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Handbook of Size Exclusion Chromatography and Related ...

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was noted <strong>and</strong> categorized as excellent, good, poor, or bad, based on both the age<br />

<strong>of</strong> the pavement <strong>and</strong> the extent <strong>of</strong> cracking. A19-year-old road in excellent<br />

conditionwaschosenasast<strong>and</strong>ard.IthadalowLMSregion,<strong>and</strong>ahighdegree<strong>of</strong><br />

correlation was found between the condition <strong>of</strong> the other roads <strong>and</strong> the similarity<br />

<strong>of</strong> their SEC chromatograms to that <strong>of</strong> this st<strong>and</strong>ard, particularly in the LMS<br />

region. This is clearly seen in Figs 12 <strong>and</strong> 13, in which the st<strong>and</strong>ard is labeled<br />

Gallatin Gateway-South. Acorrelation with the percentage <strong>of</strong> asphaltenes was<br />

also found, which is not surprising because the percentage <strong>of</strong> asphaltenes <strong>and</strong><br />

percentageLMSregionarestronglycorrelated,althoughnotallasphaltsfit.Based<br />

on these results, arange <strong>of</strong> the LMS region from 8to 10% <strong>and</strong> an asphaltene<br />

content from 12.5 to 16.5% was recommended for Montana roads.<br />

Jennings <strong>and</strong> Pribanic (51) exp<strong>and</strong>ed this study to include samples from 15<br />

other states. The nation was divided into zones <strong>of</strong> similar climate, <strong>and</strong> the<br />

condition <strong>of</strong> roads within each zone was compared on the basis <strong>of</strong> the molecular<br />

size distribution. In general, in each zone there was a percentage <strong>of</strong> LMS<br />

abovewhichall roadswere poor or bad, <strong>and</strong> most <strong>of</strong> thegood <strong>and</strong> excellent roads<br />

were those <strong>of</strong> lower percentage LMS. However, there was avery large difference<br />

between the percentage <strong>of</strong> LMS that could be tolerated in warm zones <strong>and</strong> that in<br />

very cold zones. Furthermore, there was evidence from the warm zones that too<br />

low apercentage <strong>of</strong> LMS correlated with rutting.<br />

There were many exceptions, particularly poor <strong>and</strong> bad roads with low<br />

percentage LMS, but <strong>of</strong> course there are many factors unrelated to asphalt quality<br />

that can cause road failure. Jennings presented evidence that some asphalts failed<br />

because <strong>of</strong> poor viscosity temperature susceptibility even though they had a<br />

satisfactory percentage <strong>of</strong> LMS.<br />

There have been objections to this approach (16), partly because <strong>of</strong> the<br />

arbitrariness <strong>of</strong> the procedure in which the percentage <strong>of</strong> LMS is very much an<br />

artifact<strong>of</strong>theSECoperatingparameters.Itisalsothoughtthatitisthemechanical<br />

properties that cause failure, <strong>and</strong> these do not correlate well with chemical<br />

properties, such as SEC; thus if ex post facto measurements are to be used, they<br />

mayaswellbethephysical properties<strong>of</strong>theoldasphalt.Thereareseveralstudies<br />

thatindicatethatthereisalimitingductilitybelowwhichallroadsfail(130,131).It<br />

has been suggested (132) that penetration at 48C, agood predictor <strong>of</strong> the limiting<br />

stiffness temperature, be used to predict the tendency to crack.<br />

There are other problems in that some asphalts with avery high percentage<br />

<strong>of</strong> LMS do not fit at all; the black circles in Fig. 8are for agood-performing<br />

asphalt <strong>of</strong> very high percentage LMS. The use <strong>of</strong> old road data is also aproblem,<br />

whether for percentage LMS or physical properties. Figure 7shows that the same<br />

asphalt can have greatly different percentages <strong>of</strong> LMS at the same age depending<br />

on nonasphalt factors. High-percentage LMS is an indication <strong>of</strong> aging without<br />

regard to what caused it. In the Texas study, the asphalts at Lufkin all had lower<br />

percentage LMS because they were not aging. The same asphalts had much higher<br />

© 2004 by Marcel Dekker, Inc.

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