by the ligament area (the product of the ligament length and the thickness of the specimen) of the I-FIT specimen prior to testing.

· The Area under the Experimental Curve. The area under the load-displacement curve is calculated using a numerical integration technique.

· Peak Load.

· Slope (m) at the inflection point after the peak load.

· Critical displacement (that point where the tangential slope intersects with the displacement (x) axis)

· Flexibility Index. The Flexibility Index shall be calculated from the load displacement curve according to Illinois modified AASHTO T 393.

· A standard USB port capable of exporting data.

· Data in delineated fields that is compatible with importing to Microsoft Excel spreadsheets.

· Connectivity to standard printers with capability of printing test results and summaries in report form.

Electronic Control of Test System:

· A Servo hydraulic control system with signal conditioning and data acquisition. The software includes a universal test software for complete machine control including Mode Switching of control, Data Acquisition setup, Amplitude Control using correction matrix, Digital Monitoring and Error checking for system stopping, Limits Monitoring on all channels, Hydraulic system High/Low pressure start up and Screen Plotting with Channel selection. It also includes a custom program for the I-FIT test operation. In addition, a Multi Test Language (MTL) is provided to allow the user to create custom programs or modify custom programs and store as a callable application. The software will plot the final energy calculation curve and the values from the integration and regression. A new laptop computer with Microsoft Office pre-installed will be supplied with the system. The computer will be capable of completing the testing and analysis without internet access.

· Software shall be included which is capable of streamlined data entry and analysis, where all pertinent background supporting mixture and testing information is entered once prior to running the test and the output with required information (fracture energy, slope, strength, and flexibility index, etc.) and summary graph are outputted by the operator.

· The Illinois Center for Transportation (ICT) analysis software shall be included and installed.

· The analysis software shall consistently calculate the same result every time when the same data inputs are run multiple times.

· The software shall be supported by the equipment manufacturer and issues and updates shall be addressed in an efficient, timely manner.

· The control of the testing system shall be by internal electronic / computer control that is built into the internal components of the system or an external stand-alone computer-controlled system. If an external stand-alone computer-controlled system is utilized by the I-FIT test equipment, the computer shall be provided and is considered a part of the entire testing equipment package.

· For external stand-alone computer-controlled system – cables and wires shall be organized and protected as necessary for durable use.

· The loading device shall include one or more Ethernet cables and/or RS232 ports and/or USB output ports to interface with a stand-alone computer, printer, or other devices.

Warranty and Training:

· A one-year warranty, including parts, labor and travel to the repair location shall be included as part of the bid price.

· An operation manual will be provided that provides guidance on all features of the equipment with contact information for warranty service.

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---IL Mod AASHTO T 393-22_12-01-24.pdf

December 1, 2024 Manual of Test Procedures for Materials 286

Illinois Modified Test Procedure Effective Date: December 1, 2018 Revised Date: December 1, 2024

Standard Method of Test for

Determining the Fracture Potential of Asphalt Mixtures Using the Illinois Flexibility Index Test (I-FIT)

Reference AASHTO T 393-22

Note: Illinois Modified AASHTO T 393 replaces all references to AASHTO TP 124.

AASHTO

Section

Illinois Modification

2.1 Replace the individual AASHTO Standards with the appropriate Illinois modified AASHTO Standards:

2.1 Delete:

R 67

2.1 Add reference to:

▪ Appendix B.7, Hot-Mix Asphalt QC/QA Procedure for Determining Random

Density Locations

▪ Appendix E.3, PFP and QCP Random Density Procedure

6.1.7 Replace the second sentence with the following:

The thermometer for measuring the temperature of water baths shall have a suitable range to determine 25 ± 0.5 °C. The thermometer may optionally meet the requirements of M 339M/M 339 and optionally have an accuracy of ± 0.13 °C.

6.1.9 Replace the first three sentences with the following:

Oven—A forced-draft oven, properly standardized, thermostatically controlled, and capable of maintaining a uniform temperature of 95 ± 3 °C. More than one oven may be used, provided each is used within its proper operating temperature range. The thermometer for measuring the temperature of materials shall have a suitable range to determine 95 ± 3 °C. The thermometer may optionally meet the requirements of M 339M/M 339 and optionally have an accuracy of ± 0.75 °C.

9.1.1 Replace with the following:

SGC Specimens—Compact the gyratory cylinders to an air void level of 7.5 ± 0.5%. Obtain a total of four individual I-FIT specimens as follows:

▪ From the middle of each 160 mm ± 1 mm tall specimen, obtain two cylindrical

50 ± 1 mm thick discs with smooth, parallel faces by saw cutting each face

(see Figure 4).

