Self-healing asphalt is created by adding steel wool fibers to bitumen when asphalt is created. This allows the gluelike material to rebind the asphalt.
Self-healing asphalt could be the solution to America's infrastructure problem. Scientists out of Delft University of Technology in the Netherlands have been studying and experimenting with a way to create a more durable asphalt that could last twice as long as asphalt on the roads today. Besides healing America's infrastructure, this material could prove a reliable material for racetracks, airport runways and a host of other infrastructure-based applications.
Self-healing asphalt may not be something you deal with directly for your business as it is slowly implemented into the world's infrastructure system. But it is useful to find out how self-healing materials could improve road safety and lifespan while lowering costs for governments and private construction companies.
How it works
Asphalt is a mixture of gravel and sand held together by bitumen, a thick, viscous mixture that acts as a glue. As roads age, the bitumen wears down and pieces of asphalt erode, causing small cracks that soon balloon into big potholes. This process of erosion, called raveling, is caused by oxidation, UV rays, freeze-thaw cycles and other factors.
To combat raveling, Erik Schlangen, a professor at Delft, created a way to heal existing asphalt by heating the material using an induction machine and rebinding the bitumen to the gravel. He accomplished this by mixing tiny bits of steel wool into bitumen. This makes the bitumen conductive, or able to receive and transmit electrical energy. Once the asphalt is poured and set, the bitumen can be heated with an induction machine so it rebinds to the stones and gravel in the asphalt. The induction process creates a magnetic field so only the bitumen is heated.
"The benefit of this process is that you don't heat up the aggregates (stones) themselves," said Martin Megalla, managing partner of Epion Asphalt, a company founded by Schlangen that aims to implement his self-healing material. "You don't want to lose energy on the aggregates because you don't want to heat the stones, but the binder. So, it's more efficient."
This process – while adding efficiency by targeting the binder directly instead of wasting energy on heating the entire surface – would significantly extend the lifespan of most roads.
"By using the technology, it could approximately double the service life of the pavement," Megalla said. For this to occur, he said, the road has been healed with the induction machine approximately once every four years.
How long will the new roads last?
Schlangen and Megalla have been testing the new technology on a 400-meter stretch of highway in the Netherlands. After paving the stretch with the self-healing asphalt, teams conducted studies on induction as well as how long the asphalt could last. The average lifespan of a normal asphalt road is seven to 10 years, and Schlangen and his team installed the new asphalt in 2010. As the road approaches the end of normal asphalt's lifecycle, the material will be put to the test.
Megalla said that, in addition to testing and maintaining sections of self-healing asphalt around the Netherlands, Schlangen and Epion are developing a bigger induction machine to speed up the induction process. Right now, the team's induction machine doesn't span the width of an entire lane, so multiple passes are required to heat up and rebind the road. The team is aiming to build a machine that spans the width of a lane and will be able to heat the road while traveling at approximately 3 kilometers per hour (roughly 1.5 mph). Traditional asphalt pavers move at roughly 0.3 kilometers per hour, according to Megalla.
Impact of self-healing asphalt
Studies have said that self-healing asphalt would save the Dutch government roughly €90 million (more than $104 million) and create safer roads for travelers by eliminating potholes. If this material can be implemented on a large scale, the savings could be huge – not only for government spending on infrastructure but also for drivers.
Pothole.info, a website committed to informing the public about the dangers of bad road conditions, features several studies on its website regarding the impact of poor road conditions on economics and driver safety. Bad roads that lead to crashes cost the U.S. economy roughly $217 billion in 2006, according to a study commissioned by the Transportation Construction Coalition. Businesses paid an estimated $22 billion of this cost due to crashes involving their employees in which roadway conditions were a factor.
The study also found that road condition was the most lethal contributing factor to traffic fatalities, greater than speeding or alcohol. These statistics show that self-healing asphalt, while it would also double the lifespan of a road, would keep highways intact over time and save lives in the process.
Schlangen and Epion have been testing the new material in 12 locations around the Netherlands and are talking with the Dutch and Japanese governments about expanding the material to other areas, according to Megalla. Right now, the company isn't in talks with the United States, so it couldn't provide any timeline on when this technology could be implemented here. In addition to the induction machine's size, Megalla said a reason it's been hard to implement this technology is expected skepticism.
"With anything that is new, people are always reluctant – they want to see a lot of tests – but the good thing about this technology is that you can see it really fast," he said. "People can see with an infrared camera that there is something happening, and you can see that the binder is melting and attaching against the aggregate."
Epion's self-healing asphalt costs more than normal asphalt, but Megalla said that the cost will even out because the road will last longer. "Because you implement steel fibers in it, so your initial investment will be higher, but you will make it up in the long run because you won't have to pave the road for another seven years, of course," he said.
Self-healing asphalt could one day provide a great option for governments to create roads that last longer and save money in the process. This is something for construction companies to keep an eye on. As of right now, this technology, although proven reliable, is still being tested and implemented on a small scale. As Epion grows and larger induction machines are built, self-healing asphalt could make roads safer.