Recent advances and perspectives in circular bio-binder extender to substitute part of the fossil based binder in asphalt mixture

The interest in using bio materials in asphalt pavements is growing considerably for economic reasons and environmental benefits. In literature, many bio materials coming from different sources and obtained with different processes can be found and they can be served as additive, modifier or substitute of the fossil based binder. Most of the studies is focusing on binder's additives and modifiers with percentage less than 10%. Some patented bio-binders are able to substitute partially or completely the fossil based binder, but most of them are using expensive resin and synthetic polymers. It would be of great interest for both economic and environmental reasons to substitute higher amounts of petroleum binder with bio based binders and find alternatives to synthetic polymers, using waste ones to obtain a circular bio based binder. For this reasons, this work aimed to carry out a systemic and critical review on bio materials used as bio extenders, considering percentage of fossil binder replacement greater than 20%. The applications of polymers with bio based binders were researched and their advantages and concerns were highlighted. The current review confirmed the properties of the bio-extended binders vary substantially depending on the biomass source and on the process used to obtain them. Moreover, some critical factors and gap of knowledge that need to be studied deeply in future research efforts were highlighted.