State Study 111 - Polymer Modified Hot Mix Asphalt Field Trial.pdf

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
The following conclusions are based on laboratory and performance test results and on
activities at the HMA plant.
8. Each polymer or rubber modifier required mixing at a higher temperature than regular
HMA. These temperatures ranged from 320 o to 351 o F.
9. The modified HMA mixes were successfully produced in a normal HMA production
facility. Most of the modifiers did not require a blending unit.
10. Once the rolling pattern was established for the modified HMA, further rolling caused
the rolling pattern to break off and then to peak again. Initial rolling was with a steelwheel
vibratory roller and this was followed with a smaller steel-wheel static roller. (No
pneumatic roller was used.)
11. Comparison of laboratory acceptance tests conducted during the construction and
cores taken from the pavement the next morning showed that the laboratory air voids
were closer to the design air voids than the field results.
12. Brookfield Viscometer tests showed that the modifiers were all more viscous at the
lower temperatures.
13. Results of the GTM tests showed that the laboratory specimens had sufficient shear
strength to resist the stress state in the pavement and that the air voids were above the
flushing level and were consistent with design values.
14. Initial performance test results for the pavement test sections were low roughness and
deflection readings and high skid values. These results indicate that the test sections
were in an excellent initial condition.
15. Results to date indicate all the modifiers are out-performing the control section, both in
terms of roadway rutting and rutting in the APA. It is important to note that the rutting on
the control section is still relatively small at about 0.25 inch.
16. The selection of a modified asphalt binder grade based on the high temperature
component of the PG designation could be quite inappropriate for a given project,
especially when rubber modifiers are considered for use in the HMA.
RECOMMENDATIONS
1. It is obvious that all the modified binders are providing superior rutting resistance as
compared to the control binder. This validates the wisdom of using modified binders for
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