What if one of the most environmentally unfriendly materials in modern cities’ urban planning could be rebuilt using algal bio-binders? The importance of this innovation comes from the role that roads play beyond transportation. The asphalt pavement itself emits a mixture of volatile organic compounds while reacting to various factors. First, there is a long history of occupational safety reviews reporting that known carcinogens were detected in the emissions from asphalt. However, more recently, concerns have grown about general public exposure to such toxins, given that emissions continue even after installation and may be exacerbated by heat and sunshine.
The crucial component in the bio-binders approach is bitumen a petroleum substance used to bind the aggregate in asphalt. Scientists working with Arizona State University have investigated the possibility of introducing biomass-based binders as an alternative for some share of bitumen usage without altering the manufacturing process of asphalt. In their research, algae are used as a biomass source with subsequent conversion into a viscous bio-binder mixed with regular asphalt. For wet biomasses (as opposed to wood chips), hydrothermal liquefaction is often used as a method to obtain bio-oil.
Without considering the human element, you cannot claim to design something sustainable. This human-centric perspective makes the current research quite different from many others dealing with carbon footprint of pavement. According to the lab studies performed by the research group led by Elham Fini, while introducing algae binder into asphalt does not stop the emission process, it does reduce toxicity of released volatile organic compounds. Specifically, the experiments revealed that the mixture emitted 100 times less harmful substances compared to regular asphalt. This finding also agrees with a number of scientific reports on how asphalt emissions are connected to respiratory, neuro-, cardio- and carcinogenic effects on humans, including children being particularly sensitive to air pollution.
Materials science aspect is also interesting. Bio-binders have drawn much attention due to improved performance characteristics at low temperatures, and now a growing number of papers show increased elasticity compared to traditional asphalt. The current research moves beyond this trend. In one study, the introduction of small amounts of algae resulted in improved thermal resistance to cracking of asphalt pavements below zero degrees. Further investigation of one type of algae-derived bio-oil showed that elastic recovery rate in experiments with increasing loads increased from 0.1% to 71%.
This does not mean the research has completed. Bio-asphalt still faces some well-known challenges of bio-materials technology. For example, consistency of feedstock, aging properties in the long run, stability at storage and, probably, the most challenging one performance at high temperatures. Most publications on this subject list long-term durability and lack of testing procedures as major unsolved problems despite continuous interest in the area and pilot implementations.
However, the idea has gone beyond theorizing. The researchers chose Phoenix as the location of their experiments because of hot climate accelerating relevant aging processes. On the global level, algae and other biomass sources become increasingly common as ingredients of paving binders containing less fossil components. The most important transition may be practical: if roads can release fewer toxic substances, resist cracking better in winter and be durable for extended time periods, asphalt ceases to be a passive material and turns into environmental surface modification technology.