▪ From the middle of each 115 mm ± 1 mm tall specimen, obtain one cylindrical

50 ± 1 mm thick disc with smooth, parallel faces by saw cutting each face (see

Figure 4).

Cut each disc into two dimensionally equivalent halves.

A minimum of three individual test specimens are required for one I-FIT test.

Repeat this process if long-term aging (LTA) testing is to be conducted.

December 1, 2024 Manual of Test Procedures for Materials 287

Note 6 Replace with the following:

Although the required air voids are determined from the SGC cylinders, it is also required to determine the air voids on the individual semi-circular I-FIT test specimens to identify if 7.5 ± 0.5% air voids on the SGC cylinders is appropriate to produce individual semi-circular test specimens with 7.0 ± 1.0% air voids.

Note 7 New Note

Add after Note 6 HMA material shall be compacted into specimens using an SGC according to IL Modified AASHTO T 312. The number and selection of gyratory cylinders for testing shall be according to the Manual of Test Procedures Appendix B.9 for Mix design verification and Appendix B.4 for HMA test strips.

9.1.2 Replace the first sentence with the following:

Obtain pavement cores in accordance with Appendix B.7 or Appendix E.3.

Appendix B.7 shall be used in QC/QA applications and Appendix E.3 shall be used in QCP or PFP applications.

9.2 Re-number Note 7 to be Note 8.

10.1 Replace with the following:

Perform long-term aging on I-FIT specimens according to the procedure in Appendix X2.

Note 8 Delete

12.7 New

When four individual I-FIT specimens that are within specification are tested, the Flexibility Index value that is farthest from the average of the four test specimens shall be discarded as an outlier to lower the variability of the average Flexibility Index value that is reported. The test specimen that is discarded as an outlier shall be removed from the calculations of average and COV for peak load, post-peak slope, fracture energy, and Flexibility Index.

12.8 New

When three individual I-FIT specimens are tested, all three specimens will be included in the average and COV for peak load, post-peak slope, fracture energy, and flexibility index.

December 1, 2024 Manual of Test Procedures for Materials 287

14.1.7 Delete

14.1.8 Delete

14.1.9 Delete

Appendix X1.4.1.4.5

Replace Equation X1.10b with the following:

fG

FI A

m

December 1, 2024 Manual of Test Procedures for Materials 288

This Page Reserved image1.emf

AASHTO T393-22.pdf

Standard Method of Test for

Determining the Fracture Potential of Asphalt Mixtures Using the Illinois Flexibility Index Test (I-FIT)

Editorially Revised: 2022

AASHTO Designation: T 393-221 Adopted with Revisions: 2021

Technical Subcommittee: 2d, Proportioning of Asphalt–Aggregate Mixtures

American Association of State Highway and Transportation Officials 555 12th Street NW, Suite 1000 Washington, D.C. 20004

Accessed by account: Illinois Dept Of Transportation | Date: Fri Sep 16 19:08:17 GMT 2022 | IP address: 163.191.13.70

DKim

Line

TS-2d T 393-1 AASHTO

Standard Method of Test for

Determining the Fracture Potential of Asphalt Mixtures Using the Illinois Flexibility Index Test (I-FIT)

AASHTO Designation: T 393-221 Adopted with Revisions: 2021 Editorially Revised: 2022

Technical Subcommittee: 2d, Proportioning of Asphalt–Aggregate Mixtures

1. 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 the direction of load application. The data analysis procedure associated with this test determines the fracture energy (Gf) and post peak slope (m) of the load–load line displacement (LLD) curve. These parameters are used to develop a flexibility index (FI) to predict the fracture resistance of an asphalt 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 test 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 to establish and follow appropriate health and safety practices and determine the applicability of regulatory limitations prior to use.

1.4. The quality of the results produced by this standard are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of R 18 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with R 18 alone does not completely assure reliable results. Reliable results depend on many factors; following the suggestions of R 18 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.

2. REFERENCED DOCUMENTS

2.1. AASHTO Standards:

< M 339M/M 339, Thermometers Used in the Testing of Construction Materials < R 18, Establishing and Implementing a Quality Management System for Construction

Materials Testing Laboratories < R 67, Sampling Asphalt Mixtures after Compaction (Obtaining Cores)

© 2022 by the American Association of State Highway and Transportation Officials.

