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Handbook of Size Exclusion Chromatography and Related ...

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5 MODIFIED ASPHALTS<br />

The addition <strong>of</strong> modifiers to asphalts, polymers, or ground tire rubber has increased<br />

because <strong>of</strong> generally improved properties <strong>and</strong> the necessity <strong>of</strong> meeting more<br />

stringent specifications. The new performance grade (PG) specifications (134)<br />

require that the asphalt meet certain rheological requirements at a specified<br />

temperature. For instance, a PG 64-22 must meet the upper temperature requirement<br />

at 648C <strong>and</strong> the lower temperature requirement at 2228C. Polymers are most <strong>of</strong>ten<br />

used to improve the upper grade while allowing a s<strong>of</strong>ter base asphalt to be used to<br />

meet the lower grade, although the benefit is asphalt dependent. At the same time<br />

there is evidence that modifiers can slow the hardening <strong>of</strong> asphalt as it oxidizes.<br />

The polymers are higher molecular weight than asphalt <strong>and</strong> show a very<br />

distinct peak on the chromatograph. The polymers degrade on oxidation, reducing<br />

the peak <strong>and</strong> shifting material to longer times <strong>and</strong> this is clearly visible with SEC<br />

(90,93–95,148). Figure 17 is an SEC chromatograph <strong>of</strong> an asphalt containing 3%<br />

SBR polymer before <strong>and</strong> after one year <strong>of</strong> thin-film (1 mm) aging at 608C. This<br />

chromatograph also shows the extreme sensitivity <strong>of</strong> the viscosity detector to the<br />

Figure 17 Effect <strong>of</strong> aging on apparent molecular size for an SBR-modified asphalt as<br />

determined by refractive index (RI) <strong>and</strong> intrinsic viscosity (IV) detectors 1000/500A ˚<br />

(30cm ultrastyragel)/50A ˚ (60cm PLgel). THF at 1mL/min, 100mL <strong>of</strong> 2wt% solution.<br />

© 2004 by Marcel Dekker, Inc.

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