Review on the properties and mechanisms of asphalt modified with bio-oil and biochar

Bio-asphalt has a great application prospect in the replacement of petroleum-based asphalt to pave and maintain asphalt pavement. However, the problems of flow-induced crystallization and phase separation caused by flow-induced crystallization had severely restricted its application. This paper describes the progress of research on preparation, property evaluation and phase separation mechanism of bio-asphalt. The advantages and disadvantages of preparation methods of bio-asphalt are states. The fundamental physical and rheological properties of bio-asphalt are investigated, especially for flow-induced crystallization. There exists obvious flow-induced crystallization because bio-asphalt is rich in waxes that crystallize easily. Owing to the existence of excess biochar, bio-asphalt appears phase separation. A brief review of the effect of bio-oil and biochar on asphalt volatile organic compounds (VOCs) is presented. Research find that bio-oil/biochar are not only replenish the light components of asphalt, but also improve the flow-induced crystallization and phase separation of bio-asphalt. There exists synergistic effect of biochar and bio-oil in asphalt modification. Moreover, biochar can improve the durability of bio-oil modified asphalt, but excessive addition of biochar to bio-oil modified asphalt can cause phase separation. Adding an appropriate amount of bio-oil and biochar to asphalt can improve its high-temperature resistance, low-temperature crack resistance, and system compatibility. • Crystalline wax in bio-oil is the key of flow-induced crystallization of bio-asphalt. • The surface organic functional groups of biochar are the main inducement of VOCs adsorption. • Both bio-oil and biochar can lead to the change of four components of asphalt.