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TS-2d T 393-2 AASHTO

< T 166, Bulk Specific Gravity (Gmb) of Compacted Asphalt Mixtures Using Saturated Surface- Dry Specimens

< 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, Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the

Superpave Gyratory Compactor

2.2. ASTM Standards:

< D8, Standard Terminology Relating to Materials for Roads and Pavements < D3549/D3549M, Standard Test Method for Thickness or Height of Compacted Bituminous

Paving Mixture Specimens < E1, Standard Specification for ASTM Liquid‐in‐Glass Thermometers < E230/E230M, Standard Specification for Temperature‐Electromotive Force (emf) Tables for

Standardized Thermocouples < E879, Standard Specification for Thermistor Sensors for General Purpose and Laboratory

Temperature Measurements < E1137/E1137M, Standard Specification for Industrial Platinum Resistance Thermometers < E2877, Standard Guide for Digital Contact Thermometers

2.3. International Electrotechnical Commission Standards:

< IEC 60584‐1: 2013 Thermocouples ‐ Part 1: EMF Specifications and Tolerances < IEC 60751: 2008 Industrial Platinum Resistance Thermometers and Platinum Temperature

Sensors

2.4. Other Publications:

< Al-Qadi, I. L., H. Ozer, J. Lambros, A. El Khatib, P. Singhvi, T. Khan, and B. Doll. 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, 2015.

< Doll. B., H. Ozer, J. Rivera-Perez, J. Lambros, and I. L. Al-Qadi. Investigation of Viscoelastic Fracture Fields in Asphalt Mixtures Using Digital Image Correlation. International Journal of Fracture, Vol. 205, No. 1. Springer Nature Switzerland AG, January 2017,pp. 37–56.

< Ozer, H., I. L. Al-Qadi, J. Lambros, A. El-Khatib, P. Singhvi, and B. Doll. Development of the Fracture-Based Flexibility Index for Asphalt Concrete Cracking Potential Using Modified Semi-Circle Bending Test Parameters. Construction and Building Materials, Vol. 115.

Science Direct, Elsevier B.V., Amsterdam, Netherlands, 2016a, pp. 390–401.

< Ozer, H., and P. Singhvi, T. Khan, J. Rivera, I. L. Al-Qadi. Fracture Characterization of Asphalt Mixtures with RAP and RAS Using the Illinois Semi-Circular Bending Test Method and Flexibility Index. Transportation Research Record, Vol. 2575. Transportation Research Board, National Research Council, Washington, DC, 2016b, pp. 130–137.

< Ozer, H., I. L. Al-Qadi, P. Singhvi, J. Bausano, R. Carvalho, X. Li, and N. Gibson.

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, 2017.

< RILEM Technical Committee 50-FMC. Determination of the Fracture Energy of Mortar and Concrete by Means of Three-Point Bend Tests on Notched Beams. Materials and Structures, No. 106, July–August 1985. Springer Netherlands for International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM), Dordrecht, The Netherlands, 1985, pp. 285–290.

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TS-2d T 393-3 AASHTO

3. TERMINOLOGY

3.1. Definitions:

3.1.1. critical displacement, u1—displacement at the intersection of the post-peak slope with the displacement-axis.

3.1.2. displacement at peak load, u0—recorded displacement at peak load.

3.1.3. final displacement, ufinal—recorded displacement at the 0.1 kN cut-off load.

3.1.4. flexibility index, FI—index intended to characterize 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, Gf—energy required to create a unit surface area of a crack.

3.1.6. ligament area, Arealig—cross-sectional area of specimen through which the crack propagates, calculated by multiplying ligament width (test specimen thickness) and ligament length.

3.1.7. linear variable displacement transducer (LVDT)—sensor device for measuring linear displacement.

3.1.8. load line displacement (LLD)—displacement measured in the direction of the load application.

3.1.9. post-peak slope, m—slope at the first inflection point of the load–LLD curve after the peak.

3.1.10. semicircular bend (SCB) geometry—a half disc with a notch parallel to the direction of load application.

3.1.11. work of fracture (Wf)—calculated as the area under the load–LLD curve.

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 is conditioned and maintained through testing at 25 ± 0.5°C. 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 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 I-FIT fixture and I-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 peak load (u0), critical displacement (u1), and a flexibility index (FI) are calculated from the load and LLD results.

