Attenuated Total Reflection Fourier Transform Infrared spectroscopy has become a popular spectroscopic technique in bituminous binder analysis. However, comparable results are not obtainable yet due to differences in devices, measurement routines, sample preparation procedures, and spectral evaluation. Thus, the Task Group 1 of the RILEM TC 295-FBB: “Fingerprinting bituminous binders using physicochemical analysis” focuses on bringing this method towards pre-standardization. This study evaluates the reproducibility and consistency from round robin test, where 21 participating laboratories performed six different preparation techniques on three different binders in an unaged, short-term, and long-term aged state. A total of 6461 spectra were recorded and evaluated for their mean, standard deviation and coefficient of variation (CV) in the spectral region between 1800 and 600 cm⁻¹. The results show that the solid sample preparation methods provide excellent reproducibility, with a coefficient of variation below 2%. Only the solvent method showed a higher coefficient of variation at 7.18%. Outliers with a high CV were detected and categorized into two groups: one where only one of the four samples differed and the other where all 16 spectra showed slight scattering in the overall absorption. The consistency of the method is significantly influenced by the accuracy of sample preparation, which is crucial for minimizing differences in slope, baseline, and noise in the spectra. These findings show the excellent reproducibility of these sample preparation methods and will be further examined to establish universal indices for evaluating effects such as ageing, bringing the method closer towards standardization.

Understanding aging across material scales is critical for predicting the long-term performance of bituminous materials. This study investigates the aging of binder, mastic, and asphalt mixture samples under various temperature, pressure, reactive oxygen species (ROS), and humidity. Chemical aging processes were analysed using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), principal component analysis (PCA), and Euclidean distance. Normalisation, baseline correction, and advanced ATR correction were used to enhance the accuracy of FTIR results. Hydrated lime in mastics enhanced the resistance to oxidative aging, particularly under hygrothermal conditions. PCA identified key spectral regions for understanding aging processes of bituminous materials. Porous asphalt (PA) mixtures aged more than stone mastic asphalt under field-like conditions. PCA identified distinct aging clusters at low and high pressure. Euclidean distance analysis indicated that binder-level aging can approximate mastic and mixture aging under certain conditions. The findings confirm that FTIR indices are effective for multi-scale aging studies.

Bitumen, a crucial constituent in the composition of asphalt pavements, plays a vital role in the performance and durability of pavements. Bitumen undergoes aging over time due to complex interactions between its chemical components and various environmental factors. In this investigation, the study focuses on examining the aging process of bitumen under the combined influence of moisture and reactive oxygen species (ROS). The findings highlight the importance of considering ROS and moisture as critical factors contributing to accelerated aging. Results obtained from Fourier-transform infrared (FTIR) spectroscopy, SARA fractionation, and optical inverse microscope (OIM), as well as dynamic shear rheometer (DSR) examination, indicate that the concurrent influence of these factors induces significant aging in bitumen, with the extent of this impact being modulated by the bitumen's inherent aging susceptibility. The insights obtained from this study enhance strategies to justify the destructive impacts of aging, extending the operational lifespan of asphalt pavements.