Investigation of Short-Term Laboratory Aging of Neat and Modified Asphalt Binders (2011) / Chapter Skim
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From page 15... ...
Comparison of rheological properties between long-term microwave aging and RTFOT plus PAV aging has shown good agreement. For Project 9-36, the principal concern with basing improved binder aging methods on microwave technology is a lack of understanding of the mechanism whereby microwave energy accelerates the aging process.
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From page 16... ...
In summary, the review of the literature and research in progress identified significant post-SHRP research on binder aging methods using the three approaches of microwave technology, thin films, and air blowing. Of these three, microwave technology was eliminated because the mechanism whereby microwave energy accelerates the aging process is not well understood, and high pressures are needed for simulation of long-term aging.
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From page 17... ...
Comparisons of rheological properties and mass change revealed that the MGRF consistently aged binders less than the RTFOT. In the second and third phases the airflow was increased to 1 L/min, and 2 L/min, respectively.
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From page 18... ...
Properties considered included softening point, penetration, penetration index, Frass breaking point, ductility, complex shear modulus, creep stiffness, and m-value. 3.2.2.2 Rotating Cylinder Aging Test The Rotating Cylinder Aging Test (RCAT)
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From page 19... ...
Comparison of continuous grade temperatures from the MGRF and RTFOT from the FHWA study. -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 RTFOT MASS CHANGE, % M G RF M AS S CH AN G E, % ALF Control PG 70-22 PG 58-22 Air Blown PG 70-28 PG 58-22 EVA Grafted SBS Radial Grafted Figure 3-4.
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From page 20... ...
Parameter Condition Test Sample Size 500 g Temperature 163°C Speed 1 rpm Airflow Air at 4 L/min Short Term Aging Time 235 min Temperature 90°C Speed 1 rpm Airflow Oxygen at 4.5 L/hr Long Term Aging Time 140 hr OVEN ROTATING VESSEL SHAFT AIR SUPPLY Figure 3-5. Rotating cylinder aging test.
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From page 21... ...
(1) dismissed the poor agreement between the RTFOT mass change and the mass of condensed volatile compounds collected in the SAFT as being the result of errors in the RTFOT mass change measurements.
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From page 22... ...
The authors also concluded that the volatile loss procedure in the SAFT worked very well and provided a significant improvement of the RTFOT mass change determinations. This conclusion for the volatile loss procedure is suspect because three of the laboratories could not provide valid volatile loss data, and the corresponding data for the RTFOT were not collected.
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From page 23... ...
Comparison of candidate methods. Considerations Rotating Cylinder Aging Test Modified German Rotating Flask Stirred Air Flow Test Neat and Modified Binders Yes Yes Yes Amount of Material 500 g 200 g 250 g Equipment Cost $18,000 $3,500 $5,000 estimated Equipment Complexity Moderately complex Simple Moderately complex Availability Low High Low Test Complexity Reasonable Simple Reasonable Binder Recovery Easy Easy Easy Clean Up Solvent Ignition Oven Solvent General Active Development Yes Yes Yes Published Procedure Yes Yes Yes Further Refinement Needed No No Yes Temperature 163°C 165°C 163°C Duration 235 min 210 min 45 min Atmosphere Air at 4 L/min Air at 2 L/min Air at 2 L/min Measure Volatility None -- configuration of vessel makes volatile recovery difficult Mass change -- adaptable to volatile recovery Volatile recovery system Mimics Aged Binder Chemistry Yes Yes Yes ShortTerm Aging Repeatability/Reproducibility Limited data Limited data Some data Adaptable to Long Term Yes -- work completed Yes -- steel balls to enhance mixing Probably with new impeller Published Procedure Yes Yes No Temperature 90°C 95°C neat 103°C modified Duration 140 hr 47 hr Atmosphere Oxygen at 4.5 L/hr Oxygen at 7 L/hr NA Aging Kinetics Possible Yes Yes Yes Mimics Aged Binder Chemistry Yes Yes Likely LongTerm Aging Repeatability/Reproducibility Limited Limited None
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From page 24... ...
