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Publication Number: FHWA-RD-02-042
Date: October 2000
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.
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.
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.
|Asphalt Binder or 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|
|Novophalt (Validation Study)||77||651||2040|
|SBS Linear Grafted||72||297||1300||C|
|SBS Radial Grafted||71||249||1100||C|
|AC-20 (Validation Study)||70||226||1000|
Table 16. Replicate data for the Hamburg WTD.
|Asphalt Mixture||Creep Slope (passes/mm)||CV1 (percent)|
|Specimen No. 1||Specimen No. 2||Average|
|SBS Linear Grafted||1560||1090||1300||25.1|
|SBS Radial Grafted||610||1600||1100||63.4|
1CV = Coefficient of Variation, percent = (standard deviation ÷ average)*100.
|G*/sind, 0.9 rad/s, 70°C||High Temp.
|SBS Radial Grafted||Air-Blown||Air-Blown||ESI||EVA
|Air-Blown||SBS Linear Grafted||EVA Grafted||EVA||SBS Linear Grafted||EVA
|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|
|SST RSCH||French PRT|
|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
Table 19. Coefficients of determination, r2, using the data from the 11 mixtures.
10.0 Hz, 50°C
|SST RSCH Shear Strain, 50°C||0.14
|SST FSCH G*/sind, 10.0 Hz, 50°C||0.10
Rut Depth, 70°C
Table 20. Coefficients of determination, r2, using the data from all mixtures.
10.0 Hz, 50°C
Shear Strain, 50°C
G*/sind,10.0 Hz, 50°C
Rut Depth, 70°C
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
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 Wheel-Tracking Device, polymer-modified asphalt binders
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements