| Author: | Zhu, Xiaoxu |
| Title: | Lifecycle evolution of the physicochemical and performance-related properties of SBS-modified asphalt binders |
| Advisors: | Wang, Yuhong (CEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | x, 237 pages : color illustrations |
| Language: | English |
| Abstract: | Polymer-modified asphalt (PMA) binders are often used in the most challenging locations of road and airport pavements. The higher cost of PMA compared with neat asphalt is believed to be well justified because of its superior performance. Among a variety of polymers for the production of PMA binders, styrene-butadiene-styrene (SBS) polymer gains the widest application due to its excellent engineering properties and reasonable cost. Various types of SBS polymers with different molecular structures have been used in asphalt modification with different dosages, and the resulting binder properties vary greatly. Recent studies found that some desired properties of PMA samples dropped significantly after mixture production. Moreover, as the world is embracing long-life pavement strategies that aim to achieve more than 40 years of pavement life, the durability of PMA remains a critical question to be studied. To this end, the investigation on the lifecycle evolution of the physicochemical and performance-related properties of SBS-modified asphalt binders is necessary to produce more durable PMA materials and asphalt pavements. To fill the research gaps, three research objectives have been put forward in this study: (1) to evaluate the effects of binder formulation on the physicochemical and performance-related properties of SBS-modified asphalt binders subjected to complex short-term aging conditions; (2) to identify the evolution characteristics of the physicochemical and performance-related properties of SBS-modified asphalt binders under natural aging conditions; (3) to analyze the non-linear viscoelastic (NLVE) properties of SBS-modified asphalt binders as well as the lifecycle evolution of the properties. To achieve the research objectives, various types of SBS-modified asphalt binders were firstly prepared with different polymer structure (diblock, linear triblock and radial) and polymer content (3 % and 6 %). Subsequently, modified rolling thin film oven (RTFO) treatments were conducted on the binder samples at two temperatures and two durations to simulate the short-term aging conditions during the mixture production, transportation and paving stage. Next, an accelerated natural aging method was employed to simulate the long-term aging during the road use stage. Pressure aging vessel (PAV) aging was also performed for comparison purposes. Finally, the physicochemical and performance-related properties of modified binders were characterized from the aspects of microscopic morphology, functional groups, linear viscoelastic (LVE) properties, rutting performance and fatigue performance. In particular, asphalt binders are likely to behave in the NLVE domain under certain service conditions in the field. The NLVE responses of SBS-modified asphalt binders were acquired via large amplitude oscillatory shear (LAOS) tests, and the NLVE properties as well as the lifecycle evolution of the properties were investigated. The three research objectives have been successfully fulfilled and the main findings are introduced as follows: (1) The effects of binder formulation on the physicochemical and performance-related properties of SBS-modified asphalt binders subjected to short-term aging The physicochemical and performance-related properties of SBS-modified asphalt binders are found to be influenced by both the main effects and interaction effects of three factors: polymer structure, polymer content and short-term aging condition. Polymer structure is a predominant factor affecting polymer particle morphologies in the modified binders and storage stability. Polymer content is the leading factor for the polymeric characteristic peaks in infrared spectrum, elasticity, elastic recovery, and non-recoverable creep compliance. Aging condition contributes to the majority of variations in binder oxidization and complex shear modulus. From the perspective of engineering applications, the effects of polymer structure are limited at low polymer content, regardless of aging state. More significant property differences are observed at high polymer content, and radial SBS polymer leads to the best engineering properties, followed by linear triblock and diblock SBS. Nevertheless, the property differences caused by polymer structure decrease as the aging degree increases and even become negligible after the RTFO treatment at 183 ℃ for 2*85 min. To fully take the advantages of SBS polymer modification, the joint influences of polymer structure, polymer content, and aging must be considered. (2) The physicochemical and performance-related properties evolution of SBS-modified asphalt binders under accelerated natural aging conditions During the natural aging process, most physicochemical and performance-related indicators of SBS-modified asphalt binders experience a fast development stage followed by a steady development stage. Modified binders with 3 % of SBS exhibit similar changing trends as the base (neat) binder. At 6 % of SBS, however, some inconsistent trends can also be observed due to the opposite effects of asphalt binder aging and polymer degradation on the overall binder properties. Additionally, the evolution of performance-related indicators shows an apparent lag compared with that of physicochemical indicators. The required time for naturally-aged binders to reach the similar aging level as PAV-aged ones varies obviously with aging indicators and binder types. Overall, natural aging reveals richer, more realistic, and more comprehensive information of the modified binders as compared to PAV aging, even though the natural aging process takes longer time. (3) The NLVE properties of SBS-modified asphalt binders as well as the lifecycle evolution of the properties Based on LAOS tests, the NLVE rheological parameters determined by the magnitude of complex shear modulus and phase angle as well as the NLVE waveform parameters determined by the distorted stress waveform were obtained to quantify the NLVE responses. It is found that the NLVE properties of SBS-modified asphalt binders are affected by polymer content, polymer structure, shear strain amplitude, aging condition and the interactions of such factors. The addition of SBS polymer results in more significant and complex NLVE behaviors of modified binders, and polymer structure also plays a prominent role. With the increase of shear strain amplitude, two-stage and three-stage curves can be observed in the NLVE rheological parameters of modified binders with low (≤3%) and high (>3%) polymer content, respectively. The strain resistance of modified binders is substantially reduced due to aging, which also causes significant effects on the NLVE waveform parameters. In general, NLVE responses reveal more abundant mechanical and microstructural information of SBS-modified asphalt binders than the LVE ones, enhancing the understanding of the modification and aging mechanisms. Overall, this study systematically investigated the lifecycle evolution of the physicochemical and performance-related properties of SBS-modified asphalt binders. The research outcomes contribute to: (1) scientific insights into the working and deterioration mechanisms of PMA, (2) new approaches to PMA quality management, (3) optimized pavement structure design and material selection, (4) improvements in PMA binder and mixture production. |
| Rights: | All rights reserved |
| Access: | open access |
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