Process for the production of bioasphalt from microalgae. Credit: les films du cercle rouge

Process for the production of bioasphalt from microalgae. Credit: les films du cercle rouge

Aconsortium of French researchers has recently proved the viability of bio-asphalt, demonstrating its close similarity to the “real” asphalt used to pave roads. The findings are published in the April issue of the ACS Journal for Sustainable Chemistry and Engineering.

The project, funded by the Region Pays de la Loire, brought together a multidisciplinary team from the Universities of Nantes and Orleans alongside the French Institute for Science and Technology, Institute for Transport, Development & Networks, the National Centre for Scientific Research and the French company AlgoSource Technologies.

As part of the “Algoroute” program, researchers at laboratories based in Nantes and Orléans produced bio-asphalt from microalgae residues resulting, for example, from the extraction of hydrosoluble proteins for the cosmetics industry. They used a hydrothermal liquefaction process, i.e. pressurized water (in a subcritical state), to transform this microalgae waste into a black, viscous, hydrophobic substance (bio-asphalt) that closely resembles petroleum-derived asphalt. The process currently achieves a conversion efficiency of 55%.

Even though the chemical composition of bio-asphalt is completely different from its petroleum-derived counterpart, they have similarities, including their black color and rheological properties. A liquid at temperatures exceeding 100°C, bio-asphalt can be used to coat mineral aggregates. Viscoelastic at -20°C to 60°C, it ensures the cohesion of the granular structure while supporting mechanical loads and relaxing stress. Trials are underway to analyze the material’s behavior over time, as well as cost-effectiveness studies to evaluate its potential for large-scale production.

This innovation offers a new possible option for the road building industry, which is entirely dependent on petroleum today. The types of bio-asphalt developed so far relied on oils of agricultural origin (which could be needed for human nutrition) or from the paper industry, mixed with resins to improve their viscoelastic properties. Microalgae, whose cultivation does not require the use of arable land, thus offer an attractive solution.