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Interview | Self-healing roads pioneer


Roads that heal themselves are closer to reality than you might think. Meet Erik Schlangen, civil engineer and experimental micromechanics pioneer.

Erik Schlangen’s passion is making industrial materials more durable.

Civil engineering professor and chair of experimental micromechanics at Delft University of Technology in the Netherlands, his areas of research include durability mechanics and “self-healing” materials, like the asphalt and concrete he and his team have developed that can be repaired with induction.

This special asphalt is made with tiny steel wool fibres, which, when heated by induction, extend the life of the material. Currently Schlangen and his team are testing the asphalt on the A58 road near Vilssingen in the Netherlands, in the hope that it can be used in future roads all over the country and, potentially, the world.

Highway A58 Self Healing Asphalt

Self healing asphalt trial

Schlangen’s self healing asphalt is currently being trialled on the A58.

It’s very much a labour of love.

“We started on self-healing materials at Delft in 2005,” he notes, “11 years ago.”

A series of trials were run across several faculties. In civil engineering it began, as it often does, with concrete. “I’m in civil engineering, so we started in concrete,” observes Schlangen.

Less maintenance is very important. It means less hindrance for the public

Erik Schlangen

It showed promise and research funding was secured. “We got two, €10M (£8.5M) grants over eight years from the government,” explains Schlangen. “We started on concrete and asphalt as two materials that can repair themselves,” he adds.

Self-repairing materials have great potential because self-repair equals less maintenance, explains Schlangen.

“Less maintenance is very important. It means less hindrance for the public,” he says. There are also whole life cost benefits: because the material lasts longer it means less materials are used in the upkeep of the asset.

Difficult repairs

“Concrete is especially difficult to repair – especially when it is underground,” notes Schlangen. “So if concrete structures could repair themselves, that would be great,” he adds. “That was the main motivation.”

This is genuinely pioneering stuff.

“Back in 2005 there was some research going on in the US looking at polymers, but we were the first to start on concrete and asphalt,” states Schlangen.

“The first project was to develop a bacteria that closes cracks in concrete by precipitating calcium carbonite when exposed to water,” he explains.

“It was very successful. We hired a micro-biologist to lead self-healing concrete and it is working very well,” he says.

Indeed, that technique is one of three self-healing concrete methods currently being trialled by Costain on the Heads of the Valley highways scheme in Wales. It’s now not being led by Schlangen and his team – he handed self-healing concrete on to one of his former post-doctorate researchers so that he can now focus on self-healing asphalt.

See Erik live

  • Erik Schlangen is delivering the keynote address at this year’s Future Tech Forum this September.
  • The Future Tech Forum is an exciting new gathering for the thought-leaders, decision-makers and emerging minds from the entire built environment community to share and analyse the latest technologies and innovations that will make a mark on the industry in the next five years.
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 Why? Because he can see a real potential here, in a relatively short time frame.

“Around the world there is a lot of damaged asphalt and it costs a lot of money to repair it,” he notes.

So Schlangen and his team came up with a technique, which is admittedly not completely self-healing at present. “It needs a little help,” says Schlangen.

It’s a simple concept to understand. Steel wool fibres are mixed into the bitumen. If and when the surface starts to crack, you introduce a magnetic field which begins to heat up the fibres by induction. This then remelts the bitumen which flows into the cracks and reseals the surface.

illustratie self healing asfalt

Self healing asphalt

The magnetic field heats up steel fibres in the asphalt in by induction, causing the bitumen to melt

“It means less maintenance and you can at least double the service life of the road from typically seven or eight years to at least 15 years,” says Schlangen.

On the prototype, the magnetic field is created by a trailer mounted induction loop that is towed behind a truck, with treatment needed once every three to four years.

The prototype machine is quite small and is quite slow – it currently needs to travel at walking pace to give the induction loop time to heat the bitumen to the 85°C needed to melt it.

Erik Schlangen

Erik Schlangen

Schlangen: Self healing asphalt pioneer

“The induction coils needed are quite small. But if you create a bigger coil you can drive faster. It could take just several seconds. We are looking to get to 20mph,” explains Schlangen.

Schlangen has been fortunate in that Dutch highways authority has been very supportive. “The government and the road authority gave us 400m of highway to try it in 2010. So now it is almost six years old and still in a perfect condition after one treatment three years ago,” he says.

The contractor Schlangen worked with is clearly convinced. Says Schlangen: “The contractor that worked with us has already used it at 10 locations in the Netherlands and it is performing everywhere quite well.”

More buy in

So how do you get more people to buy in – don’t they want guarantees? They certainly do the in UK.

“The real proof will come after 15 to 20 years,” accepts Schlangen. “But all over the world people are starting to trial this.

“Even in the UK the University of Nottingham is doing some research on this, with the help of one of my post-docs.”

Schlangen doesn’t understand the caution with which the technology has been received. But he is looking squarely at clients as part of the problem.

Asphalt is easy

“Concrete structures are very difficult – they last longer and it is more serious if it goes wrong. “But asphalt is relatively easy; and if you try it and it doesn’t work you can remove it,” he observes.

For Schlangen the real issue is with the way the industry is structured and, crucially, how people get paid.

“With asphalt the real problem is who wants to pay for it? That is always the question.

“The contractor would prefer to lay a road that lasts for just seven years as he can then come back in seven years and replace it – he gets paid more money that way.

Client benefits

“When you look at the whole service life, this is cheaper. So for the contractor, their income is less,” he notes.

“With PFI it becomes interesting for the contractors as they can save money. Otherwise it needs to be stimulated by clients as they are the ones that benefit,” he insists.

Alas, there is no real UK interest yet.

“Maybe that will come in September,” says Schlangen, referencing New Civil Engineer’s Future Tech Forum where he will be the keynote speaker.

It may also come as Schlangen further develops the concept and makes it genuinely self-healing.

Built-in coils

“At the moment the induction coils are in the truck,” he recaps. “We’re now working on finding a way to build the induction coils in the road. As to be really self-healing the coils do need to be in the road,” he accepts.

There is an additional spin off benefit to that too.

“If we can do that then potentially you can also charge electric vehicles using the same induction coils,” he speculates, adding that ideally these embedded coils would be powered by roadside solar cells.

Schlangen’s team has just started a research project on that now – so watch this space.

Schlangen’s CV

2015-present: Guest Professor at Southeast University, Nanjing, China

2012-present: Professor, Delft University of Technology

2003-2012: Associate Professor, Delft University of Technology

1996-2008: Senior Research Engineer at Intron Materials Institute

1993-1995: Research assistant / Assistant Professor Delft University of Technology

1993-1994: Post-Doc, National Institute of Standards and Technology, Gaithersburg, United States.

1993: PhD: Delft University of Technology

1989: MSc: Eindhoven University of Technology

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