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C-1 APPENDIX C Draft AASHTO Standard for Steady Shear Flow and Phase Angle Methods Note: These draft specifications have been modified for the purpose of inclusion in this report.
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C-2 Standard Method of Test for Determining the Laboratory Mixing & Compaction Temperature of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) Steady Shear Flow Method AASHTO Designation: X XXX-XX
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C-3 Standard Method of Test for Determining the Laboratory Mixing & Compaction Temperature of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) Steady Shear Flow Method AASHTO Designation: X XXX-XX SCOPE This test method covers the determination of laboratory mixing and compaction temperatures using a steady shear flow test. The steady shear flow test is conducted using the Dynamic Shear Rheometer (DSR) utilizing the rheometers capability to function in constant rotation in one direction. The values stated in SI units are to be regarded as the standard. 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. REFERENCED DOCUMENTS 2.1 AASHTO Standards · M320, PERFORMANCE GRADED ASPHALT BINDER · T315, DETERMINING THE RHEOLOGICAL PROPERTIES OF ASPHALT BINDER USING A DYNAMIC SHEAR RHEOMETER (DSR) 2.2. ASTM Standard · D8, TERMINOLOGY RELATING TO MATERIALS FOR ROADS AND PAVEMENTS · D2493,VISCOSITY-TEMPERATURE CHART FOR ASPHALTS
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C-4 3. TERMINOLOGY 3.1 Definitions: 3.1.1 Definitions of terms used in this practice may be found in ASTM D8, determined from common English usage, or combinations of both. 4. SUMMARY OF TEST METHOD 4.1. A sample of unaged asphalt binder is tested in the DSR using the 25-mm plate geometry with a 0.5-mm gap setting. The sample is tested in flow mode over a range of shear stresses from 0 to 500 Pa at 3 temperatures (76, 82, 88C). 4.2. After testing is completed, the viscosity values at 500 Pa are plotted versus temperature on a log-log scale. From the plot, mixing and compaction temperatures are determined based upon specified viscosity ranges. 5. SIGNIFICANCE AND USE 5.1 This test method is designed to determine the laboratory mixing and compaction temperatures for modified and unmodified asphalt binders. 6. PROCEDURE 6.1. Sample Preparation The sample for the Steady Shear Flow test is prepared the same as samples for T 315 using the 25-mm plates with the following exceptions as noted in 6.1.1. The temperature control will also follow T 315 requirements. 6.1.1 The test gap for the Steady Shear Flow test will be 0.5 mm. An additional 0.025- mm gap will be added before trimming to allow for creation of the bulge. 6.2. Set the DSR software to perform a steady shear flow test from 50 to 500 Pa, collecting 5 data points for viscosity per log decade. 6.2.1 A 12 second data-sampling period should be used. 6.2.2 Steady state conditions will be met when 3 consecutive viscosity readings vary less than 2%. A maximum test time for each stress level of 12 minutes should be set to ensure that tests won't last interminably.
