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Publication Number: FHWARD02042 Date: October 2000 
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 r^{2} was 0.89. (See figure 15.) The number of data points was insufficient for determining if there was a relationship between the continuous hightemperature 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 r^{2} was 0.70. (See figure 20.) Without EVA, the r^{2} would be 0.88. The continuous hightemperature PG's provided a fair correlation. The r^{2} was 0.80. (See figure 23.)
Grafting and the geometry of the EVA and SBSmodified asphalt binders had no effect on their rutting resistances at a 5percent level of significance.
The main objective of this study was to determine which asphalt binders provide hightemperature 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 r^{2} was 0.93. (See figure 16.) The continuous hightemperature PG's provided a fair correlation. The r^{2} 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 r^{2} was 0.88. (See figure 22.) Without EVA, the r^{2} would be 0.93. The continuous hightemperature PG's provided a fair correlation. The r^{2} was 0.80. (See figure 24.)
The best correlations between the mixture tests were: (1) RSCH vs. French PRT, r^{2} = 0.76; (2) RSCH vs. FSCH, r^{2} = 0.73; and (3) French PRT vs. Hamburg WTD, r^{2} = 0.69. These relationships should not be used to predict one property from the other. The r^{2}'s are too low for prediction purposes.
The creep slopes from the Hamburg WTD had very low repeatability.
A change in hightemperature 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.
The correlations between mixture G*/sind and binder G*/sind were fair to good. The r^{2} 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.
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  
AirBlown  74  387  3900  A  B  
PG 7022  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  
AC20 (Validation Study)  70  226  1000  
SBS Linear  72  248  900  C  
ESI  76  321  790  C  
PG 6428  67  114  500  C 
Table 16. Replicate data for the Hamburg WTD.
Asphalt Mixture  Creep Slope (passes/mm)  CV^{1 }(percent)  

Specimen No. 1  Specimen No. 2  Average  
Elvaloy  4650  5070  4900  6.1 
AirBlown  4340  3510  3900  15.0 
CMCRA  5970  1330  3650  89.9 
CMCRA (Repeat)  3770  1555  2700  58.8 
PG 7022  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 6428  450  550  500  14.1 
^{1}CV = 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  AirBlown  CMCRA  CMCRA 
EVA Grafted  Elvaloy  ESI  CMCRA  ESI  ESI 
CMCRA  CMCRA  EVA  EVA Grafted 
AirBlown  EVA 
SBS Radial Grafted  AirBlown  AirBlown  ESI  EVA Grafted 
AirBlown 
AirBlown  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 7022  PG 7022  PG 7022  PG 7022  PG 7022  PG 7022 
SBS Linear  SBS Radial Grafted  SBS Radial Grafted  SBS Linear  EVA  SBS Radial Grafted 
PG 6428  PG 6428  PG 6428  PG 6428  PG 6428  PG 6428 
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, r^{2}, 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 LogLog: 0.12 
0.75 LogLog: 0.59 
0.20 LogLog: 0.36 
SST FSCH G*/sind, 10.0 Hz, 50°C  0.10 LogLog: 0.11 
0.00 LogLog: 0.01 

French PRT Rut Depth, 70°C 
0.38 LogLog: 0.62 
Table 20. Coefficients of determination, r^{2}, 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 LogLog: 0.73 
0.66 LogLog: 0.76 
0.33 LogLog: 0.51 
SST FSCH G*/sind,10.0 Hz, 50°C 
0.48 LogLog: 0.47 
0.09 LogLog: 0.17 

French PRT Rut Depth, 70°C 
0.51 LogLog: 0.69 
Figure 27. RSCH cumulative permanent shear strain at 50°C
vs. French PRT rut depth at 70°C for the 11 mixtures.
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. Log RSCH cumulative permanent shear strain
vs. log FSCH G*/sind for all mixtures.
Topics: research, infrastructure, pavements and materials Keywords: research, infrastructure, pavements and materials, superpave, asphalt binder specification, permanent deformation, Superpave Shear Tester, SST, French Pavement Rutting Tester, Hamburg WheelTracking Device, polymermodified asphalt binders TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements Updated: 04/23/2012
