Author: Yu, Huayang
Title: Application of warm asphalt rubber as a sustainable paving material : component interaction mechanism investigation and performance characterization
Degree: Ph.D.
Year: 2017
Subject: Hong Kong Polytechnic University -- Dissertations
Asphalt-rubber
Asphalt -- Additives
Department: Department of Civil and Environmental Engineering
Pages: xxii, 187 pages : color illustrations
Language: English
Abstract: Asphalt rubber (AR), which is defined as raw bitumen modified by no less than 15% of crumb rubber modifier (CRM) by total binder weight, has gained increasing interest in recent years, due to its excellent mechanical performance and tyre-road noise reduction function. However, its high viscosity leads to the concern on its workability. Conventionally, the construction temperatures of AR mixtures are 30-50 °C higher than those of conventional mixtures, resulting in more energy consumption and higher construction emission. Warm mix asphalt (WMA) is a sustainable paving technology which can decrease the construction temperature of asphalt mixtures, reducing energy consumption, emission and odours during asphalt pavement construction. Correspondingly, it is an ideal solution to alleviate the workability concern of AR mixtures, thus producing durable and low-noise pavements that are also low-emissive during construction. However, research on warm asphalt rubber (WAR), especially on the component interaction mechanism of AR, is relatively limited despite its significant potential merits. Therefore, this dissertation research aims to systematically investigate the component interaction mechanism of WAR and analyse the effects of WMA additives on the workability and performance of AR. To achieve this objective, various types of WMA additives, including foaming additives (Aspha-min), organic additives (56# commercial wax and Sasobit) and chemical additives (Evotherm-DAT and Evotherm-3G), were incorporated to AR binder and mixture, followed by rheological, mechanical and chemical analyses. Rheological analysis on WAR binders involved the evaluation of penetration, softening point, viscosity, rutting factor, fatigue factor and low temperature stiffness. The analysis results showed that all non-foaming WMA additives were effective in improving the workability of AR binder, but provided various effects on other rheological properties. Only Sasobit was found to further improve the rutting resistance of AR binder. All non-foaming additives led to slightly poorer fatigue and low-temperature cracking resistance. When Sasobit and Evotherm-DAT were used together, the rheological properties were significantly compromised.
Chemical analysis investigated the effects of different WMA additives on the thermal behaviours, infrared spectra and asphalt four fraction distributions of the AR binders. The Fourier Transform Infrared Spectroscopy (FTIR) test results indicated that the variance in FTIR spectrum is mainly caused by the chemical nature of WMA additives, while the thermal test results proved that not only the light fractions of the base asphalt, but also part of the WMA additives, penetrates into CRM particles during the mixing process of AR binder. Besides, WMA additives have positive effect on promoting the interaction between CRM and base asphalt. Several mixing procedures of WAR binders were also proposed and their effects on WAR's rheological and chemical properties were evaluated. It was found that incorporating Evotherm-DAT, Sasobit and 56# paraffin wax at an earlier stage during the WAR preparation process has very marginal negative effect on the rheological properties compared to the conventional mixing procedure. However, the chemical analysis on the liquid phase of wax-based WAR binders indicated that the mixing procedure affected the interaction within WAR binder. The wax content of the liquid phase of the WARs prepared by the direct mixing method is lower than that prepared by the conventional method. The mechanical tests on WAR mixtures included the evaluation of mixture compactability, moisture susceptibility, stiffness modulus, dynamic modulus, and rutting and fatigue resistance. Owing to WMA additives, the mixing temperatures of all WAR mixtures studied in this research can be 16°C lower than that of their corresponding hot AR mixtures, achieving a similar compaction level. The stiffness modulus and dynamic modulus are influenced by the type of WMA additives. All WAR mixtures exhibited acceptable moisture susceptibility, rutting resistance and fatigue resistance. Among different WMA additives, Sasobit provided the most satisfying performance of AR mixture. It further enhanced the rutting resistance and had limited negative influence on other mechanical properties. In general, the results of the mixture mechanical analyses are consistent with those of the binder rheological analysis, except for fatigue resistance. Finally, it is believed that among the selected WMA additives in this research, Sasobit works best with AR binder and mixture. It is also expected that the data generated in the present research would be helpful to understand the overall performance of WAR binders and mixtures.
Access: open access

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