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C-5 6.3. After testing is completed, increase temperature by 6°C and repeat steps 6.1 6.3 until the number of desired test temperatures has been reached. 7. HAZARDS 7.1. Use standard laboratory safety procedures in handling the hot asphalt binder when preparing specimens for this test method. 8. CALCULATION 8.1. Using the results obtained in Section 6, create a log-log plot of Viscosity (Pa-S) at 500 Pa versus Temperature (°C). Information on the construction of viscosity temperature charts can be found in ASTM D2493. 8.2. Construct a line through the 3 data points on the plot created in section 8.1. Extend the line as necessary to cross mixing and compaction target viscosity ranges. 8.3. Using target ranges of 0.15 to 0.19 Pa-S for mixing and 0.32 0.38 Pa-S for compaction, determine the mixing and compaction temperature ranges either visually or using a computer graphing program. 9. REPORT 9.1 Report the following information: 9.1.1 Sample identification; 9.1.2. Test Temperatures, nearest 0.1 °C; 9.1.3. Viscosity at 500 Pa for each test temperature, cP; 9.1.4. Mixing temperature range, nearest °C; 9.1.5. Compaction temperature range, nearest °C;
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C-6 10. PRECISION AND BIAS 10.1. Precision The research required to develop precision estimates has not been conducted. 10.2. Bias The research required to establish the bias has not been conducted. 11. KEYWORDS 11.1. Steady Shear Flow; laboratory mixing temperature; laboratory compaction temperature, Dynamic Shear Rheometer (DSR); modified asphalt binder, target viscosity range. APPENDIX X.1. SAMPLE CALCULATIONS X1.1. Table X1.1 shows a set of test results at 3 temperatures: Table X1.1 Steady Shear Flow Test Results Test Temperature, °C Viscosity at 500 Pa, Pa-S 76.0 34.1 82.0 18.8 88.0 10.7 X.1.2. Figure X1.1 shows the data in Table X1.1 plotted on a log-log Temperature - Viscosity chart:
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C-7 500 100 10 Viscosity, Pa-s 1 Compaction Range 0.1 Mixing Range 52 58 64 70 76 82 88 100 120 135 150 165 180 200 Temperature, C Figure X1.1 Test Data Plot Showing Viscosity at 500 Pa and 3 Test Temperatures X.1.3 Using a compaction temperature range of 0.32 0.38 Pa-S, the laboratory compaction temperature of this asphalt binder will be 137 140°C. X.1.4. Using a mixing temperature range of 0.15 0.19 Pa-S, the laboratory mixing temperature of this asphalt binder will be 152 157°C.
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C-8 Standard Method of Test for Determining the Laboratory Mixing & Compaction Temperature of Asphalt Binder Using a Dynamic Shear Rheometer (DSR). The Phase Angle Method. AASHTO Designation: X XXX-XX American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001
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C-9 Standard Method of Test for Determining the Laboratory Mixing & Compaction Temperature of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) The Phase Angle Method AASHTO Designation: X XXX-XX ________________________________________________ SCOPE This test method covers the determination of the dynamic shear modulus and phase angle of asphalt binder when tested in dynamic (oscillatory) shear using parallel plate test geometry. It is applicable to asphalt binders having dynamic shear modulus values in the range from 50 Pa to 10 MPa. This range in modulus is typically obtained between 40°C and 150°C at an angular frequency of 0.1 to 100 rad/s. This test method is intended for determining the linear viscoelastic properties of asphalt binders over a range of both frequency & temperature in order to determine a reasonable master curve of the visco-elastic properties of asphalt binder. This master curve will be used to determine the appropriate laboratory mixing & compaction temperatures. This standard is appropriate for unaged material or material aged in accordance with T 240 and R 28. Particulate material in the asphalt binder is limited to particles with longest dimensions less than 250µm. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. ____________________________________________________________________
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C-10 REFERENCED DOCUMENTS AASHTO Standards: · M 320, Performance-Graded Asphalt Binder · R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) · R 29, Grading or Verifying the Performance Grade of an Asphalt Binder · T 40, Sampling Bituminous Materials · T 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) ASTM Standards: · C 670, Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials · E 1, Specification for ASTM Thermometers · E 77, Standard Test Method for Inspection and Verification of Thermometers · E 563, Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature · E 644, Standard Test Methods for Testing Industrial Resistance Thermometers · D 2170, Standard Test Method for Kinematic Viscosity of Asphalts (Bitumens) · D 2171, Standard Test Method for Viscosity of Asphalts by Vacuum Capillary Viscometer Deutsche Industrie Norm (DIN) Standards: · 43760, Standard for Calibrations of Thermocouples National Cooperative Highway Research Program Report: · NCHRP Report xxx, Procedure for Determining Mixing and Compaction Temperatures of Asphalt Binders in Hot Mix Asphalt _______________________________________________________________________ TERMINOLOGY Definitions: asphalt binder--an asphalt-based cement that is produced from petroleum residue either with or without the addition of non-particulate organic modifiers.
