TY - JOUR
T1 - Role of Chemical Composition of Recycling Agents in Their Interactions with Oxidized Asphaltene Molecules
AU - Fini, Elham
AU - Rajib, Amirul Islam
AU - Oldham, Daniel
AU - Samieadel, Alireza
AU - Hosseinnezhad, Shahrzad
N1 - Funding Information:
This research is sponsored by the National Science Foundation (Award Nos. 1935723 and 1928807). The authors would like to acknowledge the invaluable assistance provided by Dr. Albert Hung at the Arizona State University Innovation Center for Materials. The contents of this paper reflect the view of the authors, who are responsible for the facts and the accuracy of the data presented. All data, models, and code generated or used during the study appear in the submitted article.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - The use of reclaimed asphalt pavement (RAP) in neat asphalt mixtures has received significant attention because of its economic and environmental advantages. However, bitumen contained in RAP is severely aged; when RAP is blended with virgin asphalt at a high percentage, it can negatively affect the properties of the resulting blend. Therefore, recycling agents have been used to improve the properties of aged asphalt and consequently the performance of the mixture. This paper uses computational modeling and laboratory experiments to examine the role of chemical structure and the composition of recycling agents on their interactions with oxidized bitumen. To do so, rheometry as well as Fourier transform infrared spectroscopy, thin-layer chromatography with flame ionization detection, gel permeation chromatography, and contact-angle measurements were used to track changes in physicochemical and surface properties of oxidized bitumen in the presence of four recycling agents with widely different compositions. The study results show that oxidized bitumen became softer after adding recycling agents (regardless of their source) and that all recycling agents were able to increase the phase angle and the colloidal stability index of aged bitumen. However, not all the recycling agents restored molecular conformation. The most effective recycling agent was found to be recycling agent A, which led to a concurrent increase in the crossover modulus and crossover frequency of aged bitumen. In contrast, recycling agent C had the least effect on crossover values. Molecular dynamics simulation showed that recycling agent A restored molecular conformation and reduced the size of asphaltene nanoaggregates, while recycling agent C promoted agglomeration, causing an increase in the size of nanoaggregates. Recycling agent A was also effective in reducing the moisture susceptibility of aged bitumen, as shown by a smaller change in contact angle of aged bitumen between wet and dry, compared to other recycling agents. Based on the study results, the efficacy of a recycling agent in the deagglomeration of oxidized asphaltenes is shown by a concurrent increase in both the crossover modulus and the crossover frequency; these two rheology-based indicators can be used to distinguish recycling agents that can accurately be called rejuvenators.
AB - The use of reclaimed asphalt pavement (RAP) in neat asphalt mixtures has received significant attention because of its economic and environmental advantages. However, bitumen contained in RAP is severely aged; when RAP is blended with virgin asphalt at a high percentage, it can negatively affect the properties of the resulting blend. Therefore, recycling agents have been used to improve the properties of aged asphalt and consequently the performance of the mixture. This paper uses computational modeling and laboratory experiments to examine the role of chemical structure and the composition of recycling agents on their interactions with oxidized bitumen. To do so, rheometry as well as Fourier transform infrared spectroscopy, thin-layer chromatography with flame ionization detection, gel permeation chromatography, and contact-angle measurements were used to track changes in physicochemical and surface properties of oxidized bitumen in the presence of four recycling agents with widely different compositions. The study results show that oxidized bitumen became softer after adding recycling agents (regardless of their source) and that all recycling agents were able to increase the phase angle and the colloidal stability index of aged bitumen. However, not all the recycling agents restored molecular conformation. The most effective recycling agent was found to be recycling agent A, which led to a concurrent increase in the crossover modulus and crossover frequency of aged bitumen. In contrast, recycling agent C had the least effect on crossover values. Molecular dynamics simulation showed that recycling agent A restored molecular conformation and reduced the size of asphaltene nanoaggregates, while recycling agent C promoted agglomeration, causing an increase in the size of nanoaggregates. Recycling agent A was also effective in reducing the moisture susceptibility of aged bitumen, as shown by a smaller change in contact angle of aged bitumen between wet and dry, compared to other recycling agents. Based on the study results, the efficacy of a recycling agent in the deagglomeration of oxidized asphaltenes is shown by a concurrent increase in both the crossover modulus and the crossover frequency; these two rheology-based indicators can be used to distinguish recycling agents that can accurately be called rejuvenators.
KW - Adhesion
KW - Agglomeration
KW - Complex modulus
KW - Contact angle
KW - Moisture
KW - Nanoaggregates
KW - Reclaimed asphalt pavement (RAP)
KW - Self-assembly
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U2 - 10.1061/(ASCE)MT.1943-5533.0003352
DO - 10.1061/(ASCE)MT.1943-5533.0003352
M3 - Article
AN - SCOPUS:85087200045
SN - 0899-1561
VL - 32
JO - Journal of Materials in Civil Engineering
JF - Journal of Materials in Civil Engineering
IS - 9
M1 - 04020268
ER -