Spectroscopic ellipsometry studies on optical constants of crystalline wax-doped asphalt binders

ABSTRACT

Asphalt pavement possesses the characteristics of strong sunlight absorption, which lead to the aging of asphalt binder. Asphalt aging is one of the leading causes of the performance deterioration in the asphalt pavement, and the appearance of crystalline wax (paraffin wax) during aging has a significant effect on optical properties (absorption and reflection) of the asphalt binder. In this paper, effects of the crystalline wax on optical properties of the asphalt binder were investigated using the spectroscopic ellipsometry (SE) technique, and a new method for the quantification of the crystalline wax in asphalt was also developed. Cold Lake asphalt doped with different contents of n-alkanes (eicosane, triacontane, and tetracontane) were tested by the SE. The results showed that there is a close linear relationship between the optical constants and wax content of the asphalt binder. In addition, with increasing both the chain length of n-alkanes and their content, the reflection intensity of the asphalt binder decreased, and the refractive index and extinction coefficient increased accordingly. On the whole, ellipsometry-based optical testing is a promising method for rapid and non-destructive identification of wax in asphalt.

KEYWORDS:

• Crystalline wax
• asphalt binder
• spectroscopic ellipsometry
• quantitative analysis
• optical properties

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Fundamental Research Funds for the Central Universities, SWJTU under Grant 2682021CX017, National Natural Science Foundation of China under Grant 52008352, Sichuan Applied Basic Research Project (2021YJ0533), and Sichuan Science and Technology Programme (2021JDTD0023). The authors appreciate the Analysis and Testing Centre of Southwest Jiaotong University for their assistance of the spectroscopic ellipsometry analysis.