Quantification of crystalline wax in asphalt binders using variable-temperature Fourier-transform infrared spectroscopy

Solid crystalline wax content is an important parameter to control the quality and durability of asphalt binders produced for flexible pavement construction. Although a significant number of methods have been published for the quantification of wax in crude oil and lubricants, the direct use of these for asphalt binder characterization has faced a number of obstacles. In order to develop a precise, accurate and practical methodology for the measurement of in situ wax in binders at various temperatures, Variable-Temperature Fourier-Transform Infrared Spectroscopy (VT-FTIR) is used for the first time to determine wax contents in asphalt binders over the entire temperature domain that typical pavements experience. Cold Lake asphalt doped with varying amounts of n-alkanes, as well as a variety of commercial binders, were tested to validate the effectiveness of the VT-FTIR method. The results show that the crystalline wax contents determined by VT-FTIR are reasonably consistent with traditional cold precipitation and differential scanning calorimetry (DSC) methods. In contrast with DSC, the VT-FTIR method is able to observe the continuing increase in crystalline wax with decreasing temperature, and is able to do so over extended periods of time. On the whole, the VT-FTIR method provides a fundamental chemical analysis that probes the formation of crystalline unit cells in the asphalt binder. Hence, it is a promising approach for the accurate determination of solid crystalline wax content with the ultimate aim of controlling wax-associated pavement distresses such as raveling, cracking and moisture damage.