Zhou, et al (2024) Review on the properties and mechanisms of asphalt modified with bio-oil and biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More. Journal of Road Engineering. https://doi.org/10.1016/j.jreng.2024.06.001

The growing demand for sustainable materials has led researchers to explore bio-oil and biochar as potential substitutes or additives for petroleum-based asphalt in road construction. Bio-oil, derived from biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More through pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More or hydrothermal liquefaction, is renewable and eco-friendly. Biochar, a carbon-rich byproduct of the same processes, offers additional benefits, including the reduction of volatile organic compound (VOC) emissions. Together, these materials could contribute to greener infrastructure.

When mixed with asphalt, bio-oil enhances flexibility and reduces the softening point, making it suitable for high-grade applications. Its optimal content ranges from 15–20%. On the other hand, biochar’s porous nature and high adsorption capacity improve high-temperature performance and reduce VOC emissions by trapping harmful compounds. However, excessive biochar can lead to phase separation and compromise material integrity.

The challenge lies in balancing the proportions to optimize properties like durability, resistance to aging, and temperature stability. Studies also reveal the phenomenon of flow-induced crystallization, where crystalline wax in bio-oil can lead to structural changes in the composite asphalt. While moderate crystallization improves rheology, excessive crystallization causes brittleness.

Combining bio-oil and biochar offers synergistic benefits, such as improved road performance and reduced environmental impact. However, further research is needed to refine these materials’ interactions and establish cost-effective production methods. With the right advancements, bio-oil and biochar could significantly enhance sustainability in road construction.