Variable-temperature Fourier-transform infrared spectroscopy study of asphalt binders from the SHRP Materials Reference Library

A wide range of asphalt binders were studied by variable-temperature Fourier-transform infrared spectroscopy (VT-FTIR) to understand how peak position and intensity are affected by temperature. Conditioning times of 20 and 60 hours were selected in the pressure aging vessel (PAV) to provide two levels of oxidative aging. Spectral intensity consistently increased at lower temperatures, but the magnitude of change varied a great deal depending on binder source. Peak positions within the 2,919-2,856 cm-1 range were found to shift to lower wavenumbers at lower temperatures. In contrast, peak positions within the 1,456-1,465 cm-1 range shifted higher. Shifts were found to both weaken or enhance by oxidation. The wax precipitation temperature (WPT) was generally found to experience a decrease after mild oxidation but increase after more extensive aging. No clear trends were found for the effect of oxidative aging on solid wax content as measured by VT-FTIR. These results provide new and important insights on how binder structure changes at cold temperatures.