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C-11 Descriptions of Terms Specific to This Standard: annealing--heating the binder until it is sufficiently fluid to remove the effects of steric hardening. complex shear modulus (G*)--ratio calculated by dividing the absolute value of the peak-to-peak shear stress, , by the absolute value of the peak-to-peak shear strain, . calibration--process of checking the accuracy and precision of a device using NIST- traceable standards and making adjustments to the device where necessary to correct its operation or precision and accuracy. dummy test specimen--a specimen formed between the dynamic shear rheometer (DSR) test plates from asphalt binder or other polymer to measure the temperature of the asphalt binder held between the plates. The dummy test specimen is used solely to determine temperature corrections. loading cycle--a unit cycle of time for which the test sample is loaded at a selected frequency and stress or strain level. phase angle ()--the angle in radians between a sinusoidally applied strain and the resultant sinusoidal stress in a controlled-strain testing mode, or between the applied stress and the resultant strain in a controlled-stress testing mode. loss shear modulus (G´´)--the complex shear modulus multiplied by the sine of the phase angle expressed in degrees. It represents the component of the complex modulus that is a measure of the energy lost (dissipated during a loading cycle). storage shear modulus (G´)--the complex shear modulus multiplied by the cosine of the phase angle expressed in degrees. It represents the in-phase component of the complex modulus that is a measure of the energy stored during a loading cycle. parallel plate geometry--refers to a testing geometry in which the test sample is sandwiched between two relatively rigid parallel plates and subjected to oscillatory shear. oscillatory shear--refers to a type of loading in which a shear stress or shear strain is applied to a test sample in an oscillatory manner such that the shear stress or strain varies in amplitude about zero in a sinusoidal manner. linear viscoelastic--within the context of this specification refers to a region of behavior in which the dynamic shear modulus is independent of shear stress or strain.
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C-40 X11. DETERMINATION OF TIME TO THERMAL EQUILIBRIUM X11.1.1 Reason for Determining Time Required to Obtain Thermal Equilibrium: X11.1.2 After the test specimen has been mounted in the DSR, it takes some time for the asphalt binder between the test plates to reach thermal equilibrium. Because of thermal gradients within the test plates and test specimen, it may take longer for the test specimen to come to thermal equilibrium than the time indicated by the DSR thermometer. Therefore, it is necessary to experimentally determine the time required for the test specimen to reach thermal equilibrium. X11.1.3. The time required to obtain thermal equilibrium varies for different rheometers. Factors that affect the time required for thermal equilibrium include: X11.1.4. Design of the rheometer and whether air or liquid is used as a heating-cooling medium; water has roughly 25 times more thermal conductivity to that of air. Air conductivity is improved by increasing the velocity of air flow. X11.1.5. Difference between ambient temperature and the test temperature, different when testing below room temperature, and above room temperature, X11.1.6. Difference in temperature between the trimming and test temperature, and X11.1.7. Plate size, different for the 8-mm and 25-mm plate. X11.2. It is not possible to specify a single time as the time required to obtain thermal equilibrium. For example, thermal equilibrium of the asphalt sample is reached much quicker with liquid-controlled rheometers than with air-cooled rheometer. This requires that the time to thermal equilibrium be established for individual rheometers, typical trimming and testing temperatures, and testing conditions. ________________________________________________________________________ X12. METHOD TO DETERMINE THE TIME REQUIRED TO OBTAIN THERMAL EQUILIBRIUM FOR BOTH THE DSR & THE SAMPLE X12.1.1. The time to reach thermal equilibrium is the time required to reach a constant modulus regardless of heating to that temperature or cooling down to that temperature. Typically, this time will be greater than the time for the DSR reports on its display reading for temperature to be stable. The asphalt sample heats and cools much slower then the response of the environmental chamber. Thus, it is important to determine the precise time required for a DSR to achieve thermal equilibrium for the asphalt sample. X12.2. As a guide, safe values which can be used with most modern are as follows. Rheometers using a total fluid immersion principle of the sample in water will require a minimum of 3 minutes from the time the chamber stabilizes within ±0.1°C. A forced gas oven will require a minimum of 60 minutes from the time the chamber stabilizes within ±0.1°C. Refer to the manufacturer for specific help to determine the required time to stabilize the
