Laboratory characterisation of biochar-modified bitumen: A combined rheological and spectroscopic approach

The present study explores the investigation of olive-waste derived biochar as an alternative, bio-based modifier for conventional bitumen. Three bio-modified binders were produced with different biochar contents (5%, 10% and 15% by weight of bitumen) using a 70/100 penetration grade bitumen as the base binder. At the first stage, all four binders underwent a series of evaluations to assess their conventional properties. In addition, the rheological behavior was examined via a Dynamic Shear Rheometer (DSR). The structural impact and the physicochemical properties were analyzed using two spectroscopic methods, Fourier Transform Infrared (FTIR) and Proton Nuclear Magnetic Resonance ( 1 H-NMR), determining how biochar alters the structure of bitumen at a molecular level. The tests were conducted before and after applying Rolling Thin Film Oven Test (RTFOT) ageing. To further evaluate the effect of biochar on the ageing susceptibility of bitumen, ten different ageing indexes were calculated, two rheological and eight physicochemical. Based on the above studies, three key findings were identified: (a) biochar enhanced the high-temperature performance of bitumen by improving the rutting resistance attributed to biochar’s stiffening effect, (b) biochar contents above 5% led to a decline of fatigue behavior and storage stability and (c) the evaluation of the ageing susceptibility was not decisive across the different ageing metrics, revealing the selectivity in distinguishing between physicochemical and rheological evaluation factors. Consequently, the applicability of the standardized evaluation methods for bio-modified binders requires further investigation.