Climate change concerns and continuously increasing costs of bituminous pavement materials are an ongoing challenge for the pavement industry and road owners. Reduced demand for paper is an ongoing challenge for the forest industry. To help overcome these challenges, FPInnovations, with partners and collaborators involved with in the production and use of asphaltic concrete pavements, have initiated research into a lignin-modified bitumen for Canadian pavements. This greener modified bitumen, first developed in 1980 by the Federal Highway Administration (FHWA), shows great promise but mainly in European trials with climatic conditions and geological contexts that are different from North America. Although the Canadian study aims at analyzing the technical, economic, and environmental feasibility of lignin-modified bitumen, this paper will emphasize research on the thermo-mechanical properties of lignin-modified bitumen to optimize the bitumen mixture for the Canadian context.
Lab testing, conducted at École de Technologie Supérieure (ETS) laboratories, consisted, first, in evaluating the optimum lignin-bitumen ratio, mixing time and temperature, and mixing apparatus. First phases of testing were conducted on one source of lignin and a PG58-28 bitumen using a conventional and a high shear mixer. Up to 30% of the bitumen was replaced by lignin. To evaluate short-term and long-term impacts of the mixtures, testing included storage stability, viscosity, measurement of rheological properties at high and low temperatures (dynamic shear, creep stiffness, creep recovery), aging, specific gravity, etc. Preliminary results show very good homogeneity of the lignin-bitumen mix using a conventional mixer at 150°C mixing temperature and promising thermal and mechanical properties of the optimal mix. Upon conclusive results on the first phases of this work, a hot mix asphalt will be formulated using the optimum lignin-modified bitumen and tested. Testing on HMA will be focused on rutting, thermal cracking, complex modulus, compaction, resistance to moisture induced damage, etc. The new product has the potential to reduce the environmental impact of asphaltic concrete while offering enhanced performance and reduced cost.