Fundamental Properties of Asphalts and Modified Asphalts, III

Work Conducted This Quarter
A Topical Report, anticipated to be delivered early in the next quarter, summarizes findings from
the past two to three years of research. This report describes the present state of practice for the
investigation of the compositional nature of asphalts and aggregates, as studied by atomic force
microscopy and presents modeling approaches for integrating asphalt/aggregate physichemical
properties into continuum-damage models of pavement performance. Finally, this report will
suggest how work elements from the ARC work plan; ARC Work Element Subtask M1b-2-
Work of Adhesion at Nano-Scale using AFM, ARC Work Element Subtask M2a-2-Work of
Cohesion Measured at Nano-Scale using AFM, Work Element Subtask F1d-7-Coordinate with
AFM Analysis, and Work Element F3a-Asphalt Microstructural Modeling [Western Research
Institute 2008], will be coordinated with this task.
Work Plan Next Quarter
• Research conducted to date in this subtask has been primarily concerned with defining
and measuring compositional properties of material thin-films which exhibit and/or cause
crazing phenomena. This is thought to be a result of material discontinuity
(heterogeneity) caused by variations in wax and asphaltene content in the film. It is
hypothesized that this heterogeneity may be considered an indicator of cracking and
embrittlement in asphaltic materials. Thus, a natural avenue for future research would
then be to conduct measurements at micron and nano-scale that focus more on
physical/rheological properties of thin films related to the stiffness and embrittlement
propensity, in addition to continuing compositional/chemical characterization of these
materials, in order to draw correlations between compositional and rheological properties.
• In the next quarter, a revised SARA separation method will be employed to separate
asphalt into saturate, aromatic, polar aromatic, and asphaltene fractions. In this
procedure, iso-octane asphaltene/maltene separations will be conducted, and the maltenes
from this separation will be further separated employing the modified SARA separation
procedure. Based on the information gained from these studies, a revised method for
ASTM 4124 will be submitted to the ASTM D4 committee for approval.
• A solidification stage is being assembled as part of the atomic force microscope by
employing both a heating stage and a cooling stage fabricated along with micrometer
positioning devices, figure 2-3.2. This apparatus will be used to impart a thermal
gradient across an asphalt thin-film resulting in a moving solidification front (liquidsolid)
interface that may be monitored in time with AFM. Furthermore, an automated
wetting apparatus will also be assembled to better control the spin casting procedure and
to observe and quantify lubrication dynamics (see figure 2-3.3). Finally, metrology and
nanoindentation accessories have been added to the existing AFM equipment to enhance
capabilities to include micro/nano-rheological testing of material thin-films.
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