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

ductility (61). King characterizes the low ductility of the latter as a function of “too much”
rather than “too little” strength, as SB/SBS modified mixes are comparatively thick when
elongated and snap much in the way a thick rubber band does when pulled too far (61).
This suggests that with some SB and SBS modified mixes, ductility testing could underpredict
performance measures of strength.
Desmazes et al (2000) have developed a testing protocol for measuring the zero shear
viscosity (ZSV) which the authors assert provides for a more accurate estimate of rutresistance
in binders modified with certain elastomeric polymers (e.g., SBS) (62).
Conceptually, ZSV represents the viscosity of a fluid which is at rest. In elastic mixes at
very low shear rates, the structures of the fluid deform slowly enough that they can
adapt to the point where a form of equilibrium is reached. Measurements are collected
at lower and lower shear rates, and the results extrapolated to yield the zero shear
viscosity. Demazes observes that rutting is a demonstrably slow process, and as such,
the “resting” viscosity of a modified binder more closely approximates its capacity to
resist permanent deformation (62). In contrast, studies have shown that conventional
DSR testing tends to underestimate high temperature performance in modified binders
characterized by high delayed elasticity.
The SPG developed by Epps (2001) uses the following modified testing program:
• Residue Recovery – the researchers utilized the Stirred-Can method;
• Aging – pavements located at the surface are most susceptible to aging. RTFO
was disregarded due to the comparatively low application temperatures
associated with surface treatment applications. A Pressure Aging Vessel test
(PAV) was utilized instead for long-term aging only;
• RV – viscosity was determined for un-aged binders, as this parameter generally
reflects how easily the resulting asphalt emulsion can be pumped and sprayed.
Multiple temperatures were utilized to simulate the wide-range of typical surface
treatment application temperatures, as opposed to the single (135º C.) utilized for
HMA binders under the standard PG;
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