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72
CHAPTER 4
Conclusions and Recommendations
Summary of Key Findings differs among the binders. No links were evident between
opacity and binder high grade number, binder low grade
The results of the experiments conducted as part of this number, grade spread, whether the binder was modified, or
study have led to the following conclusions. crude source. Grading of the binders after SEP tests showed
that the critical high temperatures and critical low temper-
1. The high shear rate viscosity method does not provide an atures increased slightly with higher SEP temperatures.
improvement in selecting mixing and compaction tem- Also, the non-recoverable compliance values (Jnr) decrease
peratures for modified binders compared with the equiv- (i.e., the binders became more elastic) with higher SEP
iscous method. The mixing and compaction temperatures temperatures. However, there was no evidence of degra-
determined by the high shear viscosity method are very dation of the binders due to exposure at elevated temper-
similar to the temperatures determined by the equiviscous atures in the SEP test. The lack of evidence of degradation
method that are considered too high for modified binders from the SEP test does not mean that binder degradation
based on general field experience of binder suppliers. is not possible. It is entirely possible that the conditions in
2. Mixing and compaction temperatures determined with SEP test are not sufficiently severe to cause breakdown of
the SSF method are substantially lower than the equivis- polymer modifiers. Although the SEP test may have value
cous mixing and compaction temperatures. The differ- in identifying binders with opacity problems, it is not rec-
ences between the results are greater for the modified ommended as a test for establishing maximum tempera-
binders. This indicates that many of the modified asphalt tures for mixing with aggregates.
binders exhibit shear thinning behavior. However, the SSF 5. Coating experiment results showed that the binder, mix-
method also results in lower mixing and compaction tem- ing temperature, and mixer type significantly affected the
peratures for unmodified binders; in most cases, the SSF coating percentage. However, neither of the lab mixers
mixing temperatures are more than 10°F lower than the consistently provided reasonable mixing temperatures
equiviscous mixing temperatures. for all of the binders. Coating test results with completely
3. For modified asphalt binders, the mixing and compaction dry aggregates and wet aggregates were not significantly
temperatures determined by the Phase Angle method are different. Foaming of the asphalt was not observed dur-
also substantially lower and more reasonable than by the ing the tests with the wet aggregates. Correlations between
equiviscous method. For unmodified binders, compar- the mixing temperatures from the candidate methods
isons of mixing and compaction temperatures between and the coating test results were weak. The poor correla-
the Phase Angle method and the equiviscous method were tions were likely due to inconsistencies with the subjective
mixed. In some cases, the Phase Angle method yielded tem- coating test.
peratures within a few degrees of the equiviscous method 6. Poor repeatability was also a problem with the workability
results. However, some Phase Angle results were also more experiments. This test did not provide dependable results
than 10°F above or 10°F below the results from the equi- by which to evaluate relationships between temperature
viscous method. and workability of mixes with different binders.
4. The results of the SEP test showed that opacity and mass 7. Compaction experiments using the SGC indicate that a
loss from asphalt binders increase with higher tempera- mixture's aggregate components have a greater affect on
tures. However, the amount and rate of emissions increase compaction behavior than the binder characteristics. How-
