Reduction of carbon footprint is one of the key focus areas in the asphalt industry. Over the last decade, a comprehensive research and development program has been executed by Nynas to explore renewable materials in bitumen and asphalt, including various plant-based oils and different types of lignin obtained for example from the wood and paper industry or derived from biomass conversion. In the program, the biogenic materials were systematically studied through extensive laboratory tests on bituminous binders and asphalts. This presentation particularly deals with lignin, in which various bitumen and polymer modified bitumen (PMB) binders were formulated by incorporating Kraft lignin and lignin from bio-refinery.  

Lignin materials were analyzed with respect to elemental compositions and solubility. The binders containing lignin were investigated mostly in accordance with the standards SS-EN 12591 (paving grade bitumen) and SS-EN 14023 (polymer modified bitumen). Asphalt properties were also evaluated basically according to the standardized CEN methods.  

As expected, lignin differs in chemistry, for example in terms of carbon, sulfur, and oxygen contents. Properties (e.g. rheology and compatibility) of the binders containing lignin also vary, depending on the base bitumen, and the content and the type of lignin. In general, the binders containing lignin show comparable or improved properties compared with normal bitumen. Besides increased consistency and decreased temperature susceptibility, anti-aging effect was observed for lignin. Lignin also provides a wider binder performance grade. What should be particularly mentioned is that, for one of the PMB binders containing lignin which was targeted to 40/100-75 grade, remarkably enhanced low temperature properties were observed. 

With regards to asphalt properties, no significant differences were found between the asphalts with lignin-extended and conventional binders in terms of stiffness, fatigue, and cracking resistance. But asphalts with the binders containing lignin displayed lower aging susceptibility, which agrees with the observation made on the binders.

 This study shows that lignin is a potential renewable component both for bitumen and polymer modified bitumen. For further work, studies of long-term field performance (especially in PMB) and recyclability of the materials are recommended.