Phase transition process of sulfur in bitumen and its effect on rheological properties of bitumen

Sainan Xie, Junyan Yi, Tao Zhou, Elham H. Fini, Decheng Feng

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Partial substitution of sulfur for bitumen helps reduce bitumen consumption while promoting recycling of the sulfur in waste residues. The properties of sulfur-extended bitumen (SEB) are closely related to the chemical reaction process and the phase transition process of sulfur in bitumen, and these two processes are influenced by sulfur dosage and curing time. Therefore, SEB samples with sulfur dosages of 1 %, 5 %, 10 %, 15 %, 20 %, 25 % and 30 % were prepared and cured for 0, 15, 30, or 60 days. Differential scanning calorimetry was conducted to understand the sulfur recrystallization process in bitumen, and a dynamic shear rheometer was used to analyze the rheological properties of SEB samples. Results show that molten sulfur can turn to monoclinic sulfur immediately after cooling; the monoclinic sulfur gradually turns to orthorhombic sulfur, and the ratio between the two forms stabilizes after curing for 15 days. The recrystallization of sulfur in bitumen needs sufficient curing time, and the sulfur states in bitumen vary depending on the sulfur dosage. When the sulfur dosage is lower than 15 %, sulfur dissolves into bitumen. The dissolved sulfur softens the bitumen and increases its low-temperature properties and resistance to fatigue cracking. When the sulfur dosage is 10 %, 15 %, 20 %, 25 %, or 30 %, surplus sulfur is recrystallized to orthorhombic sulfur. When the sulfur dosage is 35 % or more (the dosages evaluated in the former study), surplus sulfur is recrystallized to monoclinic sulfur. The chemically crosslinked sulfur and recrystallization sulfur help increase the elastic component in bitumen and improve the rutting resistance and fatigue life of bitumen. However, when the sulfur dosage exceeds 20 %, the effect of stress concentration stands out due to bulk gathering of recrystallized sulfur, and this effect stops further improvement in the fatigue life of SEB samples. The effects of recrystallization sulfur on bitumen are mainly concentrated in the first 15 days of curing time, even though much more recrystallized sulfur is detected after more curing time, even at 60 days (the longest curing time evaluated in this study). Therefore, a curing time of 15 days is sufficient for accurate evaluation of SEB properties.

Original languageEnglish (US)
Article number129914
JournalConstruction and Building Materials
StatePublished - Jan 18 2023
Externally publishedYes


  • Chemically crosslinked sulfur
  • Curing time
  • Dissolved sulfur
  • Recrystallized sulfur
  • Rheological properties
  • Sulfur extended bitumen

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • General Materials Science


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