Next-generation bitumen: a review on challenges and recent developments in bio-bitumen preparation and usage

Bitumen is a dark brown to black colour glue material majorly used in the construction of bound layers of pavements. It is treated as a hazardous material because of its higher PAH (polycyclic aromatic hydrocarbons) content and presence of hydrogen sulphide. These characteristics of conventional bitumen affect humans as well as the environment, and conventional bitumen is a non-renewable resource that is getting depleted at a very rapid rate. This demands the need for an alternative binder that can mitigate ill effects created by conventional bitumen and address the future requirements of bitumen such as sustainability and circular economy for pavement construction. This review analysis focuses on biomass characterization in terms of an industrial, elemental, structural component and fraction content analysis. Along with these biomass sources and their upgrade techniques, conversion methods or preparation processes used to produce bio-oil and bio-bitumen from different biomass forms, practical application and life cycle inventory were reviewed, and their performance on physical, mechanical, rheological and chemical properties was studied. In addition to this, the effect of biochar as bitumen additive or filler on the performance characteristics of bitumen was studied. It is concluded that with the type and dosage of bio-oil used, the bio-binder production varies, and this bio-binder is only effective at moderate and low temperatures. Bio-oils do not evaporate or degrade with time; instead, they become a permanent part of the binder, preventing phase separation. Optimal usage of biochar improves the properties like viscosity, failure temperature, ageing resistance and deformation.