It appears that for short-term aging, this approach is much more efficient at mixing air with the binder because the duration of the test is approximately one-half to one-quarter of that for the tests involving thin films with similar temperatures and airflow rates. It is not known whether the more rapid aging observed in the SAFT is the result of more rapid volatile removal or more rapid oxidation.
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From page 25... ...
The measure of the degree of aging shown in Figure 3-9 is defined by Equation 1. The relative aging according to this equation is simply the change in viscosity above RTFOT aging caused by the prototype long-term test divided by the increase in viscosity that occurs during PAV aging.
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Figure 3-10. Schematic of 2,000-mL Morton flask with three steel balls.
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From page 27... ...
The measure of the degree of aging shown in Figure 3-14 is the same used in Figure 3-9 and defined in Equation 1. The relative aging according to this equation is simply the change in viscosity above RTFOT aging caused by the prototype long-term test divided by the increase in viscosity that occurs during PAV aging.
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From page 28... ...
The relative aging according to this equation is simply the change in viscosity above RTFOT aging caused by the prototype long-term test divided by the increase in viscosity that occurs during PAV aging. The dynamic viscosity was measured at 60°C, 0.1 rad/s.
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From page 29... ...
The following properties were measured for the RTFOT, PAV, and long-term SAFT: • Shear modulus and phase angle from a DSR frequency sweep at 60°C using frequencies from 0.1 to 100.0 Hz. • Shear modulus and phase angle from a DSR frequency sweep at 25°C using frequencies from 0.1 to 100.0 Hz.
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From page 30... ...
Testing conditions for the long-term SAFT. Condition Value Sample Size 250 g Aging Temperature 100°C Impeller Type Helix + 8-Bladed Turbine Impeller Speed 350 rpm Airflow Rate 36 L/h Aging Time 40 hours Table 3-10.
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From page 31... ...
3.4.2 Improved VCS Design The design of an improved VCS was an incremental process. In the first iteration, called VCS-I, silica gel and activated carbon filters were added after the condenser from the prototype VCS to collect moisture and hydrocarbon material passing through the condenser.
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From page 32... ...
0.00 0.10 0.20 0.30 0.40 0.50 0.60 70 90 101 Absolute Pressure, kPa Qu an tit y C ol le ct ed , w t % Condenser Hydrocarbon Trap Moisture Trap SAFT Mass Loss RTFOT Mass Loss Figure 3-20. Mass of material collected in the improved VCS, VCS-I.
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From page 33... ...
The resulting system is shown in Figure 3-22. Although not shown in Figure 3-22, the inlet silica gel and activated carbon filters from the VCS-I were retained to condition the incoming nitrogen and air.
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From page 34... ...
Three replicate samples of each binder were conditioned in the commercial SAFT and the RTFOT. The amount of material collected on the HayeSep Q and the molecular sieve for each of the asphalt binders is shown in Table 3-13 and Figure 3-25.
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From page 35... ...
Mass collected on VCS-III filters and RTFOT mass change. Mass Collected on Filters, % of Original Mass Binder HayeSep Q Molecular Sieve Combined HayeSep Q and Molecular Sieve Negative of RTFOT Mass Loss, % of Original Mass AAC-1 0.072 0.141 0.214 0.058 AAD-2 0.041 0.134 0.175 1.058 AAF-1 0.043 0.114 0.157 0.008 ABM-2 0.024 0.113 0.137 0.349 ABL-1 0.049 0.129 0.178 0.654 AAM-1 0.014 0.085 0.100 -0.122 Citgoflex 0.020 0.052 0.072 0.196 ALF 64-40 0.046 0.007 0.053 0.207 Airblown 0.020 0.061 0.081 -0.031 Elvaloy 0.000 0.003 0.003 0.173 EVA 0.020 0.005 0.026 0.132 Novophalt 0.025 0.006 0.031 0.132 Indicating Silica Gel Moisture Trap Bottled Nitrogen SAFT VESSEL BINDER Activated Charcoal Hydrocarbon Trap Kolby Junior Laboratory Air Supelco HaySepQ® Supelco Molecular Sieve 5A Ambient 100 mm Figure 3-24.
