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Publication Number: FHWA-RD-02-042
Date: October 2000

Modified Asphalt Binders in Mixtures - Topical Report: Permanent Deformation Using A Mixture With Diabase Aggregate

11. Conclusions

a. Conclusions Provided by the 11 Mixtures

The G*/sind's of the asphalt binders at 50°C and 0.125 rad/s had a high correlation to mixture rutting resistance as measured by the cumulative permanent shear strains from RSCH. The r2 was 0.89. (See figure 15.) The number of data points was insufficient for determining if there was a relationship between the continuous high-temperature PG and cumulative permanent shear strain.

The G*/sind's of the asphalt binders at 70°C and 0.9 rad/s had a weak correlation to mixture rutting resistance as measured by the French PRT at 70°C. The r2 was 0.70. (See figure 20.) Without EVA, the r2 would be 0.88. The continuous high-temperature PG's provided a fair correlation. The r2 was 0.80. (See figure 23.)

Grafting and the geometry of the EVA- and SBS-modified asphalt binders had no effect on their rutting resistances at a 5-percent level of significance.

The main objective of this study was to determine which asphalt binders provide high-temperature properties that do not agree with mixture rutting resistance. In general, the number of obvious discrepancies was low. The G*/sind for EVA at 70°C and 0.9 rad/s was found to be low, based on the French PRT.

b. Conclusions Provided by All Mixtures

The G*/sind's of the asphalt binders at 50°C and 0.125 rad/s had a high correlation to mixture rutting resistance as measured by the cumulative permanent shear strains from RSCH. The r2 was 0.93. (See figure 16.) The continuous high-temperature PG's provided a fair correlation. The r2 was 0.76. (See figure 14.)

The G*/sind's of the asphalt binders at 70°C and 0.9 rad/s had a high correlation to mixture rutting resistance as measured by the French PRT at 70°C. The r2 was 0.88. (See figure 22.) Without EVA, the r2 would be 0.93. The continuous high-temperature PG's provided a fair correlation. The r2 was 0.80. (See figure 24.)

The best correlations between the mixture tests were: (1) RSCH vs. French PRT, r2 = 0.76; (2) RSCH vs. FSCH, r2 = 0.73; and (3) French PRT vs. Hamburg WTD, r2 = 0.69. These relationships should not be used to predict one property from the other. The r2's are too low for prediction purposes.

The creep slopes from the Hamburg WTD had very low repeatability.

A change in high-temperature PG from 70 to 76 significantly increased rutting resistance based on both RSCH and the French PRT. The reduction in cumulative permanent shear strain from RSCH at 50°C was 37 percent. The reduction in rut depth from the French PRT at 70°C was 21 percent. Based on these reductions, it could be concluded that there can be differences in rutting performance for asphalt binders within a grade, but this conclusion has to be balanced against the increase in the number of grades if the increment between grades was to be reduced.

12. Recommendations

The correlations between mixture G*/sind and binder G*/sind were fair to good. The r2 for the 16 materials was 0.79 using 10.0 Hz and 10.0 rad/s, and 0.85 using 2.0 Hz and 2.0 rad/s. There is no fundamental reason for choosing these pairs of frequencies, and they do not relate mathematically to each other. Therefore, the data could be correlated using a matrix of several asphalt mixture frequencies vs. several asphalt binder frequencies.

The asphalt binders should be tested using other aggregate types or gradations, and, if possible, the test temperature for the SST should be increased so that it is closer to the PG's of the asphalt binders.

Determine whether the elimination of the hydrated lime from the mixture caused the change in ranking for the Novophalt and Styrelf mixtures and the changes in the moduli shown in table 1.

13. References

  1. K. D. Stuart, W. S. Mogawer, and P. Romero, Validation of Asphalt Binder and Mixture Tests That Measure Rutting Susceptibility Using the Accelerated Loading Facility, Publication No. FHWA-RD-99-204, Federal Highway Administration, McLean, VA, December 1999, 348 pp.

  2. AASHTO Provisional Standards, American Association of State Highway and Transportation Officials, Washington, D.C., April 2000 Edition.

  3. NCHRP Project 90-07, "Understanding the Performance of Modified Asphalt Binders in Mixtures," Work Plan, Study in Progress, National Cooperative Highway Research Program (NCHRP), Transportation Research Board, National Research Council, Washington, D.C., 2001.

  4. AASHTO TP5, "Method for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer," AASHTO Provisional Standards, American Association of State Highway and Transportation Officials, Washington, D.C., April 2000 Edition.

