Sunflower oil microcapsules and asphalt mix

Self-healing asphalt road method inspired by oily Masterchef technique

Image credit: University of Nottingham

A team of researchers based at the University of Nottingham have developed a novel method to help roads self-heal from cracks, using beads of sunflower oil.

Dr Alvaro Garcia, a lecturer in the Nottingham Transportation Engineering Centre, hit upon inspiration for the problem while watching an episode of MasterChef, in which a hopeful contestant performed spherification.

This is a technique used by some chefs to form small edible spheres of food by controlling the jellification of a liquid when submerging or dropping it in a chemical bath. This can be used, for instance, to produce caviar-like beads of sauce which burst when pierced. This culinary technique, Dr Garcia said, could be applied in other sectors, such as road maintenance.

Dr Garcia and his team created spherified microcapsules of sunflower oil and added them to asphalt mixes, commonly used to surface roads.

As a road wears with use and cracks begin to form, these capsules burst open. This releases a small amount of oil into the road, softening the brittle, broken asphalt around it by reducing the viscosity of the binder in the mix.

As the oil seeps into the asphalt mix, the road is ‘stuck’ back together, preventing these cracks from developing further and becoming a inconvenience or danger to passing traffic.

“Our preliminary results showed that the capsules can resist the mixing and compaction processes without significantly reducing the physical and mechanical properties of asphalt, and they also increase its durability,” said Dr Garcia.

“More importantly, we found that the cracked asphalt samples were restored to their full strength, two days after the sunflower oil was released.”

According to the researchers, the microcapsules can be placed in precise problem areas, preventing them having to be added to the bulk of the mix.

According to Dr Garcia, self-healing roads currently in use in the Netherlands and Switzerland fill their cracks by heating metal fibres worked into the road. While this approach is effective, it is also expensive and requires frustrating road closures. The Nottingham team’s automated approach to road maintenance, which they have named “Caphael”, could increase the lifespan of a road by one-third from 12 to 16 years at little extra cost.

“We needed a different way to create self-healing roads without the use of an external aid, so I decided to design capsules containing oil that can break by themselves when the mechanical loading on a carriageway caused it to crack.”

Dr Garcia and his team are currently coming to the end of initial testing of the microcapsules in the lab. Next, they intend to develop microcapsules of different sizes, shapes and strengths and investigate how they perform for a range of road mixes and traffic conditions. After their pilot trials, Highways England will test bed Caphael on some roads and monitor the self-healing technology for its effectiveness in real world conditions.

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