Innovative materials come to aid to tackle one of the drivers' worst nightmare.
Potholes are not just annoying things to drive along, but they make our roads slower, costly and unsafe. They are responsible for 1 out of 10 mechanical failure in the UK, mainly concerning cars axles and suspensions, while public authorities pay about 30 million pounds per year for compensations due to poor roads condition. Furthermore, private and public costs are expected to rise, as road maintenance in England and Wales is underfunded by 1 billion every year. Potholes are also responsible for traffic congestion, and that generates sensible spots with high emission of greenhouse gases and particulates.
The reasons for the formation of potholes are many, but mainly due to traffic and water. The passage of cars can cause ravelling of aggregates that lead to an uneven surface: the following passages further erode the edges of the area, and the accumulation of water worsens the situation. Sometimes potholes follow problems in the road foundation, due to water infiltration or wrong execution, and cause the typical 'alligator' crackings that foreshadow the issue. Frost is also responsible for the formation of potholes, as it changes the elasticity of bitumen to a more fragile structure that causes cracks once the pavement is loaded.
Today exist many ways to repair potholes, with different degree of effectiveness, time and costs requirements. The simpler ways, 'throw and roll' or semi-permanent repairs, are the most widely used. In the US, the so-called 'pothole killer', uses a mechanical arm to spray compressed air, binding agent and asphalt mix to deal with the problem. In some countries infrared technology is used to heat the surface and recycle the existing macadam, to re-create the surface with a minimum of new material. Special coating sealers could be applied to reduce micro-cracks and improve durability.
The main problem with the traditional approaches is that potholes might stay in the roads for weeks, or even months, before treatment. The reason is due to costs and budget limitations, so the maintenance is usually provided under set periods. To overcome the issue, at least for in the short run, some students have invented the 'silly putty' patch: basically a bag filled with a non-newtonian fluid. That type of fluid has a liquid form when a slow force is applied, while it becomes rock solid when a force is applied faster. The material is then perfect to be modelled to fit the shape of the pothole and support the passage of vehicles.
But the real deal is to avoid the formation of potholes in the first place, and here is where self-healing asphalts come into play. In this case, asphalt is enhanced with the addition of materials to gain new thermal, electrical and mechanical properties. Those can be nano-materials (nano-tubes, nano-fibres), ionomers or micro-capsules. Then the healing of microcracks is achieved with special equipment (microwaves and induction heating processes) or full-auto: capsules in contact with water release bacterias that produce limestone and seal.
In the Netherlands, a test track went under trials: with the addition of special fillers and Steelwool fibres, connected in closed-loop circuits, the asphalt was made magnetic and electrically conductive. Then, a piece of equipment induced loops of electric current that generated heat and caused the successfully sealing of microcracks. So, is this the future? The first tests are incredibly encouraging: the process is cheaper than traditional methods, and carbon footprint is also reduced as there is no need for 'heavy' maintenance.
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