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C-41 sample for accurate asphalt measurements for specific DSR model. Dry directly heated plates or oven chambers employing radiant heating or not pre-conditioned gas may take significantly longer then 60 minutes to achieve thermal equilibrium on the asphalt sample with acceptable thermal gradients. X12.3. The following procedure can be used to determine the appropriate time required to achieve sample thermal equilibrium for a specific DSR. X12.3.1 A reliable estimate of the time required for thermal equilibrium can be obtained by monitoring the DSR temperature and the complex modulus of a sample mounted between the test plates. Because the modulus is highly sensitive to temperature, it is an excellent indicator of thermal equilibrium. The following procedure is recommended for establishing the time to thermal equilibrium: X12.3.2. Mount a binder sample in the DSR and trim in the usual manner. Create a bulge and bring the test chamber or fluid to the test temperature. X12.3.3. Operate the DSR in a continuous mode at 10 rad/s using an unmodified asphalt binder sample--one that does not change modulus with repeated shearing. If testing at grade temperature use 10% strain. If testing at other then grade temperature, use the smallest strain value that gives good measurement resolution. X12.3.4. Perform a series of temperature steps, each held for at least 2000 seconds, while recording the modulus at 30 s time intervals. These steps should approach the nominal temperature from heating and cooling in order to identify any thermal hysteresis within the sample. Results should be displayed on a plot of the modulus versus time (Figure X12.1). As the example in Figure X12.1, the temperature profile was 70°C, 76°C, 70°C, 64°C, 70°C, 76°C, 70°C. Results as shown in Figure X12.1. can be graphed as an overlay of G* to permit the comparison of the 70°C results of modulus as shown in (Figure X12.2). Where the G* data for 70°C overlay defines the instrument's time to reach thermal equilibrium. In this example, the time to thermal equilibrium is reported as 0.6k seconds (600 seconds).
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C-42 Figure X12.1--Results of the test to determine a DSR's temperature performance Figure X12.2--Comparison of Modulus at 70C; Thermal equilibrium reached where the center G* values agree (at about 500sec in this example) X12.3.5. By approaching the nominal temperature from both heating and cooling, enables the identification of actual Thermal Equilibrium from the effects of apparent thermal hysterisis. Thermal hysteresis is the effect of the inefficient thermal conductivity of the environmental chamber in which the sample core or sample edge contains greater then the required ±0.1°C thermal gradient over the time permitted to achieve thermal equilibrium The appearance of thermal equilibrium may be mistaken for the slow response of the asphalt to change temperature as asphalt is a poor thermal conductor. This effect is obvious in Figure X12.3. Given longer time to achieve thermal equilibrium the amount of thermal hysteresis should reduce.
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C-43 Figure X12.3--Identifying Thermal Hysteresis; G* does not recover post. X12.3.6. Once the DSR's time to thermal equilibrium has been identified, a small buffer time of 2 minutes should be added as a conditioning period to the testing programmed time for equilibrium. From the example of Figure X12.3., where the DSR's time to thermal equilibrium is 600 seconds (DSR TE), and the additional conditioning buffer of 120 seconds gives the total time to use for testing as 720 seconds. Testing thermal equilibrium (Sample TE would be 720 seconds (12min), as shown in (Figure X12.4.).
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C-44 Figure X12.4--Identifying the Sample time for Thermal Equilibrium X12.4. Because the time required to reach thermal equilibrium can vary with the test temperature and testing conditions, the time to thermal equilibrium should be established separately for any new testing protocol. Once the time to thermal equilibrium has been established, it does not have to be repeated unless the test conditions change. ________________________________________________________________________
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C-45 X13. EXAMPLE OF FREQUENCY SWEEP ISOTHERMS X13.1 Graph of G* and phase angle for each of the individual frequency sweeps at each temperature on a single graph (Figure X13.1) Figure X13.1-Graph of frequency sweeps for each temperature. X14. EXAMPLE OF MASTER CURVE AT 80°C AND DETERMINATION OF FREQUENCY WHERE THE PHASE ANGLE IS EQUAL TO 86 DEGREES. X14.1. Display of Isotherms (Figure X14.1) The example in Figure X14.1 shows 4 sets of isotherms for an asphalt binder.
