Mutual compatibility aspects and rheological assessment of (modified) lignin–bitumen blends as potential binders for asphalt

Recent innovations in pavement engineering are driven by sustainability and circularity. Bitumen is a fossil fuel-based binder, traditionally used for asphalt pavement. In recent years, variation in bitumen quality and consistency have raised concerns in performance and workability. To achieve the sustainability target and ensure the quality, the market is exploring renewable alternatives to bitumen: such as lignin. A partial (i.e., 25 wt.%) replacement of bitumen with native and chemically modified lignin is evaluated in this study where the influence of chemical modification, compatibility and rheological properties of the lignin-bitumen blends are assessed. By introducing lignin into bitumen, the binder becomes stiffer depending on the extent and type of modification. An exception is observed in lignin modified with ethyl hexyl glycidyl ether resulting in a comparable viscoelastic property to the original bitumen. The blends show an improvement in the high-temperature properties and introduce more flexibility to the low-temperature properties. The influence of molecular fractions, i.e., SARA and acid value of bitumen are evaluated in relation to compatibility.