Chemical and Rheological Properties of Bitumen Partially Substituted with Rice-Straw-Based Lignin from Bio-Ethanol Industry Residue

The objective of this study is to evaluate the changes in the chemical and rheological properties of bitumen when partially substituted, up to 15%, with rice-straw-based lignin materials, namely isolated lignin (IL) and fermentation residue lignin (FRL), obtained from second-generation bio-ethanol industry residues. Attenuated total reflectance-Fourier transform infrared spectroscopy was used to evaluate the alterations in chemical properties. The rheological properties that were assessed include Superpave upper performance grade (PG), rutting resistance using the multiple stress creep recovery test, and fatigue resistance using the linear amplitude sweep test. The results indicated that the addition of IL and FRL materials to the base bitumen is a physical process. Furthermore, IL and FRL substituted bitumen blends exhibited distinct trends for carbonyl (C=O) and sulfoxide (S=O) functional groups with ageing, depending on the chemical structure of the additive. Specifically, the IL materials showed a reduction in the rate of increase of ageing products and a decrease in the combined ageing index, up to 10% IL dosage, suggesting some antioxidant effect within the group. The addition of IL up to 15% dosage and FRL up to 10% dosage also led to an increase in the base binder high-temperature grade from PG70-XX to PG76-XX. Moreover, both IL and FRL materials enhanced rutting resistance and reduced fatigue resistance with an increase in dosage. It is worth noting that bitumen blends with different additives showed varying trends between chemical and rheological properties.