The present dissertation investigates the use of bio-derived materials as modifiers for petroleum-based bitumen. Six solid-phase (Kraft lignin, microchlorella, chlorella, olive-waste biochar, rice husk, spent coffee grounds) and two liquid-phase (corn oil, sunflower seed oil) bio-modifiers were incorporated into different reference binders at varying contents. The binders were assessed in terms of their characteristic, rheological and physicochemical properties and short-term ageing susceptibility using a multiscale chemomechanical approach. Correlation and hierarchical cluster analyses were employed to quantify interproperty relationships. Results indicate that Kraft lignin most effectively enhanced high-temperature performance, though its content must be carefully controlled to avoid negative impacts on fatigue resistance. Bio-derived oils improved fatigue behavior, particularly at concentrations ≥3%, while all bio-modifiers maintained satisfactory storage stability up to 5%. Additionally, BET (Brunauer-Emmett-Teller) surface area proved a more reliable storage stability predictor than total pore volume. Sulfoxide and carbonyl functional groups were identified as primary indicators of bitumen’s short-term ageing, whereas the polar region better reflected molecular changes in the bio-materials. Rice husk and microchlorella demonstrated superior ageing resistance. To better capture these molecular transformations, different spectroscopic techniques should be applied in a complementary manner. Cluster analysis revealed that, despite structural differences, solid- and liquid-phase bio-modified binders exhibit similar property correlations, indicating the potential future development of effective bio-material frameworks. Nevertheless, given the diversity of bio-materials and their structural and functional variability, universal approaches may be unsuitable, emphasizing the need for tailored, material-specific evaluation criteria.
Σταύρος Καλαμπόκης (Thu,) studied this question.