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TS-2d T 393-4 AASHTO

Figure 1—I-FIT SGC Laboratory Compacted Specimen Configuration (dimensions in millimeters)

5. SIGNIFICANCE AND USE

5.1. The I-FIT is used to determine fracture resistance parameters of 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 Gf and 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 cracking. The range for an acceptable FI will vary according to local environmental conditions, application of mixture, nominal maximum aggregate 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 mixture’s overall capacity to resist 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 ranking 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 temperature. Fracture mechanisms for viscoelastic materials are influenced by crack front viscoelasticity and bulk material (far from the crack front) viscoelasticity. Total calculated Gf from 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) (Doll 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 cohesive 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 experiment.

Ligament Length

≤2.25

150.0 (±1.0) a = 15.0 (±1.0)

.0

1.

0)

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TS-2d T 393-5 AASHTO

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 pavement cores with a diameter of 150 mm.

6. APPARATUS

6.1. Testing Machine—An I-FIT system consists of a closed-loop axial loading device, a load measuring device, a bend test fixture, specimen deformation measurement devices, and a control and data acquisition system. A constant displacement-rate device, such as a closed loop, feedback-controlled servo-hydraulic load frame, shall be used.

Note 1—An electromechanical, screw-driven machine may be used if results are comparable to a closed loop, feedback-controlled servo-hydraulic load frame.

6.1.1. Axial Loading Device—The loading device shall be capable 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 Fixture—The fixture 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 curvature 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 Figures 2 and 3.

6.1.2.1. Method A—Typically 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 slight specimen variations. A distance of 120 ± 0.1 mm between the two steel rollers is maintained throughout the test.

6.1.2.2. Method B—An alternate fixture design uses 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 allowed to rotate away from the backstops during the test; but remain in contact with the sample.

6.1.3. Internal Displacement Measuring Device—The displacement measurement can be performed using the machine’s stroke (position) transducer if the resolution of the stroke is sufficient (0.01 mm or lower). The 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 Device—If an internal displacement measuring device does not exist or has insufficient precision, 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 System—Time and load, and LLD (using external and/or internal displacement measurement 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 load–LLD curve.

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TS-2d T 393-6 AASHTO

6.1.6.

6.1.7.

6.1.8.

6.1.9.

Note 2—The use of two LLD transducers 180 degrees from one another and 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.

Saw—Laboratory saw capable of cutting asphalt specimens; must be capable of cutting the notch described in Figure 1.

Conditioning Chamber—Water bath or environmental chamber of sufficient size, capable of maintaining a uniform temperature, used within their proper operating temperature range, to conditioned samples at 25 ± 0.5°C. The thermometer for measuring the temperature of water baths shall meet the requirements of M 339M/M 339 with a temperature range of at least 20 to 30°C, and an accuracy of ±0.13°C.

Note 3—Thermometer types suitable for use include ASTM E1 mercury thermometers; ASTM E879 thermistor thermometer, Special order; ASTM E1137/E1137M Pt-100 RTD platinum resistance thermometer, Special order; or IEC 60751: 2008 Pt-100 RTD platinum resistance thermometer, Special order.

Measuring Device—Caliper or ruler accurate to ±0.1 mm for specimen thickness and area measurement.

Oven—A forced-draft oven, properly standardized, thermostatically controlled, and capable of maintaining a uniform temperature of 95°C within ±3°C. More than one oven may be used, provided each is used within its proper operating temperature range. The thermometer for measuring the temperature of materials shall meet the requirements of M 339M/M 339 with a temperature range of at least 25 to 185°C, and an accuracy of ±0.75°C.

Note 4—Thermometer types suitable for use include ASTM E1 mercury thermometers; ASTM E230/E230M thermocouple thermometer, Type T, Special Class; IEC 60584 thermocouple thermometer, Type T, Class 1; or E2877 digital metal stem thermometer.

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TS-2d T 393-7 AASHTO

Figure 2—Method A—Isometric, Cross-Section, and Elevation of the I-FIT Fixture (dimensions in millimeters)

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TS-2d T 393-8 AASHTO

Figure 3—Method B—Isometric, Cross-Section, and Elevation of the I-FIT Fixture (dimensions in millimeters)

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TS-2d T 393-9 AASHTO

7. HAZARDS

7.1. Standard laboratory caution should be used in handling, compacting, and fabricating asphalt mixtures test specimens in accordance with T 312 and when using a saw for cutting specimens.

8. CALIBRATION AND STANDARDIZATION

8.1. A water bath as used in AASHTO T 283 or an environmental chamber will be used to maintain the specimen at a constant and uniform temperature.

