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Short-term aging characterization of asphalt binders using gel permeation chromatogr

Both the rolling thin film oven test (RTFOT) and the short-term oven aging (STOA) methods are used in the laboratory to represent
the aging of an asphalt binder during plant mixing, transportation and paving. The RTFOT is conducted at 163 C for 85 min, and the
recommended STOA methods are to heat the loose mix in a forced draft oven either at 135 C for 4 h or at 154 C for 2 h dependent on
the asphalt binder s stiffness. The actual time of short-term aging in the field varies depending on hauling distances or paving times.
This research was initiated to compare the aging effects of the RTFOT and the STOA methods using the gel permeation chromatography
(GPC) and selected Superpave binder tests. For this study, nine asphalt binders were prepared, and five aging periods were used
for the RTFOT and four aging treatments were selected for the STOA. Loose asphalt mixes were obtained from six field projects. The
results of GPC test showed that the RTFOT method has less aging effect on the binders than the STOA methods for asphalt mixtures
prepared in the laboratory. Given the limited number of samples from the field, it was difficult to find any correlation of short-term aging
between the laboratory and the field. The longer the aging time in the RTFOT led to an increase in the high temperature viscosity and the
high failure temperature of asphalt binders, the only exception being the rubber-modified binders. The GPC was effective in evaluating
the aging effect of rubber-modified binders using different RTFOT aging times.
1. Introduction
1.1. Background

The properties of binders in asphalt mixtures change
over time during mixing, transportation and construction.
As time increases, the binders become more stiff and brittle.
Both the rolling thin film oven test (RTFOT) and the shortterm
oven aging (STOA) methods in the laboratory are
intended to represent the aging of an asphalt binder during
hot-mix asphalt (HMA) production and construction. The
RTFOT measures the effect of heat and air on a moving
film of semi-solid asphaltic binder [3]. The aging time of
85 min in the RTFOT is expected to produce aging effects
comparable to average field conditions, although given the
number of variables, the aging in the field is often different
from that of RTFOT [12]. For asphalt mixtures, the recommended
laboratory procedure for short-term aging is to
heat the loose mix in a forced draft oven for 4 h at a temperature
of 135 C [10], while for the stiffer mixes, shortterm
aging of 2 h at 154 C is commonly used. The actual
time of short-term aging in the field varies and it is dependent
on hauling distances or paving delays.
This aging, in general, results in a change in the molecular
size distribution of an asphalt binder. Specifically, an
increase in the large molecular size (LMS) results in an
increase in the viscosity and stiffness of an asphalt binder.
This viscosity change is predicted well by gel permeation
chromatography (GPC) [5,6,8].

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