Use of bio-based products towards more sustainable road paving binders: A state-of-the-art review

Many industrial sectors exploit fossil sources to develop useful and necessary materials for our needs, such as bituminous paving materials. Bitumen, a key component of asphalt mixtures, is derived from oil refining and its properties are influenced by the crude oil source and refining process, resulting in a significant carbon footprint. With growing awareness of resource depletion and environmental concerns, pavement researchers are exploring sustainable alternatives to reduce dependence on fossil sources. This includes a rising trend in using renewable materials like biomasses to produce bio-based binders as substitutes for bitumen, aiming for a more sustainable approach. Biomasses, including vegetal and animal wastes, and waste cooking oils, as substitutes for crude oil in the production of bio-binders. Through thermochemical conversion (TCC), such as pyrolysis, biomasses can be converted into bio-char and bio-oils, which can replace fossil-based components in binders. Researchers have utilized these bio-products to reduce the dependency on fossil fuels in binders. However, there are no set minimum requirements for bio-components in bio-based binders. As the percentage of replaced bitumen increases, various types of binders are produced, including modified bitumen, extended bitumen, and alternative binders, where the fossil replacement is gradual. Overall rheological tests on bio-binders, reveal that those containing bio-char exhibit increased viscosity, stiffness, rutting resistance, and sometimes antioxidant properties. Conversely, bio-binders with bio-oils as bitumen substitutes show poorer performance at high temperatures but improved behavior at low temperatures. These results suggest that bio-binders could provide versatile solutions for various climatic and loading conditions in road construction. However, the development of pavement mixtures based on bio-binders has not been studied in depth and requires further attention to unlock its full potential. As sustainability considerations, including life cycle assessments (LCA) and life cycle cost analyses (LCC), are crucial aspects for future studies. It is essential not only to collect data on the performance characteristics of bio-binders but also to understand their environmental impact and recyclability. In-depth evaluations using methods such as LCA and LCC will provide valuable insights into the overall sustainability and long-term viability of these products.