8.2. Verify the calibration of all measurement components (such as load cells and LVDTs) of the testing system.

8.3. If any of the verifications yield data that does not comply with the accuracy specified, correct the problem prior to proceeding with testing. Appropriate action may include maintenance of system components, calibration of system components (using an independent calibration agency, service by the manufacturer, or in-house resources), or replacement of the system components.

9. PREPARATION OF TEST SPECIMENS AND PRELIMINARY

DETERMINATIONS

9.1. Test Specimen Size—For mixtures with an NMAS of 19 mm or less, prepare the test specimens from a lab compacted SGC specimen or from pavement cores. If laboratory compacted SGC specimens are used, the final I-FIT specimens shall have smooth parallel faces with a thickness of 50 ± 1 mm and a diameter of 150 ± 1 mm (see Figure 4). If pavement cores are used, refer to Figure 1 for the notch width and notch length dimensions and tolerances. The final pavement core I-FIT specimen dimensions shall be 150 ± 8 mm in diameter with smooth parallel faces 25 to 50 ± 1 mm thick depending on available field layer thickness.

Note 5—A typical laboratory saw for mixture specimen preparation can be used to obtain cylindrical discs with smooth parallel surfaces. A tile saw is recommended for cutting the 15 ± 1 mm notch in the individual I-FIT specimens. Diamond-impregnated cutting faces and water cooling are recommended to minimize damage to the specimen. When cutting the I-FIT specimens into semi-circular halves, it is recommended not to push the two halves against each other because it may create an uneven base surface of the test specimen that can affect the I-FIT results.

9.1.1. SGC Specimens—Prepare one laboratory SGC specimen according to T 312 in the SGC with the compaction height a minimum of 160 ± 1 mm. From the middle of each 160 ± 1 mm tall specimen, obtain two cylindrical 50 ± 1 mm thick discs with smooth, parallel faces by saw cutting (see Figure 4). For laboratory compacted specimens, the bulk specific gravity and the air voids shall be determined for each of the two circular discs according to T 269. The air voids for each disc shall be 7.0 ± 1.0 percent. Cut each disc into two dimensionally equivalent halves resulting in four individual I-FIT specimens. A minimum of three individual test specimens are required for one I-FIT result.

Note 6—The height of the gyratory compacted specimens should be 160 ± 1 mm to achieve a target 7.0 ± 1.0 percent air voids in each disc (see Figure 4). If a lab does not have the capability to compact 160 ± 1 mm tall gyratory specimens, then two 115 ± 1 mm tall gyratory specimens may be compacted and used instead to replace each 160 ± 1 mm tall gyratory specimen. A 50 ± 1 mm thick disc will be cut from the middle of each gyratory specimen, which will result in four individual I-FIT specimens (see Figure 4).

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TS-2d T 393-10 AASHTO

OR

Figure 4—Specimen Preparation from 160 mm or 115 mm Tall SGC Specimens

9.1.2. Pavement Cores—Obtain pavement cores in accordance with R 67. Obtain one 150 mm diameter pavement core if the lift thickness is greater than or equal to 100 mm, or two 150 mm diameter pavement cores if the lift thickness is less than 100 mm.

9.1.2.1. Pavement Core Specimen Preparation—Prepare four replicate I-FIT specimens using pavement cores obtained from a pavement lift, with smooth, parallel surfaces that conform to the height and diameter requirements specified herein. To preserve and maximize core thickness, the as-compacted face shall be utilized as well as a sawed face. The thickness of test specimens in most cases for pavement cores may vary from 25 to 50 ± 1 mm. If the lift thickness is less than 50 ± 1 mm, test specimens should be prepared as thick as possible but in no case be less than two times the nominal maximum aggregate size of the mixture or 25 ± 1 mm, whichever is greater. If lift thickness is greater than 50 ± 1 mm, a 50 ± 1 mm disc shall be prepared as specified in Section 9.1. Cores from pavements with lifts greater than 75 ± 1 mm may be cut to provide two cylindrical specimens of equal thickness. In the upper-most pavement layer when cored, the as-compacted face will remain intact and one cut will be made to produce a disc at least two times the nominal maximum aggregate size of the mixture or 25 ± 1 mm, whichever is greater. In all subsequent discs cut from that pavement core, two sawed faces may be used to produce smooth, parallel surfaces.

9.1.2.2. Determining the Bulk Specific Gravity—Determine the bulk specific gravity directly on each disc obtained from pavement cores according to T 166.

9.1.2.3. Determining the Air Voids—The air void contents of each disc shall be determined according to T 269. Pavement cores will not be subject to air void content tolerances.

