A Novel FTIR Double-Layer Approach to Binder Diffusion: Lessons Learned and Challenges

The present study focuses on the investigation of the effect of spent cof-fee grounds (SCG) on the rheological and molecular characteristics of bitumen. A 70/100 penetration grade bitumen was utilized as the reference binder and the basis for the production of three spent coffee grounds-modified binders with distinct bio-modifier contents (5%, 10% and 15% content by weight of bitumen). The rhe-ological investigation was conducted with a Dynamic Shear Rheometer (DSR) via the rutting (G*/sinδ) and fatigue cracking (G* × sinδ) factors, whereas the molec-ular characterization was carried out with two distinct spectroscopic techniques, namely Fourier Transform Infrared (FTIR) and Proton Nuclear Magnetic Reso-nance (1H-NMR). The above multi-technique assessment was executed before and after applying Rolling Thin Film Oven Test (RTFOT) to assess the impact of short-term ageing on bitumen. It was concluded that spent coffee grounds improved the rutting resistance of bitumen at the expense of the fatigue crack-ing performance. Furthermore, the FTIR and 1H-NMR spectroscopic techniques should be used in a complementary manner since each technique offers distinct structural information. Finally, the assessment of the binders’ ageing sensitivity was not conclusive across the various ageing indexes, revealing the selectivity in differentiating between physicochemical and rheological evaluation parameters.