Using Polymer Modified Asphalt Emulsions in Surface Treatments A ...

Figure 16: Effect of SBS Concentration on Complex Modulus at 60º C. (16)
Thus, it is suggested that a polymer content of around 6% is required to generate the
continuous polymer network which is believed to impart the desirable rubber-like
elasticity characteristics associated with polymer modified binders. It should be noted
however, that a form of direct bitumen modification (i.e., pre-blending) was utilized to
prepare samples for this study. Similar results were obtained by Airey et al (2002),
which indicate that SBS concentrations of 4% to 8% are required to establish a
continuous polymer network when direct bitumen modification methods are utilized (17).
However, as previously discussed, others have shown that pre-blending may fail to
result in the formation of a continuous polymer network unless the content of polymer
added is sufficiently high to promote phase separation and swelling (4, 12, and 50).
Thus, the optimal polymer contents presented in the Chen and Aiery studies might
prove to be higher than necessary should a polymer modifier be employed which would
permit co-milling or soap pre-batching (e.g., SBR) in an analogous PME application.
Chen et al have also examined the impact of variable SBS concentrations on Brookfield
viscosity (ASTM D789, D4878) as shown in Figure 16. In this regard, the researchers
note that polymer modified binder pumping generally does not become problematic until
mixture viscosities begin to exceed about 3,000 cP (16). Thus, as Figure 17 illustrates,
SBS weight concentrations in excess of 6% appear to be contraindicated with respect to
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