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Handbook of Size Exclusion Chromatography and Related ...

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utobviouslynotbythesamemechanisms.Asphaltsoxidizedtothesameviscosity<br />

at 100 <strong>and</strong> 1038C also show differences in the chromatographs (128).<br />

Asphaltsalsotendtoageoncontactwithsolvents,<strong>and</strong>thisismanifestedby<br />

both viscosity <strong>and</strong> LMS increases (35). Simply dissolving an asphalt in agood<br />

solvent <strong>and</strong> recovering it immediately produces about a10% viscosity increase;<br />

2days contact at room temperature causes a50% or greater increase inviscosity.<br />

Ifsamplesaremade<strong>and</strong>runimmediatelyorwithinhoursatroomtemperature,the<br />

effect on the SEC chromatogram is negligible, but days or even hours at ahigher<br />

temperature can produce significant growth in the LMS region.<br />

The Corbett analysis <strong>of</strong> an asphalt is also altered by aging. In Fig. 11<br />

chromatograms are shown <strong>of</strong> Corbett fractions <strong>of</strong> a tank asphalt <strong>and</strong> a 1984<br />

core from one <strong>of</strong> the Texas test sections. As expected, there is no change in the<br />

saturates. There is a decrease in quantity but not in elution time for naphthene<br />

aromatics. The polar aromatics change little in quantity as material is gained from<br />

the naphthene aromatic fraction <strong>and</strong> lost to the asphaltenes, which increase in<br />

quantity. Despite this considerable shifting <strong>of</strong> material, the elution time is little<br />

changed. The large tailing effect with asphaltenes is probably caused by column<br />

adsorption.<br />

The change in molecular size <strong>of</strong> Corbett fractions with oxidation was studied<br />

extensively by Liu et al. (22,129) using SEC. They found that while naphthene<br />

aromatics oxidize to polar aromatics, they subsequently converted to asphaltenes<br />

only after extensive oxidation. Newly produced polar aromatics <strong>and</strong> asphaltenes<br />

produced by oxidation <strong>of</strong> naphthene <strong>and</strong> polar aromatics respectively tend to be<br />

smaller than the original material. Large-sized polar aromatics <strong>and</strong> naphthene<br />

aromatics are converted to asphaltenes <strong>and</strong> polar aromatics more rapidly than<br />

smaller sized material.<br />

Huang <strong>and</strong> Bertholf (20) oxidized previously separated Corbett fractions<br />

using UV irradiation. SEC analysis before <strong>and</strong> after oxidation showed an increase<br />

in molecular size <strong>of</strong> all fractions. The saturate fractions showed a striking increase,<br />

which is significant as saturates do not normally react with oxygen.<br />

3.2 Use <strong>of</strong> SEC to Predict Pavement Performance<br />

Plummer <strong>and</strong> Zimmerman (46) studied roads in Michigan <strong>and</strong> Indiana <strong>and</strong> found<br />

that an increase in the LMS region correlated with increased cracking. Hattingh<br />

(29) found that in the hot South African climate, roads with a low asphaltene<br />

content <strong>and</strong> a small LMS region were subject to bleeding. By far the most<br />

extensive effort <strong>of</strong> this kind is that <strong>of</strong> Jennings <strong>and</strong> co-workers (42,47–51),<br />

conducted primarily in Montana but extended nationwide. The principal road<br />

problem addressed was that <strong>of</strong> cracking.<br />

A total <strong>of</strong> 39 roads in Montana constructed with asphalt from four refineries<br />

were cored, extracted, <strong>and</strong> analysed by SEC (42,48). The condition <strong>of</strong> the roads<br />

© 2004 by Marcel Dekker, Inc.

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