Construction Corner: ‘Green’ liquid asphalt cement?

Researchers looking for alternatives to products made from fossil fuels have been interested in algae for some time. Some of the tiny plants contain a lot of natural oil. That’s why science has made significant progress in using them to manufacture "biodiesel" as a sustainable alternative to conventional diesel.

A group of researchers in France have come up with a way to use algae in the manufacture of "green" asphalt, since it’s made without using petroleum.

Microalgae is useful for making more than biodiesel. French researchers have recently demonstrated the viability of what they’re calling bioasphalt.  They’ve published the results of their work in the April issue of the journal ACS Sustainable Chemistry & Engineering.

Microalgae are single-celled plants that range in size from a few micrometres to a few hundreds micrometres, depending on their species. They have no roots, stems or leaves, but they are capable of performing photosynthesis and are thus important for life on earth.

Scientists tell us there are somewhere between 200,000 and 800,000 species, only about 35,000 of which have been scientifically described. Researchers in France have used them to make compounds of use to the cosmetics industry, and it is the residue from that process that they use to create a black, viscous material that closely resembles the asphalt derived from oil petroleum.

The chemical composition of bioasphalt is completely different from its oil-based counterpart. But it can be used to coat mineral aggregates, instead of coating them with what road builders call liquid asphalt cement, or bitumen.

Researchers have already found that aggregates treated with bioasphalt are capable of supporting mechanical loads. Now they’re testing its behaviour over time, as well as studying costs in an attempt to evaluate its potential for large-scale production. But algae-based asphalts are not the only bioasphalts being studied.

In the Netherlands, research is being done in the use of lignin, a natural adhesive material, in another form of synthetic asphalt. Lignin gives structure to all kinds of plants and trees. It is, for example, an important part of straw.

People have long guessed that both algae and straw could be important as we make the transformation to a low-carbon economy, and several governments and companies have shown interest in these two scientific projects.

Dutch researchers are busy testing their lignin-based bioasphalt, and expect to be able to improve functional properties of their asphalt, including its rolling resistance, and making road running surfaces quieter.

As part of that, they hope to have a section of road and/or a parking area paved with their lignin bioasphalt this year, so they can enlarge their testing program.

Liquid AC has been an excellent product, used by road builders and in the production of roofing felt, and for sealing flat or low-slope roofs. But it is obtained from the distillation of crude oil, a process that releases a lot of carbon dioxide, a greenhouse gas. If we’re to make the transition to a low-carbon economy, we’ll need to have access to not only biofuels, but bioasphalts as well. The work of these teams in France and Holland will be closely watched.

Korky Koroluk is a regular freelance contributor to the Journal of Commerce. Send comments or questions to editor@journalofcommerce.com.