Renewable materials in bituminous binders and mixtures: speculative pretext or reliable opportunity?

Bitumen is the most employed binder in road pavements and derives from petroleum, which is a non-renewable resource that is progressively depleting. Therefore, the current challenge for road industry is to use renewable materials (i.e. bio-materials not subjected to depletion) in partial replacement of bitumen, thus reducing carbon footprint and making the sector less dependent on petroleum-based products. Specifically, the trend is to utilize bio-materials that are obtained as by-products from industrial processes or as wastes from the everyday life, avoiding their disposal in landfills, in accordance with the principles of sustainability and circular economy. Thus, research in this field is very promising and attractive nowadays. However, in order to understand whether the application of renewable materials represents a reliable and viable solution or just a speculative pretext for research, a rigorous scientific approach must be adopted. For this purpose, the paper provides an overview of the use of renewable materials in bituminous binders and mixtures, focusing on the necessary requirements that they should meet, their effects on performance, and health, safety and environment aspects. Based on the analysis of available literature, a comprehensive experimental approach for evaluating bio-materials in bituminous applications is also proposed.