Rheological behavior and chemical characterization of bio-bitumen modified by castor oil and rice husk ash: Sustainable alternatives to conventional bitumen

Conventional bitumen is a byproduct of petroleum refining often used in flexible pavement applications. Due to the rapid depletion of bitumen, its non-renewable nature, and its environmental and economic implications, researchers are seeking an alternative material that is naturally occurring, renewable, poses minimal risks to environmental and human health, and is cost-effective. This study explores castor oil (CO) and rice husk ash (RHA) modified bio-bitumen (CORMBB) as a sustainable alternative binder for flexible pavements. CORMBB was synthesized by partially replacing the base binder with 9 % CO, 6 % RHA, and 85% base binder (BB) and characterized through physical, chemical, structural, and rheological analyses. Physical test findings demonstrated increased penetration and decreased softening point of CORMBB, indicating greater flexibility and reduced thermal rigidity. The storage stability analysis demonstrated that CORMBB achieved difference of softening point (ΔT) values well below the limit, confirming adequate compatibility and homogeneity. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) investigations validated the successful chemical interaction between CO, RHA, and BB. They also disclosed the integration of silica from rice husk ash, enhancing structural rigidity and moisture resistance. Rheological evaluations conducted through, temperature sweep, amplitude sweep, flow sweep, and frequency sweep tests utilizing a dynamic shear rheometer (DSR) demonstrated reduced complex modulus and phase angle values for CORMBB, alongside increased viscosity at low shear rates. This indicates improved elasticity, temperature sensitivity, enhanced rutting resistance, and sustained compaction ease at elevated shear rates. These findings highlight the potential of CORMBB as a renewable and eco-friendly substitute for conventional binders in pavement applications.