Nobody likes potholes, nor do they like the environmental damage associated with the petroleum utilized in traditional asphalt bitumen. That's why scientists are now looking at replacing the latter with a binder derived from everyone's green friend, algae.
Essentially a form of heavy crude oil, bitumen is one component of conventional asphalt, along with aggregate materials such as rocks and sand. It serves as a flexible binder, holding the aggregate together while stretching and contracting back again under the weight of traffic passing overhead.
The substance does this job reasonably well, as long as the ambient temperature is reasonably warm. Once temps dip below the freezing mark, however, the bitumen becomes brittle and is subject to cracking. Cracked bitumen in turn leads to roadway fissures and potholes.
With that problem and bitumen's eco-unfriendly petroleum content in mind, a team led by Arizona State University's Assoc. Prof. Elham Fini recently set about developing an algae-based alternative. Previous research conducted by the scientists indicated that oil extracted from algae could be utilized to produce a bitumen-like material that remains flexible at cold temperatures.
In the new study, the team started by assessing oils from four different types of algae. The oil from one freshwater green microalga, Haematococcus pluvialis, showed the most resistance to permanent deformation under simulated traffic-induced stress, plus it was the most resistant to moisture-induced damage.
Additionally, in lab tests that simulated road traffic combined with freezing cycles, asphalt samples containing the H. pluvialis binder exhibited up to a 70% improvement in deformation recovery as compared to asphalt made with traditional bitumen.
Because the algae-based binder wouldn't necessarily be as cheap as bitumen, however, it would likely be used to substitute/offset some of the bitumen in asphalt mixes – not to completely replace it.
Based on computer models, it is estimated that for every 1% of the "biobinder" that would make up an asphalt mix, the net carbon emissions of that mix would be reduced by 4.5%. Therefore, if a mix were to contain about 22% of the biobinder, it would theoretically be carbon neutral.
"Algae-derived compounds can improve moisture resistance, flexibility and self-healing behavior in asphalt, potentially extending pavement life and reducing maintenance costs," says Fini. "In the long term, algae asphalt could help create more sustainable, resilient and environmentally responsive roadways."
A paper on the research, which also involved scientists from the Pacific Northwest National Laboratory, was recently published in the journal ACS Sustainable Chemistry & Engineering.
Source: American Chemical Society
