Influence of hemp-based biochar from pyrolysis on bitumen properties and bituminous mixture performance

This study investigates the effects of biochar additives obtained from pyrolysis of industrial hemp stalks by rapid and slow cooling methods on bitumen and bituminous mixture’s performance. Biochar was incorporated into the bitumen at contents of 5%, 10%, and 15% by weight. A series of binder-level tests, including penetration, softening point, rotational viscosity, and surface free energy measurements, were performed to evaluate the conventional and physicochemical properties of the modified bitumen. The mixture-level tests such as indirect tensile strength (ITS), Hamburg rutting test, and aging test were conducted to assess moisture susceptibility (TSR), rutting, and aging performance of the asphalt mixtures. The test results quantitatively confirmed the effectiveness of biochar incorporation in improving the performance of asphalt mixtures. Biochar-modified mixtures showed improvements of up to 17.6% under short-term aging and 11.2% under long-term aging conditions, while rutting resistance increased by up to 68.6%. Furthermore, the ITS values increased by approximately 22%, indicating enhanced mechanical strength. Although a slight reduction in moisture damage resistance was observed with biochar addition, all mixtures remained above the accepted 80% threshold. Overall, within the scope of the laboratory tests conducted in this study, these findings indicate that hemp-derived biochar can contribute to improving the aging resistance, rutting resistance, and tensile strength characteristics of asphalt mixtures.