Investigation of Thermo-Mechanical Characteristics of Wax-doped Aged Asphalt Binder

This paper investigates effects of paraffin wax on molecular conformation of aged asphalt and consequently on asphalt’s thermo-mechanical properties. Although paraffin wax is one of the prevalent components of many recycling agents and rejuvenators commonly used in the asphalt industry, its effect on performance characteristics of asphalt binder has not been thoroughly understood. This paper uses combination of computational and experimental approach to study properties of aged asphalt binder specimens in presence of 1, 3, 5 and 10% paraffin wax. Differential scanning calorimetry (DSC) showed introduction of paraffin wax to aged asphalt significantly reduced glass transition temperature of aged asphalt, with 10% wax-doped aged asphalt having 9 degrees lower glass transition temperature than the control asphalt. The above observations can be attributed to plausible role of straight alkane chains of wax to disturb asphaltene clusters and increase overall asphaltene mobility. The latter was also reflected in wax-doped aged asphalt’s rheology with its percent recovery reducing by 50% in presence of 10% wax compared to the control. Thermo-gravimetric analysis (TGA) showed that addition of wax to aged asphalt binder increased the onset temperature of degradation; an increase of 25 degrees was recorded when wax dosage was increased from 1 to 10%. However, the overall thermal stability of asphalt binder was reduced as evidenced by the lower residual mass in samples with higher wax content. In addition, the difference in critical cracking temperatures (determined based on stiffness and stress relaxation ability of the asphalt binder) increased as the wax content increased. This in turn indicates cracking properties of wax-doped binder is controlled mainly by stiffness rather than stress relaxation ability. The latter could be attributed to formation of lamellar in wax-doped asphalt causing significant increase in stiffness. Molecular dynamics simulations results revealed how paraffin wax molecules change overall aggregation pattern of aged asphalt binder as evidenced by reduced formation of nano-aggregates in oxidized asphaltene in presence of wax molecules. The latter was described via a three-step mechanism including attraction of wax molecule to nano-aggregates of oxidized asphaltene, its penetration to self-assembled asphaltene stack, and disturbing formation of parallel stacks. Accordingly, the results showed the average aggregation number reduced after adding paraffin wax molecules to an equilibrated system of oxidized asphaltene molecules. Furthermore, radial distribution function confirmed that after addition of paraffin wax molecules, formation of parallel stacks of oxidized asphaltene is less likely. Molecular level understanding of wax-asphaltene interaction helps explain how wax contents of warm-mix additives, recycling agents and rejuvenators commonly used in asphalt industry can impact performance characteristics of asphalt binder.

  • Supplemental Notes:
    • This paper was sponsored by TRB committee AFK20 Standing Committee on Asphalt Binders.
  • Corporate Authors:

    Transportation Research Board

    ,    
  • Authors:
    • Samieadel, Alireza
    • Høgsaa, Bjarke
    • Fini, Ellie H
  • Conference:
  • Date: 2019

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; References; Tables;
  • Pagination: 6p

Subject/Index Terms

Filing Info

  • Accession Number: 01698398
  • Record Type: Publication
  • Report/Paper Numbers: 19-04197
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 7 2018 9:24AM