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C-46 Figure X14.1- Graph of Isotherms. X14.2. Performing the Time Temperature Superposition model to the data using a reference temperature of 80°C would produce the master curve shown in Figure X14.2. Figure X14.2.- Master Curve created to an 80°C reference from isotherms. X14.3. From the master curve, identify the phase angle of 86 degrees and determine the frequency at which it occurs (Figure X14.3). Most modern DSRs provide features within their software in which enables the operator the ability to identify specific points from the graph or table. In the event the exact value is not provided, interpolate between the two nearest points bracketing the 86 degree value. The exactness required for the reporting of frequency in this process is ±10%. Small errors in reporting have little to no effect on the final determination of both mixing & compaction temperature.
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C-47 Figure X14.3- Determination of Frequency at a phase angle of 86 degrees from the master curve _______________________________________________________________________ X15. VERIFICATION OF MASTER CURVE WORKING DATA BY USING BLACK SPACE DIAGRAM X15.1 A good example of a Black Space diagram where there is shown a continuous curve exhibited in the results (Figure X15.1). This is where there are not obvious discontinuities. FIGURE X15.1- Good example of Black Space diagram X15.2. A poor example of a Black Space diagram, where there are obvious discontinuities in the results (Figure X15.2). In the case of a poor Black Space, the data should be retested with particular attention to ensuring all the data are collected in the linear visco-elastic region by ensuring the correct strains are applied properly to all frequencies and that the temperatures are correct for each frequency tested. (Figure X15.2)
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C-48 FIGURE X15.2- Poor example of Black Space diagram X16. DETERMINATION OF LABORATORY MIXING TEMPERATURE X16.1. Use the following equation to determine laboratory compaction temperature in ºF. Mixing Temperature (ºF) = 325-0.0135 (X16) Where = the frequency in rad/s for the phase angle of 86 degrees as reported from the master curve. 12.2.4 ________________________________________________________________________ X17. DETERMINATION OF LABORATORY COMPACTION TEMPERATURE X17.1. Use the following equation to determine laboratory compaction temperature in ºF. Compaction Temperature (ºF) = 300-0.012 (X17) Where = the frequency in rad/s for the phase angle of 86 degrees as reported from the master curve. 12.2.4 ________________________________________________________________________
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C-49 X18. SAMPLE REPORT Header Information: Item Data Group 1 Item Data Group 2 Operator's Name: 24 Alpha-Numeric Date of Test (dd/mm/yy): __/__/__ 18 Alpha Time of Test (hr:min): __:__ Test Specimen ID No.: DSR Manufacturer: 12 Alpha-Numeric Project ID No.: 12 Alpha-Numeric File Name: 12 Alpha-Numeric DSR Model: 12 Alpha-Numeric DSR Serial Number Or Sample Grade: 18 Alpha-Numeric 12 Alpha-Numeric Other Identifying ID No.: Frequency, rad/s for Phase Angle of 86 0.000 Software Version: 12 Alpha-Numeric degrees at a temperature of 80°C Mix Temperature, °F 000 Compaction 000 Temperature, F ________________________________________________________________________
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C-50 X19. REFERENCES X19.1. Anderson, D. A. and M. Marasteanu. "Manual of Practice for Testing Asphalt Binders in Accordance with the Superpave PG Grading System." The Pennsylvania Transportation Institute, The Pennsylvania State University, PTI 2K07, November 1999 (Revised February 2002). X19.2. Wadsworth, H., ed. Handbook of Statistical Methods for Engineers and Scientists. McGraw-Hill, New York, NY, 1990. X19.3. Anderson, D. A., C. E. Antle, K. Knechtel, and Y. Liu. Interlaboratory Test Program to Determine the Inter- and Intra-Laboratory Variability of the SHRP Asphalt Binder Tests. FHWA, 1997. X19.4. Cox, W. P. and E. H. Merz. Correlation of Dynamic and Steady Flow Viscosities, Journal of Polymer Science, Volume 28, 1958, pp. 619622. X19.5. West, R. Procedure for Determining Mixing and Compaction Temperatures of Asphalt Binders in Hot Mix Asphalt, NCHRP Report XXX, 2008.