Multi-scale Studies of Aging, Rejuvenation, and Extrinsic Self-healing in Bituminous Materials
Advisor: Assistant Professor Ramez M. Hajj
Abstract
Oxidative aging is a crucial factor that influences the performance of asphalt mixes in flexible
pavements. The aged asphalt mix is more susceptible to fatigue and thermal cracking, the most
critical distress at intermediate and low temperatures, respectively. An emerging technology to
mitigate the cracking of asphalt pavements is the use of self-healing capsules embedded in asphalt
mixtures. To better design self-healing capsules, it is imperative to understand the aging and
rejuvenation mechanisms from chemical, mechanical, and micro-surface structure changes of
asphalt.
Because aging happens to the asphalt binder region, the aging effect of asphalt binder was
investigated based on static surface topography and time-sensitive asphalt binder microstructure.
They were also correlated with a recently validated asphalt binder cracking test, the poker chip
test. When the dominant effect of virgin asphalt binder in blended asphalt binder was realized in
this dissertation, an optimal dosage determination method was developed based on the response
on long-term aging effect of rejuvenated asphalt. Based on the trend of dosing rejuvenators,
encapsulated rejuvenators were optimized from healing agent type, concentration, capsule shell
thickness, and capsule percentage perspectives. The capsules' applicable scenarios and potentials
were also expanded from the fine aggregate matrix (FAM) scale to the asphalt concrete (AC) scale.
Finally, the benefits of capsules compared to solely rejuvenating were explained.
In this dissertation, asphalt material characterization tools provided micro morphology damage
indicators, chemical analysis, and anti-cracking analysis methods based on the understanding of
extended aging. This dissertation also revealed that both optimum dosages and fundamental
mechanisms of rejuvenation were affected by rejuvenator type, base binder selection, recycled
material content, and the aging level of the binder. The prospect of self-healing asphalt was
explored. This research therefore established a framework for engineering a combination of
capsules for use at pavement scale based on an understanding of chemical interactions, mechanical
properties, and multiscale experimental verification.