  5. T. Aschenbrener, "Evaluation of the Hamburg Wheel-Tracking Device to Predict Moisture Damage in Hot-Mix Asphalt," Transportation Research Record 1492, Transportation Research Board, Washington, D.C., 1995, pp. 193-201.

  6. T. Aschenbrener, R. Terrel, and R. Zamora, Comparison of the Hamburg Wheel-Tracking Device and the Environmental Conditioning System to Pavements of Known Stripping Performance, Publication No. CDOT-DTD-R-94-1, Colorado Department of Transportation, Denver, CO, January 1994.

  7. M. Hines, "The Hamburg Wheel-Tracking Device," Proceedings of the Twenty-Eighth Paving and Transportation Conference, Civil Engineering Department, The University of New Mexico, Albuquerque, NM, 1991.

  8. K.D. Stuart, J.S. Youtcheff, and W.S. Mogawer, "Understanding the Performances of Modified Asphalt Binders in Mixtures: Evaluation of Moisture Sensitivity," Publication No. FHWA-RD-02-029, Federal Highway Administration, McLean, VA, December 2001, 17 pp.

Table 15. G*/sind's of the binders vs. the creep slopes from
the Hamburg WTD with the materials listed from highest
to lowest slope (highest to lowest resistance to rutting).

Asphalt Binder or Mixture
Designation 
Binder  Mixture 
High Temp. PG  G*/sind, 0.125 rad/s, 58°C (Pa)  Creep Slope, 58°C (passes/mm) 
Styrelf (Validation Study) 88 2480 7000        
Elvaloy 77 639 4900 A      
CMCRA 76 482 3200 A      
Air-Blown 74 387 3900 A B    
PG 70-22 71 213 2200   B C  
Novophalt (Validation Study) 77 651 2040        
EVA 75 751 2000     C  
SBS Linear Grafted 72 297 1300     C  
EVA Grafted 74 727 1300     C  
SBS Radial Grafted 71 249 1100     C  
AC-20 (Validation Study) 70 226 1000        
SBS Linear 72 248 900     C  
ESI 76 321 790     C  
PG 64-28 67 114 500     C  

Table 16. Replicate data for the Hamburg WTD.

Asphalt Mixture  Creep Slope (passes/mm)  CV1 (percent) 
Specimen No. 1  Specimen No. 2  Average 
Elvaloy 4650 5070 4900 6.1
Air-Blown 4340 3510 3900 15.0
CMCRA 5970 1330 3650 89.9
CMCRA (Repeat) 3770 1555 2700 58.8
PG 70-22 1000 3390 2200 80.0
EVA 2770 1200 2000 55.9
SBS Linear Grafted 1560 1090 1300 25.1
EVA Grafted 1080 1430 1300 19.7
SBS Radial Grafted 610 1600 1100 63.4
SBS Linear 690 1130 900 34.2
ESI 690 930 800 21.0
PG 64-28 450 550 500 14.1

1CV = Coefficient of Variation, percent = (standard deviation ÷ average)*100.

Table 17. Rankings by test type with the material
having the most resistance to rutting listed at the top.

SST  French PRT 
Mixture  Binder  Mixture  Binder 
Cumulative
Permanent
Shear Strain,
50°C  
G*/sind,
0.125 rad/s,
50°C 
High Temp.
Continuous PG 
Rut Depth,
70°C 
G*/sind, 0.9 rad/s, 70°C  High Temp.
Continuous PG
 
EVA EVA Elvaloy Elvaloy Elvaloy Elvaloy
Elvaloy EVA Grafted CMCRA Air-Blown CMCRA CMCRA
EVA Grafted Elvaloy ESI CMCRA ESI ESI
CMCRA CMCRA EVA EVA
Grafted
Air-Blown EVA
SBS Radial Grafted Air-Blown Air-Blown ESI EVA
Grafted
Air-Blown
Air-Blown SBS Linear Grafted EVA Grafted EVA SBS Linear Grafted EVA
Grafted
ESI ESI SBS Linear Grafted SBS Linear Grafted SBS Radial Grafted SBS Linear Grafted
SBS Linear Grafted SBS Linear SBS Linear SBS Radial Grafted SBS Linear SBS Linear
PG 70-22 PG 70-22 PG 70-22 PG 70-22 PG 70-22 PG 70-22
SBS Linear SBS Radial Grafted SBS Radial Grafted SBS Linear EVA SBS Radial Grafted
PG 64-28 PG 64-28 PG 64-28 PG 64-28 PG 64-28 PG 64-28

Table 18. Numerical rankings by test type where No. 1 has the most resistance
to rutting according to the test and No. 11 has the least resistance to rutting.

