Preliminary Rheological Characterization of Spirulina-Derived Bio-Based Binders from Hydrothermal Liquefaction

Petroleum-based asphalt binders are still essential for pavement construction, but contribute significantly to greenhouse gas emissions and dependence on finite fossil resources. Renewable bio-binders are increasingly studied as sustainable alternatives, with microalgae showing particular promise due to their high productivity and suitability for thermochemical conversion. This work investigates hydrothermal liquefaction (HTL) of Spirulina as a route to produce bio-binders and evaluates their rheological performance relative to conventional binders. HTL was conducted under controlled conditions in a batch autoclave, yielding an average of 30% hydrophobic bio-crude. Rheological characterization was carried out using a Dynamic Shear Rheometer (DSR) through three key protocols: rotational plate viscosity (RPV) to estimate mixing and compaction temperatures, temperature sweeps to assess thermo-mechanical stability, and frequency sweeps to develop master curves of complex modulus and phase angle. Results show that Spirulina-derived binders exhibit high stiffness and rutting resistance, exceeding those of 50/70 bitumen and approaching the performance of polymer-modified binders. However, elevated viscosity and workability challenges indicate suitability as a high-stiffness bio-based component for blending rather than direct substitution.