9.1.2.4. Cutting Semicircular Test Specimens—Cut each cylindrical disc in half to produce two dimensionally equivalent semicircular test specimens.

9.2. Notch Cutting—Cut a notch along the axis of symmetry of each individual semicircular specimen to a depth of 15 ± 1 mm and ≤2.25 mm in width (see Figure 1).

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TS-2d T 393-11 AASHTO

Note 7—If the notch terminates in an aggregate particle 9.5 mm or larger on both faces of the specimen, the specimen shall be discarded.

9.3. Determining Specimen Dimensions—Measure the notch depth on both faces of the specimen and record the average value to the nearest 0.5 mm. Measure and record the ligament length (see Figure 1) and thickness of each specimen. The ligament length may be measured directly on both faces of the specimen with the average value recorded, or the ligament length may be measured indirectly by subtracting the notch depth from the entire width (radius) of the specimen on both faces of the specimen and averaging the two measurements. Measure the specimen thickness approximately 19.0 mm on either side of the notch and on the curved edge directly across from the notch. Average the three measurements and record as the average thickness to the nearest

0.1 mm.

10. LONG-TERM AGING

10.1. Perform a long-term aging procedure on I-FIT specimens as defined by the specifying agency.

Note 8—The I-FIT specimen long-term aging procedure in Appendix X2 may be used.

11. TEST PROCEDURE

11.1. Conditioning—Test specimens shall be conditioned in a water bath or an environmental chamber at 25 ± 0.5°C for 2 h ± 10 min.

11.1.1. Test Temperature Control—Immediately after removing the test specimen from the conditioning water bath or environmental chamber, complete positioning and testing of the I-FIT specimen within 5 ± 1 min to ensure that the specimen temperature is maintained.

11.2. Position Specimen—Position the test specimen in the test fixture on the rollers so that it is centered in both the “x” and the “y” directions and so that the vertical axis of loading is aligned to pass from the center of the top radius of the specimen through the middle of the notch.

11.3. Contact Load—First, impose a contact load of 0.1 ± 0.01 kN in stroke control with a loading rate of 0.05 kN/s.

11.3.1. Record Contact Load—Record the contact load to ensure it is achieved.

11.3.2. Loading—After the contact load of 0.1 kN is reached, the test is conducted using LLD control at a rate of 50 mm/min. The test stops when the load drops below 0.1 kN.

11.3.3. Repeat Sections 11.1 through 11.3.2 for each test specimen.

12. PARAMETERS

12.1. Determining Work of Fracture (Wf)—The work of fracture is calculated as the area under the load–LLD curve (see Figure 5). If the test is stopped prior to reaching 0.1 kN, the remainder of the load–LLD curve should be produced by extrapolation techniques.

The area under the load–LLD curve is calculated using a numerical integration technique. In order to apply the numerical integration, raw load-displacement data shall be divided into two curves described by an appropriate fitting equation. A polynomial equation with a degree of six is sufficient for the curve prior to peak load (Equation 1). An exponential-based function (Equation

2) is used for the post-peak load portion of the curve. Then, analytical integration shall be applied to calculate the area under each curve (Equation 3).

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TS-2d T 393-12 AASHTO

For displacements (u) prior to the peak load (Pmax):

6 5 4 3 2 1 1 1 2 3 4 5 6 7( )P u c u c u c u c u c u c u c= ´ + ´ + ´ + ´ + ´ + ´ + (1) where:

ci = polynomial coefficients.

For displacements (u) after the peak load (Pmax) to the cut-off displacement (ufinal):

d

4 exp( ) u en idii fi

P u é ùæ ö-= ê úå -ç ÷ê úè øë û

= (2) d, e, f = polynomial coefficients, n is the number of exponential terms.

Work of fracture can be analytically or numerically calculated using the integral equation below and boundaries of displacement:

0 final

1 2 u u f u

W P u du P u du= +ò ò (3) u0 = displacement at the peak load;

ufinal = displacement at the 0.1 kN cut-off load.

Note 9—Due to the relative difference between the compliance of testing frame and specimen, displacement recorded may vary. A correction factor may need to be considered to correct recorded displacements when applicable.

