Wax in Asphalt: A comprehensive literature review

Wax in asphalt is an important factor that affects the life cycle cost of flexible pavements. Due to limitations in characterization methods for asphalt microstructure, deficiencies in our understanding of how wax affects physical and chemical properties of asphalt still exist today. However, thanks to the construction of carefully controlled pavement trials in support of the development of asphalt binder specifications, researchers now have a better understanding of long-term performance issues, and how waxes of various types influence these. Therefore, this article reviews early research on wax in asphalt as well as new insights obtained with modern characterization methods. The classification of wax in asphalt is discussed in relation to its chemical characterization by advanced spectroscopic methods. Physical characterization techniques of wax in asphalt are presented. Modern microscopy methods are shown to help researchers capture the detailed morphology of wax crystalline phases in asphalt. Wax content is one of the most important factors affecting asphalt performance yet its quantification by different methods can vary greatly. Therefore, the advantages and disadvantages of various methods are systematically reviewed here. Potential effects of wax on the different kinds of performance indices of asphalt and its mixtures are summarized. Shortcomings of the exsisting specifications are also discussed. Moreover, the current status of the use of wax-based, warm-mix additives in pavement engineering are analyzed. This paper provides a detailed review of the mechanisms by which waxes affect asphalt properties. It helps asphalt manufacturers to produce high-quality products and, last but not least, allows user agencies to avoid the use of inferior binders that lead to early and excessive cracking in the asphalt pavement.