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From page 36... ...
0.00 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 0.05 0.10 0.15 0.20 0.25 M as s Co lle ct ed o n Ab so rb en ts , % o f O rig in al B in de r M as s Negative of the RTFOT Mass Change, % Hayesep Q Molecular Sieve Combined Hayesep Q & Molecular Sieve Figure 3-26. Material collected on molecular sieve and HayeSep Q versus RTFOT mass change.
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From page 37... ...
3.5.2 Operating Parameters Experiment The purpose of this experiment was to determine the effect of three operating parameters -- impeller speed, airflow rate, and conditioning time -- on the properties of asphalt binder aged in the commercial SAFT. Three different unmodified binders, listed in Table 3-15, were chosen for this experiment.
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From page 38... ...
Since degassing is needed to remove entrapped air from stiff modified binders, this experiment shows that it must be included as part of the procedure for all binders, and that the degassing must be standardized. The second analysis that was performed investigated the effects of impeller speed, airflow rate, and conditioning time on the degree of aging that occurs in the SAFT to determine the sensitivity of the SAFT aging to these parameters.
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From page 39... ...
The final operating parameters selected from the operating parameters experiment for the commercial SAFT for use in the verification study were • 163°C aging temperature, • 2,000 mL/min airflow, 39 Table 3-18. Summary of degassing effects.
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In the oven-aged mixtures experiment, hot mix asphalt using the binders from the RTFOT verification experiment were prepared and aged in accordance with AASHTO R30. Dynamic modulus master curve tests were performed on the mixture samples.
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From page 41... ...
The trend line for the MGRF data coincides with the line of equality, while that for the SAFT 41 SAFT oven heated to 176°C Binder Temperature = 163°C Oven maintained at 176°C Process controller adjusts oven temperature as needed to bring binder to 163°C N2 flowing at 2,000 mL/min Vessel placed in oven, Binder Temperature 120°C Air flowing at 2,000 mL/min End of conditioning period Heat-up phase Conditioning period, 50 min Binder Temperature = 160°C < 10 min < 20 min Note: 1,000 rpm impeller speed and 250 g sample Figure 3-30. Sequence of operations used in final SAFT configuration.
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From page 42... ...
Difference in continuous-grading temperature for SAFT and MGRF residue compared to RTFOT residue.
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From page 43... ...
that was discussed earlier in Section 3.2.2.1. 3.6.1.3 Christensen-Anderson Master Curve Parameters Binder master curves were developed from the combined DSR and BBR data using the Christensen-Anderson Model (33)
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From page 44... ...
The parameter, ωc, changes with temperature and therefore is always given at the reference temperature, selected as 22°C for direct comparison with the data back-calculated from the mixture master curves. To construct the complete master curve, the bending beam rheometer creep stiffness was converted to shear modulus using the following approximate interconversions.
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From page 45... ...
The glassy modulus is the limiting maximum modulus and is approximately equal to 1 GPa, reflective of the stiffness of carbon–carbon bonds that predominate in asphalt binders. The viscous asymptote is the 45° line that the master curve approaches at low frequencies and is an indicator of the steady-state viscosity of the binder.
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From page 46... ...
As shown, there is significant scatter in the data because the master curve parameters are somewhat interrelated and depend on the quality of the data. Trend lines are shown for the SAFT and the MGRF data in Figures 3-35 and 3-36 to make it easier to interpret these plots.
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From page 47... ...
0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Ch an ge in T d fo r M G RF A gi ng , ° C Ch an ge in T d fo r S AF T Ag in g, °C Change in Td for RTFOT Aging, °C SAFT MGRF MGRF SAFT Figure 3-37. Comparison of change in defining temperature for RTFOT, SAFT, and MGRF aging.
