Author: Zhao, Kecheng
Title: Physicochemical characterization of neat asphalt binders in oxidative aging and rejuvenation
Advisors: Wang, Yuhong (CEE)
Degree: Ph.D.
Year: 2019
Subject: Hong Kong Polytechnic University -- Dissertations
Pavements, Asphalt
Binders (Materials)
Asphalt -- Additives
Department: Department of Civil and Environmental Engineering
Pages: 410 pages : color illustrations
Language: English
Abstract: Asphalt aging and rejuvenation are two closely related phenomena. Asphalt binder as an organic material is susceptible to oxidative aging, which causes the hardening of asphalt binder and further leads to the embrittlement, cracking, and fracturing of asphalt pavements. Conversely, rejuvenation attempts to restore the engineering properties of aged asphalt binders to extend the service life of in-situ asphalt pavements or enhance the properties of reclaimed asphalt pavements (RAP). Understanding the mechanisms of asphalt binder aging will naturally help the development of effective rejuvenation methods because the latter aims to reverse the former process. Asphalt aging and rejuvenation as key issues in pavement engineering have been examined in numerous studies. There are, however, several key challenges that have not been fully addressed before this study. Firstly, researchers are aware that different conditions affect asphalt aging kinetics and the generated aging products, but deviations in the physicochemical properties of asphalt binders created in accelerated aging conditions and those in more realistic aging conditions are not clear. Secondly, asphalt aging and rejuvenation are commonly studied from the perspective of asphalt's rheological property changes; there is lack of in-depth understanding of the fundamental physicochemical property evolutions during the aging and rejuvenation processes. Thirdly, the methods and tools used for investigating fundamental physicochemical properties are limited. Therefore, there is a great need to systematically investigate asphalt aging and rejuvenation using state-of-the-art methods, tools, and theories. An overall introduction to this study is provided in Chapter 1 of the dissertation. The rest contents of the dissertation are organized into three parts. In part one, the physicochemical property changes of asphalt binders in different aging conditions are studied, and the findings are presented from Chapter 2 to Chapter 4. In Chapter 2, the influences of three aging conditions on the rheological properties of asphalt binders are examined. The aging conditions include a warm chamber to simulate more natural situations, an autoclave with pure oxygen with high pressure, and a pressure aging vessel (PAV). The longest aging treatment in the warm chamber lasted for 1.5 years, while that in the autoclave and in the PAV lasted for 28 days and 60 hours, respectively. The aged specimens are used for subsequent analysis. Chapter 2 is focused on the influences of the aging conditions on the rheological properties. Chapter 3 is focused on the influences of the aging conditions on the functional groups—characteristic molecular segments in asphalt binders. Chapter 4 is focused on the influences of the aging conditions at the nano-scale, i.e., microstructures in asphalt binders and the four general fractions: saturates, naphthene aromatics, polar aromatics, and asphaltenes. Chapter 5 is focused on the influences of the aging conditions at the molecular level. In this chapter, a major drawback in using the gel permeation chromatography (GPC) was found and correction methods were proposed. The four chapters provide a multiscale view of the physicochemical property changes of asphalt binders subjected to different aging conditions.
The part two of the dissertation includes two chapters. In Chapter 6, the phenomenological connections between the chemical properties and rheological properties of the aged asphalt binders are analyzed. The oxygen-containing functional groups, asphaltenes content and microstructures are found to be the driving factor for the rheological property changes. In Chapter 7, the oxidation kinetics of different aging conditions are discussed. Attempts are made to explain why different aging conditions lead to different chemical reactions, which generate different aging products. The part three of the dissertation is focused on the physicochemical property changes of aged asphalt binders in the rejuvenation process. Part three includes three chapters. Chapter 8 examines the effects of rejuvenation on the changes of asphalt binders in rheological properties, at the molecular level and at the nano-scale. It is argued that rejuvenation is unlikely to change the already formed chemical bonds. In Chapter 9, a new method is developed to examine the rejuvenation effect by using the continuous relaxation spectrum (CRS). The CRS, based on sound theoretical foundations, can be used to explain the rejuvenation phenomenon as well as to assess the rejuvenation effectiveness of different rejuvenators. Based on all the investigations, anti-aging agents and rejuvenators are developed. The results of using the anti-aging agents and rejuvenators are presented in Chapter 10. Chapter 11 summarizes the overall study and recommends future research directions. The findings of this study are expected to contribute to a better understand of the physical, chemical and microstructural behaviors of asphalt binders during aging, rejuvenation and antiaging processes. The newly developed theories, methods, and tools are expected to help researchers and practitioners in selecting more aging-resistant asphalt binders and more effective rejuvenators, more accurately presenting and analyzing the research results, and developing more effective recycling practices.
Rights: All rights reserved
Access: open access

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