Author: Li, Fangjin
Title: Changes in asphalt binder at molecular and microstructural levels during aging and rejuvenation and the effects on binder rheological properties
Advisors: Wang, Yuhong (CEE)
Degree: Ph.D.
Year: 2023
Subject: Pavements, Asphalt concrete -- Design and construction
Pavements, Asphalt concrete -- Maintenance and repair
Hong Kong Polytechnic University -- Dissertations
Department: Department of Civil and Environmental Engineering
Pages: ix, 257 pages : color illustrations
Language: English
Abstract: Asphalt binder is a widely used engineering material containing colloidal particles suspended in an oily medium. Its aging and rejuvenation are of great concerns to practitioners and researchers. During aging and rejuvenation, binders are subject to fundamental physicochemical changes, which are translated into engineering property changes. However, even with extensive studies, there are still many unknowns about the realistic structure of asphalt binders at molecular and microstructural levels and the underlying mechanisms that drive the property variations of asphalt binders. Therefore, the purpose of the study is to systematically investigate asphalt binders at molecular and microstructural levels with the aid of experiments and theories.
Firstly, a variety of techniques were used to characterize asphalt binders from different crude sources, aging states, and rejuvenation states at molecular and microstructural levels. Corbett fraction was used to analyze the chemical compositions of asphalt binders based on differences in polarity. Fourier-transform infrared (FTIR) spectroscopy was used to determine different functional groups. A modified gel permeation chromatography (GPC) method was used to characterize the molecule or microstructure size distribution. Scanning transmission electron microscopy (STEM) was used to capture the microstructure morphology (size, area, and shape) of asphaltene particles in asphalt binders. Secondly, rheological tests were performed on asphalt binders by using a dynamic shear rheometer (DSR). Rotational tests were used to measure the zero shear viscosity (ZSV) of binders and their maltene phases, as well as rejuvenator viscosity. Temperature and frequency sweep tests were used to obtain basic rheological parameters, based on which commonly used performance-related properties and diagrams were derived. Strain-controlled time sweep test and linear amplitude sweep test (LAS) were used to characterize the fatigue behaviors of asphalt binders. Thirdly, the fundamental physicochemical properties of asphalt binders and the rheological properties were systematically and quantitatively analyzed. At last, connections between the physicochemical properties and rheological properties were investigated.
The major findings of this study are introduced as follows. (1) The combined information from fundamental physicochemical characterization revealed a clearer picture of the hierarchal structure of asphalt binders at molecular and microstructural levels. (2) Asphaltene content and the ZSV of maltenes can well explain most of the commonly reported rheological properties of asphalt binders, including binder ZSV, dynamic viscosity, phase angle, crossover frequency, rutting parameter, fatigue parameter, and Glover-Rowe (G-R) parameter. (3) Neither asphaltene content nor maltene viscosity is directly related to the binders' fatigue lives, for which asphaltene morphology plays a predominant role. (4) Three indicators were derived from the relaxation spectrum. Two of them, the strength of long relaxation time and the longest relaxation time, could well capture the binders' fundamental physicochemical property changed. These two parameters are also sensitive to the asphaltenes' morphological changes in aging and rejuvenation. Another indicator is newly developed in this study, named equivalent asphaltene particle size, which provides a theoretically sound parameter to understand what occurs at the microstructural level in binder aging and rejuvenation. (5) In view of the fact that asphalt binder treated by a pressure aging vessel (PAV) does not create a physicochemical state that matches the state created by natural aging, the use of a natural aging condition to simulate and predict the long-term asphalt binder aging is also investigated in this study.
The above findings are believed to contribute to a deeper understanding of the fundamental mechanisms behind engineering property variations in asphalt binders. Moreover, the findings may provide a solid theoretical background to guide binder selection, rejuvenation or modification, and aging simulation. Eventually, the findings may help the industry reach the ultimate goal of prolonging the service life of asphalt pavements.
Rights: All rights reserved
Access: open access

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