Influence of Temperature on the Chemical and Rheological Aging Kinetics of Corn Starch-Modified Bitumen

The increasing demand for sustainable bitumen modifiers has stimulated interest in bio-based materials capable of improving binder performance while reducing environmental impact. This study investigates the influence of corn starch on the thermo-oxidative aging kinetics of paving-grade bitumen. Unmodified 50/70 bitumen and binders containing 4, 6 and 8 wt.% corn starch were subjected to laboratory aging at 100 °C and 140 °C for up to 120 h. The aging process was evaluated using dynamic viscosity measurements, FTIR spectroscopy and Multiple Stress Creep Recovery (MSCR) testing. The obtained results demonstrated that corn starch significantly affected both the rate and temperature dependence of aging. The effect of corn starch was strongly dependent on both the aging temperature and modifier dosage, indicating that starch does not uniformly inhibit all aging processes but rather modifies their kinetics in a process-specific manner. Increasing the aging temperature from 100 to 140 °C accelerated the viscosity growth by approximately 9–11 times, depending on the binder composition. The apparent rate constants for carbonyl formation ranged from 9 × 10−6 to 7 × 10−5 h−1 for the reference binder and from 1 × 10−5 to 5 × 10−5 h−1 for starch-modified binders. The calculated apparent activation energies varied between 1.31 and 67.6 kJ mol−1, confirming that starch altered the temperature sensitivity of oxidation and structural transformation reactions. Among the investigated formulation (4–8 wt.% corn starch), the binder containing 4 wt.% corn starch exhibited the most favorable balance between aging resistance and production cost. Overall, the results demonstrate that corn starch modifies rather than universally inhibits bitumen degradation, with the optimum performance depending on the investigated aging parameter, modifier dosage and aging temperature, with 4 wt.% providing the most favorable overall balance between chemical aging behavior, rheological performance and production cost.