Suggested Citation:
Hofko, Bernhard, Mohammad Zia Alavi, Hinrich Grothe, David Jones, John T. Harvey (2018) Infrared Spectroscopy on Asphalt Binders: Improving Repeatability and Sensitivity. Transportation Research Board 97th Annual Meeting

Asphalt binders as organic materials are susceptible to aging, triggered primarily by oxidation. The mechanical behavior of asphalt changes over time towards higher stiffness and brittleness. Infrared spectroscopy (FTIR) is an efficient analysis method to study the effects of oxidative aging on the chemical composition of asphalt binders. In infrared spectra, the carbonyl and sulfoxide areas are strongly affected by oxidation and commonly used to describe changes due to aging of a binder. However, analysis of infrared spectra can be carried out in various ways. The analysis method applied to a spectrum has a strong effect on the derived oxidative indices, as well as on repeatability and sensitivity to oxidative changes over aging. For the research presented in this paper, a PG 64-16 was aged by rolling thin-film oven (RTFO) and pressure aging vessel (PAV). FTIR spectra were measured for the unaged, the RTFO and RTFO+PAV aged samples. The spectra (up to 90 individual spectra per aging state) were subjected to different analysis techniques: spectra were looked at in the original or a normalized way, absolute and tangential baselines were taken into consideration and indices were calculated based on band maxima or integration. The coefficient of variation derived from the different analysis methods was used as a benchmark to rank applied analysis methods in terms of repeatability and sensitivity. From the outcomes of the study it is recommended to work with normalized spectra, use an absolute baseline and calculate indices by integration of bands.