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From page 48... ...
3.6.2 Oven-Aged Mixture Experiment In the oven-aged mixture experiment, binder properties back-calculated from mixture dynamic modulus test data were used to assess how well the binder aging procedures simulate the aging that occurs in mixtures during shortterm oven conditioning. Dynamic modulus master curve tests were performed on samples prepared from unconditioned mixture and from mixture conditioned for 4 hours at 135°C as specified in AASHTO R30.
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From page 49... ...
Three replicate specimens were tested in this project. Dynamic modulus master curves were fitted to the measured data using the procedure in AASHTO PP61.
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From page 50... ...
Temperatures and frequencies used in the dynamic modulus master curve testing. Temperature, °C Frequency, Hz 4.0 10, 1, and 0.1 20.0 10, 1, and 0.1 34.0 or 40.0 10, 1, 0.1, and 0.01 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.
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From page 51... ...
VFA = voids filled with asphalt, % ⏐G⏐binder = shear complex modulus of binder, psi Table 3-33 summarizes the dynamic modulus master curve parameters obtained by numerical optimization of Equation 9 after substitution of the limiting maximum modulus obtained from Equation 10. Figure 3-39 shows a typical comparison of unconditioned and conditioned mixture master curves and temperature shift factors as well as the measured data for ABL-1.
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From page 52... ...
, k si UNAGED STOA -3 -2 -1 0 1 2 3 0 20 30 40 Temperature, C Lo g Sh ift F ac to r 10 Figure 3-39. Mixture dynamic modulus master curves for ABL-1.
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From page 53... ...
3.6.2.2 Comparison of Master Curve Parameters The purpose of the oven-aged mixture experiment was to compare the degree of aging from the short-term binder aging procedures with that from mixtures conditioned at 135°C for 4 hours in accordance with AASHTO R30. The first approach for comparing the short-term binder and mixture aging procedures was to compare the Christensen-Anderson master curve parameters obtained from the short-term binder aging procedures with those obtained from the backcalculated binder moduli from the mixture dynamic modulus testing.
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From page 54... ...
0 1 2 3 4 5 0 1 2 3 4 5 lo g 1 0 c fo r T an k Bi nd er log10 c for Backcalculated from Unaged Mixture Figure 3-42. Comparison of crossover frequency from unaged mixture and tank binder tests.
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From page 55... ...
The slopes of the relationships indicate that the aging index from the short-term binder aging tests is less than that obtained from short-term aging of mixtures in accordance with AASHTO R30. Rankings for the aging indices can be used to compare the short-term binder aging procedures to AASHTO R30.
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From page 56... ...
for R30 Aging SAFT RTFOT RTFOT SAFT Figure 3-45. Comparison of change in crossover frequency for short-term mixture and binder aging.
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From page 57... ...
Table 3-39 summarizes average aging indices for the neat and modified binders for 10 kPa unaged binder stiffness. Data are presented for four aging procedures (AASHTO R30 mixture aging and binder aging using the RTFOT, MGRF, and SAFT)
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From page 58... ...
Rank Binder R30 RTFOT SAFT MGRF AAC-1 5 7 1 1 AAD-2 1 2 3 3 AAF-1 2 1 2 2 AAM-1 9 6 7 10 ABL-1 6 5 6 8 ABM-2 10 10 5 9 Airblown 3 3 4 6 ALF 7 9 8 7 Citgoflex 11 11 11 11 Elvaloy 4 4 10 4 Novophalt 8 8 9 5 0.91 0.60 0.80 Spearman Rank Correlation Coefficient p-value 0.0001 0.0510 0.0031 Table 3-39. Average 10 kPa aging indices for neat and modified binders.
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From page 59... ...
59 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 R30 RTFOT MGRF SAFT A gi ng In de x Aging Procedure Neat Modified Figure 3-48. Comparison of average 10-kPa aging indices for neat and modified binders.
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