Figure 5—Recorded Load (P)–Load Line Displacement (u) Curve

12.2. Fracture Energy (Gf)—The fracture energy Gf, determined as per the RILEM TC 50-FMC (1985) approach, is calculated by dividing the work of fracture (the area under the load–LLD curve; see Figure 5) by the ligament area (the product of the ligament length and the thickness of the specimen) of the I-FIT specimen prior to testing:

Peak Load

Slope at Inflection Point ( m)

Critical Displacement (u1)

Final Displacement (ufinal)

Displacement, u (mm)

Lo ad

,P (k

N

0 1 2 3 4 5 6

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TS-2d T 393-13 AASHTO lig

Area

W

G = ´ (4)

Gf = fracture energy (Joules/m2);

Wf = work of fracture (Joules);

P = load (kN);

u = load line displacement (mm);

Arealig = ligament area = (r – a) × t, (mm2);

r = specimen radius (mm);

a = notch length (mm);

t = specimen thickness (mm).

Note 10—Gf is a size dependent property. This specification does not aim at calculating size independent Gf. Therefore, cracking resistance of asphalt mixtures quantified with Gf may vary when the notch length to radius ratio changes.

12.3. Determining Post-Peak Slope (m)—The inflection point is determined on the load–LLD curve (Figure 5) after the peak load. The slope of the tangential curve drawn at the inflection point represents post-peak slope.

12.4. Determining Displacement at Peak Load (u0)—The displacement when peak load is reached.

12.5. Determining Critical Displacement (u1)—Intersection of the tangential post-peak slope with the displacement axis yields the critical displacement value. A straight line is drawn connecting the inflection point and displacement axis with a slope m.

12.6. Flexibility Index (FI)—FI can be calculated from the parameters obtained using the load–LLD curve (Al-Qadi et al. (2015), Ozer et al. (2016a), Ozer et al. (2016b)). The factor A is used for unit conversion and scaling. A is equal to 0.01. Complete details of the analysis procedure are provided in Appendix X1.

FI A

= ´ (5)

|m| = absolute value of post-peak load slope m (kN/mm).

13. CORRECTION FACTORS

13.1. Correction Factors for Flexibility Index—Flexibility index correction factors for pavement core specimen thickness and differences between field and lab compaction may be needed. A thickness correction factor may be applied for pavement cores tested at thickness less than 45 mm. The correction factors may require local calibration to consider locally available materials and mixture design requirements.

14. REPORT

14.1. Report the following information:

14.1.1. Bulk specific gravity of each specimen tested, to the nearest 0.001;

14.1.2. Air void content of each disc, to the nearest 0.1 percent;

14.1.3. The number of cut faces for each specimen tested, if pavement cores were used;

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TS-2d T 393-14 AASHTO

14.1.4. Average thickness t and average ligament length of each specimen tested, to the nearest 0.1 mm;

14.1.5. Initial notch length a, to the nearest 0.5 mm;

14.1.6. Average and coefficient of variation (COV) of peak load, to the nearest 0.1 kN;

14.1.7. Average and COV of recorded time at peak load, to the nearest 0.1 s;

14.1.8. Average and COV of load-line displacement at the peak load (u0), to the nearest 0.1 mm;

14.1.9. Average and COV of critical displacement (u1), to the nearest 0.1 mm;

14.1.10. Average and COV of post-peak slope (m), to the nearest 0.1 kN/mm;

14.1.11. Average and COV of fracture energy Gf, to the nearest 1 J/m2; and

14.1.12. Average and COV of flexibility index to the nearest 0.1.

15. PRECISION AND BIAS

15.1. Precision:

15.1.1. Single-Operator Precision—The single-operator coefficient of variation of flexibility index has been found to be 27.1 percent. Therefore, results of two properly conducted tests by the same operator on the same material are not expected to differ from each other by more than 75.9 percent of their average.

15.1.2. Multi-laboratory Precision—The multi-laboratory coefficient of variation of flexibility index has been found to be 34.1 percent. Therefore, results of two properly conducted tests by two different laboratories on specimens of the same material are not expected to differ from each other by more than 95.5 percent of their average.

Table 1—Precision Estimatesa

Material Average FI

Components of Variance Variances

Single Operator Between Laboratory Single Operator Multi-laboratory 2017 5.2 2.36 0.49 2.36 2.85

2018 23.1 36.85 7.64 36.85 44.49

2019 9.6 5.90 9.55 5.90 15.44

Material Average FI

Standard Deviations Coefficients of Variation (%)

Single Operator Multi-laboratory Single Operator Multi-laboratory 2017 5.2 1.54 1.69 29.6 32.5

2018 23.1 6.07 6.67 26.3 28.9

2019 9.6 2.43 3.93 25.3 41.0 a Based on a multi-laboratory study of state departments of transportation, private, and academic laboratories in 2017, 2018, and 2019. Three materials (all

9.5-mm NMAS mixtures) with varying contents of RAP were used (a different mixture was used each year). Approximately 12 specimens were tested per material on at least 30 devices per year.

