Conclusions

1. Based on the binder consistency results, it was concluded that the addition of Elvaloy® improved the temperature susceptibility of both the AC-120/150 and AC-10 virgin asphalt cement. This improvement in temperature susceptibility (as measured by the VTS-viscosity temperature susceptibility parameter) was found to be related to the percentage of Elvaloy® used in the mix. For the AC-120/150 mixture, the VTS value changed from -3.697 to -3.452 to -3.118 as the percent Elvaloy® varied from 0% (virgin) to 1.5% to 2.0%. Comparable VTS values found for the AC-10 mix were -3.737; -3.376 and -3.098. The Elvaloy® had the characteristic of improving (increasing) the high temperature viscosities of both binders while showing very little viscosity change at colder temperatures.

2. As a natural consequence of the previous conclusion, higher mixing and compaction temperatures were required for both modified mixtures (AC-120/150 and AC-10) as the percentage of Elvaloy® was increased in the binder. Increases in mixing temperature, compared to the virgin binder, were approximately 30 degrees F for 1.5% Elvaloy® binder and 60 degrees F for the 2.0% Elvaloy® binder.

3. Marshall Design/Stability tests (75 blow compaction) indicated that mix design binder contents were increased for the Elvaloy® modified mixtures, compared to the virgin AC-120/150 and AC-10 mixes. For the 1.5% Elvaloy® mixtures, design asphalt contents were about 0.4% more than the virgin mix. At 2.0% Elvaloy®, this increase was 0.5% for both mixtures. For both mixtures investigated, it was found that addition of Elvaloy® (at the specific design binder content established for each mix) caused slight improvements in the Marshall Stability, slight increase in the flow and a general reduction in the Marshall Quotient (Stability/Flow ratio).

4. SHRP SUPERPAVE Level I mix designs were also conducted on all six mixtures studied using a gyratory compactor. The "design" asphalt contents determined from the SUPERPAVE procedure showed no correlation to values found from the Marshall analysis. For the AC-120/150 mix, the two Elvaloy® modified mixtures yielded lower gyratory based design asphalt contents compared to the Marshall design. The opposite trend was found for the AC-10 mixtures.

5. Modified Lottman tests were performed to evaluate the influence of Elvaloy® upon the moisture susceptibility of the mixtures. Tensile Strength Ratio values (TSR) were determined for the AC-120/150 modified mixtures and the AC-10 modified mixtures. For each mix, the final design asphalt content used was 0.2% greater than the virgin blend for each polymer percent increment. The results of this study indicated that the addition of the Elvaloy® greatly enhances the moisture susceptibility properties of both mixes. At a 0% modifier (i.e., virgin binder); both the AC-120/150 and AC-10 mixtures have TSR values near 0.7. The addition of 1.5% Elvaloy® increased the TSR value to 0.96 (AC-120/150) and 0.88 (AC-10); while the 2% modified mixtures yielded TSR values near 1.0 for both mixtures.

6. Dynamic Complex Modulus tests were conducted over a range of temperatures and frequencies. The following results were obtained.
   • The addition of Elvaloy® to both mixtures tends to reduce the maximum phase angle (f). This reduction is in the order of 3 - 4 degrees. It was also observed that a 10 - 20% reduction in the |E*| value, corresponding to the maximum f angle, occurred for both the AC-120/150 and AC-10 mixtures. These observations imply that the polymer tends to make each mix more elastic (less viscous) at higher temperatures (lower moduli).

   • By using time-temperature shift principles, master modulus curves were developed for each of the six mixtures evaluated. The addition of the Elvaloy® modify tended to "flatten" out the shift factor-temperature relationship of each mix. This implies that lower dynamic modulus values will occur at cooler temperatures while higher modulus values will result at warmer temperatures.

   • Dynamic modulus ratios ® were computed to reflect the ratio of the dynamic modulus of the Elvaloy® modified mix to that of the virgin (0% modifier) mix. In general, all of the mixtures exhibited the same typical pattern of modular ratio with temperature. At very high temperatures, the modular ratio is greater than unity (1.2 - 1.5 at 130 degrees F). As the temperature decreases, the R value also decreased for all of the Elvaloy® mixtures. At a test temperature of 40 degrees F, the R values had decreased to values of less than one, implying that the stiffness of the modified mixtures was less than that of the conventional (binder) mixtures. At 0 degrees F, the modular ratio trend appears to reverse itself again. The specific reason for this occurrence is unknown but further research on verification of this cold temperature trend should be pursued.

7. Repeated load permanent deformation tests on all of the mixtures clearly demonstrated that the addition of Elvaloy® enhanced the rutting resistance of both the AC-120/150 and AC-10 mixtures. The major effect of the Elvaloy® appears to be in the reduction of the slope parameter of the permanent strain - repetition relationship. The percent reduction in permanent strain was found to be slightly greater for the AC-10 mix compared to the AC-120/150 mix. At 1.5% Elvaloy®, typical percent reductions varied between 50% and 75%, while at the 2% Elvaloy® level, the percent reduction was between 70% to 90%.

8. The evaluation of the flow point (number of cycles where shear deformation of the mix is initiated) clearly demonstrated the superiority of the Elvaloy® modified mixtures. As a comparison, virgin AC-120/150 and virgin AC-10 mixtures all exhibited flow points less than 10,000 cycles for stress ranges of 10, 20 and 30 psi. In direct contrast, no flow points were found for either mix, modified at 2% Elvaloy®. It is concluded that the addition of Elvaloy® must increase the shear strength of the mix and hence greatly improve the rutting resistance of both conventional mixtures.

9. The results of static creep tests (load only) show the enhancement of mixture creep resistance due to the addition of the Elvaloy® modifier. Creep moduli values for the AC-120/150 mix were found to be 2640 psi, 3061 psi and 4848 psi for 0%, 1.5% and 2.0% Elvaloy®, respectively. Comparable values for the AC-10 mixtures were 2738 psi, 2884 psi and 5069 psi.

10. In final summary, it appears that the Elvaloy® polymer is an effective binder modifier that enhances the high temperature properties of asphalt mixes. This is observed through improvements in the binder temperature susceptibility, dynamic (complex) modulus, repeated load permanent deformation and static creep behavior of the mixtures. In addition, Elvaloy® modified mixtures also appear to demonstrate significant improvement in the moisture susceptibility properties of asphaltic mixtures.

     

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