SST RSCH  French PRT 
Mixture  Binder  Mixture  Binder 
Cumulative Permanent Shear Strain, 50°C  G*/sind, 0.125 rad/s, 50°C  Continuous High Temp. PG  Rut Depth, 70°C  G*/sind, 0.9 rad/s, 70°C  Continuous
High Temp.PG 
1 1 2 1 1 1
2 3 4 2 3 3
3 2 7 3 5 5
4 4 1 4 2 6
5 6 6 5 4 2
6 8 3 6 7 4
7 7 8 7 8 7
8 10 10 8 10 10
9 9 9 9 9 9
10 5 5 10 6 8
11 11 11 11 11 11

Table 19. Coefficients of determination, r2, using the data from the 11 mixtures.

  SST FSCH
G*/sind,
10.0 Hz, 50°C 
French PRT
Rut Depth,
70°C 
Hamburg WTD
Creep Slope,
58°C 
SST RSCH Shear Strain, 50°C  0.14
Log-Log: 0.12
0.75
Log-Log: 0.59
0.20
Log-Log: 0.36
SST FSCH G*/sind, 10.0 Hz, 50°C    0.10
Log-Log: 0.11
0.00
Log-Log: 0.01
French PRT
Rut Depth, 70°C
 
    0.38
Log-Log: 0.62

Table 20. Coefficients of determination, r2, using the data from all mixtures.

  SST FSCH
G*/sind,
10.0 Hz, 50°C 
French PRT
Rut Depth,
70°C 
Hamburg WTD
Creep Slope,
58°C 
SST RSCH
Shear Strain, 50°C 
0.56
Log-Log: 0.73 
0.66
Log-Log: 0.76 
0.33
Log-Log: 0.51
SST FSCH
G*/sind,10.0 Hz, 50°C 
  0.48
Log-Log: 0.47
0.09
Log-Log: 0.17
French PRT
Rut Depth, 70°C 
    0.51
Log-Log: 0.69 

Figure 27. Graph. Repeated Shear at Constant Height cumulative permanent shear strain at 50 degrees Celsius versus French Pavement Rutter Tester rut depth at 70 degrees for the 11 mixtures. This graph shows that the repeated shear at constant height cumulative permanent shear strain at 50 degrees Celsius increases with an increase in the French pavement rutter tester rut depth at 70 degrees Celsius for the 11 mixtures. The shear strains are given in table 9, while the rut depths are given in table 13. The R-square of 0.75 indicates that there is too much scatter in the data for predicting one mixture property from the other. Also, the figure shows that if the data from the performance grade 64-28 mixture were to be excluded, the range in the rut depths is small, only 6.5 to 8.5 millimeters. The equation of the line is Y equals 4,182 X minus 11,900.

Figure 27. RSCH cumulative permanent shear strain at 50°C
vs. French PRT rut depth at 70°C for the 11 mixtures.

Figure 28. Graph. Log Repeated Shear at Constant Height cumulative permanent shear strain at 50 degrees Celsius versus log French pavement rutter tester rut depth at 70 degrees for all mixtures. This graph shows that the log repeated shear at constant height cumulative permanent shear strain at 50 degrees Celsius increases with an increase in log French pavement rutter tester rut depth at 70 degrees Celsius for all mixtures. The shear strains are given in table 9, while the rut depths are given in table 13. The R-square of 0.76 indicates that there is too much scatter in the data for predicting one property from the other. The additional data points did not improve the relationship. The equation of the line is Y equals 1.79 X plus 2.74.

Figure 28. Log RSCH cumulative permanent shear strain at 50°C vs.
log French PRT rut depth at 70°C for all mixtures.

Figure 29. Graph. Log cumulative permanent shear strain from repeated shear at constant height versus log absolute value of the complex shear modulus from frequency sweep at constant height divided by the sine of the phase angle for all mixtures. This graph shows that the log cumulative permanent shear strain at 50 degrees Celsius decreases with an increase in the log absolute value of the complex shear modulus divided by the sine of the phase angle at 50 degrees Celsius for all mixtures. The shear strains are given in table 9, while the absolute value of the complex shear modulus divided by the sine of the phase angle values are given in table 6. The R-square of 0.73 indicates that there is too much scatter in the data for predicting one property from the other. The equation of the line is Y equals negative 1.06 X plus 6.25.

Figure 29. Log RSCH cumulative permanent shear strain
vs. log FSCH G*/sind for all mixtures.

 

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