TY - JOUR
T1 - Interplay between wax and polyphosphoric acid and its effect on bitumen thermomechanical properties
AU - Samieadel, Alireza
AU - Fini, Elham H.
N1 - Funding Information:
This research is sponsored by the National Science Foundation (Award Numbers 1935723, and 1928795). Authors are also thankful for access to instrumentation at Eyring material center of Arizona State university (ASU). The authors acknowledge Dr. Shahrzad Hosseinnezhad with NC A&T, and Amirul Rajib with ASU for assistance with laboratory experiments. Furthermore, the help of Mr. Daniel Oldham in BBR testing and the support provided by Gil Speyer for usage of AGAVE cluster is greatly appreciated is much appreciated. The contents of this paper reflect the view of the authors, who are responsible for the facts and the accuracy of the data presented.
Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2020/5/20
Y1 - 2020/5/20
N2 - Most bitumen contains some level of wax, and the widespread use of wax-based additives in asphalt industry further increases bitumen's wax content. Wax-based additives reduce viscosity at high temperatures, facilitating the mixing and compaction of asphalt mixtures. However, the added wax leads to increased stiffness and physical hardening at low temperatures. In addition, wax may have an interplay with other bitumen additives and modifiers such as polyphosphoric acid (PPA), which is typically used by refineries and asphalt blending terminals. PPA has been shown to enhance high-temperature properties without negatively impacting the low-temperature performance of asphalt pavement. However, due to the interplay between wax and PPA, it is hypothesized that the presence of wax may moderate PPA-bitumen interactions. This paper uses laboratory experiments and computational modeling to investigate mechanisms of interaction between PPA and bitumen in the absence and presence of wax. The results of a molecular dynamics simulation showed that PPA has a strong interaction with fused aromatics such as those classified as resins in bitumen, such interactions lead to reduced solubility of resins in heptane, causing them to precipitate out in heptane and fall into the asphaltene category. The presence of wax appears to reduce the efficacy of PPA on increasing bitumen's elasticity, as evidenced by lower complex modulus and higher creep compliance compared to those of no-wax bitumen doped with PPA. This was further observed in our computational analysis, which showed a good interaction between resin molecules and PPA molecules. However, the interaction between resins and PPA was reduced when wax was added, causing resins to become more scattered, as evidenced by a significant reduction in the radial distribution function of resin molecules. The study results help inform formulators and manufacturers about interplay between bitumen additives such as wax and PPA which may lead to unwanted consequences on pavement performance.
AB - Most bitumen contains some level of wax, and the widespread use of wax-based additives in asphalt industry further increases bitumen's wax content. Wax-based additives reduce viscosity at high temperatures, facilitating the mixing and compaction of asphalt mixtures. However, the added wax leads to increased stiffness and physical hardening at low temperatures. In addition, wax may have an interplay with other bitumen additives and modifiers such as polyphosphoric acid (PPA), which is typically used by refineries and asphalt blending terminals. PPA has been shown to enhance high-temperature properties without negatively impacting the low-temperature performance of asphalt pavement. However, due to the interplay between wax and PPA, it is hypothesized that the presence of wax may moderate PPA-bitumen interactions. This paper uses laboratory experiments and computational modeling to investigate mechanisms of interaction between PPA and bitumen in the absence and presence of wax. The results of a molecular dynamics simulation showed that PPA has a strong interaction with fused aromatics such as those classified as resins in bitumen, such interactions lead to reduced solubility of resins in heptane, causing them to precipitate out in heptane and fall into the asphaltene category. The presence of wax appears to reduce the efficacy of PPA on increasing bitumen's elasticity, as evidenced by lower complex modulus and higher creep compliance compared to those of no-wax bitumen doped with PPA. This was further observed in our computational analysis, which showed a good interaction between resin molecules and PPA molecules. However, the interaction between resins and PPA was reduced when wax was added, causing resins to become more scattered, as evidenced by a significant reduction in the radial distribution function of resin molecules. The study results help inform formulators and manufacturers about interplay between bitumen additives such as wax and PPA which may lead to unwanted consequences on pavement performance.
KW - Glass transition temperature
KW - Molecular dynamics
KW - Poly phosphoric acid
KW - Rheology
KW - Warm mix asphalt
KW - Wax
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U2 - 10.1016/j.conbuildmat.2020.118194
DO - 10.1016/j.conbuildmat.2020.118194
M3 - Article
AN - SCOPUS:85080076489
SN - 0950-0618
VL - 243
JO - Construction and Building Materials
JF - Construction and Building Materials
M1 - 118194
ER -