28.02.2013 Views

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

40% was fractionated into four fractions by pentane <strong>and</strong> pentane–cyclohexane<br />

mixtures underambientconditions.Theslighthumpinfraction4probablyresults<br />

fromthesmallamount<strong>of</strong>asphaltenesinthisfraction.Figure4showssaturates<strong>and</strong><br />

Fig.5polararomaticsfromthesupercriticallyseparatedtopfractions.Thesaturate<br />

curves are typical, being symmetrical <strong>and</strong> having relatively little variation in<br />

molecularsizefromonefractiontothenext.Thepolararomatics,incontrast,grow<br />

progressively higher in molecular size in heavier fractions <strong>and</strong> show signs <strong>of</strong><br />

considerableassociationinthehighermolecularsizefractionsbythegrowinghump<br />

in the LMS region. Asphaltenes (Fig. 6) from fraction 4, separated from the top<br />

material, are markedly lower in size than the material from the fractions <strong>of</strong> the<br />

bottom 40%.<br />

Asasphaltsage,thecharacteristicchangetotheSECchromatogramisgrowth<br />

inthe LMSregion,whichsometimes changesshape inthe process.Figure 7shows<br />

tank asphalts <strong>and</strong> cores for asingle asphalt used in test sections at three Texas<br />

locations. The difference in the cores is primarily the percentage <strong>of</strong> air voids in the<br />

finishedconcrete.In1987,theairvoidsatLufkinwere1.8%<strong>and</strong>the608Cviscosity<br />

was5400P(1P¼1dPa sÞ.AtDumasitwas8.5%<strong>and</strong>55,000P,<strong>and</strong>atDickensit<br />

was11%<strong>and</strong>376,000P.Thesedifferencesareclearlyshowninthechromatograms.<br />

This percentage LMS growth is directly related to oxidation but may be<br />

highly asphalt dependent. Figure 8shows the change in percentage LMS with<br />

Figure 4 SEC analyses <strong>of</strong> the saturates from an asphalt’s supercritical fractions 1–4<br />

(500/50 A ˚ , 60 cm PLgel, THF at 1 mL/min, 100 mL <strong>of</strong> 5 wt% solution, RI detector).<br />

© 2004 by Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!