Snow and ice can damage paved surfaces, leading to frost heaves and potholes. These become potential hazards for drivers and pedestrians and are expensive to fix. Now, researchers propose in ACS Sustainable Chemistry & Engineering a figurative and literal green solution to improve the durability of roads and sidewalks: an algae-derived asphalt binder. For temperatures below freezing, results indicated that the algae binder reduced asphalt cracks when compared to a conventional, petroleum-based binder.
“Algae-derived compounds can improve moisture resistance, flexibility and self-healing behavior in asphalt, potentially extending pavement life and reducing maintenance costs,” says research team lead Elham Fini. “In the long term, algae asphalt could help create more sustainable, resilient and environmentally responsive roadways.”
Currently, asphalt is held together with bitumen: a thick, glue-like substance made from crude oil. Bitumen binds the sand and rocks that make up paved surfaces and allows the asphalt to expand and contract in hot and cold conditions, respectively. However, when the temperature rapidly drops below freezing, the binder becomes brittle and can crack, leading to roadway damage. To improve asphalt’s flexibility and durability at subzero temperatures, Fini and colleagues developed a sustainable and rubbery binder from algae oil.
Bitumen-like product
Fini’s previous studies showed that oil extracted from algae can make a bitumen-like product that is particularly durable at low temperatures. Continuing this work, Fini and colleagues used computer models to evaluate oils from four algae species for their abilities to produce bitumen-like products that mixed well with asphalt solids and retained functionality in freezing temps.
Of the four algal species, oil from the freshwater green microalga Haematococcus pluvialis appeared to impart the most resistance to permanent deformation under simulated traffic-induced stress, as well as enhanced resistance to moisture-induced damage.
In laboratory demonstrations that mimicked road traffic and freezing cycles, H. pluvialis algae-asphalt samples created by the researchers showed up to a 70% improvement in deformation recovery compared to pavement made with a crude oil-based binder.
In addition to strengthening roads, the team estimates that substituting 1% of the petroleum-based binder with algae-based binder would cut net carbon emissions from asphalt by 4.5%. At around 22% algae-based binder, asphalt could potentially become carbon neutral. The researchers say this approach paves the way toward high-performance, cost-effective and sustainable pavement infrastructure.
The authors acknowledge funding from the U.S. Department of Energy.
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