Researchers in France have proven for the first time the viability of bioasphalt, demonstrating its close similarity to the “real” asphalt used to pave roads. (The press release is a pdf file) The micro algae offer a highly promising alternative to petroleum products without competing for resources used in the food industry.

The group’s research paper has been published in the April issue of ACS Sustainable Chemistry & Engineering.

The group used a hydrothermal liquefaction process, i.e. pressurized water (in a subcritical state), to transform this micro algae waste into a black, viscous, hydrophobic substance (bioasphalt) that closely resembles petroleum-derived asphalt (see illustration below). The process currently achieves a conversion efficiency of 55%.

Bioasphalt From Algae Production Steps.  Click image for the largest view.  Image Credit: CNRS.Fr

Bioasphalt From Algae Production Steps. Click image for the largest view. Image Credit: CNRS, France.

Even though the chemical composition of the bioasphalt is completely different from its petroleum-derived counterpart, they have similarities, including their black color and rheological properties. As a liquid at temperatures exceeding 100°C, the bioasphalt can be used to coat mineral aggregates. The bioasphalt is viscoelastic at -20°C to 60°C, thus ensuring the cohesion of the granular structure while supporting mechanical loads and relaxing stress.

Trials are now underway to analyze the material’s behavior over time, as well as cost-effectiveness studies to evaluate its potential for large-scale production.

The bioasphalt innovation offers a new possible option for the asphalt road building industry, which is entirely dependent on petroleum today. The types of bioasphalt 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. Micro algae, whose cultivation does not require the use of arable land, thus offers an attractive solution.

Micro algae have long been known for their use in applications like cosmetic dyes and food supplements. In more recent years, the idea has emerged of refining them, for example to produce biofuels. Today, micro algae are recognized as a promising alternative to petroleum. The development of efficient, cost-effective processes could make a whole range of useful micro algae derivatives available.

The development comes from a part of the “Algoroute” program, funded by France’s Pays de la Loire region. Researchers at laboratories based in Nantes and Orléans produced the bioasphalt from micro algae residues resulting, for example, from the extraction of hydro soluble proteins for the cosmetics industry.

It seems that there could be many algae resources whose remains might well be precursors to bio asphalt.

Asphalt has been a by product of petroleum product refining for decades. Originally and for some time asphalt was an abundant product used for roads, parking lots and roofs. Modern refining and lighter more profitable products drove refining technology to leave almost no asphalt from crude oil refining. Today asphalt is much more expensive and must be competitive to other products. Asphalt really isn’t a leftover product anymore – its a production choice.

That makes the French work welcome indeed. Congratulations are in order for developing a useful process.


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