15.2. Bias—No information can be presented on the bias of the procedure because no material having an accepted reference value is available.

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TS-2d T 393-15 AASHTO

16. KEYWORDS

16.1. Asphalt mixture; flexibility index; fracture energy; Illinois flexibility index test (I-FIT);

semicircular bend (SCB); stiffness; work of fracture.

APPENDIXES

X1. CALCULATIONS2

X1.1. Scope:

X1.1.1. This appendix presents the framework and algorithms used to process the load–LLD curve and to compute the critical variables such as fracture energy, slope (after the crack begins propagating), and flexibility index. The algorithm consists of the following steps:

X1.1.1.1. Preprocessing the raw load–LLD curve;

X1.1.1.2. Pre-peak calculations; and

X1.1.1.3. Post-peak calculations.

X1.2. Preprocessing:

X1.2.1. The algorithm starts with preprocessing the raw test output file containing the load and displacement data. The first step of pre-processing is to trim the tail of the curve. The data points whose load values are smaller than 0.1 kN are removed. Because the load–LLD curve exhibits different characteristics before and after the peak load, the trimmed load–LLD curve is divided into two parts: pre-peak and post-peak. To do this, the peak load at which maximum load value is reached is identified. The values of the load–LLD curve before the peak load are assigned to the pre-peak segment; the remaining data are assigned to the post-peak segment. The calculations required for pre-peak and post-peak segments are explained in Sections X1.3 and X1.4.

X1.3. Pre-Peak Calculations:

X1.3.1. The following steps are completed to process the pre-peak segment of the load–LLD curve:

X1.3.1.1. The beginning (ui, Pi) and end (u0, Pmax) coordinates of the load–LLD curve are captured.

X1.3.1.2. A polynomial equation with a degree of six is fitted to the pre-peak segment of the load–LLD curve (Equation X1.1).

6 5 4 3 2 1 1 1 2 3 4 5 6 7( )P u c u c u c u c u c u c u c= ´ + ´ + ´ + ´ + ´ + ´ + (X1.1) ci = polynomial coefficients.

X1.3.1.3. A new set of data is generated with equal displacement increments using the polynomial function bounded by the beginning and end points found in Section X1.3.1.1. The increments used to divide the data are found by dividing the displacement at the peak load by 1000. A new displacement vector (upre) is generated from ui to u0 with calculated increments. The new loading vector is computed by substituting the value of the displacement vector in Equation X1.1. The purpose of generating a dataset with higher resolution is to increase the accuracy of the numerical integration described in Section X1.3.1.4.

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TS-2d T 393-16 AASHTO

X1.3.1.4. Numerical integration is applied to calculate area under the pre-peak segment of the load–LLD curve. The integral for area calculation is given in Equation X1.2. A trapezoidal integration technique is used for the numerical integration of Equation X1.2. When analytical integration tools are available, analytical integration is recommended to improve accuracy.

(pre-peak) ( ) fW P u du= ò (X1.2)

X1.3.1.5. When the load–LLD curve starts with a residual load at zero displacement, the curve needs to be extrapolated to modify the area calculated in the previous step. In such cases, the curve is linearly extrapolated to the displacement coordinate where the load is zero. The displacement at the zero load (ur) is found. The area under the extrapolated segment is added to calculate total pre-peak area X1. Numerical integration is applied to find the residual area shown by the additional term in Equation X1.3. The second part of the sum comes from the additional area of extrapolation.

(pre-peak) ( ) 0.5 f r rW P u du u P= + ´ ´ò (X1.3)

Pr = residual load at zero displacement; and ur = calculated displacement at zero load.

X1.4. Post-Peak Calculations:

X1.4.1. An algorithm was developed to process the post-peak segment of the load–LLD curve to calculate area under the curve as well as the inflection point and slope at the inflection point. Explanations of each step are given in Sections X1.4.1.1 through X1.4.1.3.

X1.4.1.1. The beginning (u0, P0) and end (uf, Pf) coordinates of the post-peak load–LLD curve are captured (see Figure X1.1). The raw data records are stored in two vectors as upost = {u0, …, uf} and Ppost = {P0,…, Pf}.

X1.4.1.2. In this step, candidate lower bounds for parameter f in Equation X1.4 are initialized and kept in a…