Handbook of Size Exclusion Chromatography and Related ...

Haley (26) showed that the large molecular size material increased greatly
following air blowing. A series of studies on Texas test sections (8,9,27,28)
showed a progressive growth in large molecular size (LMS) material. This material
is usually defined as that comprising about the first third of the chromatogram
elution time. Similar results are reported for oven aging (12,29–32) and for aging
during the hot-mix operation (30,33,34). Asphalts also change when in contact
with solvents, and this is detected by an increase in the LMS region (35).
A procedure has been developed (36) using preparative chromatography
with toluene as the carrier and a florescence detector (36–40). The normal
florescence of aromatics under UV radiation is apparently quenched by
association. The nonradiating fraction I is largely LMS material. The remaining
fraction II is also sometimes further fractionated. Jennings et al. (18) ran SECs on
fraction I, II, and whole asphalts. Values of LMS calculated from fraction I and II
were usually less than the whole asphalt measured values. McCaffrey (41) has
described an “ultra-rapid” procedure using one column and a high flow rate of a
95:5 chloroform:methanol carrier solvent. Three distinct peaks are obtained,
which are correlated with both physical and chemical properties.
Many tests have been proposed for simulating hot mix and road aging, and
SEC may be used to compare laboratory and field aging (33,42). The effectiveness
of recycling agents in restoring aged asphalt for reuse has also been studied
by comparing the SEC chromatograms of the old, new, and restored asphalts
(14,42–45).
Since Bynum and Traxler (4) there have been a number of attempts to relate
road performance to SEC results. Plummer and Zimmerman (46) studied test
sections in Michigan and Indiana and found that a greater LMS percentage seemed
to correlate with cracking. Jennings and co-workers (14,42,47–51) conducted a
major study relating cracking of roads to higher percentage LMS, primarily in
Montana but also in other regions of the United States. Both Jennings and Pribanic
(50) and Hattingh (29) showed that low-percentage LMS can result in rutting.
There have been many attempts to correlate asphalt properties to the shape
of the SEC chromatograph, including both aged and unaged material. Beazley
et al. (52) used SEC and nuclear magnetic resonance to estimate asphalt yield and
viscosity from crude oil. Woods et al. (53) used SEC fractions to study the
differences in maltenes from tar sand bitumens. The most common procedure has
been to divide the chromatograph into segments, ranging in number from 3 to 12,
and correlating properties to the relative size of these segments (10,54–65). When
the chromatograph is divided into many segments, a reduced set is often chosen on
the basis of statistical significance. Some of these studies include modified
material (32,65,66). The properties of compacted mixes were correlated by Price
and Burati (66) to the SEC chromatograph of the base asphalt.
The measurement of molecular weight by SEC, as with other methods, is
greatly complicated by the tendency of the more polar asphalt constituents to
© 2004 by Marcel Dekker, Inc.