From virgin to recycled bitumen: A microstructural view |
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| Affiliation: | 1. Dipartimento di Architettura, University of Roma Tre, 00184 Rome, Italy;2. Dipartimento di Ingegneria Strutturale e Geotecnica, University of Roma La Sapienza, 00184 Rome, Italy;1. School of Highway, Chang’an University, The middle section of the South Second Ring of Xi''an, Xi''an, Shaanxi 710064, China;2. Department of Civil, Construction, and Environmental Engineering, North Carolina State University, 915 Partners Way, Raleigh, NC 27695-7908, USA;1. Dept. of Civil and Environmental Engineering, The University of Tennessee, Knoxville, TN 37996, USA;2. College of Chemical Engineering, State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, PR China;1. School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin 150090, China;2. School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150090, China;3. Laboratory of molecular engineering for asphalt, China Academy of Transportation Sciences, Beijing 100029, China |
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| Abstract: | In the present work, soft and hard bitumens recovered from unaged, aged and recycled asphalt concrete (AC) mixtures, which in laboratory tests performed mechanically as well as an AC mixture produced with virgin materials, were investigated regarding rheological, thermal and surface microstructural aspects. For comparison purposes, bitumen containing 50 wt% of virgin bitumen and 50 wt% of bitumen recovered from reclaimed asphalt pavement (RAP) was studied. Some properties of the bitumens remained unchanged throughout the preparation of the AC mixture, aging and recycling: Soft and hard bitumens retained their general rheological properties significantly, and their thermal and surface microstructural properties partially. Soft bitumens presented larger “bee” structures and, therefore, higher surface roughness, while hard bitumens presented smaller “bee” structures and, thus, lower surface roughness. Furthermore, soft bitumens seemed to contain higher crystalline-like content than hard bitumens. For the soft cases, the unaged recovered bitumen did not show the same characteristics (rheological and surface microstructure) as the virgin bitumen. Similarly the recovered recycled bitumen did not show the same characteristics (surface microstructure) as the bitumen prepared from the mixture of virgin bitumen and RAP bitumen. Aging of the AC mixture changed the rheological properties of the soft bitumen by increasing the complex modulus and decreasing the phase angle. Similarly, recycling changed the rheological properties by increasing the complex modulus and decreasing the phase angle. Compositional changes occurred during AC mixture preparation (possibly also aging and recycling) for both soft and hard bitumens. Consequently, more “phases” were observed on the surface microstructure for the recovered bitumens as compared with the virgin bitumens. However, no significant trend was found for the surface microstructure characteristics between the unaged, aged and recycled recovered bitumens. Moreover, the nature of the virgin bitumen influenced the properties of the recycled recovered bitumen, e.g. the glass transition temperature. |
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| Keywords: | A Recycling B Microstructures B Rheological properties B Surface properties Atomic force microscopy |
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