If you want to prevent potholes from appearing on your asphalt pavement, you have to patch them while they are still tiny cracks. Using spores extracted from moss, a new type of self-healing asphalt could one day do just that. Scientists at Swansea University in the UK and King's College London are currently working with colleagues at the University of Bio-Bío in Chile to develop the experimental material.
The researchers first used machine learning algorithms to simulate the way asphalt, the black sticky substance in asphalt, oxidizes and hardens in response to environmental factors. Once asphalt hardens to a certain point, it will crack when subjected to heavy loads rather than stretching.
In order to heal the initial microcracks before they form larger cracks (and eventually potholes), there needs to be a way to rejuvenate the oxidized asphalt. That's what spores are for.
The scientists first obtained spores from the Northeastern stone pine (Lycopodium clavatum). Using various chemical treatments, the researchers were able to remove the reproductive cells from these spores, making them hollow.
Next, the scientists added sunflower oil to the spores using vacuum and centrifugal encapsulation techniques. The loaded spores are then added to the bitumen, which in turn is used to produce small pieces of bitumen.
When a sample of asphalt is subjected to conditions that cause microcracks in the asphalt, the spores in the cracks rupture and release sunflower oil. Sunflower oil rejuvenates oxidized asphalt, causing cracks to disappear in less than an hour.
Dr Francisco Martínez, of King's College London, said: "In our research we wanted to mimic the healing properties observed in nature. For example, when trees or animals are cut, their wounds heal naturally over time using their own biology. Creating asphalt that heals itself would improve the durability of roads and reduce the need for people to fill potholes."
A paper on the research was recently published in the journal ACS Applied Materials & Interfaces.